VIBRATIONAL PROPERTIES OF 2D COPPER ISLANDS ON THE CU(111) SURFACE BY MD SIMULATIONS

摘要

Using molecular dynamics simulations based on an effective potential in analogy to the tight-binding theory in the second-moment approximation, we have studied the vibrational behaviour of various 2D Cu islands on the Cu(111) surface. We found that, in the direction normal to the surface, the mean-square-displacements of the island atoms do not depend on the size of the island, but are increased by a factor of five in the in-plane directions. These findings are compatible with the behaviour of the cluster phonon modes. Indeed, we found that small islands introduce new vibrational modes that diminish with increasing cluster size beyond a certain critical size (N > N_c), eventually recovering the surface vibrational behaviour. This characteristic size, N_c, coincides with the island size above which the migration energy of the island atoms saturates to the value of the step energy barrier.