The Structural Change of Lanthanum Thin Films by Hydrogenation and Dehydrogenation

Abstract

Structural change in hydrogenation and dehydrogenation processes of La films was investigated. La/Pd films were produced at substrate temperatures of 300 K-573 K on a SiO₂ substrate using magnetron-sputtering equipment. La/Pd films were hydrogenated under a pressure of 1.0×10⁵ Pa in a vacuum chamber. Phase transition from La to LaH_x (2<x<3) by hydrogenation resulted in a 6- to 10-fold increase of resistivity. Hydrogenation and dehydrogenation readily occurred near room temperature for La/Pd films. The ratio of the growth direction of [0001] to [1010] changed with substrate temperature in the as sputtered La films. When the growth direction of La film was [1010], the rate of hydrogenation became slow in comparison with that of [0001]. The direction of the La films changed to the [111] direction of LaH_x after hydrogenation, though the initial directions of La films were [0001] and [1010]. The processes of hydrogenation and dehydrogenation may affect oxygen which remains inside the La films. In dehydrogenation at room temperature, LaH_x (2<x<3) was transformed to LaH₂, but not to La.