Comparison of Diffusion Processes of Cu and Au Adatoms on the Cu(111) Surface by Molecular Dynamics

Abstract

The self-diffusion of the adatoms on the low index copper surfaces is a very important subject and has been extensively studied [1–5] during the last few years. From these studies it was determined that the copper adatoms on the Cu(111) face diffuse more easily, compared to the other two low index faces, while a rather large discrepancy exists concerning the values of the migration energy, ΔE_m, needed for the self-diffusion of the adatoms. In static calculations the values of this energy vary from 0.028eV[6] to 0.15eV[4], with an intermediate value of 0.044eV in another publication[3]. The same quantity determined from the Arrhenius diagram of MD simulations has been found as 0.064eV when a Morse potential is used and 0.059eV with a Finnis-Sinclair potential model[2]. These values have to be compared with those from electron microscopy experiments for the (111) surfaces (0.15eV[7] and 0.10eV[8]). What is interesting about these discrepancies is that, with the exception of the value 0.15eV given in Ref.[4], all other values resulting from energy minimizations are significantly smaller (almost half) than the theoretical ones, which use the Arrhenius diagram and than the experimental results; since in static calculations the exact diffusion path is only approximately known, these computations can give at best an estimation of the upper limit of the energy required and hence one would expect an opposite trend.