Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session B4: Materials Physics I |
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Chair: Boris Kiefer, New Mexico State University Room: Macey Center Auditorium |
Friday, October 26, 2012 10:40AM - 10:52AM |
B4.00001: Quantifying amorphous and crystalline phase content with the atomic pair distribution function Joseph Peterson, James TenCate, Thomas Proffen, Timothy Darling, Heinrich Nakotte, Katharine Page Pair distribution function (PDF) analysis has been a long established technique for studying the local structure of amorphous and disordered crystalline materials. In today's increasingly complex materials landscape, the coexistence of amorphous and crystalline phases within single samples is not uncommon. Though a couple of reports have been published studying samples with amorphous and crystalline phases utilizing PDF analysis, to date little has been done to determine the sensi- tivity the method currently has in resolving such contributions. Here we conduct a series of experiments on samples with known ratios of crystalline quartz and amorphous glassy silica to examine this question in detail. We propose systematic methods to obtain the best possible resolution in samples with unknown phase ratios and we discuss some problems one might encounter during analysis. [Preview Abstract] |
Friday, October 26, 2012 10:52AM - 11:04AM |
B4.00002: Extending the Band Model of Disordered SiO$_{2}$ Through Cathodoluminescence Studies Amberly E. Jensen, J.R. Dennison, Gregory Wilson, Justin Dekany Optical coatings of disordered thin film SiO$_{2}$/SiO$_{x}$ dielectric samples on reflective metal substrates exhibited electron-induced luminescence (cathodoluminescence) under electron beam irradiation in an ultrahigh vacuum chamber at the USU facilities. These experiments provided measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures (300 K to 40 K). Early results from these experiments have led to a preliminary model of the band structure of highly disordered trapped states within the band gap of SiO$_{2}$. We now extend this model to further describe the excitation of electrons from the valence band to the conduction band and subsequent relaxation into trapped states. The model for cathodoluminescence is used to describe the experimental observations, providing a fundamental basis for understanding the dependence of cathodoluminescence on irradiation time, incident flux and energy, and sample thickness and temperature. [Preview Abstract] |
Friday, October 26, 2012 11:04AM - 11:16AM |
B4.00003: Wet Nano-Bonding of Silica-to-Si and Silica-to-Silica below 200$^{\circ}$ C by H2O catalysis and a 2-D precursor phase: TMAFM, Hydroaffinity and Surface Free Energy Analysis Ross Bennett-Kennett, Shawn Whaley, Nicole Herbots, Clarizza Watson, Robert Culbertson, Peter Rez, Ashlee Murphy, Sam Farmer, David Sell, Brett Hughes, Ajju Acharya Hydroxylated silica about 2.1 $\pm$ 0.1 nm thick are nucleated on OH(1x1)Si(100) as precursor phase to cross-bond directly silica to Si, and silica to silica using planarization via extended atomic terraces, T$\le $ 200$^{\circ}$C, an H2O/O2 ambient, and p $\ge $ 1 atm. This method,``Wet Nano-Bonding\texttrademark,'' relies on the Herbots-Atluri process [1] to nucleate precursor phases to bond via direct hydroxylated silica molecular cross-bridges two surfaces brought into contact at the nano-scale. Ordered Si2(OH)4 $\beta $-cristobalite precursor phases exhibit atomic terraces that extend to \textgreater 20 nm, in contrast to the 2 nm width in ``as received'' Si(100) wafers. $\beta $-cristobalite nano-phases can desorb at low temperatures (T \textless / $\sim$ 200$^{\circ}$ C) [3]. These ordered oxides can promote the growth of flatter, smoother, better controlled oxides at low temperatures in ambient air. When put into close contact at T$\ge $ 200$^{\circ}$ C with oxygen-deficient phases of SiOx used in microelectronics, they can consistently nucleate a cross-bridging between the two substrates, or ``nano-bonding'' inter-phase [4] between various combinations Si and silica provided an H2O/O2 ambient catalyzes low temperature oxidation and nano-contacting is achieved via pressurization in the nano-bonding chamber. [Preview Abstract] |
Friday, October 26, 2012 11:16AM - 11:28AM |
B4.00004: Temperature-Dependent Radiation Induced Conductivity of Diverse Highly Disordered Insulating Materials J.R. Dennison, Gregory Wilson Incident high energy electron radiation deposits energy in highly disordered insulating materials, exciting electrons from localized trap states into the conduction band, thereby enhancing the radiation induced conductivity (RIC) of these extremely poor conductors. RIC depends on the power deposited in the material and sample temperature, through the details of the energy density of disordered states within the band gap. We compare RIC measurements from 30 K to 300 K for two materials---polymeric polyimide (Kapton) and glassy fused silica (SiO$_{2}$/SiO$_{x})$---that exhibit different temperature dependence and response as the electron beam is turned on and off. A simple theory for RIC, based on thermally-assisted hopping conductivity, is presented to explain the observed differences in terms of constant, exponential and Gaussian densities of disordered states. We also discuss the differences seen which result from the use of very high energy (10's MeV) penetrating radiation (which deposits primarily energy in the thin samples) and high energy (100's keV) nearly-penetrating radiation (which deposits both energy and some charge in the materials). [Preview Abstract] |
Friday, October 26, 2012 11:28AM - 11:40AM |
B4.00005: Space Impact Ejecta Model of Micrometeoroid Collision on MISSE-6 Kelby Peterson, J.R. Dennison The Utah State University SUSpECS project allowed for pre- and post-flight analysis of various materials used in space-component design. Approximately 180 samples were flown on MISSE-6 and spent 18 months suspended off the side of the International Space Station. This presentation focuses on a thin film of polyethylene terephthalate (PET) MylarTM coated with Vapor Deposited Aluminum (VDA). Samples that were part of the Materials International Space Station Experiment (MISSE) experienced diverse effects whilst exposed to the space environment. This sample displayed evidence of atomic oxygen erosion of the VDA, UV-induced discoloration of the polymer, and a crater created by a micrometeoroid impact. There is a lack of data pertaining to the effects of micrometeoroids on space components; in order to further understand these effects, a simulation of the UV radiation was tested on similar polymers at varying intensities. Vaporization energy calculations were used to estimate the pre-impact velocity and mass of the micrometeoroid, the trajectory of the impact ejecta and its effects on surrounding material. It is of particular interest to note that VDA-coated MylarTM is a major component in the construction of astronaut suits, which could be penetrated by such impacts. [Preview Abstract] |
Friday, October 26, 2012 11:40AM - 11:52AM |
B4.00006: High Temperature and High Pressure Mixtures of Iron Oxides from the Impact Event at the Bee Bluff Crypto-Meteorite Impact Crater of South Texas R.A. Graham Disturbed geology within a several km diameter surface area of sedimentary Carrizo Sandstone near Uvalde, Texas, indicates the presence of a partially buried meteorite impact crater. Identification of its impact origin is supported by detailed studies but quartz grains recovered from distances of about100 km from the structure also show planar deformation features (PDFs). While PDFs are recognized as uniquely from impact processes, quantitative interpretation requires extension of Hugoniot materials models to more realistic grain-level, mixture models. Carrizo sandstone is a porous mixture of fine quartz and goethite. At impact pressures of tens of GPa, goethite separates into hematite and water vapor upon release of impact pressure. Samples from six different locations up to 50 km from the impact site preserve characteristic features resulting from mixtures of goethite, its water vapor, hematite and quartz. Spheroids resulting from local radial acceleration of mixed density, hot products are common at various sites. Local hydrodynamic instabilities cause similar effects. [Preview Abstract] |
Friday, October 26, 2012 11:52AM - 12:04PM |
B4.00007: Power and Charge Deposition in Multilayer Dielectrics from Monoenergetic Electron Bombardment Gregory Wilson, J.R. Dennison, Amberly Evans Jensen, Justin Dekany Power and charge deposition in multilayer dielectrics from electron bombardment is dependent upon the flux and electron range of the electron beam, where the range,--also known as the penetration depth---is dependent upon the incident beam energy. Using the Continuous Slow Down Approximation (CSDA), a composite analytical formula has been developed to relate the electron range to the dose rate and subsequently to the deposited power in each subsequent layer. Based on the constituent layer geometry and material, the deposited charge can also be inferred. To validate these models two separate experiments were conducted, one based on the net surface potential and the second on electron induced luminescence. The first experiment used a disordered SiO$_{2}$ based multilayer dielectric with a conductive middle layer. The sample was charged using 15 s pulses from an electron beam with an energy range from 200 eV to 5 keV. The second experiment also used a disordered SiO$_{2}$ based multilayer dielectric, but with energies from 5 keV to 25 keV. Results of these experiments showed the power and charge deposition's dependence on electron beam flux and incident energy, which compare favorably with the model predictions. [Preview Abstract] |
Friday, October 26, 2012 12:04PM - 12:16PM |
B4.00008: Muon Contribution to Cathodoluminescence Tests? Justin Dekany, Allen Andersen, J.R. Dennison Tests of composites incorporating highly disordered insulating materials that were bombarded with low-flux keV electron beams exhibited three distinct forms of light emission: short-duration ($<<$1 s) luminous bridge between the insulator and the grounded sample mount - ``arcs,'' intermediate-duration (10-100 s) dramatic increase in surface brightness - ``flares,'' and continuous cathodoluminescent ``glow.'' During long-duration experiments at temperatures $<$150 K, relatively intense flare events occurred at rates of $\sim $2 per min. Rapid increase in photon emission and electron displacement current were observed, with long exponential decay times $>$1 min. We propose that the source of the flares is the interactions of high energy muons, of cosmic ray origin, with the highly-charged insulating components of the composite materials which trigger avalanche electrostatic discharge and subsequent recharging along with concomitant light emission. We review evidence from the insulator conductivity at low temperatures, the rates and magnitude of surface charging, the flare frequency, and the magnitude and time-dependence of currents and light emission with regard to this muon hypothesis. A muon coincidence detection experiment using scintillation detectors is proposed to investigate the potential correlation between incident muons and the observed flares. [Preview Abstract] |
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