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Molecular structure determination for photogenerated intermediates in photoinduced electron transfer reactions using steady-state and transient XAFS

Description: Many photoinduced electron transfer reactions are accompanied by nuclear rearrangements of the molecules involved. In order to understand the reactivities of the molecules and the reaction mechanisms, precise information on the molecular structural changes accompanying the electron transfer is often required. We present here conventional XAFS and transient energy dispersive XAFS studies on structures of excited and photoinduced charge separated state of porphyrin and porphyrin based supermolecules, and structures of TiO{sub 2} colloid and the heavymetal ions that bind to the colloid surfaces during photocatalytic reductions.
Date: October 1, 1996
Creator: Chen, L.X.; Wasielewski, M.R. & Rajh, T.
Partner: UNT Libraries Government Documents Department

Ab-initio calculations of density of states for Ti-oxide

Description: Electron energy-loss spectroscopy has been shown to be a powerful tool to determine the chemistry and the electronic structure at grain boundaries by analyzing the energy loss near edge structure (ELNES). This paper describes the ability of ab-initio density of state calculations to perform detailed quantitative analysis at interfaces.
Date: April 1, 1997
Creator: Duscher, G.; Koestlmeier, S. & Elsaesser, C.
Partner: UNT Libraries Government Documents Department

Rutherford backscattering analysis of the failure of chlorine anodes

Description: Rutherford Backscattering Spectrometry, carried out at the ORNL Surface Modification And Characterization Collaborative Research Center (SMAC) facility, has been applied to the nondestructive analysis of Ru02-Ti02 electrodes of 5000A, which mimic the DSA anodes in composition and the method of preparation. Occidental Chemical Corporation provided electrodes, which had been subjected to lifetime testing in H2S04 solution, for analysis by ORNL. The results were used to test the hypothesis of degradation of these, and similar electrodes, from a process involving a decrease in the Ru02:Ti02 ratio at and near the electrode surface and the related decrease in the electrode electrical conductivity. The drop in electrode activity is closely linked to a decrease in Ru content, and the measured profiles show that the loss takes place across the thin Ru02-Ti02 coating. No buildup of a pure Ti02 layer is apparent. The data agree quantitatively with the critical concentration previously reported by ORNL for materials produced by ion implantation and characterized by Rutherford Backscattering Spectrometry and Photoacoustic Spectrometry. The study has brought a better understanding of the degradation process in electrodes of great technological importance, and has given a more solid background in designing new fabrication procedures for improved electrodes.
Date: June 1996
Creator: Tilak, B. V. & Vallet, C. E.
Partner: UNT Libraries Government Documents Department

Several Technical Measures to Improve Ultra-High and Extreme-High Vacuum

Description: Achieving UHV/XHV with out high temperature bake outs is becoming essential in many applications. In this study, we investigated the use of inexpensive silica and titanium oxide thin film coatings on UHV/XHV chambers/components to reduce the adsorption of water on the chamber walls. Water can be cracked into oxygen and hydrogen in the material and act as one of the sources of hydrogen. We have also implemented backing of the turbo pump with an ion pump for reducing the vacuum chamber pump down times into UHV/XHV pressure range. The results of these investigations are summarized in this paper.
Date: November 1, 2002
Creator: Dong, Changkun; Mehrotra, Parixit & Myneni, Ganapati Rao
Partner: UNT Libraries Government Documents Department

Dye Sensitization of Semiconductor Particles

Description: In this project electron transfer at semiconductor liquid interfaces was examined by ultrafast time-resolved and steady-state optical techniques. The experiments primarily yielded information about the electron transfer from titanium dioxide semiconductor particles to absorbed molecules. The results show that the rate of electron transfer depends on the structure of the molecule, and the crystalline phase of the particle. These results can be qualitatively explained by Marcus theory for electron transfer.
Date: January 13, 2003
Creator: Hartland, G. V.
Partner: UNT Libraries Government Documents Department

Optical Isolation of Scintillating Tiles Using TiO{subscript 2} Doped Epoxy for the D-Zero ICD in Run II

Description: A Run II D0 Inter Cryostat Detector tile array will be composed of 16 identical modules. Each module contains 12 optically isolated scintillating tile elements, each with dimension of 0.1 x 0.1 in {eta} and {phi} in the pseudora-pidity region from 1.1 to 1.4. The 12 tiles in a module are formed by routing grooves in a single piece of scintillator - optical isolation is achieved by fill-ing the grooves with a white re ective epoxy. The procedure for filling these isolation grooves is described here.
Date: February 16, 1999
Creator: Gallas, Elizabeth
Partner: UNT Libraries Government Documents Department

Development and testing of spheroidal inorganic sorbents

Description: Objective was to develop sodium titanate (ST) microspheres, made by the HMTA (hexamethylenetetramine) internal gelation process, to remove radionuclides and heavy metals from waste streams at DOE sites. to determine the optimum amount of ST that can be embedded in hydrous Ti oxide (HTO) microspheres, batches of 9.2 to 23.3% ST in HTO were prepared. Crush strength of the air-dried microspheres was found to be highest. Sr was removed from simulated supernatant by all composite microspheres; 13.2% ST/HTO worked best.
Date: December 3, 1996
Creator: Collins, J.L.; Egan, B.Z. & Anderson, K.K.
Partner: UNT Libraries Government Documents Department

Development of high performance refractory fibers with enhanced insulating properties and longer service lifetimes: Phase 2, Improved refractory fiber and industrial benefit development. Final report

Description: This is Phase II of a three-phase study for the development of high performance refractory fibers with enhanced insulating properties and longer service lifetimes, for use in the aluminum, glass, cement, and iron and steel industries. Fiberization of 24 out of 25 compositions in the Al{sub 2}O{sub 3}-Si0{sub 2}-Zr0{sub 2} system were achieved. These 24 and three existing fiber compositions were evaluated: The shrinkage and the crystalline and vitreous phases were determined vs heat treatment time and temperature. Four theoretical models were developed: Shrinkage, devitrification kinetics, density change, and fiberization. Although some of the fibers formed during Phase II had properties as good as the reference ASZ fiber, no fiber had a significantly improved performance. This work, although not entirely successful, did produce significant benefits to refractory insulating fiber manufacturers and users: Mechanisms of both linear and thickness shrinkage for vitreous refractory fibers were determined, devitrification kinetics were quantified and used in models to predict shrinkage during service, and the mechanism of fiber formation in the melt spinning process was studied.
Date: May 1, 1995
Creator: Cai, Yifang; Curtis, J.M.; DePoorter, G.L.; Martin, P.C. & Munoz, D.R.
Partner: UNT Libraries Government Documents Department

Novel Carbon Nanotube-Based Nanostructures for High-Temperature Gas Sensing

Description: The primary objective of this research is to examine the feasibility of using vertically aligned multi-wall carbon nanotubes (MWCNTs) as a high temperature sensor material for fossil energy systems where reducing atmospheres are present. In the initial period of research, we fabricated capacitive sensors for hydrogen sensing using vertically aligned MWCNTs. We found that CNT itself is not sensitive to hydrogen. Moreover, with the help of Pd electrodes, hydrogen sensors based on CNTs are very sensitive and fast responsive. However, the Pd-based sensors can not withstand high temperature (T<200 C). In the last year, we successfully fabricated a hydrogen sensor based on an ultra-thin nanoporous titanium oxide (TiO{sub 2}) film supported by an AAO substrate, which can operate at 500 C with hydrogen concentrations in a range from 50 to 500 ppm.
Date: August 31, 2008
Creator: Chen, Zhi & Saito, Kozo
Partner: UNT Libraries Government Documents Department

High Breakdown Strength, Multilayer Ceramics for Compact Pulsed Power Applications

Description: Advanced ceramics are being developed for use in large area, high voltage devices in order to achieve high specific energy densities (>10 6 J/m 3 ) and physical size reduction. Initial materials based on slip cast TiO2 exhibited a high bulk breakdown strength (BDS >300 kV/cm) and high permittivity with low dispersion (e�100). However, strong area and thickness dependencies were noted. To increase the BDS, multilayer dielectric compositions are being developed based on glass/TiO2 composites. The addition of glass increases the density (�99.8% theoretical), forms a continuous grain boundary phase, and also allows the use of high temperature processes to change the physical shape of the dielectric. The permittivity can also be manipulated since the volume fraction and connectivity of the glassy phase can be readily shifted. Results from this study on bulk breakdown of TiO2 multilayer structures with an area of 2cm 2 and 0.1cm thickness have measured 650 kV/cm. Furthermore, a strong dependence of breakdown strength and permittivity has been observed and correlated with microstructure and the glass composition. This paper presents the interactive effects of manipulation of these variables.
Date: July 20, 1999
Creator: Gilmore, B.; Huebner, W.; Krogh, M.L.; Lundstrom, J.M.; Pate, R.C.; Rinehart, L.F. et al.
Partner: UNT Libraries Government Documents Department

Biomimetic TiO{sub 2} photocatalysis: A model system for pyotosynthesis

Description: Illumination of semiconductor colloids with light having energy greater than the band gap leads to the formation of electron/hold pairs. Similar to the natural photosynthetic systems, rapid recombination of photogenerated carriers is prevented by removal of one or both carriers from the semiconductor particle. Since the lifetime of charged pairs is very short, only very fast reactions with adsorbed species lead to efficient charge separation. Concurrently, surface adsorption also results in the blocking of the surface states that thermalize photogenerated charges and convert useful energy into heat. Thus, if the surface of the colloid is properly engineered the kinetics of the photochemical reactions and the redox properties of photogenerated charges in the modified colloids may be enhanced for stabilized charge separation, such as in natural photosynthesis. We have shown that adsorption of {alpha}-substituted mercapto-carboxylic acids on small particle TiO{sub 2} colloids results in the bidentate coordination of surface Ti atoms with carboxyl and mercapto groups. This complex is stabilized by the formation of a five membered ring which is the optimal configuration for octahedral coordination of Ti atoms. This surface modification of TiO{sub 2} results in the formation of a charge transfer complex that shifts the optical absorption threshold to the visible region of the spectrum (520 nm). These complexes provide more favorable absorbance properties for solar energy conversion. In this work we are applying electron paramagnetic resonance (EPR) to study the transient species formed by the reactions initiated by charge transfer or colloid photoabsorption.
Date: March 1, 1996
Creator: Thurnauer, M.C.; Rajh, T. & Tiede, D.M.
Partner: UNT Libraries Government Documents Department

Growth and properties of PbTiO{sub 3}/PLT heterostructures

Description: Ferroelectric superlattice structures composed of three-dimensionally epitaxial PbTiO{sub 3} and PLT thin films have been successfully grown on SrTiO{sub 3} substrates by metalorganic chemical vapor deposition. The modulation structures were confirmed by {theta}-2{theta} XRD, and the excellent in-plane orientational relationship between the superlattice film and the substrate by (100), (110), and (111)-pole figures. The {phi}-scans through the (110) and (111) reflections were used as additional evidence for three-dimensional epitaxy. The substrate dependence of the epitaxial orientation of PLT and PbTiO{sub 3} single-layered thin films was investigated. PbTiO{sub 3} thin films with very high crystalline perfection can be successfully grown on KTaO{sub 3} substrates.
Date: April 1, 1995
Creator: Kim, Yeongkwan; Han, Y.H. & Erbil, A.
Partner: UNT Libraries Government Documents Department

Final flush of the shielded cells melter

Description: A flush of the Savannah River Technology Center (SRTC) Shielded Cells melter was performed after the completion of a campaign to vitrify loaded crystalline silicotitanate (CST) ion exchange medium. The purpose of the flush was to lower levels of radioisotopes accumulated during the campaign and to lower the level of titanium dioxide present in the glass. This in turn would ready the melter for future campaigns involving the Defense Waste Processing Facility (DWPF).
Date: September 29, 1997
Creator: Marshall, K.M.; Fellinger, T.L. & Harbour, J.R.
Partner: UNT Libraries Government Documents Department

Magnetic excitations in a random exchange system Fe{sub x}Mn{sub 1-x}TiO{sub 3}

Description: In order to examine the influence of exchange frustration on spin wave excitations, inelastic neutron scattering experiments have been performed on a random exchange system Fe{sub x}Mn{sub l-x}TiO{sub 3} with x = 0.00, 0.10, 0.25 and 0.33. For all three mixed systems, the magnetic excitation spectra consist of two components: a well-defined spin wave component and a broad damped component. The latter can be well fitted to a spectral weight function for a damped harmonic oscillator.
Date: August 24, 1994
Creator: Kawano, H.; Yoshizawa, H.; Nicklow, R.M. & Ito, A.
Partner: UNT Libraries Government Documents Department

Effective medium approximation of the optical properties of electrochromic cerium-titanium oxide compounds

Description: Cerium titanium oxide samples derived from a solution have been compared against sputtered films over a wide range of different compositions. X-ray diffraction was used to investigate the structural properties of the compound material existing in a two-phase mixture M{sub A}O{sub 2}-M{sub B}O{sub 2}. The optical properties were evaluated over the whole solar spectrum by variable angle spectroscopic ellipsometry combined with spectrophotometry. The spectral complex refractive index was determined for CeO{sub 2} and TiO{sub 2}, as well as for their compounds. To reduce the large number of permutations in composition of multi-component oxides it would be useful to be able to predict the properties of the mixtures from the pure oxide components. Therefore these results were compared to those obtained by effective medium theory utilizing the optical constants of CeO{sub 2} and TiO{sub 2}. In order to investigate the performance as passive counter-electrode in Li{sup +} based electrochromic devices the films were tested by cyclic voltammetry with in-situ transmission control. Chemical composition was measured by Rutherford backscattering spectrometry. Surface morphology was analyzed by atomic force microscopy.
Date: July 1, 1997
Creator: von Rottkay, K.; Richardson, T.; Rubin, M. & Slack, J.
Partner: UNT Libraries Government Documents Department

RTDS: A continuous, rapid, thermal synthesis mode

Description: The Rapid Thermal Decomposition of precursors in Solution (RTDS) Process is a flow-through hydrothermal powder synthesis method capable of producing nanophase oxide and oxyhydroxide catalysts and catalyst precursors. The RTDS technique utilizes a brief exposure of dissolved precursors to high pressure/high temperature aqueous conditions to initiate crystallite nucleation. The resulting nanocrystalline suspension is removed from the hydrothermal environment through a pressure let-down device before significant crystallite growth can occur. The RTDS process is discussed as a method to produce nanocrystalline iron oxide and oxyhydroxide powders that exhibit high activity as carbon-carbon bond cleavage catalyst precursors. Nanocrystalline TiO{sub 2} and ZrO{sub 2} powders having prospective catalytic applications are also produced by the RTDS process.
Date: April 1, 1995
Creator: Matson, D.W.; Linehan, J.C.; Darab, J.D.; Buehler, M.F.; Phelps, M.R. & Neuenschwander, G.G.
Partner: UNT Libraries Government Documents Department

Determination of the 3-dimensional atomic structure at internal interfaces by electron energy loss spectroscopy

Description: The fine structure of a core-loss edge contains detailed information on the local atomic environment. It can be used as an extremely sensitive probe of the fluctuations in structure and bonding that can occur at internal interfaces. Interpretation of such fluctuations requires only a knowledge of the location of the electron probe when the spectrum is acquired and a means of interpreting the spectrum. The location of the probe can be controlled with atomic precision in the STEM by the use of the Z-contrast image, while the real space cluster methodology of multiple scattering analysis is ideally suited to the task of interpretation. This approach is used here to derive 3-dimensional models for tilt grain boundaries in TiO{sub 2} and SrTiO{sub 3}.
Date: January 1, 1997
Creator: Browning, N.D.; Wallis, D.J. & Pennycook, S.J.
Partner: UNT Libraries Government Documents Department

Parameter optimization of a microfabricated surface acoustic wave sensor for inert gas detection

Description: This work is related to designing, fabricating, and testing a surface acoustic wave sensor to be used for detecting metastable inert gases, particularly helium. The assembly consists of two microsensor configurations: (a) a reference device with no deposition at the delay line and (b) a sensing device with an Au-activated TiO{sub 2} e-beam-deposited thin film on the delay line. The interdigitated transducers and delay lines are fabricated by photolithography techniques on a single Y-cut LiNbO{sub 3} substrate oriented for Z-propagation of the acoustic waves. Variation in electrical conductivity of the Au-activated TiO{sub 2} film due to exposure to metastable He is translated as a frequency change in the assembly. Various characteristics of the surface acoustic microsensor have been studied to better understand and optimize the variation of acoustic wave velocity and the operating frequency of the microdevice. Methods for the TiO{sub 2} thin-film deposition are discussed.
Date: December 31, 1996
Creator: Ahuja, S.; Ross, C.; Chien, H.T. & Raptis, A.C.
Partner: UNT Libraries Government Documents Department

Influence of stoichiometry on the electrochromiccerium-titanium oxide compounds

Description: CeO<sub>2</sub>-TiO<sub>2</sub> finds use as passive counter-electrode in electrochromic devices. Thin films were produced by de-sputtering in a wide range of compositions. Influence of total pressure and oxygen partial pressure on the optical constants of TiO<sub>2</sub> was investigated. Slightly substoichiometric Ti0<sub>2</sub> films exhibit a red-shift of the bandgap. The Ti0<sub>2</sub> content in the compound essentially determines the degree of cathodical coloring upon Li<sup>+</sup> intercalation [1]. However, pure TiO<sub>2</sub> films with comparable visible transmittance in the clear state behave differently during electrochemical cycling depending on oxygen stoichiometry. Films that are deposited at higher total pressure are more oxygen rich and require initial formatting until current voltage cycles become stable. CeO<sub>2</sub>-Ti0<sub>2</sub> films of intermediate compositions have the relatively highest charge capacity. Comparison with atomic force microscopy indicates a correlation of small grain size with high charge capacity.
Date: November 1, 1997
Creator: Kullman, L.; Richardson, T.; Rubin, M.; Slack, J. & von Rottkay, K.
Partner: UNT Libraries Government Documents Department