Mass spectrometry of and deposition-rate measurements from radiofrequency-induced plasmas of methyl isobutyrate, methyl methacrylate and n-butyl methacrylate

Abstract

Radiofrequency-induced plasmas of methyl isobutyrate, methyl methacrylate and n-butyl methacrylate have been investigated using mass spectrometry. Both neutral and positively charged species were detected and their relative abundances were monitored as a function of the characteristic power : flow-rate ratio of the plasma. This enabled two regimes to be distinguished, characterised by the different rôles of uniragmented molecules and fragments of the starting material in the process of plasma polymerisation. The mechanism of gas-phase polymerisation of the α,β-saturated esters, methyl methacrylate and n-butyl methacrylate, is shown to differ from that of the saturated monomer, methyl methacrylate. In a second experiment, the depostion rates of plasma polymers of methyl isobutyrate and methyl methacrylate were monitored. The deposition rates of both plasma polymers were found to increase with increasing power and to have very similar values at a given power and flow rate, a typical value being 0.1, µg s^–1 at 2 W and ϕ= 0.11 cm³_STP min^–1. The combined results are discussed in the light of previously reported SIMS data acquired from plasma polymers of the three molecules studied.