AGGREGATE FORMATION UNDER HOMOGENEOUS SILANE THERMAL DECOMPOSITION

A complete model of aerosol particle formation by thermal decomposition of silane is presented, which includes all steps from aerosol precursor formation in the homogeneous reactions to particle coagulation. The model predicts silane conversion, concentrations of gaseous intermediates (disilane, trisilane, and others), size and concentration of aerosol particles, chemical composition of aerosol particles (number of SiH and SiH2 groups in the particles). Additionally, we report measurements of aggregate fractal dimensions on the basis of electron microscopy micrographs. These data are required to link the chemical kinetic steps of the model with predictions about the particle size. Calculated time dependencies of gaseous concentrations, particle size and concentration, particle chemical composition are in reasonable agreement with the experimental data obtained in the present work as well as in our earlier papers (Onischuk et al., 1997a,b, 1998a). The numerical simulations showed that the relative contribution of vapor and clusters (containing not more than 10 silicon atoms) to the rate of particle growth is in the range of 20-30%. The contribution from the particles containing more than 106 silicon atoms is in the range 70-80%.