Bulletin of the American Physical Society
Inaugural Fall 2009 Meeting of the Prairie Section of the APS
Volume 54, Number 17
Thursday–Saturday, November 12–14, 2009; Iowa City, Iowa
Session P2: Condensed Matter Physics IV |
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Chair: Craig Pryor, University of Iowa Room: IMU 243 (Ballroom) |
Saturday, November 14, 2009 10:30AM - 10:42AM |
P2.00001: Magnetic losses, critical currents and pinning in coated conductors Anota Ijaduola, James Thompson, David Christen, R. Feenstra, A. Goyal, C.L.H. Thieme, K.R. Marken The discovery of high temperature superconductors (HTS) in particular $YBa_{2}Cu_{3}O_{7-\delta}$ (YBCO) ($T_{c} \approx$ 92 K), sparked great interest in the use of HTS materials in practical applications such as transmission lines, motors and generators. Different techniques are used to fabricate these `coated conductors' from YBCO and other HTS. Ferromagnetic losses arise from the substrates that are used in the fabrication processes. I will talk about the studies we have done on these losses and also discuss the critical current ($J_c$) that flow in these coated conductors. On the other hand, exposing a type II superconductor to magnetic field generates vortices which are detrimental to the current carrying capabilities. These vortices have to be pinned (made immobile) in order to have significant and useful $J_c$ flow in these conductors. I will discuss the different pining mechanisms used in these coated conductors and particularly focus on the pinning features we studied on some set of YBCO thin films. [Preview Abstract] |
Saturday, November 14, 2009 10:42AM - 10:54AM |
P2.00002: An unusual way to control the surface doping of cuprate superconductors in Angular Resolved Photoemission Spectroscopy (ARPES) experiments. Ari D. Palczewski, Takeshi Kondo, A. Kaminski, G.Z.J. Xu, G. Gu, J.S. Wen We study the variation of the electronic properties at the surface of a high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) as a function of vacuum conditions in angle resolved photoemission spectroscopy (ARPES) experiments. Normally, under less than ideal vacuum conditions the carrier concentration of (Bi2212) increases with time due to the absorption of oxygen from CO2 and CO molecules that are prime contaminants present in ultra high vacuum (UHV) systems. We find that in a high quality vacuum environment at low temperatures, the surface of Bi2212 is quite stable (the carrier concentration remains constant), however at elevated temperatures the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. These two effects can be used to control the carrier concentration in-situ. Allowing us to probe the doping phase diagram of cuprates on a single sample. Support: Department of Energy DE-AC02-07CH11358 \& DE-AC02-98CH10886 and National Science Foundation DMR-0537588 [Preview Abstract] |
Saturday, November 14, 2009 10:54AM - 11:06AM |
P2.00003: Structured illumination for stress reduction gloss reduction and 3 dimensional patterning of photopolymers Chris Coretsopoulos, Peter Ganahl, Alec Scranton ``Structured illumination'' method is based upon a two-stage illumination process in which a photoactive polymer is first illuminated in a pattern of light and dark regions. During this structured illumination stage, unreacted monomer from the dark region will migrate in response to the polymerization and the resulting shrinkage thereby preventing the development of stress. At the end of the structured illumination stage, the system contains patterned regions of stress-free polymer among pools of unreacted monomer. After a specified duration of structured illumination, the second, flood cure, stage begins. Here the entire system is illuminated to achieve a consistently high conversion throughout the coating. Experimental results confirm that over 90{\%} of the polymerization shrinkage stress can be eliminated using this approach. A further benefit of this method is the production of 3 dimensional curved objects that can be photo-patterned with simple mask structures. This is in contrast to steep walled structures produced by conventional photolithography. The resulting polymer has been used to reduce gloss in surface coatings without the need of using additives, and to make micro scale 3D features and optical elements and microstructures. [Preview Abstract] |
Saturday, November 14, 2009 11:06AM - 11:18AM |
P2.00004: Characterization of Large-Core Photonic Bandgap Fibers for Spectrally Broad Visible Light Transmission E. Schiavone, A. Stolyarov, Y. Fink Snell's law imposes a fundamental limitation on the transmission efficiency of randomly directed, broadband fluorescence signals through solid core fibers. On the other hand, guiding light through an air core fiber clad with perfect mirrors would make possible perfect collection and guidance of non-collimated and spectrally broad signals. Approaching this idealization, hollow core photonic bandgap fibers offer a flexible, light weight and concealable platform for diffuse light transport and remote chemical sensing applications. While in the small core regime, these fibers possess discrete modal properties, larger core PBG fibers have the advantage of better collection efficiencies for ambient analyte sensing and are expected to have lower losses arising from a smaller overlap of the core field with the cladding. Therefore, large-core ($\sim $300 micron) visible transmission fibers are characterized, with cutback measurements, in order to determine the achievable transmission efficiency of these fibers along with the optimal materials and geometries for the production of optical devices that propagate light from a diffuse broadband light source. These measurements conclude that larger cores exhibit lower losses in transmission than smaller cores constructed despite a more ideal mirror. [Preview Abstract] |
Saturday, November 14, 2009 11:18AM - 11:30AM |
P2.00005: Synchrotron Radiation Studies of Environmental Materials Daniel Olive, Jeff Terry In the case of environmental contaminants, the mobility of elements changes depending on oxidation state. Remediation techniques often focus on changing the oxidation state in order to immobilize, by forming an insoluble species, or removing by binding a soluble species to an insoluble material. In order to accomplish this immobilization one has to understand all the possible reactions that can change the oxidation state. One of the techniques that can be used to determine the oxidation state and local atomic structure of environmental contaminants under aqueous conditions is x-ray absorption spectroscopy (XAS). Synchrotron radiation was used to excite the absorption edges of As, Tc, and Pu, in order to characterize their oxidation states and structures under environmentally relevant conditions. Granular activated carbon treated with iron has shown promise for the removal of arsenic from contaminated ground water, where XAS measurements have determined that the arsenic bound to iron oxide as AsO$_{4}^{3-}$. Pertechnetate (TcO$_{4}^{-})$ was found to be reduced to TcO$_{2}$ in a reaction with amorphous iron sulfide (FeS). Bio-reduction of plutonium has also been studied using bacteria that may be found in nuclear waste repositories resulting in an end product of Pu(III). [Preview Abstract] |
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