Work function of scratched silicon surface during O2 and N2 adsorption

The Si(111)7 x 7 surface was scratched under an ultrahigh-vacuum (UHV) of 10(-8) Pa. Oxygen and nitrogen gas molecules were then adsorbed on the scratched silicon surface at a gas pressure of 10(-6) Pa for various exposure times. The distribution of the contact potential difference (CPD) on the scratched surface was measured using a scanning Kelvin probe force microscope (SKPM). When scratched under UWV, the work function of the Si surface increased. With oxygen exposure time, the work function of both the scratched and nonscratched Si surfaces first increased and then decreased after reaching a peak. The rate of work function increase of the scratched silicon surface in the initial period was lower than that of the nonscratched surface. Nitrogen exposure produces a negligible effect on the work function of both the scratched and nonscratched silicon surfaces.