Extremely long surface diffusion of Ga and critical nucleation on As-rich GaAs(001) surfaces caused by phase transitions

The phase transitions between $(2\mathrm{}\times 4)/c(2\times 8)$ and $c(4\mathrm{}\times 4)$ on GaAs(001) surfaces are studied by ultrahigh-vacuum scanning tunneling microscopy. It is evident that the Ga diffusion is remarkable for length up to the micrometer range at the beginning of the transition, but the diffusion is prevented by nucleation at the final stage of the transition. We found that the size of the minimum nucleus depends on reconstruction. The structural stability is discussed, taking the surface electronic properties into account.