Synthesis of Hard Si-C Composite Films by Ion Beam Irradiation of Polymer Films

ABSTRACTWe propcoe a novel technique to convert polymer films into useful inorganic films by ion beam irradiation. Along the track of an ion the polymer is dissociated into smaller fragments. volatile fragments diffuse through the film and escape. Any element which is not removed in the form of volatile species is subsequently enriched with respect to the other elements. We demonstrate this effect in a polymer poly(dimethylsilylene-co-methylphenylsilylene), which initially has a C:Si ratio of 45:1. Upon irradiation with 2 MeV Ar+ ions at a dose of 1015 ions/cm2 the C:Si ratio changes to 3.4:1 as verified by Rutherford backscattering spectrometry. We believe that the effect of the ion beam irradiation is to produce more Si-C bonds at the expeme of the C-H and Si-Si bonds, with ≲10% of the original hydrogen being present in the film at high doses. The loss of the H atoms is further confirmed by a nuclear reaction technique. The IR spectra of the film as a function of the irradiation dose shows a progressive loss of fine molecular features with significant increase of the refractive index. The IR spectrum at the high doses appears to be due to a mixture of various Si and C bonds. However, the irradiated films are very hard and scratch resistant (knoop value ≳1300) suggesting an increase in the number of silicon carbide bonds