In-situ X-ray-absorption Spectroscopy Study of Hydrogen Absorption by Nickel-Magnesium Thin Films

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. Co-deposition 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

Electronic and Structural Properties of \u27Smart Windows\u27 and Liquids Using in-situ X-ray-Absorption Spectroscopy

A new experimental set-up to measure in-situ X-ray absorption spectra under ambient conditions in the 400–2000-eV photon-energy region using both transmission and total-fluorescence-yield detection techniques has been developed, and its utility has been demonstrated by studying optically switchable and amorphous metal thin films (Mg–TM, where TM=Ti, Mn, Co and Ni) in the solid state, as well as Al3+ and Br−ions in aqueous solution. The structural and electronic properties of the freshly co-sputtered Mg–TM thin films in metallic and hydride states were investigated by X-ray diffraction and Mg K- and TM L-edge X-ray absorption spectra. The optical switching of Mg–TM thin films from a mirror-like metallic state to an optically transparent state by exposure to 4% H2 in He is demonstrated by optical transmission and reflectivity in the 350–2500-nm region. The corresponding edge shifts in the Mg K- and TM L-edge X-ray absorption spectra indicate the presence of hydrogen as near neighbors, and its influence on the chemical states of metal thin films is demonstrated using Mg–Ni thin films as a representative example. Aluminum K-edge X-ray absorption spectra in the near-edge region were investigated to study the coordination of Al in crystalline and 0.1 M aqueous solutions of NaAlO2, Al(NO3)3 and Al2(SO4)3. Aluminum in NaAlO2 occupies both tetrahedral and octahedral sites unlike Al in Al(NO3)3 and Al2(SO4)3, where it retains its six-fold coordination irrespective of hydration. Bromine L-edge X-ray absorption spectra for crystalline and 0.1 M aqueous solutions of NaBr, KBr and KBrO3 were carried out to study the ligand-field splittings of core excitations which depend on inter-atomic distances, dissociation in aqueous solution, and the resulting hydration