Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W12: Insulators: Synthesis and Experiment |
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Sponsoring Units: DCMP Chair: Ben White, University of California, San Diego Room: 007C |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W12.00001: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W12.00002: Growth Mechanism of Pumpkin-Shaped Vaterite Hierarchical Structures Guobin Ma, Yifei Xu, Mu Wang CaCO$_3$-based biominerals possess sophisticated hierarchical structures and promising mechanical properties. Recent researches imply that vaterite may play an important role in formation of CaCO$_3$-based biominerals. However, as a less common polymorph of CaCO$_3$, the growth mechanism of vaterite remains not very clear. Here we report the growth of a pumpkin-shaped vaterite hierarchical structure with a six-fold symmetrical axis and lamellar microstructure. We demonstrate that the growth is controlled by supersaturation and the intrinsic crystallographic anisotropy of vaterite. For the scenario of high supersaturation, the nucleation rate is higher than the lateral extension rate, favoring the ``double-leaf'' spherulitic growth. Meanwhile, nucleation occurs preferentially in $<11\bar{2}0>$\ as determined by the crystalline structure of vaterite, modulating the grown products with a hexagonal symmetry. The results are beneficial for an in-depth understanding of the biomineralization of CaCO$_3$. The growth mechanism may also be applicable to interpret the formation of similar hierarchical structures of other materials. [Preview Abstract] |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W12.00003: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W12.00004: Athermal fading of luminescence in Al2O3 ceramic substrates Ian Terry, Eftychia Kouroukla, Ian K. Bailiff Retrospective dosimetry aims to reconstruct ionising radiation dose to populations following a radiological incident using materials not designed for that purpose. Sintered alumina ceramic can function as a dosimeter with its luminescence properties and related trapped charge storage mechanism. Its widespread use as a substrate in surface mount devices and incorporation in devices such as mobile phones make it a ubiquitous potential dosimeter. We investigated the optically (OSL) and thermally (TL) stimulated luminescence properties of sintered alumina substrates. In contrast to their single crystal analogue developed for personal dosimetry, Al$_2$O$_3$:C, the substrates exhibit a significant loss of trapped charge (fading) within hours following irradiation at RT that seriously limits their utility for dosimetry over an extended timescale. The fading rates of OSL and TL signals of 0402 resistors were analysed under various storage conditions (time and temperature), complemented by a study of their microstructure. The results support a model of athermal loss of trapped charge due to electron tunnelling from trapping states; this contrasting behaviour is attributed to a physical modification of the trap environment arising from the manufacturing process. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W12.00005: Ion Channeling study of Jahn-Teller lattice distortions and the phonon properties in magnetic transition element implanted SrTiO$_{3}$ Crystals Kalyan Sasmal, D. Wijesundera, Y. He, B. Tilakaratne, Q. Chen, J.H. Miller, Wei-Kan Chu SrTiO$_{3}$ is perovskite functional material. STO doped with magnetic transition element (Cr, Fe etc.) is important for electro- and magneto-optical applications. Cr$^{4+}$ (d$^{2})$, Cr$^{5+}$(d$^{1})$ and Fe$^{4+}$ (high-spin d$^{4})$ substituting host Ti$^{4+}$ exhibits Jahn-Teller distortion. Rutherford backscattering spectrometry (RBS) in ion channeling orientation is sensitive method for determining structure, position of impurity atom to study defects of crystals and provides direct evidence for JT effect at Cr$^{4+}$,Cr$^{5+}$ and Fe$^{4+}$ centers in STO lattice. Different masses of STO elements helps to investigate such impurities using ICh method by determining distortions of sub lattices without taking into account of small ICh effect from impurities. Axial ion channeling of 2.0 MeV He$^{+}$ ions was applied to study JT lattice distortions of ion implanted STO crystals. Angular ICh spectra of Sr and Ti sub lattices (crystal axes [110] {\&} [100]) were obtained for pure and ion implanted STO crystals. The ratio of minima of ICh yield for Sr and Ti sub lattices was used for quantitative determination of lattice distortions observed in STO: Cr/Fe crystals due to presence of impurities. JT Cr$^{4+}$ and Fe$^{4+}$ impurity could induce Raman-active localized oxygen vibrational mode, which does not involve motion of nearest Fe or Ti ions. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W12.00006: Rapid Microwave Synthesis of Perovskite Oxide Nanostructures with Enhanced Functionality Gregory Salazar, Anuja Datta, Pritish Mukherjee Perovskite oxides are an important class of materials having high dielectric and piezoelectric coefficients, switchable ferroelectric (FE) polarization and interesting optical and electrical properties. Realization of functional devices based on classic perovskite oxides such as Pb(Zr$_{\mathrm{0.52}}$Ti$_{\mathrm{0.48}})$O$_{\mathrm{3}}$ (PZT), and emerging Pb-free noncentrosymmetric (NCS) oxides, such as, ZnSnO$_{\mathrm{3,\thinspace }}$ZnTiO$_{\mathrm{3}}$ and CaTiO$_{\mathrm{3}}$ have reinforced the investigation of these materials in multiple dimensions and length scales. However, large-scale synthesis and integration of ordered low-dimensional structures is a challenge, due to their complicated methodologies, high-cost and difficulties with phase stability. We discuss a generalized, cost-effective, rapid microwave synthesis route for size and shape selective nanostructure growth of these functional perovskite oxides on industrially viable flexible and hard substrates, stabilized by an enhanced ionic covalence. The rational synthesis approach allowed improved tunability of the size, shape, and orientation of the structures with improved electrical and FE properties. The facile fabrication route of these nanostructures may expand the outreach of probes for understanding the structure-property relationships in these hitherto unexplored and technologically important materials. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W12.00007: Possible Phase Transition in H$_{2}$O Ice Ih near 110 K David T. W. Buckingham, Sueli H. Masunaga, Forrest C. Gile, John J. Neumeier The thermal expansion of single-crystalline H$_{2}$O ice Ih was measured with $\sim$$10^{4}$ times greater relative resolution than has previously been done. Plots of the thermal expansion coefficient, \textit{$\mu$}, along the a- and c-axes reveal features which have \textit{never before been observed} in thermal expansion measurements of H$_{2}$O ice: \begin{itemize} \item A jump in $\mu$ of magnitude $\Delta$\textit{$\mu$} $\approx$ $10^{-5}$ $K^{-1}$ in the temperature range 98--117 K along the c-axis, which appears to be a phase transition. No such transition is observed along the a-axis. \item Hysteresis of the transition temperature, \textit{T$_{c}$}, of as much as 5 K for cooling rates from -5.0 to -0.1 K/min. \end{itemize} There is reason to believe this transition is the ferroelectric transition reported by Dengel et al.\footnote{Dengel et al., \textit{Physics Letters}, \textbf{9}, pp. 291-292, 1964.} If so, the shift in \textit{T$_{c}$} would result from the freezing-in of the H$_{2}$O molecular configurations. We will discuss our own measurements of the dielectric constant in the vicinity of \textit{T$_{c}$}. [Preview Abstract] |
(Author Not Attending)
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W12.00008: Raman and Luminescence Investigation of Rare Earth Doped Laser-Induced Crystals-in-Glass Brian Knorr, Adam Stone, Himanshu Jain, Volkmar Dierolf Laser induced crystallization of glasses is a highly spatially selective process which has the potential to produce compact, integrated optics within a glass matrix. In LaBGeO$_5$ low temperature Combined Excitation Emission Spectroscopy (CEES) revealed that erbium incorporates into both glass-ceramics and laser-induced crystals-in-glass in predominantly one type of environment (site). The energy levels of this site were quantified. The fluorescence characteristics of the erbium ions in any site in the laser-induced crystals were found to be only weakly influenced by the irradiation conditions during growth. On the other hand, a hidden parameter, potentially boron deficiency-related defects, resulted in a significant change in the incorporation behavior of the erbium ions. Scanning confocal Raman and fluorescence spectroscopy showed that the energies of the Raman modes are shifted and the erbium fluorescence intensity is inhomgeneously distributed, despite the host glass being homogeneously doped, across the cross-sections of laser-induced crystals in glass. These fluctuations within the Raman and fluorescence are spatially correlated, implying that different erbium sites form preferentially at different locations in the crystal cross-section. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W12.00009: Brillouin light scattering as a probe for low frequency quasiparticles in solids Nikita Klimovich, Kevin Olsson, Kyongmo An, Sean Sullivan, Annie Weathers, Li Shi, Xiaoqin Li In increasingly small electronic and spintronic devices, electrons, optical phonons, acoustic phonons, and magnons are often driven out of local thermal equilibrium. Thermal transport based on equilibrium dynamics does not adequately describe these systems necessitating a better understanding of non-equilibrium transport processes. Measuring the specific temperatures of the different energy carriers is therefore crucial in understanding the thermal transport. Brillouin light scattering (BLS) has recently been explored as a temperature sensor for low frequency acoustic phonons in glass, and also magnons in metallic and insulating ferromagnetic materials. We report the measured BLS spectra of acoustic phonons in Silicon at different temperatures. The temperature dependence of the BLS peak frequency, linewidth, and integrated intensity are examined to evaluate their potential uses as temperature sensors of acoustic phonons. We also observe a large nonequilibrium in phonon-magnon temperature in YIG under the effects of laser heating and thereby extract a value for the phonon-magnon coupling coefficient. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W12.00010: Model for Charge Injection with Electron Beams into Highly Disordered Insulating Materials John Dennison, Alec Sim, Greg Wilson The Walden-Wintle model for charge injection and transport through highly disordered insulating materials has been extended to include charge injection with a charged particle beam. The original model is applicable to charge injection in a dielectric material from a pair of electrodes in a parallel-plate geometry. It provides a versatile approach to predict the time-dependent current at a rear grounded electrode and the incident surface voltage, as the injection current density evolves over time with the development of a space charge barrier near the injection electrode. The Walden-Wintle model has been applied to many standard cases including Fowler-Nordheim injection, Schottky injection, space charge limited injection, and various tunneling mechanisms. The present model modifies the approach to include electrode-less charge injection via a charged particle beam, along with concomitant effects for the injection current, surface voltage, and electron emission as a charge is built up in the insulator. The approach is equally valid for near-surface injection and for bulk injection of both non-penetrating and penetrating radiation. The results are based on our dynamic emission model for electron emission yields dependent on accumulating charge in both the positive and negative charging regimes. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W12.00011: Plasmon Polariton Modes in High Index Dielectric Structures Kodiak Murphy, Kyle Hoke, Brad Johnson, Janelle Leger The need to interface optical signals with high density electronic devices has led to an interest in subwavelength waveguides. Surface plasmon polaritons (SPPs) are surface charge density oscillations localized to a metal/dielectric interface, and as such are capable of confining energy in a structure which is not diffraction limited. Waveguides based on the excitation of SPPs are promising for short-range application, but in these structures Ohmic damping limits propagation length due to the bulk of the electric field propagating along a metal interface. Here we show that by selecting a core dielectric with a higher refractive index than the substrate, high index dielectric plasmon polariton modes (HID-PPMs) can be supported. Modes in the core dielectric exhibit electric fields with the bulk of their electric field confined in the dielectric layer. Therefore, damping may be reduced in such structures. Here we report the demonstration of HID-PPMs in Au/TiO2/Au MIM devices using attenuated total reflectance. Characterization of these modes was performed for devices of differing core dielectric thickness. Results are in good agreement with theory. We will discuss the application of these waveguides to several technologies related to solar energy conversion. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W12.00012: Optical and vibrational properties of YBO$_{3}$:Eu$^{3+}$, Ce$^{3+}$, Tb$^{3+}$ microstructures for light emitting diodes Sandeep Sohal, Mohammad Nazari, X. Zhang, E. Hassan-Zadeh, V.V. Kuryatkov, J. Chaudhuri, L. Hope-Weeks, Juyang Huang, Mark Holtz Structural and optical properties of yttrium orthoborate YBO$_{3}$:Eu$^{3+}$, Ce$^{3+}$, Tb$^{3+}$ microstructures, focusing on the role of terbium concentration, are investigated by x-ray diffraction (XRD), photoluminescence (PL) $\sim$ 363.8 nm excitation wavelength, photoluminescence excitation (PLE) and Raman spectroscopies. For constant cerium and europium concentrations, the PL bands belong to Ce$^{3+}$ and Tb$^{3+}$ color centers are diminished with increasing concentration of Tb$^{3+}$. Simultaneously, the intensities of PLE bands related to both Ce$^{3+}$ and Tb$^{3+}$, for red emission from the Eu$^{3+}$, are increased. The results are consistent with a Ce$^{3+}\to $(Tb$^{3+})_{n}\to $Eu$^{3+}$ energy transfer scheme, where $n$ denotes a chain of terbium ions. Raman spectroscopy shows a systematic change, with Tb$^{3+}$ concentration, in the terminal oxygen bending mode of B$_{3}$O$_{9}$ ring structure related to the host lattice. The terminal oxygen atoms of the ring structure are coordinated to yttrium sites where dopant ions substitute. The structural changes are interpreted as variations in the local neighborhood of these sites in the YBO$_{3}$:Ce$^{3+}$,Tb$^{3+}$,Eu$^{3+}$ crystal structure. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W12.00013: Scintillation properties of polycrystalline La$_{\mathrm{x}}$Y$_{\mathrm{1-x}}$O$_{3}$ ceramic Sunil Sahi, Wei Chen, Rasool Kenarangui Scintillators are the material that absorbs the high-energy photons and emits visible photons. Scintillators are commonly used in radiation detector for security, medical imaging, industrial applications and high energy physics research. Two main types of scintillators are inorganic single crystals and organic (plastic or liquid) scintillators. Inorganic single crystals are expensive and difficult to grow in desire shape and size. Also, some efficient inorganic scintillator such as NaI and CsI are not environmental friendly. But on the other hand, organic scintillators have low density and hence poor energy resolution which limits their use in gamma spectroscopy. Polycrystalline ceramic can be a cost effective alternative to expensive inorganic single crystal scintillators. Here we have fabricated La$_{0.2}$Y$_{1.8}$O$_{3}$ ceramic scintillator and studied their luminescence and scintillation properties. Ceramic scintillators were fabricated by vacuum sintering of La$_{0.2}$Y$_{1.8}$O$_{3}$ nanoparticles at temperature below the melting point. La$_{0.2}$Y$_{1.8}$O$_{3}$ ceramic were characterized structurally using XRD and TEM. Photoluminescence and radioluminescence studies were done using UV and X-ray as an excitation source. We have used gamma isotopes with different energy to studies the scintillation properties of La$_{0.2}$Y$_{1.8}$O$_{3}$ scintillator. Preliminary studies of La$_{0.2}$Y$_{1.8}$O$_{3}$ scintillator shows promising result with energy resolution comparable to that of NaI and CsI. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W12.00014: Prediction of Silicon-Based Layered Structures for Optoelectronic Applications Wei Luo, Yanming Ma, Xingao Gong, Hongjun Xiang A method based on the particle swarm optimization (PSO) algorithm is presented to design quasi-two-dimensional (Q2D) materials. With this development, various single-layer and bi-layer materials in C, Si, Ge, Sn, and Pb were predicted. A new Si bi-layer structure is found to have a much-favored energy than the previously widely accepted configuration. Both single-layer and bi-layer Si materials have small band gaps, limiting their usages in optoelectronic applications. Hydrogenation has therefore been used to tune the electronic and optical properties of Si layers. We discover two hydrogenated materials of layered Si$_{8}$H$_{2}$ and Si$_{6}$H$_{2}$ possessing quasi-direct band gaps of 0.75 eV and 1.59 eV, respectively. Their potential applications for light emitting diode and photovoltaics are proposed and discussed. Our study opened up the possibility of hydrogenated Si layered materials as next-generation optoelectronic devices. [Preview Abstract] |
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