Carbonization of Si(001) surfaces with ethylene gives rise to the Si1-xCx alloy layer (x≤0.2) growth with surface reconstructions of 2×n (6≤n≤12) and c(4×4), due to the carbon impurity caused strain locally present at the surface. In the previous paper [S. Ogawa et al., Mater. Sci. Eng. B 135 (2006) 210], we found a significant increase of initial oxide growth rate on the Si1-xCx alloy layer (x=0.1), compared with that on a Si(001)2×1 surface without carbonization. In this study, real-time ultraviolet photoelectron spectroscopy was employed to clarify the surface reaction mechanism for the oxide growth rate enhancement from the viewpoint of surface electronic state and work function.
For oxidation on the Si1-xCx alloy layer (x=0.1) at room temperature, initial oxide growth rate is considerably enhanced in comparison to that on the Si(001)2×1 surface without carbonization. The enhanced initial oxide growth is accompanied by the interesting change of work function due to the surface dipole layer of adsorbed oxygen, which steeply increase up to ~1 eV upon O2 introduction and then decreases by ~0.7 eV at the end of initial rapid oxide growth. This suggests that adsorbed oxygen remains on the surface at the initial stage and then diffuses to the subsurface. By contrast, adsorbed oxygen occupy preferentially a dimer-atom backbond site on the Si(001)2×1 surface, leading to an initial rapid decrease of work function followed by the gradual increase with O2 dosage. The difference in the initial oxidation reaction kinetics between Si(001) surfaces with and without carbonization is clearly observed regarding O 2p spectral feature: Oπ state (~7 eV) grows predominantly with a doublet structure, while both Oπ and Oi (~11 eV) state appear similarly for the Si(001)2×1 surface, indicating a difference in oxidation state. Based on the results observed, the surface oxidation reaction mechanism on the Si1-xCx alloy layer (x=0.1) is discussed.
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