title: Infrared spectroscopic investigation of the reaction of hydrogen-terminated, (111)-oriented, silicon surfaces with liquid methanol.
abstract: 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.
authors.affiliation: Division of Chemistry and Chemical Engineering, Kavli Nanoscience Institute, and Beckman Institute, 210 Noyes Laboratory, 127-72, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Michalak
authors.forename: Sandrine
authors.initials: S
authors.lastname: Rivillon
authors.forename: Yves J
authors.initials: YJ
authors.lastname: Chabal
authors.forename: A
authors.initials: A
authors.lastname: Estève
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Lewis