Lattice expansion and contraction in sputtered metal films due to hydrogen charging

Abstract

Hydrogen charging of Ti-30Mo plates (where the composition is in approximate weight per cent) sputtered with thin films of iron, tantalum or titanium results in an increase or decrease in the film lattice parameter, depending on the circumstances. Films thinner than 200 nm show continuous decreases in lattice parameter during charging, whereas relatively thick films show positive changes in the lattice parameter. The decrease in the lattice parameter of the film metal is a consequence of fine-scale plastic deformation caused by the hydrogen charging. Mesa-like protruberances are formed in the film, which oxidize in air, causing compression of their volumes. At very small film thicknesses the contraction effect prevails because most of the film is converted into protruberances. The charging of relatively thick films causes positive changes in the lattice parameter because the expansion caused by hydrogen dissolved in the film overcomes the contraction experienced by the small volume of film near the free surface.