Structural and Optical Properties of Thin Film β-Ta upon Exposure to Hydrogen to Asses Its Applicability as Hydrogen Sensing Material

Abstract

Here, we study the structural and optical properties of tetragonal βtantalum-sputtered thin films both ex situ and when exposed to hydrogen, with a focus on optical hydrogen sensing applications. Using optical transmission measurements, out-of-plane and in-plane X-ray diffraction, and X-ray and neutron reflectometry, we show that thin film β-tantalum gradually, reversibly, and hysteresisfreely absorbs hydrogen with an increasing hydrogen pressure/concentration. The gradual absorption of hydrogen with increasing hydrogen concentrations induces a change in the optical transmission and reflection. These quantities change reversibly and are hysteresis-free over at least 5 orders of magnitude in hydrogen pressure/ concentration, making β-tantalum a suitable hydrogen sensing material. At all partial hydrogen pressures studied, we observe that the volumetric expansion, hydrogen-tometal ratio, and lattice expansion are substantially smaller than for body-centered cubic α-tantalum.