Bulletin of the American Physical Society
85th Annual Meeting of the APS Southeastern Section
Volume 63, Number 19
Thursday–Saturday, November 8–10, 2018; Holiday Inn at World’s Fair Park, Knoxville, Tennessee
Session D03: Condensed Matter II |
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Chair: Paolo Vilmercati, University of Tennessee, Knoxville Room: Holiday Inn Knoxville Downtown LeConte |
Thursday, November 8, 2018 4:30PM - 4:42PM |
D03.00001: Low Frequency Neutron Spectroscopy of Organic Molecular Solids and Parallel First-Principles Calculations Ada Sedova, Anup Pandey Vibrational contributions are essential to thermodynamic properties of materials. We present spectra of organic molecular crystals and polymorphs using the next-generation, high-signal VISION spectrometer in the far-infrared (FIR) and mid-infrared (MIR) range. Different spectral signatures were found for polymorphic forms, and numerous modes undetectable with optical methods are observed. In addition to correct calculation of peak positions, highly accurate line-shape features are reproducible by simulation using solid-state density functional theory (DFT) vibrational calculations on OLCF resources. High confidence spectral assignments and thermodynamic information are thus obtainable, and new benchmarks for DFT calculations are provided. Detection of soft modes provides information for theoretical exploration of phase transitions based on experiment. |
Thursday, November 8, 2018 4:42PM - 4:54PM |
D03.00002: Lattice dynamics and local structure in AMg2Sb2 thermoelectric Zintl phases Raphael Hermann, Junjie Zhang, Wanuye Peng, Douglas Abernathy, Alexandra Zevalkink The layered compounds AMg2Sb2 are interesting Zintl phases with a rather simple trigonal structure that hosts only five atoms per unit cell. An outstanding thermoelectric figure of merit of zT~1.5 was reported for n-type Mg3Sb2. This performance can be ascribed to multi-valley conduction but also to its low thermal conductivity and anomalous lattice dynamics. To understand the relation between structure and functionality, we have studied phonons in Mg3Sb2 and Mg3Bi2 by inelastic neutron scattering, which reveals sharp modes that contrast with the low thermal conductivity. Complementary 121Sb Mössbauer spectroscopy yields precise Sb thermal factors. A lattice hardening is observed as the mass of A increases in the series A=Mg, Ca, Sr. In parallel, the local environment of Sb distorts, as revealed by the electric field gradient. We will discuss our results in relation with phonon calculations and elastic constants measurements by resonant ultrasound spectroscopy. |
Thursday, November 8, 2018 4:54PM - 5:06PM |
D03.00003: The interaction of carbon and boron nitride nanotubes as well as graphene with metals Christoph Rohmann, Michael P. Zwolak The interaction of carbon and boron nitride nanotubes as well as graphene with metals is significant for a wide variety of applications. For example, the binding of tubes to transition metal nanoparticles plays a role in their catalytic growth, as well as in their nucleation. Similarly, the strength of nanotube-metal composites crucially depends on the interaction strength between the tube and the metal matrix. While metal doped graphene is also of interest in the field of catalysis, it is of major interest in spintronics due to the controllable spin transport and its perfect spin filtering. We performed quantum chemical calculations to investigate the binding strength and geometry of a variety of metals with graphene, carbon and boron nitride nanotubes. We examined both binding by individual metal atoms and the interaction with metallic surfaces. |
Thursday, November 8, 2018 5:06PM - 5:18PM |
D03.00004: 3D Anti-Brownian ELectrokinetic (ABEL) trap for studies on nanoparticles and biomolecules Kapila D. Dissanayaka, Brian K. Canfield, Lloyd M. Davis A three-dimensional ABEL trap with fast feedback cycle of 13.5 μs was developed for confocal microscopy studies on fluorescent nanoscale objects in aqueous solution. The trap contains a microfluidic cross-channel made by bonding two glass coverslips having 25 μm thick PDMS layers with tapered channels. The geometry was designed using COMSOL to enable four ±10 V potentials to drive the fluid via electroosmosis in any direction at a speed sufficient to counteract Brownian diffusion. Four laser beams are focused in the middle of the crossed channels to ~0.5 μm by a 1.2 NA objective. The foci partially overlap but are slightly offset in a tetrahedral pattern. When a molecule diffuses into the foci, fluorescence is excited by 304 MHz interleaved pulses in the four beams and collected onto two single-photon avalanche diodes to feed an FPGA circuit, which performs time-gated photon counting and applies an algorithm to adjust the voltages to trap the molecule. Results show trapping of 40 nm FluoSpheres—for a remarkable time of ~5 minutes—as well as 20 nm FluoSpheres and even single molecules of Streptavidin-Alexa 647. The 3D design avoids collisions of the trapped molecule with glass surfaces and sticking, which have limited previous biophysical studies using 1D and 2D ABEL traps. |
Thursday, November 8, 2018 5:18PM - 5:30PM |
D03.00005: Helically Coiled Carbon Nanotubes as Supercapacitor Electrodes Anthony Childress, Kevin Ferri, Apparao M Rao Despite their low specific surface area (<500 m2 g-1) relative to that of activated carbon (1500-2000 m2 g-1), carbon nanotubes are attractive as effective electrode materials for supercapacitors due to their excellent electrical and mechanical properties. Electrodes comprised of arrays of helically coiled carbon nanotubes (HCNTs) and multi-wall carbon nanotubes (MWCNTs) were prepared and evaluated as novel electrode materials for electric double layer capacitors (EDLCs). While both types of electrodes exhibited a linear dependence on array height and a diffusion limited behavior below the 1 V s-1 scan rate, the electrodes comprised of HCNT arrays exhibited a better performance. Freestanding HCNT and MWCNT buckypapers were also prepared and used as electrodes, and the former showed a higher energy density relative to the latter with no loss in its power density and capacity fade. Collectively, this study concludes that HCNTs are well suited as binder-free electrodes that can be augmented with electroactive polymers for improved EDLC performance. |
Thursday, November 8, 2018 5:30PM - 5:42PM |
D03.00006: Fracture mechanics based on deformation wave theory and its verification with optical interferometry Shun Ashina, Dmytro Obolenskyi, Sanichiro Yoshida, Tomohiro Sasaki The goal of this research is to test a theory of deformation and fracture (the field theory) we develop via experiment using the optical technique known as Electronic Speckle Pattern Interferometry (ESPI). The field theory formulates all stages of deformation and fracture on the same theoretical basis. According to this theory, the plastic deformation is represented by an elastoplastic wave. Under a certain condition (the fracturing condition), the elastoplastic wave loses its oscillatory feature, and consequently, the object fractures. ESPI can image the displacement field of an object under deformation in the form of a whole field image consisting of interferometric fringes. The fracturing condition can be found from a certain pattern of the interferometric fringes. In this study, we try to validate the fracturing condition via interferometric fringe analysis by applying a tensile load to the plate specimen. |
Thursday, November 8, 2018 5:42PM - 5:54PM |
D03.00007: Acoustic probing based on Gaussian ray tracing Kyohei Miyasaka, Emily Laprime, Sanichiro Yoshida, Tomohiro Sasaki Ultrasonic Testing is one of the most popular non-destructive inspection techniques. It uses acoustic transducer and receiver to find a defect inside the material. The technique usually utilizes a pulsed wave and identifies the defect based on the time-of-flight algorithm. Since it relies on the reflection, it cannot detect abnormality unless the reflection is sufficiently high. In contrast, our method introduces the concept of Gaussian beam propagation widely used in optics. A continuous ultrasonic wave is injected into the specimen and the transverse profile of the transmitted signal is analyzed in the amplitude and phase. The abnormality in the specimen is detected as the distortion in the transverse profiles. It is expected that our method is useful to applications where the conventional method is unable to identify the abnormality because the acoustic impedance is too close to the base material. |
Thursday, November 8, 2018 5:54PM - 6:06PM |
D03.00008: Evaluation of resonance characteristics of thin film specimen with improved opto-acoustic method Jongsung Kim, David Didle, Sanichiro Yoshida Opto-Acoustic method is a technique evaluating adhesion characteristics of the thin film using optics and acoustic. The test specimen is oscillated by an acoustic transducer and micro-displacement induced by the transducer is detected as a form of interference patterns with Michelson Morley interferometer. And then evaluate resonance characteristics of the thin film by analyzing the interference pattern with Fast Fourier Transform. In this study, we improved our previous optical configuration by better controlling the interferometric light beams. It helps reduce the wave-front curvature in the interference patterns and evaluate the whole thin film specimen. In addition, simulation based on finite element analysis was conducted. An eigenmode study was performed to find eigenfrequencies and mode shapes of a structure. By comparing simulation results and experimental results, we tried to ensure the reliability of Opto-Acoustic method. |
Thursday, November 8, 2018 6:06PM - 6:18PM |
D03.00009: "Striped" lanthanum cobaltite films: tracking oxygen vacancies formation, ordering, and transport through scanning electron microscopy and density functional theory Axiel Yael Birenbaum, Liang Qiao, Valentino R Cooper, Albina Borisevich Oxide-fuel solid cells are efficient at converting fuel to electricity and can function at very high temperatures. Since they rely on fast oxygen transport, it is crucial to understand the formation and transport of oxygen vacancies in candidate electrolytes. However, these properties are subtly dependent on the physics and electrochemistry of the target material. Oxygen-deficient lanthanum cobaltites are a family of perovskite-related materials known for their excellent oxygen transport. We employ a combination of density functional theory and scanning transmission electron microscopy to examine the energetics and dynamics of oxygen vacancy ordering in the (1 1 1) oriented LaCoO3-δ on SrTiO3. Specifically, we track the formation, spontaneous ordering, and transport of oxygen vacancies, and conclude on the effects of high index interfaces on oxygen transport properties. |
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