The effects of ion irradiation on the composition, structure, compactness, and surface hardness of
polyorganosiloxane films synthesized by plasma-enhanced chemical vapor deposition were investigated
as a function of the ion mass and fluence. The films were obtained from a glow discharge plasma of a
hexamethyldisiloxane (HMDSO)−O2−Ar mixture, and the irradiations were carried out with 170 keV
He+, Ne+, Ar+, and Kr+ ions at fluences between 1 × 1014 and 1 × 1016 cm-2. To characterize the film
elemental composition, two ion-beam analysis techniques were used: Rutherford backscattering
spectroscopy (RBS) and forward recoil spectroscopy (FRS). The ion-beam-induced hydrogen loss from
the films was significant. For the He+-irradiated samples, a H loss of about 50% with respect to the
pristine or unirradiated film was observed for the highest fluence. The surface hardness measurements,
performed with a nanoindenter, in films irradiated at a fluence of 1 × 1016 cm-2 were 8.1, 6.0, 4.7, and
1.6 GPa for He+, Ne+, Ar+, and Kr+, respectively. To examine the ion-induced structural transformations
in the films, infrared reflection−absorption spectroscopy (IRRAS) was employed. From analysis of the
spectra of the irradiated samples several conclusions could be drawn. For example, as the ion fluence
increased, (i) the densities of methyl- and Si−O-related groups changed, (ii) film disorder increased, and
(iii) groups such as Si−CH2−Si, and Si−OH, which were not present in the pristine film, were formed
at lower fluences but disappeared when the latter attained their highest values. Furthermore, some of the
absorption peaks that appeared at low fluences and increased with increasing fluence strongly indicate
formation of carbon domains in the film. Finally, differences in the ion-induced modifications produced
by the different ion species were analyzed in terms of the electronic and nuclear collisions of the ions
traversing the film using the well-known SRIM simulation program.
