Fourier transform infrared spectroscopy and first principles calculations have been used to investigate the reaction of atomically smooth, hydrogen-terminated Si(111) (H-Si) surfaces with anhydrous liquid methanol. After 10 min of reaction at room temperature, a sharp absorbance feature was apparent at approximately 1080 cm(-1) that was polarized normal to the surface plane. Previous reports have identified this mode as a Si-O-C stretch; however, the first principles calculations, presented in this work, indicate that this mode is a combination of an O-C stretch with a CH3 rock. At longer reaction times, the intensity of the Si-H stretching mode decreased, while peaks attributable to the O-C coupled stretch and the CH3 stretching modes, respectively, increased in intensity. Spectra of H-Si(111) surfaces that had reacted with CD3OD showed the appearance of Si-D signals polarized normal to the surface as well as the appearance of vibrations indicative of Si-OCD3 surface species. The data are consistent with two surface reactions occurring in parallel, involving (a) chemical attack of hydrogen-terminated Si(111) terraces by CH3OH, forming Si-OCH3 moieties having their Si-O bond oriented normal to the Si(111) surface and (b) transfer of the acidic hydrogen of the methanol to the silicon surface, either through a direct H-to-D exchange mechanism or through a mechanism involving chemical step-flow etching of Si-H step sites.

The reaction of hydrogen-terminated Si(111) and oxide-terminated silicon surfaces with neat anhydrous liquid methanol (CH 3 OH) has been studied with Fourier transform infrared spectroscopy (FTIR) as a function of solution temperature and immersion time. At 65°C, reaction of atomically smooth H-Si(111) surfaces with CH 3 OH (l) results in partially methoxylated silicon surfaces that are free of any detectable subsurface oxidation (Si-O-Si bonds); this is in contrast to observable oxidation found after similar reactions on H-Si(100) surfaces. At long reaction times (t > 3 h), the Si(111) surface saturates with Si-OCH 3 sites at a coverage of approximately 30% of a monolayer, with the residual ∼70% comprised of unreacted Si-H sites. The lack of any detectable silicon oxide makes it possible to conclude the following: (i) Reaction mechanisms involving insertion of oxygen atoms from the CH 3 OH molecule into the subsurface Si-Si back bonds cannot be dominant for (111)-oriented silicon under these conditions. (ii) The vibrational modes of the oxide-free surface are very sharp and can be clearly distinguished from blue-shifted modes observed for methoxyl groups chemisorbed on oxidized surfaces. For surfaces that display subsurface oxidation, no evidence for oxygen atoms directly below atop Si-H sites has been observed. Instead, FTIR analysis demonstrates that subsurface oxidation selectively exists underneath atop Si-OCH 3 sites. Finally, H-terminated oxide surfaces, prepared by reacting trichlorosilanes on OH-terminated SiO 2 surfaces, react with methanol to form a methoxy-terminated oxide surface.