Bulletin of the American Physical Society
2016 Annual Meeting of the APS Mid-Atlantic Section
Volume 61, Number 16
Saturday–Sunday, October 15–16, 2016; Newark, Delaware
Session D2: Spectroscopy in Condensed Matter I |
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Chair: Ed Nowak, University of Delaware Room: Sharp Laboratory 130 |
Saturday, October 15, 2016 4:00PM - 4:36PM |
D2.00001: Coherent phenomena in semiconductor microcavities Invited Speaker: Alan D Bristow Monolithic semiconductor microcavities are platforms for understanding many-body interactions, cavity quantum electrodynamics and are analogues of ultracold atoms, giving rise to polaritonic Bose condensation. Detuning between cavity mode and exciton mode (of the quantum well absorber) varies their coupling, resulting in an avoided-crossing when in resonances. Two-dimensional coherent spectroscopy isolates photonic, excitonic, polaritonic, biexcitonic and bipolaritonic contributions, which are coherently controlled to determine their interactions and measure their dephasing times. Polarization and detuning dependences reveal uncoupled biexcitons, separate from bipolaritons. The presence of biexcitons suppresses the emission of the polaritons. Interactions between polaritons and biexcitons indicate a polaritonic Feshbach behavior. [Preview Abstract] |
Saturday, October 15, 2016 4:36PM - 4:48PM |
D2.00002: Focused Laser Dewetting of Metallic Thin Films Tianxing Ma, Michael Nitzsche, Jonathan Singer Focused Laser Spike (FLaSk) Annealing generates extreme thermal gradients from a microscale laser spot, which in turn initiate thermocapillary dewetting. Through this controllable mobility and driving force spike, FLaSk has shown the ability to pattern polymer thin films, resulting in direct write of submicron-resolution trench-ridge structures. Due to the lower viscosity and higher surface tension of metallic melts, the gradient-induced dewetting occurs simultaneously with Rayleigh droplet formation, resulting in a trench-ridge-dot feature. When lines are overlapped, the moving instead of removing of metal will result in sub-spot features at a sub-micron scale. Shrinking the line distance coalesces droplets into continuous chains of small islands, reconstructing a trench-ridge structure, which generates visible plasmonic effects. Additionaly, gratings with similar features were generated both on the smooth and roughened films, indicating that to obtain highly uniform final structures does not require defect-free starting materials. Further, continuous samples were generated from an initially discontinuous starting condition, opening the possibility for building conductive pathways. [Preview Abstract] |
Saturday, October 15, 2016 4:48PM - 5:00PM |
D2.00003: Micromagnetic simulated magnetization reversal of nickel three-dimensional anti-sphere arrays Andy Clark, Le Yu, Cassie Wang, Kristen Buchanan, Xuemei Cheng Technical advances in electrochemical deposition using self-assembled colloidal polystyrene templates has resulted in efficient and low-cost fabrication of large samples containing three-dimensional anti-sphere arrays (3DAAs). 3DAAs with periodic structure and high surface-to-volume ratio provide an ideal system for studying the effect of dimensionality and morphology on magnetic properties. Micromagnetic simulations were performed using the object oriented micromagnetic framework (OOMMF) and mumax3 to study the magnetization reversal behaviors in a nickel 3DAAs structure with anti-sphere radii of 98nm and 252nm and varying sample thickness between 98nm-1.5$\mu $m. The simulation results show that domain propagation dominates in the lowest quasi-continuous layer, whereas the reversal process becomes more localized in the void-heavy upper layers. As the structure thickness increases, the proportion of the quasi-continuous layer decreases and stronger pinning appears in the upper layers, resulting in a transition from a domain-growth reversal to a localized reversal.~ [Preview Abstract] |
Saturday, October 15, 2016 5:00PM - 5:12PM |
D2.00004: Precision Displacement Measurement Using Shearing Interferometer Raju KC, Jaxon Lee, Edward Flagg The emission spectra from some fluorescent sources, like semiconductor quantum dots, consists of closely spaced peaks, which are difficult to resolve with a conventional grating spectrometer. One way to solve this problem is to use a scanning Fabry-Perot interferometer (FPI), which acts as a narrow bandwidth tunable spectral filter, to increase the measurement resolution. This technique requires a precise control of the distance between the two FPI mirrors with a precision of 1 nm. Direct optical measurement of the mirror separation would provide the best feedback, but at the cost of an expensive tunable laser. Here we propose a less expensive way to achieve the required precision by connecting the FPI cavity to a shearing interferometer whose mirror separation can be measured using an interference pattern created by a relatively inexpensive single-frequency laser. The interferogram can be recorded with a photodiode array connected to an Arduino microcontroller, which can also provide the feedback signal and is affordable to any lab. [Preview Abstract] |
Saturday, October 15, 2016 5:12PM - 5:24PM |
D2.00005: Confined Plamons in graphene-graphene heterostructure Dan You, Slava Rotkin Graphene, a two-dimensional network with honeycomb lattice, attracted great interest in electronics and optics. Surface Plasmon (SP) modes exist in graphene with stronger confinement and lower losses than in noble metals, which makes graphene a great promising material for RF. Response of confined graphene lake structure depends on both the geometry and the properties of underlying substrate. In narrow graphene nanostructure, such as graphene nano-disk, quantum effects become very important, so continuum plasmon modes are transformed into a discrete set of levels, quantized in angular and radial directions. Moreover, when combined with other materials, graphene SP exhibits hybridization, for example, with surface phonon polaritons, providing additional flexibility for fine tuning of composite plasmons. In our work, we investigate surface plasmon hybridization between small and an infinite monolayer graphene. We also consider the case of angular mismatched lattice of the disk and the monolayer. For this we introduce a scalar field of a moire pattern may induce periodic modulation in charge density and therefore in conductivity. We observe plasmon coupling between modes with different angular quantum numbers. [Preview Abstract] |
Saturday, October 15, 2016 5:24PM - 5:36PM |
D2.00006: Scintillator for low accelerating voltage SEM imaging Christopher Bowser, Marian Tzolov, Nicholas Barbi Scintillators are materials that emit light very efficiently when excited by electromagnetic radiation or charged particles with suitable energy. This property gives them great importance in many applications requiring the detection of high energy particles such as electrons in a Scanning Electron Microscope (SEM). We will present results showing that conventional scintillators such as YAP and YAG have poor emissions at low accelerating voltages due to a top conductive layer. We have developed a thin film ZnWO$_{\mathrm{4}}$ scintillator with high photoluminescence quantum efficiency of about 60{\%} to increase the signal at low accelerating voltages. We have further integrated the ZnWO$_{\mathrm{4}}$ scintillator with YAP and YAG scintillators by replacing the conductive layer with a ZnWO$_{\mathrm{4}}$ film which has enough conductivity to prevent charging. We will compare the spectral intensities over a range of accelerating voltages between 1 and 30kV between the conventional and coupled thin film scintillator. We have quantified the charging effect by measuring the sum of the secondary and backscattered electron coefficients. We have built detectors with the above mentioned scintillators and we will compare SEM images recorded simultaneously by conventional and ZnWO$_{\mathrm{4}}$-based scintillators. [Preview Abstract] |
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