Bulletin of the American Physical Society
16th Annual Meeting of the Northwest Section of the APS
Volume 60, Number 6
Thursday–Saturday, May 14–16, 2015; Pullman, Washington
Session B1: Condensed Matter Physics I |
Hide Abstracts |
Chair: Leah Bergman, University of Idaho Room: Smith Center for Undergraduate Education (CUE) 203 |
Friday, May 15, 2015 1:30PM - 2:00PM |
B1.00001: High-absorbance chalcogenide semiconductors Invited Speaker: Janet Tate If the absorption coefficient of a material exceeds 10$^{5}$ cm$^{-1}$, 95{\%} of the incident light is absorbed in 300 nm. Higher absorption enables thinner solar cells, which saves material and also reduces constraints on carrier mobility. Chalcogenide semiconductors such as CuSbS and CuTeS tetrahedrite and the metastable Sn$_{1-x}$Ca$_{x}$S alloy offer a route to such absorbers. The optical, structural and transport properties of these systems will be discussed. [Preview Abstract] |
Friday, May 15, 2015 2:00PM - 2:12PM |
B1.00002: Sb$_{x}$O$_{y}$ thin films using pulsed lased deposition James Haggerty, Bethany Mathews, Janet Tate We demonstrate synthesis of Sb$_{2}$O$_{3}$ and Sb$_{2}$O$_{4}$ thin films on heated glass, and fused SiO$_{2}$ slides in an oxygen atmosphere using pulsed laser deposition and ex-situ annealing in air. GW calculations with spin-orbit corrections predict that the band gap of Sb$_{2}$O$_{3}$ changes from 3.4 eV in the orthorhombic $\beta $-phase to 4.7 eV in the cubic $\alpha $-phase. Sb$_{2}$O$_{4}$ also forms two polymorphic structures, orthorhombic $\alpha $-Sb$_{2}$O$_{4}$, and monoclinic $\beta $-Sb$_{2}$O$_{4}$. Optical absorption and crystal structure are investigated using transmission/reflection spectroscopy and grazing incidence x-ray diffraction. Optical absorption measurements of $\alpha $-Sb$_{2}$O$_{4}$ show a band gap of 3.9 eV which is far from the DFT predicted band gap of 2.1 eV but agrees with previous measurements. Structural analysis shows that from an $\alpha $-Sb$_{2}$O$_{4}$ target, $\alpha $- Sb-$_{2}$O$_{4}$ thin films are formed at a temperature and pressure of 400 $^{\circ}$C and 3 mTorr. Deposition at higher pressures (6 and 12 mTorr) produces amorphous films that, when annealed at 500 $^{\circ}$C become a mixture of $\alpha $-Sb$_{2}$O$_{4}$ and an additional cubic phase of Sb$_{2}$O$_{4}$. [Preview Abstract] |
Friday, May 15, 2015 2:12PM - 2:24PM |
B1.00003: Spectral analysis of resonant X-ray scattering for quantitative measurement of ordering in organic matter Brian Collins The nano-to-mesoscale structure of carbon-based materials is of interest in diverse fields such as organic electronics, directed nanostructures, biomimetic materials, and even biological tissues. However, measurement of such structure is particularly difficult due to the materials' radiation sensitivity, low contrast with traditional probes, and low degree of crystallinity. Recent developments in resonant (or `anomalous') X-ray techniques utilizing unique electronic transitions in the molecules have demonstrated exquisite sensitivity to ordering in these materials. Due to the complex interactions involved in these measurements, however, results have been limited to qualitative interpretations. Here we demonstrate the extraction of quantitative information on the nano-to-mesoscale structure of organic thin films utilizing spectral analysis of resonant, polarized x-ray scattering experiments across an absorption edge. We demonstrate reciprocal space mapping techniques that minimize exposure, a proper yet simple scattering model beyond the Born Approximation, and analysis methods to separate multiple sources of scattering to achieve robust, quantitative measurement of molecular composition and conformation within domains and nanostructures. [Preview Abstract] |
Friday, May 15, 2015 2:24PM - 2:36PM |
B1.00004: Decoupling the Effects of Hydrophobicity and Confinement Within Nanoporous Materials Used for Water-Alcohol Separation Chun-Hung Wang, Aurora Clark The separation of water and alcohol within biofuel refinement has been studied extensively using nanoporous materials that include zeolites and metal-organic-frameworks (MOFs). The emerging theory for high selectivity of a material for alcohol over water is based upon the combined effects of hydrophobicity of the interior and the response of the water vs. alcohol to confinement inside the porous structure. However, to date, there has been little fundamental research that attempts to decouple the effects of these two very different properties (one chemical and one structural) upon the selectivity value. Toward this end, the solvent organization within zeolitic-imidazolate frameworks (ZIFs) will be discussed as a function of hydrophobicity/hydrophilicity of the interior, pore size/structure, and accessible volume/surface area. Using grand-canonical Monte Carlo (GCMC) and classical molecular dynamics (MD) simulations, the hydrogen-bond (H-bond) networks of water and alcohols adsorbed inside the material from the bulk liquid is investigated using network analysis algorithms. The topology of the H-bond networks has been quantified by use of the geodesic distribution (the shortest intermolecular interaction pathways between molecular vertices), and the adsorbate-adsorbate and adsorbate-adsorbent distributions of intermolecular interactions. The GCMC configurations have been used as starting points for subsequent MD simulations where the hydrophobicity is quantified based upon H-bond lifetimes and mechanisms of orientational dynamics of adsorbates. [Preview Abstract] |
Friday, May 15, 2015 2:36PM - 2:48PM |
B1.00005: Unusual thermal behavior in uranium dioxide Krzysztof Gofryk, Marcelo Jaime, David Andersson, Jason Lashley, Chris Stanek Since their discovery more than two hundred years ago, the actinides have defied efforts of solid-state physicists to understand their unusual properties. These materials are among the most complex of the long-lived elements, and, in the solid state they display some of the most unusual behaviors of any series on the Periodic Table. A perfect example is uranium dioxide (UO$_{2}$). It is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Although UO$_{2}$ is best known as an engineering material, its properties indicate rare interactions between charge, spin and lattice, reminiscent of emergent phenomena. In particular, it is unclear how different degrees of freedom and quasiparticle excitations interact and what is the relationship to the thermal behavior. We report our new experimental and theoretical studies on uranium dioxide single crystals. Our results indicate that strong spin-lattice coupling and resonant scattering are important for understanding the general thermal behavior in this material. We will discuss implications of these results. [Preview Abstract] |
Friday, May 15, 2015 2:48PM - 3:00PM |
B1.00006: ABSTRACT WITHDRAWN |
Friday, May 15, 2015 3:00PM - 3:30PM |
B1.00007: Break |
Friday, May 15, 2015 3:30PM - 4:00PM |
B1.00008: Phonon decay and anharmonicity in MgZnO alloys Invited Speaker: Jesse Huso Embedded structural domains in MgZnO film were studied via selective resonant Raman scattering at temperatures from ambient up to 870K. The resonant conditions provided by excitation with different ultraviolet laser lines enabled the detection of longitudinal optical (LO) phonons from structural domains with the wurtzite structure, and domains with the cubic rocksalt structure which, due to alloying, lack inversion symmetry. Phonon decay channels and anharmonicities in MgZnO were studied for both structural types and phonon behavior was modeled in terms of three- and four-phonon decay processes using Ridley and Klemens type decay processes. The wurtzite phase was found to display dominantly three-phonon decay with a small four-phonon component. In contrast, the cubic phase displays a higher degree of anharmonicity, in which the four-phonon processes also contribute significantly to the temperature dependent frequency shift. At the elevated temperature range, the LO frequency shift rate is measured to be -2.6x 10$^{-2}$ cm$^{-1}$/K for the wurtzite structure while that of the cubic structure exhibits a much larger temperature dependent shift of -1.6x10$^{-1}$ cm$^{-1}$/K. The larger anharmonicity of the domains with the cubic structure is discussed in terms of strain and deformation effects. We acknowledge the National Science Foundation under Grant No. DMR-1202532 for their support of this research.\\[4pt] In collaboration with Leah Bergman, Department of Physics, University of Idaho. [Preview Abstract] |
Friday, May 15, 2015 4:00PM - 4:12PM |
B1.00009: A Metastable Alloy (Sn$_{1-x}$Ca$_{x}$)S: Growth and Characterization Bethany Matthews, James Haggerty, Stephan Lany, Janet Tate Two sulfide systems with different crystal structures SnS (orthorhombic) and CaS (rocksalt) were deposited by pulsed laser deposition to form metastable alloys of varying composition (Sn$_{1-x}$Ca$_{x}$S). The film composition was controlled using separate SnS$_{2}$ and CaS targets: a) a layering technique using 2 different targets and b) using a single target of a mixture of the two systems and varying $T_{sub}$ to evaporate the more volatile cation Sn. The alloyed films' optical and structural properties were analyzed as a function of composition by optical spectroscopy and grazing incidence x-ray diffraction (GIXRD) respectively. Film stoichiometry was determined by electron probe microanalysis (EPMA). EPMA results indicated that, for Sn$_{1-x}$Ca$_{x}$S$_{y}$ layered films, the cation ratio was as expected, allowing for tuning of $x$; however, films were severely sulfur deficient. DFT calculations of the alloy predict a structural transition at $x $\textgreater 0.18; however, GIXRD indicates films are still predominantly orthorhombic for $x =$ 0.25. [Preview Abstract] |
Friday, May 15, 2015 4:12PM - 4:24PM |
B1.00010: Urbach Analysis of Band-Edge in ZnO and MgZnO Thin Films Amrah Canul, Jesse Huso, Dinesh Thapa, Leah Bergman ZnO has gained popularity as a material of choice for UV applications. It has a benign chemical nature, a deep excitonic energy level, and a direct bandgap of about 3.4 eV. The latter two properties make ZnO a highly efficient light-emitter at and above room temperature. Alloying ZnO with magnesium creates the MgxZn1-xO alloy system which can tune the bandgap by design and add new optical and electronic functionalities to ZnO. The goal of this study is to investigate the nature of defect states at the band-edge introduced by alloying in ZnO and Mg$_{0.07}$Zn$_{0.93}$O thin films. To investigate the band-edge dynamics, we study in-gap states via temperature dependent absorption spectroscopy in the range 150-500K. The in-gap states at the band-edge were analyzed via the Urbach Energy model, where the Urbach Energy is a measure of the extent of defect states in the bandgap. In parallel, we also analyze the absorption spectra via the Wasim model, which gives the interaction between defect states and phonons. The Wasim model of the Urbach Energy allows deconvolution of the relative contributions of static defect states and temperature dependent phonon modes to the in-gap states. It was found that the defect contribution to in-gap states at the band-edge was significantly higher for Mg$_{0.07}$Zn$_{0.93}$O than in ZnO. Additionally, the phonon contribution to in-gap states was also higher in Mg$_{0.07}$Zn$_{0.93}$O than in ZnO. These effects will be discussed in terms of the distortion of the periodicity in the Mg$_{0.07}$Zn$_{0.93}$O lattice. The authors gratefully acknowledge the National Science Foundation under grant No. DMR-1202532. [Preview Abstract] |
Friday, May 15, 2015 4:24PM - 4:36PM |
B1.00011: In$_{2}$Se$_{3}$ phase transitions at high pressure and high temperature Anya Rasmussen, Matthew McCluskey Indium selenide (In$_{2}$Se$_{3}$), a III-VI semiconductor and phase change material, has potential for use in phase change memory devices. Multiple crystalline phases of In$_{2}$Se$_{3}$ are stable or metastable under atmospheric conditions and transitions between the phases can be induced through either thermal or optical stimulations. However, large stresses on a phase change material in a memory device could affect the phase switching behavior of the material. Therefore, it is important to understand both the thermal and elastic properties of In$_{2}$Se$_{3}$ to achieve controlled switching between phases. We are studying the pressure-dependent structural properties of In$_{2}$Se$_{3}$ powders and nanocrystals using synchrotron x-ray diffraction and a diamond-anvil cell. In previous works we have reported on two pressure-induced phase transitions in In$_{2}$Se$_{3}$. The $\alpha $ to $\beta $ phase transition occurs at 0.7 GPa, an order of magnitude lower than critical pressures observed in other semiconductors. The size dependent $\gamma $ to $\beta $ phase transition occurs between 2.8 GPa and 3.2 GPa in bulk powder samples and at slightly higher pressures, between 3.2 GPa and 3.7 GPa., in nanowire samples. Now we report our preliminary findings on how pressure affects the thermal phase transitions of In$_{2}$Se$_{3}$. A diamond anvil cell outfitted with an external heater was used to observe phase transitions in In$_{2}$Se$_{3}$ samples under high pressure and high temperature conditions. [Preview Abstract] |
Friday, May 15, 2015 4:36PM - 4:48PM |
B1.00012: Discovery of a New Memory switching Mechanism in Phase-Change Nanowires Elham Mafi In phase-change memory, the structure-property relation is critical to understanding and controlling the memory switching process. Here we correlate the local electrical and structural properties of phase-change In$_{2}$Se$_{3}$ nanowires, by performing high-resolution transmission electron microscopy and scanning Kelvin probe microscopy on the same nanowires. This approach reveals a direct correlation between a presence of dislocations and a high local electrical resistance in nanowires subject to the RESET switching (i.e. switching from low to high electrical resistance state). This correlation indicates that the RESET switching, commonly understood as the amorphization process, can occur entirely via the generation of dislocations at temperatures much below the melting point. From a fundamental perspective, this discovery provides new insight into the critical structure-property relation in phase-change materials and the important role of dislocations. Practically, since the RESET switching is commonly considered as the most energy-consuming process that requires heating above the melting point, our findings suggest that a more energy-efficient phase-change memory can be realized based on In$_{2}$Se$_{3}$. [Preview Abstract] |
Friday, May 15, 2015 4:48PM - 5:00PM |
B1.00013: Scanning Confocal Microscopy Using CCD and Image Processing Xianjun Ye, Matthew McCluskey Confocal microscopy has been a powerful imaging technique in both biomedical research and industrial metrology application for decades. In conventional confocal microscopy, a pinhole and photomultiplier tube (PMT) combination is used as the standard detection scheme. The pinhole is placed at image plane in front of the detector to block out-of-focus light, which dramatically improves optical resolution and contrast at selected depth. PMT's fast response time and large dynamic range make it the preferred choice as light detector, especially in fluorescence imaging mode. In this work, we propose a detection scheme using CCD camera to replace the pinhole and PMT combination in reflectance mode. This approach not only reduces the complexity and cost of the system, but also provides extra information about the sample which can be extracted through image processing to improve the resolution. Proof-of-concept experiments are run on a mirror surface and a microchip housing. The reconstructed 3D images not only show the surface topography, but also reveal the inclination of the surface with respect to the optical axis of the microscope. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700