ELECTRONIC-STRUCTURE OF NANOMETRIC SI C, SI/N, AND SI/C/N POWDERS STUDIED BY BOTH X-RAY-PHOTOELECTRON AND SOFT-X-RAY SPECTROSCOPIES/

The electronic structure of nanometric Si/C, Si/N, and Si/C/N powders prepared by laser synthesis from appropriate gas mixtures has been inv estigated by using two complementary experimental methods. The total a nd partial Si 3p valence-band (VB) distributions were obtained from X- ray-photoelectron and soft-x-ray-emission spectra, respectively; the c onduction-band (CB) Si p states were studied through the Si K x-ray-ph otoabsorption spectrum. For the binary compounds, the results confirm that the laser-synthesized (LS) powders are very similar to stoichiome tric silicon carbide or silicon nitride. The valence states distributi ons are significantly different for the two compounds, due essentially to the presence of the lone pair N 2p pi orbital at the top of the VB in silicon nitride. For ternary systems, differences are observed bet ween the VB and CB distributions observed from two LS powders correspo nding tp C/N values 0.22 and 0.93. They are interpreted in terms-of di fferences in local bonding of Si atoms. In one case, for C/N (atomic r atio) = 0.93, both Si-C-4 and Si-N-4 groups associated, respectively, with silicon carbide and silicon nitride compounds are present in the network while for C/N = 0.22, the results are consistent with the exis tence of a local Si environment in which both Si-C and Si-N are presen t around the same Si atom, as already proposed from previous x-ray-pho toelectron and extended x-ray-absorption fine-structure studies of the same samples.