Kinetics of Hydrogenation and Variations in Resistance of Vanadium Thin Films Treated in Atomic Hydrogen Flow

Methods of nuclear reactions, x-ray diffraction analysis, transmission electron and nuclear microscopy were used to investigate the mechanism of hydrogenation of thin vanadium films in their treatment in a flow consisting of a mixture of molecular and atomic hydrogen. It has been shown that the main component penetrating into the metal from the gas phase is atomic hydrogen. At a gas pressure of 10^–2 Pa and room temperature, the dissolution of particles which, in the gas phase, are in molecular form, occurs at a much lower rate. It has been established that the (initially high) rate of variation of the hydrogen concentration in the film decreases during hydrogenation and gradually approaches zero. As this takes place, the hydrogen concentration in vanadium reaches its limiting value equal to about 42.5 at. %. A mathematical model of the hydrogenation of a vanadium film is proposed which describes experimental results based on the relaxation dependence of the hydrogen concentration on hydrogenation time. Comparative analysis of the variations in hydrogen concentration in a film and in film resistance is performed. It has been established that the dependence of the resistance on hydrogen concentration for a thin film hydrogenated in a flow of atomic hydrogen differs from the similar dependence for a bulk material hydrogenated in the atmosphere of molecular hydrogen under the conditions of thermodynamic equilibrium. The features of the behavior of the resistance of a thin film on hydrogenation time revealed experimentally are caused, as in the case of a bulk material, by the formation of the phase of vanadium hydride in the film. The possibility of using vanadium thin films for measuring absolute values of the atomic hydrogen flow density is discussed.