Browsing by Subject "silicon"
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Item Chemical Vapour Deposition of Amorphous Ru(P) Thin Films from Ru Trialkylphosphite Hydride Complexes(2012-09) McCarty, W. Jeffrey; Yang, Xiaoping; Anderson, Lauren J. D.; Jones, Richard A.; McCarty, W. Jeffrey; Yang, Xiaoping; Anderson, Lauren J. D.; Jones, Richard A.The ruthenium phosphite hydride complexes H2Ru(P(OR)(3))(4) (R = Me (1), Et (2), Pr-i (3)) were used as CVD precursors for the deposition of films of amorphous ruthenium-phosphorus alloys. The as-deposited films were X-ray amorphous and XPS analysis revealed that they were predominantly comprised of Ru and P in zero oxidation states. XPS analysis also showed the presence of small amounts of oxidized ruthenium and phosphorus. The composition of the films was found to depend on ligand chemistry as well as the deposition conditions. The use of H-2 as the carrier gas had the effect of increasing the relative concentrations of P and O for all films. Annealing films to 700 degrees C under vacuum produced films of polycrystalline hcp Ru while a flowing stream of H-2 resulted in polycrystalline hcp RuP.Item Chemically Directing D-Block Heterometallics to Nanocrystal Surfaces as Molecular Beacons of Surface Structure(2015-07) Rosen, Evelyn L.; Gilmore, Keith; Sawvel, A. M.; Hammack, April T.; Doris, Sean E.; Aloni, Shaul; Altoe, Virgina; Nordlund, Dennis; Weng, Tsu-Chien; Sokaras, Dimosthenis; Cohen, Bruce E.; Urban, Jeffrey J.; Ogletree, D. Frank; Milliron, Delia J.; Prendergasta, David; Helms, Bret A.; Milliron, Delia J.Our understanding of structure and bonding in nanoscale materials is incomplete without knowledge of their surface structure. Needed are better surveying capabilities responsive not only to different atoms at the surface, but also their respective coordination environments. We report here that d-block organometallics, when placed at nanocrystal surfaces through heterometallic bonds, serve as molecular beacons broadcasting local surface structure in atomic detail. This unique ability stems from their elemental specificity and the sensitivity of their d-orbital level alignment to local coordination environment, which can be assessed spectroscopically. Re-surfacing cadmium and lead chalcogenide nanocrystals with iron- or ruthenium-based molecular beacons is readily accomplished with trimethylsilylated cyclopentadienyl metal carbonyls. For PbSe nanocrystals with iron-based beacons, we show how core-level X-ray spectroscopies and DFT calculations enrich our understanding of both charge and atomic reorganization at the surface when beacons are bound.Item Development Of Third Harmonic Generation As A Short Pulse Probe Of Shock Heated Material(2007-12) Grigsby, W.; Cho, B. I.; Bernstein, A. C.; Quevedo, H. J.; Colvin, J.; Downer, M. C.; Ditmire, T.; Grigsby, W.; Cho, B. I.; Bernstein, A. C.; Quevedo, H. J.; Downer, M. C.; Ditmire, T.We are studying high-pressure laser produced shock waves in silicon (100). To examine the material dynamics, we are performing pump-probe style experiments utilizing 600 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. Sustained third harmonic generation (THG) during a similar to 100 kbar shock breakout indicate that the rear surface remains crystalline for at least 3 ns. However, a decrease in THG during a similar to 300 kbar shock breakout suggests a different behavior, which could include a change in crystalline structure.Item Discussion On Device Structures And Hermetic Encapsulation For SiOx Random Access Memory Operation In Air(2014-10) Zhou, Fei; Chang, Yao-Feng; Wang, Yanzhen; Chen, Yen-Ting; Xue, Fei; Fowler, Burt W.; Lee, Jack C.; Zhou, Fei; Chang, Yao-Feng; Wang, Yanzhen; Chen, Yen-Ting; Xue, Fei; Lee, Jack C.An edge-free structure and hermetic encapsulation technique are presented that enable SiOx-based resistive random-access memory (RRAM) operation in air. A controlled etch study indicates that the switching filament is close to the SiOx surface in devices with an exposed SiOx edge. Electrical test of encapsulated, edge-free devices in 1 atmosphere air indicates stable switching characteristics, unlike devices with an edge. This work demonstrates that SiOx RRAM is able to operate in air with proper encapsulation and an edge-free structure. The resistive switching failure mechanism when operating in air is explained by the oxidation of hydrogen-complexed defects in the switching filament. (C) 2014 AIP Publishing LLC.Item Effect of Si on the SLM Processability of IN738LC(University of Texas at Austin, 2015) Engeli, R.; Etter, T.; Geiger, F.; Stankowski, A.; Wegener, K.Selective laser melting of high gamma-prime strengthened superalloys such as IN738LC is of interest in stationary gas turbine applications. Differences have been obtained for the hot cracking susceptibility of different powder batches during SLM processing and indications were found that also minor elements influence the SLM processability. By processing a specific powder batch blended by different amounts of pure silicon, the detrimental effect of this element during SLM could be shown. Therefore, the control of this minor element is crucial to decrease the hot cracking tendency and can extend the SLM processing window of this alloy.Item Hydrogen Studies Including Simulations for Three Body Association and Development of In-Situ Silicon Passivation(2015-05) Morrison, Tharon D.; Raizen, Mark G.Hydrogen, for many years, has been a gateway for understanding physics in all measures and strides. This paper adds to this vibrant tradition of hydrogen, first with a computational analysis of a proposed experiment to investigate the formation via three body association of the first molecules of the universe, diatomic hydrogen and secondly with development of a technique to terminate the surface of a silicon crystal with hydrogen isotopes to eventually make measurements of the neutrino mass. In order for the three body association of hydrogen to occur, particular temperature and density constraints must be met. These have been fleshed out in the following pages. A computational simulation of a hexapole lens acting on the hydrogen atoms suggests that it would be possible to create an experiment to make the first ever measurements of the spin-depolarized chemical process that created the first molecules. The simulation shows that using a Gaussian cube of 1E6 hydrogen atoms at a temperature of 10E-9 K and a hexapole lens capable of creating a field gradient of 1E6 Tesla per square meter, a density of 1E21 atoms per cubic meter would be achieved. Then with a laser probing for hydrogen molecules, the first spin-depolarized measurements of three body association of hydrogen could be made. This work also reviews a technique in the final stages of development for tritium passivated silicon in vacuum. There are many advantages to using tritium passivated silicon as a source for beta decay electrons. The passivation quality from the developing technique can be addressed using elastic scattering of helium off of the passivated surface.Item Letter to H.B. Stenzel from H.J. Sawin on 1962-02-16(1962-02-16) Sawin, H.J.Item The Model Marine Diatom Thalassiosira Pseudonana Likely Descended from a Freshwater Ancestor in the Genus Cyclotella(2011-05) Alverson, Andrew J.; Beszteri, Bank; Julius, Matthew L.; Theriot, Edward C.; Theriot, Edward C.Publication of the first diatom genome, that of Thalassiosira pseudonana, established it as a model species for experimental and genomic studies of diatoms. Virtually every ensuing study has treated T. pseudonana as a marine diatom, with genomic and experimental data valued for their insights into the ecology and evolution of diatoms in the world's oceans. Results: The natural distribution of T. pseudonana spans both marine and fresh waters, and phylogenetic analyses of morphological and molecular datasets show that, 1) T. pseudonana marks an early divergence in a major freshwater radiation by diatoms, and 2) as a species, T. pseudonana is likely ancestrally freshwater. Marine strains therefore represent recent recolonizations of higher salinity habitats. In addition, the combination of a relatively nondescript form and a convoluted taxonomic history has introduced some confusion about the identity of T. pseudonana and, by extension, its phylogeny and ecology. We resolve these issues and use phylogenetic criteria to show that T. pseudonana is more appropriately classified by its original name, Cyclotella nana. Cyclotella contains a mix of marine and freshwater species and so more accurately conveys the complexities of the phylogenetic and natural histories of T. pseudonana. Conclusions: The multitude of physical barriers that likely must be overcome for diatoms to successfully colonize freshwaters suggests that the physiological traits of T. pseudonana, and the genes underlying those traits, might differ from those of strictly marine diatoms. The freshwater ancestry of T. pseudonana might therefore confound generalizations about the physiological and metabolic properties of marine diatoms. The freshwater component of T. pseudonana's history merits careful consideration in the interpretation of experimental data collected for this important model species.Item Pulsed-Duty Characterization of Turn-off for a Population of SCRs and the Effect of Variation on Equalization Circuit Design(IEEE, 2003-01) Pappas, J.A.; Gattozzi, A.L.; Hebner, R.E.Turn-off characteristics of silicon-controlled rectifiers (SCRs) drive the design of snubber circuits for single devices in power converters. Turn-off characteristics also drive the design of equalization circuits for series-connected devices in power converters. For single devices, the important characteristics are peak recovery current, recovery time, and recovered charge. These characteristics are also important for series-connected devices, but it is the variation in these characteristics that define the equalization requirements. In fact, these variations are used to determine the size and power dissipation of the equalization circuit. A population of SPCO 402b pulse-rated silicon controlled rectifiers was tested and recovery characteristics were measured. The differences in recovery characteristics were tabulated and discussed. A method of equalization circuit design based on circuit variations was discussed and circuit design trades are made in light of the variations in recovery characteristics.Item Si/SiC-Ceramic Prototypes via LS2I-Process (Liquid Silicon Infiltration of Laser Sintered C-SiC Parts)(1998) Stierlen, Peter; Eyerer, PeterThe liquid silicon infiltration of laser sinteredC-~iC parts (LS2 I) is solidfreeform fabrication technique which allows the production of complexshapedSi/SiC prototypes. A mixture of SiC powder and reactive polymer binder isused in the las~r sinteringprocessto generate a porous green part. In the\postprocessing, the porous green part structure has to be infiltrated with a.precursor·resin, carbonised and finally·.infiltrated•. with molten silicon. The infiltrated silicon reacts with the residualcarbontobuild~~SiC.Results generated by the use of reduced primary particle sizes as well asaltemative infiltration materials and the use of other·RPtechniquesfor the green partfabrication will be discussed in this paper.Item Silicon Gets an Assist(The Texas Scientist, 2021) The Texas Scientist