Electrochemically induced switching in SmHx thin films

Discovery of optical and electrical switching in yttrium and lanthanum hydride thin films in 1996, has triggered large scale investigations of rare earth hydride thin films. Both light and heavy rare earths have been shown to exhibit this so called ‘switchable mirror’ effect. Besides gas phase loading, solid as well as liquid electrolytes have been used as means of hydrogen loading. In this paper, we report on the ability of samarium films to switch between the reflecting and transparent states electrochemically by altering the hydrogen content. Samarium films of typical thickness 55 nm deposited by vacuum evaporation and covered with Pd overlayer of thicknesses 5, 8 and 11 nm were loaded with hydrogen and deloaded in a 1 M KOH solution galvanostatically at room temperature. Our studies have shown that thickness of palladium overlayer plays the most crucial role in observing fast transition between the as deposited metallic and the semiconducting nearly samarium trihydride states as well as to obtain a very high optical contrast. The large reversible change in transparency between di and trihydride states suggests possibilities of use of samarium films as an optical shutter as well as a hydrogen sensor material.