Effect of the Pd Layer on Optical Regulation Properties of the Oxygen Containing Yttrium Hydrides

Abstract

Photochromic materials of oxygen-containing yttrium hydride exhibit reversible switching properties that can find applications in the energy saving windows, optical switching devices. However, the photochromic mechanisms of the oxygen-containing yttrium hydride has been not clarified yet. The optical modulation and durability of the films need to be improved. In this paper, oxygen-containing yttrium hydride films covered with hydrogen catalytic-palladium layers were prepared on a glass substrate by a direct-current (DC) magnetron sputtering methods. Firstly, oxygen-containing yttrium hydride thin films were deposited by DC magnetron sputtering of the Y targets in a 0.4 Pa with argon (purity 6N) and hydrogen (5N) mixed gas. Secondly, a thin film of Pd was deposited on the surface of YHx:O layer. Moreover, the effects of the Pd layer in the optical regulation state, crystal structure, surface microstructure and the content of each element of the oxygen-containing yttrium hydride films were investigated by means of SEM, XRD, and XPS methods. In the initial state, the films showed a transparent state with high transmittance in the visible and near-IR range same with single layer of the YHx:O. After exposure to xenon or visible light, the solar transmittance (T sol) of the films sharply decreased by 37.39%. The result can be found that the coloring process (illumination process) of YHx:O thin films can be promoted and the optical regulation range can be increased after covered with a Pd layer. Investigation of the crystal structure by XRD demonstrates YHx:O covered with Pd, the same crystalline state with the YHx:O thin films has been found. After illumination, all reflection peaks of the YHx:O films slightly moving towards the larger angles with smaller lattice parameter (～5.30 Å) due to the deoxidation of YHx:O films. It can be seen from the EDS data that the oxygen contents in the YHx:O film decreases, while the yttrium contents increases, which is consistent with that of the single layer films. The XPS survey scans analysis of the YHx:O and Pd/ YHx:O was also studied. After illumination, all peaks of the single layer slightly moving towards the larger angles. But the double layer have reverse result with above.