Molecular Dynamics Study of the Deposition of Palladium-Silver Films on a Silver Substrate

The formation of PdxAg1-x thin films from the gas phase on silver substrates is modeled by molecular dynamics. The effect of substrate temperature on the structure of coatings of various compositions (x = 0, 0.25, 0.5, 0.75, 1) is studied in the range from 300 K to 900 K. The films are shown to have an unevenly deformed fcc structure over the entire range of considered temperatures and compositions. The surface of the coating is not smooth; it contains holes and cavities with a characteristic height difference of several angstroms. No misfit dislocations are formed in the studied systems. Higher substrate temperatures during the deposition of the coating lead to the increased average adsorption energy in the formed layer (which is true for all elemental compositions of the films.) This is caused by the fact that diffusion rate is higher on hotter substrates, and the surface of the coating is therefore smoothed. It is notable that the change of adsorption energy as a function of the substrate temperature during film deposition is directly proportional to the palladium content in the film. A high accuracy (above 0.01 eV) procedure is proposed for the calculation of cohesive energy in the film. This characteristic is shown to be virtually independent on the substrate temperature during nanolayer deposition. This is a direct indication that the structure of the coating volume is not changed, regardless of its elemental composition, as the temperature of formation increases.