Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session I5: Materials VI: Xrays, Ions, and Electrons for Materials Characterization |
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Chair: Stefan Zollner, New Mexico State University Room: PSA102 |
Saturday, October 17, 2015 11:00AM - 11:24AM |
I5.00001: Novel X-ray Light Sources Invited Speaker: William Graves For over 100 years X-rays have been our most important probe of atomic and molecular structure due to their angstrom-scale wavelength. With the advent of powerful synchrotrons in the late 20th century, x-ray beams became a billion times brighter than the small lab-based sources that had existed previously. Then 5 years ago, with the advent of x-ray free-electron lasers (XFFELs), the beam brightness increased by another factor of a billion. I will discuss the performance of these extraordinary sources and the science they enable. While these powerful accelerator facilities produce superb science, they are large and expensive with only a few in the world. However new laser and accelerator technologies are on the cusp of x-ray production that retains the performance of the large facilities while shrinking their size to a university scale lab. I will discuss R&D into these new laser-based x-ray sources. [Preview Abstract] |
Saturday, October 17, 2015 11:24AM - 11:36AM |
I5.00002: Superconducting Nuclear Recoil Sensor for Directional Dark Matter Detection Ann Junghans, Nina Weisse-Bernstein, Kevin Baldwin, Randy Lafler, Nguyen Phan, Dinesh Loomba, Markus Hehlen The Universe consists of 72{\%} dark energy, 23{\%} dark matter and only 5{\%} of ordinary matter. One of the greatest challenges of the scientific community is to understand the nature of dark matter. Current models suggest that dark matter is made up of slowly moving, weakly interacting massive particles (WIMPs). But detecting WIMPs is challenging, as their expected signals are small and rare compared to the large background that can mimic the signal. The largest and most robust unique signature that sets them apart from other particles is the day-night variation of the directionality of dark matter on Earth. This modulation could be observed with a direction-sensitive detector and hence, would provide an unambiguous signature for the galactic origin of WIMPs. There are many studies underway to attempt to detect WIMPs both directly and indirectly, but solid-state WIMP detectors are widely unexplored although they would present many advantages to prevalent detectors that use large volumes of low pressure gas. We propose a novel multi-layered architecture in which WIMPs would interact primarily with solid layers to produce nuclear recoils that then induce measureable voltage pulses in adjacent superconductor layers. [Preview Abstract] |
Saturday, October 17, 2015 11:36AM - 11:48AM |
I5.00003: Study of an MeV Nuclear Resonance to Increase Sodium Detection by Ion Beam Analysis Abijith Krishnan, Nithin Kannan, Tiffanie S. Cappello-Lee, Rachel A. Neglia, M. W. Mangus Jr., R. J. Culbertson, Nicole Herbots, B. J. Wilkens, C. F. Watson Blood percolation into implanted glucose sensors for diabetics limits sensor lifetime to 3-7 days. Na$^+$ mobile ions from blood permanently damage Si-based devices. Ion Beam Analysis (IBA) can detect Na in sensors. However, due to the low atomic number of Na (Z=11) and low mass ratio of Na to Si, Na that has percolated into implanted sensors is difficult to detect via standard 2 MeV $^{4}$He Rutherford backscattering. Nuclear resonance can increase the Na scattering cross-section. This work characterizes a $\sim4.7$ MeV resonance, annotated $^{23}$Na($\alpha$,$\alpha$)$^{23}$Na, between $^{23}$Na atoms and $\alpha$ particles. To increase precision of measurements for resonance energy, width, and factor, ion beam energy is calibrated via 3 signals: $5.486\pm0.007$ MeV emission of $\alpha$ particles by $^{241}$Am, and two nuclear resonances, $4.265\pm0.055$ MeV $^{4}$He with $^{12}$C, and $3.038\pm0.003$ MeV $^{4}$He with $^{16}$O. The $^{23}$Na($\alpha$,$\alpha$)$^{23}$Na nuclear resonance is found to have an energy of $4.696\pm0.180$ MeV and cross-section increase of $41\pm7.0\%$. Increase of Na detection in IBA via the studied resonance is statistically significant. Future research can determine if the cross-section increase is sufficient for Na detection in glucose sensors. [Preview Abstract] |
Saturday, October 17, 2015 11:48AM - 12:00PM |
I5.00004: Separation of the spin Seebeck effect and anomalous Nernst effect using Exchange Bias Miguel Bueno, Bochao Li, Gejian Zhao, Dongrin Kim, Ji Zhang, Jessica Gifford, Tingyong Chen In a pure spin current, electrons with opposite spins flow in opposite directions, thus information is conveyed only by spin current without any charge current, which has the potential to realize ultra-low-power-consumption electronics. Thermal gradient ($\nabla $T) across a magnetic insulator has been proposed to generate pure spin currents using the spin Seebeck effect. However, when a temperature gradient is applied perpendicular to a magnetic metallic thin film and a magnetic insulator, the magnetic insulator induces a Spin Seebeck effect (SSE) in the magnetic layer. In addtition, this temperature gradient also causes an Anomalous Nernst effect (ANE) in the magnetic layer with similar magnitude to that of the SSE. Separation of these two effects is important to improve the understanding of spin transport in these systems. Previously, a difference in coercivity between the two layers has been utilized to separate these two effects. In this work we use Exchange Bias (EB) to shift the magnetic metal and separate the SSE from the ANE. First, we optimize the thickness of the antiferromagnetic FeMn layer to achieve the largest EB. We then grew a Cu wedge between the magnetic insulator Yttrium Iron Garnet, Y3Fe2(FeO4)3, (YIG) and the ferromagnetic Py layer to achieve the separation of the two effects. [Preview Abstract] |
Saturday, October 17, 2015 12:00PM - 12:12PM |
I5.00005: Enhanced Electron Yield Measurements of Extremely Low-Conductivity High-Yield Dielectrics Justin Christensen, JR Dennison New methods to measure intrinsic (uncharged) electron yield have been developed and used to study high-yield, low-conductivity dielectrics.~ Electron yield---the ratio of emitted to incident electrons---determines how a material will acquire charge under electron bombardment and is extremely difficult to measure for highly insulating materials due to both negative and positive charge build up. The enhanced method uses a pulsed (3 \textmu s), low-flux (3\textbullet 10$^{\mathrm{4}}$~electrons per cm$^{\mathrm{2}}$~per pulse) electron beam to probe materials and a hemispherical grid retarding field analyzer to measure the absolute energy spectra of emitted charge. A low-energy electron flood gun and a high-energy high-intensity UV LED are used between pulses to neutralize accumulated charge. Data for each pulse are analyzed to determine the total incident and emitted charge, and hence the yield; point-wise analysis of pulse oscilloscope trace data allows yield determination for charge accumulation as low as 300 electrons per cm$^{\mathrm{2}}$.~ Electrons yields down to \textasciitilde 20 eV incident energy can be measured due to enhanced beam stability and reduced noise. To validate these system changes, measurements of common materials are compared to previous measurement methods used by several investigators.~The resulting yield curves more closely match the expected model compared to previous methods. Charging due to electron bombardment is very important to understand and mitigate in applications such as spacecraft charging, electron microscopy, and other electron gun applications.~ [Preview Abstract] |
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