TY - JOUR T1 - In Situ X-Ray Absorption Spectroscopy Study of Hydrogen Absorption by Nickel-Magnesium Thin Films JF - Physical Review B Y1 - 2003/02// A1 - Baker Farangis A1 - Ponnusamy Nachimuthu A1 - Thomas J. Richardson A1 - Jonathan L. Slack A1 - Rupert C.C. Perera A1 - Eric M. Gullikson A1 - Dennis W. Lindle A1 - Michael D. Rubin AB - 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. VL - 67 IS - 8 U1 -

Windows and Daylighting Group

U2 - LBNL-51067 JO - Phys. Rev. B DO - 10.1103/PhysRevB.67.085106 ER - TY - CONF T1 - Structural and Electronic Properties of Magnesium-3D Transition Metal Switchable Mirrors T2 - Fifth International Meeting on Electrochromism Y1 - 2002/12// A1 - Baker Farangis A1 - Ponnusamy Nachimuthu A1 - Thomas J. Richardson A1 - Jonathan L. Slack A1 - Bruno K. Meyer A1 - Rupert C.C. Perera A1 - Michael D. Rubin KW - EXAFS KW - Hydrogen storage materials KW - NEXAFS KW - thin films KW - x-ray diffraction AB - We have observed reversible mirror-to-transparent state switching in a variety of mixed metal thin films containing magnesium and first-row transition elements including Ni, Fe, Co, Mn, and Ti. The very large changes in both reflectance and transmittance on loading these films with hydrogen are accompanied by significant structural and electronic transformations. The valence states and coordination of metal atoms during hydrogen loading were followed using dynamic in situ transmissionmode X-ray absorption spectroscopy. Time-resolved Mg K-edge and Ni, Co, Mn, and Ti L-edge spectra reflect both reversible and irreversible changes in the metal environments. These spectra are compared to those of reference materials and to predictions from calculations. JF - Fifth International Meeting on Electrochromism CY - Golden, CO U1 -

Windows and Daylighting Group

U2 - LBNL-51415 DO - 10.1016/j.ssi.2003.08.041 ER - TY - JOUR T1 - X-Ray Absorption Spectroscopy of Transition Metal-Magnesium Hydride Thin Films JF - Journal of Alloys and Compounds Y1 - 2003/08// SP - 204 EP - 207 A1 - Thomas J. Richardson A1 - Baker Farangis A1 - Jonathan L. Slack A1 - Ponnusamy Nachimuthu A1 - Rupert C.C. Perera A1 - Nobumichi Tamura A1 - Michael D. Rubin KW - EXAFS KW - Hydrogen storage materials KW - NEXAFS KW - thin films KW - x-ray diffraction AB - Mixed metal thin films containing magnesium and a first-row transition element exhibit very large changes in both reflectance and transmittance on exposure to hydrogen gas. Changes in electronic structure and coordination of the magnesium and transition metal atoms during hydrogen absorption were studied using dynamic in situ transmission mode X-ray absorption spectroscopy. Mg K-edge and Ni, Co, and Ti L-edge spectra reflect both reversible and irreversible changes in the metal environments. A significant shift in the nickel L absorption edge shows it to be an active participant in hydride formation. The effect on cobalt and titanium is much less dramatic, suggesting that these metals act primarily as catalysts for formation of magnesium hydride. VL - 356-357 U1 -

Windows and Daylighting Group

U2 - LBNL-50574 DO - 10.1016/S0925-8388(02)01237-9 ER -