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 investigated by using two complementary experimental methods. The total and partial Si 3p valence-band (VB) distributions were obtained from X-ray-photoelectron and soft-x-ray-emission spectra, respectively; the conduction-band (CB) Si p states were studied through the Si K x-ray-photoabsorption spectrum. For the binary compounds, the results confirm that the laser-synthesized (LS) powders are very similar to stoichiometric silicon carbide or silicon nitride. The valence states distributions 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 between the VB and CB distributions observed from two LS powders corresponding tp C/N values 0.22 and 0.93. They are interpreted in terms-of differences in local bonding of Si atoms. In one case, for C/N (atomic ratio) = 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 existence of a local Si environment in which both Si-C and Si-N are present around the same Si atom, as already proposed from previous x-ray-photoelectron and extended x-ray-absorption fine-structure studies of the same samples.