Plasma- and vacuum-ultraviolet (VUV) photo-polymerisation of N- and O-rich thin films

Nitrogen (N)- and oxygen (O)-rich organic thin films were deposited by vacuum-ultraviolet (VUV)-assisted photo-chemical polymerisation of flowing ethylene (C2H4)-ammonia (NH3) and C2H4-nitrous oxide (N2O) mixtures of varying ratios, R, respectively. The reaction mechanism of these binary gas mixtures was investigated as a function of the wavelength, λ, of two near-mono-chromatic VUV sources. Surface-near compositions of these 'UV-PE:N' and 'UV-PE:O' films were determined by X-ray photoelectron (XPS), and by Fourier transform (reflection-absorption) infrared (FTIR) spectroscopies. The two types of films were compared with plasma polymers deposited using low-pressure radio-frequency (r.f.) glow discharges in similar gas flow mixtures, 'PPE:N' and 'PPE:O'. VUV-photochemistry appears to be superior to plasma-chemistry in its capability to produce nearly 'mono-functional' organic thin films, ones that are rich in primary amines, -NH2, and in carboxylic acid groups, -COOH, respectively.