Adatom self-diffusion processes on (001) copper surface by molecular dynamics

Using molecular dynamics and an n-body potential adapted to copper we have studied the self-diffusion of Cu adatoms on Cu(001) surface. The simulations covered the temperature range between 700 and 1100 K. Besides the simple hopping and the exchange mechanism, the detailed trajectory analysis revealed multiple hopping events and complicated multi-particle exchange processes, involving several atoms that do not necessarily belong to the same nearest-neighbor row. These processes exhibit Arrhenius behavior from which we derived the migration energies associated with each process. It is found that the hopping mechanism requires an energy of 0.43 eV, in very good agreement with available experimental data, while the energy associated with the exchange mechanism is 0.70 eV. These results are in qualitative agreement with recent ab-initio calculations. In addition, we found that all mechanisms, even the most complicated, require about the same migration energy with the simple exchange and that for temperatures above 900 K they contribute almost equally to the total diffusion, Furthermore, the activation barriers for the hopping and the exchange mechanism deduced from energy minimizations, at T = 0 K, compare well with the simulation values.