235 Matching Results

Search Results

Advanced search parameters have been applied.

Edmonds et al. Reply

Description: This article is a response to an article by M. Adell et al. [Phy. Rev. Lett. 94, 139701 (2005)] about semiconductor-based spintronics research.
Date: April 8, 2005
Creator: Edmonds, Kevin; Boguslawski, Piotr; Wang, K. Y.; Campion, Richard Paul; Novikov, Sergei; Farley, N. R. S. et al.
Partner: UNT College of Arts and Sciences

First principle thousand atom quantum dot calculations

Description: A charge patching method and an idealized surface passivation are used to calculate the single electronic states of IV-IV, III-V, II-VI semiconductor quantum dots up to a thousand atoms. This approach scales linearly and has a 1000 fold speed-up compared to direct first principle methods with a cost of eigen energy error of about 20 meV. The calculated quantum dot band gaps are parametrized for future references.
Date: March 30, 2004
Creator: Wang, Lin-Wang & Li, Jingbo
Partner: UNT Libraries Government Documents Department

Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials

Description: Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.
Date: August 1, 2010
Creator: Kim, K. H.; Bolotnikov, A. E.; Camarda, G. S.; Marchini, L.; Yang, G.; Hossain, A. et al.
Partner: UNT Libraries Government Documents Department

The Effect of Temperature on the Breakdown and Repassivation Potentials of Welded Alloy 22 In 5 M CACI2

Description: The study of the electrochemical behavior of wrought and welded Alloy 22 was carried out in 5 M CaCl{sub 2} as a function of temperatures between 45 and 120 C with Multiple Crevice Assembly (MCA) specimens. The susceptibility to corrosion was found to increase with increase in electrolyte temperature in both the wrought (in the mill annealed condition) and the welded forms of the alloy. The weld metal was found to be less susceptible to localized corrosion under the conditions tested.
Date: July 5, 2006
Creator: IIevbare, G.O.
Partner: UNT Libraries Government Documents Department

REPASSIVATION STUDIES OF ALUMINUM USING A ROTATING STRIP ELECTRODE

Description: In this work a technique was described to study the repassivation of bare metal surfaces. The advantage of this approach over other techniques is the ease with which multiple repassivation events can be studied. The repassivation rate of aluminum was found to depend on the anion in solution. Repassivation rates are higher for aluminum in phosphate and sulfate solutions compared to borate. It is possible that borate may interact more strongly than sulfate or phosphate on the bare aluminum surface blocking the diffusion of oxygen or changing the rate of repassivation.
Date: September 1, 1977
Creator: ALDYKIEWICZ,A.J.,JR. & ISAACS,H.S.
Partner: UNT Libraries Government Documents Department

The Effects of Nitrogen on the Interface State Density Near the Conduction Band Edge in 4H and 6H-SiC

Description: Results are reported for the passivation of interface states near the conduction band edge in SiO{sub 2}/SiC MOS capacitors using post-oxidation anneals in nitric oxide, ammonia and forming gas (N{sub 2}5%H{sub 2}). Anneals in nitric oxide and ammonia reduce the interface state density significantly for 4H-SiC, while forming gas anneals are largely ineffective. Results suggest that interface states in SiO{sub 2}/SiC and SiO{sub 2}/SiC have different origins, and a model is described for interface state passivation by nitrogen in the SiO{sub 2}/SiC system. The peak inversion channel mobility measured for lateral 4H-SiC MOSFETs increases following NO passivation.
Date: June 12, 2000
Creator: Chung, G.Y.; Tin, C.C.; Isaacs-Smith, T.; Williams, J.R.; McDonald, K.; DiVentra, M. et al.
Partner: UNT Libraries Government Documents Department

Pressure Gradient Passivation of Carbonaceous Material Normally Susceptible to Spontaneous Combustion

Description: This invention is a process for the passivation or deactivation with respect to oxygen of a carbonaceous material by the exposure of the carbonaceous material to an oxygenated gas in which the oxygenated gas pressure is increased from a first pressure to a second pressure and then the pressure is changed to a third pressure. Preferably a cyclic process which comprises exposing the carbonaceous material to the gas at low pressure and increasing the pressure to a second higher pressure and then returning the pressure to a lower pressure is used. The cycle is repeated at least twice wherein the higher pressure may be increased after a selected number of cycles.
Date: July 15, 1999
Creator: Ochs, Thomas L.; Sands, William D.; Schroeder, Karl; Summers, Cathy A. & Utz, Bruce R.
Partner: UNT Libraries Government Documents Department

Passivation effects of surface iodine layer on tantalum for the electroless copper deposition.

Description: The ability to passivate metallic surfaces under non-UHV conditions is not only of fundamental interests, but also of growing practical importance in catalysis and microelectronics. In this work, the passivation effect of a surface iodine layer on air-exposed Ta for the copper electroless deposition was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Although the passivation effect was seriously weakened by the prolonged air exposure, iodine passivates the Ta substrate under brief air exposure conditions so that enhanced copper wetting and adhesion are observed on I-passivated Ta relative to the untreated surface.
Access: This item is restricted to the UNT Community Members at a UNT Libraries Location.
Date: May 2004
Creator: Liu, Jian
Partner: UNT Libraries

Excellent Passivation and Low Reflectivity Al2O3/TiO2 Bilayer Coatings for n-Wafer Silicon Solar Cells: Preprint

Description: A bilayer coating of Al2O3 and TiO2 is used to simultaneously achieve excellent passivation and low reflectivity on p-type silicon. This coating is targeted for achieving high efficiency n-wafer Si solar cells, where both passivation and anti-reflection (AR) are needed at the front-side p-type emitter. It could also be valuable for front-side passivation and AR of rear-emitter and interdigitated back contact p-wafer cells. We achieve high minority carrier lifetimes {approx}1 ms, as well as a nearly 2% decrease in absolute reflectivity, as compared to a standard silicon nitride AR coating.
Date: June 1, 2012
Creator: Lee, B. G.; Skarp, J.; Malinen, V.; Li, S.; Choi, S. & Branz, H. M.
Partner: UNT Libraries Government Documents Department

Final Report for Department of Energy grant DE-FG02-91ER45455, "Theoretical Study of Reactions at the Electrode-Electrolyte Interface"

Description: In this project, reaction rates were predicted by numerical methods, in a collaboration with Argonne National Laboratory . Emphasis is on electron transfer and transport involving ions known to be important in enhancing stress corrosion cracking in light water reactors and on electron transfer at oxide surfaces. In the latter part of the grant period we placed increased emphasis on development and use of self consistent tight binding methods for this kind of study. We showed that by careful fitting of results from first principles plane wave calculations,we could model surfaces and interfaces oxides and metals using these methods. We obtained results for the titanium/titanium oxide interface in this way and completed a model of the ruthenium dioxide surface using our innovative self consistent tight binding molecular dynamics methods. We completed development of a description of liquid water within the self consistent tight binding context and studied the rutile water 110 interface to determine if it is hydroxylated. A self consistent tight binding study of titanium metal surfaces demonstrated the usefulness of this method for metals. In collaboration with the Argonne group, we extended the tight binding calculations on rutile titania to the anatase form and made the first calculations of the relative stability of anatase and rutile as a function of crystallite size. We completed studies of small anatase particles in water using the method and found significant distortions of nanoparticle crystallite shapes as a consequence of interactions with the water.
Date: May 19, 2009
Creator: Halley, J. W.
Partner: UNT Libraries Government Documents Department

Passivation of Aluminum in Lithium-ion Battery Electrolytes withLiBOB

Description: A combination of cyclic polarization tests, electrochemical impedance spectroscopy, and electrochemical quartz crystal microbalance (EQCM) measurements indicate a film is formed when aluminum is polarized above 4.5V in 1:1 EC+DMC with 1M LiBOB. The quantity of film that is formed increases with increasing applied potential. Results of EQCM tests suggest the film is AlBO{sub 3}. The film is very protective against corrosion and inhibits pitting corrosion of aluminum in normally corrosive 1M LiTFSI.
Date: September 9, 2006
Creator: Zhang, Xueyuan & Devine, Thomas M.
Partner: UNT Libraries Government Documents Department

Mutual Passivation in Dilulte GaNxAs1-x Alloys

Description: The dilute GaN{sub x}As{sub 1-x} alloys (with x up to 0.05) have exhibited many unusual properties as compared to the conventional binary and ternary semiconductor alloys. We report on a new effect in the GaN{sub x}As{sub 1-x} alloy system in which electrically active substitutional group IV donors and isoelectronic N atoms passivate each other's activity. This mutual passivation occurs in dilute GaN{sub x}As{sub 1-x} doped with group IV donors through the formation of nearest neighbor IV{sub Ga-}N{sub As} pairs when the samples are annealed under conditions such that the diffusion length of the donors is greater than or equal to the average distance between donor and N atoms. The passivation of the shallow donors and the N{sub As} atoms is manifested in a drastic reduction in the free electron concentration and, simultaneously, an increase in the fundamental band gap. This mutual passivation effect is demonstrated in both Si and Ge doped GaN{sub x}As{sub 1-x} alloys. Analytical calculations of the passivation process based on Ga vacancies mediated diffusion show good agreement with the experimental results.
Date: March 21, 2005
Creator: Yu, K.M.; Walukiewicz, W.; Wu, J.; Mars, D.E.; Scarpulla, M.A.; Dubon, O.D. et al.
Partner: UNT Libraries Government Documents Department

Spectroscopic properties of colloidal indium phosphide quantum wires

Description: Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photo-oxidation, without a significant influence on quantum-wire photoluminescence. However, photo-oxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation, and that colloidal quantum wires have intrinsically low photoluminescence efficiencies.
Date: July 11, 2008
Creator: Wang, Lin-Wang; Wang, Fudong; Yu, Heng; Li, Jingbo; Hang, Qingling; Zemlyanov, Dmitry et al.
Partner: UNT Libraries Government Documents Department

Pressure gradient passivation of carbonaceous material normally susceptible to spontaneous combustion

Description: This invention is a process for the passivation or deactivation with respect to oxygen of a carbonaceous material by the exposure of the carbonaceous material to an oxygenated gas in which the oxygenated gas pressure is increased from a first pressure to a second pressure and then the pressure is changed to a third pressure. Preferably a cyclic process which comprises exposing the carbonaceous material to the gas at low pressure and increasing the pressure to a second higher pressure and then returning the pressure to a lower pressure is used. The cycle is repeated at least twice wherein the higher pressure may be increased after a selected number of cycles.
Date: January 29, 2002
Creator: Ochs, Thomas L.; Sands, William D.; Schroeder, Karl; Summers, Cathy A. & Utz, Bruce R.
Partner: UNT Libraries Government Documents Department

The Electrochemical Behavior of Alloy in Extreme Chloride and Bitrate Environments

Description: Alloy 22 specimens were tested in high temperature (100 to 160 C), high concentration chloride and nitrate environments. Results of this study indicate that increasing nitrate to chloride ratio to 0.5 in these electrolytes increases resistance to localized breakdown and enhances repassivation. In these extreme environments, localized corrosion occurred by pitting even though specimens were tested using artificial crevice formers. Open circuit (E{sub corr}), breakdown and repassivation potentials all increase, and pitting morphology changes as nitrate to chloride ratio increases from 0.05 and 0.15 to 0.5. Results also indicate that increasing the temperature from 100 to 160 C increases E{sub corr} values, while breakdown potentials and repassivation potentials peak at 130 C for the 0.5 nitrate to chloride ratio electrolytes.
Date: July 27, 2006
Creator: Etien, R.A.; Gordon, S.R. & Ilevbare, G.O.
Partner: UNT Libraries Government Documents Department

Deuterium adsorption on water preadsorbed uranium-niobium alloys

Description: We have investigated the adsorptiodreaction of deuterium on water pre-adsorbed oxidized uranium-niobium alloys at pressures near 1 Torr. Deuterium exposures were conducted at pressures from 1 to 4 Torr at surface temperatures between 300 and 600 K using a fixed dosing time of 30 seconds. Water is preadsorbed at room temperature at a pressure of {approx} 1 Torr for 30 seconds. Subsequent to gaseous exposure the surface temperature of the alloy was increased in a controlled manner and deuterium desorption was monitored using mass spectroscopy. Deuterium is observed to adsorb both at the surface and in the bulk of the uranium-niobium alloys. Water preadsorption prevents deuterium adsorption on all surfaces. The water forms a surface passivation layer at low temperatures that prevents deuterium uptake into the bulk and surface of the sample. As the adsorption temperature of the deuterium increases the amount of deuterium that adsorbs also increases.
Date: January 1, 2002
Creator: Jachimowski, T. A. (Thomas Alan); Paffett, M. T. (Mark T.); Kelly, D. (Daniel) & Hanrahan, R. J. (Robert J.)
Partner: UNT Libraries Government Documents Department

REVERSIBLE AND IRREVERSIBLE PASSIVATION OF A LA-NI-AL ALLOY

Description: This paper seeks to explore some of the effects of passivating a LaNi{sub 4.25}Al{sub 0.75} sample by air oxidation under controlled conditions. Passivation of this metal hydride alloy seems to have two distinct regimes. The first occurs with air oxidation at 80 C and 20 C. It is characterized by complete reversibility upon hydrogen readsorption, although said readsorption is hindered substantially at room temperature, requiring the material to be heated to produce the reactivation. The second regime is illustrated by 130 C air oxidation and is characterized by irreversible loss of hydrogen absorption capacity. This passivation does not hinder hydrogen readsorption into the remaining hydride material.
Date: June 25, 2009
Creator: Shanahan, K. & Klein, J.
Partner: UNT Libraries Government Documents Department

AIR PASSIVATION OF METAL HYDRIDE BEDS FOR WASTE DISPOSAL

Description: Metal hydride beds offer compact, safe storage of tritium. After metal hydride beds have reached the end of their useful life, the beds will replaced with new beds and the old beds prepared for disposal. One acceptance criteria for hydride bed waste disposal is that the material inside the bed not be pyrophoric. To determine the pyrophoric nature of spent metal hydride beds, controlled air ingress tests were performed. A simple gas handling manifold fitted with pressure transducers and a calibrated volume were used to introduce controlled quantities of air into a metal hydride bed and the bed temperature rise monitored for reactivity with the air. A desorbed, 4.4 kg titanium prototype hydride storage vessel (HSV) produced a 4.4 C internal temperature rise upon the first air exposure cycle and a 0.1 C temperature rise upon a second air exposure. A total of 346 scc air was consumed by the bed (0.08 scc per gram Ti). A desorbed, 9.66 kg LaNi{sub 4.25}Al{sub 0.75} prototype storage bed experienced larger temperature rises over successive cycles of air ingress and evacuation. The cycles were performed over a period of days with the bed effectively passivated after the 12th cycle. Nine to ten STP-L of air reacted with the bed producing both oxidized metal and water.
Date: July 2, 2007
Creator: Klein, J & R. H. Hsu, R
Partner: UNT Libraries Government Documents Department

Ge Interface Engineering with Ozone-oxidation for Low Interface State Density

Description: Passivation of Ge has been a critical issue for Ge MOS applications in future technology nodes. In this letter, we introduce ozone-oxidation to engineer Ge/insulator interface. Interface states (D{sub it}) values across the bandgap and close to conduction bandedge were extracted using conductance technique at low temperatures. D{sub it} dependency on growth conditions was studied. Minimum D{sub it} of 3 x 10{sup 11} cm{sup -2} V{sup -1} was demonstrated. Physical quality of the interface was investigated through Ge 3d spectra measurements. We found that the interface and D{sub it} is strongly affected by the distribution of oxidation states and quality of the suboxide.
Date: June 2, 2008
Creator: Kuzum, Duygu; Krishnamohan, T.; Pethe, Abhijit J.; Okyay, Ali K.; Oshima, Yasuhiro; Sun, Yun et al.
Partner: UNT Libraries Government Documents Department