Besides the two-dimensional intralayer mass transport, we have also studied the interlayer mass transport across step-edges. An additional energy barrier E ES , also known as the Ehrlich-Schwöbel barrier (ESB), must be exceeded while crossing the step-edge. The additional energy contribution results from the under-coordination of the diffusing species during the step-down migration. Here, the step-down diffusion via atom hopping (ESB 0 ↔ESB 1 ) and the push-out mechanism (ESB 0 ↔ESB 1 (Ex.)) were examined. Our parameterised potential function is capable of correctly reproducing the energetic sequence of the activation energies.