Bulletin of the American Physical Society
19th Annual Meeting of the APS Northwest Section
Volume 63, Number 6
Thursday–Saturday, May 31–June 2 2018; Tacoma, Washington
Session B2: Condensed Matter I |
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Chair: Janelle Leger, Western Washington University Room: Thompson Hall 193 |
Friday, June 1, 2018 1:30PM - 2:00PM |
B2.00001: The diverse properties of two-dimensional topological semimetal WTe$_{\mathrm{2}}$ Invited Speaker: David Cobden Semimetals have recently received renewed attention as hosts of topological band structure features such as Dirac and Weyl points. Many have van der Waals layered structures and can readily be exfoliated. In the case of WTe$_{\mathrm{2}}$ we have found a surprising range of phenomena in monolayer and few-layer samples. The edges of a monolayer conduct electricity in a manner consistent with the existence of protected helical boundary modes on a 2D topological insulator, while the internal conductivity ranges between insulating, metallic and superconducting behavior as a function of temperature and gate voltage. Signs of a Fermi surface persist down to the level of a bilayer. Finally, two- or three-layer WTe$_{\mathrm{2}}$ is spontaneously polarized in the stacking direction and can switched by an external electric field, that is, it is ferrolectric. We speculate that electron-hole correlations connect all these phenomena. [Preview Abstract] |
Friday, June 1, 2018 2:00PM - 2:12PM |
B2.00002: Conformational Impact on Amino Acid-Surface $\pi $-$\pi $ Interactions on a (7,7) Single-Walled Carbon Nanotube: A Molecular Mechanics Approach Linda Grabill, Andreas Riemann A study of $\pi $-$\pi $ interactions between a (7,7) single-walled carbon nanotube (SWNT) and three different aromatic amino acids (AAA), namely L-tyrosine (Tyr), Ltryptophan (Trp), and L-phenylalanine (Phe) was conducted with a molecular mechanics (MM) approach. For each of the amino acids we investigated the behavior of six different conformers. We examined the impact of the so-called edge effects by testing the parameters of the built-in switching function in MM. We found the optimal SWNT length to be approximately 80 angstroms for the size of the molecules in our conformational studies. The positional effect of electron withdrawing groups with respect to the aromatic tail was studied to understand the influence of this interaction specific to adsorption strength and geometry. We decomposed the aromatic amino acid$-$surface interactions into three components: overall energy, aromatic ring, and amino acid head adsorption energies. We found that the ability of the amino acid's head to interact with the surface $\pi $-densities had a greater impact on the overall energy than the amino acid head interaction with its substituent's aromatic ring's $\pi $-electrons. [Preview Abstract] |
Friday, June 1, 2018 2:12PM - 2:24PM |
B2.00003: Thermal boundary resistance between carbon nanotube bundle and silicon Mohamed Osman, Taejin Kim Heat transfer between different materials is strongly affected by the discontinuity in the atom arrangement at the interface which influences the propagation of phonons responsible for heat flow across the interface. Molecular dynamics simulations has been used to investigate the thermal boundary resistance (TBR) between a bundle of (5,5) nanotubes and surrounding silicon. The thermal boundary resistances from MD simulations at 100K and 300K, were 7.1x10$^{\mathrm{-9}}$ m$^{\mathrm{2}}$K/W and 4x10$^{\mathrm{-9}}$ m$^{\mathrm{2}}$K/W respectively. The decrease in TBR at 300K compared to 100K is due to increased phonon population. However, the TBR value at 300K is four times larger than the results reported in [1]. The difference can attributed to the fact that in our simulated structure, heat flow is in the radial direction and the bonding between Si and C atoms at the interface changes the carbon nanotube sp$^{\mathrm{2}}$ bonding to sp$^{\mathrm{3}}$ bonding, where as in [1] heat flow is axial and the bonding at the CNT open end does not affect the sp$^{\mathrm{2}}$ bonding significantly. \\ \\$[1]$ Y. Feng, J. Zhu, and D. Tang, \textbf{AIP Advances}, \textbf{4}, 127118 (2014). [Preview Abstract] |
Friday, June 1, 2018 2:24PM - 2:36PM |
B2.00004: Magnetic Resonance in an Iron Oxide Nanaoparticle Suspension at RF and Microwave Frequencies Jake Bobowski, Jacqueline Dubreuil We measured the complex permeability of an iron oxide nanoparticle suspension at RF/microwave frequencies in zero-field and in static magnetic fields up to 50 mT. The measurements were made using a toroidal loop-gap resonator that can be modelled as an LRC circuit. With the bore of the resonator partially filled with the nanosuspension, the change in resonant frequency and quality factor were used to determine the real and imaginary parts of the suspension's permeability. By filling the gap of the resonator with various low-loss dielectrics, we were able to make these measurements over a frequency range that spanned 600 to 1300 MHz. The zero-field measurements, surprisingly, suggest a weak diamagnetic response that is suppressed as frequency is lowered. As the static magnetic field was scanned, the real part of the permeability increased sharply and then saturated above a frequency-dependent critical field. At this same critical field, the imaginary part of the permeability exhibited a peak. The value of the critical static magnetic field was found to be proportional to the frequency of the applied RF/microwave fields. [Preview Abstract] |
Friday, June 1, 2018 2:36PM - 2:48PM |
B2.00005: Enhanced magnetization of Magnetite Nanoparticles at High- Temperature. Lokendra Khanal, Mostafa Ahmadzadeh, John McCloy, You Qiang Magnetic nanoparticles (MNPs) have been used promisingly since decades in environmental, and biomedical applications. Recently, iron-based MNPs have been discovered as a potential nanomaterial for nuclear radiation sensing and monitoring system as well. Studies have shown that the superparamagnetic behavior of the magnetite nanoparticles (NPs) becomes ferromagnetic under irradiation at room temperature, which is accompanied by the particles size growth and microstructural evolution. In this work, to simulate the high-temperature core (\textasciitilde 500 $^{\mathrm{0}}$C) of the nuclear reactor, the magnetite NPs synthesized by using magnetron sputtering techniques were heat treated up to 800 $^{\mathrm{0}}$C. The NPs are then characterized by using vibrating sample magnetometer, scanning electron microscope and X-ray diffraction in order to understand the property-structure relationships and microstructural evolution at the elevated temperature. The results have shown interesting results with the enhanced magnetization of the NPs due to increase in size caused by the agglomeration of the particles at high-temperature. The results we have obtained, and the evolution mechanism will be discussed during this presentation. [Preview Abstract] |
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