Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session C4: Surfaces and Nanostructures |
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Chair: Jose de la Venta, Colorado State University Room: Lory Student Center 322 |
Friday, October 20, 2017 10:30AM - 10:54AM |
C4.00001: Local Structure of Decahedral Gold Nanoparticles Invited Speaker: Heinz Nakotte The five-fold symmetry FCC-derived nanoparticles is inconsistent with the translational symmetry of a Bravais lattice and it is generally explained by multiple twinning of a tetrahedral subunit about a (joint) symmetry axis, with or without structural modification to the \textit{fcc} motif. In order to verify theoretical models, it is therefore pertinent that the local structural features of such materials can be fully characterized. The small size of nanoparticles severely limits the application of traditional analysis technique, such as Bragg diffraction. We present the application of Debye scattering and Pair Distribution Function (PDF) analysis towards modeling of the total scattering data for the example of decahedral gold nanoparticles. PDF measurements provide a statistical description of the pair correlations of atoms within a material. We explored the sensitivity of existing neutron and synchrotron X-ray PDF instruments using different models for decahedral gold nanoparticles: a multiply-twinned FCC decahedron model with a gap, a relaxed body-centered orthorhombic BCO and a hybrid model. The predictions of the three models were then compared with experimental data from synchrotron X-rays and we present our experimentally derived atomistic models of the gold nanoparticles, with surprising results and a perspective on remaining challenges. Our findings provide evidence for the suitability of PDF analysis in the characterization of other nanosized particles that may have commercial applications. [Preview Abstract] |
Friday, October 20, 2017 10:54AM - 11:06AM |
C4.00002: Hemocompatibility of Superhemophobic Titania Surfaces Sanli Movafaghi, Victoria Leszczak, Wei Wang, Jonathan Sorkin, Ketul Popat, Arun Kota Titanium-based implants have received a great deal of attention for their biocompatibility with many different tissues in the human body. However, when these implants come in contact with blood, platelet adhesion and activation occur, which may lead to further thrombosis and sometimes failure of these implants. In this work, we demonstrated a novel strategy to improve the hemocompatibility of titanium-based implants. This strategy consists of altering the blood-contacting surfaces of titanium-based implants and making them superhemophobic (i.e., extremely repellent to blood). The superhemophobic surfaces are so repellent to blood that droplets of blood bead up and roll off from the surface without sticking to it. Further, we investigated the blood platelet adhesion and activation of superhemophobic surfaces and compared them with that of hemophobic surfaces (i.e., surfaces display contact angles \textgreater 90\textdegree with blood) and hemophilic surfaces (i.e., surfaces display contact angles \textless 90\textdegree with blood). Our results indicate that superhemophobic surfaces display significantly lower platelet adhesion and activation and so an improved hemocompatibility compared to hemophobic and hemophilic surface. We envision this simple and scalable fabrication technique will lead to improved hemocompatible, superhemophobic medical implants. \newline [Preview Abstract] |
Friday, October 20, 2017 11:06AM - 11:18AM |
C4.00003: Electron Yield Measurements of Vertically Aligned Multi-Walled Carbon Nanotubes Brian Wood, JR Dennison, Justin Christensen, Greg Wilson Surface modification of materials---including roughness, modulation, and contamination---can act to decrease the electron yield$_{\mathrm{\thinspace }}$(EY). Many applications require very low EY materials to eliminate unwanted emission in critical processes. Vertically grown carbon nanotubes (CNT) are an ideal candidate for low EY, due to their surface morphology, high aspect ratio, and carbon's propensity to absorb radiation. Using a chemical vapor deposition method, a CNT forest sample of height \textasciitilde 40 \textmu m was grown on a silicon substrate capped with a 3 nm thick Al diffusion barrier. Data of total, secondary, and backscatter EY were taken for energies between 20-5000 eV, allowing a comprehensive characterization of the nanotube's response to electron bombardment normal to the sample, both in low and high energy ranges. Spectra of the emission flux as a function of emission energy were also acquired, detailing the emission profile and giving insight into possible charging effects. Preliminary results of this study include the CNT's effect of reducing the yield due to its inherent absorbing capabilities, along with any possible contribution from the substrate. Comparing yields of vertically grown CNT to yields of bulk and microcrystalline graphite, graphitic amorphous carbon, and unaligned CNT provides a quantitative estimate of the specific nanostructure contribution to the CNT yields. These results can be extended to similar geometries in other structured materials. [Preview Abstract] |
Friday, October 20, 2017 11:18AM - 11:30AM |
C4.00004: Optical and Magnetic Properties of Single- and Multi-layer, Colloidal Ag$_2$S Nanoplatelets Joseph R. Murphy, Subash Kattel, Lenore Kubie, Bruce Parkinson, William D. Rice We report the synthesis, characterization, and magneto-optical behavior of ultrathin, nontoxic, silver sulfide (Ag$_2$S) nanoplatelets (NPLs) synthesized via a one-pot method. These colloidally synthesized nanoplatelets are the thinnest ever reported, with a thickness of only $3.5\pm0.2$ \AA, which is an order of magnitude smaller than the excitonic Bohr diameter of Ag$_2$S ($44$ \AA). The extent of nanoplatelet confinement is controlled by synthesis conditions and quantized, which is evident in both absorption and photoluminescence (PL) spectroscopy. We measure the excitonic PL quantum yield of these NPLs to be approximately $30\%$, suggesting their potential use in biomedical imaging. To investigate magnetic properties, we used magnetic circularly polarized photoluminescence (MCPL) and magnetic circular dichroism (MCD) techniques as a function of both temperature ($1.5 \mathrm{K} - 300 \mathrm{K}$) and magnetic field ($\pm7 \mathrm{T}$). These measurements of single- and multi-layer Ag$_2$S platelets were used to extract their temperature-dependent excitonic $g$-factors and probe the electronic structure. The implications of extremely high excitonic quantum confinement on the magnetic properties of the excitons will also be presented. [Preview Abstract] |
(Author Not Attending)
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C4.00005: Switchable wettability on superoleophobic surfaces fabricated with a thermo-responsive shape memory polymer. Wei Wang, Joshua Salazar, Hamed Vahabi, Alexandra Joshi-Imre, Walter E.Voit, Arun Kota Superomniphobic surfaces are extremely repellent to virtually all liquids. Prior work have emphasized the importance of low solid surface energy and re-entrant texture (i.e., multi-valued or convex or overhang texture) in the design of superomniphobic surfaces. While superomniphobic surfaces with a wide variety of textures have been reported in literature, to the best of our knowledge, there are no reports of superomniphobic surfaces with metamorphic textures (i.e., textures that transform their morphology in response to an external stimulus). In this work, we present the first-ever metamorphic superomniphobic (MorphS) surfaces fabricated with a thermo-responsive shape memory polymer. Unlike prior work, utilizing our MorphS surfaces, we demonstrate the distinctly different wetting transitions of liquids with different surface tensions and elucidate the underlying physics. The wetting transitions on our MorphS surfaces are solely due to transformations in morphology of the texture. We envision that the rapid and reversible wetting transitions on our MorphS surfaces will have a wide range of applications including controlled drug release systems, liquid-liquid separation membranes, lab-on-a-chip devices, and biosensors. [DOI: 10.1002/adma.201700295] [Preview Abstract] |
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