Electron ionization, mechanistic steps

Since dithio- and selenocarbamates and their derivatives are used so widely in the deposition of thin films and nanoparticles that a mechanistic study of their decomposition behavior was carried out by O Brien et al. [ 107]. Wold et al. [78] studied the decomposition products of Zn(S2CNEt2)2 using gas-chromatography mass spectrometry (GC-MS) and their reported deposition path shows clean ehmination of ZnS from the precursor (Eqs. 1 and 2 below). However, the proposed decomposition route is somewhat different to the step-by-step fragmentation observed in the electron-ionization mass spectrometry (EI-MS) of the compoimd, (Eq. 3). This difference can be attributed to inherent differences between the two techniques. 

Three types of ionization processes were distinguished ( 1) as contributing to the ions observed in molecular SIMS spectra direct desorption of precharged materials, cat ionization/anionization, and electron ionization (Equations 1-3, respectively). The equations illustrate overall reactions and do not attempt to explain detailed mechanistic steps. 

Very limited mechanistic studies of these reactions indicate that electron impact induced processes, such as dissociation and ionization, are the primary steps This conclusion is likely to apply to most systems since the contribution of uncharged radicals to the overall reaction rates is small in weak discharges at low temperatures However, caution is advisable in considering any mechanistic interpretations of such complicated processes. For example, more recent results show that ion- and electron-impact induced process taking place on the surface of the deposit are those actually controlling the deposition rate of microcrystalline silicon 55.i59.i60)... 

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