91 Matching Results

Search Results

Advanced search parameters have been applied.

Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds

Description: The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.
Date: December 31, 2002
Creator: Classen, Nathan Robert
Partner: UNT Libraries Government Documents Department

Magnetic phase diagrams of UNiGe

Description: UNiGe undergoes two magnetic transitions in zero field. Here, the magnetic diagrams of UNiGe for B {parallel} b and B {parallel} c are reported. We performed temperatures scans of the magnetization in static magnetic fields up to 19.5T applied along the b and c axes. For both orientations 3 magnetic phases have been identified in the B-T diagrams. We confirmed the previously reported phase boundaries for B {parallel} c, and in addition we determined the location of the phase boundaries for B {parallel} b. We discuss a possible relationship of the two zero-field antiferromagnetic phases (commensurate: T<42K; incommensurate: 42K<T<50K) and the field-induced phase, which, at low temperatures, occurs between 18 and 25T or 4 and 10T for B {parallel} b or B {parallel} c, respectively. Finally, we discuss the field dependence of the electronic contribution {gamma} to the specific heat for B {parallel}c up to 17.5T, and we find that its field dependence is similar to the one found in more itinerant uranium compounds.
Date: November 1, 1997
Creator: Nakotte, H.; Hagmusa, I.H.; Klaasse, J.C.P.; Nakotte, H.; Lacerda, A.H.; Hagmusa, I.H. et al.
Partner: UNT Libraries Government Documents Department

Amorphous/crystalline structure and phase transformations in metastable semiconducting Ge{sub 1{minus}x}Sn{sub x}

Description: The semiconducting crystalline alloys, Ge{sub 1{minus}x}Sn{sub x}, are of interest due to theoretical predictions about their electronic band structures which make them useful in infrared photodetectors. However the composition region where these alloys have the desired properties is greater than the equilibrium solid solubility limit of Sn in Ge (x {le} 0.01). The authors have circumvented the solubility limits and produced thin (2,000 {angstrom}) and thick (4--8 {mu}m) films of Ge{sub 1{minus}x}Sn{sub x} (x {le} 0.31) by rf sputtering. Differential scanning calorimetry (DSC) measurements were performed to study grain growth and crystallization processes in these highly metastable semiconductors. X-ray and electron diffraction measurements indicated the materials were amorphous, but the fact that some of the films were fine grained polycrystalline samples only became apparent in their DSC spectra. The authors present models that describe quantitatively the transformation behavior in both sets of films.
Date: December 1, 1993
Creator: Lee, S. M. & Barmak, K.
Partner: UNT Libraries Government Documents Department

Radio-frequency measurements of UNiX compounds (X= Al, Ga, Ge) in high magnetic fields

Description: We performed radio-frequency (RF) skin-depth measurements of antiferromagnetic UNiX compounds (X=Al, Ga, Ge) in magnetic fields up to 60 T and at temperatures between 1.4 to {approx}60 K. Magnetic fields are applied along different crystallographic directions and RF penetration-depth was measured using a tunnel-diode oscillator (TDO) circuit. The sample is coupled to the inductive element of a TDO resonant tank circuit, and the shift in the resonant frequency {Delta}f of the circuit is measured. The UNiX compounds exhibit field-induced magnetic transitions at low temperatures, and those transitions are accompanied by a drastic change in {Delta}f. The results of our skin-depth measurements were compared with previously published B-T phase diagrams for these three compounds.
Date: January 1, 2009
Creator: Mielke, Charles H; Mcdonald, David R; Zapf, Vivien; Altarawneh, Moaz M; Lacerda, Alex H; Adak, Sourav et al.
Partner: UNT Libraries Government Documents Department

Research in chemical kinetics. Progress report, July 20, 1988--August 30, 1989

Description: A major aspect of our research over the past decade under this contract has been the application of radioisotopes generated by nuclear reactions for the study of various kinetic mechanisms. Two general theoretical concepts have been explored in detail by this technique: (a) The addition of halogen atoms to olefins, which have been described for fifty years by the phrase {open_quotes}anti-Markownikoff{close_quotes} to indicate that the preference for one or the other end of an unsymmetric olefin is opposite to that ({open_quotes}Markownikoff addition{close_quotes}) for hydrogen halide addition. (b) The redistribution of internal energy within a molecule after an energetic addition reaction, for which the usual assumption is rapid equilibration into all available degrees of freedom, as calculated by the Rice-Rarnsperger-Kassel-Marcus (RRKM) model. In both instances, significant results have been obtained which expand the overall view of each of these two concepts.
Date: September 1, 1996
Creator: Rowland, F.S.
Partner: UNT Libraries Government Documents Department

Anisotropic Exchange Interactions in UNiGe

Description: UNiGe crystallizing in the orthorhombic TiNiSi-type of structure orders magnetically below T{sub N}= 50 K with an additional magnetic phase transition at 42 K. Both structures (below 42 K commensurate antiferromagnetic, between 42 K and T{sub N} incommensurate) are non- collinear with significant a-axis component ({mu}{sub x} = 0.35 {mu}{sub B}U at 20 K). The magnetic properties are highly anisotropic both in the ordered and the paramagnetic state. There are two metamagnetic transitions both with the field applied along the b- and the c-axis. While the magnetic structure above the second metamagnetic transition is forced ferromagnetic for both field orientations, for the field applied along the a-axis the magnetization curve at 4.2 K is linear up to 38 T and no change in magnetic structure is observed.
Date: April 25, 1997
Creator: Chatel, P.F. de; Prokes, K.; Bruck, E.; Boer, F.R. de; Nakotte, H.; Purwanto, A. et al.
Partner: UNT Libraries Government Documents Department

High-temperature borate liquids: physical properties of glass-forming compositions

Description: Several experimental routes can be used to develop a better understanding of the polymeric constitution (polyanionic and/or polyhedral distribution) of borate, germanate, and silicate glasses. Spectral, chemical, physical-chemical, and mechanical property information can be determined directly for the glass compositions of interest. Generally, only physical-chemical information is readily accessible for the corresponding high temperature liquids. It will be shown that information on each state of matter has its own particular merits. Most of the evidence thus far published suggests an excellent agreement between polyhedral distributions in an oxide glass and its corresponding high temperature liquid state. There is no well known oxide glass forming system for which such a state of affairs does not exist. In spite of this, occasional efforts are put forth which ignore some of what is known for oxide liquids, glasses, and crystals. Such attempts therefore invariably imply, if only indirectly, that significant changes occur in the polyhedral distributions close to the glass transition temperature region. Specific examples to be discussed will include efforts that avoid well known coordination change equilibria such as BO/sub 3/ reversible BO/sub 4/ and GeO/sub 4/ reversible GeO/sub 6/.
Date: May 6, 1977
Creator: Riebling, E.F.
Partner: UNT Libraries Government Documents Department

Alkylene-bridged polygerm- and polygermsilsesqui-oxanes: New hybrid organic-inorganic materials

Description: Alkylene-bridge polygerm- and polygermsilsequioxanes have been formed by hydrolysis-condensation of their corresponding (EtO){sub 3}M(CH{sub 2}){sub n}Ge(OEt){sub 3} monomers under HCl- and NEt{sub 3}-catalyzed conditions in ethanol. Solid state {sup 13}C and {sup 29}Si NMR indicate the retention of the alkylene bridging moiety during polymerization. The resulting aerogels are mesoporous materials with high surface areas. Incorporation of the short ethylene bridging unit results in higher surface areas than when heylene bridges are present. The porous nature of hexylene-bridged hybrid network [Si(CH{sub 2}){sub 6}GeO{sub 3}]{sub n} appears insensitive to the acidic or basic nature of the catalyst employed in it formation, in contrast to its polysilsesquioxane counterpart. Work is underway to determine the origin of porosity in these materials, and to characterize xerogel materials generated from these monomers.
Date: December 31, 1993
Creator: Jamison, G. M.; Loy, D. A.; Zender, G. & Shea, K. J.
Partner: UNT Libraries Government Documents Department

Improved thermal storage module for solar dynamic receivers

Description: This invention relates to a thermal storage apparatus and more particularly to an apparatus for use in conjunction with solar dynamic energy storage systems. The invention is comprised of a thermal energy storage system comprising a germanium phase change material and a graphite container.
Date: December 31, 1990
Creator: Beatty, R. L. & Lauf, R. J.
Partner: UNT Libraries Government Documents Department


Description: When processing High Level Waste (HLW) glass, the Defense Waste Processing Facility (DWPF) cannot wait until the melt or waste glass has been made to assess its acceptability, since by then no further changes to the glass composition and acceptability are possible. Therefore, the acceptability decision is made on the upstream feed stream, rather than on the downstream melt or glass product. This strategy is known as 'feed forward statistical process control.' The DWPF depends on chemical analysis of the feed streams from the Sludge Receipt and Adjustment Tank (SRAT) and the Slurry Mix Evaporator (SME) where the frit plus adjusted sludge from the SRAT are mixed. The SME is the last vessel in which any chemical adjustments or frit additions can be made. Once the analyses of the SME product are deemed acceptable, the SME product is transferred to the Melter Feed Tank (MFT) and onto the melter. The SRAT and SME analyses have been analyzed by the DWPF laboratory using a 'Cold Chemical' method but this dissolution did not adequately dissolve all the elemental components. A new dissolution method which fuses the SRAT or SME product with cesium nitrate (CsNO{sub 3}), germanium (IV) oxide (GeO{sub 2}) and cesium carbonate (Cs{sub 2}CO{sub 3}) into a cesium germanate glass at 1050 C in platinum crucibles has been developed. Once the germanium glass is formed in that fusion, it is readily dissolved by concentrated nitric acid (about 1M) to solubilize all the elements in the SRAT and/or SME product for elemental analysis. When the chemical analyses are completed the acidic cesium-germanate solution is transferred from the DWPF analytic laboratory to the Recycle Collection Tank (RCT) where the pH is increased to {approx}12 M to be released back to the tank farm and the 2H evaporator. Therefore, about 2.5 kg/yr of GeO{sub ...
Date: August 15, 2011
Creator: Jantzen, C. & Laurinat, J.
Partner: UNT Libraries Government Documents Department

Bismuth germanate's role in the new revolution in gamma-ray spectroscopy

Description: Some of the considerations on how to effectively incorporate bismuth germanate into complex detection systems are covered, and some of these new systems now in operation or under construction are discussed. Significant achievements in gamma ray spectroscopy are reviewed as well as some recent results based on data taken with coincidence arrays of germanium detectors and Compton-suppression spectrometers. Then the first impact of bismuth germanate detectors on our understanding of the properties of nuclei that have high energy and very high angular momentum states are addressed. (LEW)
Date: January 1, 1983
Creator: Johnson, N.R.; Baktash, C. & Lee, I.Y.
Partner: UNT Libraries Government Documents Department

The crystal and molecular structure of azatranes: Azavanadatran (Z=t-Bu), monoazasilatrane (Z=H), azalithatrane (Z=Clo*4*), azaphosphatrane (Z=Me), azagermatrane (Z=t-Bu) and Azaalumatran (Z=nothing)

Description: The crystal and molecular structures of azatranes have been extensively studied for a variety of M atoms. The crystal and molecular structures of six similar cage compounds: (t-Bu)NV(MeNCH{sub 2}CH{sub 2}){sub 3}N, HSi(OCH{sub 2}CH{sub 2}){sub 2}(HNCH{sub 2}CH{sub 2})N, O{sub 4}ClLi(HNCH{sub 2}SH{sub 2}){sub 3}N, MeP(Me{sub 3}NCH{sub 2}CH{sub 2}){sub 3}N, t-BuGe(HNCH{sub 2}CH{sub 2}){sub 3}N, and Al(Me{sub 3}SiNCH{sub 2}CH{sub 2}){sub 3}N were determined by the use of three-dimensional, single crystal x-ray diffraction.
Date: April 23, 1996
Creator: Wang, T.
Partner: UNT Libraries Government Documents Department

Target selection for the HRIBF Project

Description: Experiments are in progress at the Oak Ridge National Laboratory (ORNL) which are designed to select the most appropriate target materials for generating particular radioactive ion beams for the Holifield Radioactive Ion Beam Facility (HRIBF). The 25-MV tandem accelerator is used to implant stable complements of interesting radioactive elements into refractory targets mounted in a high-temperature FEBIAD ion source which is on-line at the UNISOR facility. These experiments permit selection of the target material most appropriate for the rapid release of the element of interest, as well as realistic estimates of the efficiency of the FEBIAD source. From diffusion release data information on the release times and diffusion coefficients can be derived. Diffusion coefficients for CI implanted into and diffused from CeS and Zr{sub 5}Si{sub 3} and As, Br, and Se implanted into and diffused from Zr{sub 5}Ge{sub 3} have been derived from the resulting intensity versus time profiles.
Date: December 31, 1994
Creator: Dellwo, J.; Alton, G.D. & Batchelder, J.C.
Partner: UNT Libraries Government Documents Department

Improved thermal storage module for solar dynamic receivers

Description: This invention relates to a thermal storage apparatus and more particularly to an apparatus for use in conjunction with solar dynamic energy storage systems. The invention is comprised of a thermal energy storage system comprising a germanium phase change material and a graphite container.
Date: January 1, 1990
Creator: Beatty, R.L. & Lauf, R.J.
Partner: UNT Libraries Government Documents Department

In situ TEM studies of the growth of strained Si sub 1 minus x Ge sub x by solid phase epitaxy

Description: In this paper we report on the epitaxial growth of strained thin films Si{sub 1-x}Ge{sub x} on Si by solid phase epitaxy. For these solid phase epitaxy experiments, a 180-nm-thick strained-layer of Si{sub 1-x}Ge{sub x} with x{sub Ge} = 11.6 at. % was epitaxially grown on {l angle}001{r angle} Si using chemical vapor deposition. The near surface region of the substrate, including the entire Si{sub 1-x}Ge{sub x} film, was then amorphized to a depth of 380 nm using a two step process of 100 keV, followed by 200 keV, {sup 29}Si ion implantation. The epitaxial regrowth of the alloy was studied with in situ TEM heating techniques which enabled an evaluation of the activation energy for strained solid phase epitaxial regrowth. We report that the activation energy Si{sub 1-x}Ge{sub x} (x = 11.6 at. %) strained-layer regrowth is 3.2 eV while that for unstrained regrowth of pure Si is 2.68 eV and that regrowth in the alloy is slower than in pure Si over the temperature range 490 to 600{degree}C. 8 refs., 3 figs., 1 tab.
Date: January 1, 1990
Creator: Paine, D.C.; Howard, D.J. (Brown Univ., Providence, RI (USA). Div. of Engineering); Evans, N.D. (Oak Ridge Associated Universities, Inc., TN (USA)); Greve, D.W.; Racanelli, M. (Carnegie-Mellon Univ., Pittsburgh, PA (USA). Dept. of Electrical and Computer Engineering) & Stoffel, N.G. (Bellcore, Red Bank, NJ (USA))
Partner: UNT Libraries Government Documents Department

Crystal growth from the vapor in low gravity environments

Description: Effects of earth's gravity on fluids and gases are discussed. Crystal growth in microgravity has been studied since the first Skylab mission. Crystal growth from the vapor has been accomplished in space using the chemical vapor transport method, and the principles behind this method and the results obtained in space are discussed, particularly in the germanium chalcogenide systems. Chemical vapor deposition in space offer promising applications. (DLC)
Date: January 1, 1985
Creator: Santandrea, R.P.
Partner: UNT Libraries Government Documents Department

Monte Carlo calculations of the optical coupling between bismuth germanate crystals and photomultiplier tubes

Description: The high density and atomic number of bismuth germanate (Bi/sub 4/Ge/sub 3/O/sub 12/ or BGO) make it a very useful detector for positron emission tomography. Modern tomograph designs use large numbers of small, closely-packed crystals for high spatial resolution and high sensitivity. However, the low light output, the high refractive index (n=2.15), and the need for accurate timing make it important to optimize the transfer of light to the photomultiplier tube (PMT). We describe the results of a Monte Carlo computer program developed to study the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency. The program simulates total internal, external, and Fresnel reflection as well as internal absorption and scattering by bubbles.
Date: October 1, 1981
Creator: Derenzo, S.E. & Riles, J.K.
Partner: UNT Libraries Government Documents Department

Photochemistry and radiation chemistry of volatile silanes and germanes. Progress report, September 1, 1978-August 31, 1979

Description: The following are reported: reactions of methyl cations with ethylsilanes; reactions of ethyl, propyl, and butyl cations with methyl and ethylsilanes; the 147-nanometer photolysis of disilane; lifetimes and collisional stabilization of chemically activated ethylsilyl cations; formation of GeH/sub 5//sup +/ and the proton affinity of GeH/sub 4/; and multiphoton infrared decomposition of silanes.
Date: January 1, 1979
Creator: Lampe, F.W.
Partner: UNT Libraries Government Documents Department

Oxide effects on photoemission from high current GaAs photocathodes

Description: During four years of on line operation of the SLAC polarized electron gun (PEGGY) and polarized LEED (PLEED) system, we have observed and characterized the failure modes of the GaAs (100) photocathodes (PC's) used in these systems. Several modes are observed. Gradual decreases in electron polarization and intensity are attributed to the physisorption of CO/sub 2/ on the PC's during running at LN/sub 2/ temperatures. Such PC's can be rejuvenated by warming to 90K, i.e., above the CO/sub 2/ desorption temperature. These PC's recover 90% of their original intensity. A second well-characterized failure mode results from overheating the PC during in-situ heat cleaning prior to activation. In this mode, As is preferentially evaporated from the GaAs, leaving a Ga/sub 2/O/sub 3/ layer on the surface. This effect has been studied by AES sputter profiling which indicates that the substantial thickness of the oxide layer blocks photoemission. These PC's may only be recovered by chemically removing the oxide layer. A third mode which is not as well characterized appears for thin Ga oxide layers. Properties of these PC's include reduced emission and the presence of a cutoff bias level. Such PC's are also not recoverable in-situ.
Date: March 1, 1981
Creator: Garwin, E.L.; Kirby, R.E.; Sinclair, C.K. & Roder, A.
Partner: UNT Libraries Government Documents Department

Electron microscopy study of microsegregation and defects in Czochralski grown calcium gallium germanium garnet single crystals

Description: Microstructural defects in single crystal specimens of calcium gallium germanium garnet (CGGG or Ca/sub 3/Ga/sub 2/Ge/sub 3/O/sub 12/) have been investigated using electron microscopy techniques. High voltage transmission electron imaging and diffraction were used to characterize the observed defects with respect to their morphology, structure, and crystallography. Scanning transmission electron microscopy (STEM) with x-ray microanalysis was employed to determine the elemental composition of certain defects.
Date: September 1, 1978
Creator: Roth, T.F.
Partner: UNT Libraries Government Documents Department

Photoluminescence of ZnGe{sub 0.68}Si{sub 0.32}As{sub 2}

Description: A ZnGe{sub 0.68}Si{sub 0.32}As{sub 2} layer epitaxially grown on GaAs was investigated for polarized photoluminescence. The luminescence peaks found around 1.5 eV were attributed to the GaAs substrate. Within our detection limits and with 2.4 eV excitation we could not detect photoluminescence in the energy range between 1.4 and 2.3 eV from the layer. The luminescence characteristics of the layer sample were the same as for the GaAs reference sample except for a small shift of the low energy peak towards higher energies at temperature below 30 K. The luminescence polarization as a function of the excitation energy agrees with the curve found for the reference GaAs samples. The maximum luminescence polarization of 25% is not exceeded. The absorption behavior of the layer indicated an indirect bandgap at approximately 1.55 eV at 10 K. An indirect bandgap can account for the absence of luminescence, however such material is not suitable for an efficient spin polarized electron cathode.
Date: January 1, 1991
Creator: Kimmel, M.
Partner: UNT Libraries Government Documents Department