Optical and electrical properties of holmium thin films as a function of hydrogen concentration

We measure the evolution of the optical transmission (200-760 nm) and the electrical resistivity of Ho films, 50 nm thick, as a function of H concentration up to 2.9 [H]/[Ho]. The Ho films are covered with a 15 nm thick Pd overcoat for hydrogenation and ex situ measurements. Concentration is measured using a quartz crystal microbalance; the films are deposited in a high vacuum chamber and all measurements are made at room temperature. From the measured transmission spectra, using an inversion method, the complex refraction index of the Ho film is determined: from it the dielectric function, epsilon = epsilon(1) + i epsilon(2) is calculated. This procedure is applied to the hydrogenated Pd coated Ho films finding the evolution of epsilon as a function of hydrogen concentration. Furthermore, using the inversion method in the trihydrided films the plasma frequency and the band gap are calculated. (C) 2007 Elsevier B.V. All rights reserved.