Infrared (IR) spectra of ultrathin silicon-oxide layers, grown by pulsed F2-laser (157 nm) photoinduced oxidation of H-terminated Si(111) and Si(110) in an oxygen atmosphere, were monitored in situ with monolayer sensitivity. Oxygen atoms play an essential role in this laser-induced oxidation process occurring at room temperature. The IR spectra of the various oxidation states of silicon (suboxides) in the interfacial region recorded for oxides grown by the self-limiting photochemical oxidation process are compared with those of thermal oxide layers of 22 nm thickness obtained by a top-down wet-chemical thinning procedure. The characteristic features of the suboxide spectra recorded for normal and oblique incidence of the analyzing IR beam are discussed.

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