Initial stages of the nitridation of the Si(111) surface observed by scanning tunneling microscopy

The initial stages of the nitridation processes on Si(111) have been investigated by scanning tunneling microscopy. Two nitridation processes are tried: one is an exposure to a clean Si(111)7×7 surface at room temperature followed by annealing, and another is an exposure on the hot substrate. In either case, the initial reaction occurs at the center adatom sites and they tend to pair with each other across the adjacent dimer row. At high coverage, very flat monolayer films with an 8×8 superstructure are clearly observed, the surface of which seems to contain misfit dislocation presumably due to relaxation of the surface stress.