Hydriding kinetics of Pd capped YHx switchable mirrors

The kinetics of the metal-insulator transition in polycrystalline, Pd-capped YHx switchable mirrors upon hydrogenation is investigated. Using the accompanying optical transition, we study switching of matrix-like samples with many (similar to 200) combinations of Pd and Y layer thicknesses. We find that: (i) With increasing Y thickness d(Y), the switching time tau increases for any constant Pd thickness d(Pd). (ii) With increasing d(Pd), there are three regimes. In regime I, it is impossible to switch a device. This can mainly be related to Pd-Y compound formation consuming all Pd within the UHV system, followed by surface oxidation in air. In regimes II and III switching is possible, but only in regime III does Pd form a closed cap layer. The Pd thickness needed for a closed cap layer depends on d(Y). (iii) An oxide buffer layer hinders Pd-Y interdiffusion, so that a thinner Pd cap layer is needed for switching than in the case without buffer layer. This is interesting for potential applications since it yields a higher optical transmission in the open state of the device. (C) 1999 American Institute of Physics. [S0021-8979(99)05923-X].