Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session K1: Poster Session II (2:00 pm - 5:00 pm) |
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Room: Exhibit CD |
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K1.00001: UNDERGRADUATE RESEARCH (Including Society of Physics Students) |
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K1.00002: How does diffusion affect radiative efficiency measurements? Caroline Vaughan, Tim Gfroerer, Mark Wanlass Defect-related recombination can lower the efficiency of many semiconductor devices. We measure the radiative efficiency (the ratio of emitted to incident light) as a function of excitation laser power to investigate defect-related recombination in GaAs. Images of the emitted light reveal isolated dark regions where the radiative efficiency is reduced. When the laser is focused onto one of these defective regions, the dependence of the radiative efficiency on excitation power is dramatically different. Using these results, we model the distribution of defect-related energy levels near and far from the isolated defect. But our defect-related recombination model is incomplete because it does not account for diffusion. Our radiative efficiency measurements depend strongly on laser focusing, suggesting that diffusion is important. We seek to understand how diffusion modifies our experimental results. [Preview Abstract] |
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K1.00003: Influence of vapor annealing on the electrical properties of chalcogenide misfit layered compounds Sara Tepfer, Qiyin Lin, Colby Heideman, Ngoc Nguyen, Matt Beekman, David Johnson A new class of semiconducting misfit layered compounds [(PbSe)$_{0.99}$]$_{m}$(WSe$_{2})_{n}$ have been prepared. These thin film materials show promise for thermoelectric applications due to their extremely low thermal conductivities. To fully assess the potential these materials hold, a thorough understanding of electrical transport properties must be obtained. Toward this end, we have conducted a systematic study of the compound [(PbSe)$_{0.99}$]$_{1}$(WSe$_{2})_{1}$ by annealing under controlled Se vapor in order to reduce defect levels and tune chemical composition. Both annealing temperature and time were found to have a significant influence on the electrical properties of the specimens. Carrier concentrations are reduced and carrier mobilities are increased upon annealing. These results could be attributed to defect diffusion and compositional tuning resulting from the annealing conditions and indicate the capacity for reproducible electrical properties. [Preview Abstract] |
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K1.00004: Investigating Superfluid $^4$He Using Commercially Available Quartz Tuning Forks Joshua Wiman, Robert DeSerio, Neil Sullivan, Yoonseok Lee Mechanical oscillators such as vibrating wire oscillators, torsional oscillators, and acoustic transducers have been widely used to measure the properties of cryogenic liquids. Commercial quartz tuning forks, which can be found in almost every electronic device, have shown promise as viscometers and thermometers for low temperature experiments. These devices are inexpensive, easy to install, and insensitive to magnetic fields. Before a fork can be used, it must be calibrated against a hydrodynamic model. We measured changes in the frequency and width of the fork's resonance response in superfluid $^4$He down to 1.5 K. Analysis of the tuning fork's response as a function of temperature shows that its behavior is well-described by the hydrodynamic model for superfluid helium. We will also discuss our future plans. [Preview Abstract] |
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K1.00005: Optical Limiting in Capillary Waveguides at 1300nm Ryan Ford, James Butler Optical limiting at 1300nm, a commonly used telecommunications wavelength, was observed in glass capillaries filled with a solution of (polypridyl) osmium (porphinato) zinc II, or OsPZnOs, in dimethyl sulfoxide. The refractive index of the solution was such that incident light was guided through the cores of the capillaries. This allowed for an increase of the interaction length between the light and the solution, thereby enhancing the optical limiting relative to a bulk sample. The nonlinear transmissions of the capillaries were determined using measurements of the entering and exiting optical energies. The data collected will be compared to previous data taken at shorter wavelengths. Possible models of the mechanism responsible for the observed optical limiting will be discussed. [Preview Abstract] |
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K1.00006: Raman imaging of defects in single-layer and multi-layer graphene Pubudu Galwaduge, Jospeh Lambert, Roberto Ramos Graphene is a two-dimensional crystal that has caught the attention of many research groups around the world. Raman spectroscopy is commonly used to identify single and multi-layer graphene. We report on the use of Raman imaging as a tool for studying structural defects in graphene. We focus on identifying defects and observing defect evolution using this technique. [Preview Abstract] |
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K1.00007: Annealing variation of the morphology, elemental composition, stiffness and elastic modulus of the self assembled Ag nano structures on clean undoped Si(100) under ambient conditions Matthew Pautz, Joshua Buchheit, Jeffery Parks, Indrajith Senevirathne Understanding self assembly of Ag nanostructures on surface support is interesting due to various possible plasmonic and catalytic applications. It can be hypothesized that the mechanical strength and elemental composition of these nanostructures also vary with temperature variations. Out layer oxidation resulting from ambient exposure gives complex characteristics for these nanostructures. RT(300K) Magnetron sputter deposited Ag, on clean, undoped Si(100) was studied under ambient conditions by contact mode and non contact mode Atomic Force Microscopy (AFM) and Scanning Electron Microcopy (SEM). Surface elemental composition on the deposited system was measured with Energy Dispersive X ray Spectroscopy (EDX). Self assembled Ag nano structures on Si were observed to have $\sim $60nm in width and $\sim $10nm in height. Annealing at 373K and above they ripen into bigger structures of $\sim $400nm length. At different annealing stages O, Si and Ag concentrations were measured using EDX. Surface stiffness and elasticity at each stage were measured using force curve method via nano indentation using contact mode AFM. [Preview Abstract] |
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K1.00008: Defect-related recombination and free-carrier diffusion near an isolated defect in GaAs Mac Read, Tim Gfroerer, Mark Wanlass When defects are present in semiconductors, localized energy levels appear within the bandgap. These new electronic states accommodate heat-generating recombination -- a problematic energy loss mechanism in many semiconductor devices. But at high excitation, the density of electrons and holes is higher, so they encounter each other more frequently. Early encounters augment light-emitting recombination, reducing the average lifetime and diffusion distance so the carriers are less likely to reach defects. In images of the light emitted by GaAs, we observe isolated dark regions (defects) where the darkened area decreases substantially with increasing excitation. When we modeled the behavior with a simulation that allows for lifetime-limited diffusion and defect-related recombination only through mid-bandgap energy levels, we did not obtain good agreement between the experimental and simulated images. We are now testing a more sophisticated model which allows for an arbitrary distribution of defect levels within the bandgap. [Preview Abstract] |
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K1.00009: Structure and morphology variation at annealing of self assembled Ag nanodots on HOPG under ambient conditions. Indrajith Senevirathne, Matthew Pautz, Jeffrey Parks, Anura Goonewardene Self assembly of noble metal nanostructures on surface support under ambient conditions is interesting due to various possible plasmonic and catalytic applications. These nanostructures have altered and complex characteristics due to their outer oxide layer resulting from ambient exposure. RT ($\sim $300K) Magnetron sputter deposited Ag, on clean, freshly cleaved HOPG was studied using ambient Scanning Tunneling Microscopy (STM), contact mode Atomic Force Microscopy (AFM) and Scanning Electron Microcopy (SEM). Surface elemental composition and distribution on the deposited system was measured with Energy Dispersive X ray Spectroscopy (EDX). Self assembled Ag nano dot structures on the surface was observed with Volmer - Weber growth mode at incremental Ag coverage. At Ag coverage of $\sim $32 ML nucleated nano dots observed to have $\sim $25nm diameter and $\sim $4nm in height. At an increased Ag coverage of $\sim $128ML, micron size super clusters were observed to coexist with the primary nano dots. Surface morphological and elemental (O and Ag) variations at annealing under successively higher temperatures will also be discussed. [Preview Abstract] |
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K1.00010: AFM, SEM and EDX study of morphology, elemental composition and spore surface stiffness/elasticity measurements for \textit{Hypocrea} and \textit{Phomopsis} spores. Brittany Ganther, Ekaterina Yarunova, Barrie Overton, Indrajith Senevirathne Surface morphology of \textit{Hypocrea} and \textit{Phomopsis} spores were investigated with contact and non contact mode Atomic Force Microscopy (AFM). Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX) are used to quantitatively measure the rodlet composition and elemental composition variations at different stages. Size characteristics indicate \textit{Hypocrea} to be 3 -- 4 $\mu $m in diameter and \textit{Phomopsis} to be 2 -- 3$\mu $m in diameter, from High resolution AFM and SEM images. \textit{Hypocrea} conidia are unprotected and produced on conidiophores exposed to environmental conditions while \textit{Phompsis} conidia are protected with in a pycnidium. It can be hypothesized that spore surface stiffness measurements and elastic moduli of these two spores should give different values as an evolutionary response. Spore surface stiffness and elastic moduli measurements by nanoindentation obtained from force curve method in contact mode AFM will be discussed. The chemical composition variation of the spores, pre and post germination will also be discussed. [Preview Abstract] |
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K1.00011: Numerical Analysis of EKG Data Kelly Loman, Guoping Zhang We develop a method to computationally examine irregularities in the EKG data of a human's heart beat. Using a complete period of the heart's contraction and then release, a program was created to compare the healthy heart model's p-wave (x-axis) to a patient's p-wave (y-axis). While studying the p-waves, the need for an optimum width was noted in order to accurately analyze the standard p-wave and patient p-wave relationship. The width of the left and right shoulder of several p-waves in relation to their qrs-complexes was recorded and found to be very similar for individual patients. A code was created that found the p-wave via the qrs-complex using the width ranges that had been established. At this time, the code has been run for 60 seconds of patient data with great success. [Preview Abstract] |
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K1.00012: Ultrasound Thermometry for Therapy-level Radiation Dosimetry Courtney Taylor Radiation oncology is the process of administering a specified dose of radiation to a patient currently receiving treatment for a form of cancer. In this process, it is vital to know the delivered dose for a given radiation beam to correctly treat a patient. The primary reference standard for absorbed dose is established using water calorimetry. The absorbed dose, typically of order 1 Gy (J/kg) at therapy levels, is realized by measuring sub-millikelvin temperature changes using a thermistor in a sensitive Wheatstone bridge. Ultrasound technology has been investigated as an alternative to thermistor measurements since the speed of sound propagation in water varies with temperature. With ultrasonic time-of-flight and highly sensitive phase detection techniques, temperature sensitivity comparable to that of the thermistor bridge has been achieved without introducing non-water materials into the test area. A single ultrasound transducer transmitting and receiving at 5.0 MHz throughout the length of the water phantom, and the phase change of the sound wave was used to determine temperature increase from an irradiative source at specified depths of the phantom. In this experiment, the exposure period was varied from 15s to 160s cyclically by modulating a heat lamp, and a profile of the measured temperature response as a function of the period was obtained using Fourier analysis. Due to the large temperature gradient in the water phantom, measurements are prone to convection which was indeed observed and will be discussed. [Preview Abstract] |
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K1.00013: Computational Simulation of a Simple Pendulum Driven by a Natural Chaotic Function Trevor Tomesh A simple pendulum is computationally modeled and driven according to the natural non-linear dynamical functions that arise out of the Hodgkin-Huxley membrane model of squid giant axons. Driving a neural membrane with a sinusoidal current can stimulate chaotic potential oscillations that can be modeled mathematically. The solution of the Hodgkin-Huxley membrane model provides the amplitude of the impulse to the simple pendulum at the lowest point in its swing. The phase-space plot of a simple harmonic oscillator, randomly driven chaotic oscillator, and Hodgkin-Huxley driven chaotic oscillator are compared. The similarities and differences between the motion of the pendulum as the result of the Hodgkin-Huxley driving impulse and a random impulse are explored. [Preview Abstract] |
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K1.00014: Properties of Thermo Responsive Polymer Particles Kathleen Anderson, Brian Simpson, Kyriaki Kalaitzidou The formation of thermally responsive polymer particles is done by utilizing the strain of two dissimilar materials at the interface of a bilayer. The inherent strain forces the bilayer to curl into a scroll configuration. When these scrolls are triggered by use of heat, the geometry changes and there are abrupt changes in their properties. The viscosity of solutions containing the scrolls is measured as a function of temperature in the range of 25$^{o}$C to 120$^{o}$C using a spindle and cup viscometer. It is found that although the viscosity of the silicone oil solvent decreases with temperature, there is a ``hump'' in the viscosity upon addition of scrolls. The viscosity increase is due to the geometry change associated with the opening of the scrolls. The geometry changes are also reflected in the electrical conductivity and the optical properties of the scroll solutions. [Preview Abstract] |
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K1.00015: Introduction to Numerical Modeling of the Atmosphere Joseph Wilkins, Benjamin MacCall A set of governing partial differential equations (PDE) derived from fundamental physical principles can describe the behavior of a fluid, but due to nonlinearity they cannot be analytically solved. Instead, they must be approximated. This work is a survey of well established finite-difference methods applied to two sets of equations-- the linear advection equation (LAE) and the linearized shallow-water equations (LSWE). Finite difference schemes replace the partial derivatives of a variable with the differences between discrete points in space and time. The resulting equations only approximate the original PDE leading to unwanted behavior, such as computational instability, damping, dispersion, and unphysical solutions. The following numerical schemes were applied to both the LAE and the LSWE: forward-in-time-and-space, Euler, backward, leapfrog, ~Lax-Wendroff. While there are many types of numerical schemes used for solving PDE, the schemes we employed show the necessity of weighing the characteristics of a particular scheme against the physical behavior being simulated and the resources available for computation. [Preview Abstract] |
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K1.00016: East-West Asymmetry of Muon Flux in Nashville, TN Sean Nomoto, Daniel Soto, Medford Webster In the summer of 2008, results from measuring the muon flux from cosmic radiation by scintillator detectors were showed a favored Easterly flux with an asymmetry of 0.965$\pm $0.005. The East-West Effect model predicts that the Earth shields trajectories from the Eastern direction so the asymmetry should have been greater than one. However, the East-favored asymmetry may have been due to background flux from low energy secondary particles. First, the cosmic radiation attenuation through one, three, four, and then five layers of brick was observed. The total flux was reduced by approximately 10 {\%} between one and three layers of brick. The flux was measured unshielded, with one layer of bricks, and with five layers of bricks. The measurements showed less asymmetry than in 2008, and the unshielded ratios from 2009 statistically disagreed with the unshielded asymmetries from 2008 by $\sim $4$\sigma $. A possible explanation may be that a change in the flux of charged ions from solar winds are perturbing the Earth's magnetic field---changing the trajectories of incoming cosmic particles, but it is also possible that the observed effect was a statistical fluctuation. This research was supported in part by the U. S. National Science Foundation --- NSF Grant PHYS - 0649123. [Preview Abstract] |
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K1.00017: ABSTRACT WITHDRAWN |
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K1.00018: Black Hole Growth Excites Spin Thomas Pope, John Blondin An x-ray telescope reveals hundreds of thousands of x-ray sources invisible to our eyes. These objects are powered by accretion. The theory of hydrodynamic accretion was first described 70 years ago by Hoyle and Lyttleton (1939), and has become a fundamental building block for understanding compact x-ray sources. Modern research on gravitational accretion has focused on the use of numerical simulations to study the stability of accretion and the possibility of accretion of angular momentum, which does not exist in the steady- state theory of Hoyle and Lyttleton. After 20 years there is still no consensus on the stability of such. We have addressed this confusion by using high- fidelity numerical simulations run on the NSF's `Ranger' supercomputer. By starting from an initially steady-state axisymmetric solution we are now able to show that Hoyle-Lyttleton accretion is unstable to small perturbations. We use these simulations to quantify the growth rate and oscillation period of the unstable accretion shock. Provided the star is sufficiently small, the secular evolution is described by sudden jumps between states with counter rotating semi-Keplerian accretion disks feeding the star with a specific angular momentum comparable to a Keplerian orbit at the surface of the star. [Preview Abstract] |
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K1.00019: HISTORY OF PHYSICS |
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K1.00020: How Rosalind Franklin Discovered the Helical Structure of DNA: Experiments in diffraction Heidrun Schmitzer, Dennis Tierney, Gregory Braun Rosalind Franklin, a chemical physicist (1920-1958), used X-Ray diffraction to determine the structure of DNA. In 1953 she described the DNA has a helical structure with a period of 34 A and a radius of 10 A. We suggest experiments of varying equipment and difficulty which enable students to follow in the footsteps of Rosalind Franklin's discovery. To do this we increase the scale; instead of a tiny DNA molecule we examine the diffraction pattern of a helical spring from a ballpoint pen, and instead of X-Rays we use light rays. Students can then apply their experiences with diffraction on a helical spring to R. Franklin's X-Ray diffraction photo, which should be made available to them in original size. They can determine the angle, pitch, and radius of the DNA molecule, just like Rosalind Franklin. Our experiments can be used as demonstration experiments in interdisciplinary history and science lectures, or as lab experiments for undergraduate non science and science majors. [Preview Abstract] |
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K1.00021: PHASE TRANSITIONS AND STRONGLY CORRELATED SYSTEMS |
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K1.00022: ABSTRACT WITHDRAWN |
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K1.00023: Nonequilibrium dynamical mean-field analysis of strongly photoexcited states of a Mott insulator Naoto Tsuji, Takashi Oka, Hideo Aoki Recent progress in pump-probe reflectivity and photoemission spectroscopy measurements has enabled us to drive correlated electron systems into highly excited states to detect their ultrafast relaxation dynamics. Theoretically, a crucial interest is how a Mott insulator changes its nature when the pump light creates photo-carriers that should significantly alter the physical properties from the Mott's insulating state.\\ In order to explore this, we adopt Floquet's method (for strong ac fields) as combined with the nonequilibrium dynamical mean-field theory, and apply this to the Hubbard model at half-filling. As a solver for the nonequilibrium impurity problem, we mainly use the iterated perturbation theory. The result for the optical conductivity exhibits that a low-energy peak of the spectral weight evolves with the intensity of the pump light, where the width of the peak does not follow the Fermi-liquid behavior, which implies that the system turns into an anomalous metallic state. A change from the insulator to a metallic behavior is also observed in the single-particle spectrum and the nonequilibrium distribution function. We will further discuss how such excited states relax after the pump light is turned off. [Preview Abstract] |
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K1.00024: Multifractal analysis with the probability density function at the three-dimensional Anderson transition Louella Vasquez, Alberto Rodriguez, Rudolf Roemer The probability density function (PDF) for critical wavefunction amplitudes is studied in the three-dimensional Anderson model. We present a formal expression between the PDF and the multifractal spectrum $f(\alpha)$ in which the role of finite-size corrections is properly analyzed. We show the non-gaussian nature and the existence of a symmetry relation in the PDF. From the PDF, we extract information about $f(\alpha)$ at criticality such as the presence of negative fractal dimensions and the possible existence of termination points. A PDF-based multifractal analysis is shown to be a valid alternative to the standard approach based on the scaling of inverse participation ratios. [Preview Abstract] |
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K1.00025: Voltage triggered resistance switching in two terminal VO$_{2}$ nano-junctions fabricated by electron-beam lithography Gokul Gopalakrishnan, Dmitry Ruzmetov, Changhyun Ko, Venkatesh Narayanamurti, Shriram Ramanathan Vanadium dioxide (VO$_{2}$) thin films have been shown to undergo an abrupt decrease in resistivity, both in response to increasing temperature as well as an increasing electric field. The ultra-fast electrically triggered transition has made VO$_{2}$ an exciting platform to explore a range of potential applications, from high speed switches to memory elements. Particularly valuable to such investigation is characterization of the electronic properties of VO$_{2}$ thin films, in which transport is additionally constrained within nanoscale dimensions along the in-plane directions. In this poster, we describe the results of transport measurements on VO$_{2}$ nanojunctions grown on a conductive substrate and patterned by electron-beam lithography. We analyze the out-of-plane I-V data and present a detailed discussion on electron transport mechanisms and on the origin behind the electrically triggered conductivity jumps that we observe in these nano-junctions. [Preview Abstract] |
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K1.00026: Metal-Insulator Transition in W-doped VO2 Nanowires Gen Long, James Parry, Luisa Whittaker , Sarbajit Banerjee, Hao Zeng We report a systematic study of the metal-insulator transition in W-doped VO2 nanowires. Magnetic susceptibility were measured for a bulk amount of VO2 nanowire powder. The susceptibility shows a sharp drop with decreasing temperature corresponding to the metal-insulator transition. The transition shows large temperature hysteresis for cooling and heating. With increasing doping concentration, the transition temperatures decreases systematically from 320 K to 275K. Charge transport measurements on the same nanowires showed similar behavior. XRD and TEM measurements were taken to further determine the structure of the materials in study. [Preview Abstract] |
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K1.00027: ABSTRACT WITHDRAWN |
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K1.00028: Interplay between ferroelastic and metal-insulator domains in quasi-2D VO$_{2}$ nanoplatelets A. Tselev, E. Strelcov, I.A. Luk'yanchuk, K. Jones, R. Proksch, S.V. Kalinin, A. Kolmakov Significant effort has been spent to date to investigate behavior of VO$_{2}$ nanostructures in the vicinity of the metal-insulator transition (MIT). However, one important aspect of this material---the fact that low temperature VO$_{2}$ phase is ferroelastic---has been almost completely left out of consideration. Using variable temperature scanning microwave microscopy (SMM) and polarized-light microscopy, we imaged development of domains of metallic and semiconducting phases during the MIT in single crystalline quasi-2D nanoplatelets and observed non-trivial strain-driven phenomena. Ferroelastic domains in VO$_{2}$ nanosystems can significantly affect local strain distributions, and hence couple to the strongly strain-dependent MIT. In contrast to quasi-1D nanobeams, the presence of the second dimension results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. [Preview Abstract] |
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K1.00029: The random phase property and the Lyapunov spectrum for disordered multi-channel systems Rudolf Roemer, Hermann Schulz-Baldes A random phase property establishing a link between quasi-one-dimensional random Schroedinger operators and full random matrix theory is advocated. Briefly summarized it states that the random transfer matrices placed into a normal system of coordinates act on the isotropic frames and lead to a Markov process with a unique invariant measure which is of geometric nature. On the elliptic part of the transfer matrices, this measure is invariant under the full hermitian symplectic group of the universality class under study. While the random phase property can up to now only be proved in special models or in a restricted sense, we provide strong numerical evidence that it holds in the Anderson model of localization. A main outcome of the random phase property is a perturbative calculation of the Lyapunov exponents which shows that the Lyapunov spectrum is equidistant and that the localization lengths for large systems in the unitary, orthogonal and symplectic ensemble differ by a factor 2 each. In an Anderson-Ando model on a tubular geometry with magnetic field and spin-orbit coupling, the normal system of coordinates is calculated and this is used to derive explicit energy dependent formulas for the Lyapunov spectrum. [Preview Abstract] |
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K1.00030: Finite-temperature properties of PMN-PT from atomistic simulations Abdullah Al-Barakaty, Sergey Prosandeev, Laurent Bellaiche Relaxor-based single crystals such as (PbMg$_{1/3}$Nb$_{2/3}$O$_{3})_{1-x}$-(PbTiO$_{3})_{x }$(denoted as PMN-PT) have been reported to exhibit excellent electromechanical properties. The high electromechanical performance characteristics of the relaxor-PT solid solutions is found for compositions at or near the morphotropic phase boundary (MPB) separating the rhombohedral and tetragonal phases. In addition to this MPB area, PMN-PT solid solutions are very interesting and complex to mimic because one of its end-member (PMN) is considered as the prototype of relaxors while its other end-member (PT) is a prototype of classical ferroelectrics. In this work, we developed an effective Hamiltonian technique to theoretically investigate the MPB area of PMN-PT and the symmetries of its phases and to reveal the effect of atomic ordering on physical properties of PMN-PT. If time allows, we will also discuss the effect of oxygen vacancies on the finite-temperature properties of PMN-PT. [Preview Abstract] |
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K1.00031: A Model Study of Structural Phase Changes in Clusters of Derivatized Fullerenes on Au(111) Gregory Bubnis, Howard Mayne Self-assembled adsorbate layers incorporating derivatized fullerenes have been studied extensively and recently reviewed. [S\'{a}nchez et al.\textit{ Chem. Rev.}, 2009, \textbf{109}, pp 2081--2091] But the prediction and rational design of their preferred structures remains challenging. We have initiated a systematic modeling study of pattern formation of derivatized fullerenes on the Au(111) surface. We focus on a family of fullerenes with carboxyl functionality capable of strong intermolecular hydrogen bonds. The carboxyl groups are bonded to the fullerene using phenyl, biphenyl, and (linear) polyphenylene linkages. The relevant intermolecular interactions are described by simplified potential energy functions and we constrain the molecules and surface to be rigid. Metropolis Monte Carlo simulations are carried out on clusters at a range of temperatures and the adlayer structure is inferred from the heat capacity as well as several structure parameters. Our coarse-grained approach permits the study of clusters as large as fifty molecules at a relatively modest computational expense. Our results show that fullerene moieties prefer to form hexagonal close-packed monolayers and the substituent groups dictate additional orientational order. Extended one-dimensional hydrogen bonded chains can be formed for bifunctional fullerenes. For monofunctional fullerenes, hydrogen bonding leads to the formation of herringbone adlayers. Furthermore, we show pure dispersion intermolecular interactions can also lead to herringbone patterns. The largest substituents hinder pattern formation. [Preview Abstract] |
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K1.00032: Surface reconstruction of Y-doped HoMnO$_{3}$ and LuMnO$_{3}$ Relja Vasic, Jerzy T. Sadowski, John E. (Jack) Rowe, S.W. Cheong, Y.J. Choi, H.D. Zhou, C. R. Wiebe We investigate (0001) surfaces of several hexagonal perovskites by low-energy electron diffraction (LEED) to determine the surface periodicity which is different from the bulk materials. Our LEED studies were conducted at the BNL-CFN using a normal incidence geometry with a LEEM/LEED apparatus from room temperature to 1200\r{ }C and with an electron energy in the range of 15eV to 200eV. Diffraction patterns showed features of bulk terminated periodicity and a 3$\times $3 surface reconstruction. Possible origins for this surface structure are discussed and comparisons are made with surface studies of other complex oxides. The temperature dependence of the data is also used to estimate the surface Debye temperature of these manganates. Additional diffraction patterns of cleaved or polished (1010) surfaces showed bulk terminated periodicity corresponding to a real space 11.4{\AA}\r{ }---10.5{\AA} unit mesh. [Preview Abstract] |
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K1.00033: Magnetic ordering in RB$_{66}$ boron-rich borides. Karol Flachbart, Slavomir Gabani, Takao Mori, Konrad Siemensmeyer Magnetic ordering in TbB$_{66}$ and GdB$_{66}$ borides which belong to extremely boron-rich borides was investigated at very low temperatures. Measurements of ac susceptibility and of heat capacity of these compounds with a very low concentration of magnetic ions have shown rather clear features of magnetic ordering. They were observed at 0.34 K for TbB$_{66}$ and at 0.2 K for GdB$_{66}$. However, no direct evidence of long range magnetic order was found by neutron scattering experiments at these temperatures. Reasons leading to these observations / results will be discussed. [Preview Abstract] |
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K1.00034: Isolated dimers in a 2D-like quantum spin system Li$_{x}$Cu$_{2-z}$Zn$_{z}$O$_{2}$ Hung Chang Hsu, Hsiang-Lin Liu, F.C. Chou The existence of isolated dimers induced by the non-magnetic dopant Zn in a 2D-like quantum spin system Li$_{x}$Cu$_{2-z}$Zn$_{z}$O$_{2}$ is found. Low Zn substitution ($<$ 5 {\%} substituted CuO$_{2}$ chain) reduces spiral ordering temperature and a finite size effect is found to support a picture of phase separated domains with aggregated dimers near Zn dopant centers at the domain boundaries. Higher Zn substitution ($>$ 5{\%} substituted CuO2 chain) introduces a novel phase transition to show a cusp shape anomaly on the magnetic susceptibility. The isotropic magnetic susceptibility reduction for high Zn level at low temperature suggests an incomplete spin gap opening and the magnetic-field dependence of the new transition temperature shows a character of weak spin-phonon coupling. Moreover, susceptibility data fitting using isolated dimer plus frustrated spin chain model describes the magnetic behaviors of samples of high Zn level between 2 - 400 K well. [Preview Abstract] |
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K1.00035: Multiple magnetic transitions in multiferroic BiMnO$_{3}$ under high pressure Chih Chieh Chou, Sudip Mukherjee, Quark Yung-Sung Chen, Kuo Feng Tseng, Subhrangsu Taran, Jim Long Her, Chia Pin Sun, Chien-Lung Huang, Hiroya Sakurai, Alexei A. Belik, Eiji Takayama-Muromachi, Hung-Duen Yang Multiple magnetic transitions, named as kinks I, II and III, under hydrostatic pressure on multiferroic BiMnO$_{3}$ have been studied by the dc magnetization, magnetic hysteresis, and ac susceptibility. The proposed phase diagrams at ambient pressure, 9.4 and 11.9 kbar show the different magnetic features with various magnetic fields. These findings are believed to result from the variations of crystal structure influenced by the external pressure. These results also indicate the common complicated correlation between the lattice distortion and the spin configuration in multiferroic system. [Preview Abstract] |
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K1.00036: Competition between Magnetocaloric and Elastocaloric effect in Phase Separated Manganites under pressure Y.J. Choi, T. Fisher, A.L. Lima Sharma, Z. Qin, T. Zhou, S.-W. Cheong We investigated the hydrostatic pressure and magnetic field dependent entropy changes in single crystal samples of the phase separated manganite La$_{0.25}$Pr$_{0.375}$Ca$_{0.375}$MnO$_{3}$. Magnetization measurements combined with the Maxwell relations were used to compute the magnetocaloric and elastocaloric effects. The coexistence of ferromagnetic (FM) metallic and charge ordered (CO) insulating regions are related to the proximity of their respective free energies. The phase separated state changes under applied field and pressure due to the interplay between the rates at which the system is generating and releasing heat, forming FM and CO regions respectively. The measurements also allow an estimate of the magnetic viscosity in the sample. [Preview Abstract] |
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K1.00037: Analysis of the multiple phase behavior of BiMnO$_{3}$ system under pressure with pseudospin model B.K. Chaudhuri, C.C. Chou, H.D. Yang A two sub-lattice pseudo-spin-lattice coupled mode model has been used to describe phenomenologically the origin of the appearance of a new phase in the multiferroic BiMnO$_{3}$ under pressure. The pseudo-spins are considered to be associated with the local ordering of the Mn-O-Mn bonds in the crystal lattice structure. In such a system ferromagnetic (FM) and ferroelectric (FE) orderings co-exist and there is strong coupling of the spin with the lattice. Statistical Green's functional analysis has been made to find the energy spectrum which give two transition temperatures T$_{c1} \quad \sim $F(J,K,V) and T$_{c2} \quad \sim $ F(J,K) for this system indicating the presence of two energetically different incipient structures in the crystal lattice ( J and K represents the spin-spin coupling constants between the same and different sub-lattices, respectively). One of these transitions T$_{c1}$ being coupled to the spin-lattice coupling (V) is activated only under pressure and the other one free or loosely coupled to the lattice is observed at ambient pressure with change of temperature. The FM transition around 100K where the spins are not strongly coupled to the lattice appears first, even at ambient pressure and than the other coupled to the lattice appears with decrease of temperature from ambient. Corresponding expressions for susceptibility and heat capacity have also been derived. Heat capacity might show logarithmic singularity depending on the pseudo-spin lattice coupling strength. The model is applicable to similar other systems. [Preview Abstract] |
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K1.00038: Crystal field and Kondo effect in CeMIn$_{5}$, M=Rh, Ir, and Co: a polarized soft XAS and neutron scattering study Thomas Willers, Andrea Severing, Eric D. Bauer, Zhiwei Hu, Liu Hao Tjeng We have determined the crystal-field scheme and the 4f conduction electron interaction in CeMIn5, M= Rh, Ir, and Co with linear polarized soft X-ray absorption and neutron scattering. Soft-x-ray absorption spectroscopy (XAS) at the Ce M4,5 edges can be used as a complementary technique to neutron scattering. XAS is highly sensitive to the symmetry of the initial state and through the polarization dependence direct information about the Jz admixtures of the ground state wave function can be obtained. Sensitivity to higher lying states is achieved by thermally populating those states. From soft XAS we find that the ground state wave functions of the CeMIn5 have increasingly Jz=3/2 character when going from M=Rh, Ir and largest for Co, and we find from the neutron line widths and the 4f0 contribution to the M4,5 edges that the 4f conduction electron interaction increases in the same sequence. [Preview Abstract] |
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K1.00039: Huge ac magnetoresistance of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in sub-kilogauss magnetic fields Ramanathan Mahendiran, Alwyn Rebello, Vinayak B. Naik, Sujit Kumar Barik We report radio frequency (f = 0.1 5 MHz) magnetotransport of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in sub kilogauss magnetic fields (H = 0-1 kG). We measured ac resistance (R) and reactance (X) simultaneously. In zero field, R decreases smoothly around the Curie temperature $T_{C}$ when $f$ = 100 kHz, but it increases abruptly and shows a peak close to T$_{C}$ for $f $= 0.5-5 MHz. The peak decreases in amplitude, broadens and shifts downward in temperature as the bias field increases. The peak is completely suppressed under $H_{dc}$ = 1 kOe when $f $= 0.5 MHz. A huge low-field \textit{ac} magnetoresistance ($\Delta R$/$R$ = 40 {\%}) and magnetoinductance ($\Delta $X/X = 12 {\%}) are found in a field of $H_{dc}$ = 700 Oe and $f $= 2 MHz. We suggest that the observed ac magnetoresistance arises from the suppression of ac permeability and enhanced magnetic skin depth under a magnetic field. The dynamical magnetotransport reported here will be interesting from view points of fundamental physics and applications. [Preview Abstract] |
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K1.00040: CeNbO4 a potential electrolyte for solid oxide fuel cells Martin Amft, Natalia Skorodumova CeNbO4 is a material of considerable interest for solid oxide fuel cells and other environmentally friendly applications. The low-temperature monoclinic phase of this material tends to be hyperstoichiometric incorporating extra oxygen up to CeNbO4.25. Materials containing cerium are challenging to treat theoretically as strongly correlated materials are not well described by standard density functional theory. Here we study CeNbO4 using the co-called LDA+U approach. We consider different interstitial positions for extra oxygen atoms and study how the formation energies of such defects depend on the degree of the localization of Ce f-states described by parameter U. We propose most likely interstitial sites for extra oxygen to occupy in the CeNbO4 lattice and paths of oxygen migration. [Preview Abstract] |
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K1.00041: Domain walls in magnetic and multiferroic undoped manganites Juan Salafranca, Rong Yu, Elbio Dagotto We study the structure and properties of Domain Walls in antiferromagnetic and in multiferroic undoped manganites. We use a model Hamiltonian [1] including double exchange, neareast and next nearest neighbors superexchange, and Jahn Teller distortions; the effect of the Dzyaloshinskii-Moriya interaction is also considered. As magnetism, electronic density, and lattice are strongly coupled in these systems, a gradient in one of these properties has remarkable effects in the others. We find interesting effects such as finite conductance at a magnetic domain wall within an insulating material, or electric dipoles associated with with an antiferromagnetic domain wall, for different values of the parameters. The possibility of observing these effects in real undoped manganites is discussed. [1] S. Dong {\it et al}, Phys. Rev. B 78, 155121 (2008) [Preview Abstract] |
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K1.00042: INSTRUMENTATION AND MEASUREMENTS |
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K1.00043: Calibration and optimization of proportional counter modules using Garfield Kiwhan Chung, Jesse Green, Konstantin Borozdin, Michael Brockwell, Gary Hogan, Fesseha Mariam, Christopher Morris Prototypes of radiation detector arrays used for charged-particle radiography require initial calibration to correlate the distribution of electron arrival time to the particle track locations. This step is crucial to obtaining the spatial resolution necessary to separate particle tracks traversing the individual proportional counters in the arrays. Our past attempts to use cosmic rays alone for the initial calibration have fallen short of obtaining the desired resolution due to the insufficient cosmic ray flux to provide the necessary number of particle tracks. A theoretical relation between electron drift time and radial drift distance is obtained with Garfield, a CERN gas detector simulation program. This relation is then used as an effective starting point for the initial calibration and results in a shorter calibration period and improved spatial resolution of the detectors. [Preview Abstract] |
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K1.00044: Laminated magneto-electric structures for tunable contactless magnetic sensing and energy harvesting Peter Finkel Multiferroic materials attracted increasingly high attention due to their potential in various multifunction sensing, filtering and energy transduction applications. In this work we investigated the magnetoelectric laminated multiferroic structure exhibiting a strong magneto-electric (ME) effect. We report here the magnetetoelctric coupling properties of the magnetoelastic/piezoelectric laminated FeNi42{\%}/ polyvinylidene fluoride (PVDF) clamped composite structure as a function of stress and magnetic field. The magnetically and elastically tunable, flexural resonant mode was probed using Doppler laser spectroscopy. Most commercially available methods of magnetic sensing involve electrical current or voltage measurements requiring electrical wiring or similar contact connections to measure an electric signal correlated with a magnetic field; and therefore are not immune to EMI and shot-noise. Our solution could overcome this shortcoming is to implement a completely remote contactless, i.e. optical, measurement approach. Here we demonstrate that this bimorph structure can be used for low-frequency contactless detection of magnetic field fluctuation and magnetic field monitoring for non-contact resonant optical magnetic field sensing and energy harvesting. [Preview Abstract] |
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K1.00045: A cantilever-based measurement of short-range deviations from Newtonian gravity Thomas Bay, Aharon Kapitulnik We describe an apparatus for measuring deviations from Newtonian gravity down to a length scale of 20~$\mu$m. The apparatus consists of a cryogenic gas-bearing drive mass actuator used to excite the resonance of the test-mass-bearing microcantilevers. A Fabry-P\'{e}rot interferometer measures the cantilever position. An optical radiation pressure feedback system is used to adjust the cantilever Q$_{\mathrm{eff}}$ and T$_{\mathrm{eff}}$ without loss of measurement sensitivity. We discuss expected increases in detector sensitivity as a result of recent upgrades and future related experiments. [Preview Abstract] |
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K1.00046: High k oxides on Germanium: High energy x-ray detector R{\&}D Abdul Rumaiz, Gabriella Carini, Peter Siddons, Pavel Rehak The higher density of Germanium (Ge) makes it an ideal candidate for high energy x-ray detectors. The higher mobility of carriers combined with a low effective mass in Ge as compared to Silicon has generated a lot of interest in Ge based devices for high speed devices. However the challenge associated with native oxide makes pixel isolation in a diode array very challenging. Furthermore suitable implants and activation of the implants with temperature constrain is also an issue. We have made a simple Ge diode with Boron and Phosphor as p and n implant. Low temperature grown high k oxide by direct metal sputtering and atomic layer deposition was used. Details of the Ge wafer processing and the effect of different interface layer on the capacitance-voltage characteristics will be discussed. [Preview Abstract] |
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K1.00047: Efficient and Selective Photon Detection using Amplification Without Inversion Kevin Mertes, Michael Di Rosa We describe ongoing theoretical and experimental research at Los Alamos National Laboratory of a new technology for photon detection that exploits quantum processes to attain an unrivaled combination of high quantum efficiency and sharp spectral discrimination. The amplification without inversion (AWI) scheme we are exploring consists of a lambda system found in the excited states of Hg-202. The construction of such a detector requires locking lasers to excited state transitions in Hg-202. We demonstrate how to use saturated absorption spectroscopy and a simple-to-build discharge cell to achieve this. We also describe the theoretical and experimental results obtained to date using the detector. Funding is provided from the Laboratory Directed Research and Development program of the Los Alamos National Laboratory. [Preview Abstract] |
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K1.00048: Spectroscopy With Free Electron Lasers David Bernstein, Mark Burkhardt, Andreas Scherz, Joachim St\"{o}hr, William Schlotter, Yves Acremann, Martin Beye, Torben Beeck, Florian Sorgenfrei, Annette Pietzsch, Wilfred Wurth, Alexander F\"{o}hlisch We demonstrate the feasibility of near edge x-ray absorption fine structure spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the FEL at Hamburg used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection, and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example, we recorded the $^3$D$_1$ N$_{4,5}$ edge absorption resonance of La$^{3+}$ ions in LaMnO$_3$. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities [Preview Abstract] |
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K1.00049: THz Dielectric Characterization of High Loss liquids using Total Internal Reflection Time Domain Spectroscopy Deepu George, Gayatri Venugopal, Rajagopal Panchapakeshan, Natalia Litchinitser, Andrea Markelz We introduce a technique to remotely determine the salt content of high concentration salt solutions using terahertz time domain spectroscopy.~~Terahertz is highly sensitive to water content, however the absorption strength is so high, characterization of aqueous solutions with transmission spectroscopy is not feasible with standard sources.~~Previously investigators have overcome this limitation using terahertz total internal reflection time domain spectroscopy to characterize alcohol and sugar content in solutions {\{}P. Uhd Jepsen et al, Optics Express, Vol 15 No22 (2007){\}}.~~However the optical system used mixed the incident polarization content at the interface, increasing the complexity of the analysis.~~Our method again uses total internal reflection at a silicon-aqueous sample interface, but the optics ensure the polarization of the THz beam remains the same throughout simplifying the analysis.~~We have applied the technique for measuring the dielectric constants of high concentration salt solutions such as KI and NaI in the range 0.2 to 1.5 THz.~~The dielectric strength of these solutions is modified with increasing salt concentration and can be significantly higher than pure water.~ [Preview Abstract] |
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K1.00050: Complete elimination of the secondary electron background in Auger spectra using Time of Flight Positron Annihilation Induced Auger Electron Spectroscopy Prasad Joglekar, Karthik Shastry, Sushant Kalaskar, Suman Satyal, L Lim, Alexander Weiss Time of flight- positron annihilation induced Auger electron spectroscopy (TOF-PAES) is a surface analysis technique with high surface selectivity. Almost 95{\%} of the TOF-PAES signal emerges from the topmost layer of the sample due to the trapping of positrons in an image-potential-well before annihilation. In this poster we will present new results that demonstrate how very low energy positron beams can be used together with the time of Flight (TOF) technique developed at The University of Texas at Arlington to obtain Auger spectra that are completely free of secondary electron background. [Preview Abstract] |
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K1.00051: Design of an Operando Positron Annihilation Gamma Spectrometer (OPAGS) S. Satyal, P. Joglekar, S. Kalaskar, K. Shastry, A.H. Weiss Surface properties measured under UHV conditions cannot be extended to surfaces interacting with gases under realistic pressures due to surface reconstruction and other strong perturbations of the surface. We present the design of an Operando Positron Annihilation Gamma Spectrometer (OPAGS) currently under construction at the University of Texas at Arlington. This new system will enable us to probe the surface and gather defect specific chemical and charge state information from surfaces under realistic pressures. Differential pumping will be used to maintain the sample in a gas environment while the rest of the beam is maintained under UHV. The Elemental content of the surface interacting with the gas environment will be determined from the Doppler broadened gamma spectra. This system will include a time of flight (TOF) positron annihilation induced Auger spectrometer (TOF-PAES) which correlates with the Doppler measurements at lower pressures. These new technique help to understand the charge transfer mechanisms at the surface. [Preview Abstract] |
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K1.00052: Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays Sukosin Thongrattanasiri, Justin Elser, Viktor Podolskiy We have developed a new mode matching approach capable of accurate numerical computation of wave coupling in arrays of planar structures. Building on previous mode matching algorithms, our technique identifies the full spectrum of modes needed to represent electromagnetic fields in and around the guiding system, and presents a set of analytical expressions to adequately calculate the propagation and scattering of light in coupled nonsymmetrical planar guides. The method is illustrated on examples of plasmonic and volumetric waveguides, surface waves scattering at step-coupling interfaces, and scattering at nonuniform semi-infinite dielectric-metal interfaces. The accuracies and convergences of the computed reflectance, transmittance, and scattering are in very good agreement with results of the finite-elements simulations. Compared to the latter, our mode matching technique provides significant memory-use improvement. [Preview Abstract] |
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K1.00053: Measuring X-ray Fluorescent Holograph with novel detector Yuhao Wang, Jianming Bai, Trevor Tyson, Peter Siddons, G. De Geronimo X-ray Fluorescent Holography is a promising method but requires large photon flux and prolonged signal accumulation time. In this report, holographs for samples with weak fluoresce are measured with a novel detector that provides counting rate up to 60 million counts per second , high energy-resolution and large solid angle for collecting signal. Discussions of the advantages and drawbacks of the novel detector application and analysis methods are made. This work is supported by NSF instrumentation grant DMR MRI-0722730. [Preview Abstract] |
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K1.00054: A New STM for Spin-Resolved Atomic Scale Imaging E. Main, A. E. Pivonka, I. Zeljkovic, J. E. Hoffman We have designed and constructed a new scanning tunneling microscope system for magnetic and spectroscopic imaging in UHV. The system features a variable-temperature He flow cryostat with internal vibration damping, two-axis magnet, in situ evaporator, and in situ sample and tip transfer. Atomic-resolution test images have been achieved with the new system. [Preview Abstract] |
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K1.00055: Adaptation of a commercial UHV SPM system for use with a quartz tuning fork sensor Jacob Tosado, William G. Cullen, Ellen D. Williams Dynamic force microscopy using a quartz tuning fork sensor offers many advantages over cantilever AFM, particularly for use in a UHV environment. One key advantage is the stability against jump to contact allowed by the high stiffness (k$\sim $1800 N/m) of the tuning fork. This allows complementary NC-AFM and STM, without a compromise in STM performance due to cantilever deflection. Here, we present the adaptation of a JEOL JSPM-4500A UHV STM/AFM system to accommodate a quartz tuning fork The modification is done without any alteration of the existing system capability for cantilever AFM using optical detection, and allows the same in-situ tip transfer capability of the original system. [Preview Abstract] |
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K1.00056: Photoemission electron microscopy of localized surface plasmon polaritons in nanostructured gold R.C. Word, T. Dornan, R. Konenkamp Localized surface plasmon polaritons were studied in photoemission electron microscopy using multiphoton excitation with a fs-pulse laser. Nanostructured metal layers were placed on transparent ITO-glass slides to utilize internal reflections for the resonant excitation of surface plasmons. Gold layers of varying roughness, prepared by focused ion beam milling, gold nanowires and gold nanoparticle arrangements were investigated. In all of these specimens strong localized enhancement of the photoemission is found in small areas with typical diameters of a few nm. The location of these high-emission areas changes with excitation wavelength. Experiments with two light sources, for example a dc-Hg arc-lamp in addition to the pulsed laser, allowed us to identify the exact location and the environment of the resonances at high magnification, and study proximity effects. [Preview Abstract] |
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K1.00057: Planck Spectroscopy and the Quantum-Mechanics of Microwave Beam splitters Matteo Mariantoni, Edwin P. Menzel, Frank Deppe, Miguel Angel Araque Caballero, Alexander Baust, Elisabeth Hoffmann, Tomasz Niemczyk, Achim Marx, Rudolf Gross, Enrique Solano Beam splitters occupy a central role in quantum optical architectures. We present an experimental study on the quantum-mechanical behaviour of microwave beam splitters based on a cross-correlation heterodyne detector. This method allows us to measure the covariance matrix of thermal states at the beam splitter input ports. Each matrix element represents a Planck distribution as a function of both temperature and frequency. Such a Planck spectroscopy makes possible to set an experimental limit to the measurement of vacuum fluctuations and unveils the partition noise properties of microwave beam splitters. [Preview Abstract] |
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K1.00058: Advantages of vector magnetometers in investigations of magnetic materials Alexander Bazhan Advantages of vector magnetometer with horizontal magnetic fields up to 9T at liquid helium temperatures, which present possibility to investigate separate components of samples magnetic moments and their magnetic field dependencies, used in studies of exchange and magnetic anisotropic interactions of magnetic ions, are discussed. Investigations of magnetic field behaviour of orientations of ordered magnetic moments of magnetic ions with respect to materials crystallographic axis are presented by such vector magnetometer. Advantages are discussed on examples of studies of non-collinear magnetic orderings of magnetic moments of Cu ions in Mott insulators, Nd$_{2}$CuO$_{4}$, which are of interest in studies of transformations of Cu non-collinear magnetic orderings, when additional two-dimensional correlated electrons, holes carriers systems are introduced in Nd$_{2-x}$Ce$_{x}$CuO$_{4\pm \delta }$, used in HTS investigations. Studies of, perpendicular to magnetic field, components of samples magnetic moments, which are determined by polarization of Nd magnetic system by Cu magnetic system in Nd$_{2}$CuO$_{4}$, present possibility to investigate Cu non-collinear magnetic orderings and their transformations in Nd$_{2-x }$Ce$_{x}$CuO$_{4\pm \delta }$. Such vector magnetometer can be used in experimental investigations with horizontal high magnetic field constructions. [Preview Abstract] |
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K1.00059: Instrumentation for Measuring Thermodynamic Properties of Rare-Earth Compounds Ulises I. Urbina, Jonathon Thompson, Pei-Chun Ho Current models on some Rare-Earth compounds cannot fully account for their strongly correlated electron behavior, which give rise to phenomenon such as unconventional superconductivity, heavy Fermion, and quantum critical behavior. The specific heat, thermopower, and thermal conductivity measurements give important thermodynamic properties, such as effective electronic mass, stiffness of the lattice (Debye temperature), entropy, density of states of charge carriers, and phase transitions which are crucial in characterizing these materials of interest in our laboratory. A calorimeter and a thermopower-thermal conductivity probe, which are using a modified relaxation method and standard steady-state heat flow technique, respectively, are constructed for the above purpose. Detailed schematic diagram and operating principles will be discussed in the report. [Preview Abstract] |
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K1.00060: Crystallographic Image Processing for Atomic Force and Scanning Tunneling Microscopists Bill Moon, Pavel Plachinda, Jack Straton, Peter Moeck Crystallographic image processing of atomic force and scanning tunneling microscopy [1] images from 2D periodic and preferentially highly symmetric calibration samples is demonstrated and leads to estimates of the prevailing point spread function of the microscopes. Such a point spread function is valid for one scanning probe tip at a time and the corresponding set of experimental conditions. It can subsequently be utilized to correct for all kinds of geometric distortions including the effects of a blunt scanning probe tip, image bow, and image tilt. The image to be corrected does not even need to possess 2D periodicity. The only condition is that it needs to be recorded with the same microscope under essentially the same experimental conditions and with the same scanning probe tip. \\[4pt] [1] P. Moeck, B. Moon Jr., M. Abdel-Hafiez, and M. Hietschold, Proc. NSTI 2009, Houston, May 3-7, 2009, Vol. I (2009) 314-317, (ISBN: 978-1-4398-1782-7). [Preview Abstract] |
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K1.00061: Experiments using Force Detected Nuclear Magnetic Resonance Han-Jong Chia, Rosa E. Cardenas, Isaac Manzanera Esteve, Mark C. Monti, John T. Markert We describe experiments using force detected nuclear magnetic resonance (NMR). We have developed a helium-3 system for high sensitivity measurements. An initial room temperature scan on (NH$_{4}$)$_{2}$SO$_{4}$ demonstrated 1-D resolution of 10 $\mu$m; a spin nutation experiment determined the value of the rotating magnetic field to be 13 gauss, and a spin echo was observed with a full width half maximum of 8 $\mu$s. At 77 K we obtained the first force detected boron NMR signal in a 30 $\mu$m powder sample of the superconductor MgB$_{2}$. Our measurements yielded a force of 10$^{-13}$ N with $B_{1}$ = 63 gauss. Further studies are underway to map the spin lattice relaxation with respect to temperature to elucidate the pairing symmetry of MgB$_{2}$ as well as effects due to its two nearly independent electronic bands. In addition we describe the construction of a compact room temperature probe and a variable temperature probe for dynamical imaging experiments. [Preview Abstract] |
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K1.00062: Atomic charge state determination by AFM Leo Gross, Fabian Mohn, Peter Liljeroth, Jascha Repp, Franz Giessibl, Gerhard Meyer We investigated the charge state switching of individual gold and silver adatoms on ultrathin NaCl films on Cu(111) using a qPlus tuning fork atomic force microscope (AFM) operated at 5 Kelvin with oscillation amplitudes in the sub-{\AA}ngstrom regime. Charging of a gold adatom by one electron charge increased the force on the AFM tip by a few piconewtons. Employing Kelvin probe force microscopy (KPFM) we also measured the local contact potential difference (LCPD) as a function of the tip height above differently charged adatoms. We observed that the LCPD is shifted depending on the sign of the charge and allows the discrimination of positively charged, neutral, and negatively charged atoms. [L. Gross, et al., Science 324, 1428 (2009)] [Preview Abstract] |
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K1.00063: Atomic-resolution AFM imaging of single molecules Fabian Mohn, Leo Gross, Nikolaj Moll, Peter Liljeroth, Gerhard Meyer We have recently developed a technique, which enables imaging of individual admolecules with atomic resolution using noncontact atomic force microscopy [L. Gross et al., Science 325, 1110 (2009)]. The key to achieving intramolecular contrast is a controlled functionalization of the microscope's tip apex. We compare the imaging capabilities of different tip terminations and present measurements of the distance dependence of the imaging contrast. These investigations - along with first- principle density functional theory calculations - indicate, that AFM operation in the regime of maximal attractive forces is crucial for achieving atomic contrast on molecules. Such close- distance operation is facilitated by using oscillation amplitudes in the sub-angstrom range. [Preview Abstract] |
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K1.00064: Ultrasonic Subsurface Nanostructures Detection with Frequency Modulated Height Control Rodolfo Fernandez Rodriguez, Xiaohua Wang, Mike Hopkins, Keith Parker, Richard Nordstrom, Andres La Rosa Subsurface imaging of nanostructures have applications both in the integrated circuits industry to find defects in the fabrication process of electronic components and in the biophysics research for imaging of subcellular structures. An Ultrasonic sensor has been integrated into a tuning-fork (TF) based scanning probe microscope (TF-SPM) to monitor the acoustic vibration of the sample as a result of its interaction with the TF probe. The feedback control of the probe-surface distance is performed by means of the frequency shift of the TF signal. Topography and related acoustic and phase images will be presented. [Preview Abstract] |
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K1.00065: Strong coupling of two flux qubits to a colanar waveguide resonator F. Deppe, T. Niemczyk, E. P. Menzel, E. Hoffmann, M. J. Schwarz, A. Marx, R. Gross, M. Bina, J. J. Garcia-Ripoll, E. Solano The field of circuit QED opens new possibilities in both quantum information processing and studies of fundamental quantum mechanics ``on a chip.'' Central building blocks are qubit circuits, which interact with on-chip superconducting microwave resonators. Of particular importance is the strong-coupling regime, where the coupling strength exceeds all relevant decay rates in the system. Here, we present spectroscopic measurements on two superconducting flux qubits strongly coupled to a coplanar waveguide resonator. [Preview Abstract] |
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K1.00066: ATOMIC, MOLECULAR, AND OPTICAL PHYSICS |
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K1.00067: Geometry and Acceleration Effects on Majorana Loss of Ultra-cold Atoms in a Hybrid Optical and Magnetic Trap Yafan Duan, Feng Cheng, Zhen Xu, Yuzhu Wang, Tao Hong The precise control of a hybrid optical and magnetic trap makes it possible to investigate the effects of geometry and acceleration on Majorana loss of atoms caused by nonadiabatic spin flips. We experimentally investigate how geometry and acceleration affect the loss rate of the atoms in an anisotropic magnetic trap formed by thin wires on an atom chip. Combining with a far blue detuned one dimensional optical lattice, we investigate the sealing effect of the hole in the magnetic trap. In addition, we will also explore the possible application of this technique in guided atom interferometers and quantum simulation with one dimensional quantum gases. [Preview Abstract] |
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K1.00068: Dynamics of Bose-Einstein condensates and degenerate Fermi gases in disorder potentials JiaJia Chang, Chris Hamner, Peter Engels Ultracold atoms placed in disorder potentials have recently attracted much attention from both an atomic physics perspective as well as from a condensed matter perspective. In our experiment we study the effects of a 1D disorder potential on the collective dipole motion of a Bose-Einstein condensate and a degenerate Fermi gas. We observe damping in both cases though the mechanism for the damping is predicted to be different in each case. We also investigate the damped dipole motion of a Bose-Fermi mixture in a harmonic trap. Our recent and ongoing experiments will be presented. [Preview Abstract] |
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K1.00069: ABSTRACT WITHDRAWN |
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K1.00070: Effects of three-body collisions in a two-mode Bose-Einstein condenstate Ivette Fuentes-Schuller, Cristopher Hernandez-Salinas, Pablo Barberis-Blostein, Robert B. Mann We study the effects of three-body collisions in the basic physical properties of a two-mode Bose-Einstein condensate. By finding the exact analytical solution of a model which includes two-body and three-body elastic and mode-exchange collisions, we show analytically that three-body interactions produce observable effects in the probability distribution of the ground state and the dynamics of the relative population. [Preview Abstract] |
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K1.00071: The Effect of Imperfections and Defects on the Sensitivity to Inertial Rotations in Arrays of Coherently Coupled Atomic Interferometers John Toland, Daniel Dayon, Christopher Search The ability to interferometrically detect inertial rotations via the Sagnac effect has been a strong stimulus for the development of atom interferometry because of the potential $10^{10}$ enhancement of the rotational phase shift in comparison to optical Sagnac gyroscopes. Here we analyze ballistic transport of atomic matter waves in a one dimensional chain of N coherently coupled ring shaped atom interferometers in the presence of an inertial rotation of angular frequency, $\Omega$. The transmission through the interferometer chain exhibits an interference pattern as a function of the Sagnac phase shift with large regions of zero transmission interspersed with regions of near unity transmission. We numerically study the phase sensitivity of such chains for varying amounts of atomic velocity fluctuations and random disorder in the size and shapes of the rings. We show that the phase sensitivity is an order of magnitude below the shot noise limit for experimentally reasonable size and velocity fluctuations. We additionally consider the phase sensitivity of a non-uniform chain of rings containing individual defect rings. The defect states make it possible to achieve significant enhancements in the phase sensitivity in response to rotations in comparison to a uniform chain. [Preview Abstract] |
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K1.00072: Precision Atom Interferometry with Bose-Einstein Condensates Alan Jamison, Vladyslav Ivanov, Nathan Kutz, Subhadeep Gupta Interferometry using laser cooled atom sources diffracted by standing waves of light can achieve remarkable sensitivity in diverse measurements such as that of local gravity, gravity gradients, and atomic photon recoil. A key feature of these achievements is the small velocity distribution of laser cooled atom sources. While a Bose-Einstein condensate (BEC) source provides an even narrower velocity distribution, the higher atomic interaction energy (mean field) introduces a new systematic error to the measurement. Using a contrast atom interferometry technique with sodium Bose-Einstein condensates (BEC), atomic photon recoil has been measured [1] to 7 parts per million (ppm) precision but 200 ppm accuracy, limited by the mean field systematic. We analyze the complete effect of the mean field interaction by numerically simulating the experiment using the nonlinear Gross-Pitaevskii equation. Together with this analysis we will also present our plans to extend the experimental technique to ytterbium BECs to achieve part-per-billion (ppb) level sensitivity. A measurement of the photon recoil at this level will provide a new competitive measurement of the fine structure constant ? at the sub-ppb level. This work is supported by the National Science Foundation. [1] S. Gupta et al, Phys Rev Lett 89, 140401 (2002) [Preview Abstract] |
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K1.00073: ABSTRACT WITHDRAWN |
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K1.00074: Application of the positive-P representation to self-organization in optical lattices Ray Ng, Erik S. Soresen The study of real time dynamics in a quantum system is very difficult. The recent development of simulational methods based on the positive-P representation in quantum optics have demonstrated the feasability of obtaining reliable results out to intermediate time scales. The method converts the master equation of a quantum mechanical system to a Fokker-Planck Equation (FPE), which can then be mapped on to a set of Stochastic Differential Equations (SDEs) making the method ideal for treating This makes it an ideal open systems. In this poster we discuss how the positive-P representation is applied to a the problem of self-organization of atoms in an optical lattices with a coupling to a resonant mode. We explicitly show how the final SDEs are derived and discuss strategies for simulating these equations. Improvements on the positive-P representaion of the model in terms of so called gauge-P representations is also discussed. [Preview Abstract] |
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K1.00075: ABSTRACT WITHDRAWN |
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K1.00076: ABSTRACT WITHDRAWN |
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K1.00077: Large N Model of Bose Gas Ke Ke, Leo Radzihovsky We construct the large N model of bose gas. Using an artificial parameter 1/N to do the perturbative analysis to study two models: $U(N)$ bose gas and $U(1) \times O(N)$ bose gas. We find that for $U(N)$ bose gas we get Bogoliubov spectrum and LHY thermal dynamical relations which is the same as the usual weak coupling bose gas models. For $U(1) \times O(N)$ bose gas model, however, we calculate the non-perturbative quantum correction to the depletion, chemical potential, free energy and dispersion relations. [Preview Abstract] |
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K1.00078: Ground State Properties of Cold Bosonic Atoms At Large Scattering Lengths Junliang Song, Fei Zhou In this letter, we study bosonic atoms at large scattering lengths using a variational method where the condensation amplitude is a variational parameter. We further examine momentum distribution functions, chemical potentials and speed of sound, and spatial density profiles of cold bosonic atoms in a trap in this limit. The later two properties turn out to bear similarities of those of Fermi gases. Estimates obtained here are applicable near Feshbach resonances, particularly when the fraction of atoms forming three-body structures is small and can be tested in future cold atom experiments. [Preview Abstract] |
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K1.00079: Impurities in the hardcore Bose-Hubbard model and the xxz model on the triangular lattice Sebastian Eggert, Xuefeng Zhang, Yuchuan Wen The ferromagnetic-antiferromagnetic xxz model is equivalent to the hardcore Bose-Hubbard model. On a triangular lattice frustration effects give rise to interesting physical behavior, including a realization of a supersolid phase. We now consider vacancies in this model using a combination of numerical Monte Carlo simulations and analytic calculations. The solid order and the superfluid density show characteristic changes locally around the impurity depending on the phase. In some cases a single impurity can affect the physical behavior of the entire system. The results show an interesting competition of the different order parameters and illustrate the nature of the excitations in the different phases. [Preview Abstract] |
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K1.00080: Bose-Einstein condensate in an all-optical ring trap Anand Ramanathan, Sergio Muniz, Kevin Wright, William Phillips, Gretchen Campbell, Kristian Helmerson We demonstrate Bose-Einstein condensation of atoms in an all-optical ring geometry, created by the intersection of a horizontal sheet-like trapping beam and a vertical ring-shaped trapping beam. The BEC is continuous azimuthally around the ring. By tuning the relative intensities of the trapping beams, we can make a continuous transition from an elongated, quasi-1D system to a flat, quasi-2D system. We characterize the system by watching the BEC expansion in time-of-flight. We plan to use the system to study persistent currents and the effects of geometry and of a Josephson-like tunnel barrier on superflow. [Preview Abstract] |
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K1.00081: In situ Microscopy of a Two-dimensional Quantum Gas Xibo Zhang, Chen-Lung Hung, Peter Scherpelz, Nate Gemelke, Cheng Chin Two-dimensional (2D) atomic quantum gases exhibit many unique many-body phenomena. By directly probing coexisting local phases in an inhomogeneous atomic cloud, in situ imaging provides a powerful tool to study quantum many-body physics. Starting from a cesium-133 Bose-Einstein condensate loaded into a 2D potential, we ramp up a 2D optical lattice. The surface density is measured by high-resolution absorption imaging along the tightly confined direction. Our system holds promise for directly probing quantum many-body physics, including the bosonic superfluid to Mott insulator quantum phase transition, as well as the Berezinskii-Kosterlitz-Thouless (BKT) transition of a 2D system. From the density profile, we derive the local compressibility and local density fluctuations to characterize the local phases of the atomic cloud. At deep optical lattice depths, the Mott insulating phase provides an ideal starting point to study few-body physics. [Preview Abstract] |
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K1.00082: The Molecular Hubbard Hamiltonian Lincoln D. Carr, Michael L. Wall We present the Molecular Hubbard Hamiltonian [1], which describes ultracold heteronuclear diatomic molecules in an optical lattice in a strong DC electric field. Using time-evolving block decimation, we describe the quantum dephasing and entangled many body dynamics of the molecules due to an additional AC electric field driving rotational state transitions. We also discuss the effect of nuclear hyperfine structure and strong magnetic fields. [1] M. L. Wall and L. D. Carr, ``Emergent Time Scales in Entangled Quantum Dynamics of Ultracold Molecules in Optical Lattices,'' New Journal of Physics {\bf 11}, 055027 (2009). [Preview Abstract] |
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K1.00083: Toward Ultracold Mixtures and Polar Molecules from Lithium and Ytterbium Atoms Alexander Khramov, Anders Hansen, William Dowd, Vladyslav Ivanov, Subhadeep Gupta We are building a system for the combined cooling and trapping of lithium and ytterbium atoms. We plan to study interspecies interactions and also prepare diatomic polar LiYb molecules. Such molecules are important as novel strongly interacting quantum systems, for sensitive tests of the standard model of physics, and as building blocks for quantum computers. Our apparatus is based on separate effusive ovens and Zeeman slowers for the two species, a common ultrahigh vacuum chamber for simultaneous trapping of the two species, and the requisite magnetic and optical fields to induce strong interactions between trapped atoms. We will present our experimental setup including the achievement of simultaneous magneto-optical trapping of lithium and ytterbium atoms, and report on our latest experiments on dual species trapping and cooling in a far off resonance optical trap. This work is supported by the National Science Foundation, Sloan Research Foundation, and the University of Washington Royalty Research Fund. [Preview Abstract] |
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K1.00084: Microwave field modification of elastic and inelastic collisions of cold and ultra cold polar molecules Sergey Alyabyshev, Roman Krems We present a detail study of microwave laser field effects on collisions of polar molecules and atoms in the presence of a static magnetic field. We use the dressed-state formalism to describe the interaction of the radiation field with collision complex and perform rigorous scattering calculation to study Feshbach scattering resonances and inelastic spin changing transitions in collisions of CaH and NH molecules with He atoms. Our results indicate that microwave fields enhance collisional spin relaxation and can significantly modify the position and width of magnetic Feshbach resonances. We show that Feshbach resonances and spin-changing transitions in cold and ultracold collisions of polar molecules can be efficiently manipulated with microwave fields of moderate strength and discuss the mechanism of microwave field control of molecular collisions. [Preview Abstract] |
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K1.00085: Non-Linear Interactions in Pump-Probe Optical Phenomena for Moving Atomic Systems Verne Jacobs Reduced-density-matrix descriptions are developed for pump-probe optical phenomena involving moving many-electron atomic systems, taking into account the center-of-mass motion, collisions, and external magnetic fields. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. A semiclassical perturbative treatment of the electromagnetic interaction is used to obtain compact Liouville-space operator expressions for the n'th order non-linear macroscopic electromagnetic-response tensors. Coherent atomic excitations and the full tetradic-matrix form of the collision operator in the Markov approximation are taken into account. [Preview Abstract] |
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K1.00086: Transient XUV lasing without inversion via He triplet states E.A. Sete, S. Suckewer, A.A. Svidzinsky, M.O. Scully We demonstrate transient inversionless laser oscillation in short wavelength regions where population inversion is difficult to achieve. It was shown some time ago that when the excitation of an ensemble of two-level atoms is swept in the direction of lasing, so that atoms are prepared in the excited state just as the radiation from previously excited atoms reaches them, the resulting laser amplifier is ``highly anomalous" and yields superradiant emission without population inversion. We here show that transient lasing without inversion in a three-level system has common features with Dicke superradiance and can yield strong XUV lasing in, for example, He atoms (at 58 nm) or He-like ions such as B$^{3+}$ (at 6.1 nm). [Preview Abstract] |
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K1.00087: Two Ising-coupled quantum spins in the presence of a bosonic bath Peter P. Orth, Karyn Le Hur, David Roosen, Walter Hofstetter A system of two coupled quantum spins in contact with a common harmonic oscillator bath is a paradigm for the study of the interplay between quantum control and dissipation. It also constitutes the elementary building block of a quantum computer. Using the time dependent numerical renormalization group (TD-NRG), we study the system's rich dissipative dynamics arising from the competition between spin-spin and spin-bath coupling, and compare it to a perturbative Bloch-Redfield approach. As an example, we show that spin oscillations can be synchronized using the bath induced interaction. We also address how the well-known localization quantum phase transition of the single spin-boson model is affected by the presence of a second spin. We employ the NRG to calculate the zero temperature phase diagram as a function of dissipation and Ising coupling, for both ohmic and subohmic baths. In the subohmic case, we study the scaling of spin expectation values and entanglement entropy close to the phase transition. [Preview Abstract] |
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K1.00088: Analysis of current and shot noise correlations in a double dot interferometer coupled to a quantized bosonic field Brandon Langley, Marko Zivkovic, Ivana Djuric, Christopher Search We examine a ballistic electron Aharonov-Bohm interferometer with a single dot embedded in each of two arms that are connected in parallel to leads allowing the flow of current by sequential tunneling of electrons through the dots. We focus on the effect that correlations between dots due to the inter-dot spin-spin interactions have on the current-voltage(I-V) and frequency dependent current shot noise. The inter-dot spin-spin interaction is created by embedding the interferometer in an optical microcavity whose modes are far off-resonant with the intra-dot transitions and allows for a cavity mediated exchange of virtual photons between dots. With proper AB phase, inter-dot Coulomb repulsion, and inter-dot cavity mediated coupling, we can control the probability amplitudes for different tunneling paths of the interferometer and the probability of formation of inter-dot entangled spin triplet/singlet states. We analyze the dual effects of inter-dot cavity coupling and two-path interference on the I-V characteristics and shot noise correlations for charge and spin resolved currents in order to determine the conditions for optimal spin triplet/singlet state formation and how they are revealed in the current and noise. We also quantify the level of entanglement between the dots and investigate correlation of shot noise with entanglement measures. [Preview Abstract] |
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K1.00089: Absolute Measurement of STIRAP Efficiency Xiaoxu Lu, Yuan Sun, Claire Allred*, Harold Metcalf Driving atoms from an initial to a final state of the same parity via an intermediate state of opposite parity is most efficiently done using STIRAP\footnote{U. Gaubatz et al., {\it J. Chem. Phys.}, \textbf{92}, 5363 (1990).}, because it doesn't populate the intermediate state. For optical transitions this requires appropriate pulses of light in the counter-intuitive order - first coupling the intermediate and final states. We populate Rydberg states of He ($n = 26$) in a beam of average velocity 1070 m/s by having them cross two laser beams in a tunable dc electric field of $\sim 100$ V/cm. The ``red" light near $\lambda =$ 796 nm connects the 3$^3$P states to the Rydberg states and the ``blue" beam connects the metastable 2$^3$S state atoms emitted by our source to their 3$^3$P states. By varying the relative position of these beams we can vary the order and overlap encountered by the atoms. We vary the dc field to sweep across several Stark states \nolinebreak of the Rydberg manifold. We measure the absolute efficiency using a curved wavefront beam of $\lambda = 1.083\, \mu$m light to deflect residual 2$^3$S atoms out of the beam, and we measure their flux with and without the STIRAP beams. This uncontaminated measurement has high absolute accuracy. \newline *Presently at Columbia Univ., 1027 Pupin Hall, New York, NY 10027 [Preview Abstract] |
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K1.00090: High-lying resonances in Ps-H scattering below the H$^{- }$- e$^{+}$ threshold Z.-C. Yan, Yew Kam Ho In this work, we carry out an investigation of high-lying $S$-wave resonances in Ps-H scattering below the (H$^{-}$ - e$^{+})$ threshold. The method of complex-coordinate-rotation [1] is used together with employing highly correlated wave functions containing all six inter-particle coordinates. Using such Hylleraas-type bases [2] up to 6412 terms, the energy positions and widths up to the 7$S$ state in the Rydberg series converging to the H$^{-}$ threshold are calculated. The high-lying resonances from our present calculations are fitted to a quantum defect formula, and from which the energies of even higher members of the Rydberg series can be deduced. [1].Y. K. Ho, \textit{Phys. Rept}. \textbf{99}, 1 (1983). [2]. Z.-C. Yan and G. W. F. Drake\textit{, J. Phys. B} \textbf{30}, 4723 (1997). [Preview Abstract] |
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K1.00091: Rubidium-Strontium collisions Michaela Kleinert, Garrett Potter, Marc Whitehead, Elyse McEntee, Christopher J. Koll The invention of the magneto-optical trap (MOT) in 1987 - which was awarded the Noble Price in Physics 10 years later - has enabled many new and exciting experiments. Among them are precision measurements of basic atomic properties, ultracold collisions, Bose-Einstein Condensates, atom lasers, etc.. Recent developments in the field of atomic and molecular physics have included the creation of diatomic (homo- and heteronuclear) molecules. These ultracold molecules promise to revolutionize physical chemistry, few-body physics, precision measurements and quantum information processing, similar to how ultracold atoms revolutionized AMO physics several years ago. We will present our first results of a mixed alkaline (rubidium) and alkaline-earth (strontium) magneto-optical trap. [Preview Abstract] |
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K1.00092: Confinement of the hydrogen molecular ion H2+ under a magnetic field inside a spheroid Martin Molinar A study of the confinement of the hydrogen molecular ion H2+ is done. The molecular ion is subject to the action of a magnetic field. In the Born -- Oppenheimer approximation, we solve numerically the Schr\"{o}dinger's equation, using trial functions and one algorithm that allows us to calculate the energies for different given values of the confinement parameters. We use the variational method in order to estimate the energy of the ground state. Some properties of the system as the pressure exerted by the confinement, the polarizability in the approximations of Kirkwood and Buckingham and the energies of the vibrational states are calculated. The behavior of the internuclear separation is analyzed for the geometry considered. [Preview Abstract] |
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K1.00093: Demonstration of high harmonic plateau supercontinuum driven by a 6.5 fs/800 nm laser field Yinghui Zheng, Zhinan Zeng, Hui Xiong, Ruxin Li, Zhizhan Xu, Yan Peng, Xuan Yang, Heping Zeng Isolated attosecond pulses in the plateau region have been demonstrated by using nearly single-cycle laser pulses. However, so far the single-cycle laser pulses is not available for most of the laboratories. Recently, several methods have been put forward for generating isolated attosecond pulses using longer laser pulses. In our work, we demonstrate experimentally the high harmonic plateau supercontimuum driven by a 6.5 fs, 800 nm phase-stabilized laser pulse due to the successful selection of single quantum path of the returning electrons. The high harmonic generation is controlled on the basis of the big difference of ionization between the adjacent half optical cycle of ultrashort driving laser pulses. Moreover, we predict the possibility to generate isolated 100 as pulses using a driving laser pulse longer than 2 cycles. [Preview Abstract] |
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K1.00094: Streaking of shake-up ionization Renate Pazourek, Stefan Nagele, Johannes Feist, Andreas Kaltenb\"ack, Emil Persson, Barry I. Schneider, Lee A. Collins, Joachim Burgd\"orfer We investigate whether an apparent ``time delay'' between electrons ionized by an attosecond XUV pulse with and without shake-up excitation of the remaining ion can be extracted using XUV-IR streaking setups. The classical interpretation of attosecond streaking states that the release time of an electron can be directly mapped to the momentum shift which the electron acquires from the IR pulse. However, detailed quantum mechanical investigations show that the ionization and shake-up process itself are modified by the IR field, leading to additional momentum shifts of the ionized electrons which are not related to a real ``time delay.'' We address this problem for the helium atom for which we solve the full time-dependent Schr\"odinger equation including all correlation effects. [Preview Abstract] |
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K1.00095: p-Wave Resonant Bose Gas: A Finite-Momentum Spinor Superfluid Sungsoo Choi, Leo Radzihovsky We study a degenerate gas of two-species bosonic atoms interacting through a $p$-wave Feshbach resonance (as realized in, e.g., a $^{85}$Rb-$^{87}$Rb mixture). We show that this model exhibits a finite-momentum atomic-molecular superfluid(AMSF), sandwiched by a molecular $p$-wave (orbital spinor) superfluid and by an s-wave atomic superfluid at large negative and positive detunings, respectively. The magnetic field can be used to tune the modulation wave vector of the AMSF state, as well as to drive quantum phase transitions in this rich system. [Preview Abstract] |
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K1.00096: Routes to Quantum Vortex Nucleation Andreas Nunnenkamp, Ana Maria Rey, Keith Burnett We study and compare quantum vortex nucleation of a dilute ultracold bosonic gas trapped in three different configurations: a one-dimensional ring lattice, a one-dimensional ring superlattice and a two-dimensional asymmetric harmonic trap. In all of them there is a critical rotation frequency, at which the ground state becomes a fragmented Bose-Einstein condensate and is therefore highly entangled. However, the entanglement properties vary significantly from case to case. We explain these differences by characterizing the intermediate states that participate in the vortex nucleation process. Finally, we show that noise correlations are sensitive to these differences. [Preview Abstract] |
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K1.00097: Mixing of Bose and Fermi Superfluids B. Ramachandhran, S.G. Bhongale, H. Pu We construct the finite temperature phase diagram of an interacting mixture of Bose and Fermi superfluids. Our study reveals a unique region of phase space where the BCS instability of the Fermi surface coincides with the first-order instability of the mixture towards phase separation. We illustrate how this intriguing interplay manifests in trapped configurations, thereby providing important constraints for observing superfluidity in experiments involving Bose-Fermi mixtures. [Preview Abstract] |
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K1.00098: Effects of magnetic dipole-dipole interactions in Bose-Einstein condensates: geometry and stability Abraham Olson, Yong Chen Under normal conditions, the dominant atom-atom interaction in Bose-Einstein condensates (BECs) is the isotropic, short-range, s-wave scattering. With Feshbach resonances, those interactions can be tuned to near zero, allowing for the study of the anisotropic and long-range magnetic dipole-dipole interaction (MDDI). Motivated by the recent developments in this area, we study MDDI effects for $^{52}$Cr and various alkali atomic species which have stable BEC. We employ a variational calculation to model the MDDI effects on the BEC both in static and dynamic situations. With this model, we reproduce the MDDI effects that have been experimentally observed in $^{7}$Li and $^{52}$Cr. In addition, we present experimentally realizable predictions for other alkali species. As the theoretical understanding and experimental investigations of MDDI effects on BECs are only growing, these results should provide a helpful guide for further exploration. [Preview Abstract] |
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K1.00099: SUPERCONDUCTIVITY |
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K1.00100: Leggett's collective modes in multi-band superconductors: multiple dynamical classes Yukihiro Ota, Masahiko Machida, Tomio Koyama, Hideo Aoki One important way to characterize multi-band superconductors should be to look at their collective modes, which are expected to reflect the broken gauge symmetry that involves multi-bands. We extend Leggett's 1966 analysis for a massive out-of-phase mode coexisting with the Nambu-Goldstone mode in two-band superconductors to the case where there are three or more bands. Crucial, as we find here, is to classify the inter-band Josephson coupling energy which is the origin of the Leggett's modes. Namely, three-band superconductors are shown to accommodate more than one collective modes, which are classified in terms of the ``dynamical class'' that distinguishes the action of the inter-band Josephson coupling. The mass of the multiple Leggett's modes is then shown to dramatically depend on the class. We expect that the present prediction can be tested in the iron-based superconductor (with a gap function involving three bands) and ultracold fermionic atom gases with multiple atomic species. [Preview Abstract] |
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K1.00101: Epitaxial Growth of (111) Al/Al$_{2}$O$_{3}$/Al Trilayers on Sapphire Fabio da Silva, Brian Gorman, Michael Kaufman, Hamid Fardi, David Wisbey, Jeffrey Kline, Danielle Braje, David Pappas Microstructural defects in tunnel junction trilayers epitaxially grown on basal plane sapphire are observed using transmission electron microscopy techniques. The ?lms grow nominally (111) oriented with grain sizes ranging from 100 nm to 1 $\mu $m. Both twinning and low angle grain boundaries are observed in the bottom Al electrode. The rotations for the low-angle boundaries are consistent with alignment to the various $\alpha -$Al2O3 oxygen sublattice layers. The epitaxial Al2O3 tunnel barrier is approximately 1 nm thick, which is about a factor of 2 lower than necessary for use in a phase qubit, and showed defects that can be associated with the electrode grain boundaries and strain. On the other hand, grain boundaries present in the top Al electrodes were only weakly influenced by the bottom layer structure. Island formation was also observed in the Al electrodes grown on the epitaxial tunnel barriers. This is proposed to be the formation mechanism of the grain structures that is observed for the thicker top electrodes. These defects appear to be inherent to many metal/sapphire growth systems, and may limit the applicability of crystalline (111) Al on basal-plane sapphire for superconducting Josephson junctions. [Preview Abstract] |
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K1.00102: Specific heat for high $T_{c}$ superconductors P. Salas, M. Fortes, F.J. Sevilla, M.A. Solis In this work we model high-$T_{c}$ superconductors as a mixture of paired and unpaired electrons within an infinite layered structure [1]. The electron pairs are assumed to be non interacting, zero-spin bosons with a linear dispersion relation while the layers are simulated by a Delta-Kronig-Penney potential in one direction. The unpaired and paired electrons are free to move in the other two perpendicular directions. We use experimental parameters of cuprates to fix the plane separation and adjust the plane ``impenetrability'' to replicate the superconductor critical temperature as the Bose-Einstein condensate temperature of the electron pairs. The total specific heat, obtained as a sum of the electronic (paired plus unpaired) and lattice specific heat, reproduces the experimental linear behavior of $C_{V}(T)/T$ just below $T_c$. \newline [1] P. Salas, M. Fortes, M. de Llano, F.J. Sevilla and M.A. Sol\'{\i}s, {\it ``Condensation Bose-Einstein in multilayeres,"} to be published. [Preview Abstract] |
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K1.00103: Acoustic Attenuation in the Borocarbide Superconductor \textit{LuNi}$_{2}B_{2}C$ in High Magnetic Fields Sasha Dukan, Russell Flaum We present a detailed numerical investigation of sound wave attenuation in the borocarbide superconductor~ LuNi$_{2}$B$_{2}$C subjected to a high magnetic field in the limit of low temperatures. At high magnetic fields, the Landau level quantization of electronic energies results in the appearance of gapless quasiparticle excitations at the Fermi surface. A powerful probe of such low-energy excitations in superconductors is measurement of the attenuation of sound waves passing through the superconductor in the limit of low frequencies. In a clean superconductor, at or near the gapless points, quasiparticles can absorb energy from ultrasonic waves and, as a result, there is an algebraic temperature dependence of the attenuation coefficient in the superconducting state.~ We investigate the influence of non-magnetic disorder on the attenuation coefficient and apply our theory to the borocarbide superconductor \textit{LuNi}$_{2}B_{2}C.$ [Preview Abstract] |
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K1.00104: Bose Operators as Linear Combination of Fermi Operators. Correlated Electron Pairs Formation Carlos Figueroa, Ra\'ul Riera, Rodrigo Rosas, Mart\'In Molinar In this work, the formation of correlated electron pairs by the interchange of a phonon in a conductor material is studied. The process of electron pairs formation is graphically represented and physically interpreted. The representation of phonons creation and annihilation operators as a linear combination of products of electron creation and annihilation operators is also studied. The end is obtained BCS Hamiltonian. [Preview Abstract] |
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K1.00105: Transport theory of superconductors with singular interaction corrections Alex Levchenko We study nonlinear transport properties of superconductors near the classical critical point $T_c$ where fluctuation effects play the dominant role. In this regime conductivity is set by the interplay of two competing effects. The first is that strong electron-electron interactions in the Cooper channel increase the life time of fluctuation Cooper pairs and thus enhance conductivity. On the other hand, dynamic pair breaking effects tend to suppress superconductivity. An interplay between these processes defines the new transport regime $Gi\ll\frac{T-T_c}{T_c}\ll\sqrt{Gi}$ where fluctuation induced conductivity becomes more singular, here $Gi$ is the Ginzburg number. The crossover temperature $T_c\sqrt{Gi}$ is generated as the result of scattering on dynamic fluctuations of the order parameter. The most singular contributions to conductivity stem from the dynamic Aslamazov-Larkin term, and novel Maki-Thompson and interference corrections. We suggest that the natural way to probe nonlinear fluctuation regime in superconductors is by magnetoconductivity measurements in the perpendicular field. [Preview Abstract] |
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K1.00106: Imaging Vortices in YBa$_{2}$Cu$_{4}$O$_{8}$ using a Transmission Electron Microscope Charlotte Bowell, James Loudon, Janusz Karpinski, Paul Midgley When magnetic flux penetrates a Type-II superconductor, it does so in the form of superconducting vortices. The study of these vortices can reveal information about the nature of the superconductivity in the material as well as being important for applications. These vortices can be imaged using a transmission electron microscope (TEM), as the electron beam is deflected by the penetrated magnetic flux. This technique was pioneered by Tonomura et al. [1], using a specially adapted microscope. Recently, it has been demonstrated that vortex imaging is also possible on a commercial TEM [2]. Here we present results on the cuprate superconductor YBa$_{2}$Cu$_{4}$O$_{8}$, in which CuO chains running along the crystal b-direction are thought to become superconducting via a proximity effect with the CuO$_{2}$ planes. A difficulty encountered with the TEM technique is in producing samples thin enough to be electron transparent. A sample, of size 30 $\mu$m x 30 $\mu$m x 200 nm, was cut from a bulk YBa$_{2}$Cu$_{4}$O$_{8}$ single crystal using focussed ion beam milling. To look into the influence of the CuO chains, Lorentz imaging was used to investigate the vortex configuration and movement in real time, while holography was employed to study the vortex field profile. [1] Harada et al., Nature 360, 51 - 53 (1992) [2] J. C. Loudon and P. A. Midgley, Ultramicroscopy 109: 700-729 (2009) [Preview Abstract] |
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K1.00107: Two magnetically distinct environments in Cu-O planes in an underdoped High-Tc cuprate: La(2-x)Sr(x)CuO(4) seen via $^{17}$O NMR Robert Smith, Philip Kuhns, Arneil Reyes, Greg Boebinger, Takashi Imai, K. Hirota Using high magnetic fields (30T) we investigate the normal state of the underdoped superconductor La(1.885)Sr(0.115)CuO(4) using $^{17}$O NMR. The high field $^{17}$O NMR spectrum shows evidence for two distinct planar oxygen signals, $^{17}$O(p1) and $^{17}$O(p2). The Knight Shift of $^{17}$O(p1) drops linearly with decreasing temperature to zero near 60K, twice the zero field T$_{C}$. $^{17}$O(p2) Knight Shift drops non-linearly to zero below 40K. The $^{17}$O(p2) line broadens with decreasing temperature while $^{17}$O(p1) slightly narrows. Comparing the Knight Shift and linewidth of the two lines suggests very different magnetic environments. [Preview Abstract] |
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K1.00108: Time-Reversal Symmetry Breaking in the Non-Linear Distortion from Superconducting Circuits Evan Pease, Stephen Remillard Microwave filters made from high temperature superconductors (HTS) are known to produce measurable harmonic and intermodulation distortion (IMD) at incident power levels as low as a small fraction of a microwatt. Distortion created by the filters sets a limit for use in microwave technologies, and its observation provides a better understanding of the electrodynamics of the HTS materials. Multi-tone measurements have been performed to detect the distortion, and with a three-tone technique even and odd order distortion currents are measured at the same frequency. Both even and odd order IMD are measured at the resonant frequency, permitting the experimental observation of time-reversal symmetry breaking in superconducting current. A catastrophic increase in only the odd order IMD near the transition temperature, Tc, is consistent with the expectations of the non-linear Meissner effect. The absence of such a catastrophe in the even order distortion indicates a higher order of time-reversal symmetry in the currents near Tc. The slopes of the IMD curves approach their ideal values close to Tc consistent with the linear-nonlinear interaction theory. [Preview Abstract] |
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K1.00109: Electronic Raman scattering in Bi-based superconductors under pressure Xiaojia Chen, Viktor V. Struzhkin, Alexander F. Goncharov, Russell J. Hemley, Ho-kwang Mao, Cheng-Tian Lin, Jian-Xin Zhu Determining the nature of interaction responsible for the Cooper-pair formation in cuprates remains unsettled. The most probable candidates are lattice vibrations (phonons) and spin fluctuation modes. Recently, it has been argued that Raman scattering in $B_{1g}$ symmetry may serve as a probe to distinguish between phonon-mediated and magnetically mediated $d$-wave superconductivity. Here we report the results of electronic Raman scattering measurements in Bi-based bilayer and trilayer superconductors at high pressures and at temperatures around 12 K. As a clean and effective tool, pressure enhances $T_{c}$ and thus increases the pairing interaction in these materials. Meanwhile, we find that pressure also brings about the change of the $B_{1g}$ mode. The observed evolution of $B_{1g}$ modes with pressure sheds important insight on the pairing mechanism of high-$T_{c}$ superconductivity. [Preview Abstract] |
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K1.00110: Interaction corrections to tunneling conductance in ballistic superconductors Alex Levchenko It is known that in the two-dimensional disordered superconductors electron-electron interactions in the Cooper channel lead to the negative logarithmical in temperature correction to the tunneling conductance, $\delta g_{DOS}\propto-\ln\big(\frac{T_c}{T-T_c}\big)$, above the critical temperature $T_c$. Physically this result appears due to the density of states suppression by superconductive fluctuations near the Fermi level. It is interesting that the other correction, which accounts for the Maki-Thompson type interaction of fluctuations, is positive and exhibits strong power-law, $\delta g_{MT}\propto \big(\frac{T_c}{T-T_c}\big)^3$, which dominates the logarithmic term in the immediate vicinity of the critical temperature. This presentation is devoted to the fate of such interaction corrections in the ballistic superconductors. It turns out that ballistic dynamic fluctuations perturb single particle density of states near the Fermi level at the energy scale $\epsilon\sim\sqrt{T_c(T-T_c)}$, which is different from $\epsilon\sim T-T_c$, relevant in the diffusive case. In this regime we confirm that correction to the tunneling conductance remains negative and logarithmic not too close to the critical temperature, while in the immediate vicinity of the transition we find novel power-law for the Maki-Thompson contribution, $\delta g_{MT}\propto\big(\frac{T_c}{T-T_c}\big)^{3/2}$. [Preview Abstract] |
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K1.00111: Observation of Josephson coupling through an interlayer of antiferromagnetically ordered chromium Martin Weides, Mario Disch, Hermann Kohlstedt, Daniel Buergler The supercurrent transport in metallic Josephson tunnel junctions with an additional interlayer made up by chromium, being an itinerant antiferromagnet, was studied. Uniform Josephson coupling was observed as a function of the magnetic field. The supercurrent shows a weak dependence on the interlayer thickness for thin chromium layers and decays exponentially for thicker films. The diffusion constant and the coherence length in the antiferromagnet were estimated. The antiferromagnetic state of the barrier was indirectly verified using reference samples. Our results are compared to macroscopic and microscopic models. [Weides et al., Phys. Rev. B 80, 064508 (2009)] [Preview Abstract] |
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K1.00112: Excess noises and its correlation with vortex motion Fulin Zuo, Hengsong Zhang We report voltage noise studies in the superconducting transition of thin Tin (Sn) films. Voltage noises are measured as a function of temperature and applied current. Simultaneous measurement of the noise power and I-V characteristics suggest strong correlation of the excess noises with vortex motion. The noise power displays the same temperature dependence as that of the third harmonics voltage signal. The results will be discussed in terms of vortex- antivortex pair and pair-pair interactions. [Preview Abstract] |
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K1.00113: Depressions of T$_C$ in the superconducting dome of La-Bi2201 and PbLa-Bi2201 L. Dudy, B. M\"uller, A. Krapf, H. Dwelk, O. L\"ubben, A.K. Ariffin, C. Janowitz, R. Manzke In the generic phase diagram of the hole-doped cuprates, the superconducting transition temperature (T$_C$) versus hole-doping is typically illustrated as a flipped parabola which exhibits the maximum at around 16\% of hole doping. But there is also the possibility of a generic existence of depressions within this superconducting dome: At certain hole-dopings, the TC drops. For La$_{2-x}$Ba$_x$CuO$_4$, the famous 1/8 depression [1] is widely accepted. La$_{2-x}$Sr$_x$CuO$_4$ also exhibits this 1/8 depression, but other fractional depressions (``magic doping fractions'') are suggested for this material [2]. We will show that for two structurally quite different single-layered Bi cuprates, namely La-Bi2201 and PbLa-Bi2201, also depressions at certain hole dopings exist. Possible consequences of the assumed generality of these depressions will be discussed.\\[4pt] [1] A. R. Moodenbaugh et al., Phys. Rev. B 38, 4596 (1988).\\[0pt] [2] S. Komiya et al., Phys. Rev. Lett. 94, 207004 (2005). [Preview Abstract] |
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K1.00114: Manipulation of quantum vortex states by local supercurrent injection into mesoscopic superconductors Akinobu Kanda, Milorad V. Milosevic, Shinya Hatsumi, Youiti Ootuka, Francois M. Peeters When vortices are confined in a small space, they take a formation which is quite different from that of bulk samples; the vortices tend to be arranged to fit the sample shape (multivortex state (MVS)), and/or, when the confinement is strong enough, a multiply-quantized vortex called a giant vortex may appear (giant vortex state (GVS)). In most studies, transitions between vortex states take place by the change in magnetic field or temperature. For the manipulation of the vortex states, however, temperature or magnetic fields are not necessarily suitable parameters. In this talk, I report a trial to induce vortex state transitions by local supercurrent injection into mesoscopic superconductors. Samples are thin mesoscopic superconducting square made of Aluminum, and the multiple-small-tunnel-junction (MSTJ) method is used to detect the vortex states. We have succeeded in inducing vortex penetration/expulsion, and transitions between a GVS and an MVS or between different MVSs with a fixed vorticity. The details of the transitions and possible applications of current-induced transitions will be discussed. [Preview Abstract] |
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K1.00115: Four-probe resistivity measurement on a Bi Nanowire Mingliang Tian, Jian Wang, Thomas Mallouk, Moses Chan While bulk Bi is a semimetal down to at least 50 mK, its electronic properties in a confined geometry are more complex. Here, we carry out four-probe measurements of electrical transport properties on individual single-crystal Bi nanowires of different diameter ranging from 100 nm down to 20 nm. The nanowires were fabricated by electrodeposition in porous membranes and contacted by focus ion beam technique. The wires show a superconducting transition near 1.5 K. Little-Parks--like oscillations in parallel field were seen in larger diameter wires but disappeared when the diameter of the wire is less than 30 nm. [Preview Abstract] |
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K1.00116: Superconductivity and Magnetism in In$_{2}$O$_{3}$-ZnO Observed in Bulk and Nano Samples Roberto Escudero, Francisco Ascencio, Karla Hernandez We prepared and studied compounds with In$_{2}$O$_{3}$ powders and ZnO nanoparticles. Samples were prepared under different stoichiometric conditions and reacted at different temperatures. The initial temperatures where the oxides are mixed were in the range of 300 $^{\circ}$C, final temperatures are close to 1100 $^{\circ}$C. Samples were annealed in oxygen and argon atmospheres. The resulting black compounds present superconducting behavior with maximum transition temperatures above 4.5 K. Magnetic measurements show bulk superconducting diamagnetism to the maximum value about -1/4$\pi $. This type II superconducting material presents a critical magnetic file H$_{C1}$ of 55 Oe and H$_{C2 }$of 345 Oe, at 1.7 K. Isothermal magnetic measurements, below and above the superconducting transition temperature show that the compounds are also ferromagnetic. [Preview Abstract] |
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K1.00117: Superconductivity in an Alkali Doped Polycyclic Aromatic Hydrocarbon, Picene Madoka Tokumoto, Fumihiko Shimizu, Yoshiaki Hata, Shinya Sawai, Jing Han, Katsuya Inoue The effect of carrier doping into polycyclic aromatic hydrocarbons, including perylene and pentacene, has been extensively studied.[1] As a result of halogen or alkali metal doping, a drastic increase in electrical conductivity was observed. However, superconductivity has not been reported except the one by Sch\"{o}n et al.[2] Recently, Kubozono reported that one of them, i.e. picene (C$_{22}$H$_{14})$ showed superconductivity at 20 K by doping with potassium.[3] We anticipate that it will lead to surprising findings of hidden organic molecular superconductors. In this presentation, we will report on the characterization of superconducting properties of alkali doped picene. Instead of ordinary vapor phase alkali metal doping, we employ thermal decomposition of alkali azides, i.e. AN$_{3}$ where A = K, Rb. We followed the doping procedure of thermal decomposition applied to fullerene C$_{60}$.[4] A systematic variation of the superconducting transition temperature and fraction are studied as a function of alkali metal composition. [1] H. Akamatu, H. Inokuchi, and Y. Matsunaga, Nature 173 (1954) 168. [2] J. H. Sch\"{o}n, Ch. Kloc {\&} B. Batlogg, Nature 406 (2000) 702; retraction, Nature 422 (2003) 93. [3] R. Mitsuhashi, Y. Kubozono et al.: private communication. [4] M. Tokumoto, et al. , J. Phys. Chem. Solids, 54 (1993) 1667. [Preview Abstract] |
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K1.00118: Attempt of MgB$_{2}$ Powder Alignment in Magnetic Field Moohee Lee, Kihyeok Kang, B.J. Mean, Sung Hoon Kim, B.K. Cho We have attempted magnetic alignment of MgB$_{2}$ powder grains in an epoxy resin under the magnetic field of 8 T. Since we do not know of direction and magnitude of a magnetic anisotropy tensor in the normal state, we devise difference alignment schemes assuming two cases; Case I for the easy along the c-axis and Case II for the easy axis perpendicular to the c-axis. For each case, we have built different devices. For example, for Case II, we have to apply rotation perpendicular to the magnetic field. Also, the device is designed to get rid of gravitational sedimentation by rotating the powder in an epoxy resin. For assessment of the c-axis alignment, XRD measurements are utilized. However, the three XRD data for the unaligned power, the Case I and the Case II are same and show no evidence of alignment. Possible reasons for the results will be discussed in detail. [Preview Abstract] |
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K1.00119: Fresnel aperture diffraction: a phase-sensitive probe for pairing symmetry of a superconductor Cheng-Shi Liu, Wen-Chin Wu Fresnel single aperture diffraction is proposed as a phase-sensitive probe for studying the pairing symmetry of a superconductor. It is shown that in case of gap symmetry $\Delta(-\mathbf{k})=\Delta(\mathbf{k})$ with wavevector ${\bf k}$ normal to the tunnelling junction of a superconducting film, the quasiparticle diffraction pattern developed at the image plane is zeroth-order minimum. In contrast, the corresponding diffraction pattern is zeroth-order maximum for the case of $\Delta(-\mathbf{k})=-\Delta(\mathbf{k})$. Observable consequences are discussed and proposed for studying the iron- arsenic based superconductor to which gap symmetry may be complicated as a result of multiple Fermi surface pairings. [Preview Abstract] |
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K1.00120: Multiple Resonators as a Multi-Channel Bus for Coupling Josephson Junction Qubits Zechariah Thrailkill, Joseph Lambert, Roberto Ramos Josephson junction-based qubits have been shown to be promising components for a future quantum computer. A network of these superconducting qubits will require quantum information to be stored in and transferred among them. Resonators made of superconducting metal strips are useful elements for this purpose because they have long coherence times and can dispersively couple qubits. We explore the use of multiple resonators with different resonant frequencies to couple qubits. We find that an array of resonators with different frequencies can be individually addressed to store and retrieve information, while coupling qubits dispersively. We show that a control qubit can be used to effectively isolate an active qubit from an array of resonators so that it can function within the same frequency range used by the resonators. [Preview Abstract] |
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K1.00121: Angular dependence of x-ray absorption spectrum for field-aligned Fe-based superconductors Y.B. You, B.C. Chang, M.F. Tai, H.C. Ku, Y.Y. Hsu, L.Y. Jang, J.F. Lee Anisotropic Fe $K$-edge and As $K$-edge x-ray absorption near-edge spectrum measurements on superconducting ($T_c$=52 K) (Sm$_{0.95}$La$_{0.05}$)FeAs(O$_{0.85}$F$_{0.15}$) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe $1s$ electrons to Fe $3d$/As $4p$ hybrid bands) relative to the tetragonal $ab$ plane of aligned powder indicates larger density of state along the $c$ axis and is consistent with the local-density approximation band-structure calculation. The anisotropic Fe $K$-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe$^{2+}$ $3d^6$ orbitals. The anisotropic As $K$-edge spectra are more or less the mirror images of Fe $K$-edge due to the symmetrical Fe-As hybridization in the FeAs layer. Angular dependence of As main peak (dipole transition of As $1s$ electrons to higher-energy hybrid bands) was observed suggesting character of As $4d$ $e_g$ orbitals. [Preview Abstract] |
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K1.00122: First-principles Study of Electronic Structures and Phonons in FeSe$_{1-x}$ Anil Kumar, Ajay K. Sood, Umesh V. Waghmare We present first-principles density functional theory based calculations to assess the effects of Se vacancies (which are essential for the material to be superconducting) and strength of on-site correlation on (a) phonon frequencies, and (b) electronic density of states of the non-magnetic and different magnetic phases of $FeSe_{1-x}$. Our calculations show that energetically anti-ferromagnetic stripe ordering is favorable compared to the non-magnetic and other magnetic phases. We also find that the phonon frequencies are quite sensitive to the vacancies, magnetic ordering and on-site correlation parameter U, and interpret these results in terms of spin-spin and spin-phonon couplings. Our estimate of the spin-phonon coupling is comparable to the superconducting transition temperature of FeSe. The presence of Se vacancies in the system results in a large peak in the density of states near the Fermi level, which possibly enhances the superconducting transition temperature. [Preview Abstract] |
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K1.00123: Superconductivity in new iron pnictide oxide Fe$_{2}$As$_{2}$Sr$_{4}$(Mg,Ti)$_{2}$O$_{6}$ Shinya Sato, Hiraku Ogino, Kohji Kishio, Jun-ichi Shimoyama A new iron arsenide oxide Fe$_{2}$As$_{2}$Sr$_{4}$MgTiO$_{6}$, which is isostructural with the iron-based superconductor Fe$_{2}$\textit{Pn}$_{2}$Sr$_{4}M_{2}$O$_{6}^{[1,2]}$, has been successfully synthesized by the solid-state reaction in quartz ampoules. Fe$_{2}$As$_{2}$Sr$_{4}$MgTiO$_{6}$ has antifluorite-type iron arsenide layer and K$_{2}$NiF$_{4}$-type oxide layer, while the $M$-site is composed of a combination of divalent (Mg$^{2+})$ and tetravalent (Ti$^{4+})$ cations as in the case of a double perovskite La(Mg,Ti)O$_{3}$. This fact indicates chemical flexibility of the perovskite-related layer in this system. This compound showed bulk superconductivity with $T_{c}$ of $\sim $20 K by partial substitution of Co for Fe. Moreover, high $T_{c}$ above 35 K was recorded by samples starting from Co-free and Ti-rich compositions, Fe$_{2}$As$_{2}$Sr$_{4}$(Mg$_{1-x}$Ti$_{x})_{2}$O$_{6}$ ($x$ =0.7$\sim $0.8). [1] H. Ogino \textit{et al}., \textit{Supercond. Sci. Technol.} \textbf{22} (2009) 075008. [2] X. Zhu \textit{et al}., \textit{Phys. Rev. B} \textbf{79} (2009) 220512(R). [Preview Abstract] |
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K1.00124: Physical properties of new iron arsenide oxide with thick perovskite-type oxide layer Naoto Kawaguchi, Hiraku Ogino, Koji Kishio, Junichi Shimoyama Since the discovery of high-$T_{c}$ superconductivity in LaFeAsO, a large number of layered compounds having anti-fluorite type Fe- or Ni-pnictide layer have been discovered. Among them, a series of pnictide oxides having perovskite-type oxide layers\footnote{H. Ogino \textit{et al}., \textit{Supercond. Sci. Technol.} \textbf{22} (2009) 075008} are attractive because of their chemical flexibility particularly at the perovskite-type oxide layer, which may results in new compounds. In the present study, various physical properties have been investigated for the new iron pnictide oxides with thick perovskite-type blocking layers, i.e., large interlayer distance between Fe-layers more than 1.7 nm. These samples showed metallic and paramagnetic behaviors in resistivity and magnetization measurements, respectively, down to 2 K without any signs of superconductivity and other anomalies. Relationship among crystal structure, constituent elements and physical properties will be discussed for the newly discovered system. [Preview Abstract] |
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K1.00125: Development of new layered selenide oxides with perovskite-type oxide layers Koichi Ushiyama, Hiraku Ogino, Kohji Kishio, Jun-ichi Shimoyama Several Fe-based superconductors with perovskite-type oxide layers, such as Sr$_{2}$ScFePO$_{3}$ ($T_{c} \quad \sim $ 17 K)$^{[1]}$, were discovered in our previous study. These compounds are composed of alternate stacking of superconducting layers with antifluorite structure and perovskite-type blocking layers. Since both layers are flexible in terms of chemical composition, development of various new functional materials can be expected from this family. In the present study, we have attempted to synthesize new layered selenide oxides with CuSe layers and discovered more than ten compounds, such as Sr$_{2}M$Cu$_{2}$Se$_{2}$O$_{2}$ ($M$ = Mn, Co, Ni, Cu, Zn) and Sr$_{2}M$CuSeO$_{3}$ ($M$ = Sc, Cr, Mn, Fe, Ga, In), thus far. These indicated that the CuSe layer can accommodate various types of blocking layers, which may lead various functions. Among them, Sr$_{2}$Cu$_{3}$Se$_{2}$O$_{2}$ has a potential as for the mother compound of superconductor, if appropriate concentration of carrier is introduced to the CuO$_{2}$ layer. Crystal structure and physical properties of these newly found compounds will be reported. [1] H. Ogino \textit{et al.}, \textit{Supercond. Sci. Technol.} \textbf{22} (2009) 075008 [Preview Abstract] |
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K1.00126: Tc amplification in pnictides due to Feshbach shape resonance in multigap superconductivity realized by tuning the Fermi level at the electronic topological transiton to one of the subbands Antonio Bianconi, Davide Innocenti, Nicola Poccia, Alessandro Ricci The new high Tc superconducting Pnictides AFe2As2 (A=Ba,Sr or Ca) are heterostructures at atomic limit like cuprates as described in the patent [A. Bianconi ``Process of increasing the critical temperature Tc of a bulk superconductor by making metal heterostructures at the atomic limit'' United State Patent No. :US6, 265, 019 B1, July 24, 2001] in fact are made of superconducting layers intercalated by spacer layers. ( R. Caivano, et al., Superconductor Science and Technology 22, 014004+ (2009), A. Ricci et al. Journal of Superconductivity and Novel Magnetism 22, 589 (2009)) where the Fermi level is tuned to a electronic topological transition in one of the subbands by doping, pressure or substitutions. Here we present the calculation of the Tc amplification by shape resonance or Feshbach resonance in a superlattice of layers in a narrow range where the chemical potential is tuned to the electronic topological transition as measured recently by NMR (H. Shishido et al. arXiv:0910.3634v1). The computer code tested now in the diborides and pnicitdes can be used for material design of new high Tc superconductors. [Preview Abstract] |
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K1.00127: Engineering Superconductivity by Molecular Charge Transfer Sajida Khan, K. Clark, A Hassesnien, K.-F. Braun, H. Tanaka, S.-W. Hla By mixing donor and acceptor molecular systems, different classes of materials such as insulators, metals, semiconductors and superconductors can be formed. Here we engineer nanoscale superconducting clusters by depositing donor BETS and acceptor GaCl$_{4}$ on a Ag(111) surface. First, we probe the electronic properties of individual species, BETS and Et4N-GaCl$_{4}$ on Ag(111) using tunneling spectroscopy at 5.4 K. Based on strong molecule-molecule interactions, both molecular species form clusters on the surface, and the corresponding tunneling spectroscopy data do not reveal any features around the Fermi level. A surprising structural transformation occurs when both molecular species are put together on this surface where the BETS start forming long chains. Tunneling spectroscopy data of the molecular clusters with mixed species shows formation of new HOMO-LUMO level. Most astoundingly, high resolution spectroscopy data reveal the existence of the superconducting gap within these clusters, thus opening a novel avenue of molecular superconductivity at the nanoscale spatial limit. [Preview Abstract] |
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K1.00128: Design for a Superconductor Discovery Engine (SCODEngine) O. Paul Isikaku-Ironkwe One of the grand challenges of superconductivity is achieving a paradigm shift from discovery by serendipity to discovery by design. Periodic Table-based Maps that involve electronegativity, valence electrons and atomic number that correlate with superconducting transition temperature can be used to design novel superconductors. Combining these maps with experimental databases on superconductors, databases of crystal structures and integrating material design software engine, we can re-design many known superconductor families and predict novel systems. By adding search engine technology with a ``knowledge discovery engine'', we produce a superconductor discovery engine (SCODEngine). The SCODEngine enables us to discover novel superconductors with the accelerated speed of a Google search. We have produced a primitive SCODEngine that may revolutionize novel superconductor search and discovery. [Preview Abstract] |
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K1.00129: ABSTRACT HAS BEEN MOVED TO SESSION A40 |
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K1.00130: SURFACES, INTERFACES, AND THIN FILMS |
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K1.00131: Studies of the interfaces of polar perovskites grown on SrTiO$_{3}$ Carl J. Stolle, Mark C. Monti, John T. Markert We report on our methods used for growth and characterization of epitaxial oxide thin films, such as LaAlO$_{3}$ (LAO) grown on single crystal SrTiO$_{3}$ (STO) substrates. We have deposited epitaxial thin films on STO using a KrF (248 nm) pulsed excimer laser with a typical fluence of 3.3 J/cm$^{2}$ and a pulse repetition rate of 5 Hz incident on a polycrystalline LAO target. The deposition takes place under low oxygen pressures (0.1-10 mtorr) and on a heated substrate (700-900$^{\circ}$C). We performed a systematic study of the chemical etch and anneal process used to create uniform TiO$_{2}$ terminated STO substrates. Two different chemical etchants were studied for a variety of etch times, a 6:1 mixture of NH$_{4}$F:HF and a 3:1 mixture of HCl:HNO$_{3}$. Substrates were then annealed in either air or oxygen for two hours at 750-950$^{\circ}$C. An atomic force microscope was used to characterize the chemical etch and final film topography. X-ray diffraction rocking curves and ${\theta}$-2${\theta}$ scans of deposited films demonstrate an epitaxial growth of LAO. Four-wire resistivity measurements of the interface were made via ohmic chromium contact pads created by thermal evaporation through a contact shadow mask. This work was supported by: Texas Advanced Research Program 003658-0126, The Robert A. Welch Foundation F-1191, and the National Science Foundation DMR-0605828. [Preview Abstract] |
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K1.00132: Vapor-Fluid Chemical Deposition: the effects of fluid solubility on sub-monolayer growth kinetics Ryan Neff, Charles Moran, David Patrick, Brad Johnson It is well known that sub-monolayer growth kinetics may be described by scaling laws. In particular, the distribution of the sizes of clusters coalescing under driven diffusive aggregation will scale with cluster size, a result that has been demonstrated by numerical simulation and verified by experiment (under vacuum deposition conditions). We study a system wherein monomers are dropped on a fluid surface with a given flux rate, allowed to diffuse and aggregate though a 3-D fluid volume, and deposit on a 2D substrate bounding the fluid in the vertical direction. We find 3 regimes with different deposition outcomes: i) the solubility of the monomers in the fluid is low, in which case aggregates form a ``crust'' near the top fluid surface, ii) the solubility is high and the monomers ``stick'' to the substrate (a minimum surface energy) but retain the activated diffusion appropriate to the fluid, and iii) the same, except that the monomers/aggregates undergo standard 2-D DDA once they reach the substrate. We find that the scaling laws do not apply to the case ii), where there is no peak in the size distribution, but are regained for the case iii). These results agree with preliminary data modeling deposition of tetracene under fluid-interface conditions. [Preview Abstract] |
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K1.00133: Structural properties of nanometric and micrometric TiCN/TiNbCN supperlattices Julio Caicedo, Luis Yate, Juan Ram\'Irez, Maria Elena G\'omez, Arturo Lousa, Joan Esteve, Pedro Prieto TiCN and TiNbCN systems have broadly been used as protective hard and anticorrosive coatings. [TiCN/TiNbCN]$_{n}$ multilayers were deposited on silicon substrates by two-target-r.f. magnetron sputtering with alternatively changing the sputtering plasma composition between pure Ti+C and Nb elements under a reactive mixture Ar/N$_{2}$. TiCN/TiNbCN bilayer period varied from nanometric range (15~nm) to higher micrometric range (1.5~$\mu $m) values. Structural, morphological and stoichiometric of the coatings were analyzed by high-angle- and low-angle X-ray diffraction, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (TEM). We determined multilayer period, $\Lambda $, and individual layer thicknesses. We found a cube-on-cube epitaxial growth structure and with epitaxial relationship between layers inside each columnar crystallite given by (111)[110]$_{TiCN}$//(111)[110]$_{TiNbCN}$. [Preview Abstract] |
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K1.00134: Structure determination of Co(0001)-(r3xr3)-Ga surface by LEED Patterson inversion Hiu Lung Li, Han Dong Li, Hua Sheng Wu, Mao Hai Xie A low-energy electron diffraction Patterson function (PF) with multiple incident angles was used to determine the structure of the Co(0001)-(r3xr3)-Ga surface. The experimental LEED I-V data were first inverted as Patterson function map which gives the inter-atomic distances between all atomic pairs in the structure. By comparing the experimentally obtained PF map and the simulated PF map of all proposed atomic structure models, impossible atomic structure models were effectively eliminated. Finally, the true atomic structure and detailed atomic positions on surface were deduced from tensor-LEED I-V curve fitting. Our result shows that Ga adatoms situate on T4 sites above the bulk surface of Cobalt. [Preview Abstract] |
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K1.00135: Simulation of Step-Biased Evolution Cobalt Silicide islands on (5x2) reconstructed Au/Si(111) surfaces Hung-Chih Kan, Ti-Li Lin, An-Li Chin, Fu-Kwo Men We report our simulation for the evolution of Cobalt Silicide islands on (5x2) reconstructed Au/Si(111) surfaces during annealing process in an ultra-high vacuum (UHV) environment. Our observation based on scanning electron microscopy shows that all the Co atoms deposited on the surface at room temperature form cobalt silicide islands on the terraces and across the steps at the beginning of the annealing. Subsequent annealing causes the islands to evolve: Islands grow in size while their number density decreases. The terrace islands eventually disappeared, only the step island survived. The ripening process clearly favors the islands cross the steps. We developed a model based on mean field theory that includes the energetic effects of the interfaces of the island and that of the steps buried under the island to simulate the competition between these two types of islands. Our numerical simulation based on this model reproduces the experiment qualitatively. [Preview Abstract] |
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K1.00136: Prussian Blue thin films: electrochemical deposition and characterization Andre A. Pasa, Marilia F. Alamini, Rene C. da Silva, Vin\'Icius C. Zoldan, Eduardo A. Isoppo, Ubirajara P. Rodrigues Filho, Alo\'Isio N. Klein Prussian Blue thin films Fe$_{4}$[Fe(CN)$_{6}$]$_{3}$ are relevant for many applications such as molecular magnets, electrochromism and electrochemical sensors. In this work, Prussian Blue layers were grown through electrochemical deposition on 50 nm Au coated n-type Si (100) substrates, at room temperature, from electrolyte containing HCl, KCl, FeCl$_{3}$ and K$_{3}$[Fe(CN)$_{6}$]. The layer formation was promoted by scanning sequentially the applied voltage, varying the scan rate and the number of cycles. Emphasis was given to the characterization of the samples with scanning and transmission electron microscopy, X-ray diffraction and atomic force microscopy. Pyramidal grains were typically observed with size increasing with the deposition time. The analysis of the topographic images allowed the determination of important practical parameters as the saturation roughness and correlation length, and scaling regime and exponents. [Preview Abstract] |
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K1.00137: Characterizing the wetting process of Ag films on Cu(111) with the angle-resolved photoelectron spectroscopy Dah-An Luh, Kuan-Chun Liu, Cheng-Maw Cheng, Ku-Ding Tsuei Electronic states of a metallic thin film are closely related to its surface morphology. The dynamics in the change of the surface morphology of a metallic thin film can become explored if its electronics states are measured. In this study, we demonstrate that the wetting process of a Ag film on Cu(111) is characterized by monitoring the evolution of its surface states with the angle-resolved photoelectron spectroscopy (ARPES). A Ag film on Cu(111) is disordered when Ag is deposited at low temperature, but it wets on Cu(111) for up to 2 ML when Ag is deposited at and above room temperature. To study the wetting of a Ag film on Cu(111), we constructed a special disordered Ag film, and monitored its layer-resolved surface states with the real-time ARPES during the wetting of the Ag film. The result shows that there exists a transitional state before the wetting is complete, and suggests a two-process model of wetting. [Preview Abstract] |
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K1.00138: Hydrogen adsorption configurations on Ge(001) probed with STM Amirmehdi Saedi, Bene Poelsema, Harold Zandvliet The adsorption of hydrogen on Ge(001) has been studied with scanning tunneling microscopy at 77 K. For low doses (100 L) a variety of adsorption structures has been found. We have found two different atomic configurations for the Ge-Ge-H hemihydride and a third configuration that is most likely induced by the dissociative adsorption of molecular hydrogen. The Ge-Ge-H hemihydride is either buckled antiparallel or parallel to the neighboring Ge-Ge dimers. The latter configuration has recently been predicted by M. W. Radny et al. J. Chem. Phys. 128, 244707 (2008), but not observed experimentally before. [Preview Abstract] |
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K1.00139: Phonons in Bi2Te3 and Bi2Se3 Thin Films Shang-Fen Ren, Wei Cheng Bi2Te3 and Bi2Se3 are topological insulators with interesting surface properties that have attracted great research attention in recent years. In this research, phonon dispersion curves and phonon density of states of Bi2Te3 and Bi2Se3 thin films with five atomic-layers are calculated by Medea-VASP program, and thermal dynamic functions are also analyzed. Phonon results of these two thin films are compared with each other and are also compared with available bulk measurements. Symmetry broken is found in the Brillouin zone center phonon modes. [Preview Abstract] |
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K1.00140: Microstructure and Electron Transport in ZnO:Al Thin Films Rafael Jaramillo, Shriram Ramanathan Transparent, conducting ZnO:Al thin films deposited by sputtering may figure prominently in emerging opto-electronics and energy conversion technologies. However, there remain significant unanswered questions regarding the relationship between the microstructure of sputtered ZnO:Al films and the fundamental electronic transport properties. We will present initial results of a study which aims to address some of these questions by using microscopic probes to measure the effect of grain boundaries on electron transport in reactively sputtered films. Particular emphasis will be on how oxygen concentration affects local electron conduction. [Preview Abstract] |
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K1.00141: Quantum-size induced giant spin-orbit splitting S. Mathias, A. Ruffing, F. Deicke, I. Sakar, M. Aeschlimann, M. Wiesenmayer, M. Bauer, G. Bihlmayer, Y.M. Koroteev, E.V. Chulkov, P.M. Echenique We report on the observation of a giant spin-orbit splitting of quantum-well states in the unoccupied electronic structure of a Bi monolayer on Cu(111). Up to now, Rashba-type splittings of this size have been reported exclusively for surface states in a partial bandgap. With these quantum-well states we have experimentally identified a second -- and broader -- class of states that show a huge spin-orbit splitting. First-principle electronic structure calculations show that the origin of the spin-orbit splitting is due to the perpendicular potential at the surface and interface of the ultrathin Bi film. This finding allows for the direct possibility to tailor spin-orbit splitting by means of thin film nanofabrication. [Preview Abstract] |
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K1.00142: Non-linear second harmonic generation (SHG) studies of BaTiO$_{3}$/SrTiO$_{3}$ superlattices Eftihia Vlahos, Che-Hui Lee, Pingping Wu, Chung Wung Bark, Ho Won Jang, Chad Folkman, Seung Hyub Baek, J. W. Park, Mike Biegalski, Dmitri Tenne, Darrell Schlom, Long-Qing Chen, Chang-Beom Eom, Venkatraman Gopalan Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO$_{3})_{n}$/(SrTiO$_{3})_{n }$layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO$_{3})_{m}$/(SrTiO$_{3})_{n}$ superlattices, as a function of epitaxial strain. In addition, in-plane electro-optic measurements were carried out. The experimental results are in excellent agreement both with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from UV Raman studies. The ferroelectric, in-plane SHG signal, from the tensile strained SrTiO$_{3}$ layers reveals an \textit{mm2} point group symmetry, whereas the point group symmetry of the compressively strained BaTiO$_{3}$ layers, was determined to be \textit{4mm}. [Preview Abstract] |
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K1.00143: Molecular Dynamics simulations of tetracosane (C$_{24}$H$_{50})$ bilayers physisorbed onto the basal plane of graphite Michael Roth, E. Maldonado, L. Firlej, B. Kuchta, Carlos Wexler We present and discuss the results of explicit - hydrogen Molecular Dynamics computer simulations of tetracosane (C$_{24}$H$_{50})$ bilayers deposited on a graphite substrate in the temperature range 100 K $\le \quad T \le $ 450 K. Both layers exhibit strong coupling between the internal molecular degrees of freedom and bulk behavior but because of the different boundary conditions between layers, they exhibit distinctly different dynamics and phase transition signatures. Structural, thermodynamic and bond - orientational distributions and parameters are utilized in understanding the solid, intermediate and liquid phases presented in and phase transitions presented by the system. [Preview Abstract] |
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K1.00144: Low-temperature Surface Structure of w-GaN(000-1) Tianjiao Chen, Kangkang Wang, Yinghao Liu, Kendal Clark, Danda Acharya, Muhammad Haider, Arthur Smith, Saw-Wai Hla The surface structures of the w-GaN(000-1) surface have been investigated using a combination of reflection high energy electron diffraction and low-temperature scanning tunneling microscopy. The sample is prepared using radio-frequency plasma molecular beam epitaxy on sapphire substrates. Cooling to room-temperature after growth shows 3x streaks, a signature of the N-polar surface. Initially, the samples were investigated using LT-STM at both 75 K and 4.6 K, revealing complex surface reconstructions not seen at room temperature. To gain further insights into the low-temperature structures, we have more recently carried out RHEED experiments to follow the surface as it is cooled from room temperature down to low temperature. Initial results on samples prepared in similar ways to those in the LT-STM experiments show a phase transition from the room-temperature diffraction pattern to a different pattern at 255 K. On-going work is attempting to understand this transition in comparison to the observed LT-STM images. Authors acknowledge support by NSF (grant Nos. 0304314 and 0730257). [Preview Abstract] |
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K1.00145: Underlying physical principles of subsurface force microscopy Laurene Tetard, Ali Passian, Thomas Thundat The understanding of material nanosystems necessitates the development of tools that can capture their spatial and temporal behavior with minimum disturbance. Atomic force microscopy has emerged as a powerful tool for such measurements. As many forms of nanoparticles are emerging, a better understanding of their physical properties and response in various environments is of great importance. We used a variation of force microscopy that utilizes elastic excitations to determine if mice that have been exposed to nanoparticles by inhalation possess cells invaded by manufactured particles. We demonstrate that the high resolution non-invasive imaging is also of potential for characterizing extensive as well as intensive material properties of nano-bio systems. Distributions of single-walled carbon nanohorns, and silica nanoparticles located within macrophages from the mice lungs were imaged with a resolution of a few nanometers. [Preview Abstract] |
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K1.00146: ABSTRACT WITHDRAWN |
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K1.00147: The Third Order and the Second Order Shot Noise in Nanoscale Junctions from First Principles Yu-Chang Chen, Yu-Shen Liu We propose a field-theoretic theory allied to first principles calculations to study the third order cumulant of quantum shot noise in nanoscale junctions. Our starting point is the second-quantized field operator in terms of the effective single-particle wave-functions obtained self-consistently within the density-functional theory. The approach is valid in both linear and nonlinear response regime and is particularly suitable in studying the third order quantum shot noise in atomic-scale junctions. As an example, we investigate the conductance, the second order shot noise, and the third order shot noises in the carbon atomic wires connected between two metal electrodes. We observe that all these physical quantities display an oscillatory behavior for even and odd number of carbon atoms. [Preview Abstract] |
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K1.00148: Photoinduced Potential Shift of Gold Nanoparticle Overlaid with Photochromic Molecules in the Nano-junction Toshifumi Terui, Yukito Naitoh, Rieko Ueda, Akira Otomo, Yutaka Noguchi, Hidehiro Yamaguchi, Kenji Matsuda We fabricated single eletctron tunneling (SET) device structure of photochromic molecule -- gold nanoparticle compound to know the photo irradiation dependence of the electron transport properties. It will be able to detect signals according to structural change of single molecule. Nanogap electrodes were fabricated by using electromigration technique. We measured the properties of the SET devices of molecule -- gold nanoparticle compounds in vacuum prober system. The real-time profile of the source -- drain current (I$_{SD}$) of the SET was measured under irradiation with UV light. I$_{SD}$ indicated a discontinuing jump when SET was irradiated by UV light. This result leads us to the conclusion that the jump of I$_{SD}$ is change of the potential energy of gold nanoparticle due to the photochromism of molecule at single molecular level by UV excitation. [Preview Abstract] |
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K1.00149: Velocity Dependence of the Kinetic Friction of Nanoparticles Dirk Dietzel, Michael Feldmann, Andre Schirmeisen The velocity dependence of interfacial friction is of high interest to unveil the fundamental processes in nanoscopic friction. So far, different forms of velocity dependence have been observed for contacts between friction force microscope (FFM) tips and a substrate surface. In this work we present velocity-dependent friction measurements performed by nanoparticle manipulation of antimony nanoparticles on atomically flat HOPG substrates under UHV conditions. This allows to analyze interfacial friction for very well defined and clean surface contacts. A novel approach to nanoparticle manipulation, the so called 'tip-on-top' technique [1], made it possible to manipulate the same particle many times while varying the velocity. The antimony particles exhibit a qualitatively different velocity dependence on friction in comparison to direct tip-HOPG contacts. A characteristic change in velocity dependence was observed when comparing freshly prepared particles to contaminated specimen, which were exposed to air before the manipulation experiments. [1] Dietzel et al., Appl. Phys. Lett. 95, 53104 (2009) [Preview Abstract] |
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K1.00150: Nanowire friction with an applied bias Hakan Pettersson, Gabriela Conache, Struan Gray, Aline Ribayrol, Linus Froberg, Lars Samuelson, Lars Montelius Recently, we have shown how the friction experienced by nanowires pushed by an AFM tip can be determined by measuring their radius of curvature after manipulation [1]. It is of fundamental interest to know whether the wires behave like macroscopic objects, or if they are more like true atomic-scale point contacts where friction becomes independent of the applied normal force. Here we study how the friction between InAs nanowires and a SiN layer on conductive silicon varies when a DC voltage is applied. The tip charges the capacitor formed by the wire and the silicon back contact, causing attractive Coulomb forces and so increasing the contact pressure. A monotonic increase of the sliding friction with voltage was observed. This implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite being only nanometers in size in the direction of motion.\\[4pt] [1] Conache et al. Small 5(2) 203 (2009) [Preview Abstract] |
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K1.00151: COMPLEX STRUCTURED MATERIALS |
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K1.00152: Simulation studies of electroless metal deposition using gold nano-clusters on polymeric surfaces Mike Lively, Aniket Bhattacharya, Chris Grabill, Stephen M. Kuebler, Aniruddha Dutta, Helge Heinrich We report lattice Monte Carlo (MC) simulation studies of deposition of metallic silver on randomly distributed gold nano clusters on a polymeric surface. The gold nano-clusters act as seeds for further deposition of silver atoms. We assume ballistic growth for the growth of metallic silver on gold clusters but treat the lateral growth (which eventually form bridges among original clusters) with different rules and study the evolving morphologies of the deposited silver atoms as a function of the surface density and the size distribution of gold nano-clusters and compare simulation results with those obtained from TEM studies of the prepared samples. [Preview Abstract] |
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K1.00153: ABSTRACT WITHDRAWN |
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K1.00154: Dynamic Heat Capacity of the East Ising Model Jonathan Brown, John McCoy, Brian Borchers, Douglas Adolf It has been shown in experiment that the heat capacity of glass formers has a frequency dependence, this is called the dynamic heat capacity. The dynamic heat capacity for a simple spin model known to be a glass former, the east Ising model, is measured by simulation. The result shows stretched exponential decay like relaxation, and the data is fit to the appropriate form. For low temperatures, the relaxation time grows proportionally to exponential inverse temperature squared, which is the theoretical low temperature limit. Another model is applied where the overall relaxation is made up of the relaxations of subdomains that each have their own characteristic times. Using Markov Chains, these times are computed numerically and symbolically, and the data is seen to fit the simulations very well in the low temperature limit. The dynamics of the east model are tracked very well by this procedure, and we compare this to the parameters of the stretched exponential fits showing that a discrete number of relaxation times can give rise to stretched exponential like behavior. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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K1.00155: Synchrotron x-ray diffraction and infrared spectroscopy studies of C$_{60}$H$_{18}$ under high pressure Bingbing Liu \textit{In situ} high-pressure angle dispersive synchrotron X-ray diffraction and high-pressure mid-IR spectrum measurements of C$_{60}$H$_{18}$ were carried out up to 32 GPa and 10.2 GPa, respectively. Our diffraction data indicated the fcc structure of C$_{60}$H$_{18 }$was stable up to 32GPa. The bulk modulus B0 was determined to be 21$\pm$1.16 GPa, about 40{\%} higher than that of C$_{60}$. The C-H vibrations still existed up to 10.2 GPa and the vibration frequencies decreased with increasing pressure. IR active vibrational frequencies and their corresponding eigenvectors of C$_{60}$H$_{18}$ were simulated by DMOL$_{3}$. The effects of hydrogen in the fullerene molecular cage on the stability of structure under high pressure were discussed. [Preview Abstract] |
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K1.00156: Modeling electron transport in metallic single wall carbon nanotubes Ronald Cosby, Evan Wilson First principles atomistic calculations of electrical conductance for single-wall metallic carbon nanotubes on copper electrodes are described. Density functional theory and a non-equilibrium Green's function technique are used to calculate electronic structure and current-voltage characteristics. The computed effects of selected impurities and nanotube strains on the conductance are displayed and discussed. Progress in studying the impacts of copper-nanotube interface characteristics on the electrical properties is reported. [Preview Abstract] |
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K1.00157: Effects of Annealing on the Electronic Properties of ZnO Nanowires in Field Effect Transistors Abhishek Prasad, Archana Pandey, Yoke Khin Yap Controlled doping of ZnO nanowires (ZnO NWs) is important for their application in field effect transistors (FETs). However, native defects are always presented in the as-grown ZnO NWs and have complicated the doping efforts. Here we report on effective elimination of these native defects. Our ZnO NWs were grown in a double-quartz tube thermal CVD system [1, 2]. These samples were then subjected for a series of annealing in various gas ambients, durations, and temperatures. All these samples were characterized by SEM, TEM, Raman and PL spectroscopy. FETs fabricated by these ZnO NWs were characterized to correlate all these investigation. Results indicate that hydrogen annealing suppresses some native defects in ZnO NWs and enhance their conductivity by three orders of magnitude. \\[4pt] [1]. Prasad et al, in Chapter 4 of \textit{Sensors Based on Nanostructured Materials} (Springer, 2009). \\[0pt] [2]. Mensah et al, Appl. Phys. Letts. 90, 113108 (2007). [Preview Abstract] |
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K1.00158: Characterizing the electronic properties of single Titania nanotube using e-beam lithography Mohamed AbdElmoula, Latika Menon Titania Nanotubes arrays fabricated by anodization became the main interest of many research groups mainly due to its promising applications. Solar energy harvesting is one of the most anticipated applications, in which the light conversion to electron-hole pairs can be carried out on the surface of these nanotubes. Extensive research work has been carried out to increase the aspect ratio of these tubes and up to our knowledge no previous work has been done to explore the transport properties of a single titania nanotube. In our work we are studying the electron transport properties of a single titania nanotube using e-beam lithography, first, for a amorphs titania nanotubes, where we will investigate the effect of wall thickness and tube length on the transport properties. Second, for annealed titania nanotubes, where we will investigate the effect of annealing conditions on the transport properties. Also we will investigate the response of these properties to different gases, in which we will learn more about the ability of single titania nanotubes to work as nanosensor and its selectivity to specific gases. As a result, we will get a more clear understanding of the charge transport properties, and explore new functions for these cheap and easily fabricated nanotubes. [Preview Abstract] |
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K1.00159: Energetics and electronic structure of M-DNA Simone Alexandre, Jos\'e Soler, F\'elix Zamora Charge transport in DNA is currently an open issue, that has defied both theory and experiments. An important possibility is the introduction of a transition metal atom into the DNA structure, forming the so-called M-DNA, in attempt to produce a DNA with a metallic band-structure. In the present work we investigate the incorporation of zinc into the DNA, at three different sites: (i) in the major groove in the crosslink position; (ii) in the minor groove in the crosslink position; (iii) bound to the N(7) of the guanine. We find that the most stable position is the third altrenative, where the Zn atom is bound to the guanine. For the electronic structure, we find that while the most stable position presents the larger band gap ($\sim$2.2 eV within GGA-DFT). No such trend is found between band gap and stability for the other alternatives: the crosslink positon in the major groove is a more favorable site than in in the minor groove, but with a smaller band gap. These results corroborate our previous finding of a strong metal-site dependence of the electronic and magnetic properties of M-DNA [1].\\[4pt] [1] S. S. Alexandre {\textit et al.}, PRB 73, 205112 (2006). [Preview Abstract] |
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K1.00160: ABSTRACT WITHDRAWN |
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K1.00161: Ultrafast Mid-Infrared Intra-Excitonic Response of Individualized Single-Walled Carbon Nanotubes Jigang Wang, Matt Graham, Yingzhong Ma, Graham Fleming, Robert Kaindl We report a femtosecond mid-infrared study of the broadband low-energy response of individualized (6,5) and (7,5) single-walled carbon nanotubes. Strong photoinduced absorption is observed around 200 meV, whose transition energy, oscillator strength, chirality enhancement and dynamics manifest the observation of quasi-1D intra-excitonic transitions. A model of the nanotube 1$s$-2$p$ intra-excitonic cross section yields excellent agreement. Our study further reveals a saturation of the photoinduced absorption with increasing phase-space filling of the correlated $e-h$ pairs. [Preview Abstract] |
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K1.00162: Terahertz Generation by Polar Nanowires Subjected to a Perpendicular Magnetic Field Gary Pennington Experiment and theory have indicated the generation of coherent terahertz (THz) radiation in III-V semiconductors electronically biased so that charge carriers enter a streaming distribution. [1] Under such conditions, the large polar optical phonon scattering rate of these materials allows for phonon emission assisted transit-time resonance (TTR). Since acoustic phonon scattering acts to de-phase TTR current oscillations, generation typically occurs at low temperatures ($<$10K). A reduction of the acoustic phonon scattering rate would enable TTR based THz generation at higher temperatures. A possible mechanism for such a reduction may be found using III-V nanowires which are subjected to a perpendicular magnetic field. The field would allow transport in skipping orbits along the nanowire edges with suppressed acoustic phonon backscattering.[2] To investigate such an effect, Monte Carlo simulations of carrier transport are employed. The effect of an applied magnetic field is accounted for within the confined electronic sub-band energy levels. Charge carrier scattering by confined and surface phonons are considered. [1] L. E. Vorob'ev et al., JETP Lett. 73, 219 (2001); P. Shiktorov et al., Acta Phys. Polonica A 113, 795 (2008) [3] A. Svizhenko et al., Phys. Rev. B 57, 4687 (1998) [Preview Abstract] |
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K1.00163: Size effect and sp$^3$ bond formation in carbon nanotube bending Chun Tang, Wanlin Guo, Changfeng Chen We report molecular dynamics simulations of bending behaviors of carbon nanotubes (CNTs). Due to the interlayer interaction, single- walled CNTs (SWCNTs) and multi-walled CNT (MWCNTs) show different buckling characters both in deformation pattern and energetic evolution. Simulations in post-buckling region show that large bending strain leads to sp$^{3}$ bond formation in kink areas and that the capability of sp$^{3}$ bond formation is sensitive to tube size. These results suggest a new route for structure engineering of CNTs. [Preview Abstract] |
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K1.00164: Zinc oxide nanostructure grown by chemical vapor transport Bradley Golder, Marian Tzolov ZnO is a versatile platform thanks to the unique combination of optical, semiconducting, and piezoelectric properties of ZnO. We have grown zinc oxide nanostructures by chemical vapor transport. The formation of the nanoparticles was studied by Scanning Electron Microscopy and the incorporation of impurities by Energy Dispersive X-Ray Spectroscopy. The photoluminescence spectra were used to quantify the presence of electronic defects and this was related to the parameters of the deposition process. The electrical conductivity along the nanorods was investigated together with the sensitivity to different gas environment. This way the applicability of the synthesized nanostructures for gas detection was evaluated. [Preview Abstract] |
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K1.00165: Structures of $\sim 100$ nm Size Produced by Atom Lithography with Metastable He Jason Reeves, Christopher Corder, Xiaoxu Lu, Claire Allred*, Harold Metcalf We have used neutral atom lithography with metastable 2$^3$S He (He*) to produce structures of size $\sim 100$ nm. A beam of He* from our source is collimated by the bichromatic force\footnote{M. Partlow et al., Phys. Rev. Lett. {\bf 93,} 213004 (2004)} and then by optical molasses. Atoms cross a standing wave of $\lambda =$ 389 nm light tuned $\sim$80 MHz below the 2$^3$S$_1 \rightarrow 3^3$P$_2$ transition and are focussed into lines striking a self assembled monolayer (SAM) of nonanethiol coated over a gold film on a single crystal Si wafer. The 20 eV internal energy of He* destroys the SAM molecules ultimately leaving a pattern of SAM on the gold. Subsequent etching of the unprotected region of the gold results in these features\footnote{C. Allred et al., submitted to J. Appl. Phys.}$^,$\footnote{C. Allred, Ph.D. Thesis, Stony Brook, NY (2009) - unpublished.}. The lines are separated by 194.5 nm and they occupy about 60\% of their spacing. AFM measurements of our first samples show their width to be $\sim 120$ nm and their depth to be $\sim 10$ nm. [Preview Abstract] |
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K1.00166: Electron emission from functionalized carbon nanotubes and its thermionic cooling effect Feng Jin, Scott Little, Guogang Qiang Thin film of carbon nanotubes (CNTs) were grown on metal foil substrates using plasma enhanced CVD technique. The surface of the CNTs was further functionalized by sputter deposition a thin layer of low-work function barium strontium oxide. Strong thermionic emission was observed from these functionalized CNTs thin film. The electron emitted were mostly hot electrons which carried energy away from the emitting surface. A large thermionic cooling effect was observed. Temperature drops as large as 100 C was observed. The detail characterization of the electron emission properties of these functionalized CNTs including work function will be presented. The thermionic cooling effect or temperature drops at various initial temperatures and emission currents will also be presented. The potential to use this functionalized CNTs thin film as a micro thermionic cooler will also be discussed. [Preview Abstract] |
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K1.00167: Helical Nanotube Structures of MoS2 with Intrinsic Twisting: An Objective Molecular Dynamics Study Traian Dumitrica, Dong-Bo Zhang, Gotthard Seifert Objective molecular dynamics combined with density-functional-based tight-binding makes possible to compute chiral nanotubes as axial-screw dislocations. This methodology enables the surprising revelation of a large catalog of MoS$_{2}$ nanotubes that lack the prescribed translational symmetry and exhibit chirality-dependent electronic band-gaps and elastic constants. Helical symmetry emerges as the natural property to rely on when studying quasi-one dimensional nanomaterials formally derived or grown via screw dislocations. [Preview Abstract] |
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K1.00168: Characterization of electrospun GaN nanofibers Idalia Ramos, Anamaris Melendez, Kristle Morales, Eva M. Campo, Jorge J. Santiago-Aviles Gallium Nitride shows characteristics pertinent to optoelectronics and gas sensing applications. Nanofibers have been produced using electrospinning and a precursor composed of Gallium (III) Nitrate Hydrate dissolved in Dimethyl-Acetamide and Cellulose Acetate in Acetone and DMA. The resulting nanofibers were sintered at 400C in nitrogen for one hour to decompose the polymer, the furnace atmosphere switched to ammonia and the fibers sintered for periods of 3, 5 and 7 hrs at 900C. They showed morphologies with unclear dependence on processing parameters. X-ray Diffraction revealed the evolution towards wurtzite phase through annealing. From line broadening we estimate a crystalline domain size of about 12 nm. Transmission Electron Microscopy suggests nucleation and growth of X-tallites while Fourier-Transform Infrared Spectroscopy and Ultraviolet-Visible Spectroscopy confirm the material evolution towards crystallinity and the production of wurtzite GaN nanofibers. I-V characteristics of single nanofibers show linearity with increments in conductivity for those fibers ammoniated during longer periods of time. Ongoing efforts aim at improving fabrication, sensing and photoluminescence characterization. [Preview Abstract] |
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K1.00169: Hydrogen adsorption and storage in porous single-wall carbon nanotubes Walter Orellana Efforts to increase the hydrogen capacity in carbon nanotubes (CNTs) point to find energetically favorable access to its inner space. Following this way, we investigate the incorporation of H$_2$ molecules inside CNTs through pores in their walls by density functional theory calculations and molecular dynamic simulations. The pores are constructed by multivacancies defects ($n$V) with $n$ missing atoms. CNTs of 1.1 and 1.4~nm in diameter were considered. We find that 16V has the limit size where the defect reconstruction is unlikely, preserving the unsaturated border. Under hydrogenation, the border is passivated by H$_2$ dissociative reactions, leaving an inert pore of about 6~\AA\ in diameter (16V-H).We verify that the incorporation and release of H$_2$ molecules through this pore occur barrierless and its stability in contact with a gas of 32 and 64 H$_2$ molecules for exohedral and endohedral adsorption is preserved at high temperatures up to 600~K. Our results show that at room temperature, the endohedral adsorption energy is high enough for a reversible adsorption-desorption process, suggesting that porous CNTs, as produced for instance by electron irradiation under a H$_2$ atmosphere, could be an effective H$_2$ storage medium, allowing the access to the CNT inner space. [Preview Abstract] |
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K1.00170: Molecular dynamics simulation of spontaneous self rolling of (100)/(111) oriented bilayer aluminum nanofilms into nanotubes Dorel Moldovan, Jijun Lao We report molecular dynamics simulation studies that introduce a new methodology for forming metallic nanotubes and nanocoils via spontaneous self rolling-up of initially planar free standing (001)/(111) bilayer metallic nanofilms. Our studies on aluminum reveal that the self rolling of the bilayers is controlled by both energetic and kinetic processes accompanying the spontaneous structural reorientation of the top (001) layer to the (111) orientation of the substrate layer. The simulations indicate that the (001) to (111) reorientation of the top layer proceeds via nucleation from multiple sites and growth of the (111) oriented domains. While a newly formed (111) domain grows free of defects, a region containing a surface dislocation defect forms when two such domains meet. The bilayer reaches a lower energy state by undergoing multiple localized bendings of finite angles about the common direction that coincides with the corresponding surface dislocation line. The radii of the resulting structures are determined by bilayers thickness and temperature. [Preview Abstract] |
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K1.00171: Improved modeling of the percolation behavior of conductor-insulator composites with modulated granular size distributions Kazuhito Shida, Ryoji Sahara, Madhvendra Tripathi, Hiroshi Mizuseki, Yoshiyuki Kawazoe The percolation threshold shows a universality that may cause a strict limit on the mixture ratio of composite materials. When particles A and B are randomly filling a material and A must form an interconnected cluster (e.g. for electrical conduction), there is a strict limit on the fraction of A (for example, 0.598 in 2D). A solution to solve this problem is introducing size distribution on B particles (N.Lebovka J.Phys.D (2006) and WJ Kim J.Appl.Phys (1998)). However, theoretical understanding of this phenomenon is still in a quite immature stage despite of its importance in applications. We report the reduction of the percolation threshold observed in square lattices with a number of binary size distributions, as well as our approach toward semi-empirical theoretical method, that is based on an enumeration of local particle configurations generated in a totally random manner. This is a notable advance because most of previous theoretical methods were considering only limited combination of configurations, in which the positions of the B particles are not fully randomized. [Preview Abstract] |
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K1.00172: Argon adsorption on Co-FA porous metal-organic framework Vaiva Krungleviciute, Aldo Migone, Kunhao Li, Jing Li We have measured Ar adsorption isotherms on Co-FA at several temperatures between 60 and 100 K. Co-FA (C$_{9}$H$_{13}$Co$_{3}$O$_{13})$ is a porous, 3D metal-organic framework material produced by heating a mixture of Co(II) nitrate hexahydrate and formic acid in dimethylformamide. The Co-FA sample was annealed at 100$^{o}$C (under vacuum) for about 20 hours prior to the adsorption measurements. The measurements were conducted using a volumetric adsorption apparatus. Only one step was observed in the isotherm data, from the lowest loading up to saturation. Values for the pore volume, effective surface area and isosteric heat will be presented. [Preview Abstract] |
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K1.00173: Crosslinked Matrix-free Nanocomposites Benjamin Dach, Hernan Rengifo, Nicholas Turro, Jeffrey Koberstein Matrix-free polymer-silica nanocomposites are formed by crosslinking polymer coated nanoparticles via the `click' reaction. The `click' reaction is also known as H\"{u}isgen 1, 3-dipolar cycloaddition of terminal alkyne and azide functional groups to give 1, 2, 3-triazoles. Silica nanoparticles are functionalized with alkyne and azide moieties. Heterobifunctional $\alpha $,$\omega $-trimethylsilane-alkyne,azide-poly(styrene) (TMS-PS-N$_{3})$ and $\alpha $,$\omega $-trimethylsilane-alkyne,azide--poly(\textit{tert}-butyl acrylate) (TMS-PtBA-N$_{3})$ are then covalently bound to the surfaces of the nanoparticles via the `click' reaction. The bare and modified nanoparticles are analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The thermal, morphological, and mechanical properties of the systems are investigated by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and dynamic rheology, respectively. . [Preview Abstract] |
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K1.00174: Ab initio study of alkali metals adsorption with varying coverage on graphene Kyung-Hwan Jin, Seon-Myeong Choi, Seung-Hoon Jhi Graphene exhibits many interesting physics and promises potential application to electronic devices. In addition, graphene is considered as a supporting template for catalysts and hydrogen storage. Understanding the contact of graphene with metal is one of key processes in such applications. We carried out first principles calculations to study electrical properties of graphene with adsorption of alkali metals at varying coverage. The adsorption energy and distance, the charge transfer and the Fermi level shift of graphene are particularly investigated as the coverage of metals is changed. It is found that the charge transfer from the metal to graphene shows a strong coverage dependence, which is fit into a model that incorporate the graphene electronic structure and the Coulomb interaction of metal-graphene and metal-metal. [Preview Abstract] |
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K1.00175: Origin of universal optical conductivity and optical stacking sequence identification in multilayer graphene Hongki Min, Allan H. MacDonald Recently, experiments have demonstrated that the conductivity per layer in multilayer graphene has the universal value $\sigma_{uni}=(\pi/2) \, e^2/h$ in the optical frequency range. We show that the origin of the universal optical conductivity in normal $N$-layer graphene multilayers is an emergent chiral symmetry which guarantees that $\sigma(\omega)=N\sigma_{uni}$ in both low and high frequency limits. In the intermediate frequency regime, the optical conductivity shows qualitatively different trends depending on the stacking sequence; thus, the optical conductivity measurement can provide a convenient qualitative characterization of multilayer graphene stacks. \\[4pt] Ref) Hongki Min and A. H. MacDonald, Phys. Rev. Lett. {\bf 103}, 067402 (2009). [Preview Abstract] |
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K1.00176: Optical analogy of electron Transport in bilayer Graphene in presence of electromagnetic potential barriers and its possible applications Sankalpa Ghosh , Neetu Aggarwal (Garg), Manish Sharma The dispersion relation for electrons near Fermi level for a graphene bilayer is very different from that of a monolayer graphene. Moreover applying a bias voltage it is possible to create and tune a gap at the Fermi level for such bilayers. Given this context we have extended a recently proposed analogy ( see references 1 and 2) between geometrical optics and ballistic transport of electrons in graphene monolayer in presence of certain combinations of magnetic vector potential and electrostatic potential barriers to the case graphene bilayer. We shall particularly show how optical analogy can be used to understand various transport regime in bilayer graphene and suggests possible applications exploiting this optical analogy. We also consider the effect of localized impurities on such transport. References: 1. Sankalpa Ghosh and Manish Sharma - J. Phys. Cond. Matt 21, 292204(2009) 2. Manish Sharma and Sankalpa Ghosh -- arXiv: cond-mat 0907.1631(submitted) [Preview Abstract] |
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K1.00177: Negative c-axis Magnetoresistance in Graphite Yakov Kopelevich, Robson R. da Silva, J.C. Medina Pantoja, Alex M. Bratkovsky Aiming to verify the possible behavior of graphite as a stack of graphene layers, we have studied in this work the c-axis (interlayer) magnetoresistance (ILMR), R$_{c}$(B). The measurements have been performed on strongly anisotropic highly oriented pyrolytic graphite samples in magnetic field of up to B = 9T applied both parallel and perpendicular to the sample c-axis, and temperatures 2 K $\le $ T $\le $ 300 K. We observed the negative magnetoresistance (MR), dR$_{c}$/dB $<$ 0, for B$\vert \vert $c above a certain field B$_{m}$(T) that reaches its minimum value B$_{m}$ = 5.4 T at T = 150 K. The results can be consistently understood assuming that ILMR is related to a tunneling between zero-energy Landau levels of quasi-two-dimensional Dirac fermions, in a close analogy with the behavior reported for $\alpha $-(BEDT-TTF)$_{2}$I$_{3}$ [N. Tajima et al., Phys. Rev. Lett. 102, 176403 (2009)], another multilayer Dirac electron system. [Preview Abstract] |
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K1.00178: Magneto-Response Of Graphene N.J.M. Horing, V. Fessatidis, J.D. Mancini We determine the dielectric polarizability of graphene in a perpendicular magnetic field inducing Landau quantization, taking account of arbitrary temperature dependence. The result is expressed in terms of a tractable integral representation involving only elementary functions (which generate the Landau-quantized eigenfunction representation). [Preview Abstract] |
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K1.00179: Graphene Plasmons In Interaction With A Surface N.J.M. Horing, J.D. Mancini Recent experimental research on the plasmon spectrum of both carbon nanotubes and graphene has revealed a linear $\pi$ plasmon dispersion, which has been attributed to local field effects. Here we examine other possible sources of the linear plasmon dispersion found in graphene. In particular, we study the dispersion which may arise from the interaction of the intrinsic graphene plasmon ($\omega\sim q^{1/2}$) with the surface plasmon of a nearby thick substrate hosting a semi-infinite plasma. [Preview Abstract] |
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K1.00180: Polarized Vibrational Infrared Absorption of Graphene Nanoribbons Guangfu Luo, Jing Lu, Lu Wang, Lin Lai, Jing Zhou, Rui Qin, Hong Li, Zhengxiang Gao, Wai-Ning Mei In this study, we present the first systematic \textit{ab initio }study of the linearly polarized vibrational IR spectra of the edge-hydrogenated armchair and zigzag GNRs. We reveal that the vibrational IR spectra that provide abundant structural information of GNRs: (1) There is a prominent and width-insensitive IR peak in both GNR types, which can be used as a convenient benchmark in experiment; (2) The major IR absorption of the two GNR types occurs in distinct regions and thus assures a robust feature to distinguish them; (3) In armchair GNRs, the spectra for in-plane polarization oscillate with the ribbon width, while in zigzag GNRs, the dispersion relationship bears close resemblance with that of graphene; (4) One special peak reflecting the mirror symmetry property of zigzag GNRs, which has been proven to be significant in the electronic transport is also discovered; (5) The edge magnetism in zigzag GNRs is found to greatly influence the IR intensity. We expect this work to offer insight into the experimental research and confront the current problem of edge structure identification of GNRs. [Preview Abstract] |
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K1.00181: Electric-Field Induced Semimetal-to-Metal Transition in Few-Layer Graphene Richard S. Thompson, Yi-Chen Chang, Gerd Bergmann, Jia G. Lu An electric-field induced semimetal-to-metal transition is observed in five-layer graphene produced by the peeling process based on the temperature dependence of the resistance for different applied gate voltages. For small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs, as characteristic of a semimetal. For large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the decrease in mean free path due to electron-phonon scattering, characteristic of a metal. The electron and hole mobilities are almost equal, so we have approximate electron-hole symmetry. The data are analyzed according to theoretical models for few-layer graphene. The simplest model used has two overlapping bands with quadratic energy-versus-momentum dispersion, a conduction band and a valence band. The energy range of the overlap is of the order of 20 meV in order to fit the residual resistance at low temperatures at zero gate voltage. The fitting at low temperatures is improved by adding a second pair of quadratic bands that just touch with zero overlap. Finally, the addition of a pair of touching Dirac bands with linear dispersion is considered, but shown to be unimportant due to the low density of states in the Dirac bands. [Preview Abstract] |
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K1.00182: Detection of Molecular Mechanics on Graphene surface: An Electromechanical Logic Device Kabeer Jasuja, Nihar Mohanty, Vikas Berry The integration of molecular mechanics with electronics is a promising route for building molecular electromechanical devices, nano machines and actuating nano circuits. In this talk, we demonstrate the effect of molecular mechanics of a monolayer of two azo-molecules attached to a graphene surface on the electrical properties of the azo-graphene device. We show that the reversible, photo-induced conformational change of the azo-molecule on graphene surface redistributes the fermionic density on graphene \textit{via} the motion of the electron-rich benzene moiety of the azo molecules. Further, increasing the proximity of the electron cloud of the azo group's benzene ring increases the hole density of the graphene-azo hybrid. The carrier confinement and the high density of pi-electrons on graphene enable the sensitive detection of this molecular motion of the azo-monolayer. These results indicate the potential of graphene as a responsive coupling medium, which is sensitively influenced by molecular-scale mechanics. The research will potentially lead to development of novel graphene based molecular electromechanical systems. [Preview Abstract] |
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K1.00183: Magneto-electronic properties of nanographene ribbons under the external electric field Sz-Chao Chen, Cheng-Peng Chang, Ming-Fa Lin The electronic properties of the nanographene ribbons under the perpendicular magnetic field and external electric fields are calculated through the tight-binding model. The dispersionless quasi-Landau levels are greatly affected by the external fields. Subbands with sinusoidal (linear) dispersions are induced by the spatial modulated (uniform) electric field and some extra band-edge states are found. The external electric field can change the characteristics of the Landau wave function, such as the destruction of spatial symmetry, the change of the distribution width, and the shift of the localization position. The modification of the electronic properties would be directly reflected on the optical absorption spectra. The number, the shape, the intensity and the position of the absorption peaks are altered. The selection rule of the optical excitations between the quasi-Landau levels is disappear under the influence of the external electric field. The predicted results can be directly verified by the optical measurement. [Preview Abstract] |
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K1.00184: Magnetoelectronic excitations in monolayer graphene Jhao-Ying Wu, Ming-Fa Lin Coulomb excitation of monolayer graphene in the presence of a magnetic field is studied by the tight-binding model and the random phase approximation. The energy-loss spectrum exhibits many peak structures and the most prominent ones can be identified as the collective excitations mainly coming from the longitudinal charge oscillation. The plasmon frequency and strength oscillate with the transferred momentum because of the competition between the Coulomb interaction and the Lorentz force. The resonant inelastic light-scattering measurements are available in verifying the predicted results. [Preview Abstract] |
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K1.00185: A Density Functional Theory Study of Chain-like Structures Derived from Graphite Nanoflakes Brahim Akdim, Ruth Pachter Recently, chain-like structures of about 2 nm in lengths were fabricated from graphite nanoflakes by controlled electron beam irradiation in a 3 stage process [C. Jin, et al. PRL, 102, 205501 (2009)], opening up possibilities for designing all-carbon nano-electronic devices, with \textit{sp}-hybridized carbon atomic chains as the conducting channel, bridged by the \textit{sp}$^{2}$-hybridized graphene leads. Although formation, migration and breakage in the material has been addressed theoretically by Jin et al., effects of chain length and chain orientation have not been explored thus far. In this work, we report on the electronic and mechanical properties of chain-like structures bridged between the two-dimensional sheets, to further understanding of the material's behavior. [Preview Abstract] |
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K1.00186: Electromagnetic properties of graphene junctions Serhii Shafranjuk A photon-assisted resonant chiral tunneling across a graphene junction (GJ) induced by an external a.c. electromagnetic field is examined. We find that the a.c. field impacts the directional diagram of the charge transport across the GJ since it modulates the phase shift $\phi$ between the electron and hole wave functions. This results in an angular redistribution of the tunneling current. We also report our study of a directional photon-assisted resonant chiral tunneling through a bilayer graphene barrier [1]. We find that an external electromagnetic field applied to the barrier switches the transparency T in the longitudinal direction from its steady state value T = 0 to the ideal T = 1 at no energy costs. The switch happens because the ac field affects the phase correlation between the electrons and holes inside the graphene barrier, changing the whole angular dependence of the chiral tunneling (directional photoelectric effect). The directional a.c. charge transport phenomena may be utilized in novel nanoelectronic devices working in the THz diapason. \\[4pt] [1] S. Shafraniuk, J. Phys.: Condens. Matter 21 (2009) 015301 [Preview Abstract] |
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K1.00187: Effect of Energetic Charged Particle Irradiation on Graphene Isaac Childres, Luis A. Jauregui, Romaneh Jalilian, Jifa Tian, Helin Cao, Mike Foxe, Leonid Rokhinson, Igor Jovanovic, Yong P. Chen Energetic charged particles are commonly used in the fabrication and characterization of graphene devices. For example, oxygen ions are used in plasma etching processes and energetic electrons are used for electron beam lithography as well as electron microscopy. Using electronic transport measurements and Raman spectroscopy, we have studied the effect of exposure to electrons and oxygen ions on exfoliated graphene on a SiO2/Si substrate and the performance of electronic devices made from such graphene. Electronic transport measurements show an overall decrease in graphene's conductivity and shift of the charge-neutral point to the negative when irradiated with electrons and to the positive when irradiated with oxygen ions. Raman spectra indicate emergence of characteristic defects. We have studied these effects on suspended and non-suspended graphene devices to determine the influence of the SiO2 substrate. Our results are valuable for understanding the possible defects generated in graphene by charged particle irradiation. [Preview Abstract] |
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K1.00188: Electro-Raman measurement of thermal conductivity of suspended single and few-layer graphene Luis A. Jauregui, Jiuning Hu, Gabriel A. Lopez, Romaneh Jalilian, Qingkai Yu, Zhigang Jiang, Yong P. Chen We present measurements of the thermal conductivity of suspended graphene, using Raman spectroscopy on graphene subject to electrical heating. Joule heating is generated by passing a current through the suspended graphene, while the Cr/Au contact leads act as heatsinks. Raman spectrum is used as a thermometer for graphene, because of the temperature dependence of the amplitude and frequency for the G and 2D peaks. In order to extract the thermal conductivity of graphene, we measure the temperature distribution on the suspended graphene by Raman mapping of the 2-D and G peaks with graphene driven by various heating current. We can also determine the temperature dependence of the thermal conductivity. Our technique provides a simple method to measure thermoconductivity of graphene and can be generalized to other nanomaterials. [Preview Abstract] |
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K1.00189: Micro-Raman Spectroscopy of Atomically-Thin Graphite Kevin Mead, John Hasslinger, Jeff Simpson The unique linear energy vs. momentum relationship leads to interesting fundamental physics including massless particles studied in quantum electrodynamics, a unity tunneling paradox, and an anomalous quantum Hall effect. We will use mechanical exfoliation of highly-oriented pyrolytic graphite (HOPG) to produce single and multilayer graphene flakes on Si/S0$_{2}$ substrates. We will analyze the graphene using a combination of microscopy techniques including optical, micro-Raman spectroscopy, and atomic force microscopy (AFM). The Raman spectra exhibit phonon modes common to graphitic carbon, specifically known as the D, G, G'$_{2D}$. Fitting the peaks with Lorentzian(s) quantifies the number of graphene layers. The peak frequency and intensity of Raman modes provides information about electron-phonon coupling and defects. We compare the Raman spectra of graphene prepared using mechanical exfoliation and CVD growth, both in contact with and suspended above substrate surfaces. Additionally, we will correlate Raman spectral maps with AFM topological contours. [Preview Abstract] |
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K1.00190: Interaction of Lithium and Low-Dimensional Graphene Chananate Uthaisar, Juan Peralta, Veronica Barone The lithium storage properties of low-dimenstional graphene present a great potential for more efficient rechargeable lithium ion batteries and hydrogen technologies. We study the rich variety of electronic and magnetic properties of graphene nanoribbons with two different edges, zigzag and armchair, by using density functional theory. We found that Li adsorption is stronger in zigzag nanoribbons than in two-dimensional graphene, fullerene and armchair nanoribbon. The strongest binding occurs when the Li-atom is located at the edge of zigzag nanoribbons. The evaluation of Li diffusion coefficient on the surfaces of graphene nanoribbons will be discussed. We will also show that the enhanced Li-zigzag nanoribbon interaction affects significantly their magnetic properties by quenching the magnetization in the areas neighboring the absorption site. Moreover, based in our first-principles calculations, we will report their Li intake capacity and rationalize it in terms of their peculiar properties and morphology. [Preview Abstract] |
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K1.00191: Ultrafast Dynamics of Photoexcited Dirac Fermions in Few-layer Epitaxial Graphene Tianqi Li, Liang Luo, Myron Hupalo, Michael Tringides, Jigang Wang Graphene -- a single layer of carbon atoms --has been a topic of strong current interest due to its basic physical properties and application potential arising from two-dimensional (2D) quantum confinement and unique massless Dirac Fermion quasiparticles. The recent success in preparation of single- and few-layer epitaxial graphenes has rendered intrinsic optical properties and ultrafast electronic relaxation experimentally accessible in a well-controlled manner. We used ultrafast visible, mid-IR and terahertz spectroscopy to reveal various decay pathways of photo-excited, highly non-equilibrium carriers in graphene. We will discuss some evidence of multi-particle Auger scattering, manifestating in the pump power, and temperature and probe wavelength dependence of the transient signals. The new ultrafast carrier processes reported here have clear implications for designing future graphene-based high-speed nanoelectronic devices. [Preview Abstract] |
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K1.00192: Synthesis and charge transport properties of CVD graphene films obtained by precipitation and catalytic formation on metal substrates Lewis Gomez, Yi Zhang, Alexander Badmaev, Chuan Wang, Zhen Li, Chongwu Zhou Chemical vapor deposition is considered a reliable approach to large-scale graphene, however the influence of aspects such as the graphene formation mechanism, carbon precursor and synthesis conditions, over the ultimate transport properties of the films remain to be explored. In this work we synthesized CVD graphene by catalytic formation and surface precipitation using methane and alcohol as carbon feedstock. AFM, SEM and TEM microscopy, as well as electron diffraction, XPS, Raman spectroscopy and electrical measurements were employed to characterize the films, showing a strong influence of the carbon source and formation mechanism on the uniformity and defect density of the synthesized CVD graphene, and hence, on their charge transport properties. [Preview Abstract] |
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K1.00193: Effects of electric fields on energy gap in bilayer graphene nanoribbons Y.C. Huang, S.J. Chiou, P.L. Huang, S.F. Yang, C.L. Lu Electronic properties of bilayer graphene nanoribbons are investigated by using the tight-binding model with transverse electric fields. They are mainly determined by the external fields, the ribbon edges, and the ribbon width ($N_y$). All bilayer zigzag ribbons are semiconductors, while bilayer armchair ribbons are semiconductors for $N_y \ne 3I+2$ ($I$ an integer). The electric fields modifies the energy dispersions, alters the subband spacing, switches the band gap ($E_g$), and causes the semiconductor-metal (or metal- semiconductor) transitions. In bilayer zigzag ribbons, electric fields not only lifts the degeneracy of partial flat bands at $E_F$ but also switches off $E_g$. $E_g$ is dependent on the ribbon width, ribbon edges, and the field strength. The semiconductor-metal transitions occur in both armchair ribbons and zigzag ribbons in the increase in electric fields. Due to electric fields, the above-mentioned effects are completely reflected in the features of density of states, such as the generation of special structures, the shift of peak position, and the alternation of band gap. The predicted electronic properties could be verified by scanning tunneling microscope conductance and optical absorption measurements. [Preview Abstract] |
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K1.00194: A DFT look at transport properties of Graphene nano-ribbons coupled to DNA Base pairs Jacob Gayles, Luis Agapito, Christian Woloweic, Nicholas Kioussis This study investigates the electronic structure and transport properties of DNA base pairs coupled to reconstructed zigzag edge Graphene Nano-Ribbons (z-GNRs PRL 101, 115502 (2008)$^{1}$ ). \textit{Ab initio} electronic structure calculations show reconstructed z-GNR to be more stable compared to the unreconstructed$^{1}$. By cleaving these metallic reconstructed ribbons, we create two graphene electrodes separated by a 5 {\AA} wide gap. The DNA base pair is then coupled to the graphene electrodes and relaxed using density functional theory. Transport properties are calculated in the ATK commercial packages (Atomistix ToolKit version 7.0, QuantumWise A/S). We compare tunneling currents for different base pairs, at finite biases. Understanding transport properties of the base pairs will potentially benefit areas such as DNA sensors and DNA sequencing. [Preview Abstract] |
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K1.00195: Edge Structures of Graphene Layers Grown on the 6H-SiC(0001) Surface Ilyou Kim, C. Hwang, Wondong Kim We investigated the edge structures of graphene nano-patches on the vicinal 6H-SiC(0001) surface using Scanning Tunneling Microscopy. We observed the formation of the ribbon-like single-layer graphenes with sharp edge structures at the initial stage of thermal graphitization process of the SiC(0001) surface. However, the overall long-range ordering of the steps of the bare vicinal surface was found out to be lost during graphitization process, and only the local short range ordering of the steps with graphene layer patches existed on the entire surface. From the atom-resolved STM images, we clearly identified the hexagonal interference pattern near edge of graphene layers. By analyzing this interference pattern we could conclude that armchair edge structure were more frequently observed than the zigzag structure. Scanning tunneling spectroscopy experiment was also carried out over the graphene nano-patches to examine the local electronic states at the edge structures. [Preview Abstract] |
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K1.00196: Unusual frictional signals in exfoliated mono layer graphene Jin Sik Choi, Ik Su Byun, Jin-Soo Kim, Sang Ho Jeon, In Rok Hwang, Sa Hwan Hong, Seung-Woong Lee, Sung-Oong Kang, Bae Ho Park, Duhee Yoon, Hyerim Moon, Hyeonsik Cheong, Young-Woo Son We have investigated abnormal friction phenomena on graphene mono-layer using atomic force microscopy (AFM). The graphene sample was prepared by exfoliation method on thermal oxidized 3000{\AA}-thick SiO2 buffer layer using 3M scotch tape. In order to analyze the friction phenomena, we have changed sample loading direction, scan direction, contact force, and scan speed. Moreover, influence of H2O was checked. Through the experiments, we confirmed that these phenomena are related with graphene itself, not from the SiO2 buffer layer. These friction phenomena may provide information for defect structures or for detecting artifacts of mono layer graphene surface. [Preview Abstract] |
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K1.00197: Measuring thermal expansion of graphene and understanding modal dispersion at low-temperature using graphene NEMS resonators Mandar Deshmukh, Vibhor Singh, Shamashis Sengupta, Hari S. Solanki, Rohan Dhall, Adrien Allain, Sajal Dhara, Prita Pant We use suspended graphene electromechanical resonators to study the evolution of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300K to 30K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that it is negative for all temperatures between 30K and 300K. We also study the dispersion of the electromechanical modes due to the application of a DC gate voltage and find a high degree of tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With lowering of temperature, we find that the positively dispersing electromechanical modes evolve to negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature compensated sensors. [Preview Abstract] |
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K1.00198: Direct TEM observation of dislocations of graphene and bilayer graphene Y. Abe, T. Tanaka, H. Sawada, E. Okunishi, Y. Kondo, Y. Tanishiro, K. Takayanagi Graphene is attracted much attention because it exhibits outstanding electronic transport properties arising from two-dimensional carbon atomic structure and it is expected for electronic devices. Recently, the long-range modulation of graphene lattice has been discussed to be an important factor of fluctuations of electronic properties. In this study, we found periodic dislocation of graphene and its bi-layer. We use novel aberration corrected transmission electron microscope (TEM), R005, which can resolve single carbon atoms of graphene. The periodic dislocations suggest long-range interactions and the mechanisms are discussed in the present study. [Preview Abstract] |
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K1.00199: The effects of strain on structural and electronic properties of graphane Mehmet Topsakal, Seymur Cahangirov, Salim Ciraci Based on first-principles calculations, we reveal the elastic properties of recently synthesized monolayer hydrocarbon, graphane. The in-plane stiffness and Poisson's ratio values are found to be smaller than those of graphene, and its yielding strain decreases in the presence of various vacancy defects and also at high ambient temperature. We also found that the band gap can be strongly modified by applied strain in the elastic range. We also showed that beyond the yielding point, the nonmagnetic graphane honeycomb structure changes into magnetic atomic chains and small flakes made by various polygons. [Preview Abstract] |
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K1.00200: Remote plasma assisted growth of graphene films: structure and physical properties Sergei Rouvimov, Gopichand Nandamuri, Raj Solanki The unique electrical properties of graphene, in particular ballistic transport and tunable transport properties have opened up exciting possibilities for this material as a replacement for silicon [1-2]. While graphene is commonly produced in research laboratories by mechanical exfoliation of highly oriented pyrolytic graphite, mass production of graphene-based devices requires technological approach to synthesize thin graphene films such as chemical vapor deposition. In present work, single and multiple layers of graphene films were grown on (111) oriented single crystals of nickel and polycrystalline nickel films using remote plasma assisted chemical vapor deposition. Remote plasma was employed to eliminate the effect of the electrical field on the orientation of the grown graphene films, as well as reduce the growth temperature compared to conventional chemical vapor deposition. The electrical and optical properties, including high resolution transmission electron microscopy of these films, suggest that this approach is both versatile and scalable for potential large area optoelectronic applications. \\[4pt] [1] T. Ohta, et al.\textit{ Science} 2006, \textbf{313,} 951- 954 \\[0pt] [2] Y. B, Zhang, et al. \textit{Nature }2005, \textbf{438,} 201- 204 [Preview Abstract] |
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K1.00201: Dislocations in graphene Luis L. Bonilla, Ana Carpio We study the stability and evolution of various elastic defects in a flat graphene sheet using a periodized discrete elasticity model. Two types of dislocations are found to be stable: ``glide'' dislocations consisting of heptagon-pentagon pairs, and ``shuffle'' dislocations, an octagon with a dangling bond. Unlike the most studied case of carbon nanotubes, Stone Wales defects are dynamically unstable in the planar graphene sheet and they annihilate when the dynamics is overdamped. Similar defects in which one of the pentagon-heptagon pairs is displaced vertically with respect to the other one are found to be dynamically stable. Effects of curvature of the graphene sheet are also introduced and do not change the previous results. A discussion of the origin of damping is provided. [Preview Abstract] |
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K1.00202: Monolayer Honeycomb Structures of Group-IV Elements and III-V Binary Compounds: First-principles Calculations Hasan Sahin, S. Cahanagirov, M. Topsakal, E. Bekaroglu, E. Akturk, R. Tugrul Senger, Salim Ciraci Using first-principles plane-wave calculations, we investigate two-dimensional (2D) honeycomb structure of group-IV elements and their binary compounds as well as the compounds of group III-V elements. Based on structure optimization and phonon-mode calculations, we determine that 22 different honeycomb materials are stable and correspond to local minima on the Born-Oppenheimer surface. We also find that all the binary compounds containing one of the first row elements, B, C, or N have planar stable structures. On the other hand, in the honeycomb structures of Si, Ge, and other binary compounds the alternating atoms of hexagons are buckled since the stability is maintained by puckering. For those honeycomb materials which were found stable, we calculated optimized structures, cohesive energies, phonon modes, electronic-band structures, effective cation and anion charges, and some elastic constants. The band gaps calculated within density functional theory using local density approximation are corrected by \textit{GW}$_{0}$ method. Si and Ge in honeycomb structure are semimetal {\ldots} [Preview Abstract] |
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K1.00203: Coulomb Effects in DNA-functionalized Single-Walled Carbon Nanotubes Benjamin Tayo, Slava Rotkin We study how many-body effects (Coulomb effects) affect the optical and electronic properties of DNA-functionalized SWCNTs. Coulomb effects are very strong in one-dimensional systems and hence play a greater role in their optical and electronic properties. Coulomb interactions contribute to the optical and electronic properties of carbon nanotubes in two main ways: band gap renormalization which comes from electron-electron interaction and the formation of excitons due to electron-hole coupling. The procudure for obtaining the optical exitation energies for DNA-SWCNTs involves incorporating Coulomb interaction within the Bethe-Salpeter (BS) equation combined with the tight-binding approximation (with self-energy contributions restricted to the screened Hartree-Fock approximation). The DNA-SWCNT interaction is modelled by applying a perturbation operator of the Coulomb interaction which breaks both translational and rotational symmetry. This lowering of symmetry induced by DNA-wrapping changes the band gap of the nanotube thus modulating its electronic and optical properties. The role of these effects are elucidated. [Preview Abstract] |
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K1.00204: Gapping by Twisting: Analysis of the Band-Gap Variations in Rippled Carbon Nanotubes Traian Dumitrica, Dong-Bo Zhang Recent experimental and theoretical [1] developments represent an opportunity to further our understanding on the carbon nanotubes electronic response in rippled morphologies. The mechanisms effective in collapsed nanotubes are not sufficient to explain the band-gap changes in rippled states. In this talk we uncover the important role played by the inhomogenous shear strain present in the nanotubes wall, a mechanisms that was not considered before. Relying on objective molecular dynamics combined with density-functional-based tight-binding, and introducing the concept of effective strain, we are able to delineate the physical mechanisms responsible for the band-gap variations and formulate a perturbative model in terms of the shear stress located at the ridges. This approach offers a clear interpretation such that the previous observations can be convincingly explained. We first focus on an isolated wall and later study the consequences of the gradual presence of inner walls, until the idealized behavior is regained. The galore of band-gap variations with the applied strain encuntered in the intermediate behavior has clear experimental implications. It suggests that some caution should be taken when interpreting the conductivity measurements carried out in nanotube-pedal devices. [1] D.B. Zhang, R.D. James, and T. Dumitrica, ``Electromechanical Characterization of Carbon Nanotubes in Torsion via Symmetry-Adapted Tight-Binding Objective Molecular Dynamics,'' Physical Review B 80, 115418 (2009). [Preview Abstract] |
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K1.00205: Electromechanical Characterization of Carbon Nanotubes in Torsion via Symmetry-Adapted Tight-Binding Objective Molecular Dynamics Dong-Bo Zhang, Traian Dumitrica, Richard James The nonlinear elastic response of carbon nanotubes (CNTs) in torsion is derived with objective molecular dynamics and a density-functional-based tight-binding model. The critical strain beyond which CNTs behave nonlinearly, the most favorable rippling morphology, and the twist- and morphology-related changes in fundamental band gap are identified from a rigorous atomistic description. There is a sharply contrasting behavior in the electronic response: While in single-walled CNTs the band gap variations are dominated by rippling, multi-walled CNTs exhibit an unexpected insensitivity. Results are assistive for experiments performed on CNT-pedal devices. References: D.B. Zhang, R.D. James, and T. Dumitrica, ``Electromechanical Characterization of Carbon Nanotubes in Torsion via Symmetry-Adapted Tight-Binding Objective Molecular Dynamics,'' Physical Review B 80, 115418 (2009). [Preview Abstract] |
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K1.00206: Biosensors and Biofuel Cells based on Vertically Aligned Carbon Nanotubes for Integrated Energy Sensing, Generation, and Storage (SGS) Systems Archana Pandey, Abhishek Prasad, Yoke Khin Yap Diabetes is a growing health issue in the nation. Thus \textit{in-situ} glucose sensors that can monitor the glucose level in our body are in high demand. Furthermore, it will be exciting if the excessive blood sugar can be converted into usable energy, and be stored in miniature batteries for applications. This will be the basis for an integrated energy sensing, generation, and storage (SGS) system in the future. Here we report the use of functionalized carbon nanotubes arrays as the glucose sensors as well as fuel cells that can convert glucose into energy. In principle, these devices can be integrated to detect excessive blood glucose and then convert the glucose into energy. They are also inline with our efforts on miniature 3D microbatteries using CNTs [1]. All these devices will be the basis for future SGS systems. Details of these results will be discussed in the meeting. [1] Wang et al., in 206$^{th}$ Meeting of the Electrochemical Society, October 3-8, Honolulu, Hawaii (2004), Symposium Q1, abstract 1492. Y. K. Yap acknowledges supports from DARPA (DAAD17-03-C-0115), USDA (2007-35603-17740), and the Multi-Scale Technologies Institute (MuSTI) at MTU. [Preview Abstract] |
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K1.00207: High yield assembly and transport properties of semiconducting carbon nanotubes Eliot Silbar, Kristy Kormondy, Paul Stokes, Saiful I. Khondaker AC-dielectrophoresis (DEP) typically yields a low percentage of semiconducting single-walled nanotube (SWNT) devices due to the greater force metallic SWNTs feel during the trapping process. Here we show that DEP combined with a commercially available semiconducting enriched solution allows for the large scale assembly of SWNT field effect transistors (FETs) from solution. Individual or small bundle SWNTs we assembled between 1 um spaced Pd source and drain electrodes using DEP. We observed FET behavior in 87{\%} of the as-assembled devices using this fabrication method. After annealing in Ar/H$_{2}$ gas, the devices displayed mobilities up to 463 cm$^{2}$/Vs and current on-off ratios as large as 4x10$^{5}$. We will present scanning electron micrographs, full electronic characteristics, and statistics on the FET devices. [Preview Abstract] |
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K1.00208: Resonance Raman Excitation of Double-Walled Carbon Nanotubes Jeffrey Simpson, Ji Yeon Huh, Jeffrey Fagan, Angela Hight Walker The opto-electronic properties of carbon nanotubes depend sensitively on their environment. Double-walled carbon nanotubes (DWCNTs) offer an ideal configuration in which to study interlayer electron-phonon coupling effects. Dispersed sub-populations (MM, MS, SM, SS where M is metal and S is semiconducting) of individualized DWCNTs were prepared in a three part process consisting of purification to remove catalysts, density gradient ultracentrifugation to remove dispersed SWCNT and MWNT nanotubes, followed by additional ultracentrifugation of purified DWCNT dispersions to separate the sub-species by buoyancy. Extracted fractions were concentrated and dialyzed for measurement. We perform resonance Raman spectroscopy (RRS) of DWCNTs using a wide range of laser excitation wavelengths, from NIR through UV, for vibrational modes including the radialbreathing mode (RBM) and higher order graphite modes. In order to measure the effects of electron-phonon coupling, we will compare the Raman spectra for specific chirality nanotubes in a double-walled complex with the behavior of individual SWCNTs of the same chirality. [Preview Abstract] |
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K1.00209: High yield semiconducting local-gated carbon nanotube field effect transistors Kristy Kormondy, Eliot Silbar, Paul Stokes, Saiful I. Khondaker Carbon nanotube field effect transistors (CNT-FETs) have displayed exceptional electrical properties that are superior to the traditional silicon MOSFET. Directed assembly of individually addressable CNT-FETs at selected positions of the circuit with high throughput needs to be demonstrated for future integrated circuits. Here, we utilize a commercially available semiconducting enriched SWNT solution in combination with ac-dielectrophoresis for the fabrication of CMOS compatible {\&} local gated CNT-FETs with low power consumption and high-speed operation. We assemble the SWNTs between 1 um spaced Pd source and drain electrodes with a 100 nm wide local Al/Al2O3 gate in the middle using DEP. We find that $\sim $80{\%} of the as-assembled device show semiconducting behavior. Measurements on $\sim $30 devices show that the majority of them displayed subthreshold slopes less than 300 mV/dec and as low as 120 mV/dec. The threshold voltage for the local gated devices is 0.5 V on average. Directed assembly of local gated CNT-FETs at selected position of the circuit via DEP may pave the way for large scale fabrication of CMOS compatible nanoelectronic devices. [Preview Abstract] |
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K1.00210: Environmental doping of graphene: Calculation of charge transfer and molecular binding energies David Carey, Nathanael Roome, Alexander Samuels The adsorption of molecules from the environment can strongly affect the electronic properties of graphene by doping and/or by producing scattering centers. We have studied the nature of the interaction between common important molecules such as CO$_{2}$, NO$_{2}$ and NH$_{3}$ with graphene. Using density functional theory estimates of the molecular binding energies, molecular positions and orientations as well as charge transfer have been calculated. It is found that ammonia has a binding energy of 122 -- 162 meV depending on the position and orientation of the N atom relative to the graphene layer and is an n-type dopant transferring 0.006 e -- 0.01 e per NH$_{3}$ molecule adsorbed to graphene. NO$_{2}$ is found to be a p-type dopant accepting $\sim $0.01 e per NO$_{2}$ molecule adsorbed from the graphene layer and has a binding energy of 150 - 188 meV. Finally, CO$_{2}$ is found to be an n-type dopant with a binding energy and charge transfer that depends strongly on orientation and adsorption site. We discuss these results in the context of understanding the electrical and electronic behaviour of graphene after environmental exposure and their significance for graphene based devices. Such studies are significant, in particular, for graphene based molecule sensors where charge transfer is important. [Preview Abstract] |
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K1.00211: Transfer of Graphene Layers Grown on SiC Wafers to Other Substrates and Their Integration into Field Effect Transistors Sakulsuk Unarunotai, Yuya Murata, Cesar Chialvo, Hoon-sik Kim, Scott MacLaren, Nadya Mason, Ivan Petrov, John Rogers An approach to produce graphene films by epitaxial growth on silicon carbide substrate is promising, but its current implementation requires the use of SiC as the device substrate. We present a simple method for transferring epitaxial sheets of graphene on SiC to other substrates. The graphene was grown on the (0001) face of 6H-SiC by thermal annealing in a hydrogen atmosphere. Transfer was accomplished using a peeling process with a bilayer film of Gold/polyimide, to yield graphene with square millimeters of coverage on the target substrate. Back gated field-effect transistors fabricated on oxidized silicon substrates with Cr/Au as source-drain electrodes exhibited ambipolar characteristics with hole mobilities of $\sim $100 cm$^{2}$/V-s, and negligible influence of resistance at the contacts. This work was supported by the U.S. DOE, under Award No. DE-FG02-07ER46471, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign. [Preview Abstract] |
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K1.00212: Quantum Manifestations of Graphene Edge Stress and Edge Instability Bing Huang, Miao Liu, Ninghai Su, Jian Wu, Wenhui Duan, Feng Liu We have performed first-principles calculations of graphene edge stresses, which display two interesting quantum manifestations absent from the classical interpretation: the armchair edge stress oscillates with nanoribbon width and the zigzag edge stress is noticeably reduced by spin polarization [1]. Such quantum stress effects in turn manifest in mechanical edge twisting and warping instability, showing features not to be captured by empirical potentials or continuum theory. Edge adsorption of H and Stone-Wales reconstruction are shown to provide alternative mechanisms in relieving the edge compression and hence to stabilize the planar edge structure. We also demonstrate that the quantum manifestation of mechanical properties such as stress to exist generally in many low-dimensional nanostructures, such as BN system. [1] Huang et al., Phys. Rev. Lett. 102, 166404 (2009). [Preview Abstract] |
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K1.00213: Hydrogen, methane and water adsorption on a carbon-silicon surface Fernando Maga\~na, Gerardo Vazquez Density functional theory and molecular dynamics were used at 300 K to study the adsorption of several molecules on a graphene layer modified with silicon, with the \textit{Si} atoms located substitutionally. We studied the adsorption of H$_{2}$, CH$_{4}$, H$_{2}$O. [Preview Abstract] |
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K1.00214: Fluctuation effects of local electric field induced by water on graphene dot band gap Sergio Dalosto, Silvia Tinte Graphene, a two-dimentional single plane of carbon atoms, has shown to have favorable chemical sensor properties. In particular, ubiquitous molecules such as water could affect the sensitivity and selectivity of graphene. We investigate the fluctuations in the HOMO-LUMO gap of graphene dots due to the interaction with water using a combination of first principles and molecular mechanics (QM/MM) and classical molecular dynamics (MD). Our major conclusion is that the HOMO-LUMO gap for both spin flavors fluctuates following the variation of the local electric field at both zigzag and armchair edges. The local electric filed is not uniform at the edges along the MD simulations. These results may be useful in the design of sensors based on graphene. [Preview Abstract] |
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K1.00215: Graphene-metal contact: a momentum and spin filter Jesse Maassen, Wei Ji, Hong Guo We perform a first principles study of a graphene-metal contact using Cu, Ni, Co as the metallic leads. These metals have in-plane lattice constants that almost perfectly match that of graphene allowing the possibility of an atomically clean interface. Structural optimizations are carried out before calculating the nonequilibrium transport properties using a combination of density functional theory (DFT) and nonequilibrium Green's functions (NEGF). In the case of Cu, two Dirac-points are observed in the transmission resulting from electron doping of graphene from the Cu electrode. For the magnetic Ni and Co, significant spin filtering is predicted with efficiencies reaching 60\% and 80\% respectively. In all cases, near the Fermi level, electrons can travel only along specific directions depending on the orientation of the graphene. [Preview Abstract] |
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K1.00216: Controlled Etching and Characterization of Multiple Graphene Layers on Copper Joshua Wood, Jae Won Do, Roshan Choxi, Scott Schmucker, Justin Koepke, Joseph Lyding Graphene growth on copper has attracted much interest due to the large graphene domain sizes and the high percentage of monolayer graphene coverage$^{1}$. To use this grown graphene for other applications, one must characterize both the graphene coverage and number of graphene layers. We identify graphene coverage on as-grown copper samples by oxidizing the copper foil at $\approx $400\r{ }C. Due to graphene's low oxygen permeability$^{2}$, graphene-covered copper regions will not oxidize, leading to large contrast between the oxidized copper and graphene. The high contrast allows us to identify monolayer and few-layer graphene (FLG) sheets with a stereo microscope. With this, we find that our graphene domains are around 200$\mu $m in size, with some pieces as large as 2mm. We also use an oxygen plasma to etch the graphene on copper samples. Graphene sheets act as a shadow mask for the plasma, preventing portions of the copper from oxidizing. By controlling the plasma energy and etching time, we can selectively etch the graphene layer by layer, leaving only monolayer regions on the oxidized copper. We show that graphene grown on copper is not necessarily monolayer, with multiple layers forming at rough nucleation sites on the copper. $^{1}$Li \textit{et al}., \textit{Science }\textbf{324}, 1312 (2009). $^{2}$Bunch \textit{et al}., \textit{Nano Lett.} \textbf{8}, 2458 (2008). [Preview Abstract] |
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K1.00217: Monolayer Graphene Grown on Copper Substrates and Studied by Transmission Electron Microscopy Scott Schmucker, Joseph Lyding We report transmission electron microscopy studies of graphene grown by chemical vapor deposition on copper foils.\footnote{Li, X., et al., Science, \textbf{324}, 5932, 1312-1314 (2009)} An understanding of the quality and transferability of these graphene films is prerequisite to their application in device structures. In our work, graphene has been fabricated on copper for transfer to perforated carbon films and study by Transmission Electron Microscopy (TEM). The resulting suspended graphene structure offers both a superior imaging platform and a method for the characterization of copper-grown graphene films. Here, TEM elucidates microstructure and nanostructure visible in solution-transferred copper-grown graphene sheets. By comparison of this structure to Scanning Electron Microscopy (SEM) images of the copper/graphene surface those features created during growth and during transfer can be distinguished. [Preview Abstract] |
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K1.00218: High-pressure crystal growth and magnetic and electrical properties of the quasi-one dimensional osmium oxide Na$_2$OsO$_4$ Y.G. Shi, Y.F. Guo, S. Yu, M. Arai, A.A. Belik, A. Sato, K. Yamaura, E. Takayama-Muromachi, T. Varga, J.F. Mitchell Na$_2$OsO$_4$ crystals were grown by a NaCl flux method under high pressure. It was found that Na$_2$OsO$_4$ crystallizes in the Ca$_2$IrO$_4$-type structure, which consists of OsO$_6$ octahedra chains, rather than in the K$_2$NiF$_4$-type. A chain-magnetism was thus expected for the crystal because of the electronic configuration of Os^{6+}O$_6$ (5$d^2$, $S =$ 1). However, experimental data suggested the $S =$ 0 state for the crystal rather than the $S =$ 1 state. We carefully investigated the crystal to resolve the contradiction between the expectation and the observation, and found that the absence of the chain-magnetism is likely due to statically uniaxial compression of the OsO$_6$ octahedra, resulting in splitting of the $t_{\rm 2g}$ band. The localized 2 electrons per Os are probably paired in the $t_{\rm 2g}$ band, forming the $S = 0$ state. We will discuss details of the issue. This research was supported in part by the WPI Initiative on Materials Nanoarchitectonics from MEXT, Japan, and the Grants-in-Aid for Scientific Research (20360012) from JSPS. Work at Argonne National Laboratory supported under Contract No. DE-AC02- 06CH11357 by UChicago Argonne, LLC, Operator of Argonne National Laboratory, a U.S. Department of Energy Office of Science Laboratory. [Preview Abstract] |
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K1.00219: High-pressure synthesis and physical properties of the BaIrO$_{3}$ polytypes J.-G. Cheng, J.-S. Zhou, J.B. Goodenough, J.A. Alonso, E. Suard, Y. Sui, K. Matsubayashi, Y. Uwatoko The ambient 9R-BaIrO$_{3}$ exhibits a ferromagnetic transition at T$_{c}\approx $ 180 K followed by a charge density wave at nearly the same temperature.\footnote{G. Cao\textit{, et al}., Solid State Comm. \textbf{113}, 657 (2000).} By using the 9R phase as the staring material, we were able to synthesize a series of the polytypes of BaIrO$_{3,} \quad i.e.$ 5H, 6H and 3C phases under high pressure up to 10 GPa at 1000\r{ } C.\footnote{J.-G. Cheng, \textit{et al}, J. Am. Chem. Soc. \textbf{131}, 7461 (2009).} These high-pressure phases are quenchable to ambient pressure. The 5H phase has the stacking sequence \textit{hchcc} that is a new member in the hexagonal polytypes of AMO$_{3}$ perovskites. With increasing fraction of the corner- to face-sharing IrO$_{6/2}$ octahedra in the sequence 9R$\to $5H$\to $6H, the ground states of BaIrO$_{3}$ evolve from a ferromagnetic insulator with T$_{c }\approx $ 180 K in the 9R phase to a ferromagnetic metal with T$_{c} \approx $ 50 K in the 5H phase, and finally to an exchange-enhanced paramagnetic metal near a quantum critical point in the 6H phase.\footnote{J.-G. Cheng, \textit{et al}., Phys. Rev. B \textbf{80}, 104430 (2009).} [Preview Abstract] |
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K1.00220: Unconventional metamagnetism and orbital ordering in transition metal oxides (I) Congjun Wu, Wei-Cheng Lee We extend the study of the Fermi surface instability of the Pomeranchuk type into systems with orbital band structures, which are common features in transition metal oxides. Band hybridization significantly shifts the spectral weight of the Landau interactions from the conventional s-wave channel to unconventional non-s-wave channels, which results in anisotropic (nematic) Fermi surface distortions even with ordinary interactions in solids. The Ginzburg-Landau free energy is constructed by coupling the charge-nematic, spin-nematic, and ferromagnetic order parameters together, which shows that nematic electron states can be induced by metamagnetism. The connection between this mechanism and the anisotropic metamagnetc states observed in Sr$_3$Ru$_2$O$_7$ at high magnetic fields is studied in a multiband Hubbard model with the hybridized quasi-one-dimensional d$_{xz}$ and d$_{yz}$ bands. [Preview Abstract] |
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K1.00221: First principles studies of the oxygen reduction reaction on the Pd-Co surfaces. Sebastian Zuluaga, Sergey Stolbov Fuel cells (FC) are promising means for obtaining clean energy, however Pt-based catalysts currently used in FC are too expensive for practical application. Since Pd-Co nanostructures are found to show enhanced electro-catalytic properties for the oxygen reduction reaction (ORR) on FC's cathode catalysts, we focus on these materials. We carry out density functional theory calculations using the Vienna AB initio Simulation Package (VASP) in order to investigate ORR characteristics of the Pd$_{x}$-Co$_{1-x}$ (x=0.75 {\&} 0.5) surfaces. We have calculated the absorption energies of O and OH for different sites in the surface and use them to build a free energy diagram, which helps us to estimate the ORR rate as proposed in [1]. Since experiment suggests an alloy segregation leading to formation a single Pd layer on the surface, we have performed the calculations for this system as well. The calculation results suggest that the Pd layer on Pd$_{0.75}$-Co$_{0.25}$ has the unset potential for ORR higher than that for non-segregated systems and clean Pd. We also trace these properties to calculated densities of electronic states of the materials. [1]J.K N{\o}rskov,et al,J.Phys.Chem.B,108,17886(2004) [Preview Abstract] |
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K1.00222: Atomistic polarizable force field for molecular dynamics simulations of azide anion containing ionic liquids and crystals. Oleg Starovoytov, Justin Hooper, Oleg Borodin, Grant Smith Atomistic polarizable force field has been developed for a number of azide anion containing ionic liquids and crystals. Hybrid Molecular Dynamics/Monte Carlo (MD/MC) simulations were performed on methylguanazinium azide and 1-(2-butynyl)-3-methyl-imidazolium azide crystals, while 1-butyl-2,3-dimethylimidazolium azide and 1-amino-3-methyl-1,2,3-triazolium azide ionic liquids were investigated using MD simulations. Crystal cell parameters and crystal structures of 1-(2-butynyl)-3-methyl-imidazolium azide were found in good agreement with X-ray experimental data. Density and ion transport of 1-butyl-2,3-dimethylimidazolium azide predicted from MD simulations were in good agreement with experiments. Details of the ionic liquid structure and relaxation mechanism will be discussed. [Preview Abstract] |
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K1.00223: Energetics and Molecular Dynamics Simulations of Hydrogen Adsorption on a Silicon Nanosheet Tim H. Osborn, Amir A. Farajian, Lok C. Lew Yan Voon, Rachel Aga The energies and temperature-dependent dynamics of hydrogen chemisorption on a silicon nanosheet were studied using density functional theory and molecular-dynamics (MD) simulations. Energy calculations were performed by utilizing generalized-gradient approximation with the Perdew-Burke-Ernzerhof exchange correlation functional. The adsorption energies of hydrogen on the silicon nanosheet were calculated for different hydrogenation ratios corresponding to weight percents between 0 and 3.59 \%. The preferred adsorption configurations were determined based on these energy calculations. MD simulations revealed the stability of adsorption configurations, and possible transitions between them, at different temperatures. [Preview Abstract] |
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K1.00224: A First-Principles Study of Zinc Oxide Honeycomb Structures Mehmet Topsakal, Seymur Cahangirov, Erman Bekaroglu, Salim Ciraci We present a first-principles study of the atomic, electronic and magnetic properties of two dimensional (2D), single and bilayer ZnO in honeycomb structure and its armchair and zigzag nanoribbons. In order to reveal the dimensionality effects, our study includes also bulk ZnO in wurtzite, zincblende and hexagonal structures. The stability of 2D ZnO, its nanoribbons and flakes are analyzed by phonon frequency, as well as by finite temperature ab-initio MD simulations. 2D ZnO and its armchair nanoribbons are nonmagnetic semiconductors, but acquire net magnetic moment upon the creation of zinc vacancy defect. Zigzag ZnO nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms at the edges and have high spin polarization at the Fermi level. However, they change to nonmagnetic metal upon termination of their edges with hydrogen atoms. Under tensile stress the nanoribbons are deformed elastically maintaining honeycomb like structure, but yield at high strains. Beyond yielding point honeycomb like structure undergo a structural change and deform plastically by forming large polygons. The variation of the electronic and magnetic properties of these nanoribbons have been examined under strain. [Preview Abstract] |
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K1.00225: Effect of Stone-Wales defect on the electronic structure of Silicon Nanoribbons Sumit Saxena, Trevor A. Tyson We have investigated the electronic properties of Silicon nanoribbons using density functional theory within the local density approximation. It has been reported that the armchair Silicon nanoribbons can be metallic or semiconducting depending on their width. We present the ab-initio studies of the electronic properties of Silicon nanoribbons with structural defects like the Stone-Wales defects. Comparisons with grapheme nano-ribbons will be made. [Preview Abstract] |
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K1.00226: Honeycomb Structures of Transition Metal-Group 6A Elements Can Ataca, Hasan Sahin, Ethem Akturk, Salim Ciraci In this study, we investigated the structural, electronic, magnetic properties and stability of MoS$_2$ like honeycomb structures, namely MX$_2$ where M is a transition metal atom (Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, W) and two group (X) 6A elements (O, S, Se, Te) in a unit cell, using first-principles density functional theory. The structure consists of three layers, two for group 6A elements and one for the transition metal atom. The stabilities of various new structures are further testified by phonon dispersion analysis. Unlike graphene, some of the new honeycomb structures resulted in magnetic ground states. It is also noted that metallic honeycomb structures also exist. [Preview Abstract] |
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K1.00227: Electronic Structure Properties of Nickel Carbides Angela Wilson, Joshua Gibson, Thomas Cundari Our analyses of nickel carbides have shown that hexagonal Ni$_{3}$C ($\Delta $E = 6.4 kcal/mol) is more stable than NiC ($\Delta $E = 48.6 kcal/mol). To understand the change in stability between these nickel carbides, we have examined the electronic stability and structure of Ni$_{2}$C. Using the Vienna Ab-initio Simulation Package (VASP) code, the most stable ground state arrangement of Ni$_{2}$C was determined. The total density of states of Ni$_{2}$C, the density of states for each nickel and carbon atom within the primitive lattice, and the band structure of Ni$_{2}$C were examined. The electronic structure of Ni$_{2}$C was compared to those of diamond, NiC (rock salt), and Ni$_{3}$C (hexagonal). For Ni$_{2}$C, the Fermi energy was obtained and the behavior of the band structure around the Fermi energy was classified. The density of states for nickel and carbon within the relaxed lattice were used to understand the bonding mechanism that exists within Ni$_{2}$C. [Preview Abstract] |
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K1.00228: ABSTRACT WITHDRAWN |
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K1.00229: LEED study of the orthorhombic Al$_{13}$Co$_{4}$ (100) surface and its interaction with Xe Renee D. Diehl, Heekeun Shin, Katariina Pussi, Peter Gille The (100) surface of orthorhombic Al$_{13}$Co$_{4}$ is a periodic approximant of the decagonal Al-Ni-Co 10-fold quasicrystalline surface. An STM study [1] of Al$_{13}$Co$_{4 }$ shows the surface has two different terminations and that the relative amounts of each are dependent on the surface preparation. We will present a dynamical LEED study of the T1-termination of the Al$_{13}$Co$_{4}$(100) surface, obtained by annealing at 1173K for 2 hours. Xe adsorbs on this surface in a layer-by-layer growth mode, and at a sufficiently high coverage it orders into four domains of close-packed Xe. These domains are rotationally aligned along certain crystallographic directions, where they appear to lock into uniaxial higher-order commensurate structures. The structures and thermodynamics of Xe film growth will be presented.\\[4pt] [1] R. Addou et.al, Physical Review B 80, 014230(2009). [Preview Abstract] |
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K1.00230: FLUIDS AND SOFT MATTER II |
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K1.00231: Crystallography on Spherical Surfaces Guangnan Meng, Vinothan Manoharan We encapsulate micron sized colloidal particles inside w/o emulsion droplets. We control particle-particle and particle-interface interactions, so that the particle stay close to the interface but without penetrating the w/o interface. Monolayered colloidal crystallite form near the spherical interface at equilibrium. We use this system to study how the topological defects and disclinations diffuse and relax on spherical surfaces. [Preview Abstract] |
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K1.00232: Dynamics of Vorticity Aligned Structures in Attractive Colloidal Suspensions Ajay Negi, Michelle Bebrin, Cinedum Osuji Shear rate jumps from high to low flow rates in an attractive colloidal suspension of carbon black particles in a non-polar solvent result in the formation of transient vorticity aligned log-like structures. We study the dynamics of these elongated flocs using optical microscopy in situ with bulk rheology. The appearance of the vorticity aligned aggregates is attended by an increase in the suspension viscosity which peaks quickly and then gradually recedes with passage of time under flow. The occurrence in time of the viscosity maximum scales inversely with the shear rate applied to the system. This emergence of the peak appears to be controlled by a critical strain and rescaling in these terms produces a common response across several different shear rates. Alteration of the attraction strength between particles by the addition of surfactant severely inhibits the structure formation. We present a simple model to account for these observations. [Preview Abstract] |
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K1.00233: Pack and split: a simulation study of structural transitions of sodium dodecyl sulfate micelles Maria Sammalkorpi, Mikko Karttunen, Mikko Haataja Surfactants are important interfacial agents in many biological and industrial systems. Their self-assembly and versatility of the aggregates lies at the heart of all biological membrane, vesicle and micelle formation, and many industrial solubilization processes. While biologically and industrially extremely important, surprisingly little is known about molecular details of the self-assembly of surfactants and the dynamics of the formed structures. Here we extend our previous work of model construction and structural properties of self-assembled sodium dodecyl sulfate (SDS) micelles [J. Phys. Chem. B 111, 11722 (2007)] to structural transitions of these self-aggregates. We present the results of detailed molecular dynamics simulations of anionic micelle fission, and structural changes in the micelles brought forth by differences in the ionic strength of the solution [J. Phys. Chem. B 113, 5863 (2009);J. Am. Chem. Soc. 130, 17977 (2008)]. We demonstrate the existence of a new fission pathway which consists of a Rayleigh instability driven by Coulombic interactions, and a formation of a long interdigitating stalk. [Preview Abstract] |
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K1.00234: Secondary order inside 2D crystals of Janus colloidal spheres Jing Yan, Shan Jiang, Stephen Anthony, Qian Chen, Steve Granick Colloidal particles are known to crystallize into hexagonal packing in 2D. When particles are made to be hydrophilic on one side and hydrophobic on the other, a secondary orientation order emerges, with the striking appearance of stripe structures. Factors that determine the crystal structure are investigated, including ionic strength, volume fraction, and Janus balance. Statistical thermodynamic analysis and computer simulations are performed to understand the underlying mechanism. Attempts are also made toward complicated structures in 3D. By modulating the shape of the building blocks, different ordered structures could be obtained. [Preview Abstract] |
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K1.00235: From molten to frozen Janus colloidal clusters Qian Chen, Joshua Ritchey, Jing Yan, Jeffrey Moore, Steve Granick Colloidal clusters self-assembled from amphiphilic Janus spheres in aqueous solutions are dynamic and interchangeable between different configurations. Here by grafting photosensitive polymeric coumarin onto one hemisphere of Janus particles, we freeze the clusters covalently by forming [2+2] cycloaddition of coumarin upon UV exposure. Monodisperse trimers and tetrahedron are harvested and used as secondary self-assembly building blocks. [Preview Abstract] |
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K1.00236: Physics of local rule-based self-assembly Sahand Hormoz, Michael Brenner Recent experimental advances have opened up the possibility of equilibrium self- assembly of functionalized nanoblocks with high degree of controllable specific interactions. The notion of the number of types of components and the corresponding energetic interactions (set of local rules) needed for successful assembly has been studied from an algorithmic point of view, and applied, for example, to assembly of viral shells. Similar questions have also been asked in protein folding, in particular, on the minimum number of amino acids required for successful folding. We extend the algorithmic notion of self-assembly by accounting for its physical nature. We discuss bounds on the number of monomer types and the energetic interactions, as a function of fundamental system parameters, required for thermodynamic stability of the final structure and kinetic feasibility of assembly. [Preview Abstract] |
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K1.00237: Coil-Globule Transition of PNIPAM in Non-Ionic Surfactant Mesophase V.J. Jijo, K.P. Sharma, R. Mathew, P.R. Rajamohanan, K. Guruswamy We investigate the Coil-Globule transition of linear poly N-isopropylacrylamide (PNIPAM) in the hexagonal (H$_{1})$ mesophase of a non ionic surfactant, C$_{12}$E$_{9}$ in water, by Turbidimetry, NMR and SAXS. For aqueous PNIPAM, the LCST (coil-globule transition temperature), $T_{PNIPAM}$, is 35\r{ }C, whereas the H$_{1}$ phase transitions to a micellar phase at a temperature, $T_{HI}$, of 45\r{ }C. As PNIPAM is added to the C$_{12}$E$_{9}$/H$_{2}$O system; depending on the ratio of C$_{12}$E$_{9}$:H$_{2}$O,$ T_{PNIPAM}$ changes. It is observed that at 42wt{\%} of C$_{12}$E$_{9}$ (viz. 58wt{\%} water; micellar phase), the $T_{PNIPAM}$ is 33\r{ }C. At 44wt{\%} of C$_{12}$E$_{9}$ (viz. 56wt{\%} water), the H$_{1}$ phase forms and the the coil-globule transition for PNIPAM starts at 28\r{ }C. For 50wt{\%} C$_{12}$E$_{9,}$ the transition starts from 13\r{ }C and for 60wt{\%} C$_{12}$E$_{9}$ in water, PNIPAM does not even shows the phase transition even as below as 5\r{ }C. It is observed using optical microscopy that the PNIPAM is trapped at the domain boundaries of the H$_{1}$ phase. The decrease in the coil globule transition temperature,$ T_{PNIPAM}$, is not only because of the hydrophobic interactions but also due to the competition between polymer and C$_{12}$E$_{9}$ for water in the H$_{1}$ phase. The inability of PNIPAM to become a complete globule at higher temperature may be due to the adsorption of C$_{12}$E$_{9}$. [Preview Abstract] |
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K1.00238: Contact line dynamics of colloids in vertical deposition subjected to electric fields Wenceslao Gonz\'alez-Vi\~nas, Moorthi Pichumani, Maximiliano Giuliani We observe the dynamical behavior of receding contact line of an evaporating colloidal suspension subjected to electric fields. The dynamics is explored by evaluating the velocity of contact line at micro and macroscopic length scales. The measured speeds are further correlated with the structures that evolved at the diverse scales during the deposition process. Pinning and depinning of contact line results in its rapid advancement, which could explain the different morphologies obtained. [Preview Abstract] |
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K1.00239: Morphology and Fluctuations of Suspended Graphene Oxide Sheets Matthew Gratale, Daniel T. N. Chen, Zexin Zhang, Zhengtang Luo, Erik Smith, Peter Collings, Alan T. Johnson, Arjun Yodh We study the morphology and fluctuations of suspended graphene oxide sheets by phase contrast and confocal microscopy. The morphology of graphene oxide sheets is manipulated by changing solvent pH. Labeling the graphene oxide sheets with quantum dots permits further study of morphology, as well as the possible study of the fluctuations, through the use of confocal microscopy. The direct imaging studies of the morphology are complimented by light scattering studies, conventionally used to characterize morphology of colloidal membranes. These direct imaging studies can lead to measurements of the mechanical properties of graphene oxide in solution. [Preview Abstract] |
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K1.00240: Specific heat at the micellization and phase transitions in a triblock copolymer-water system David Simpson, D.T. Jacobs The triblock copolymer ("unimer") of PPO-PEO-PPO (commercially known as 17R4) has hydrophobic ends and a hydrophilic center. When placed in water a network of unimers can self-assemble to micelles of different geometries at higher concentrations or temperatures, We have measured the micellization line marking the transition from only unimers in solution to some micelles forming. There is also a one- to two-phase transition at higher temperatures that is an Ising-like, LCST critical point. Specific heat measurements from our adiabatic calorimeter provide important information about the type of transition seen at both the critical point and at the micellization transition. We have also used an Isothermal Titration Calorimeter to further probe the micellization line. We acknowledge the support from Research Corporation, NSF-REU grant DMR 0649112, and The College of Wooster. [Preview Abstract] |
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K1.00241: Cell Penetration by Transportan Amir Mohsen Pourmousa Abkenar, Jirasak Wong-ekkabut, Michael Patra, Mikko Karttunen Translocation of peptides through cellular membranes is a fundamental problem in developing antimicrobial peptides and also in drug delivery. It is known from experiments that there are a number of very different classes of peptides, all known as cell-penetrating peptides, that are able to penetrate membranes and, for example, carry pharmacological compounds- thus a promising strategy for drug delivery. The common characteristics of these peptides is only their high charge density. It is not known, however, what are the physical mechanisms that facilitate the translocation. We have used large-scale Molecular Dynamics simulations to study the penetration of one of these peptides, namely Transportan, across Dipalmitoylphosphatidylcholine (DPPC) lipids. In particular, we have calculated the potential of mean force (PMF) by umbrella sampling. The energy profile has a deep minimum inside the the bilayer showing the tendency of peptide to go inside the bilayer. Our objective is to find the controlling mechanisms of translocation through a detailed analysis of peptide-lipid interactions and free energy analysis. [Preview Abstract] |
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K1.00242: Micellization and phase transitions in a triblock copolymer-water system Alison Huff, Kelly Patton, D.T. Jacobs, Bryna Clover, S.C. Greer The triblock copolymer ("unimer") of PPO-PEO-PPO (commercially known as 17R4) has hydrophobic ends and a hydrophilic center. When placed in water at lower concentrations and temperatures, only a network of unimers exists. However, at higher concentrations or temperatures, micelles of different geometries can form. We have measured the micellization line marking the transition from only unimers to some micelles, as well as a one- to two-phase transition at higher temperatures. This second transition is an Ising-like, LCST critical point. We compare our results to earlier measurements and use micelle size measurements from dynamic light scattering to interpret the interesting behavior of this system. We acknowledge the support from Research Corporation, NSF-REU grant DMR 0649112, The College of Wooster, and (for BC and SG) to the donors of the American Chemical Society Petroleum Research Fund Grant 01433212. [Preview Abstract] |
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K1.00243: Melting in two dimensional directionally bonded solids: a Monte Carlo study Donald Priour, James Losey We examine melting in two dimensional membranes where there is directional covalent bonding between atomic species, and the bonds are treated as harmonic potentials. We use large scale Monte Carlo simulations to calculate thermodynamic equilibrium variables. We examine square, triangular, and honeycomb lattices for single and dual-layer configurations. The corresponding three dimensional lattices, where long range order is intact, are examined as a reference. We calculate the Root Mean Square (RMS) displacement, finding RMS displacements to vary logarithmically with the system size. Using realistic parameters, we provide quantitative estimates for the RMS displacements for various temperatures. We find swift equilibration times for triangulated systems, but very slow progress toward ergodicity in square and simple cubic systems, a phenomenon similar to the lengthy equilibration times encountered by Fermi, Pasta, and Ulam in the context of anharmonically one dimensional systems. [Preview Abstract] |
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K1.00244: Colloids clustering in meniscus free surface with alternate electric fields Maximiliano Giuliani, Moorthi Pichumani, Wenceslao Gonz\'alez-Vi\~nas To fabricate colloidal crystals of appreciable homogeneity by the vertical deposition method, it is necessary to maintain throughout the process: (a) a constant and homogeneous colloid concentration and (b) a constant speed of the contact line. We study the effect of alternate electric fields on charged colloidal particles suspended in water. The experimental setup recalls the vertical deposition configuration but without evaporation. We explore and report experimental results on clustering instabilities that appear due to electrowetting at electric fields and frequencies of the order of 1V/mm and 1Hz respectively. [Preview Abstract] |
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K1.00245: Order Parameter and Response to External Fields in a Spatiotemporal Chaotic System Rinto A Nur Qomaru Zaman, Tatsuhiro Ueki, Koyo Tamura, Yoshiki Hidaka, Noriko Oikawa, Shoichi Kai For Soft-Mode Turbulence (SMT) which is a new type of spatiotemporal chaos generated by the nonlinear interaction between the Nambu-Goldstone modes and the convective modes in electroconvection of homeotropic nematic systems, a new order parameter called $pattern ordering$ is introduced to measure the degree of order of the convective pattern. It is revealed that two types of SMT pattern called oblique roll and normal roll patterns have zero and finite pattern ordering, so that they can be regarded respectively, as a disordered and an ordered pattern when the so-called Lifshitz frequency is the transition point. Later, by applying an external magnetic field for the oblique roll regime, the Nambu-Goldstone modes is suppressed and therefore leads to a nonzero pattern ordering which behaves as a response. By using an analogy with magnetic susceptibility, we investigate a kind of $pattern susceptibility$ as a degree of order in response of the convective pattern to the applied field. In addition, ac susceptibility due to the modulating field is also discussed. [Preview Abstract] |
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K1.00246: Computational modeling of three-dimensional gel membrane in temperature gradient Olga Kuksenok, Anna C. Balazs Gel membranes are used in a variety of applications, from controlled release of chemicals in drug delivery systems to flow regulation within microfluidic devices. The degree of swelling within the gel membrane regulates its permeability and hence, offers an opportunity to effectively control transport of different species through the layer. One of the efficient ways to control the degree of swelling of gels is by varying the temperature of the system. Here, we develop a computational model that allows us to simulate the three-dimensional dynamics of a gel membrane in a temperature gradient. We use this model to investigate the structural evolution of gel membranes that are clamped by two of its edges. We show that dynamics of forming patterns consisting of regions of more or less swollen gel strongly affects the membrane's properties. We demonstrate that by varying the temperature gradient, one can effectively control the permeability of the membrane. [Preview Abstract] |
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K1.00247: Stability analyses of the model for responsive gels undergoing photosensitive Belousov-Zhabotinsky reaction Pratyush Dayal, Olga Kuksenok, Anna C. Balazs Via theory and simulations, we investigate the behavior of polymer gels undergoing Belousov-Zhabotinsky (BZ) reaction. Driven by the periodic reduction and oxidation of the ruthenium catalyst, which is grafted to the polymer network, the BZ gels undergo rhythmic mechanical oscillations and thereby exhibit chemo-mechanical transduction. However, the oscillations within the BZ gels can be completely suppressed with light of a certain wavelength. We exploit this property to direct the movement of these BZ gels along complex paths, guiding them to bend, reorient and turn. However, there is a particular range of parameters where this mechanism works. Through linear stability and normal form analyses, we isolate parameters for which the gel switches from oscillatory mode to stationary mode and vice versa. Specifically, we characterize the nature of Hopf bifurcations and identify regimes where this bifurcation is subcritical or supercritical. We also determine several other types of bifurcations within our system. These analyses allow us to establish necessary and sufficient conditions required to guide the movement of these active gels along complex paths. [Preview Abstract] |
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K1.00248: Experimental evidence of wave propagation phenomena inside a cylindrical cavity of liquid metal produced by an oscillating magnetic field Montserrat Ana Miranda, Javier Burguete We report results on the magnetic instability that takes place inside a cylindrical cavity containing a liquid metal alloy at room temperature (InGaSn). The cell remains static while an oscillating frame of coils perturbs the initially quiescent metal liquid. The gradient of the non-oscillating magnetic field at the boundaries is obtained from the grid measurements over an axisymmetric plane. The flow in the bulk is studied from potential differences. We report the internal-wave dynamics for different frequencies of the oscillating magnetic field. [Preview Abstract] |
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K1.00249: Viscosity and surface drag in quasi-two-dimensional flows Edward C. Titmus, Adrian T. Kirn, Paul W. Fontana Seattle University -- The effects of kinematic viscosity and surface drag are both significant factors in many experimental and natural quasi-two-dimensional (Q-2D) flows. These effects, however, are difficult to distinguish from one another. In a Q-2D experiment involving soap films in a circular Couette cell, we demonstrate precise independent measurement of both kinematic viscosity and surface drag as a function of film thickness using decay rates of vortices of varying scales. As theoretically expected, we have found both the kinematic viscosity and the surface drag to depend inversely on film thickness. This result allows quantitative experimentation in the realm of stability theory in basic Q-2D flows. [Preview Abstract] |
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K1.00250: CHEMICAL PHYSICS |
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K1.00251: Bridging the momentum distribution and the potential energy surface of protons in hydrogen bonds Joseph Morrone, Lin Lin, Roberto Car, Michele Parrinello Open path integral Car-Parrinello molecular dynamics studies have uncovered the proton momentum distribution in various phases of ice [1,2]. These systems exhibit a wide range of behavior, including symmetric hydrogen bonds and quantum tunneling. In this work, we provide an in-depth statistical analysis of the simulation results. This analysis reveals a direct relation between the open path formalism of quantum particles and their underlying potential energy surface. Application of this analysis to ice systems provides quantitative information about the principle axes of the potential energy surface that the proton experiences, and indicates that the oxygen-oxygen distance is a proper reaction coordinate for such systems. Our analysis also facilitates a direct observation of anharmonic effects along the principle axes. [1] J. A. Morrone and R. Car, Phys. Rev. Lett. 101, 17801, 2008. [2] J. A. Morrone, L. Lin and R. Car, J. Chem. Phys. 130, 204511, 2009. [Preview Abstract] |
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K1.00252: Partition-of-unity finite elements for electronic structure: have planewaves finally met their match? John Pask Over the past few decades, the planewave (PW) pseudopotential method has established itself as the dominant method for large, accurate, density-functional calculations in condensed matter. However, due to the underlying Fourier representation of the required quantum mechanical wavefunctions, the PW method suffers from substantial inefficiencies in parallelization and applications involving highly localized states, such as those with 1st-row, transition-metal, or other atoms at extreme conditions. Modern real-space approaches, such as finite-difference (FD), finite-element (FE), and wavelet based methods, can address these deficiencies but have until now required much larger bases to attain the required accuracy. In this talk, we discuss our recent work on a new real-space FE based method which employs modern partition-of-unity FE techniques to substantially reduce the number of basis functions required by building known atomic physics into the basis, while retaining both locality and systematic improvability. Initial results show order-of-magnitude improvements relative to current state-of-the-art PW and adaptive-mesh FE methods for systems involving localized states such as d- and f-electron metals and/or other atoms at extreme conditions. [Preview Abstract] |
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K1.00253: Imaging the Dynamics of Cl($^{2}$P$_{3/2})$ Reactions with Selected Hydrocarbons Laura Visger, Armando Estillore, Arthur Suits The crossed molecular beam method coupled with dc slice ion imaging technique provides promising results in understanding the dynamics of complex reaction processes. Advances in beam intensities and probe sensivity, in conjunction with the sliced imaging approach, yield the means to study this reactivity rapidly and in a systematic way. Using these strategies, we studied the reaction of Cl($^{2}$P$_{3/2})$ atoms with selected hydrocarbons: $n$-butane; \textit{cis}-2-butene; hexane; 1-hexene; 2-hexene; 1,5-hexadiene; $n$-heptane; and 2-methylhexane. The product alkyl radical images were detected \textit{via} single photon ionization at 157 nm, directly yielding the product flux-velocity contour maps. [Preview Abstract] |
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K1.00254: Visualizing the Hydrogen Molecule Using Monte Carlo Methods S.A. Alexander, Sumita Datta, R.L. Coldwell Many concepts in chemistry are based on localized groups of electrons (e.g. atomic shells, binding and lone pairs, $\pi $ and $\sigma $ electrons). These concepts have been related to the results of quantum mechanical calculations through a wide variety of atomic and molecular functions. Using explicitly correlated wavefunctions and variational Monte Carlo we calculate the electron density, the electron density difference, the intracule density, the extracule density, two forms of the kinetic energy density, the Laplacian of the electron density, the Laplacian of the intracule density and the Laplacian of the extracule density on a dense grid of points for the ground state of the hydrogen molecule with symmetry X${ }^1\Sigma _{\mbox{g}}^{\mbox{+}} $, B${ }^1\Sigma _{\mbox{u}}^{\mbox{+}} $, a${ }^3\Sigma _{\mbox{g}}^{\mbox{+}} $, b${ }^3\Sigma _{\mbox{u}}^{\mbox{+}} $, I${ }^1\Pi _{\mbox{g}}$, C${ }^1\Pi _{\mbox{u}}$, i${ }^3\Pi _{\mbox{g}}$, c${ }^3\Pi_{\mbox{u}}$, J${ }^1\Delta _{\mbox{g}}$ and j${ }^3\Delta _{\mbox{g}}$. With these values we construct a contour plot of each function and describe how it can be used to visualize the distribution of electrons in this molecule. [Preview Abstract] |
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K1.00255: Accurate ab initio energy gradients in chemical compound space Anatole von Lilienfeld The design of chemical compounds with specific physical, chemical, or biological properties is a central goal of many fundamental as well as industrially relevant research fields. Analytical gradients in chemical space promise significant speedup in predicting properties of compounds without need to visit them. I will present analytical potential energy difference derivatives, based on the Hellmann-Feynman theorem, for any pair of iso-electronic compounds. The energies not being a monotonic function between compounds, these derivatives are insufficient to predict the right trends. Quantitative estimates can be made when the Hellmann-Feynman derivative is multiplied with a linearization coefficient that is defined for a reference pair of compounds. The results suggest that accurate predictions can be made regarding any molecule's energetic properties as long as energies and gradients of three other molecules have been provided. The linearization coefficient can be interpreted as a quantitative measure of chemical similarity. Presented numerical evidence includes predictions of electronic eigenvalues of saturated and aromatic molecular hydrocarbons. See J. Chem. Phys. 131 164102 (2009). [Preview Abstract] |
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K1.00256: Catchment basin self-avoiding simulated annealing for global optimization method Minghai Li, Xi Lin We develop a generic global minimization algorithm which can escape from catchment basins on the 3N-dimensional potential energy surface. The essential idea is to combine the simulated annealing with our recently developed history-penalized basin filling method. In this work, we present the most energetically favorable configurations of all Lennard-Jones (LJ) clusters up to 60 atoms, including the most challenging 38-atom cluster which the conventional simulated annealing algorithm failed. In addition, we report for the first time the most energetically favorable configurations for polymer chains consisting of up to 60 LJ monomers and their potential energy disconnectivity graphs. [Preview Abstract] |
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K1.00257: Molecular applications of analytical gradient approach for the improved virtual orbital-complete active space configuration interaction method. Karl Freed, Rajat Chaudhuri The improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method is extended to determine the geometry and vibrational frequencies for ground and excited electronic states using an analytical total energy gradient scheme involving both first and second order analytical derivatives. Illustrative applications consider the ground state geometries of the benzene, biphenyl, and alanine dipeptide molecules and the first excited singlet and triplet states of benzene. Comparisons with Hartree-Fock, second order Moller-Plesset perturbation theory, complete active space self-consistent field (CASSCF), and density functional theory demonstrate that the IVO-CASCI approach generally fares comparable to or better for all systems studied, demonstrating the efficacy and potential of the method. The close similarity between CASSCF and IVO-CASCI optimized geometries and the greater computational efficiency of the IVO-CASCI method suggests the replacement of CASSCF treatments by the IVO-CASCI approach which is free of the convergence problems that often plague CASSCF treatments. [Preview Abstract] |
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K1.00258: Rovibrational Phase-Space Analysis of the $\nu_3 / 2 \nu_4$ Polyad Band of $CF_4$: Qualitative study of high-resolution molecular spectroscopy Justin Mitchell, William Harter Advances in astronomy are driving the need for high-resolution spectroscopy of small and symmetric molecules, such as methane. These molecules have proven difficult to evaluate qualitatively for nearly a century. As other groups are providing line lists, this study strives to evaluate the spectra using the rovibrational phase-space tool of Rotational Energy Surfaces (RES). Some such analysis exists in the literature, but advances in computing hardware and computational tools have made it much easier and more practical. Previous efforts have evaluated the rotational level clustering in vibrational singlet and doublets. Here we show a more complicated RES analysis, evaluating the $\nu_3 / 2 \nu_4$ polyad band of $CF_4$ and offer insights into possible analyses of other systems. [Preview Abstract] |
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K1.00259: First-principles Simulation of Electrochemical Systems at Fixed Applied Voltage: Vibrational Stark Effect for CO on Platinum Electrodes Ismaila Dabo, Eric Cances, Yanli Li, Nicola Marzari Chemisorbed molecules at a fuel-cell electrode are a very sensitive probe of the surrounding electrochemical environment, and one that can be accurately monitored with different spectroscopic techniques. We calculate from first principles the dependence of vibrational frequencies as a function of the electrode voltage (the vibrational Stark effect) for chemisorbed CO molecules, finding excellent agreement with electrochemical spectroscopic experiments and resolving previous controversies. In the process, we develop a comprehensive electrochemical model to study quantum-mechanical systems as a function of the applied voltage. [Preview Abstract] |
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K1.00260: Calculation of potential energy surfaces using explicitly correlated methods Grant Hill, Kirk A. Peterson Recent developments in explicitly correlated wavefunctions mean that highly accurate potential energy surfaces for small molecules can be obtained with a low computational cost. Key components of these composite surfaces will be presented, including extrapolation of explicitly correlated CCSD(T) correlation energies and correcting for core-valence correlation effects using F12 methods. Recent applications will be highlighted, including high-resolution spectroscopy of CCN, CCO$^{+}$ and COC$^{+}$. [Preview Abstract] |
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K1.00261: Signatures of Coherent Vibrational Energy Transfer in IR and Raman Line Shapes for Liquid Water Mino Yang, James Skinner We calculate theoretical IR and Raman line shapes for the OH stretch region of liquid water, using the mixed quantum/classical and electronic-structure/molecular-dynamics methods. Our approach improves upon the time-averaging approximation used earlier for the same problem, and our results are in excellent agreement with experiment. Previous analysis of theoretical results for this problem considered the extent of delocalization (over local OH stretch excitations) of the instantaneous vibrational eigenstates. In this work we present a complementary analysis in the time-domain, by decomposing the appropriate response functions into diagonal and off-diagonal contributions (in the local mode basis). Our analysis indicates that all vibrational spectra show signatures of coherent vibrational energy transfer. This is manifest in different (IR, isotropic and depolarized Raman) experiments to different extents, because of the competition between coherent energy transfer and rotational disorder. [Preview Abstract] |
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K1.00262: Cumulant Expansion Line Shape Theory Applied to Photoexcitation Spectrum of Protonated Tyrosine Mino Yang, Jang Sook Kwon, Chang Min Choi, Nam Joon Kim, Joonkyung Jang Photodepletion spectrum of gaseous protonated tyrosine molecules was obtained at 150 K by UV laser spectroscopic technique in conjunction with mass spectrometry and interpreted by theoretical methods. The spectrum exhibits distinct three bands separated each other by about 800 $cm^{-1}$. The whole pattern of the spectrum was reasonably reproduced by a combination of theoretical methods, the second order cumulant expansion, a semi-empirical quantum chemistry method, molecular dynamics simulation, and a semi-classical time-correlation function approach. The three spectral bands turned out to arise from the vibronic transition of two vibrational modes constituted by the ``benzene breathing'' mode and a torsional mode of the amino acid backbone. It is suggested that the major factor of the spectral broadening is not conformational disorder nor lifetime broadening but the thermal fluctuation of the stable conformers. The good agreement between the experimental and theoretical spectra exemplifies the validity of the theoretical methods applied for the present molecular system. [Preview Abstract] |
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K1.00263: ABSTRACT WITHDRAWN |
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K1.00264: Semiclassical Treatment for Small-Molecule Dynamics in Low-Temperature Crystals Using a Fixed Vibrational Basis and Gaussian Bath Wave Packets Xiaolu Cheng, Craig Chapman, Jeffrey Cina The dynamics of small molecules in low-temperature crystals has been studied by several methods of time-resolved coherent nonlinear optical spectroscopy. Successful interpretation of these ultrafast signals will help illuminate basic aspects of quantum molecular dynamics in condensed media. We outline a mixed quantum/semiclassical theory that enables the systematic simulation of experimental signals from samples featuring a high-frequency vibrational mode immersed in a lower-frequency environment. We treat as the ``system'' a small number of high- frequency intramolecular degrees of freedom, those driven to large-amplitude motion by direct laser excitation. The low frequency bath of crystal phonons experiences indirectly induced, smaller-amplitude motion. We expand the overall wave function using the eigenstates of the system Hamiltonian as a vibrational basis, and adopt a Gaussian ansatz for the multi- dimensional bath wave packet. Computational details will be described along with representative numerical simulations illustrating the strengths and limitations of the theory. [Preview Abstract] |
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K1.00265: Methyl-Group Rotational Tunneling Perturbations in Zeolitic Imidazolate Framework-8 Terrence Udovic, John Rush, Jason Simmons, Taner Yildirim, Wei Zhou, Hui Wu, Juscelino Leao Using neutron inelastic scattering and diffraction techniques, we have extended our studies of the quantum methyl-group rotations in the metal organic framework: zeolitic imidazolate framework-8 (ZIF-8: Zn(MeIM)$_{2}$, MeIM=2-methylimidazolate). The framework-bonded methyl groups are oriented toward the large cavities of the nanoporous ZIF-8 structure and thus exhibit very rapid one-dimensional rotations. Indeed, the rotational potential was previously shown$^{ }$[1] to be primarily 3-fold in character with a very low rotational barrier of $\approx $7~meV and a ground-state tunneling energy of 334~$\mu $eV at 1.4~K. In this talk, we discuss the observed changes to this potential upon various perturbations to the ZIF-8 system, including Co substitution for Zn; site-specific adsorption of H$_{2}$, D$_{2}$, and CD$_{4}$; and high-pressure ($\le $10 kbar) He infiltration. Depending on the perturbation, the tunneling energy was found to vary by more than an order of magnitude, with values ranging from 408~$\mu $eV to $<$30~$\mu $eV. [1] W. Zhou, H. Wu, T. J. Udovic, J. J. Rush, and T. Yildirim, J. Phys. Chem. A \textbf{112}, 12602 (2008). [Preview Abstract] |
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K1.00266: Effective potential energy surfaces for the Inelastic Collision B($^{2}$P$_{1/2})$ + H$_{2}(j, n) \quad \leftrightarrow $ B($^{2}$P$_{3/2})$ + H$_{2}(j$', $n$') David Weeks, Luke Barger The Born-Oppenheimer approximation breaks down when two adiabatic potential energy surfaces become sufficiently close. Under these conditions, the nuclear dynamics are governed by a set of coupled diabatic surfaces. Derivative coupling matrix elements can be used to compute the transformation from the adiabatic to the diabatic potential energy surfaces. Diabatic surfaces governing the dynamics of the inelastic collision between atomic boron and molecular hydrogen are used to compute effective potential energy surfaces. These effective surfaces couple the rotational dynamics with the vibrational dynamics of the hydrogen molecule and with the relative dynamics of the atomic boron and the molecular center of mass. These surfaces will be used to explore the inelastic B($^{2}$P$_{1/2})$ + H$_{2}(j , n) \quad \leftrightarrow $ B($^{2}$P$_{3/2})$ + H$_{2}(j$', $n$') collision (1). (1) D.E. Weeks, T.A. Niday, and S.H. Yang, J. Chem. Phys, 125, 164301 (2006). [Preview Abstract] |
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K1.00267: Proton NMR Relaxometry of Portland Cement Hydration P.K. Babu, R. James Kirkpatrick In situ proton NMR relaxometry measurements on the hydration of Portland cement pastes were carried out to follow the hydration process. The spin-spin (T$_{2})$ relaxation times are about 3 orders of magnitude smaller than the spin-lattice relaxation times (T$_{1})$, indicating the presence of high amounts of paramagnetic ions. The hydration time dependence of T$_{2}$ is still determined by the confined nature of exchangeable water in the micropores. T$_{1}$ evolution with hydration time is dominated by the enhanced self-diffusion due to fast molecular exchange of confined water molecules. A ``hump'' structure is seen in T$_{1}$ during the middle stages of hydration and is attributed to the development of transient high concentration of polymeric ions in the solution phase. The present NMR investigations provide convincing evidence that even in the presence of high concentrations of paramagnetic impurities, molecular self-diffusion is the principal mechanism governing the spin-lattice relaxation of fluids confined in porous media. [Preview Abstract] |
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K1.00268: Dimer Adsorption on (100) Terraces With First- and Second-Neighbor Interactions$^{1}$ Alain Phares, Marcelo Pasinetti, David Grumbine, Jr., Francis Wunderlich Adsorbed particles that binds to two nearest-neighbor sites, such as CO/Ni(100), are simulated as dimers covering infinitely long (100)-terraces of finite width $M$, with first- and second-neighbor interaction energies, $V$ and $W$. The set {\{}coverage, number of first-neighbors per site, number of second-neighbors per sites{\}}, and the entropy characterize the adsorption system. For attractive first-neighbors ($V>$0) there are two series of phase diagrams, for $M$ even and odd, which coincide in the infinite-$M$ limit, with one non-trivial phase {\{}$\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $, $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 4$} $, 0{\}} for $W/V \quad <$ -- $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $. For repulsive first-neighbors, the phase diagrams are obtained for $M \quad \le $ 7. In the infinite-$M$ limit, the non-trivial phases are, {\{}1/3, 0, 0{\}}, {\{}$\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $, $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 4$} $, 0{\}}, {\{}$\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $, 0, $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} ${\}}, and {\{}2/3, 1/3, 1{\}}. Past computations, which neglected second-neighbor interactions and considered V$<$0, found only two phases {\{}$\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $, 0, $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} ${\}}, and {\{}2/3, 1/3, 1{\}}. Here, these results are recovered, and in the infinite-$M$ limit, Monte Carlo simulation and finite-size scaling are used to obtain the heat capacity and the critical temperature of the order-disorder transitions as a function of $W/V$. $^{1}$Work supported by NSF and the PSC (AP and DG), and by CONICET and the Fulbright Foundation(MP). [Preview Abstract] |
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K1.00269: First-principles analysis of vacancy-assisted reaction on metal-doped t-$ZrO_{2}$ surfaces Santanu Chaudhuri, Hyunwook Kwak Vacancy-assisted reaction on tetragonal (t-) $ZrO_{2}$ surface is important for its potential in combustion synthesis, barrier coating and as solid electrolyte in solid-oxide fuel cells. Doping or alloying the surface could significantly enhance the surface reactivity and transport by altering the electronic structure of the surface. We performed first-principles analysis on the metal doped t-$ZrO_{2}$ surfaces to assess the role of metal doping on the vacancy-assisted reaction at t-$ZrO_{2}$. Vacancy formation energy was calculated for 14 different doping metals. Most impurity metals from 4th and 5th row of periodic table promote formation of vacancies on the surface. Electronic structure of the defect state with respect to filled states and vacancy diffusion barriers will be discussed. Furthermore, the analysis is extended to surface reactivity for oxygen adsorption during combustion reaction of Zr particles and barrier properties against water mediated corrosion processes. For both cases, an analysis of reaction rates under different temperatures and pressures for different t-$ZrO_{2}$ surfaces will be discussed. [Preview Abstract] |
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K1.00270: Creating a ``Repair and Go'' System by Using Nanoparticle-filled Microcapsules German Kolmakov, Todd Emrick, Thomas Russell, Alfred Crosby, Anna Balazs Using a hybrid computational approach, we simulate the behavior of nanoparticle-filled microcapsules that are propelled by an imposed shear to move over a substrate, which encompasses a microscopic crack. When the microcapsules become localized in the crack, the nanoparticles can tunnel through the capsule's shell to bind to and fill the damaged region. Initially focusing on a simple shear flow, we isolate conditions where the microcapsules become arrested in the cracks and those where the capsules enter the cracks for a finite time, but are driven to leave this region by the imposed flow. We also characterize the particle deposition process for these two scenarios, showing that the deposition is greater for the arrested capsules. We then determine the effect of utilizing a pulsatile shear flow and show that this flow field can lead to an effective ``repair- and-go'' system where the micro-carriers not only deliver a high volume fraction of particles into the crack, but also leave the fissure and thus, can potentially repair additional damage within the system. [Preview Abstract] |
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K1.00271: Interaction between lyotropic chromonic liquid crystals and polymers Xuxia Yao, Jung Park, Mohan Srinivasarao Lyotropic chromonic liquid crystals (LCLCs) consist of various dyes, drugs, etc., so their importance is self-evident. The interaction of chromonic molecules and polymers is involved in their real applications, such as the dyeing process of fibers, textiles and food, and the functionalization of drugs in vivo. In our research, polymer dispersed LCLC droplets and polymer coated LCLC cells have been fabricated. Effect of interaction was observed by optical texture of LCLCs, as the different polymers induce different director configuration of LCLCs. A textile dye-Benzopurpurine 4B, food dye-Sunset Yellow FCF, and drug-Disodium Cromoglycate mixed with water soluble polymers, proteins and textile polymers have been all studied and compared. [Preview Abstract] |
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K1.00272: Ab initio study of silane and disilane adsorption on Si(100)-(2x1) surface Min Huang, John Randall, Yves J. Chabal, Robert M. Wallace, Kyeongjae Cho Silane (SiH$_{4})$ and disilane (Si$_{2}$H$_{6})$ are common precursors for the growth of Si and SiO$_{2 }$thin films for microelectronic and photovoltaic devices. The adsorption of silane and disilane on Si(100)-(2x1) surface, which are important steps in the growth of Si films in atomic layer epitaxy (ALE), were investigated using density functional theory calculations. The silane molecule dissociates on the Si surface at the intra-dimer site with barrier energy of 0.22 eV. We investigate both Si-Si bond cleavage and Si-H bond cleavage mechanisms for adsorption of Si$_{2}$H$_{6}$ on Si (100) surface. A Si-H bond cleavage mechanism was found to be more favored than Si-Si bond cleavage mechanism due to the lower barrier energy of 0.04 eV. The lower barrier energy for Si$_{2}$H$_{6}$ dissociation than that of SiH$_{4}$ agrees well with the experimental results showing that Si$_{2}$H$_{6}$ has higher sticking coefficient than SiH$_{4 }$on Si surface at 300K. The vibration frequencies of Si$_{2}$H$_{5}$, SiH$_{3}$, SiH$_{2}$, SiH resulting from dissociation of silane and disilane were calculated and compared with experimental results available. The simulation results will facilitate the controlled ALE for atomically precise manufacturing applications. [Preview Abstract] |
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K1.00273: Structural properties of free nanoalloys and oxide-supported nanoparticles Giulia Rossi, Andrea C. Levi, Zdenka Kuntova, Florin Nita, Andrei Jelea, Christine Mottet, Giovanni Barcaro, Alessandro Fortunelli, Jacek Goniakowski, Riccardo Ferrando The control of the structure and chemical order of metal nanoparticles is crucial in determining their properties and possible applications. We present a computational approach able to predict stable structural motifs of oxide-supported metal nanoparticles as a function of size and composition. The interaction of metal nanoparticles with the support can induce the stabilization of different epitaxies as varying cluster size. For Ag and Au the transition from cube-on-cube (001) epitaxy to (111) epitaxy is investigated. In other cases, unusual phases can be found. For example, nanoparticles with hcp structure can be stabilized for Ni, which is an fcc metal. Results are in good agreement with experimental data on Ag, Au and Ni/MgO(100) nanodots. The approach allows to derive driving forces for the stabilization of different epitaxies of metal nanoparticles on square-symmetry oxide surfaces, thus generalizing the results to a broad class of metal/oxide systems. [Preview Abstract] |
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K1.00274: Electron conductivity and pairing instabilities in small frustrated nanoclusters Kalum Palandage, Gayanath Fernando, James Davenport, Daniil Khomskii, Armen Kocharian The thermodynamic phase diagram and electron instabilities have been computed by exact diagonalization technique in small bipartite and frustrated geometries. Here we analyze the behavior of magnetic properties and electron pairing in ensemble of triangular Hubbard clusters with various intersite couplings upon the variation of transverse and longitudinal magnetic field. Our emphasis is on the calculation of persistent currents, supercurrents and optical conductivity on the appearance of molecular magnetism produced by magnetic flux in response functions of a system to the transverse field. The conditions are found for dramatic changes in behavior of charge and spin gaps in terms of general interaction strength and of magnetic flux. [Preview Abstract] |
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K1.00275: Towards Accurate Molecular Modeling of Plastic Bonded Explosives T.L. Chantawansri, J. Andzelm, D. Taylor, E. Byrd, B. Rice There is substantial interest in identifying the controlling factors that influence the susceptibility of polymer bonded explosives (PBXs) to accidental initiation. Numerous Molecular Dynamics (MD) simulations of PBXs using the COMPASS force field have been reported in recent years, where the validity of the force field in modeling the solid EM fill has been judged solely on its ability to reproduce lattice parameters, which is an insufficient metric. Performance of the COMPASS force field in modeling EMs and the polymeric binder has been assessed by calculating structural, thermal, and mechanical properties, where only fair agreement with experimental data is obtained. We performed MD simulations using the COMPASS force field for the polymer binder hydroxyl-terminated polybutadiene and five EMs: cyclotrimethylenetrinitramine, 1,3,5,7-tetranitro-1,3,5,7-tetra-azacyclo-octane, 2,4,6,8,10,12-hexantirohexaazazisowurzitane, 2,4,6-trinitro-1,3,5-benzenetriamine, and pentaerythritol tetranitate. Predicted EM crystallographic and molecular structural parameters, as well as calculated properties for the binder will be compared with experimental results for different simulation conditions. We also present novel simulation protocols, which improve agreement between experimental and computation results thus leading to the accurate modeling of PBXs. [Preview Abstract] |
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K1.00276: Accuracy of different DFT formalisms for prediction of two-photon absorption properties of conjugated polymers Iffat Nayyar, Ivan Mikhailov, Artem Masunov The importance of organic molecules with large two-photon absorption (2PA) is realized for deep-tissue fluorescence microscopy, photodynamic therapy, three-dimensional microfabrication and optical data storage. Computer predictions provide understanding of structure/activity relationships and assist in the rational design of polymer materials as an alternative to trial and error methods. In this contribution, we compare various density functional theory (DFT) formalisms to predict two-photon absorption spectra in a series of large donor-acceptor substituted conjugated molecules. We conclude that the accuracy of a posteriori Tamm-Dancoff approximation [1] is close to the exact results obtained in Coupled Electronic Oscillators formalism [2]. Adjusting fraction of exact exchange in XC functionals allow for improved agreement with experiment. [1] Mikhailov, I.A.; Tafur, S.; Masunov, A.E., Phys. Rev. A 77, 01250 (2008) [2] Masunov, A.M.; Tretiak, S., J. Phys. Chem. B 108, 899 (2004) [Preview Abstract] |
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K1.00277: Molecular alignment and soft X-ray generation in the ultrafast intense laser field Peng Liu Molecules can be strongly aligned non-adiabatically by using the two-pulse femtosecond laser field with an optimized delay time. We propose a novel strategy to determine the optimal timings of the two laser pulses to modify the molecular rotational wave packet, by which the molecular alignment generated by the first pulse is suppressed or enhanced by adjusting the respective delay times. This provides a way to actively control the molecular rotational wave packet. The underlying physics attributes to the selective population transfer of molecular rotations. We also experimentally investigate the high-order harmonic generation (HHG) from aligned CO$_{2}$ molecules and demonstrate that the modulation inversion of harmonic yield with respect to molecular alignment can be altered dramatically by the intensity of the driving laser pulse. The laser field dependent inversion can be explained by the shift angular distribution of harmonic emission calculated with the strong field approximation (SFA) model including a ground state depletion factor. The calculation result on angular distributions using SFA model is consistent with the experimental observations for the 19$^{th}$ to 27$^{th}$ harmonics. [Preview Abstract] |
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K1.00278: Suppressed ionization in polyatomic molecules Michael C.H. Wong, J.-P. Brichta, V.R. Bhardwaj Orbital symmetry plays a critical role in molecular ionization and influences the high-harmonic generation (HHG) process. Since ionization occurs predominantly from a molecule's highest occupied molecular orbital (HOMO), nodal planes in the HOMO lead to destructive interference resulting in suppression of ionization. The degree of suppression should depend on the complexity of the molecular orbital and its signatures can be observed in extension of cut-offs in HHG spectra. We conduct experimental studies of HHG using 800nm and 1300nm infrared light in different sets of molecules where the targets have similar ionization potential but differing electronic structure. The three sets are A) non-planar chloromethanes (CH$_{2}$Cl$_{2}$, CHCl$_{3}$, CCl$_{4})$, B) ethylene (C$_{2}$H$_{4})$ and methanol (CH$_{4}$O), and C) water (H$_{2}$O), oxygen (O$_{2})$ and xenon atom (Xe). For each case we can link the degree of suppressed ionization to the number of nodal planes present in a molecule's HOMO. We expect this trend to be extendable to larger molecules with more complex orbitals where multi-electron dynamics play a larger role. [Preview Abstract] |
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K1.00279: Dispersion interactions with linear scaling DFT: a study of planar molecules on charged polar surfaces Lampros Andrinopoulos, Nicholas Hine, Peter Haynes, Arash Mostofi The placement of organic molecules such as CuPc (copper phthalocyanine) on wurtzite ZnO (zinc oxide) charged surfaces has been proposed as a way of creating photovoltaic solar cells\footnote{G.D. Sharma \textit{et al.}, Solar Energy Materials \& Solar Cells \textbf{90}, 933 (2006) }; optimising their performance may be aided by computational simulation. Electronic structure calculations provide high accuracy at modest computational cost but two challenges are encountered for such layered systems. First, the system size is at or beyond the limit of traditional cubic-scaling Density Functional Theory (DFT). Second, traditional exchange-correlation functionals do not account for van der Waals (vdW) interactions, crucial for determining the structure of weakly bonded systems. We present an implementation of recently developed approaches\footnote{P.L. Silvestrelli, P.R.L.\textbf{ 100}, 102 (2008)} to include vdW in DFT within ONETEP\footnote{C.-K. Skylaris, P.D. Haynes, A.A. Mostofi and M.C. Payne, J.C.P. \textbf{122}, 084119 (2005) }, a linear-scaling package for performing DFT calculations using a basis of localised functions. We have applied this methodology to simple planar organic molecules, such as benzene and pentacene, on ZnO surfaces. [Preview Abstract] |
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K1.00280: Fixed-Node Correlation Function Diffusion Monte Carlo: an approach to Fermi excited states Brian Austin, William Lester We have coupled the fixed-node (FN) approximation with the correlation function quantum Monte Carlo (CF-QMC) method to derive a more robust approach to computing properties of Fermi excited states. The FN constraint prevents the DMC simulation from converging to lower energy Bose states while the diagonalization step of the CF procedure orthogonalizes the FN-DMC solutions. Because the CF method wraps the FN-DMC wavefunctions with a linear variational procedure, the excitation energies will satisfy the Hylleras-Undeheim theorem. The FN-CF technique therefore improves upon FN-DMC energies for both ground- and excited-state energies. The new method is applied to nine low-energy states of the beryllium atom. [Preview Abstract] |
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K1.00281: Actinides in Solution: Disproportionation, Strong Correlations, and Emergence Brad Marston, Steven Horowitz Plutonium in acid solutions can be found in oxidation states III through VI. There is a striking near perfect degeneracy of the reduction-oxidation (redox) potentials, each being about 1 volt. Neptunium is the only other element that approaches this degree of degeneracy. One consequence of the redox degeneracy is a marked tendency of plutonium ions to disproportionate; up to four different oxidation states can coexist simultaneously in the same solution, greatly complicating the environmental chemistry of the element. While the degeneracy could simply be a coincidence, it could also be the manifestation of a higher-level organizing principle at work. Other systems that exhibit disproportionation raise the possibility of an emergent negative-U attractive interaction. The hypothesis is tested by combining first-principles relativistic density-functional calculations using the Amsterdam Density Functional (ADF) package with exact diagonalizations of Hubbard-like models of the strong correlations between the actinide 5f electrons. [Preview Abstract] |
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K1.00282: Pressure-induced hydrogen bond symmetrization in hydrogen halids HX (X=F, Cl, and Br): \textit{ab initio} Study Tian Cui, Defang Duan, Fubo Tian, Liancheng Wang, Xing Meng, Yanming Ma, Bingbing Liu, Zhi He, Guangtian Zou Although hydrogen bond symmetrization of HX (X=F, Cl, and Br) have been observed, the symmetric structure is still not direct measured by X-ray or neutron diffraction studies. The changes in hydrogen bonding of HX have been examined by pseudopotential plane-wave method. Our results show that the hydrogen bond symmetrization of HBr and HCl occurred at 25 GPa and 40 GPa, agree well with the experimental data. In the case of HF, symmetric structure happened at 30 GPa, which is higher than the experimental value of 6 GPa. Further calculation show that the hydrogen bond symmetrization is accompanied by a successive change of the potential surface in the X-H$\cdot \cdot \cdot $X direction from double-well potential to symmetric single-well potential. In addition, the stretching mode A1 of HX decreases with increasing pressure. The hydrogen bond symmetrization process is characterized as a softening of stretching vibration A1. \\[4pt] This work was supported by the National Natural Science Foundation of China under Grants No. 10574053, 2004 NCET and 2003 EYTP of MOE of China, the National Basic Research Program of China, Grants No. 2005CB724400, and The Cultivation Fund of the Key Scientific and Technical Innovation Project, No. 2004-295. [Preview Abstract] |
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K1.00283: Verwey-type transition in Pb$_{3}$Rh$_{7-x}$Mn$_{x}$O$_{15}$ Solid Solution Alvin Gatimu, Hiroshi Mizoguchi, Arthur Sleight, Mas Subramanian Mixed-valence compound Pb$_{3}$Rh$_{7}$O$_{15}$ shows an isotropic room temperature resistivity ($\sim $1 x 10$^{-3}$ ohm cm) that slowly increases with decreasing temperature until 185K where the resistivity increases more rapidly as temperature is further decreased. Magnetic susceptibility and thermopower measurements on Pb$_{3}$Rh$_{7}$O$_{15}$ also show a discontinuity at about 185 K. Structural analyses of X-ray diffraction data obtained above and below 185 K indicate that a change in space group has occurred at 185 K and it is likely that this transition at 185 K is related to a charge ordering. Pb$_{3}$Mn$_{7}$O$_{15}$ also crystallizes in a similar hexagonal structure. A complete solid solution of Pb$_{3}$Rh$_{7-x}$Mn$_{x}$O$_{15}$ has been prepared and crystals with varying Mn content have been grown in a PbO flux. The phase transition at 185 K fades away as the Mn substitutes for Rh. Structural, electrical and magnetic studies are discussed. [Preview Abstract] |
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K1.00284: Ferromagnetism in A$_{1-x}$La$_{x}$Mn$_{0.5}$Ru$_{0.5}$O$_{3}$ Perovskites: Is Double Exchange, Superexchange or Band Magnetism Responsible Patrick Woodward, Jennifer Soliz, Rebecca Ricciardo, Heather Cuthbert, Brendan Kennedy In this presentation the properties of A$_{1-x}$La$_{x}$Mn$_{0.5}$Ru$_{0.5}$O$_{3}$ (A = Ca, Sr) are presented. When A = Ca the sample displays clear magnetic phase separation into a ferromagnetic phase with T$_{C} \quad \sim $200 K and an antiferromagnetic G-type phase with T$_{N}\sim $100 K. The high conductivity suggests itinerant electron magnetism is at least partially responsible for the ferromagnetic behavior that describes the majority of the sample. Interestingly on substituting La for Ca the conductivity decreases dramatically (by 8 orders of magnitude at $\sim $20 K) but the ferromagnetism remains. This suggests that localized magnetism, presumably superexchange, is also playing an important role. Replacing Ca with Sr restores the metallic-like conductivity, while retaining the ferromagnetic behavior. In this presentation we present the structural, magnetic and electrical transport properties of these compounds to shed light on the complex underlying mechanisms that drive magnetism. [Preview Abstract] |
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K1.00285: Structure and adsorption of water in non-uniform cylindrical nanopores Greg Lakatos, Glenn Torrie, Gren Patey Grand canonical Monte Carlo simulations are used to examine the adsorption and structure of water in the interior of cylindrical nanopores with non-uniform surfaces. Nanopores with radii in the range of 0.45 to 1.2nm are considered, and the axial symmetry of the nanopores is broken by varying the radius as a function of position along the pore axis, or by introducing regions where the strength of the water-nanopore interaction is reduced. Water in filled pores with a 0.6nm radius, exists in either a weakly structured fluid-like state, or a structured polarized state, with a pentagonal cross section. This structured state can be disrupted by creating hydrophobic regions on the nanopore surface, and the degree of disruption can be controlled by adjusting the size of these regions. Similarly, spatial variation in the nanopore radius can produce two condensation transitions, and vapor-liquid, and solid-liquid co-existences at points along the filling isotherm. This ability to control water structure through nanopore surface modification holds promise for the development of tunable nanoscale fluid conduits and storage devices. [Preview Abstract] |
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K1.00286: Detecting Laser Ablation Products using Fast Passage Fourier Transform Microwave Spectroscopy: The Examination of the Open Shell Molecule, SnCl Garry Grubbs II, Stephen Cooke The rotational spectrum of the open shell molecule tin monochloride, SnCl, has been measured using a chirped pulse, Fourier transform microwave (CP-FTMW) spectrometer. Using this technique, large regions (2-4 GHz) of spectra with high resolution (kHz resolution) can be observed and averaged in short periods of time, cutting down spectral search times. Coupling this technique with a laser ablation source allows nonvolatile species such as metal containing molecules to be studied. The sensitivity to detect transient species such as SnCl will be discussed. Rotational constants, centrifugal distortion constants, and appropriate hyperfine constants will also be discussed. [Preview Abstract] |
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K1.00287: Recent advances in coherent sub-THz spectroscopy in pulsed molecular beams Liam Duffy While sub-THz/THz solid state multipliers afford outstanding resolution, rapid frequency sweeping has been problematic. In order to sweep via FM modulation the microwave synthesizer phase-lock is turned off and hence the frequency calibration is lost. One way around this, as advanced in the FASSST scan technique, is to sweep the frequency rapidly and use post-scan frequency calibration via cavity mode markers. Over the last year, we have implemented a slow version of the FASSST scan method that piecewise sweeps small portions of the spectrum (60 MHz / 100 usec / gas pulse at 300 GHz). Drift and calibration issues are removed by simply using the computer-synthesizer interface to frequently reset the frequency before it has time to change. This method, when combined with the ability to subtract sweeps with and without gas and/or laser photolysis, allows background free spectra. The technique is particularly useful in searching for the absorption features of transient vibrationally and/or electronically excited products that are difficult to observe in gas cell studies. Avoiding drift in this way also allows FM modulation to be used in coherent pulse type experiments where molecules are coherently prepared in rotational superposition states prior to scattering. [Preview Abstract] |
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K1.00288: High Momentum Transfer Shallow Core-to-valence Spectroscopy in the Actinides Subhra Sen Gupta, J. A. Bradley, M. W. Haverkort, G. T. Seidler, G. A. Sawatzky We calculate the dynamic structure factor S($q$,$\omega )$ within a renormalized atomic multiplet approach, to describe the 5d$\to $5f non-resonant inelastic x-ray scattering (NIXS) in actinide compounds ThO$_{2}$ (5f$^{0})$ and UO$_{2}$ (5f$^{2})$. For small $q,$ the spectra select the dipole-allowed transitions which are degenerate with continuum states, hindering their use in ground electronic structure determination. However dipole-forbidden multiplets reached with large $q$ are strongly bound to the core-hole, enabling the use of a renormalized atom approach to extract the ground state electronic structure. This crossover from unbound to bound states, reachable by low-$q$ and high-$q$ experiments respectively, is a result of the large multiplet spread of the 5d$^{9}$5f$^{N+1}$ multiplets exceeding the attractive core-hole potential. We discuss the details of the calculations and emphasize the importance of high-$q$ experiments in studies of the ground state electronic structure of actinides. [Preview Abstract] |
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K1.00289: Dipole-forbidden 5d-5f Electronic Structure in Actinide Systems Joseph Bradley, Subhra Sen Gupta, Gerald Seidler, George Sawatzky, Stosh Kozimor, Steven Conradson, Kevin Boland, David Clark We report the first measurements of nonresonant inelastic x-ray scattering (NIXS) from the semi-core 5$d$ levels of several actinide compounds. We find that the lowest energy electronic excitations form a rich spectrum of resonances having quite large angular momentum and whose general characteristics are predominantly dependent on the valence electron configuration rather than the nominal valence of the excited species. Comparison with atomic multiplet calculations strongly supports these observations while also illustrating a new complexity to the excited-state spectrum of actinide compounds: good agreement with experiment, subject to realistic considerations about screening effects, are achieved only when one includes the configuration interaction between the 5$f$ and 6$f$ states. [Preview Abstract] |
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K1.00290: Chemistry in Solid Parahydrogen at Low Temperature David T. Anderson, Sharon C. Kettwich, Leif O. Paulson Cryogenic solid molecular hydrogen provides a weakly perturbing crystal environment to study the low temperature (2-5 K) chemistry of embedded reactive species. Solid hydrogen is considered a quantum solid since the zero-point translational motion of the light hydrogen molecules dominates the physical properties of the crystal. Photodissociation of molecules embedded in the solid hydrogen provide a means of generating molecular species \textit{in situ} that normally would react with H$_{2}$ at room temperature, but at the low temperatures at which hydrogen is a solid these species can be trapped and studied spectroscopically. Recent studies of the photodissociation of Cl$_{2}$ in solid parahydrogen (hydrogen crystals enriched in the para-H$_{2}$ nuclear spin isomer) reveal a means to study the infrared-induced Cl + H$_{2}$(v=1) $\to $ HCl + H reaction at temperatures below 2 K. Current efforts are aimed at studying the analogous O + H$_{2}$(v=1) $\to $ OH + H reaction and the most recent results and analysis will be presented at the meeting. [Preview Abstract] |
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K1.00291: Electronic relaxation at a photoexcited nanostructured Si(111) surface Dimitri Kilin, David A. Micha A combination of time dependent density matrix and {\it ab initio} electronic structure methods provide details of the relaxation pathways of photo-induced charge redistribution at nanostructured semiconductor surfaces, giving their changes in energy and space over time. They are applied to a Ag$_3$ cluster on a Si(111) surface, initially photoexcited by a short pulse, and show how surface-localized states added by the Ag cluster enhance electron transfer. Population density distributions in energy and in space, for valence and conduction bands, explore the energy band landscape of a Si slab, with various relaxation pathways ending up in a charge-separated state, with a hole in the Si slab and an electron in the adsorbed Ag cluster. Calculated electronic relaxation times for Si(111):H are of the same order as experimental values for similar semiconductor systems. Results from a reduced density matrix propagation over time, with Hamiltonian and rates parametrized from {\it ab initio} electronic structure calculations, give new insight on electronic dynamics at nanostructured surfaces. [Preview Abstract] |
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K1.00292: Estimates of vapor pressure below the triple point for the LJ system Barbara N. Hale Vapor pressures are estimated for a full Lennard-Jones (LJ) potential system at three temperatures below the triple point. A Bennett Monte Carlo calculation of Helmholtz free energy differences for small LJ $n-$atom clusters is used to predict $\ln (\rho _{liq}/\rho _{1})$, the intercept at $n=\infty $, where $\rho_{liq}$ and $\rho _{1}$ are bulk liquid and monomer vapor number densities. The approximation that the vapor consists of monomers only provides an estimate of $\ln (P)/P_{c})$. The results are presented in a corresponding states plot comparison with experimental data for argon at higher temperatures, the extrapolated vapor pressure formula used by Iland \emph{et al} [K. Lland, J. W\"{o}lk and R. Strey, J. Chem. Phys. \textbf{127}, 54506 (2007)], and Monte Carlo results of Chen \emph{et al.} [B. Chen, J. I. Siepmann, K. J. Oh, M. L. Klein, J. Chem. Phys. \textbf{115}, 10903 (2001)] Such a plot provides a check on vapor pressure expressions extrapolated to low temperatures where no experimental data are available. [Preview Abstract] |
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K1.00293: Preparing for Petascale Computing: A look under the hood of Barnes-Hut Norman Chonacky A multitude of opportunities for advancement of science and engineering await the advent of petascale computational facilities. However, it is not clear that future computational physicists will be ready to take full advantage of these capabilities. There is a long-standing gap between our training of physics students in computation in general and high-performance computing in particular. I am offering a sample package to support efforts to change this situation. This is a family of C codes that implement a Barnes-Hut method for calculating inter-particle forces in N-body systems, with particular application to simulating a system of gravitating objects. This family has both 1-D and 3-D codes. The former are several ``toy'' programs documented to clearly expose tactics to build tree structures and actions needed to execute both Barnes-Hut and multipole methods. The latter, based on the former, are for realistic N-body calculations on parallel processors for which I have some results from testing on clusters. I will briefly describe educational use of these materials. I hope these materials will give to practitioners a transparent look at fundamentals of the Barnes-Hut method and to instructors tools for improving students' understanding of scaling issues in large computations. [Preview Abstract] |
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K1.00294: Self-assembled Colloidal Walkers: from Single Chain Motion to Controlled Surface-Induced Flows Charles Sing, Alfredo Alexander-Katz Biological flows at the microscopic scale are important for the transport of nutrients, locomotion, and differentiation. Here, we present a novel approach for creating controlled surface-induced flows inspired by a ubiquitous biological system, cilia. Our design is based on a collection of self-assembled colloidal rotors that ``walk'' along surfaces in the presence of a rotating magnetic field. These rotors are held together solely by magnetic forces, which allow for reversible assembly and disassembly of the chains. Furthermore, rotation of the magnetic field allows for straightforward manipulation of the shape and motion of these chains. This system offers a simple and versatile approach for designing novel microfluidic devices as well as for studying fundamental questions in cooperative driven motion and transport at the microscopic level. [Preview Abstract] |
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K1.00295: Cluster Formation in a Freely-Falling Granular Stream Alison Koser, John R. Royer, Scott R. Waitukaitis, Heinrich M. Jaeger Granular materials do not conform to traditional phases of matter, appearing as solid, liquid, or gas, with virtually no change to the properties of its particles. One liquid behavior that grains mimic is the break-up and formations of clusters in a freely-falling stream of matter. Previous work [Royer et al, \textit{Nature} \textbf{459} 1110-1113 (2009)] contributed clustering to a small cohesive force between particles that is much less than the surface tension in liquids. Here, the role of the nozzle diameter and particle diameter are examined in the act of forming granular clusters. Break-up distance, cluster width, and aspect ratio were measured and compared to liquid break-up. For systems that cluster, we find similar but different trends between the liquid and granular cases which surface tension alone cannot explain. [Preview Abstract] |
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K1.00296: Titania films for dye sensitized solar cells Christopher Grablutz, Marian Tzolov Dye sensitized solar cells are a relatively new concept for photovoltaic conversion of solar energy. It turns out as a very successful concept due to the commercialization that is ongoing in several countries around the world. Despite of this, there are number of open technological and fundamental problems. Titanium dioxide paste is used since the very inception of the idea and although significantly improved it is still not clear in detail how does it satisfy so successfully the contradictory requirements for good charge collection and for highly developed surface as a host for the sensitizing dye. We will present our results in a very reproducible and effective way of producing titania paste. The Scanning Electron Microscopy images show very homogeneous dispersion of the titania nanoparticles. The steady state electrical and photoelectrical measurements, together with impedance spectroscopy and photocurrent time response experiments were correlated with the morphology of the titania films. [Preview Abstract] |
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K1.00297: Cathode interface studies of polymer light emitting devices Stephen Swiontek, Marian Tzolov Efficient injection of charge carriers is a key factor for successful operation of any electronic device and especially of devices with non-crystalline or wide band gap active material. Our study concentrates on the cathode interface of light emitting devices with a conjugated polymer as light emitter. We apply two principally different methods for the cathode deposition, physical and chemical, in order to fundamentally understand if in addition to the commonly accepted notion for the matching of the work functions also material modification takes place. The completed devices are studies by steady-state electrical measurements, impedance spectroscopy, current and emission lifetime measurements, and electroluminescence spectroscopy. The morphology of the cathodes is studied by Scanning Electron Microscopy and the formation of additional phases by Energy Dispersive X-ray Spectroscopy. The results help to define ways for more cost efficient fabrication of light emitting devices with applications in displays, electronic newspapers, room illumination, etc. [Preview Abstract] |
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