Bulletin of the American Physical Society
Joint Fall 2012 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 57, Number 10
Thursday–Saturday, October 25–27, 2012; Lubbock, Texas
Session L4: Invited and Contributed Papers - Condensed Matter & Materials Physics III |
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Chair: Dwight Russell, Baylor University Room: Holiday Inn Towers Petroleum B |
Saturday, October 27, 2012 10:15AM - 10:50AM |
L4.00001: Characterization and Optimization Multiscale and Multicomponent Nanosystems Invited Speaker: Kelly Nash Materials with new combinations of properties are increasingly needed to meet the requirements of energy, transportation, and medical applications. The use of multi-component systems, with potentially complementary properties, represent a unique path to improve materials properties for a variety of applications. Among the most interesting applications of these materials is in the development of contrast agents in biological imaging and dynamic sensing applications. Although a variety of techniques to characterize these materials exist, noninvasive characterization methods, such as optical-based techniques, are ideal for studying these materials in their native states and for monitoring dynamic changes. The proposition becomes even more attractive when at least one of the components carries an optical signature.The use of optoacoustic (OA) is an emerging technology based on studying optically absorbing nano and microstructures in the sample by recording transit pressure waves generated from laser-induced thermal expansion. More recently OA has been developed as a vibrant technology for medical applications and some growing applications is for material characterization in research and industrial applications. Specifically, OA can assist in the characterization and optimization of composite materials containing nanoparticles when paired with other characterization techniques. The present work illustrates an overview of select hybrid nanomaterials, including their unique optoacoustic signatures utilizing an all optical OA technique. The results of this work show that optical based techniques such as OA, provide a noninvasive, nondestructive means to study multi-material, multi-scale, multi-functional materials are important in the development of novel multi-component nanomaterial schemes and elucidating the structure-function relationship in these materials. [Preview Abstract] |
Saturday, October 27, 2012 10:50AM - 11:02AM |
L4.00002: Characterization of Au/Rare Earth Oxide/Au Thin-films by all Optical Photoacoustic Spectroscopy Zannatul Yasmin, Nathan Ray, Edward Khachatryan, Saher Maswadi, Randolph Glickman, Kelly Nash Photoacoustic spectroscopy (PAS) is a sensitive spectroscopy based on transit pressure waves generated from laser-induced thermal expansion in absorbing medium. Over the last decade the technique has shown promise for sensing, imaging and detection in biological applications especially when using nanoparticles. The nanoscale interaction of functionalized nanoparticles (fNPs) has attracted interest due to their potential applications in biosensors and biomedical diagnostics. In particular, gold nanoparticles have been used as contrast agents for signal enhancement and time-intensity curve measurements. Moreover, rare earth ion doped rare earth metal oxide (REMO) exhibits multi-wavelength absorbance and emission that overlap well with the surface plasmon resonance of fNPs. In this work, we are characterizing gold attached Er$^{3+}$ doped Y$_{2}$O$_{3}$ coated by silanation as a thin film formed on a glass surface by use of an all optical PAS technique. We expect that, this PAS technique will provide unique information about the interaction of the fNPs and REMO and use as sensors in the biological systems without the artifacts limiting the use of current methods, such as fluorescent indicators. [Preview Abstract] |
Saturday, October 27, 2012 11:02AM - 11:14AM |
L4.00003: Heat Flow in Heterostructures Mehmet Bebek, Stefan Estreicher Existing theoretical descriptions of thermal transport through heterostructures describe the process in terms of empirical reflection and transmission. First-principles theoretical tools are required to describe at the atomic level the flow of heat at the boundary between two materials. The interactions between the (localized) phonons associated with the interface and the (delocalized) bulk phonons can be described using ab-initio molecular-dynamics simulations provided that temperature fluctuations are controlled without using a thermostat. This can be achieved by preparing the supercell using the eigenvectors of the dynamical matrix. Our approach and preliminary results dealing with a Ge layer in a Si nanowire will be discussed. [Preview Abstract] |
Saturday, October 27, 2012 11:14AM - 11:26AM |
L4.00004: Optical properties of hierarchical architectures of YBO$_{3}$:Eu$^{3+}$ phosphor Sandeep Sohal, Xianwen Zhang, Archis Marathe, Jharna Chaudhuri, Marauo Davis, Louisa J. Hope-Weeks, Mark Holtz We investigated nano- and micro-structures of YBO$_{3}$:Eu$^{3+}$ phosphor synthesized using a hydrothermal approach for white light emission applications. Optical properties using photoluminescence (PL) technique were examined under different excitation wavelengths, ranging from the deep to near ultraviolet. Single crystal nanoflakes gathered together to evolve into a hierarchical architecture through self assembly processes with eight different types of three dimensional morphologies. The samples show narrow-line width orange (O) and red (R) PL at 592, 611, 627 nm at all excitation wavelengths. The PL originates from $^{5}$D$_{0 }-^{7}$F$_{J}$ (J = 1,2,3,4) transition levels of Eu$^{3+}$. YBO$_{3}$:Eu$^{3+}$ prepared using ethanol solvent has the highest R/O ratio with chromaticity coordinates (0.64, 0.33) in Commission Internationale de I'Eclairage (CIE) diagram. We observed that the R/O ratio increases as we go from deep to near ultraviolet excitation, indicating that different luminescence centers of Eu$^{3+}$ exist in YBO$_{3}$ in samples. [Preview Abstract] |
Saturday, October 27, 2012 11:26AM - 11:38AM |
L4.00005: Theoretical Study of the Structural and Electronic Properties of K$_{x}$Si$_{136}$, (x = 1, 8, 18) Craig Higgins, Charles Myles Type II clathrate semiconductors have cage-like lattices in which Group IV atoms are tetrahedrally-coordinated and sp$^{3}$ covalently bonded. The cages can contain ``guest'' atoms; usually alkali or alkaline earth atoms. These materials are of interest because of their thermoelectric properties. Measurements of the lattice constant [1] as a function of Na concentration x in Na$_{x}$Si$_{136}$ (0 $\le $ x $\le $ 24) have shown the interesting property that, as x is increased in the range (0 $\le $ x $\le $ 8), the lattice constant decreases and that as x is increased further in the range (8 $\le $ x $\le $ 24), the lattice constant increases. We note that some measurements of the properties of K$_{17.8}$Si$_{136 }$have also recently been reported [2]. These observations have motivated us to study the behavior of the lattice constant and other properties as a function of guest concentration in other Type II clathrates. In the present paper, we report the results of a theoretical study of the properties of K$_{x}$Si$_{136}$ as a function of x. We have used density functional theory to investigate the properties of this material with guest concentrations of x = 1, 8, and 18. Our results show that, similar to previous results for Na$_{x}$Si$_{136}$, the lattice constant as a function of x has a minimum at x = 8. We also report results for other structural and electronic properties of K$_{x}$Si$_{136}$.\\[4pt] [1] M. Beekman, E. Nenghabi, K. Biswas, C. Myles, M. Baitinger, Y. Grin, G.S. Nolas, Inorg. Chem. 49 2010, DOI: 10.1021/ic1005049\\[0pt] [2] S. Stefanoski and G. Nolas, Cryst. Growth Des. 2011, dx.doi.org/10.1021/cg200756r [Preview Abstract] |
Saturday, October 27, 2012 11:38AM - 11:50AM |
L4.00006: Theoretical Study of the Properties of the Type II Clathrate A$^{x}$Sn$^{136}$, (A = alkali atom; 0 $\le $ x $\le $ 24) Dong Xue, Craig Higgins, Charley Myles Motivated by recent experimental and theoretical interest in the x dependence of the properties of the Si and Ge-based Type II clathrate materials A$^{x}$Si$^{136 }$and A$^{x}$Ge$^{136}$ (A = alkali atom) [1,2] we are carrying out a systematic theoretical study of the properties of the Sn-based Type II clathrate system A$^{x}$Sn$^{136}$. Type II clathrates have cage-like lattices in which Si, Ge, or Sn atoms are tetrahedrally-coordinated and sp$_{3}$ covalently bonded. The cages can contain ``guests''; usually alkali or alkaline earth atoms. These materials are particularly interesting because of their potential use as thermoelectrics. Recent powder X-ray diffraction experiments have found the very interesting result that, for increasing x in the range 0 $\le $ x $\le $ 8 a lattice contraction occurs, and that x is increased further (8 $\le $ x $\le $ 24), a contrasting lattice expansion results. These observations have motivated us to study the behavior of the lattice constant and other properties as a function of guest concentration in other Type II clathrates. In the present paper, we report preliminary results of a density functional based theoretical study of the properties of K$^{x}$Sn$^{136}$ as a function of x. We present results for the x dependence of the lattice constant as well as for other structural and electronic properties of this material. \\[4pt] [1] S. Stefanoski and G. Nolas, Cryst. Growth Des. 2011, dx.doi.org/10.1021/cg200756r\\[0pt] [2] M. Beekman, E. Nenghabi, K. Biswas, C. Myles, M. Baitinger, Y. Grin, G.S. Nolas, Inorg. Chem. 49 2010, DOI: 10.1021/ic1005049 [Preview Abstract] |
Saturday, October 27, 2012 11:50AM - 12:02PM |
L4.00007: Advantages and Uses of AMTEC M.A.K. Lodhi Static conversion systems are gaining importance in recent times because of newer applications of electricity like in spacecraft, hybrid-electric vehicles, military uses and domestic purposes. Of the many new static energy conversion systems that are being considered, one is the Alkali Metal Thermal Electric Converter (AMTEC). It is a thermally regenerative, electrochemical device for the direct conversion of heat to electrical power. As the name suggests, this system uses an alkali metal in its process. The electrochemical process involved in the working of AMTEC is ionization of alkali metal atoms at the interface of electrode and electrolyte. The electrons produced as a result flow through the external load thus doing work, and finally recombine with the metal ions at the cathode. AMTECs convert the work done during the nearly isothermal expansion of metal vapor to produce a high current and low voltage electron flow. Due to its principle of working it has many inherent advantages over other conventional generators. These will be discussed briefly. [Preview Abstract] |
Saturday, October 27, 2012 12:02PM - 12:14PM |
L4.00008: Pressure Induce Phonon Instabilities in BCC Tantalum Single crystals Oscar Guerrero Large-scale atomistic simulations of shock-wave propagation in single crystals exhibit large anisotropies in the elastic-plastic and solid-liquid transitions. Characteristic of this type of simulations are the large strains at which the crystal yields plastically, regardless of crystal orientation. At these large strains, uniaxial deformations, such as those produced in planar shock loading generate phonon instabilities. Using non equilibrium molecular dynamics simulatsion (NEMD), We have investigated the directional anisotropy of the elastic limit in body-centered-cubic Tantalum (bcc) crystals, under quasi-isentropic compression, and using the embedded atom method (EAM) to model the atomic interactions. We show that the elastic-plastic transition in BCC defect-free crystals is caused by the appearance of soft-phonon modes and not via homogenous nucleation of extended defects. [Preview Abstract] |
Saturday, October 27, 2012 12:14PM - 12:26PM |
L4.00009: Structural and electronic properties of high pressure phases of lead chalcogenides John Petersen, Luisa Scolfaro, Thomas Myers Lead chalcogenides, most notably PbTe and PbSe, have become an active area of research due to their thermoelectric properties. The high figure of merit (ZT) of these materials has brought much attention to them, due to their ability to convert waste heat into electricity. Variation in synthesis conditions gives rise to a need for analysis of structural and thermoelectric properties of these materials at different pressures. In addition to the NaCl structure at ambient conditions, lead chalcogenides have a dynamic orthorhombic (Pnma) intermediate phase and a higher pressure yet stable CsCl phase. By altering the lattice constant, we simulate the application of external pressure; this has notable effects on ground state total energy, band gap, and structural phase. Using the General Gradient Approximation (GGA) in Density Functional Theory (DFT), we calculate the phase transition pressures by finding the differences in enthalpy from total energy calculations. For each phase, elastic constants, bulk modulus, shear modulus, Young's modulus, and hardness are calculated, using two different approaches. In addition to structural properties, we analyze the band structure and density of states at varying pressures, paying special note to thermoelectric implications. [Preview Abstract] |
Saturday, October 27, 2012 12:26PM - 12:38PM |
L4.00010: Positron Annihilation Spectroscopy of Barnett Shale Core Samples Hayden Morgan, Milton Enderlin, C.A. Quarles Positron annihilation spectroscopy (PAS) is an experimental technique that provides information about the internal structure of an object, specifically the porous spaces or defects that are present within the object. The lifetime of a positron within the sample is measured, which depends upon the volume of the space the positron becomes ``trapped'' in. While PAS has been applied to geological samples in the past, the present project focuses on Barnett Shale core, which has not been studied extensively with PAS. PAS presents a unique opportunity to learn about the micro-pores within the shale. These micro-pores are of critical importance because they contain natural gas, oil, and other organic compounds. Our project has 3 main goals: to determine the average positron lifetimes of a shale sample, to investigate the uniformity of shale core, and to observe the effect on the internal structure of shale after a handheld micro-conical indentation test, known as a ``dimple test,'' has been performed. This dimple test is an application of a small, concentrated force onto the shale, which subsequently fractures the shale (within a small radius around the impact point). Our preliminary results conclude that shale is relatively non-uniform, and that the volume of the micro-pores within the shale sample is significantly affected by the dimple test. [Preview Abstract] |
Saturday, October 27, 2012 12:38PM - 12:50PM |
L4.00011: Photoluminescence Investigation of Oxidation on GaN Gulten Karaoglan, Vladimir Kuryatkov, Sergey Nikishin, Mark Holtz, Mary M. Coan, Derek W. Johnson, Jung Hwan Woo, Iman Rezanezhad, H. Rusty Harris We investigated the effect of oxide layers grown on GaN/sapphire using thermal oxidation and atomic layer deposition (ALD) for MOS-HEMT applications by means of photoluminescence (PL) measurements. Any influence from the oxide is expected to be at the topmost GaN layer ($<$ 100 nm) so optical measurements are performed to probe the effect of oxide. For the thermal oxide, PL spectra were measured (10 K) prior to oxidation, with oxide, and following removal. The primary PL peak blue shifts 7 meV after the oxidation, but returns to the original position upon the removal of oxide. This shift is attributed to stress from the oxide. Below-bandgap emission is observed upon oxidation; these features remain after removing of the oxide. PL for ALD HfO$_{2}$/GaN and Al$_{2}$O$_{3}$/GaN samples exhibit only minor shift for the primary PL peak. Weak sub-bandgap PL peaks may be attributed to native defects and donor-acceptor recombination. A band near 3.27 eV for samples with oxide may suggest that oxygen impurities are involved in the recombination process. [Preview Abstract] |
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