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Atomically resolved surface photovoltage imaging and tunneling barrier imaging were performed with a scanning tunneling microscope to elucidate the nature of the initial adsorption state of potassium on room temperature Si(111)7×7 surface, which appears as a missing center Si-adatom. No evidence was found to support the fact that this adsorption mode is charged. K islands start to grow (and accumulate at 7×7 domain boundaries) already at coverages as low as 4×1012 cm−2. These islands may be responsible for the previously reported work function lowering and enhanced chemical reactivity upon K deposition.

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A p-Si(111)7×7 surface was exposed to oxygen both while being illuminated with super-band-gap energy photons and while in the dark. The initial sticking probability into an adsorption mode that appears as a protrusion in scanning tunneling microscope images doubled due to illumination with 500 mW/cm 2 532 nm light. No changes were observed in the ∼3:1 preference of the "faulted" over the "unfaulted" halves of the 7×7 unit cell. However, exposure to O 2 under illumination removed the ∼5:1 preference of the "corner adatom" over the "center adatom" sites, which was observed after exposure in the dark.