Effect of Palladium Overlayer on Samarium Hydride Thin Film Switchable Mirror: Electrochemical and Topographical Study

Abstract

Samarium films with a typical thickness of 55 nm deposited by vacuum evaporation and covered with Pd overlayers with thicknesses of 5, 8, 11, and 15 nm were loaded with hydrogen and deloaded in a 1 M KOH solution galvanostatically at room temperature. Our study showed that palladium overlayer thickness plays the most crucial role in observing the fast transition between an as-deposited metallic state and a semiconducting nearly samarium trihydride state as well as in obtaining a very high optical contrast. The desorption of hydrogen from palladium-capped SmH3-δ films was studied by in situ transmission measurement during the electrochemical loading/unloading of hydrogen. It was shown that palladium cap layer thickness affects the deloading of hydrogen from the hydrided films. The effect of a palladium overlayer on the surface morphology of metallic and hydrogen-desorbed samarium films showed the sequence of nucleation and growth.