THE V(SI-H) ABSORPTION-BAND AS A SENSOR OF THE OXIDATION OF A SILICON-CARBIDE SURFACE - SPECTROMETRIC AND AB-INITIO STUDIES

Silicon carbide powders show Si-H groups on their surface whose v(Si-H ) stretching frequency is known to be very sensitive to the silicon en vironment. In this work, we correlated the oxygen content on the first atomic layer to the v(Si-H) absorption frequency. A SiC nanophase pow der was analyzed in situ by Fourier transform infrared spectrometry wh ile performing a controlled oxidation. The evolutions of the v(Si-H) s tretching bands were followed versus temperature, oxygen pressure and time. The v(Si-H) absorption range was then resolved into subbands cor responding to the possible H-SiOxC3-x (x = 0, 1, 2, 3) species. The re lative intensities of these subbands allow one to discuss their respec tive probability. Ab initio calculations based on self-consistent,lt m olecular orbital theory showed charge transfer in the SiH group when o xygen replaces carbon. The v(Si-H) absorption frequency is proven to b e a good sensor of the oxidation degree of the SiC surface. Moreover, our IR technique for surface analysis proves to be extremely relevant when a precise knowledge of the first atomic layer on a nanophase cera mic powder is required.