Creation and annihilation of single atom vacancy during subsurface diffusion

Initial reaction of Co with Ge(100) substrate was investigated using scanning tunneling microscopy (STM) in conjunction with density-functional theory (DFT) calculations. We observed that the subsurface Co atoms diffuse after the migration of a Ge atom to the metastable M site. The STM imaging in real time revealed that Ge atom vacancy was created and annihilated during the subsurface diffusion of Co atom along the Ge dimer row. Theoretical calculations confirmed that the migration of Ge atom facilitated the fast diffusion of subsurface Co atom.