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.

Influences of Doping and Crystal Orientation on Surface Roughening upon Alcohol Grafting onto Silicon Hydride

“…Recent models of thermal reactions do suggest that the surface reaction to form a stable Si-C linkage can proceed at lower temperatures (<150 • C) as reported by Horrock et al [4] but at these lower temperatures, hydrogenated silicon surface can also be prone to nucleophilic reactions [5,6]. Of these, surface reaction between alcohol and hydrogenated Silicon (Si-H) was well established in literature and many other reports had shown the formation of stable Si-O-C linkage towards the surface [7][8][9][10].…”

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

“…The exchange of some atop Si-H groups with atop Si-OCH 3 groups is demonstrated by the appearance of a CH 3 symmetric (∼2840 cm -1 ) and two CH 3 asymmetric (∼2940 and ∼2980 cm -1 ) stretching modes, a decrease in the intensity of, and a red-shift in, the Si-H stretching mode (∼2080 cm -1 ), the appearance of the CH 3 umbrella distortion (1190 cm -1 ), and the appearance of a complex mode involving an O-C stretching motion coupled with a C-H bending motion (∼1090 cm -1 ). 47,49,50,59,66 The broadening (the full width at half-max increases up to 20 cm -1 ) and red-shifting (by about 6 cm -1 ) of the remaining Si-H stretching modes indicates that dipole-dipole coupling between neighboring Si-H species is being disrupted. [67][68][69][70] This observation is consistent with random exchange of Si-H sites to Si-OCH 3 sites over the entire surface rather than the formation of separated domains of isolated Si-H and Si-OCH 3 groups.…”

“…We have previously shown using FTIR analysis that neat anhydrous liquid methanol reacts with H-terminated silicon surfaces, 59 but important questions about the reaction mechanism as well as the position of the observed oxidation still remain. This paper systematically investigates the methoxylation reaction on both H-terminated and oxidized Si surfaces.…”

Chemical approaches for doping nanodevice architectures

“…Longo et al studied an alternative approach based on work involving the grafting of OH-containing compounds by Michalak. [24][25][26] The initial process was based on a methodology to covalently bond an alcohol to an Si-H surface and was extended to phosphonic acids. This study differed by attempting to reduce the amount of potentially deleterious carbon in the process which may be a problem with current carbon-based precursors.…”