Lattice strain measurements of deuteride (hydride) formation in epitaxial Nb: Additional results and further insights into past measurements

The evolution of lattice strain during in situ gas-phase deuterium loading of epitaxial (1 1̄ 0) Nb films on the (11 2̄ 0) sapphire was measured with x-ray diffraction. Two samples with film thicknesses 208 and 1102 Å were driven through the miscibility gap. Strains in three orthogonal directions were recorded, permitting the complete set of unit cell parameters to be determined for both the solid solution and deuteride phases. The overall film thickness was simultaneously measured by recording the glancing angle reflectivity response. The behavior of the two films was markedly different, with the thicker film exhibiting a much more compliant behavior and concomitant irreversible plastic deformation. The correlation between out-of-plane lattice and film expansion for both films is also consistent with this observation. These results help explain past inconsistencies observed by others.