A method to pattern Pd over-layers on GdMg films and its application to increase the transmittance of metal hydride optical switches

Abstract.

A process to pattern Pd over-layers on reactive metal films was developed using ion milling through a tungsten trioxide mask patterned by photolithography and wet etching. The WO₃ mask exhibited a low Ar⁺ sputter yield and, unlike conventional mask materials (SiO₂, Si₃N₄), was easily etched in a mild alkaline solution. This procedure was applied to convert a 20-nm Pd cap over a 160-nm GdMg film to a Pd grid with ≈9-μm-diameter openings covering ≈40% of the surface. The Pd grid proved sufficient to catalyze the (de)hydriding reactions required to reversibly switch the GdMg film from reflecting to transparent. The maximum transmittance of the patterned Pd/GdMg hydride bi-layer was twice that of an otherwise identical sample with a continuous Pd cap, with similar hydriding kinetics.