A study of dynamical evolution of small two-dimensional Copper islands' diffusion on Ag(111) surface and observed surface effects

摘要

We study the diffusion of two-dimensional Cu-n (1 <= n <= 9) islands on Ag(1 1 1) surface using molecular dynamics (MD) simulations. The work is the extension of calculations -6 of monomer and dimer Hayat et al. [Phys. Rev. B 82 (2010) 085411] and trimer results Shah et al. [Phys. Lett. A 378 (2014) 1732]. Simulations carried out at three different temperatures 300, 500, and 700 K - show the concerted motion to be dominant for the smaller islands (2- to 4-atoms), while the shape-changing multiple-atom processes are responsible for the diffusion of larger islands. Arrhenius plots of the diffusion coefficients reveal that the effective energy barrier is less than 260 +/- 5 meV for the largest island size of Cu/Ag(1 1 1). There is a scaling of the effective energy barrier with size to some extent, but most notably it remains constant for islands with 4- to 6-atoms. The diffusion coefficient increases within a factor of 10 at the three temperatures 300, 500, and 700 K. The observed anharmonic features of the Cu-n adislands (breakage and pop up) at Ag(1 1 1) surface as well as the surface anharmonicity of the Ag-substrate (fissures, dislocations, vacancy generation, and atomic exchange), are also presented. These findings can serve as an input for kinetic Monte Carlo (KMC) simulations. For the smaller sized islands the variation in the effective energy barrier with the island size is in good agreement with the experimental findings.