COMPUTER-SIMULATION OF ELASTIC AND STRUCTURAL-PROPERTIES OF THIN-FILMS .1. (001) ORIENTATION IN FCC METALS

The structural and elastic properties of an unsupported thin metallic (001) film are investigated as function of the film thickness, Λ. The zero-temperature constant-stress relaxation procedure employed yields both the atomic structure and equilibrium dimensions as functions of Λ, for which a lattice-dynamics like calculation of the elastic constants is subsequently performed. Throughout, the results obtained by means of a Lennard-Jones (LJ) pair potential are compared with those obtained for a many-body potential of the embedded-atom-method (EAM) type. Although the detailed atomic relaxations differ substantially for the two potentials, the same generic elastic behavior as function of Λ is obtained. Quantitative differences are shown to arise from the rather different surface tensions obtained for the two potentials which, in turn, are due to the different shapes of the related cohesive-energy versus lattice-parameter curves for the perfect crystal. Remarkably, both potentials predict a strenghtening of certain elastic moduli and a softening of others. We conclude that the basic elastic properties of thin films are governed by the structural disorder associated with the very presence of the free surfaces and only indirectly by the dimensional changes. © 1990.