FT-IR Characterization and Ab Initio Study of the Surface Species of a Nanosized SiC Powder

Abstract

ABSTRACTThe v(SiH) stretching absorption band is known to be sensitive to the local environment of the silicon atom. The presence of SiH groups on silicon carbide surface can be taken advantage of to evaluate the oxidation degree of this ceramic powder.The surface analysis of a SiC nanosized powder was performed by FT-IR spectrometry. The evolution of the v(SiH) absorption band, followed in situ under controlled temperatures and oxygen pressures, consists in a frequency shift toward higher wavenumbers when oxidation proceeds. The resolution of the Sill absorption range into four subbands corresponding to the HSiOxC3−x possible surface groups showed the relative evolution of the different species. Ab initio SCF MO calculations on molecular models gave evidence of the charge transfer to the more electronegative oxygen atom, making the silicon atom more positive and seemingly strengthening the SiH bond and thus inducing an upward shift of the v(SiH) frequency.