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Strong Asymmetric Effect of Lattice Mismatch on Epilayer Structure in Metal Thin Film Deposition

We investigate the hetero-epitaxial growth of thin film deposited on a (001) substrate via molecular dynamics simulations, using six fcc transition metals as our modeling systems. By studying the radial distribution function in the film layers, we demonstrate the importance of the sign of lattice mismatch on the layer structure. For positive lattice mismatches, the film favors pseudomorphic growth, whereas for negative mismatches, a sharp transition happens within the first few monolayers of adatoms and the film layers are transformed into the close-packed (111) structure. We propose a way to quantify the compositional percentage of different planar structures in an epilayer, and demonstrate the strong asymmetric effect between the tensile and compressive cases of deposition. How temperature affects the asymmetry is also discussed.