COMPETITION BETWEEN STRAIN AND INTERFACE ENERGY DURING EPITAXIAL GRAIN-GROWTH IN AG FILMS ON NI(001)

Epitaxial Grain Growth (EGG) is an orientation-selective process that can occur in polycrystalline thin films on single crystal substrates. EGG is driven by minimization of crystallographically anisotropic free energies. One common driving force for EGG is the reduction of the fi lm/substrate interfacial energy. We have carried out experiments on po lycrystalline Ag films on Ni(001) substrates. The orientation dependen ce of the Ag/Ni interfacial energy has been previously calculated usin g the embedded atom method. Under some conditions, EGG experiments lea d to the (111) orientations calculated to be interface- and surface-en ergy-minimizing. However, when Ag films are deposited on Ni(001) at lo w temperature, EGG experiments consistently find that (111) oriented g rains are consumed by grains with (001) orientations predicted to have much higher interface and surface energy. The large elastic anisotrop y of Ag can account for this discrepancy. Strain energy minimization f avors growth of (001) grains and can supersede minimization of interfa cial energy if sufficient strain is present and if the film is initial ly unable to relieve the strain by plastic deformation.