“…The sources of the organic molecules are vapours of diffusion pump oil, grease and other chemicals adsorbed in the inner wall of the vacuum chamber. Contamination formed by electron bombardment has been studied by many workers, such as Watson (1947), Cosslett (1947), Hillier (1948, Konig and Helwig (1951), Ennos (1953), Christy (1960) and Mayer (1963), but only a few workers have studied contamination by ion bombardment (Speidel 1959, Mollenstedt and Speidel 1961and Kanaya et al 1964.…”