Optical transmission spectroscopy of switchable yttrium hydride films

The optical transmission of the recently discovered switchable yttrium hydride films is determined spectroscopically as a function of hydrogen content. This is done during electrochemical loading of Pd-capped Y film electrodes, thereby continuously changing the hydrogen concentration. The effect of the Pd cap layer on the film transmission is determined from measurements on a series of films with varying Pd layer thickness. The results are in good agreement with transmission measurements of in situ gas phase loaded, uncapped Y films. Both data sets can be consistently described with simple optical decay lengths such as 277.8 nm for YH3-delta and 15.1 nm for Pd at (h) over bar omega=1.96 eV. The hydrogen concentration dependence of the optical transmission is discussed and compared with previous optical measurements on bulk samples and band-structure calculations. [S0163-1829(98)05004-8].