In situ spectroscopic ellipsometry study of the hydrogenation process of switchable mirrors based on magnesium-nickel alloy thin films

Abstract

The hydrogenation process of switchable mirrors using magnesium-nickel alloy thin films including a thin palladium cap layer was analyzed by measuring the variation in ellipsometric angles Ψ and Δ using in situ spectroscopic ellipsometry. The process was divided into three phases and each phase was identified as follows. The first phase was the process in which the solid solution was formed because a Mg–Ni alloy in its metal state absorbs hydrogen. The second phase was the hydrogenation processes of the solid solution and the metal Pd layers. The third phase was the hydrogenation process of residual metal Pd in the Pd layer. In the initial state of the second phase, a hydride of the alloy was nucleated at the film/substrate interface as a result of hydrogenation of the solid solution, and a mixture layer of the hydride and solution was formed. With proceeding hydrogenation, the thickness of the mixture layer increased and the homogenous hydride layer was afterwards formed at the film/substrate interface. As a result of further hydrogenation, the Mg–Ni alloy layer was completely hydrogenated. After the alloy layer was completely hydrogenated, the hydrogenation of Pd was terminated.