Local Atomic Configuration in Laser Synthesized Si/C/N Powders Studied by X-Ray Photoelectron Spectroscopy

(Received 6 May 1996, revised and accepted 9 December 1996)

Abstract
Nanometric Si/C/N powders have been obtained from the laser synthesis of a liquid precursor: hexamethydisilazane. The chemical composition of the products is a function of the experimental parameters: the C/N ratio in the powders is controlled in the range 0.34 to 1.34 by varying the ammonia content in the flowing gas (argon). This paper presents some results obtained by X-ray Photoelectron Spectroscopy (XPS) about the local atomic structure of these powders. The evolution of the powders after annealing treatments at 1500 and 1600 °C under nitrogen atmosphere has been studied. The chemical composition deduced from XPS wide spectra axe compared with chemical analysis. From the analysis of the Si-2p core level, information about the local atomic bonding around silicon atoms are obtained. The different environments present in the system and their evolution with temperature have been deduced from the comparison with data obtained for stoichiometric compounds (SiC, Si ₃N ₄ and SiO ₂). The existence of local chemical disorder is shown in the as-formed powders. For powders with C/N : , the samples remains amorphous until 1500 °C; crystallization which starts around 1500 °C is total at 1600 °C. The existence of C-N bonds at 1500 and 1600 °C is evidenced. This result is in good agreement with results obtained by neutron diffraction and X-ray absorption (XAS).