Piecewise diffusion of the silicon dimer

We present a detailed view of the diffusion of silicon dimers on the silicon (001) surface. Through a combination of atom tracking and ab initio modeling, the dimer is shown to move one atom at a time rather than as a two-atom unit. The details of the pathway depend on the diffusion channel: On top of dimer rows, the two atoms of a dimer separate but remain bound during diffusion. In the troughs between dimer rows, the two atoms separate completely and move independently before rejoining in a new location.