Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 58, Number 12
Friday–Saturday, October 18–19, 2013; Denver, Colorado
Session C5: Materials Physics I |
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Chair: Davor Balzar, University of Denver Room: 253 |
Friday, October 18, 2013 11:00AM - 11:24AM |
C5.00001: Metamaterials: What They Are and How They Work Invited Speaker: Michael Petras Metamaterials are loosely defined as artificial materials engineered to have unusual properties not found in nature. Since these properties predominantly relate to the propagation of waves through the material, metamaterial engineering has a broad range of applications including photonics, acoustics and mechanical vibrations, thermal radiation and heat transfer, and even material transport (fluids). This talk presents a broad overview of these applications, and discusses the underlying physics using microwave photonic crystals as a specific example. [Preview Abstract] |
Friday, October 18, 2013 11:24AM - 11:36AM |
C5.00002: Investigation of the cycling stability of an ionically-gated organic thin-film transistor Jacob Friedlein, Robert McLeod, Sean Shaheen We have fabricated organic thin film transistors (TFTs) using a film of poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the transistor channel. In its positive oxidation state, PEDOT:PSS is a highly conductive organic semiconductor; however, when it is reduced to its neutral state, its conductivity decreases by many orders of magnitude. We have used this redox switching behavior of PEDOT:PSS as the basis for the modulation of channel current in our (TFTs). When positive ions are driven by a gate voltage into the transistor channel, they interact with the PSS anions, displacing them from the PEDOT, and ultimately reducing the PEDOT to its non-conductive state. Because these devices can operate with gate voltages \textless\ 2V and because they utilize ions, they are ideally suited for biological interfacing. In this work, we demonstrate that the redox switching of PEDOT is irreversible in some operational regimes, and we investigate the correlation between device lifetime and the ON/OFF ratio of the channel current. Finally, we explicate the implications of these behaviors on several applications for ionically-gated transistors. [Preview Abstract] |
Friday, October 18, 2013 11:36AM - 11:48AM |
C5.00003: Extensions of the Walden-Wintle Model of Charge Transport in Disordered Materials for Charge Injection with Electron Beams JR Dennison, Greg Wilson, Alec Sim, Jodie Corbridge Gillespie We have extended the Walden-Wintle model for charge transport through highly disordered insulating materials to include charge injection with a charged particle beam. The original model is applicable to charge injection in a dielectric material from a pair of electrodes in a parallel plate geometry. It provides a versatile approach to predict the time-dependant current at a rear grounded electrode, as the injection current density evolves over time with the development of a space charge barrier near the injection electrode. This includes standard Fowler-Nordheim, Schottky injection, space charge limited injection, and various tunneling mechanisms. Our new model modifies the approach to include electrode-less charge injection via a charged particle beam, along with concomitant effects for the injection current, surface voltage, and electron emission as a charge is built up in the insulator. The approach is equally valid for near-surface injection and bulk injection for non-penetrating radiation and for penetrating radiation. The results are based on our dynamic emission model for yields dependant on accumulating charge in both the positive and negative charging regimes. [Preview Abstract] |
Friday, October 18, 2013 11:48AM - 12:00PM |
C5.00004: Optical constants of Ni1-xPtx silicides from spectroscopic ellipsometry Lina Abdallah, Stefan Zollner, Christian Lavoie, Ahmet Ozcan, Mark Raymond We provide a comprehensive analysis of the dielectric function and optical conductivity for nickel platinum silicides with different platinum concentrations (0 to 30 at.{\%} Pt). After determining accurate optical constants of Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$, alloys with the same thickness were deposited directly on Si to study the optical constants of silicides. Ellipsometric measurements were performed over the same photon energy range (0.6 to 6.6 eV). During Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ deposition on Si, some metal atoms will diffuse into the Si substrate even at room temperature, creating a metal-rich silicide. Annealing the samples at 500$^{\circ}$C for 30 s creates a monosilicide layer with a thickness of about 200 {\AA}. The imaginary part of the resulting dielectric function of monosilicides shows metallic Drude behavior with two additional peaks at 1.5 eV and 4.5 eV due to interband electronic transitions. Our results will be compared to previous measurements and electronic structure calculations on NiSi and PtSi. In our results, absorption peaks broaden with increasing Pt content in the silicides, similar to our earlier results for Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ metal alloys. [Preview Abstract] |
Friday, October 18, 2013 12:00PM - 12:12PM |
C5.00005: Influences of small clusters of defects near probe nuclei in cubic structures in perturbed angular correlation models F. Sullivan, M. Adams, P. Matheson, W.E. Evenson Evenson, et al. [1] have modeled concentration-dependent inhomogenous broadening (IHB) in perturbed angular correlation (PAC) spectra for cubic structures by finding a suitable set of coordinates to represent electric field gradients (EFGs) and then characterizing their probability distribution functions (PDFs). For defect concentrations c \textgreater\ 3{\%}, a nonlinear transformation of the EFG components Vzz and Vxx produces two nearly-independent coordinates, W1 and W2. Their PDFs are well characterized by gamma and alpha-stable distributions. These can then be used to reconstruct PAC spectra for arbitrary c \textgreater\ 3{\%}. However for c \textless\ 3{\%}, chance occupations by a small number of defects near the probe nucleus can distort the PDFs. For example, a single defect in shell two produces strong secondary peaks in the PDFs. Also, the joint PDF for c \textless\ 3{\%} remains skewed, reflecting some influence of the crystal geometry. Parsing the PDFs by contributions from different arrangements of defects in near-probe shells, allows us to investigate the relative contributions of different defect configurations to the PAC spectrum. We report on progress made in modeling low defect concentration PDFs and their PAC spectra in SC, FCC and BCC structures. \\[4pt] [1] W.E. Evenson, M. Adams, A. Bunker, J. Hodges, P. Matheson, T. Park, M. Stufflebeam, M. O. Zacate, \textit{Inhomogeneous broadening of PAC spectra with} \textit{Vzz and }$\eta $ \textit{joint probability distribution functions}, Hyperfine Interact, 21 November, 2012 [Preview Abstract] |
Friday, October 18, 2013 12:12PM - 12:24PM |
C5.00006: Pre-breakdown Arcing in Dielectrics under Electric Field Stress Allen Andersen, JR Dennison High electric field stress phenomena associated with electrostatic discharge (ESD) were studied for dielectrics, including low density polyethylene, polyimide, and disordered SiO2. ESD is the free flow of current through a dielectric that has broken down due to high electric field stress. The critical field for ESD was determined by increasing the voltage across 25 $\mu$m samples in 20V steps, and monitoring the leakage current. A simple parallel-plate capacitor geometry was used, under high vacuum, to reach fields of up to 590MV/m. Prior to destructive ESD breakdown, pre-breakdown current arcs can occur through a dielectric. For polymers, pre-ESD transient current spikes were observed with measurements at 0.25Hz and 10kHz. The field at which pre-breakdown arcing begins was compared to the critical ESD field for each material studied. Arcing was also observed as part of endurance time measurements, where the sample is held at a fraction of the critical breakdown field and wait time to ESD is measured. These pre-ESD discharge phenomena are explained in terms of breakdown modes and defect generation on a microscopic scale. Pre-breakdown arcs are understood in terms of thermally repairable defects, while ESD requires the creation of defects related to bond breaking in the material. [Preview Abstract] |
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