The steady states, fluctuations, dynamics and instabilities of atom and vacancy single layer-height islands during electromigration were described; assuming an isotropic medium. Emphasis was placed on the dependence upon cluster size and upon 3 standard limiting cases of mass-transport (peripheral diffusion, terrace diffusion, evaporation-condensation), as well as the differences between atom and vacancy clusters. A general model provided power laws which described the size dependence of the drift velocity in these limits; consistent with established (peripheral diffusion) results. During peripheral diffusion, atom and vacancy islands drifted in opposite directions. Otherwise, they drifted in the same direction. Linear stability analysis revealed a new type of morphological instability which did not lead to island breakdown. Non-circular steady states were found for evaporation-condensation vacancy islands. The analytical calculations were confirmed by Monte Carlo simulations and numerical integration. For weak electromigration, the cluster responded isotropically for terrace diffusion and peripheral diffusion, but not for evaporation-condensation. In the latter case, clusters elongated perpendicular to the drift axis. In peripheral diffusion, a morphological instability under strong electromigration led to cluster splitting; in contrast to a destabilization into slits in other cases. Terrace diffusion or evaporation-condensation induced a new instability for vacancy clusters, above a threshold value. Non-equilibrium cluster diffusion constants and morphological fluctuations were derived by using the Langevin formalism. Electromigration affected the diffusion coefficient of the cluster and the morphological fluctuations, which diverged at the instability threshold. An intrinsic attachment–detachment bias exhibited the same scaling signature as peripheral diffusion in the drift velocity.

Electromigration of Single-Layer

Clusters. O.Pierre-Louis, T.L.Einstein: Applied Surface Science, 2001, 175-176, 129-33