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 F04: Condensed Matter II |
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Room: Holiday Inn Resort Oceanwatch |
Friday, November 8, 2019 10:30AM - 10:42AM |
F04.00001: Adsorption and Reaction of Methanol on Anatase TiO$_{\mathrm{2}}$(101) Arjun Dahal, Zdenek Dohnálek, Nikolay Petrik, Greg Kimmel Anatase TiO$_{\mathrm{2}}$ is used extensively in a wide range of heterogeneous and photocatalytic processes. As such, understanding the interaction of prototypical organic compound methanol with anatase is of high importance. In this study, we employ scanning tunneling microscopy and temperature programmed desorption to study the adsorption and reaction of methanol on anatase TiO$_{\mathrm{2}}$(101). We find that adsorption of molecular methanol at 80 K leads to the formation of chains along the titania rows. These chains are metastable and fall apart upon annealing due to the repulsion of neighboring molecules. Further, we find that methanol deprotonates to produce neighboring methoxy and hydroxyl groups following the annealing of high coverages to room temperature. The coverage of methoxy and hydroxyl groups can be increased with repeated adsorption and annealing cycles, and the annealing above room temperature leads to the recombinative desorption of methanol. [Preview Abstract] |
Friday, November 8, 2019 10:42AM - 10:54AM |
F04.00002: Luminescence thermometry using upconverted emissions Li Ma, Zuoling Fu, Xiaojun Wang Luminescence thermometry has been widely used for measuring temperature, the most commonly measured physical quantity. Luminescence intensity and related properties, such as emission lifetime, risetime, and profile, may change as the temperature of a measured substance varies, and any of the changes could be used, after calibration, to determine the temperature of the substance. Temperature dependent and energy downshifting luminescence from rare earth activators has been extensively studied for measuring a broad range of temperatures, but it unfits the biological applications considering the optical window for absorption in tissues. In this talk, we will present a temperature measurement using upconverted luminescence, in which the less absorbed and low energy infrared photons are converted to high energy visible photons in biological systems. Fluorescence intensity ratio (FIR) measured from a pair of thermally coupled excited states is used to obtain the local temperature where photothermal treatment or bioimaging is performed. Rare earth ions doped oxides and fluorides phosphors or nanophosphors are chosen for the demonstration1,2. The thermometry can be readily adopted for teaching advanced physics laboratory. References 1. G. Liu, Z. Sun, Z.L. Fu, L. Ma, X.J. Wang, \textit{Talanta} 169, 181-188 (2017). 2. G. Liu, Z. Fu, T. Sheng, Z. Sun, X. Zhang, Y. Wei, L. Ma, X.J. Wang, Z. Wu, \textit{RSC Adv} 6, 97676-97683 (2016).. [Preview Abstract] |
Friday, November 8, 2019 10:54AM - 11:06AM |
F04.00003: Probing spectral and directional emission properties of hybrid perovskite thin films Ravi P.N. Tripathi, Bibek S. Dhami, Uddhab Tiwari, Kannatassen Appavoo Hybrid organic-inorganic perovskites have recently emerged as promising candidate for nanophotonics and optoelectronic applications. Here we fabricate large-grain hybrid perovskites thin films using a solution-processed technique, and probe its nanoscale emission properties using Fourier imaging microscopy. Furthermore, by spectrally mapping the emission properties of our films with sub-micron resolution, we observe strong dependence of emission properties on the film morphology. Effects of domain crystallinity, emission from defect states and photon recycling are discussed within the framework of Fourier imaging spectroscopy. [Preview Abstract] |
Friday, November 8, 2019 11:06AM - 11:18AM |
F04.00004: Enhancing lasing action in nanoscale zinc oxide random media using atomic layer deposition. Bibek S Dhami, Karly Casey, Matthew Y. Sfeir, Kannatassen Appavoo Understanding how near-field environment modify carrier dynamics and resulting emission properties in nanophotonic elements is vital, especially for lasing applications. Here we have fabricated thin film of zinc oxide nanospheres with high crystal quality and modified its near-field environment by performing atomic layer deposition of various dielectrics, including zinc oxide as a control. By measuring steady-state emission of our nanoscale samples, we demonstrate that we can vary lasing threshold by more than 20 percent. Furthermore, we conduct ultrafast transient absorption spectroscopy above and below lasing threshold to understand how surface modifications using with atomic layer processing modifies carrier dynamics of our lasing media. Three-dimensional finite-difference time domain electromagnetic simulations were performed to gain further physical insights into near-field effects on emission properties of nanoscale random media. [Preview Abstract] |
Friday, November 8, 2019 11:18AM - 11:30AM |
F04.00005: Optical spectroscopy of resonating modes in molecular nanowires Saugat Ghimire, Ravi Tripathi, Kannatassen Appavoo Controlling optical fields at subwavelength resolution is at the heart of many photonic applications in the medical and sensing sectors. Recently, resonant optical nanostructures have emerged as a viable candidate to tune the strength of light-matter interaction while manipulating the flow of light below the diffraction limit. Here we discuss the resonant optical modes of an individual organic nanowire, fabricated by vapor phase growth and that was excited by a femtosecond laser pulse. Furthermore, by coupling our nanowire to various platforms --- for example nanospheres and semiconducting/metallic thin films --- we develop novel strategies to perturb the inherent resonating modes of our wire. Using Fourier imaging spectroscopy, we discussed how the emission spectrum and directionality pattern of our molecular nanowire is altered. [Preview Abstract] |
Friday, November 8, 2019 11:30AM - 11:42AM |
F04.00006: Spatial Self-Phase Modulation in Tungsten and Molybdenum Disulfide Atomic Layers Tikaram Neupane, Bagher Tabibi, Felix Seo The spatial self-phase modulation (SSPM) of optical field in tungsten and molybdenum disulfide atomic layers in liquid solution displayed a number of concentric diffraction rings at the far-field. The formation of concentric diffraction ring is due to the coherent superposition of transverse wave vectors. The number of diffraction ring as a function of applied intensity revealed the nonlinear refraction coefficient of tungsten and molybdenum disulfide atomic layers. The diffraction pattern of SSPM also identified the polarity of nonlinear refraction coefficient. The temporal evolution of the diffraction ring indicated the spatial alignment of nanoflakes at the initial time of excitation, the maximum diffraction rings at the intermediate time of excitation, and the thermal distortion of the upper vertical ring of SSPM at the longer time duration of laser excitations. The vertical asymmetric diffraction ring indicates the phase distortion of the optical field due to heat convection. The ratio between distortion- and half-cone angles of SSPM as a function of applied intensity revealed the change of the nonlinear refraction coefficient due to the thermal effect. [Preview Abstract] |
Friday, November 8, 2019 11:42AM - 11:54AM |
F04.00007: Superhard Tantalum Borides Via Microwave Plasma Chemical Vapor Deposition Kallol Chakrabarty Tantalum borides have become a subject of interest due to their excellent properties: high hardness, wear resistance, chemical inertness. Different techniques have been used to synthesize tantalum borides, including high temperature/pressure compression in diamond anvil cells$^{\mathrm{\thinspace }}$and traditional powder or pack boriding and chemical vapor deposition. These methods have some limitation such as small volumes of deposition and contamination issue. In this research work, we have used novel Microwave Plasma Chemical Vapor Deposition method to synthesize tantalum boride. H$_{\mathrm{2}}$ and B$_{\mathrm{2}}$H$_{\mathrm{6\thinspace }}$was used as a feed gas and boron was diffused into tantalum substrate. The sample was analyzed using X Ray Diffraction and Nanoindentation. The Structure of the produced sample was mixture of TaB and TaB$_{\mathrm{2\thinspace }}$Phase. XRD patterns show a clear increase in the relative intensity of the TaB$_{\mathrm{2}}$ phase with temperature, accompanied by an increase in hardness measured via nanoindentation. The hardness value of the produced sample was in superhard regime and mean hardness was 40\textpm 10 GPa. [Preview Abstract] |
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