Jumps and concerted moves in Cu, Ag, and Au(110) adatom self-diffusion

Abstract

We present a molecular-dynamics simulation of self-diffusion on the (110) surfaces of Cu, Ag, and Au. The metals are modeled by semiempirical potentials developed in the framework of the second-moment approximation to the tight-binding model. The energy barriers for the relevant diffusion processes are calculated by quenched molecular dynamics and compared with the available data in literature, obtaining a good agreement. The occurrence of long jumps is investigated in detail, showing that the three metals behave quite differently with this respect: long jumps are practically absent in Au and frequent in Cu. The effect of the specific features of the potential-energy surface and of the energy dissipation to the substrate on the probability of long jumps is investigated. The Arrhenius behavior of the jump rate is discussed, and deviations are found at high temperatures. Concerning correlated jump-exchange processes and double exchanges, we find that they are common in Cu even at rather low temperatures, whereas they are never observed in Au, Ag showing an intermediate behavior.