01932nas a2200205 4500008004100000245010200041210006900143260001200212490000700224520122700231100002001458700002601478700002701504700002401531700002501555700002401580700002301604700002301627856007601650 2002 eng d00aIn Situ X-Ray Absorption Spectroscopy Study of Hydrogen Absorption by Nickel-Magnesium Thin Films0 aIn Situ XRay Absorption Spectroscopy Study of Hydrogen Absorptio c02/20030 v673 a

Structural and electronic properties of co-sputtered Ni-Mg thin films with varying Ni to Mg ratio were studied by in situ x-ray absorption spectroscopy in the Ni L-edge and Mg K-edge regions. Codeposition of the metals led to increased disorder and decreased coordination around Ni and Mg compared to pure metal films. Exposure of the metallic films to hydrogen resulted in formation of hydrides and increased disorder. The presence of hydrogen as a near neighbor around Mg caused a drastic reduction in the intensities of multiple scattering resonances at higher energies. The optical switching behavior and changes in the x-ray spectra varied with Ni to Mg atomic ratio. Pure Mg films with Pd overlayers were converted to MgH2: The H atoms occupy regular sites as in bulk MgH2. Although optical switching was slow in the absence of Ni, the amount of H2 absorption was large. Incorporation of Ni in Mg films led to an increase in the speed of optical switching but decreased maximum transparency. Significant shifts in the Ni L3 and L2 peaks are consistent with strong interaction with hydrogen in the mixed films.

1 aFarangis, Baker1 aNachimuthu, Ponnusamy1 aRichardson, Thomas, J.1 aSlack, Jonathan, L.1 aPerera, Rupert, C.C.1 aGullikson, Eric, M.1 aLindle, Dennis, W.1 aRubin, Michael, D. uhttps://facades.lbl.gov/publications/situ-x-ray-absorption-spectroscopy01883nas a2200253 4500008004100000050001500041245008500056210006900141260003000210520107000240653001301310653002001323653004101343653001501384653002201399653001801421653000901439100002301448700002701471700002301498700002401521700001901545856006501564 1997 eng d aLBNL-4155000aInfluence of stoichiometry on the electrochromic cerium-titanium oxide compounds0 aInfluence of stoichiometry on the electrochromic ceriumtitanium  aHonolulu, Hawaiic11/19973 a

CeO2-TiO2 finds use as passive counter-electrode in electrochromic devices. Thin films were produced by dc-sputtering in a wide range of compositions. Influence of total pressure and oxygen partial pressure on the optical constants of TiO2 was investigated. Slightly substoichiometric TiO2 films exhibit a red-shift of the bandgap. The TiO2 content in the compound essentially determines the degree of cathodical coloring upon Li+ intercalation. However, pure TiO2 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. CeO2-TiO2 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.

10aband gap10acharge capacity10aelectrochromic cerium titanium oxide10agrain size10aoptical constants10arms roughness10atio21 avon Rottkay, Klaus1 aRichardson, Thomas, J.1 aRubin, Michael, D.1 aSlack, Jonathan, L.1 aKullman, Lisen uhttps://facades.lbl.gov/publications/influence-stoichiometry01697nas a2200205 4500008004100000245008500041210006900126300000800195490000800203520102000211100001901231700003101250700002101281700002501302700002301327700002301350700002101373700002101394856007601415 1996 eng d00aImpact of Growth Temperature, Pressure and Strain on the Morphology of GaN Films0 aImpact of Growth Temperature Pressure and Strain on the Morpholo a2270 v4493 a

GaN films grown on sapphire at different temperatures are investigated. A Volmer-Weber growth mode is observed at temperatures below 1000K that leads to thin films composed of oriented grains with finite size. Their size is temperature dependent and can actively be influenced by strain. Largest grains are observed in compressed films. It is argued that diffusing Ga ad-atoms dominate the observed effects with an activation energy of 2.3 ± 0.5 eV. Comparably large grain sizes are observed in films grown on off-axes sapphire substrates and on bulk GaN. This assures that the observed size limitation is a consequence of the 3D growth mode and not dependent on the choice of the substrate. In addition, the grain size and the surface roughness of the films depend on the nitrogen partial pressure in the molecular beam epitaxy (MBE) chamber,most likely due to collisions between the reactive species and the background gas molecules. This effect is utilized to grow improved nucleation layers on sapphire.

1 aFujii, Hiroaki1 aKisielowski, Christian, F.1 aKrüger, Joachim1 aLeung, Michael, S.H.1 aKlockenbrink, Ralf1 aRubin, Michael, D.1 aWeber, Eicke, R.1 aKrüger, Joachim uhttps://facades.lbl.gov/publications/impact-growth-temperature-pressure02195nas a2200277 4500008004100000022001400041245010300055210006900158260001200227300001200239490000700251520133500258653002301593653000801616653003301624653002401657100001301681700001901694700002001713700002001733700001801753700002301771700002301794700002101817856007901838 1995 eng d a0361-523500aThe Influence of Nitrogen Ion Energy on the Quality of GaN Films Grown with Molecular Beam Epitaxy0 aInfluence of Nitrogen Ion Energy on the Quality of GaN Films Gro c04/1995 a249-2550 v243 a

Since the growth of GaN using molecular beam epitaxy (MBE) occurs under metastable growth conditions, activated nitrogen is required to drive the forward synthesis reaction. In the process of exciting the nitrogen using a plasma or ion-beam source, species with large kinetic energies are generated. Impingement on the growth surface by these species can result in subsurface damage to the growing film, as well as an enhancement of the reverse decomposition reaction rate. In this study, we investigate the effect of the kinetic energy of the impinging nitrogen ions during growth on the resulting optical and structural properties of GaN films. Strong band-edge photoluminescence and cathodoluminescence are found when a kinetic energy of ~10 eV are used, while luminescence is not detectable when the kinetic energies exceeds 18 eV. Also, we find that the use of conductive SiC substrates results in more homogeneous luminescence than the use of insulating sapphire substrates. This is attributed to sample surface charging in the case of sapphire substrates and subsequent variation in the incident ion flux and kinetic energy across the growth surface.This study clearly shows that the quality of GaN films grown by MBE are presently limited by damage from the impingement of high energy species on the growth surface.

10aActivated nitrogen10aGaN10amolecular beam epitaxy (MBE)10anitrogen ion energy1 aFu, T.C.1 aNewman, Nathan1 aJones, Erin, C.1 aChan, James, S.1 aLiu, Xiaohong1 aRubin, Michael, D.1 aCheung, Nathan, W.1 aWeber, Eicke, R. uhttps://facades.lbl.gov/publications/influence-nitrogen-ion-energy-quality