Molecular dynamics simulations of the internal temperature dependent diffusing and epitaxial behaviors of Pd-Ag cluster beam deposition

The molecular dynamics simulations are applied to study the internal temperature dependence of diffusing and structural properties of Pd _1-xAg_x bimetallic clusters and the corresponding epitaxial behaviors of deposited nanostructure on the Pd substrate in this research. In the alloy cluster, Ag atoms are found to have higher activities than Pd atoms and play a role of improving the diffusibility of Pd atoms. The analysis of the mean spreading index indicates that the surface segregation phenomena due to the different surface energy of atoms are obvious if the internal temperature of the cluster is high enough. The radial composition distributions show that the Pd-core/Ag-shell structure of the cluster of 249 atoms is obtained when the internal temperature is above 770 K. The clusters of high internal temperature deposited on the substrate also present better epitaxy than that of low internal temperature as the mean spreading index. Because of the difference of the radius of Pd and Ag, the increase in the Ag atoms of the deposited cluster doesn't contribute to the epitaxial growth and only enhances the mean spreading index. The evaluations of atomic epitaxfactors for the cluster-assembled film reveal that some grain boundaries of (111) planes are formed during the cluster deposition process as well as the scattered nonepitaxial atoms. These nanostructures of low epitaxy would induce internal stresses of the cluster-assembled film and hence affect the mechanical and thermal properties of the thin film.