Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y31: Synthesis, Growth and Processing of Complex Materials |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Michael Mehl, Naval Research Laboratory Room: Colorado Convention Center 401 |
Friday, March 9, 2007 11:15AM - 11:27AM |
Y31.00001: Magnetic Resonance Studies of Crystalline Ge$_{2}$Sb$_{2}$Te$_{5 }$and Sb$_{2}$Te$_{3}$ David Bobela, P. Craig Taylor Recent technological applications of some chalcogenide materials, which are materials containing a group VI atom, have prompted studies of the local atomic structure of the amorphous phase. In particular, Ge$_{2}$Sb$_{2}$Te$_{5}$ has been employed as the prototypical phase-change memory material, since its structure can be rapidly switched from the crystalline phase to the amorphous phase with high fidelity. The metastability in the local bonding structure that produces this phase-change phenomenon is not yet understood. Magnetic resonance methods can be used to study local order as a function of the stoichiometry and phase of the material. As a starting point in understanding the magnetic resonance data for amorphous Ge$_{2}$Sb$_{2}$Te$_{5}$, we have used nuclear magnetic resonance and nuclear quadrupole resonance techniques to study crystalline Ge$_{2}$Sb$_{2}$Te$_{5}$ and Sb$_{2}$Te$_{3}$. We present estimates of the quadrupole coupling constants, and the asymmetry parameters of the electric field gradient for the $^{121}$Sb nuclei. The relationship between these parameters and the local atomic structure of crystalline Ge$_{2}$Sb$_{2}$Te$_{5}$ will be discussed. In particular, the Sb sites appear to depart from axial symmetry, a conclusion that is difficult to obtain from standard scattering experiments. [Preview Abstract] |
Friday, March 9, 2007 11:27AM - 11:39AM |
Y31.00002: Terahertz Transmission Through Quasiperiodic Arrays of Subwavelength Apertures Tatsunosuke Matsui, Amit Agrawal, Ajay Nahata, Z. Valy Vardeny The extraordinary light transmission (EOT) through optically thick metallic films perforated with two-dimensional (2D) subwavelength hole array was originally explained in terms of resonant coupling to surface plasmon polariton (SPP) modes via grating coupling; and thus numerous EOT studies have been done on periodic hole arrays. Here we demonstrate terahertz EOT through 2D quasicrystalline array of subwavelength apertures that are not Bravais lattices, but, nevertheless of which structure factor shows discrete Fourier transform components. We found that such patterns also exhibit strong EOT bands indicating that SPP interaction also occur in quasiperiodic structures. This approach dramatically expands potential design parameters for aperture arrays and opens up exciting new avenues for optoelectronic devices, especially in the THz spectral range. [Preview Abstract] |
Friday, March 9, 2007 11:39AM - 11:51AM |
Y31.00003: Terahertz Transmission Through Aperiodic Arrays of Subwavelength Apertures Amit Agrawal, Tatsunosuke Matsui, Valy Vardeny, Ajay Nahata The recent surge of interest in the field of surface plasmon polaritons (SPPs) resulted in part following the initial demonstration of extraordinary optical transmission (EOT) through periodic arrays of subwavelength apertures. Ensuing experimental and theoretical studies on these and associated structures were focused primarily on \textit{periodic} structures. In this submission, we demonstrate that aperture \textit{periodicity} is not crucial for obtaining strong EOT resonances. We demonstrate this phenomenon by measuring the EOT of \textit{aperiodic} array of subwavelength apertures fabricated on free standing metal films in the terahertz spectral range. We observed sharp resonances in the transmission spectra at frequencies matching the aperture array `structure factor'. The \textit{aperiodic} structures were designed using a general numerical approach for patterns in which no associated geometrical tiling rules exist. [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:03PM |
Y31.00004: Micro-Raman and FTIR Studies of Synthetic and Natural Apatites A. Antonakos, E. Liarokapis, Th. Leventouri B-type synthetic carbonate hydroxyapatite (CHAp), natural carbonate fluorapatite (CFAp) and silicon-substituted hydroxyapatite (SiHAp), have been studied by using micro-Raman and infrared (IR) spectroscopy. It was found that while B-type carbonate substitution predominates in carbonate apatites (CAps), A-type is also detected in all types of apatites. B-type carbonate substitution causes a broadening of the v$_{1}$ P-O stretching mode that is associated with the atomic disorder within the phosphate tetrahedron. An $\sim $15 cm$^{-1}$ shift of the v$_{3c}$ P-O antisymmetric IR mode was observed upon heat-treatment of the CFAp to drive the carbonate off. This shift indicates that the P-O bond lengths on the mirror plane increase when carbonate leaves the apatite structure suggesting that carbonate substitutes on the mirror plane of the phosphate tetrahedra. The present results support the substitution mechanism proposed on the basis of neutron powder diffraction studies of the same samples. The intensity ratios of the v$_{2}$ IR CO$_{3}$ and v$_{1}$ PO$_{4}$ bands in samples with various carbonate contents provide a calibration curve for estimating the degree of carbonization of CAps. [Preview Abstract] |
Friday, March 9, 2007 12:03PM - 12:15PM |
Y31.00005: Propagation of Electromagnetic Waves in a One Dimensional Photonic Crystal with DPS/DNG Layers Joseph Shahbazian, Aram Karakashian Although materials having positive permittivity and permeability (DPS) are well known, recently electromagnetic materials with negative permittivity and permeability (DNG) have been given much attention. Wave propagation in a double negative medium and also photonic crystals has been studied analytically and experimentally. The material parameters are complex and frequency dependent to account for both dispersion and absorption. The real part of the corresponding index of refraction can be negative only in narrow frequency bands. Here we have studied theoretically the propagation of electromagnetic waves in a one dimensional photonic crystal composed of alternating layers of DNG and DPS layers. We find that this type of photonic crystal in the visible wave range exhibits negative refraction in a wider frequency range. [Preview Abstract] |
Friday, March 9, 2007 12:15PM - 12:27PM |
Y31.00006: NMR Studies of Ba8AlxGe46-x and Ba8GaxGe46-x Clathrates Gou Weiping, Yang Li, Ji Chi, V. Goruganti, K. D. D. Rathnayaka, Joseph H. Ross, Jr. We have prepared a series of clathrates of the general form, Ba$_{8}$Al$_{x}$Ge$_{46-x}$. X-ray measurements indicate that Al occupies predominantly the 24$k$ site, similar to previous observations for the Ga analogs. $^{27}$ NMR measurements using wide-line and MAS spectrometers indicate two different local Al sites, one with a relatively small quadrupole splitting, attributed to the 24$k$ site, and one with a larger quadrupole splitting attributed to Al adjacent to a vacancy. We also discuss the results of $ab$-$initio$ calculations supporting these conclusions. $T$-dependent NMR relaxation results show roughly Korringa-type behavior for both series of compounds for $x <$ 16, characteristic of heavily-doped semiconducting materials. The lowest-carrier density Ga$_{16}$ sample shows changes in $T_{1}$ and Knight shift characteristic of incipient localization at low temperatures, however analysis indicates that the carriers remain in the regular band rather than forming an impurity band. For Ga$_{x}$ clathrates synthesized from excess Ga, the NMR $T_{1}$ changes abruptly, indicative of a change in band-edge symmetry for $p$-type material. This work was supported by the Robert A. Welch Foundation (grant A-1526), and the National Science Foundation (DMR-0103455). [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 12:39PM |
Y31.00007: Thermodynamics of type-I and type-II Si clathrates: a computer simulation study Caetano Miranda, Alex Antonelli Few years ago a guest free type-II clathrate of silicon was obtained. This new form of elemental silicon is remarkably stable up to high temperatures. It is now clear that in order to devise new synthesis routes for these materials a better understanding of their thermodynamic properties is highly desirable. In this work, we present a computational study, employing the isobaric Monte Carlo method, of the thermodynamic properties at zero pressure of different phases of silicon, namely, both clathrate forms, $\rm Si_{46}$ (type-I) and $\rm Si_{34}$ (type-II), diamond crystalline silicon, liquid silicon, and amorphous silicon (\textit{a}-Si). The Gibbs free energies, calculated by the reversible scaling method, allow us to determine the stable and metastable relations between these various phases. We have found the melting point of Si$_{46}$ and Si$_{34}$ clathrate structures to be at $1482\pm25$~K and $1522\pm25$~K, respectively. Our result for the melting point of Si$_{34}$ is in good agreement with the experimental value of 1473~K. The results also indicate that both clathrate forms are more stable than \textit{a}-Si for any temperature up to their melting point. Based on our findings we discuss the feasibility of routes for the growth of these materials, such as solid-phase epitaxy and liquid-phase epitaxy. [Preview Abstract] |
Friday, March 9, 2007 12:39PM - 12:51PM |
Y31.00008: Dielectric spectroscopy of pulsed laser deposited type Pb(Zr,Ti)O$_{3}$ (PZT)/CoFe$_{2}$O$_{4}$ (CFO) and CFO/ PZT multilayers thin films. Nora Ortega, N. Baskaran, R. Katiyar, I. Takeuchi Mutiferroics are a novel class of next generation multifunctional materials. Intensive research is being pursued towards the development of materials with high magnetoelectric (ME) coupling. In case of composite thin films, ferromagnetic (FM) columns epitaxially grown in ferroelectric (FE) matrix, exhibit large ME coefficient compared to multilayers structures. From the studies it appears that the distribution of FM phase in FE matrix plays an important role to obtain high ME effect. In the present work we fabricated composite thin films of FE Pb(Zr,Ti)O$_{3}$ (PZT) and FM CoFe$_{2}$O$_{4}$ (CFO) multilayers with 3,5, and 9 layers PZT/CFO (PC) and CFO/PZT (CP) by pulsed laser deposition. We have investigated the effect of reversing the order of FE and FM layers in the multilayer configuration on the properties. The TEM and XPS depth profile of the films, showed that the layer structure was not maintained. The dielectric constant of PC and CP multilayers showed strong frequency dispersion. Reversing the multilayers configuration from CP to PC resulted in increasing the remanent polarization. The observed dielectric relaxation has been explained by Maxwell-wagner type contributions. The ME effect of multilayer films will be discussed. [Preview Abstract] |
Friday, March 9, 2007 12:51PM - 1:03PM |
Y31.00009: Measurement of the DC resistance of thin film semiconductor-gas systems: comparison to the effective medium approximation J. Garner, B. Carrico, J. Saredy, J. Tracy, N. Patel DC resistance measurements have been made of a thin film semiconductor (indium tin oxide) that has been exposed to various gases (acetylene, methane, and sulfur dioxide). Our motivation is to use the time-dependent resistance as a means of identifying unknown gases. Three transport models were used to compare to the measurements: a simple resistor network model, a dynamic Maxwell-Garnett theory (DMGT), and a dynamic effective medium approximation (DEMA). The latter two theories are \textit{dynamic} because the volume fractions of the constituents of the thin film-gas composite vary with time during the gas adsorption process. The resistor network model gives the general trend of the data. This novel application of the DMGT and DEMA yield results that are nearly identical to each other and that are in good agreement with our measurements. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:15PM |
Y31.00010: Functionally graded, nanocrystalline, multiphase, B- and C-based superhard coatings Charles Blatchley, Fereydoon Namavar, Eric Tobin, John Adams, Michael Graham Candidate ceramic coatings for bearing applications must meet several criteria, such as hardness, to limit abrasive damage. Adhesion is essential to prevent destructive three-body wear. Toughness helps avoid brittle fracture and coating failure. Finally, temperatures during deposition must not damage the substrate. We report fabrication and testing of functionally-graded, nanocrystalline, multiphase Ti/BN coatings by ion beam assisted deposition (IBAD), with these properties. Hardness was measured $>$ 42 GPa. Structural grading transitions from metallic to covalent bonding through the film, controlling constituents (TiN, TiB$_{2}$, B$_{4}$C, BN) to optimize adhesion, internal stress, hardness, and wear resistance. Pin-on-disk wear testing for 5 million cycles at 1 GPa contact stress, showed no wear, to potentially extend lifetimes by orders of magnitude in industrial or biomedical applications. [Preview Abstract] |
Friday, March 9, 2007 1:15PM - 1:27PM |
Y31.00011: Photoemission Studies on Bulk Amorphous Steels Michael Buettner, B. Simon Mun, Peter Oelhafen, Petra Reinke The recent availability of bulk amorphous metals (BMGs) promises interesting new applications for the near future based on the superior structural, physical, and chemical properties of such materials compared to conventional steels. In order to shed light on local atomic and electronic structure photoemission studies have been performed on BMGs containing Fe, Cr, Mo, C, B, and Er. Progressing from ternary to penternary alloys we studied changes in the local electronic environment in a systematic manner by means of core-level and valence band spectroscopy. Step-by-step ion irradiation revealed differences in surface and bulk elemental composition and bonding. In particular the bonding state of B changes from oxide (surface) to boride (bulk). Iron exhibits the most prominent spectral changes of all the metal constituents, showing significantly higher core-level binding energies in penternary alloys than in ternary and quaternary compounds. Investigations of the Fe 3s multiplet splitting indicates a dependence of the splitting energy on the abundance of erbium in the alloy. Future experiments will focus on bulk material properties by preparing alloy surfaces in vacuum and addressing the constituents' chemical environment in more detail. [Preview Abstract] |
Friday, March 9, 2007 1:27PM - 1:39PM |
Y31.00012: Nanoscale Order in Marginal and Bulk Amorphous Metal Alloys Paul Voyles, William Stratton, Jinwoo Hwang, Joseph Hamann, Hongbo Cao, John Perepezko, Y. Austin Chang Using fluctuation electron microscopy (FEM), we have shown that both an Al-based marginal amorphous Al alloy, Al$_{88}$Y$_{7}$Fe$_{5}$, and a Zr-based bulk amorphous alloy, Zr$_{54}$Cu$_{38}$Al$_{8}$, have significant nanoscale structural order at a length scale of $\sim $1.5 nm. In both cases, that order can be reduced by annealing below $T_{g}$. In the Al alloy, this order is associated with proto-crystalline clusters formed in the liquid or during the rapid quench. The size and/or density of these clusters can also be modified by small additions of Cu and Ti. The nature of the structure in the Zr alloy has not been determined, but our results show that structural relaxation on aging, which in bulk metallic glasses is commonly understood in terms of redistribution of free volume in the form of atom-size voids, involves rearrangments of groups of $\sim $10-100 atoms. [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 1:51PM |
Y31.00013: Strain localization in disordered materials and implications for constitutive laws for sliding interfaces Mary Lisa Manning, James S. Langer, Jean M. Carlson We investigate localization in a model for disordered materials such as granular particles or plastically deforming asperities that are sheared between sliding interfaces. We model the dynamics of configurations of particles that are more susceptible to deformation under shear stress using Shear Transformation Zone (STZ) theory. STZ theory has recently been modified to include effective disorder temperature dynamics, which provides a mechanism for strain softening and shear localization because as the material is strained it becomes more disordered and a more disordered material is more susceptible to deformation. The STZ effective temperature model is investigated in a simple shear geometry by numerically integrating the equations of motion and analyzing their generalized stability. We find that a material with a spatially homogeneous initial effective temperature distribution (corresponding to a slowly quenched sample) supports homogeneous flow, but one with a finite spatial perturbation in the disorder (corresponding to a rapidly quenched sample) develops a shear band, which leads to a dramatic reduction in the yield stress and a modified constitutive law for the interface. [Preview Abstract] |
Friday, March 9, 2007 1:51PM - 2:03PM |
Y31.00014: A comparison between defects created by light soaking and tritium decay in amorphous silicon Tong Ju, Stefan Zukotynski, Nazir Kherani, P. Craig Taylor, Paul Stradins We compare two ways to create defects in a-Si:H, namely decay of bonded tritium and irradiation with visible light. Tritium decays to He$^{3}$, emitting a beta particle and an antineutrino. In tritium doped a-Si:H samples each beta decay of tritium bonded to silicon will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We track these defects using electron spin resonance (ESR). We have kept the sample in liquid nitrogen for two years. After two years the defect density increases without saturation to a value of 7x10$^{19}$/cm$^{3}$. In the second experiment, we have kept the sample in liquid nitrogen irradiated with white light of intensity about 100mW/cm$^{2}$. After about 6 months, the spin density increased to about 9x10$^{17}$/cm$^{3}$ with no evidence of saturation. In the tritiated sample the increase in the defect density is proportional to the time, t, while in the light-soaked sample the increase is approximately proportional to t$^{1/3}$. This difference in behavior will be discussed. [Preview Abstract] |
Friday, March 9, 2007 2:03PM - 2:15PM |
Y31.00015: Effective Mass Density of Fluid-Solid Composites Jun Mei, Zhengyou Liu, Weijia Wen, Ping Sheng We show through rigorous derivation and experimental support that the dynamic effective mass density of an inhomogeneous mixture, used in the prediction of wave velocities in the long wavelength limit, can differ from the static version---the volume average of the component mass densities. The physical reason for this difference is explained. The dynamic mass density expression, first derived by Berryman more than two decades ago, is shown to give a closer correspondence between the acoustic and electromagnetic metamaterials by allowing for negative mass densities at frequencies around resonances. [Preview Abstract] |
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