Bulletin of the American Physical Society
86th Annual Meeting of the APS Southeastern Section
Volume 64, Number 19
Thursday–Saturday, November 7–9, 2019; Wrightsville Beach, North Carolina
Session D01: Condensed Matter I |
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Chair: Weiwei Xie, Louisiana State University Room: Holiday Inn Resort Causeway/Masonboro |
Thursday, November 7, 2019 4:30PM - 4:42PM |
D01.00001: Observing real time ligand-induced structural changes at the single nanocluster limit. Joseph Reiner, Bobby Cox, Madhav Ghimire, Massimo Bertino Water-soluble metallic clusters are an important class of nanomaterial with applications in biosensing, diagnostic imaging and catalysis. These clusters require ligand molecules to stabilize their structure and prevent aggregation. It is not entirely clear what affect these ligands have on the cluster's structural kinetics and this has implications regarding cluster stability and reactivity. Direct observation of these fluctuations at the single cluster limit has been difficult to achieve because of the length scales involved ($D_{\mathrm{c}} \quad =$ 2nm). To overcome this limitation, our group has utilized resistive-pulse nanopore sensing to simultaneously trap and monitor structural fluctuations of thiolate-capped gold nanoclusters at the single particle limit. The technique is based on the Coulter-counting principle applied at the nanoscale. The nanocluster enters the pore and blocks the flow of ions through the pore giving rise to a current blockade. Fluctuations within each blockade correspond to ligand induced structural changes. Here we report our observations that show the structure fluctuations scale with the size of the ligand molecules and that by trapping the cluster in the pore, we can probe and monitor surface reactions (i.e. ligand exchange) at the single cluster limit. [Preview Abstract] |
Thursday, November 7, 2019 4:42PM - 4:54PM |
D01.00002: A Study of ZnO Thin Film Deposition Using a Modified Electrospray (MES) Technique David Hooks, Christopher O'Loughlin, Theda Daniels-Race Zinc Oxide (ZnO) is a semiconducting material (II-VI) with a wide bandgap (\textasciitilde 3.4 eV) and high electron mobility that exhibits excellent gas sensing and opto-electronic properties. Depositions of ZnO films typically involve complex chemical synthesis or extensive equipment for physical and chemical vapor deposition. The aforementioned may limit commercial or even laboratory accessibility for thin film and device applications. In this talk, we will discuss our use of a modified electrospray (MES) technique as a method of choice for the deposition of ZnO nanoparticles onto a silicon substrate. Electrospraying requires a syringe and needle, high-power voltage source, and a substrate atop a grounded collector plate. In our custom-designed MES system, we use tunable RPM control of 3-D printed collector plates. For sufficiently large applied voltages (kV range) at the needle tip, the electric field overcomes the surface tension of the ZnO solution and ejects it in the form of a Taylor cone incident to the grounded substrate. Key parameters affecting deposition quality include the distance between the needle tip and substrate, the applied voltage, and the rate at which the solution leaves the syringe. We will evaluate MES film quality with respect to thickness, coverage, and surface uniformity. Successful deposition of ZnO via this robust electrospray system would confirm its utility as alternative to more time and cost intensive methods. [Preview Abstract] |
Thursday, November 7, 2019 4:54PM - 5:06PM |
D01.00003: Study of Electrophoretic Deposition of ZnO Nanoparticles onto Silicon Substrates Fawwaz Hazzazi, Theda Daniels-Race The electrophoretic deposition of zinc oxide (ZnO) nanoscale thin films is important to a number of research areas including biosensors, photophilic dye-sensitized solar cells, optoelectronic devices, and thin film transistors. In this talk, we will discuss our use of size-controlled charged zinc oxide nanoparticle-based thin films, synthesized and grown at room temperature on various silicon substrates via electrophoretic deposition (EPD). Our experimentation plan includes the current-voltage characterization of ZnO/p-Si heterojunctions. We will discuss our results in reference to our hypothesis that the concentration of ZnO nanoparticles in the electrolytic solution is a primary factor in the attainment of the enhanced flatness of ZnO thin films necessary for device development. This work represents a potential opportunity for the integration of this method of deposition into applications where ZnO contributes to the reliability, affordability, and highly increased sensitivity needed for the next-generation of nanoscale devices and systems. [Preview Abstract] |
Thursday, November 7, 2019 5:06PM - 5:18PM |
D01.00004: The Kinetics of Tin Whisker Growth Emily Mitchell, Chad Rodekohr Tin whiskers are single-crystalline structures that grow out of tin rich surfaces. Whiskers are found to grow most notably on thin tin surfaces, such as those deposited via electroplating or sputtering [2]. Tin whiskers are highly conductive and pose a threat to many systems, specifically in computers. Whiskers can cause short circuits and bring about malfunctions in products ranging from satellites to pacemakers [3]. Much is lacking in the understanding of their growth mechanisms, however, many researchers agree that stress is a necessary factor. This research aims to evaluate the necessary components of tin whisker growth. We hypothesize that stress and nucleation points are the critical features that must be present for whiskers to form. Previous research found that chemical etching stimulates whisker growth and we hypothesize that this etching introduces nucleation points. The mathematics behind the growth kinetics are an extension of Dr. Smetana's work and describe an energetically favorable argument for proposed mechanisms [8]. Through the understanding of why whiskers grow, we hope to control the location, orientation, and time of whisker growth. These abilities will enable us to stop harmful whisker growth and implement whisker applications such as in the MEMS field. [Preview Abstract] |
Thursday, November 7, 2019 5:18PM - 5:30PM |
D01.00005: Substitutional Defects in CdZnTe using Special Quasirandom Structures Sylvester Ekpenuma, Yuriy Pershin The special quasirandom structures (SQS) are a type of supercells with constituent atoms occupying lattice sites so as to reproduce the average correlation function of a completely disordered lattice. In this way, SQS represent best periodic supercell approximation for a disordered alloy. An algorithm implemented in the Alloy Theoretic Automated Toolkit (ATAT) has been shown to be computationally efficient in generating supercell approximations to disordered lattices. In this study, we apply first principles density functional theory (DFT) electronic structure calculations to SQS for cadmium zinc telluride (CZT) generated using ATAT. Some initial results of zinc atom site occupations using the SQS approach for the study of defects in CZT will be presented. [Preview Abstract] |
Thursday, November 7, 2019 5:30PM - 5:42PM |
D01.00006: Electrophoretic Deposition of MoS2 Thin Films as a Bandgap Engineered Material Alex Young, Theda Daniels-Race Molybdenum Disulfide (MoS$_{\mathrm{2}})$ and other transition metal dichalcogenides (TMDCs) have recently been of great interest to researchers because of their electrical, optical, and catalytic properties. Monolayer TMDCs are especially sought after for their excellent optoelectronic properties due to a direct bandgap as opposed to their bulk counterparts. However, the various methods used to fabricate the monolayered structures, such as chemical vapor deposition (CVD) and lithium intercalation, are expensive, labor intensive, and hazardous. We present current research into TMDC deposition using electrophoretic deposition (EPD) with the goal of fabricating a uniform monolayer of MoS$_{\mathrm{2}}$ on a silicon wafer. The EPD parameters of applied voltage, inter-electrode distance, and deposition time will be controlled and calibrated with respect to predicted and measured MoS$_{\mathrm{2}}$ layer thicknesses. Characterization methods will be geared toward confirming coverage, uniformity, sample thickness, and material quality. Our investigation of this technique is within the context of extrapolation to different TMDCs, such as MoSe$_{\mathrm{2}}$ or WS$_{\mathrm{2}}$, for deposition upon conductive and surface treated insulating substrates. [Preview Abstract] |
Thursday, November 7, 2019 5:42PM - 5:54PM |
D01.00007: Pathways of Photoinduced Insulator-Metal Transition in VO2 and V3O5 Sergiy Lysenko Time-domain studies of ultrafast phase transition in vanadium oxides are critical for understanding of electronic and structural dynamics of these materials upon photoexcitation. By applying ultrafast diffraction conoscopy along with traditional pump-probe spectroscopy techniques we reconstructed the thermodynamic potential of the material far from equilibrium. This enables numerical modeling of the pathways for lattice transformation in terms of Ginzburg-Landau formalism. Additional numerical modeling of the molecular dynamics of VO2 and V3O5 shows a good match with the experiment. Using time- and angle-resolved light scattering techniques we visualize mesoscale statistics of the insulator-to-metal phase transition, including coherent phonon response of local domains with different sizes and orientations. We show a significant influence of the misfit strain in epitaxial films of vanadium oxides on subpicosecond phase transition dynamics. The tensile and compressive strain shifts the phase of coherent phonon oscillations in different domains. The observation of phonon mode softening at quasi-equilibrium and upon ultrafast photoexcitation enables a new understanding of symmetry-breaking in vanadium oxide materials. [Preview Abstract] |
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