Modification of Plasma-Polymerized Organosiloxane Films by Irradiation with He⁺, Ne⁺, Ar⁺, and Kr⁺ Ions

Abstract

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.

XPS Investigation of Plasma‐Deposited Polysiloxane Films Irradiated with Helium Ions

“…As reported in previous publications,5, 11 we successfully transformed PECVD‐deposited polysilazane, polysiloxane and polycarbosilane films into ceramic materials by irradiation with 170 keV noble gas ions. Modifications of the film chemical structure and elemental composition were investigated in detail using various analytical techniques, such as infrared reflection‐absorption spectroscopy (IRRAS), Rutherford backscattering spectroscopy (RBS) and forward recoil spectroscopy (FRS).…”

“…Numerous studies have shown that the elemental composition and chemical structure of Si‐based polymer films can be dramatically changed by irradiation with energetic ions 1–6. The extent of the modification depends on the nature of the ions and on their energies and fluences.…”

“…Irradiation with ions such as He + , B + , C + , Ar + and Au + with energies in the hundreds of keV to a few MeV range produces a strong dehydrogenation of the polymers,4–7 and usually transforms their structure into a highly cohesive three‐dimensional network. Actually, ion irradiation may turn the initially soft polymer into a ceramic material of high mechanical strength and thermal and chemical stability 5, 8, 9. To date, most of the work reported on the ion irradiation of Si‐based polymers has been performed with films of conventional polymers, more specifically polymers bearing a well‐defined structural formula.…”

“…To date, most of the work reported on the ion irradiation of Si‐based polymers has been performed with films of conventional polymers, more specifically polymers bearing a well‐defined structural formula. Fewer publications5, 10, 11 deal with the ion‐irradiated polymer films obtained by plasma enhanced chemical vapor deposition (PECVD), to which a structural formula can not be assigned.…”

Ion irradiation induced structural modifications and increase in elastic modulus of silica based thin films

“…It should be noted that the broad featureless peak originates from the small size of octahedrally coordinated clusters62. It is also a feature of the FT-IR spectra of ion-irradiated films that the small size of the formed compounds may render the well-defined peaks into broad featureless peaks68.…”