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 hydrog en content. This is done during electrochemical loading of Pd-capped Y film electrodes, thereby continuously changing the hydrogen concentra tion. The effect of the Pd cap layer on the film transmission is deter mined from measurements on a series of films with varying Pd layer thi ckness. The results are in good agreement with transmission measuremen ts of in situ gas phase loaded, uncapped Y films. Both data sets can b e 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 d iscussed and compared with previous optical measurements on bulk sampl es and band-structure calculations. [S0163-1829(98)05004-8].