Bulletin of the American Physical Society
87th annual meeting of the Southeastern Section of the APS
Volume 65, Number 19
Thursday–Friday, November 5–6, 2020; Virtual
Session F03: Condensed Matter and Materials Physics |
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Chair: Peizhi Mai, University of TN |
Friday, November 6, 2020 11:00AM - 11:12AM |
F03.00001: Carbon Nanotube Aerogels with High Porosity and Electrical Conductivity Angelo Porcu, Luis D. Rivas, Anamaris Meléndez, Idalia Ramos, Mohammad Islam, Arjun Yodh Carbon aerogels are promising materials for energy applications. Freestanding aerogels were created from co-gels of single-wall carbon nanotubes (SWCNT) and the conducting polymer poly(3,4-ethylenedioxythiophene)--poly(styrene sulfonate) (PEDOT:PSS). We tested several ratios of SWCNT/PEDOT:PSS to produce samples with the optimum combination of mechanical and electrical properties. The aerogels are light-weight, mechanically robust, and recover their original shape after deformation. High resolution scanning microscopy analysis shows their high porosity, filamentous structure, and the distribution of the polymer around the SWCNT. We analyzed the electrical properties of the gels using four-point I-V measurements and got high conductivities of over 100 S/cm. We will also present results of the fabrication of these co-gels in the shape of fibers. [Preview Abstract] |
Friday, November 6, 2020 11:12AM - 11:24AM |
F03.00002: Stoichiometry-Dependence of Electronic Properties in LaVO$_{\mathrm{3}}$ Thin Films Biwen Zhang, Yan Xin, Jade Holleman, Stephen McGill, Christianne Beekman LaVO$_{\mathrm{3}}$ (LVO) has been proposed as a promising material for photovoltaics because its strongly correlated 3d electrons can facilitate creation of multiple electron-hole pairs per incoming photon, which would lead to increased device efficiency. Our group grows thin films of LVO on SrTiO$_{\mathrm{3}}$ substrates using pulsed laser deposition. We control the La:V ratio of the films from \textasciitilde 60:40 to \textasciitilde 40:60 by adjusting laser fluences. We find that while V-rich films show behaviors that are similar to bulk LVO, films that are La-rich show remarkable differences in optical measurements, and more rich temperature dependent transport behaviors, which indicates the presence of electronic phase separation. This study allows us to better understand the complex physical properties of strongly correlated insulators paving the way for their use as absorbers in high performance photovoltaics. [Preview Abstract] |
Friday, November 6, 2020 11:24AM - 11:36AM |
F03.00003: Simulating Ion Trajectories at Surfaces Patrick Johnson, Chad Sosolik Low and Hyperthermal energy ion scattering can be a powerful probe of surfaces, provided the trajectories and the physics that govern them are modeled effectively. Such analysis requires predictive simulations to determine where on the surface the scattering events occurred. These simulations generally use molecular dynamics, which is a computationally expensive process. Here we will present a simulation which replicates predictive spectra of Low and Hyperthermal energy ion scattering, using molecular dynamics with constraints to reduce the required computation time. [Preview Abstract] |
Friday, November 6, 2020 11:36AM - 11:48AM |
F03.00004: The angular dependence of point defects in Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$, and how their roadmaps are used to determine the type of impurities Claudie Nardone, Suman Bhandari, Mary Ellen Zvanut One of the most significant new semiconductors for high power electronics is Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$, but the success of devices depends on the type and amount of impurities incorporated during growth. In this work, electron paramagnetic resonance (EPR) is used to investigate the presence of two common impurities, Fe$^{\mathrm{3+}}$ and Cr$^{\mathrm{3+}}$. Although the technique is ideal for detecting transition metals, the Fe and Cr signals in Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ can easily be confused due to the complexity of the crystal structure. To distinguish between the two, we have performed angle-dependent EPR measurement about three different crystal axes, and compared the results with known predictions for Fe$^{\mathrm{3+}}$ and Cr$^{\mathrm{3+}}$. Using a systematic approach for evaluating contributions for each we conclude that Fe$^{\mathrm{3+}}$, residing on both the octahedral and tetrahedral sites of Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$, dominates the bulk crystal, with little contribution from Cr$^{\mathrm{3+}}$. In addition, the angular rotation about the b-axis suggests the presence of second, minor, crystal rotated about 14$^{\mathrm{o\thinspace }}$about the b-axis. [Preview Abstract] |
Friday, November 6, 2020 11:48AM - 12:00PM |
F03.00005: Observing real time surface ligand exchange kinetics at the single nanocluster limit. Bobby Cox, Madhav Ghimire, Massimo Bertino, Joseph Reiner Thiolate ligand capped water-soluble metallic clusters have become a key nanomaterial with applications in medical imaging and diagnostics. These clusters are coated with a monolayer of thiolate ligands to stabilize, prevent aggregation, and functionalize the particle. It is often of interest to perform ligand exchange after initial preparation of the particles for either further functionalization or as a diagnostic tool. Direct observation and characterization of the kinetics of ligand exchange at the single cluster limit has previously been difficult to achieve in an experimental setting due to the small size of the clusters ($D_{c} =$ 2nm). Our group has now used resistive-pulse nanopore sensing to trap and monitor these clusters, and perform ligand exchange reactions on the trapped cluster while monitoring in real time. Once the cluster enters the pore and blocks the flow of ions through the pore, the ensuing current blockade confirms capture, and free ligands are allowed to access the cluster as it resides in the pore while we monitor the exchange reaction. Here we report our observation of rapid exchange on the order of seconds within the nanoconfined pore region, show that our results match calculated free energy profiles, and extend this to a proof of concept peptide sensor. [Preview Abstract] |
Friday, November 6, 2020 12:00PM - 12:12PM |
F03.00006: Cherenkov Excitation of Waveguide Modes in the Electron Microscope David Kordahl The classical physics of the Cherenkov effect is well-known, whereby charged particles traveling faster than the speed of light in a material radiate energy in an electromagnetic shock wave. Such effects can be observed using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS). But while Cherenkov energy losses for charged particles are traditionally derived for bulk samples (leading to the Frank-Tamm formula), one can also derive expressions for particle energy loss in dielectric geometries where the electron beam runs parallel to defined surfaces. For dielectric slabs, well-established loss models imply that transverse electric (TE) and transverse magnetic (TM) modes may be directly imaged using STEM-EELS. Likewise, recent experimental measurements of dielectric modes in silicon discs may be interpreted in terms of waveguide modes of a dielectric cylinder. A quantized model for STEM-EELS measurements of a dielectric cylinder reveals which waveguide modes may be excited, and which modes contribute most strongly to spectral maps. [Preview Abstract] |
Friday, November 6, 2020 12:12PM - 12:24PM |
F03.00007: Investigation of Ball Milling Assisted Liquid-Phase Exfoliation of WS$_{\mathrm{2}}$ Crystals Arjun Dahal With high surface area and exotic electronic properties, WS$_{\mathrm{2}}$ nanosheets are potentially useful for sensing, catalysis, and energy storage applications. The cost-effective and large-scale production of WS$_{\mathrm{2}}$ nanosheets is a fundamentally important step for its incorporation in future applications. The liquid phase exfoliation of WS$_{\mathrm{2}}$ nanosheets from its bulk counterpart using high-intensity ultrasound waves has proven to be a suitable method to produce a high yield of nanosheets. Here, we show that WS$_{\mathrm{2}}$ nanosheets' yield can be significantly increased if WS$_{\mathrm{2}}$ crystal is ball-milled prior to the ultrasonication in isopropyl alcohol. We find that the ball milling assisted sonication increases nanosheets' yield by 50{\%} compared to if the bulk crystal is solely ball milled or sonicated. The optical characterization shows the high quality of WS$_{\mathrm{2}}$ nanosheets with the yield as high as 6.4{\%}. We show that size selected nanosheets, prepared using repeated centrifugation and sedimentation method, are stable with no precipitation formation for more than two months. [Preview Abstract] |
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