Pixel switching of epitaxial Pd/YHx/CaF2 switchable mirrors

Exposure of rare-earth films to hydrogen can induce a metal-insulator trans ition, accompanied by pronounced optical changes. This 'switchable mirror' effect(1) has received considerable attention from theoretical(2-4), experi mental(5) and technological(6) points of view. Most systems use polycrystal line films, but the synthesis of yttrium-based epitaxial switchable mirrors (7) has also been reported. The latter form an extended self-organized ridg e network during initial hydrogen loading(7), which results in the creation of micrometre-sized triangular domains. Here we observe homogeneous and es sentially independent optical switching of individual domains in epitaxial switchable mirrors during hydrogen absorption. The optical switching is acc ompanied by topographical changes as the domains sequentially expand and co ntract; the ridges block lateral hydrogen diffusion and serve as a microsco pic lubricant for the domain oscillations. We observe the correlated change s in topology and optical properties using in situ atomic force and optical microscopy. Single-domain phase switching is not observed in polycrystalli ne films, which are optically homogeneous(8). The ability to generate a tun able, dense pattern of switchable pixels is of technological relevance for solid-state displays based on switchable mirrors.