| The direct synthesis of methylchlorosilanes, in particular dimethyldichlorosilane, from the copper catalyzed reaction of methyl chloride and silicon, forms the basis of the silicone industry. This high pressure heterogeneous catalytic reaction has been carried out for the first time under ultrahigh vacuum (UHV) conditions by generating surface bound CH;The reaction of methyl groups alone with copper silicide surfaces, in the absence of chlorine, produces mainly trimethylsilane. The surface Cu/Si ratio, determined by AES and low energy ion scattering (LEIS) spectroscopy, decreases with increasing annealing/sputtering temperature. The resulting change in silicon surface enrichment has a significant effect on reaction kinetics. Two distinct types of active sites are present on copper silicide surfaces for trimethylsilane formation. The reaction rate associated with Cu-rich sites is more than 5 orders of magnitude higher than that with Si-rich sites. The reaction of chlorine alone, in the absence of methyl groups, on Cu;The reaction of methyl + chlorine monolayers with Cu... |
