Rapid diffusion of magic-size islands by combined glide and vacancy mechanism

Using molecular dynamics, nudged elastic band, and embedded atom methods, we show that certain 2D Ag islands undergo extremely rapid one-dimensional diffusion on Cu(001) surfaces. Indeed, below 300 K, hopping rates for "magic-size" islands are orders of magnitude faster than hopping rates for single Ag adatoms. This rapid diffusion requires both the c(10 x 2) hexagonally packed superstructure typical of Ag on Cu(001) and appropriate "magic sizes" for the islands. The novel highly cooperative diffusion mechanism presented here couples vacancy diffusion with simultaneous core glide.