Bulletin of the American Physical Society
Fall 2009 Meeting of the Four Corners Section of the APS
Volume 54, Number 14
Friday–Saturday, October 23–24, 2009; Golden, Colorado
Session D1: Poster Session (5:00-6:30 PM) |
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Chair: Chip Durfee, Colorado School of Mines Room: Green Center Lobby |
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D1.00001: Temperature Dependence of the Electrostatic Breakdown of Polymeric Insulators Charles Sim, J.R. Dennison The temperature dependence of the electrostatic discharge of polymeric insulators has been measured by applying a high voltage across the polymer to induce an electrical breakdown. The breakdown electric field was determined by a rapid rise in I-V curves that were measured in a custom, high vacuum chamber over a temperature range of $\sim $150 K to $\sim $320 K. Our results showed the electrostatic discharge of the polymer Low Density Polyethylene (LDPE) to be 318$\pm $60 ($\pm $18{\%}) MV/m with no significant variation over the full temperature range. The results are compared with thermodynamic models of the electric field aging process and limited prior measurements. The motivation for this research was the concern of spacecraft charging and the potential damage from electrostatic breakdown of polymers to be used on the James Webb Space Telescope, which will operate at temperatures down to 30 K. [Preview Abstract] |
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D1.00002: Charge Dynamics in Disordered Insulating Materials Alec Sim, J.R. Dennison Modeling and understanding electron transport in disordered insulating materials is fundamentally based on a detailed knowledge of the distribution and occupation of the density of states of nearly free and trapped charged carriers. The conductivity of the material is a key transport parameter in determining charge mobility, how rapidly charge imbalances will accumulate or dissipate, and what equilibrium potential will be established under given experimental conditions. We motivate a discussion of conductivity mechanisms with simple physical concepts that lead to a wide variety of observed physical phenomena. In particular, we extend the standard band model for extended state conduction to include the effects of localized trap states within the band. We discuss trap controlled transport and its relation to the mobility and density of conduction electrons. We consider the following commonly observed conduction mechanisms; thermally activated and variable range hopping conductivity, radiation induced conductivity and luminescence. [Preview Abstract] |
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D1.00003: Reduction and Characterization of Error in Low Current Measurements Justin Dekany, J.R. Dennison, Alec Sim An apparatus has been developed to measure electron transport at a level low enough that radiation induced conductivity associated with the cosmic background radiation is of concern. To accurately measure such low currents, typically A, it is critical to eliminate noise in key components of the hardware setup. Improvements include highly filtered signals, ground isolation and stability, extensive shielding, vibration isolation, and signal averaging. Careful tracking of the error associated with each component in the system and examination of the limitations of each constituent part, allows for precise monitoring of error propagation as improvements are made to the system. Successful implementation of these techniques has pushed the lower current limit of a 25 year old Keithley 616 low level electrometer to these extreme limits. These methods have been employed to measure the conductivity of high resistivity polymers, commonly used in the construction of spacecraft. [Preview Abstract] |
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D1.00004: The Effects of Surface Contamination and Roughening on Diffuse Optical Reflection and Photoyields of Spacecraft Materials Amberly Evans, J.R. Dennison Modification of a material's surface affects the optical properties (reflection, transmission and absorption) and charge accumulation of that material. This project has been designed to study the properties of Kapton HN and gold and the affects that surface modification (roughening and contamination) have on them. Samples of each material were roughened with varying sizes of roughening compounds or contaminated with diffusion pump oil. Reflectivity and transmission measurements were compared for all samples. It is evident that modifying the surface changes the reflectance, implying a change in absorbance. Absorbed photons can contribute to charge accumulation in materials through photoemission, whereas reflected and transmitted photons do not. However, reflection and transmission are readily measured and can be related to absorbance. In the harsh space environment, materials are going to be damaged and contaminated, affecting the optical properties of the material and, in turn, charge accumulation. Understanding absorbance and charge accumulation is important in spacecraft construction because charging can inflict serious damage on spacecraft. [Preview Abstract] |
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D1.00005: Carbon Nanotube templated structures Ricky Wyman, Robert Davis, Richard Vanfleet, Jun Song Carbon nano tubes are of great interest to science due to their strong mechanical and exotic electrical properties. Nano tubes have potential application in transistors, micro electrical mechanical devices (MEMS), and structural materials. We have been using nanotube forests as a template to fabricate larger scale structures. The nanotube template is infiltrated with another material (like silicon or carbon). This infiltration can be thin to stabilize the forest and make a porous structure or thick to make a solid structure. Different methods employed at Brigham Young University of patterning, growing, and infiltrating nano tubes are presented on a poster along with applications. [Preview Abstract] |
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D1.00006: Ultrafast Laser-induced Structural and Electron Dynamics in Graphite Zhibin Lin, Roland Allen Ultrafast structural and electron dynamics in graphite under femtosecond (fs) laser irradiation are investigated in density-functional-based simulations. We show from our simulations that it is possible to separate a graphene mono-layer from graphite surface at moderate laser excitation where no melting occurs. Strong vibrational excitation of graphene layers is found to cause this monolayer separation. At higher laser excitation, covalent bonds between carbon atoms are significantly weakened by the presence of a large number of excited electrons leading to an ultrafast melting within a few tens of fs following the laser irradiation. In addition, we have observed a potentially useful phenomenon from our dynamic simulations: the excited electrons automatically equilibrate to a Fermi-Dirac distribution within 100 fs, solely because of their coupling to the ionic motion, even though the resulting electronic temperature is one to two orders of magnitude higher than the kinetic temperature defined by the ionic motion. Microscopic simulations like these can then provide the separate electronic and kinetic ionic temperatures, chemical potentials, pressures, and non-hydrostatic stresses as input for studies on larger length and time scales. [Preview Abstract] |
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D1.00007: Synchrotron Studies on Copper-Phthalocyanine Robert Call, Trevor Willey Studies were carried out using synchrotron radiation to investigate the properties of Copper-Phthalocyanine (CuPc) on different substrates. CuPc's have a wide variety of applications from dye to chemical sensors. This study was done at Lawrence Livermore National Laboratory in conjunction with UC San Diego to investigate properties of CuPc's for application in sensors. Near edge x-ray fine structure spectroscopy (NEXAFS) was used to determine orientations of CuPc molecules on two different substrates (gold and sapphire). Orientations were found to be drastically different on the two substrates. On gold, CuPc molecules were found to be nearly prostrate and on sapphire they were found to be almost normal to the surface. [Preview Abstract] |
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D1.00008: Quasiparticle Spectrum of 2-d Dirac Vortices in Optical Lattices Laith Haddad Bose-Einstein condensates in a honeycomb optical lattice are described by a nonlinear Dirac equaton (NLDE) in the long wavelength, mean field limit [1]. The upper and lower two-spinor equations decouple and superficially resemble the equations of previously studied NLDE's such as the Soler model for extended fermions. Although much work has been done on NLDE's, the bulk of the literature deals with models with Poincare invariant nonlinearites. In contrast our equations break Poincare symmetry providing an opportunity to study phenomenological models in cosmology and particle physics where this symmetry is not manifest. We obtain and classify localized solutions to our equations for both repulsive and attractive contact interactions. We also derive analogs of the Bogoliubov-de Gennes equations for the lattice and use these to study the stability and low energy spectrum of our solutions showing the existence of stable exotic structures such as vortices with fractional statistics.\\[4pt] [1] L. H. Haddad and L. D. Carr, ``The Nonlinear Dirac Equation in Bose-Einstein Condensates: Foundation and Symmetries,'' Physica D: Nonlinear Phenomena, v. 238, p. 1413 (2009). http://arxiv.org/pdf/0803.3039v1 [Preview Abstract] |
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D1.00009: Controlled Ag Nanopattern Formation through UV Wavelength Dependent Photochemical Interactions on PPLN Yang Sun, Robert Nemanich This study establishes that ferroelectric nanolithography is dependent on the excitation wavelength and that the process can be controlled through optimization of the wavelength dependent photochemical surface interactions. Periodically poled lithium niobate (PPLN) is used as a template for ``nanolithography'' of metallic nanoparticles and nanowires through a photochemical process. Prior research has established that above band gap UV emission is necessary to initiate the deposition process. Depending on the nature of the surface screening, the deposition will occur predominantly on the positive domains (internal screening) or at the domain boundaries (external screening). This research employs PPLN, which exhibits external screening, and it is shown that the location and rate of Ag nanostructure deposition is dependent on the wavelength of the UV excitation. The selective deposition is explained by a combined theory of band-bending, the mechanism of polarization surface charge screening, and the absorption depth of the UV light. As an application example, the Ag nanopatterns are employed for spatially specific surface enhanced Raman spectroscopy (SERS). [Preview Abstract] |
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D1.00010: Anomalous non-magnetic high field loss peak for a high Q copper TE011 microwave cavity Liam Kilcommons, Falko Kuester, Carl Patton Recent off resonance magnetic loss measurements with high quality factor (Q) TE011 cavities have revealed the presence of a small anomalous loss peak at high field overlying the usual magnetic response. Precision measurements of the cavity Q vs. field by the ABA metrological substitution method for a special 99.99{\%} pure OFHC (oxygen free high conductivity) copper cavity have now confirmed the presence of a broad and weak yet distinct magnetic field dependent empty cavity loss peak centered at about 8.8 kOe in applied field with a width of about 1 kOe. This loss peak has been confirmed to come from the copper response and not from any type of magnetic impurities or waveguide effects. Possible origins of this response are under investigation. [Preview Abstract] |
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D1.00011: Large N model of bose gases Ke Ke, Leo Radzihovsky We construct the large N model of bose gases. Using an artificial parameter 1/N to do the perturbative analysis to study two models: $U(N)$ bose gases and $U(1) \times O(N)$ bose gases. We find that for the U(N) model we get the same Bogoliubov spectrum and LHY thermal dynamical relations with ordinary bose gases. For the $U(1) \times O(N)$ model, however, we calculate dispersion relation, chemical potential and free energy when N goes to infinity and find that every quantities depends on the ration of two scattering length and $\sqrt(na^3)$. [Preview Abstract] |
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D1.00012: Thickness Dependency of Ferromagnetic Domains in CoPt Multilayers Andrew Westover, Nathan Gay, Karine Chesnel, Olav Hellwig Ferromagnetic materials have been providing and still provide large potential technological interests, especially in the data storage industry. We use Atomic and Magnetic Force Microscopy (AFM/ MFM) to study the influence of the film thickness on domain morphology in Co/Pt multilayers. While AFM is sensitive to the topography of the film, MFM allows the imaging of magnetic domains through an interaction between a sharp magnetic probe and the stray fields emanating from the sample in the perpendicular direction. Through this technique we have obtained AFM and MFM images of Co/Pt multilayers ranging from 4A to 60A and have found that as the thickness of the Co/Pt multilayers influences the morphology (periodicity, orientation, and correlation length etc.) of the magnetic domains. [Preview Abstract] |
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D1.00013: Atomic Force Microscopy Imaging Techniques for Piezoelectric Materials Jeremy Kunz, Colin Inglefield Using an Atomic Force Microscope (AFM) and a Lock-in Detector we investigated the effectiveness of two different methods of local piezoelectricity within a standard commercial piezoelectric material, Pb(Ti, Zr)O$_{3}$ (PIC 151). In the first method, sometimes known as piezo-mode AFM, we applied an AC voltage to the sample locally through the tip of the AFM; we were able to image the local piezoelectric response while taking a topographical image. For the second set of measurements, we used a sample of the PIC 151 material with a uniform silver electrode over the entire surface. The voltage was applied to the entire sample through the electrodes and the AFM cantilever measured local response. Images based on the two techniques will be compared along with the methods themselves. [Preview Abstract] |
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D1.00014: Monte Carlo modeling of the spatially dispersive carrier transport in P3HT and P3HT:PCBM blends Xin Jiang The presence of traps, arising from morpohological or chemical defects, can be critical to the performance of organic semiconductor devices. Traps can reduce the charge carrier mobility, disturb the internal electrical field, drive recombination, and reduce the overall device efficiency as well as operational stability. In this work, we investigate the role of traps in determining charge transport properties of organic semiconductors and blends such as P3HT and P3HT:PCBM through Monte-Carlo (MC) simulations in conjunction with time-of-flight (TOF) mobility measurements. We employ a Marcus theory description of individual hopping events based on the molecular reorganization energy (lambda) for the MC simulations. Trap states are modeled as diffuse bands that reside at some energy away from the main transport band. This model is used to simulate TOF transients, and the results are compared to experimental data. As is expected from the Marcus theory equation, the mobility is seen to be maximum for an optimal value of lambda. This optimal value is strongly field dependent, but is found to be independent of the trap density. In comparing MC simulations with TOF data, it is found that inclusion of traps results in a much better fit to the data and provides for a mechanism to simulate dispersive transport with a long tail resulting from trapping and detrapping of carriers before they exit the device. We present results for a range of trap densities and statistical distributions and discuss the implications on the operation of bulk heterojunction organic photovoltaic devices. [Preview Abstract] |
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D1.00015: Ab Initio Study of Carboxylated Graphene Nabil Al-Aqtash, Igor Vasiliev We investigate chemical functionalization of graphene by carboxyl (COOH) groups using first principles computational methods. The binding energies and equilibrium geometries of COOH groups covalently attached to graphene clusters with no surface defects, Stone-Wales defects, and vacancies are examined in the framework of density functional theory combined with the generalized gradient approximation. We find that the attachment of COOH groups induces substantial structural changes in graphene. Our calculations show that the binding of the COOH group to graphene is significantly stronger in the presence of surface defects. This result suggest an important role of point surface defects in the carboxylation of graphene. [Preview Abstract] |
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D1.00016: Positive, Neutral, and Negative Mass-Charges in General Relativity Dmitri Rabounski, Florentin Smarandache As shown, any four-dimensional proper vector has two observable projections onto time line, attributed to our world and the mirror world (for a mass-bearing particle, the projections posses are attributed to positive and negative mass-charges). As predicted, there should be a class of neutrally mass-charged particles that inhabit neither our world nor the mirror world. Inside the space-time area (membrane) the space rotates at the light speed, and all particles move at as well the light speed. So, the predicted particles of the neutrally mass-charged class should seem as light-like vortices. [Preview Abstract] |
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D1.00017: Less Mundane Explanation of Pioneer Anomaly from Q-Relativity Florentin Smarandache, Vic Christianto There have been various explanations of Pioneer blueshift anomaly in the past few years; nonetheless no explanation has been offered from the viewpoint of Q-relativity physics. In the present paper it is argued that Pioneer anomalous blueshift may be caused by Pioneer spacecraft experiencing angular shift induced by similar Qrelativity effect which may also affect Jupiter satellites. By taking into consideration ``aether drift'' effect, the proposed method as described herein could explain Pioneer blueshift anomaly within {\_}0.26{\%} error range, which speaks for itself. Another new proposition of redshift quantization is also proposed from gravitational Bohr-radius which is consistent with Bohr-Sommerfeld quantization. Further observation is of course recommended in order to refute or verify this proposition. [Preview Abstract] |
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D1.00018: Development of a Pressure Switched Microfluidic Cell Sorter Baris Ozbay, Alex Jones, Emily Gibson Lab on a chip technology allows for the replacement of traditional cell sorters with microfluidic devices which can be produced less expensively and are more compact. Additionally, the compact nature of microfluidic cell sorters may lead to the realization of their application in point-of-care medical devices. Though techniques have been demonstrated previously for sorting in microfluidic devices with optical or electro-osmotic switching, both of these techniques are expensive and more difficult to implement than pressure switching. This microfluidic cell sorter design also allows for easy integration with optical spectroscopy for identification of cell type. Our current microfluidic device was fabricated with polydimethylsiloxane (PDMS), a polymer that houses the channels, which is then chemically bonded to a glass slide. The flow of fluid through the device is controlled by pressure controllers, and the switching of the cells is accomplished with the use of a high performance pressure controller interfaced with a computer. The cells are fed through the channels with the use of hydrodynamic focusing techniques. Once the experimental setup is fully functional the objective will be to determine switching rates, explore techniques to optimize these rates, and experiment with sorting of other biomolecules including DNA. [Preview Abstract] |
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D1.00019: Vector Inverses and Other Powerful Applications of Geometric Algebra Tim Wendler, Manuel Berrondo Geometric algebra has an elegance and simplicity that motivates reforming traditional analytic representations in physics. I exploit the ease of the vector inverse with a sphere-to-plane mapping application on the method of images in electrostatics. I also briefly explore rotors, Green functions, and more, to illustrate the power of geometric algebra in the physics curriculum. [Preview Abstract] |
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D1.00020: A fully connected qubit network model for quantum information processing applications Mark Coffey We describe a fully connected qubit (spin-1/2) network model for quantum information processing applications. This scalable network in the case of spin 1/2 has recently been realized in the laboratory, using Josephson phase qubits, and other solid- state implementations are likely. We have very recently collaborated in the development of a rigorous protocol for producing the important maximally entangled generalized GHZ states for this implementation [1]. (GHZ states generalize the well known Bell states for two qubits.) As an additional application of the spin network model, we mention how it could be used to perform factoring or other tasks of interest to computational number theory. Joint work with Andrei Galiautdinov and Ron Deiotte. \\[4pt] [1] A. Galiautdinov, M. W. Coffey, and R. Deiotte, arXiv:0907.2225v1 (2009). [Preview Abstract] |
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D1.00021: Loss Induced via 5P$_{3/2}$ to 5D$_{5/2}$ Resonant Light in an $^{85}$Rb MOT Truman Wilson, Jacob Roberts As part of our investigations of possible routes to photoionization in a Rb MOT, we observed relatively large density-dependent loss rates induced by light at 776 nm. This light corresponds to the 5P$_{3/2}$ to 5D$_{5/2}$ transition in Rb. This poster presents our characterization of these losses. [Preview Abstract] |
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D1.00022: Self-trapped dynamics in a 2D optical lattice Shuming Li, Rafael Hipolito, Jean-Felix Riou, David Weiss, Anatoli Polkovnikov, Ana Rey We use a mean field model to study the expansion of an array of one dimensional vertical tubes of cold bosonic atoms confined in a two dimensional optical lattice after the crossed dipole trap used for the initial loading is suddenly turned off. In our model the pure mean field dynamics predicts macroscopic self trapping manifested in the accumulation of atoms at the edge of the cloud and the formation of a hole at the center. When quantum fluctuations are accounted for, the localization of the wave packet is enhanced, the formation of the hole is suppressed, and the predictions of the model are in better agreement with the experimental measurements. [Preview Abstract] |
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D1.00023: Spectroscopy of High-L Rydberg States of Nickel Kristen Voigt, Stephen Lundeen, Julie Keele, Shannon Woods In this study, the fine structure of high-L Rydberg states of nickel is measured. In these high-L Rydberg states, a highly excited ``spectator electron'' reveals, by the details of its binding energy, certain properties of the Ni+ ion which it ``orbits''. These special states are created and measured by a technique called RESIS: Resonant Excitation Stark Ionization Spectroscopy. This method involves creating a fast beam of Ni+ ions which travel through a Rb 9F Rydberg target where many of them capture a single electron~ to form Rydberg states of neutral nickel with population concentrated near n=9.~ Any unneutralized Ni+ ions are blocked by a high electric potential.~ The fast Ni Rydberg atoms then pass through a Doppler-tuned CO2 laser which may excite them from n=9 to n=19 or 20, and any atoms so excited are ionized by a strong electric field and collected and counted.~~ As the CO2 laser is tuned across the excitation resonance, the complex fine structure of n=9 L $>$ 5 levels is fully resolved, and analysis of the fine structure pattern determines properties of the Ni+ ion such as its quadrupole moment and polarizabilitiy. Currently, the data of the study is being analyzed to give unprecedented results for these properties of Ni+. [Preview Abstract] |
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D1.00024: Resolution Enhancement Through Focal Field Polarization Control in Third Harmonic Generation Microscopy Omid Masihzadeh, Philip Schlup, Randy Bartels In optical microscopy, the polarization state of the focal field strongly influences formed images due to its impact on effective focal spot size, and interactions with the sample. We demonstrate control over focal field spatial polarization state improves spatial resolution in laser-scanning third harmonic generation (THG) microscopy. The focal field is manipulated by imaging a spatial light modulator to the focal plane of a moderate numerical aperture microscope. The resolution enhancement arises as THG is quenched for circularly-polarized fundamental field in isotropic media. A transverse spatial resolution of up to 2 times is demonstrated. Moreover, a non-iterative algorithms is developed for characterization of the polarization state at the focus under moderate focusing. In this regime, the recorded THG signal is dominated by the incident paraxial polarization component, the spatial polarization state is determined non-iteratively via three linear-polarization projection THG images. A nano-particle, localizes THG scattering to a small focal volume. Scanning this nano-probe through the focal volume allows for complete reconstruction of the vector point spread function, yielding transverse field components from the focal volume. [Preview Abstract] |
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D1.00025: Metastable states and macroscopic quantum tunneling in a cold atom Josephson ring Dmitry Solenov, Dmitry Mozyrsky We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique. [Preview Abstract] |
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D1.00026: Microscopy of extreme ultraviolet lithography masks with 13.2 nm tabletop laser illumination S. Carbajo, F. Brizuela, Y. Wang, C.A. Brewer, F. Pedaci, W. Chao, E.H. Anderson, Y. Liu, K.A. Goldberg, P. Naulleau, P. Wachulak, M.C. Marconi, D.T. Attwood, J.J. Rocca, C.S. Menoni We report the demonstration of a reflection microscope that operates at 13.2 nm wavelength with a spatial resolution of 55+/-3 nm. The microscope uses illumination from a tabletop extreme ultraviolet laser to acquire aerial images of photolithography masks with a 20 s exposure time. The sample used for the initial demonstration of this EUV microscope consisted of Ni grating and elbow patterns printed onto a Mo/Si multilayer coated 2.5$\times $2.5 cm square Si wafer. Patterns with half-pitch sizes ranging from 80 nm to 500 nm were successfully printed onto the Mo/Si coated sample. The modulation transfer function of the optical system was characterized and these results constitute a first step toward the realization of table-top actinic microscopes for EUVL mask inspection. [Preview Abstract] |
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D1.00027: Matter-Wave Interferometery at BYU Christopher Erickson, James Archibald, Daniel Merrill, Aaron Bennett, Dallin Durfee We report on the progress of two matter-wave interferometers at BYU. The first device is a thermal-beam Ramsey-Bord\'e calcium interferometer. The second device is an ion interferometer based on a laser-cooled $^{87}$Sr$^+$ beam which will be split and recombined using stimulated Raman transitions. Design considerations, instrumentation development, and possible applications of the devices will be discussed. [Preview Abstract] |
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D1.00028: Intra-Annual Comparison of Mesospheric Gravity Waves Over Halley and Rothera Stations, Antarctica Jonathan Pugmire, Michael Taylor, Kim Nielsen, Allen Wall, Jonathan Thompson, Dominique Pautet We present an intra-annual study of short-period, mesospheric gravity wave events observed over Antarctica in the near infrared OH emission. The measurements were made using an all-sky airglow imager operated at either Halley Station on the Brunt Ice Shelf, or Rothera Station, situated on the Antarctic Peninsula. A total of six austral winter seasons have been analyzed (2000-2006). This study comprises the first detailed winter seasonal investigation of short-period mesospheric gravity waves at high-Antarctic latitudes. Distributions of their observed wave parameters were found to be similar to previous findings using imaging instrumentation at other latitudes in the Northern and Southern Hemispheres. However, the observed wave headings exhibited strong, but dissimilar anisotropy at both sites that was also found to be repetitive from year to year, establishing a persistent recurrent pattern. In this poster we present example wave data and seasonal summaries of their properties at both observing sites focusing on wave anisotropy and the strong year to year consistency. [Preview Abstract] |
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D1.00029: A Quantitative Analysis of the Clustering around Intermediate-Mass Pre-Main Sequence Stars Will Flanagan, Nicole van der Bliek, Jayadev Rajagopal The study of intermediate-mass pre-main sequence stars (Herbig Ae/Be stars) o?ers the possibility a more complete picture of star formation theory by bridging the gap between high and low mass star formation regimes. The clustering around Herbig Ae/Be stars has been studied by other groups, most notably Testi et al. (1999). We present preliminary results from a survey of Herbig Ae/Be stars using the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). From our results, we present implications for comparing results to and improving the analysis of the Testi et al. survey, the utility of the 2MASS catalog for such a survey, and implications for our own survey. In particular, we discuss the possibility and limitations of studying clustering as a function of mass, as well as characterizing the cluster companions of our Herbig stars with JHK colors. [Preview Abstract] |
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D1.00030: Study of Galaxy NGC 3885 Centered at 100 micro meter Far Infrared Cavity Barun Gupta A cavity in the 100 $\mu$m infrared sky is investigated and it's shaping mechanism is studied. Interestingly, a galaxy NGC 3885 is found to be located at the center of the cavity. In this work we have calculated the amount of the displaced mass emitted from the cavity. In addition, we estimated the energy required to displace the calculated mass from the cavity. For this, we used Groningen server in order to get high resolution 500 x 500 pixel image of the region of interest. The software ALADIN2.0 is used for the data processing and MATLAB6.2 is used for the calculation. The nature of the discrete sources and the multiwave-length images are studied in the field of interest. The displaced mass is found to lie in the range 8.60x10$^{-6}$ M (solar mass) to 1.73x10$^{-6}$ M (solar mass) for the distance 20$\pm $20{\%} pc and the temperature 20$\pm $20{\%} K. Active galactic nuclei of the galaxy NGC 3885 powers the surroundings by emitting a jet having energy in the range 10$^{32}$-10$^{34}$ Joule/s. In our case, we estimated $\sim $ 1.1x10$^{31}$ Joule/s to 7.5x10$^{32}$ Joule/s energy, which is essential to create the cavity. Thus, there is a very good compatibility between these estimates. We conclude that the shaping mechanism of this cavity is due to the extragalactic jets emitted from the super massive black hole of the galaxy NGC 3885. [Preview Abstract] |
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D1.00031: Characterization of Enzyme Structure-Function Relationship of Adenylosuccinate Lyase Stephen Ray, David Patterson, Kingshuk Ghosh, Terry Wilkinson, Sean Shaheen Adenylosuccinate lyase (ADSL) is an enzyme involved in de novo purine biosynthesis required for several important biological functions. Occasionally disturbances within the enzyme occur, causing a disorder known as ADSL deficiency. It is likely these mutations affect the formation of the tetramer structure by protein misfolding or aggregation. We are beginning to study fundamental properties of the enzyme structure-function relationship of Wild-Type ADSL compared to mutants associated with ADSL Deficiency with two major studies: i) Stability and formation of multimeric complexes in a heterogeneous pool of other structures, ii) Enzymatic activity and reaction kinetics studies by measuring reaction rates of the conversion of substrate into products and enzyme substrate complex formation equilibrium. Our group has successfully expressed Wild-Type (WT) and the mutants R426H and A291V in a protein expression vector and have measured their respective enzyme activity after purification. Modelling approaches for molecular interactions of monomer subunits show the trimer structure could be problematic. We have also carried out our preliminary analysis of the structure-function relationship using microscopic model for the A291V mutant compared to the WT protein. [Preview Abstract] |
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D1.00032: Field Friendly Tuberculosis Biosensor N. Proper, M.S. Scherman, K.L. Jevsevar, J. Stone, M.R. McNeil, D. Krapf Tuberculosis (TB) is a fading threat in the United States, but in the developing world it is still a major health-care concern. Given the rising number of cases and lack of resources, there is a desperate need for an affordable, portable detection system. We are working towards the development of a field-friendly immunological biosensor that utilizes florescence microscopy to undertake this task. We observe fluorescently labeled antibodies/antigens as they bind to a glass slide treated with polyethylene glycol (PEG) in order to inhibit non-specific adsorption. Antibodies against the antigens of interest are bound to the PEGylated glass slides via biotin-streptavidin interactions. Then, fluorescently labeled antibodies are mixed with different concentrations of TB antigens and this solution is incubated on the treated glass slides for 30 minutes. The slides are thoroughly rinsed with water following the incubation period. The antigens are then detected by fluorescence using a low-cost biosensor. Our system includes a ``supermarket-scanner'' HeNe laser, home-built electronics, off-the-shelf optics and a Si photodiode. Work is underway to incorporate a flow-cell into the system, in a small portable box. [Preview Abstract] |
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D1.00033: UV Photo-enhanced Adsorption of DNA on Mica Sarah Rupprecht, Yang Sun, Robert Nemanich Studies of DNA adsorption on mica have contributed to the further understanding of signal detection and immobilization for biosensors. Over the past two decades DNA adsorption has been investigated to further understand how immobilization occurs. The experiment presented here explores the effects of UV light exposure on double-strand lambda DNA immobilization on mica. In this research atomic force microscopy (in non-contact mode) was employed to image mica surfaces after exposure of the surface to a buffered solution containing DNA. The mica surfaces were immersed in the liquid for 5 min with and without UV exposure from a Hg arc lamp. The surfaces were rinsed and then imaged in the AFM, and individual DNA strands were clearly evident. The sample incubated with UV light showed a significantly enhanced adsorption. The results are discussed in terms of the photo excited carriers in the mica and charge transfer processes and their affect on the adhesion process. Further experiments are planned to observe the effects of UV exposure to adsorption of DNA on polarity patterned surfaces of ferroelectric materials. [Preview Abstract] |
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D1.00034: Fluorescence correlation spectroscopy to measure the metabolism of high-density lipoprotein Russell Deitrick, Emily Gibson, Hamid Razzaghi High-density lipoprotein (HDL), referred to as the ``good cholesterol'', carries free cholesterol to the liver to be filtered from the bloodstream and is important to our understanding of atherosclerosis. HDL is metabolized in part by the enzyme Endothelial Lipase (EL). With this project we will use fluorescence correlation spectroscopy (FCS) to study the metabolism of HDL by EL comparing wild type with different genetic mutations. FCS is an advanced microscopy technique in which we record fluctuations in the fluorescence of dye-labeled molecules (in this case, HDL labeled with Nile Red) as they freely diffuse through a small focal volume. This data can be analyzed mathematically using the cross-correlation function, from which we can ultimately ascertain much information. In our case, we are interested in the diffusion coefficient which, via the Stokes-Einstein relation for a sphere, we can determine the size of HDL as it undergoes the process of metabolism. Preliminary results seem to indicate that the metabolic process occurs very quickly, that the final size of HDL depends primarily on the concentration of EL, and that the wild and mutant variants of EL have a similar effectiveness. In following experiments, we hope to investigate these relationships further. [Preview Abstract] |
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D1.00035: Solvation and Deprotonation Dynamics in Reverse Micelles via Broadband Femtoseond Transient Absorption (BFTA) Spectroscopy Richard Cole Broadband femtosecond transient absorption (BFTA) spectroscopy is a useful tool in characterizing femtosecond and picosecond physical and chemical dynamics such as solvation, electron transfer, and deprotonation dynamics. This presentation will focus on our most recent results, which utilize BFTA spectroscopy in the ultraviolet-visible (UV-vis) spectral range to probe deprotonation and solvation dynamics in the nanoscopic confinement of reverse micelles. In these studies, pyranine, a `photo-acid', probes both solvation and deprotonation dynamics in reverse micelles formed from cationic (cetyl trimethylammonium bromide, CTAB), anionic (sodium dioctyl sulfosuccinate, AOT), and neutral (polyoxyethylene nonylphenylether, Igepal) surfactants. Dynamic behavior will be discussed in terms of the degree of nanoscopic confinement (micellar size) and the impact of varying interfacial environments. [Preview Abstract] |
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D1.00036: Reactive Inorganic Membranes for CO$_{2}$/N$_{2}$ separations: Ab-initio Density Functional Theory Calculations M. Ostwal, J.D. Way, M. Lusk The selectivity (CO$_{2}$/N$_{2})$ of mesoporous silica membranes can be enhanced by surface modification using APTS (3-aminopropyl-triethoxy silane). The hypothesized transport mechanism in such materialsis the reaction of CO$_{2}$ with surface amine groups to form a carbamate species and subsequent surface ``hopping'' of CO$_{2}$. DFT calculations were performed in order to elucidate the mechanism of CO$_{2}$ transport in APTS modified membranes, to compute the CO$_{2}$ diffusivity through the membrane, and to calculate its binding energy on an amine strand. The computed binding energy for docking one CO$_{2}$ molecule to an amine was calculated to be 15.5 kcal/mol (0.67 eV). The activation/barrier energy for a CO$_{2}$ molecule to hop from one amine strand (in form of carbamate) to another computed using Transition State Theory (TST) was 7.2 kcal/mol (0.31 eV) and compares well with our experimental data ($\sim $ 8kcal/mol; 0.35 eV). In the configuration studied, CO$_{2}$ hops from one strand to another in a zigzag fashion due to thermal motion of the strands; a strand with the CO$_{2}$ molecule undulates and eventually moves so that the CO$_{2}$ can be attracted by an adjacent strand. The CO$_{2}$ diffusivity calculated using the computed activation energy ranged from 1.1 X 10$^{-11}$m$^{2}$/sec (@ 25 C) to 5.7 X 10$^{-10}$m$^{2}$/sec (@100 C). [Preview Abstract] |
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D1.00037: Strain and edge passivation induced band gap modulation and effective mass tuning in Armchair Graphene Nanoribbons Selina Velasquez, Paul Logan, Xihong Peng We carried out a theoretical study of the effects of strains and molecular/chemical edge passivation on electronic properties in armchair graphene nano-ribbons (AGNR), using first principles calculations. The electronic properties we studied include band gaps and effective masses of the electron and hole. We found strain and edge passivation could significantly modify the gap and effective masses of AGNR. Three different patterns of strain-gap response, i.e., linear, concave and convex curves, are identified for different width of AGNR. Such kinds of modulations of electronic properties in AGNR are important for its applications in future electronics technology. [Preview Abstract] |
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D1.00038: Quantum Confinement in Strained Si/Ge Core-Shell Nanowires Paul Logan, Xihong Peng First principle calculations based on density-functional theory were performed to study quantum confinement on the electronic properties of strained Si/Ge core-shell nanowires along the [110] direction with the diameter up to 5 nm. Particularly the band gap and the effective masses of the electron and hole were investigated. As shown in the calculations, the Si/Ge core-shell [110] nanowires possess a direct band gap, in contrast to the nature of an indirect band gap in bulk Si and Ge. The band gap of the core-shell wires is decreased compared with the pure Si or Ge nanowires with the same size. This reduced gap is ascribed to the intrinsic strain in the core-shell wires, which partially counters the quantum confinement effect. Moreover, the effects of unaxial strain on the effective mass and hole will be discussed. [Preview Abstract] |
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D1.00039: Nanoparticle Interactions with Low-Frequency Electromagnetic Fields for Ablation Therapy Scott Jensen, Timothy Doyle The \textit{in vivo} ablation of malignant tumors can be significantly enhanced with nanoparticles (NPs) that absorb energy from electromagnetic (EM) waves and subsequently heat targeted regions in the body. Low-frequency EM fields can penetrate much deeper than near-infrared and visible light. Ohmic heating has primarily been the sole mechanism considered for the coupling of the EM fields to the NPs, but few quantitative analyses have been published to predict NP heating rates. To address this issue, this study identified and modeled four excitation mechanisms for the remote heating of NPs by low-frequency EM waves. These mechanisms included (1) ohmic heating of conductive NPs, (2) translational vibrations of charged NPs, (3) rotational vibrations of piezoelectric NPs, and (4) acoustic wave generation by piezoelectric NPs. Preliminary results showed that for a constant NP volume, the heating rate is independent of NP size for ohmic heating. Additionally, ohmic heating produced the lowest heating rates of the four mechanisms. These results point to possible new NP technologies to optimize heating rates and tumor ablation in patients. [Preview Abstract] |
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D1.00040: Ge and Ge-rich Group IV Alloys on Si for Photonic Device Applications Jay Mathews, Jose Menendez, Vijay D'Costa, Shui-Qing Yu, Radek Roucka, Junqi Xie, Yanyan Fang, John Kouvetakis The application of silicon photonic technologies to optical telecommunications requires the development of near-infrared detectors monolithically integrated to the Si platform. Recently, new low-temperature CVD techniques have been developed for growth of high-quality epitaxial films of Ge, Ge$_{1-y}$Sn$_{y}$, and Si$_{x}$Ge$_{1-x-y}$Sn$_{y}$ directly on Si. In this poster, we present details on the growth of these films, optimization of processes for the fabrication of photonic devices, and results from some prototype p-i-n heterostructure devices. [Preview Abstract] |
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D1.00041: Mechanical Strength of Composite Nanowires Howard Horton, Bret Hess Motivated by the recent creation of carbon nanotubes coated in silicon, we investigate the mechanical properties of carbon nanotubes embedded in silicon nanowires using empirical force models and molecular dynamics. We predict the Young's modulus and shear modulus for these composite nanowires. We also discuss the mechanical strength and ability to withstand severe deformation. [Preview Abstract] |
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D1.00042: Explicit Cross-Property connection between overall electric conductivity and fluid permeability of a porous conductor Manjita Shrestha, Igor Sevostianov Here we try to address the problem of cross-property connection between electrical conductivity and fluid permeability of a porous material with conducting solid phase. Variational inequality connecting the said two properties is obtained. Development of explicit closed-form connection is complicated by the fact that the two properties are governed by different microstructural parameters. This complication can be over-passed if certain information on phase distribution is available. As an illustration, material with randomly distributed interconnected phases is discussed in details. The cross-property connection for this case is obtained in closed explicit form. [Preview Abstract] |
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D1.00043: Hydrogen Storage in Clathrate Hydrates Joanna Haag, Takeshi Sugahara, Pinnelli S.R. Prasad, Ashleigh Warntjes, E. Dendy Sloan, Amadeu Sum, Carolyn Koh Clathrate hydrates have been investigated as a possible storage medium. There are several advantages of using clathrate hydrates as a hydrogen storage material. Firstly, an advantage is that the system is composed of water. There are no harmful byproducts when the hydrogen is released. In addition, the hydrogen can be released by simply de-pressurizing the system (by turning a valve). Therefore, no chemical reaction is required. However, the disadvantage is that the stability condition for pure hydrogen hydrates is at severe conditions, such as high pressures. In order to alleviate the severe conditions, promoter molecules, for example, tetrahydrofuran are used to shift the phase equilibrium boundary to lower pressures and higher temperature conditions. Other molecules can be used as well. However, the addition of a promoter molecule reduces the possible storage capacity for hydrogen In this work, new synthesis methods have been studied to increase the hydrogen storage capacity of a hydrogen hydrate system, while stabilizing the system at pressure conditions. The results indicate that using these new methods, the hydrogen and promoter molecules can both occupy the large cage within a certain composition range, which results in a storage amount of 3.4 wt.{\%}. [Preview Abstract] |
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D1.00044: Metal Oxide Surface Modification for Organic Photovoltaics K. Xerxes Steirer, David S. Ginley, Reuben T. Collins Organic photovoltaics devices may pose one of the least expensive routes toward conversion of solar power. Two significant obstacles are low intrinsic material stabilities as well as poor interfacial charge transfer kinetics between the transparent conducting oxide and organic semiconductor. Presented is a series of investigations for several surface preparations on a popular metal-oxide (indium tin oxide) using cyclic voltammetry, four-point probe, work function, and contact angle measurement techniques. Surface treatments are correlated with device results in a prototypical organic photovoltaic architecture with an eye toward enhanced charge transfer and material stability at the metal-oxide/organic interface. Included is an overview of main organic photovoltaic operation and degradation mechanisms in the context of surface modification studies. [Preview Abstract] |
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D1.00045: Reduction of Zinc Oxide Thin Films to Form Zinc Metallic Seeds for Silicon Nanowire Growth Louis Gerstenberger A method for reduction of poly-crystalline zinc oxide films to generate uniform pure zinc particles for VLS (vapor-liquid-solid) growth of silicon nanowires is presented. A uniform zinc oxide film is sputtered onto a glass substrate and then treated in a plasma reducing environment at 419 $^{\circ}$C to produce pure zinc metal particles on the films surface. These particles may act as the liquid metal catalyst required for VLS growth of oriented silicon nanowires. [Preview Abstract] |
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D1.00046: Use of planar organic-inorganic heterojunction architectures for understanding charge separation in hybrid solar cells Jamie Adamson, Dana Olson, Matthew White, Joseph Berry, Reuben Collins, David Ginley Organic photovoltaic cells are valued in part for their compatibility with highly scalable fabrication techniques and low-cost materials. These excitonic solar cells are engineered to create large interfacial surface area between the donor and acceptor phases to maximize the region where photoexcited excitons can be dissociated into free carriers. ZnO, in particular, is attractive for these bulk heterojunction (BHJ) devices because of the many nanostructures that can be easily fabricated from its chemical precursors. It is unclear whether poor cell performance is due to unoptimized BHJ morphology or other effects. In this study, hybrid photovoltaic devices with p-type poly(3-hexylthiophene) and n-type ZnO are made with planar geometries to enable interpretation of device performance without morphological complications of a BHJ. [Preview Abstract] |
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D1.00047: Charge generation/dissociation mechanisms at the interface oxide/polymer hybrid heterojunctions studied by microwave conductivity measurements Alexandre Nardes, Matthew White, Dana Olson, Joseph Berry, Nikos Kopidakis, Sean Shaheen, David Ginley Pulse laser deposition (PLD) has been used to obtain thin films of ZnO and a-TiO$_{x}$ to be employed as acceptor materials in hybrid oxide/polymer organic photovoltaic (h-OPV). Films with varying electrical and morphological properties can be obtained, offering a great advantage on optimizing materials and interfaces for h-OPV. P3HT is spin coated on top of the oxides to serve as donor material. A detailed insight of the charge generation mechanism at the interface oxide/polymer is provided by Time-Resolved Microwave Conductivity (TRMC) measurements and correlated to device performance. Single, bi- and tri-layers of these materials have been studied. By varying the carrier concentration of the oxide acceptor layer in the h-OPV devices, one can control the electric field at the planar donor-acceptor interface thereby enhancing charge separation at the interface. The effects of the interfacial electric field are reflected by an increase in the TRMC signal and consistent with the short-circuit current and fill factor improvements observed in devices. Moreover, we found that an interfacial layer of a-TiO$_{x}$ between the ZnO and the P3HT reduces recombination with corresponding benefits to device performance. [Preview Abstract] |
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D1.00048: Growth and Characterization of Digitally Alloyed Zinc Oxide Based TCOs Ajaya Sigdel, Sean Shaheen, John Perkins, David Ginley, Joseph Berry Transparent conducting oxides (TCOs) based on substitutionally doped zinc oxide and novel amorphous oxides offer the potential of high performance and low cost for organic solid-state lighting and organic photovoltaic (OPV) applications. We present studies on digitally alloyed amorphous indium zinc oxide (InZnO) with crystalline gallium doped zinc oxide (GaZnO) and zinc tin oxide (ZnSnO3). The films were grown using pulse laser deposition system with varying oxygen pressure. Alternating layers of two constituent materials are deposited with periodicity of around 5 nm. We find that the composite material has similar conductivity as the constituent species grown at similar conditions but the surface roughness and the work function are determined solely by the terminating layer. We observe that both IZO and GZO terminated stacks result in conductivity of 1.5E3 S/cm, but the surface roughness varies from 0.3 nm to 0.7 nm respectively. We also explore other possible combination of zinc based oxide materials in order to optimize the optical and the electrical properties of TCO for possible application in opto-electronic devices. [Preview Abstract] |
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D1.00049: Solution-processed Gallium Zinc Oxide for Inverted Organic Photovoltaics Alisha Humphries, Dana Olson, Joseph Berry, David Ginley, Sean Shaheen Organic photovoltaics (OPV) is an emerging technology with the promise of inexpensive and scalable solar power harvesting. Inverted devices typically exhibit somewhat lower efficiencies than standard OPVs, therefore this study focused on improving performances of inverted devices through gallium doping of the electron-transport layer, zinc oxide (ZnO). Introducing an n-type dopant into ZnO films is expected to increase the carrier concentration and band-bending in devices for improved charge collection. In this study, gallium zinc oxide (GZO) was fabricated through 0-20 wt. {\%} doping levels. Carrier concentrations were successfully increased as shown by conductivity measurements made on GZO films. X-ray diffraction shows GZO is converted to a crystalline oxide at higher temperatures. Crystalline GZO films show promise for improving power conversion efficiencies of OPV devices, however high temperatures are necessary and may introduce the need for an alternative transparent conducting oxide underlying the electron transport layer. [Preview Abstract] |
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D1.00050: Nickel Oxide as an Inorganic Hole Transport Layer in Organic Photovoltaics Brian Bailey, N. Edwin Widjonarko, Joseph J. Berry, Sean E. Shaheen, David S. Ginley, Dana C. Olson This work explores the use of nickel oxide as a hole transport layer in organic photovoltaics (OPV). ~The purpose of the hole transport layer (HTL) is to provide an energetic barrier to electrons at the anode of the OPV device, while facilitating extraction of holes. ~At present, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) is commonly used in this layer of the device, but it suffers from inherent problems in phase separation of the PEDOT and PSS components leading to non-uniform conductivity, incompatibility with various transparent conducting oxides due to its acidity, and high rate of water uptake that can accelerate degradation of interfaces and surrounding layers. ~Inorganic metal oxides such as nickel oxide present a potential solution to these problems. ~Using pulsed laser deposition (PLD) to deposit nickel oxide films, we show OPV device performance to be tunable by varying deposition parameters. Parameters explored include oxygen partial pressure during PLD, substrate temperature, film thickness, and post PLD surface treatments. These tune physical properties of the film such as work function and conductivity, which were measured directly, and in device performance. [Preview Abstract] |
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D1.00051: Properties of CuO Deposited by Spray Pyrolysis for Photovoltaics Matthew Bell, Cary Tippetts, Robert Davis, Richard Vanfleet We are studying the possibility of CuO as the main absorption material for a photovoltaic cell. CuO has a reported band gap of 2.1 eV, which is optimal for photovoltaics. CuO is an inexpensive material and since it is an oxide, it is stable in an oxygen rich environment. However, CuO has poor mobility, making it difficult for electrons to be carried away. We are attempting to overcome this barrier by depositing the CuO on a three dimensional surface, making it thick enough vertically to absorb photons, but thin enough horizontally for the electrons to escape. Spray pyrolysis is a promising choice because of its affordability and reported reliablility. We are spraying Cu(NO3)2 dissolved in distilled water on a heated substrate. We are testing spray pyrolysis's ability to cover three dimensional figures, and testing the properties of the CuO deposited in this method. [Preview Abstract] |
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D1.00052: Free-Standing Silicon Nanocrystals using Plasma Enhanced Chemical Vapor Deposition B.N. Jariwala, P. Stradins, J.D. Beach, R.T. Collins, J. Fields, S. Rathi, S. Agarwal Si nanocrystals (NCs) less than 5 nm in diameter exhibit a size-dependent tunable band gap, visible photoluminescence, and multiple exciton generation. These properties of Si NCs have led to an increased interest in their utilization in third-generation photovoltaic (PV) devices. In this presentation, we will discuss the synthesis of Si NCs from a SiH$_{4}$/Ar plasma. The particles are transported out of the plasma by gas flow, and are collected onto a grid. The structure and optical properties of the as-synthesized NCs have been characterized using transmission electron microscopy, infrared and Raman spectroscopy, and photoluminescence (PL) spectroscopy. The TEM measurements show that the NCs have a diameter over the range of 3 to 7 nm: the average size can be controlled by varying the residence time in the plasma volume. PL from $\sim $7 nm NCs has an emission peak centered at 850 nm, which blue shifts as the crystal size decreases due to oxidation. Our infrared measurements are consistent with the PL data and show that although the surface Si atoms of the as-synthesized NCs are H-terminated with mono-, di-, and tri-hydride species, these NCs oxidize over a few minutes. Support from NSF award number DMR-0820518 is gratefully acknowledged. [Preview Abstract] |
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D1.00053: Octadecanethiol Island Formation on Single Crystal Zinc Oxide Surfaces Andrea Yocom Organic photovoltaic devices, comprised of zinc oxide (ZnO) nanorod electron acceptor arrays intercalated with organic polymers, could lead to low-cost renewable energy generation. Surface modifications of ZnO with octadecanethiol (ODT) monolayers can help to improve charge transfer in such devices. In the present work, single crystals of ZnO provided well-defined oxygen-terminated and zinc-terminated surfaces on which to learn fundamentally about the attachment and growth of ODT. Both bare zinc oxide and ODT-functionalized surfaces were characterized with atomic force microscopy, Fourier transform infrared spectroscopy, x-ray photoemission spectroscopy, and contact angle analysis. ODT seemed to form islands of multilayers on zinc-terminated surfaces, while it formed islands of monolayers on oxygen-terminated surfaces. While ODT was expected to preferentially bond along defects and terraces on oxygen-terminated surfaces, this was not observed. ODT was also expected to more effectively bond to the zinc-terminated surface, which was observed. Finally, surface preparation treatments designed to leave atomically-flat oxygen terminated surfaces were developed. This work was made possible by the National Science Foundation Division of Materials Research and the Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines. [Preview Abstract] |
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D1.00054: Factor Analysis and the Force Concept Inventory Matthew Semak, Courtney Willis, Richard Dietz Four sections of introductory physics (n=244) at the University of Northern Colorado took the Force Concept Inventory (FCI) both before and after instruction in Newtonian mechanics. Factor analyses of the results reveal several interesting contrasts that may shed some light on the development of concept organization in the introductory physics course. Post-test FCI results indicate that at the end of the semester student responses have become more closely aligned with the particular Newtonian concept associated with each question by the authors of the FCI. [Preview Abstract] |
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D1.00055: Upper-Division Transformation in Physics Steven Goldhaber, Stephanie Chasteen, Steven Pollock, Michael Dubson, Ed Kinney, Oliver DeWolfe, Paul Beale, Katherine Perkins, Rachel Pepper While much research has informed teaching methods in lower-division courses, less attention has been granted to how we train future physicists. Aiming to improve student mastery of upper-division material, we have transformed an upper-division Electricity \& Magnetism (E\&M) course and an upper-division Quantum Mechanics (QM) course. Transformations were based on the results of observations, interviews, and analysis of student work as well as on guiding principles of learning theory. Reform efforts were focused with the help of consensus learning goals while specific classroom transformations include ``clicker'' questions, study groups, interactive lecture techniques, and tutorials. We have also developed new conceptual assessment instruments for both upper-division E\&M and upper-division QM. In this participatory poster, we present these instruments and ask for feedback from the visitors. [Preview Abstract] |
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D1.00056: The Harmony of Physics, Mathematics, and Music: A discovery in mathematical music theory is found to apply in physics Richard Krantz, Jack Douthett Although it is common practice to borrow tools from mathematics to apply to physics or music, it is unusual to use tools developed in music theory to mathematically describe physical phenomena. So called ``Maximally Even Set'' theory fits this unusual case. In this poster, we summarize, by example, the theory of Maximally Even (ME) sets and show how this formalism leads to the distribution of black and white keys on the piano keyboard. We then show how ME sets lead to a generalization of the well-known ``Cycle-of-Fifths'' in music theory. Subsequently, we describe ordering in one-dimensional spin-1/2 anti-ferromagnets using ME sets showing that this description leads to a fractal ``Devil's Staircase'' magnetic phase diagram. Finally, we examine an extension of ME sets, ``Iterated Maximally Even'' sets that describes chord structure in music. [Preview Abstract] |
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D1.00057: Comparison of Van der Waals Potential calculations to experimental results Cathy Klauss, Vincent Lonij, Will Holmgren, Alex Cronin The strength of the Van der Waals atom-surface interaction (C3) depends not only on the polarizability of the atoms but also on the permittivity of the surface. We compare calculations of C3 based on different models for metal surfaces and insulators as well as different models for the atom. The electric dipole polarizabilities of alkali atoms are calculated using a Lorentz oscillator model as well as a model that includes core electrons and relativistic effects. To model metal and insulating surfaces we compare a Drude model to models that include the band gap or interband transitions in the material. We compare the results of our calculations with recent experimental results from atom interferometer and atom diffraction experiments. [Preview Abstract] |
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D1.00058: Towards Spin Squeezing via Collective Quantum Non-Demolition Measurements Zilong Chen, Jiayan (Phoenix) Dai, Justin G. Bohnet, James K. Thompson Current state-of-the-art microwave atomic clocks are limited by quantum projection noise associated with uncorrelated atoms. The current generation of neutral atom optical atomic clocks have already reached a frequency stability very close to the projection noise limit. By using entangled atoms, precision better than the projection noise limit can be obtained, so generating significant amounts of squeezing is of practical interest to the current generation of atomic clocks and precision measurement experiments. We will report experimental progress on generating spin squeezing via optical resonator-enhanced, collective Quantum Non-Demolition measurements on large ensembles of Rubidium 87 atoms. [Preview Abstract] |
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D1.00059: Fluorescence OPA FROG of NIR Dyes Colleen Woodward, Nancy Levinger In standard applications, optical parametric amplification (OPA) is accomplished using a white light continuum as the seed. This presentation will describe a design for an ultrafast fluorescence-OPA-FROG (Frequency Resolved Optical Gating) experiment and its utility for measuring fluorescence dynamics on an ultrashort timescale. This technique has several attractive features compared to current state-of-the-art fluorescence upconversion because it has the potential to amplify weak fluorescence, detection occurs at the wavelength of the fluorescence signal in the visible or near IR spectral region, and the phase-matching condition is $\vec{k}_{pump}$ = $\vec{k}_{signal}$ + $\vec{k}_{idler}$. We will demonstrate time gating and effective amplification of the fluorescence of common near infrared dyes, IR 125, IR 132, and IR 140 in DMSO. [Preview Abstract] |
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D1.00060: Two Photon Resonant Ionization of $^{28}$Si Isotopes: Experimental Methods Jonathan Kluck*, William Czajkowski*, Siu Au Lee, William Fairbank, Katherine Zaunbrecher As part of the W.M. Keck Project for research in quantum computing, it was necessary to identify optical frequencies required for resonant photo-ionization of $^{28}$Si isotopes. This is necessary to aide in future precision on demand single atom deposition. A silicon atomic beam was excited by a 222nm CW deep ultraviolet laser at between 10 and 30mW from ground state to the 3s$^{2}$3p$^{2}$ 3p$_{2}$ state. Simultaneously a tunable pulsed dye laser operating in the 484 to 490nm range with an average energy around 5mJ was used to photo-ionize the atoms to the 3s3p$^{3}$ $^{3}$D$_{0}^{3}$ state. A channeltron was used to measure the number of ions obtained. To determine the ideal resonance frequency for the pulsed laser, initially wide wavelength scans were conducted until peaks in ion count were identified. The resonance frequency was then further refined by conducting narrower width scans while collecting ion counts at various power levels. By this method we were able to obtain saturation curves and determine photo-ionization cross sections. [Preview Abstract] |
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D1.00061: Simultaneous loading of $^{85}$Rb and $^{87}$Rb into a shallow FORT Mathew Hamilton, Anthony Gorges, Jacob Roberts We have studied the effects of simultaneous loading of $^{85}$Rb and $^{87}$Rb into a shallow Far Off Resonance Trap (FORT). To fully characterize the loading parameters both homonuclear ($\beta^{\prime}$) and heteronuclear ($\beta$) loss rates were measured. Once this characterization was completed, we could compare our measured FORT loading performance to a model of the FORT loading process. Measurements of the simultaneous load led to the observation of unexpected interferences. The presence of one isotope significantly reduced the maximum number of atoms loaded beyond the reduction expected from light assisted collisions. These observations are consistent with a disruption of laser cooling efficiency during loading due to long-ranged induced dipole-dipole inter-species collisions. [Preview Abstract] |
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D1.00062: Growth and characterization of transition metal oxide thin films by dual ion beam sputtering Erik Krous, Peter Langston, Dinesh Patel, Federico Furch, Brendan Reagan, Jorge Rocca, Carmen Menoni, Ashot Markosyan, Roger Route, Marty Fejer, Luke Emmert, Duy Nguyen, Wolfgang Rudolph The development of high power lasers operating in the near infrared heavily relies on the availability of robust optical coatings. We present results on the growth and characterization of transition metal oxide thin films by dual ion beam sputtering. Single layer films are grown under different conditions and characterized for their structural, chemical and optical properties using glancing angle x-ray diffraction, variable angle spectroscopic ellipsometry, x-ray photoelectron spectroscopy, photothermal commonpath interferometry, laser-induced damage threshold studies and atomic force microscopy. The laser damage threshold for single pulse (1-on-1) and multiple pulses ($S$-on-1) has also been measured. The results of these experiments have revealed the important role that native impurities and laser created excitonic effects have on the optical response of the single layer films. Results on interference coatings with superior performance will also be presented. [Preview Abstract] |
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D1.00063: ABSTRACT WITHDRAWN |
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D1.00064: Novel Numerical Solution to the Plasma Kinetic Equation Joseph Spencer, Eric Held, Jeong-Young Ji The finite element method (FEM) is a numerical approach to solving partial differential equations commonly used in engineering applications. In this work, we discuss the application of the FEM to velocity space to solve plasma kinetic equations. We have approached the investigation one step at a time. At first, we treat an initial value problem with the kinetic equation including the time derivative and Lorentz collision operator, a simplified form of the full, Coulomb collision operator. We show results that verify that the Lorentz operator causes generic distribution functions to evolve toward Maxwellian distributions. We also show that by refining the size of the grid and increasing the order of the 2-D polynomial basis, we obtain exponential convergence. Our next step was to look at the effects of including the speed drag and diffusion part of the Coulomb collision operator. We conclude by discussing the extension to the full Coulomb collision operator, the inclusion of external electric and magnetic fields, and the generalization to multiple spatial dimensions. [Preview Abstract] |
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D1.00065: Laboratory plasma with cold electron temperature of the lower ionosphere Shannon Dickson, Scott Robertson For the first time, plasma with cold electron temperatures less than 300K has been created continuously in the laboratory. The plasma is created in a cylindrical double-walled vacuum chamber in which the inner chamber (18cm in diameter and 30cm long) is wrapped in copper tubing through which vapor from liquid nitrogen flows, providing a cooling mechanism for the neutral gas. The inner chamber has two negatively-biased filaments for plasma generation and a platinum wire Langmuir probe for diagnostic measurements. Neutral gas pressures of 1.6mTorr and a total filament emission current of 2mA are used to obtain plasma densities near 4 x 10$^{8}$ cm$^{-3}$. When carbon monoxide is used as the working gas, decreasing the neutral gas temperature also decreases the cold electron temperatures, yielding cold electrons with 21meV (240K) when the neutral CO is at 150K. The same experiment conducted with H$_{2}$, He, or Ar results in a doubling of the cold electron temperatures, yielding 80meV (930K) when the neutral gas is at 150K. The lower electron temperature with CO is attributed to the asymmetric CO molecule having a nonzero electric dipole moment which increases the cross section for electron energy exchange. Nitric oxide, a dominant constituent of the ionosphere, has a similar dipole moment and collision cross section as carbon monoxide and is likely to be equally effective at cooling electrons. [Preview Abstract] |
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D1.00066: Design Fundamentals for Cost-Optimized Neutron Detectors Based on an Array of Helium-3 Tubes Randy Spaulding, Chris Morris, Steve Greene, Mark Makela, Tony Forest Increasing competition over the world's finite helium-3 reserves has recently created an urgent need to utilize our existing supplies of the gas in the most efficient manner possible. A new design for helium-3-based neutron detectors has been developed at Los Alamos National Laboratory which maximizes utilization of helium-3 on the basis of cost efficiency. This design employs atmospheric-pressure tubes that contain less than one bar partial pressure of helium-3 nestled inside a lattice of thin HDPE sheets. This results in a net gain of 200-300{\%} in efficiency per gram helium-3 compared to traditional high-pressure tubes. The cost efficiency is independent of surface area, making the design concept appropriate for a wide range of applications involving detector surface areas from $<$100 cm2 to $>$100 m2. A prototype detector with surface area 1.01 m2 was built at LANL and the results of benchmarking experiments are presented. [Preview Abstract] |
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