Residual gas effects on high-resolution Si 2p spectra of Si(1 0 0)c(4 × 2)

We investigated Si 2p spectra for the Si(1 0 0)c(4 × 2) surfaces exposed to CO and CO2 to clarify how the adsorbed molecules affect the clean surface spectra in ultra-high vacuum (UHV). After a small amount of CO exposure (0.05 L), the spectral shape looks sharper as compared with that of the clean surface due to the reduced intensity of the down dimer peak, because CO is preferentially adsorbed on the down dimer site. Thus the adsorption of CO from the residual gas in UHV might induce a slight change in the spectral shape within a measurement period (∼103 s). On the other hand, in the case of adsorbed CO2, the spectral shape does not change but the overall intensity decreases, since CO2 is physisorbed on Si(1 0 0).