Hydrogen-induced stress in Nb single layers

Niobium films prepared by molecular beam epitaxy (MBE) and electron beam ev aporation (EB) were loaded electrolytically with hydrogen, Out-of-plane str ain and in-plane stresses during hydrogen loading were determined using X-r ay diffraction and substrate bending measurements. Stress and strain develo pment during loading can be explained using a one-dimensional elastic expan sion model up to concentrations of X-H = 0.05 H/Nb. Deviations from elastic behavior were observed above X-H = 0.05 H/Nb and at X-H = 0.20 H/Nb for MB E and EB samples, respectively. These concentrations are where phase separa tion occurs. Additionally, the stress increase in the EB films deviates fro m a linear elastic dependence above X-H = 0.07 H/Nb within the alpha-phase. The maximum measured stress is about -2.6 GPa. (C) 1999 Published by Elsev ier Science S.A. All rights reserved.