Water induced particle formation in the ion chemistry of silane

Potential particle-forming reactions of hydrogenated silicon cations with silane and disilane, in the presence and absence of water, are summarized. The reactions are studied in the ion trap of a Fourier transform mass. spectrometer at 10(-7)-10(-5) Torr. Cations react sequentially with silane to produce larger silicon-containing ions. In general, reaction rates decrease with increasing number of silicon atoms in the ion; no ions containing more than six silicon atoms are formed in reactions with pure silane. Reaction with disilane produces larger silicon-containing ions; reaction rates decrease with increasing number of silicon atoms in the cation. The largest ion produced is larger than for tine silane system but still contains less than nine silicon atoms. There is insufficient reactivity for hydrogenated silicon cations in pure silane or disilane to produce macroscopic particles. Mixtures of silane or disilane containing 7% water, however, significantly enhance the growth of ions. In the limit of our measurements, the reactions in both silane and disilane do not terminate.