# Radiation Hardness of Oxide Thin Films Prepared by Magnetron Sputtering Deposition
## 3 Experiment Results and Discussion
### Comparing Thermally Grown a-SiO\({}_{2}\) with Magnetron-Sputtering-Deposited a-SiO\({}_{2}\)
Besides similar peak area ratios, indicating that copper ion irradiation acts in a similar manner to annealing (and 18 MeV Cu is better in this regard than 2.5 MeV Cu, indicating electronic stopping as annealing counterpart), we also note that the observed maxima redshifted further down to the high-fluence limit of 1044 cm\({}^{-1}\)[15]. The observed similarity between copper ion irradiation and thermal annealing opens up a question on the role of electronic stopping in modification of a-SiO\({}_{2}\) prepared by magnetron sputtering deposition. The value of electronic stopping clearly exceeds the threshold for ion track formation in a-SiO\({}_{2}\), estimated to be around 1.5 keV/nm [21]. A lack of changes in spectra from 23 MeV I-irradiated samples, which have an identical value of electronic stopping power as 18 MeV Cu, should then be assigned to the simultaneous production of damage via nuclear stopping [17] because iodine is much heavier ion than copper, and therefore has a much higher nuclear stopping component (see Table 2). Additional ion irradiation experiments, which should also consider the role of the ion velocity, would be required for a definite answer to this question. Next, we turn our attention to the remaining two peaks from the studied 900-1300 cm\({}^{-1}\) range. The shoulder located at \(\sim\)1175 cm\({}^{-1}\) arises due to TO4 asymmetric stretching positioned in the 1165-1200 cm\({}^{-1}\) range [17]. Previously, this peak position and area in FTIR spectra of irradiated thermally grown a-SiO\({}_{2}\) were not changing at all, and therefore were not used in the analysis [15; 17; 21]. At present, we observe radically different behaviour in irradiated a-SiO\({}_{2}\) prepared by magnetron sputtering. Again, all spectra shown in Figure 3c are similar and changes to this peak are minor. There is only a slight redshift (\(<\)5 cm\({}^{-1}\)) and an increase in the peak area (\(<\)3%) for iodine-irradiated samples when compared to unirradiated and gamma-irradiated samples. On the other hand, spectra shown in Figure 3e are different, as both peak area and width increase, likely due to a wider range of bond angles or change in the mix of ring structures, resulting in the broader peak. These changes are accompanied by a significant redshift (from \(\sim\)1175 cm\({}^{-1}\) down to \(\sim\)1135 cm\({}^{-1}\)), indicating changes in the TO4 contribution. Again, the similarity between the effects of copper ion irradiation and thermal annealing indicates an important role of electronic stopping. The shoulder peak at 945 cm\({}^{-1}\) can be observed only in Figure 3c,e. In other words, it is absent in thermally grown a-SiO\({}_{2}\) and present only in a-SiO\({}_{2}\) samples prepared by magnetron sputtering deposition. This peak arises due to stretching vibrations of SiOH (silanol) groups [36], but is not affected by irradiation. Therefore, we do not study it further here, but it was important to take it into account in the analysis in order to obtain an accurate fitting of the spectra. Similar behaviour is found for other peaks outside the range of interest. There is a peak at 450 cm\({}^{-1}\) due to the Si-O-Si rocking mode and another peak at 805 cm\({}^{-1}\) due to the Si-O-Si symmetric stretching mode. Both peaks are very insensitive to the ion and gamma-ray irradiation. Since these two peaks do not overlap with any other peak of interest, we do not analyse them here.