Optical transmission and reflection of PdHxthin films

Abstract

Transmission and reflection data (0.5-5 eV) for 300 AA PdH_x thin films (x=0.65, 0.85 and 0.92), hydrogenated under high-pressure conditions are presented and compared with similar data for pure palladium before and after hydrogen desorption. The main difference in transmission data consists of a pronounced peak around 1 eV in the transmission of PdH_x compared with the structureless continuously increasing transmission in pure palladium. This confirms the theoretical expectation of Khan and Riedinger (1982) that the inter-band absorption edge in PdH occurs at about 1 eV. The reflectivity data were measurable for PdH_0.65 only; samples with higher hydrogen contents (x=0.85 and x=0.92) exhibit a reflectivity below 0.5%, which is thus not quantitatively measurable by the method applied. This high reduction in the reflectivity cannot be explained by the increase in surface roughness only. A possible contribution from hydrogen itself is briefly discussed.