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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


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
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

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

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

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

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

Transmission electron microscopy of undermined passive films on stainless steel

Description: A study has been made of the passive film remaining over pits on stainless steel using a high resolution transmission electron microscope. Type 305 stainless steel was passivated in a borate buffer solution and pitted in ferric chloride. Passive films formed at 0.2 V relative to a saturated calomel electrode were found to be amorphous. Films formed at higher potentials showed only broad diffraction rings. The passive film was found to cover a remnant lacy structure formed over pits passivated at 0.8 V. The metallic strands of the lace were roughly hemitubular in shape with the curved surface facing the center of the pit.
Date: June 1, 1999
Creator: Isaacs, H.S.; Zhu, Y.; Sabatini, R.L. & Ryan, M.P.
Partner: UNT Libraries Government Documents Department

Mutual passivation effects in Si-doped diluted In{sub y}Ga{sub 1-y}As{sub 1-x}N{sub x} alloys

Description: We report systematic investigations of the mutual passivation effects of Si hydrogenic donors and isovalent nitrogen in dilute InGaAs{sub 1-x}N{sub x} alloys. Upon thermal annealing at temperatures above {approx}650 C, the Si atoms diffuse assisted by the formation and migration of Ga vacancies. When they find nitrogen atoms, they form stable Si{sub Ga}-N{sub As} nearest-neighbor pairs. As a result of the pair formation, the electrical activity of Si{sub Ga} donors is passivated. At the same time, the effect of an equal number of N{sub As} atoms is also deactivated. 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. Analytical calculations of the passivation process based on Ga vacancies mediated diffusion show good agreement with the experimental results. Monte Carlo simulations have also been performed for a comparison with these results. The effects of mutual passivation on the mobility of free electrons are quantitatively explained on the basis of the band anticrossing model. Optical properties of annealed Si-doped InGaAs{sub 1-x}N{sub x} samples are also discussed.
Date: July 21, 2003
Creator: Wu, J.; Yu, K.M.; Walukiewicz, W.; He, G.; Haller, E.E.; Mars, D.E. et al.
Partner: UNT Libraries Government Documents Department

Plasma etching, texturing, and passivation of silicon solar cells

Description: The authors improved a self-aligned emitter etchback technique that requires only a single emitter diffusion and no alignments to form self-aligned, patterned-emitter profiles. Standard commercial screen-printed gridlines mask a plasma-etchback of the emitter. A subsequent PECVD-nitride deposition provides good surface and bulk passivation and an antireflection coating. The authors used full-size multicrystalline silicon (mc-Si) cells processed in a commercial production line and performed a statistically designed multiparameter experiment to optimize the use of a hydrogenation treatment to increase performance. They obtained an improvement of almost a full percentage point in cell efficiency when the self-aligned emitter etchback was combined with an optimized 3-step PECVD-nitride surface passivation and hydrogenation treatment. They also investigated the inclusion of a plasma-etching process that results in a low-reflectance, textured surface on multicrystalline silicon cells. Preliminary results indicate reflectance can be significantly reduced without etching away the emitter diffusion.
Date: November 1, 1998
Creator: Ruby, D.S.; Yang, P.; Zaidi, S.; Brueck, S.; Roy, M. & Narayanan, S.
Partner: UNT Libraries Government Documents Department

Sixth workshop on the role of impurities and defects in silicon device processing

Description: The Sixth Workshop on the Role of Impurities and Defects in Silicon Device Processing was held in Snowmass Village, August 12-14, 1996. The workshop was attended by 87 participants from academic institutions and photovoltaic industry representatives, from the United States, Australia, Belgium, Canada, France, Germany, Italy, Japan, Belgium, and The Netherlands. The workshop consisted of nine sessions that addressed different aspects of impurities and defects in silicon and applications to solar-cell processing. Each session opened with some review talks summarizing recent advances in this field and introduced important issues for further discussions during a subsequent panel discussion session. In addition, the latest research results were presented in two poster sessions.
Date: September 1, 1996
Creator: Tan, T.; Swanson, R. & Sopori, B.
Partner: UNT Libraries Government Documents Department

The effect of chromate concentration on the repassivation of corroding aluminum

Description: Current density maps of anodically polarized pure aluminum in chloride solutions were measured and the effect of chromate/dichromate buffer additions monitored. The higher the polarized potential the more chromate was required to repassivate the corroding surface. Small pits repassivated easily, crevice corrosion events were the last to repassivate. Open circuit potential measurements showed the presence of meta-stable pitting at chloride concentrations of 0.3M. The lifetime and magnitude of these metastable pits was reduced on the addition of 0.05M chromate buffer.
Date: February 9, 1999
Creator: Jeffcoate, C.S.; Isaacs, H.S.; Hawkins, J. & Thompson, G.E.
Partner: UNT Libraries Government Documents Department

Recent progress on the self-aligned, selective-emitter silicon solar cell

Description: We developed a self-aligned emitter etchback technique that requires only a single emitter diffusion and no alignments to form self-aligned, patterned-emitter profiles. Standard commercial, screen-printed gridlines mask a plasma-etchback of the emitter. A subsequent PECVD-nitride deposition provides good surface and bulk passivation and an antireflection coating. We succeeded in finding a set of parameters which resulted in good emitter uniformity and improved cell performance. We used full-size multicrystalline silicon (mc-Si) cells processed in a commercial production line and performed a statistically designed, multiparameter experiment to optimize the use of a hydrogenation treatment to increase performance. Our initial results found a statistically significant improvement of half an absolute percentage point in cell efficiency when the self-aligned emitter etchback was combined with a 3-step PECVD-nitride surface passivation and hydrogenation treatment. 12 refs., 4 figs., 3 tabs.
Date: October 1, 1997
Creator: Ruby, D.S.; Yang, P. & Roy, M.
Partner: UNT Libraries Government Documents Department

Growth and Oxidation of Thin Film Al(2)Cu

Description: Al{sub 2}Cu thin films ({approx} 382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {micro} 3 nm Al{sub 2}O{sub 3} passivating layer. X-ray Photoelectron Spectroscopy (XPS) measures a 1.0 eV shift of the Cu2p{sub 3/2} peak and a 1.6 eV shift of the valence band relative to metallic Cu upon Al{sub 2}Cu formation. Scanning Electron microscopy (SEM) and Electron Back-Scattered Diffraction (EBSD) show that the Al{sub 2}Cu film is composed of 30-70 {micro}m wide and 10-25 mm long cellular grains with (110) orientation. The atomic composition of the film as estimated by Energy Dispersive Spectroscopy (EDS) is 67 {+-} 2% Al and 33 {+-} 2% Cu. XPS scans of Al{sub 2}O{sub 3}/Al{sub 2}Cu taken before and after air exposure indicate that the upper Al{sub 2}Cu layers undergo further oxidation to Al{sub 2}O{sub 3} even in the presence of {approx} 5 nm Al{sub 2}O{sub 3}. The majority of Cu produced from oxidation is believed to migrate below the Al{sub 2}O{sub 3} layers, based upon the lack of evidence for metallic Cu in the XPS scans. In contrast to Al/Cu passivated with Al{sub 2}O{sub 3}, melting/resolidifying the Al/Cu bilayer without Al{sub 2}O{sub 3} results in phase-segregated dendritic film growth.
Date: January 18, 2000
Partner: UNT Libraries Government Documents Department

Environmental scanning electron microscope (ESEM). Final report

Description: The Environmental Scanning Electron Microscope (ESEM) was acquired by a grant from the Department of Energy University Research Instrumentation Program and matching funds from Lehigh University and industry. The equipment is installed as part of the electron microscopy laboratories and is being utilized on a regular basis. Over 20 graduate and undergraduate students from the Department of Materials Science and Engineering as well as other department in the University have included this instrument in their research. In addition, the ESEM has been used in several courses including MAT 427 -- Advanced Scanning Electron Microscopy, a graduate course offered every other year. Examples are given of how the ESEM has been included in the research programs.
Date: November 1, 1998
Creator: Marder, A.; Barmak, K. & Williams, D.
Partner: UNT Libraries Government Documents Department

Advanced lithography for nanofabrication

Description: A novel method for generating lateral features by patterning the naturally forming surface hydride layer on Si is described. Because of the relatively strong chemical bonding between silicon and hydrogen, the hydride layer acts as a robust passivation layer with essentially zero surface mobility at ordinary temperatures. A focused electron beam from a scanning electron microscope was used for patterning. Upon losing the hydrogen passivation the silicon surface sites become highly reactive. Ideally, the lifetime of such a pattern in a clean environment should be infinite. Deliberate exposure of the entire wafer to a suitable gas phase precursor results in selective area film growth on the depassivated pattern. Linewidths and feature sizes of silicon dioxide on silicon below 100nm were achieved upon exposure to air. The silicon dioxide is robust and allows effective pattern transfer by anisotropic wet-chemical etching. In this paper, the mechanism of hydrogen desorption and subsequent pattern formation, and the factors that govern the ultimate pattern resolution will be discussed.
Date: June 1, 1997
Creator: Hui, F. & Eres, G.
Partner: UNT Libraries Government Documents Department