Adsorption and thermal decomposition of acetic acid on Si(111)7×7 studied by vibrational electron energy loss spectroscopy

Abstract

Vibrational electron energy loss spectroscopy (EELS) has been used to characterize the adsorption of acetic acid on Si(111)7 x 7 at room temperature and as a function of annealing temperature. At room temperature, acetic acid is found to undergo O-H dissociative adsorption to form predominantly unidentate adstructure. The equilibrium geometry and the corresponding characteristic vibrational wavenumbers of the adstructures were obtained by density functional theory calculations and are found to be in good accord with the vibrational EELS data. Annealing the sample near 473 K marked the onset of C-O dissociation of the acetate adstructure with the emergence of Si-O-Si vibrational modes at 720 and 1020 cm(-1). Further annealing to 673 K caused a marked intensity reduction in the C-C stretch at 930 cm(-1) and in the CH(3) vibrational features at 1360 and 2990 cm(-1), suggesting further dissociation of the adstructures. The complete removal of the blueshifted Si-H stretching mode at 2275 cm(-1) upon further annealing to 773 K is consistent with the recombinative desorption of H(2) from Si monohydrides expected in this temperature range. The emergence of the Si-C stretching mode at 830 cm(-1) at 873 K is in good accord with the formation of SiC. Similar thermal evolution of the vibrational features have also been observed for acetic acid adsorption on a sputtered Si(111) surface.

Direct Imaging of Hydrogen Bond Formation in Dissociative Adsorption of Glycine on Si(111)7×7 by Scanning Tunneling Microscopy

“…Among the semiconductor substrates, Si(111)7×7 represents one of the most studied surfaces and offers a variety of bonding sites to approaching bio/organic adsorbates. Different organic molecules with different functional groups, including acetic acid, benzene, pyrrole, methanol, butadiene, dimethyl- and trimethylamines, and glycine, , on Si(111)7×7 have been found to undergo different types of reactions with the surface upon adsorption. For example, benzene and butadiene adsorb on the 7×7 surface through the cycloaddition reaction, while pyrrole and methanol undergo H dissociative adsorption.…”

“…Furthermore, the carboxylic acids and the amines are especially interesting because their reaction mechanisms are quite different on the 7×7 surface. For carboxylic acids (e.g., acetic acid 15 ), H dissociative adsorption is found to produce a conjugate base with the formation of an O−Si bond, although its mechanism is far from well understood. For amines, 20 there has been evidence to support the formation of stable, datively bonded surface adducts by partially donating the lone pair electron density of the N atoms toward the Si atoms.…”