Effect of palladium cap layer thickness on desorption of hydrogen from PrHx films: A spectroscopic ellipsometry study

Optical characterization of palladium (Pd) capped PrHx films has been perfo rmed using phase modulated spectroscopic ellipsometry to study the effect o f thickness of a cap layer on the deloading of hydrogen from the capped hyd ride films. Experimental Psi and Delta spectra have been fitted to an optic al model consisting of an air/Pd/PrHx/glass substrate. The direct band gap of the PrHx films, calculated from the Tauc plots of these films, has been found to decrease with an increase in the thickness of the Pd overlayer, wh ich in fact is due to enhanced deloading of hydrogen. The removal of hydrog en from PrHx films leads to the formation of localized states, whose signat ure is clearly observed in the Tauc plots. The energy corresponding to a tr ansition involving these states and the conduction band has been found to i ncrease with increasing Pd overlayer thickness. (C) 2001 American Institute of Physics.