Track formation in two amorphous insulators, vitreous silica and diamond like carbon: Experimental observations and description by the inelastic thermal spike model

Vitreous silica thin film (a-SiO2) and mixed deuterated and hydrogenated amorphous carbon thin film (a-C:D,H), grown or deposited, respectively, on silicon, have been irradiated at GANIL in the MeV/u energy range with ions between C and U in order to reach electronic energy loss between 0.7 and 25 keV/nm. The evolution of Si–O bonds and C–D bonds contents was determined by infrared absorption spectroscopy. Complementary physico-chemical characterization was performed for a-C:D,H using Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). For a-SiO2, the band at 1076 cm−1 decreases with the appearance of a band at 1046 cm−1. In the case of the diamond like amorphous carbon, the main effects due to MeV/u ion irradiations are the decrease of sp3 bonding content and of deuterium relative concentration (D/C atomic ratio) as a function of fluence with the appearance of the sp1 bond. The cylinder radii in which these physical phenomena are confined can be deduced from a statistical analysis. Using the inelastic thermal spike model (i-TS) these track radii can be described using the electron–phonon mean free path which takes values equal to 3 and 0.9 nm for a-SiO2 and a-C:D, respectively. Extrapolation to low energy range (∼1 MeV in total or ∼0.02 MeV/u) will be made.