Initial oxidation of Si(100)-(2x1)H monohydride surfaces studied by scanning tunneling microscopy scanning tunneling spectroscopy

Initial oxidation processes of Si(100)-(2 x 1)H monohydride surfaces have been studied by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). On the Si(100)-(2 x 1)H surfaces, local density-of-states attributed to a sigma-bonding state and a sigma-antibonding state of Si-H bonds can be observed at -3.4 eV and +1.2 eV from the surface Fermi level, respectively. These states are remained after the 2.0 ML oxidation at room temperature and are vanished by subsequent annealing at 450 degrees C. A root-mean-square value of roughness on the as-oxidized surface observed in STM images is about two times larger than that of the annealed surface, which would be influenced by electronic states of Si-H bonds. The STS spectra suggest the oxygen atoms adsorb on the backbond sites of Si dimers.