Positron Tunneling and Emission from Pseudomorphically Grown Ni Films on Cu Substrates

The use of positrons to probe thin-film pseudomorphism is presented. The first use of reemitted-positron spectroscopy to determine critical thicknesses, volume expansions, and residual lattice strains for epitaxial Ni films on Cu(100), (110), and (111) substrates is explored. The effects of the substrate surface orientation and annealing of the film are systematically investigated. The positron deformation potential of Ni, which calibrates the spectroscopy, is separately determined by thermal expansion and by pseudomorphic expansion. The two results agree but are inconsistent with theory.