Photochromic Response of Encapsulated Oxygen-Containing Yttrium Hydride Thin Films

Abstract

Photochromic oxygen-containing yttrium-hydride thin films are synthesized by argon magnetron sputtering on microscope slides. Some of them are encapsulated with a thin, transparent, and nonphotochromic diffusion-barrier layer of either Al2O3 or Si3N4. Ion-beam-based methods prove that these protective diffusion barriers are stable and free from pinholes, with thicknesses of only a few tens of nanometers. Optical spectrophotometry reveals that the photochromic response and relaxation time for both protected and unprotected samples are almost identical. Ageing effects in the unprotected films lead to degradation of the photochromic performance (self-delamination), whereas the photochromic response for the encapsulated films is stable. The results show that the environment does not play a decisive role for the photochromic process and the encapsulation of oxygen-containing rare-earth hydride films with transparent and nonorganic thin diffusion-barrier layers provides long-time stability of the films, mandatory for applications as photochromic coatings on, e.g., smart windows.