# 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\({}_{2}\)  
FTIR spectrum of the as-deposited a-SiO\({}_{2}\) sample prepared by magnetron sputtering deposition exhibited six peaks [32; 33; 34; 35], as shown in Figure 2. The most prominent vibrational mode is an asymmetric stretching band, which is not a single peak but a composite of several overlapping contributions, reflecting the variety of local environments, such as different Si-O-Si bond angles and ring structure in the amorphous network. Asymmetric Si-O-Si stretching mode, usually labelled TO3, being the most intense band in the FTIR spectrum of a-SiO\({}_{2}\), is composed of two peaks and linked to vibrations of six-membered rings of Si-O tetrahedra. These two peaks are centred at 1044 cm\({}^{-1}\) and 1078 cm\({}^{-1}\), with the wavenumber difference assigned to different bond angles. The well-known high wavenumber shoulder, located around \(\sim\)1175 cm\({}^{-1}\), is labelled as a TO4 vibration mode and corresponds to the Si-O-Si bonds with smaller bond angles (closer to 120\({}^{\circ}\) or even less) in smaller ring structures, such as three-membered rings. The other lower wavenumber shoulder at \(\sim\)945 cm\({}^{-1}\) is due to SiOH (silanol) groups stretching vibrations. Finally, the peak at \(\sim\)450 cm\({}^{-1}\) is due to the Si-O-Si rocking mode and the peak at \(\sim\)805 cm\({}^{-1}\) arises due to the Si-O-Si symmetric stretching mode. Figure 2: FTIR spectrum of the as-deposited a-SiO\({}_{2}\) prepared by magnetron sputtering deposition. \begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{1}{c}{**Nominal**} & \multicolumn{1}{c}{**A-SiO\({}_{2}\)**} & \multicolumn{1}{c}{**A-Al\({}_{2}\)O\({}_{3}\)**} & \multicolumn{1}{c}{**A-MgO**} \\ \multicolumn{1}{c}{**Composition**} & & & & & \\ \hline \multirow{6}{*}{Measured composition} & H & 8.7 \(\pm\) 0.6 & \multirow{6}{*}{H} & \multirow{2}{*}{6.7 \(\pm\) 0.5} \\  & C & 2.0 \(\pm\) 0.2 & & & H & 6.7 \(\pm\) 0.5 \\  & O & 60 \(\pm\) 4 & & H & 3.9 \(\pm\) 0.3 & O & 50 \(\pm\) 3 \\  & Si & 27 \(\pm\) 1 & & O & 59 \(\pm\) 4 & Mg & 42 \(\pm\) 2 \\  & Ar & 0.05 \(\pm\) 0.02 & Al & 36 \(\pm\) 2 & Cr(7) & 0.16 \(\pm\) 0.02 \\  & Cr(7) & 0.18 \(\pm\) 0.03 & & & Fe(7) & 0.4 \(\pm\) 0.04 \\  & Fe(7) & 0.68 \(\pm\) 0.07 & & & W(7) & 0.083 \(\pm\) 0.007 \\ \hline Thickness & \multirow{2}{*}{1413} & \multirow{2}{*}{1857} & \multirow{2}{*}{1750} & \multirow{2}{*}{1750} \\ (10\({}^{15}\) at/cm\({}^{2}\)) & & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Elemental composition of oxide thin films determined by ToF-ERDA. In our previous work [21], we investigated the response of the thermally grown a-SiO\({}_{2}\) thin films to ion and gamma-ray irradiation. Here, we used and re-analysed part of that dataset which is relevant to the present study, namely samples irradiated with 23 MeV I and 1.25 MeV gamma-rays. As shown in Figure 3a, iodine ion irradiation produces large changes that are observable using IR spectroscopy, while irradiation with 1.25 MeV gamma-rays up to a dose of 5 MGy introduces only minor changes to the spectrum. In contrast to this result, iodine ion irradiation does not induce such drastic changes in the IR spectra of a-SiO\({}_{2}\) thin films prepared by magnetron sputtering deposition. These spectra, together with spectra obtained from a sample irradiated with 1.25 MeV gamma-rays up to 6 MGy, are shown in Figure 3b. To better understand this surprising result,  
Figure 3: FTIR spectra obtained from 23 MeV I and 1.25 MeV gamma-ray-irradiated (**a**) thermally grown a-SiO\({}_{2}\), (**c**) magnetron-sputtering-deposited a-SiO\({}_{2}\), and (**e**) additional IR spectra from annealed and 18 MeV Cu and 2.5 MeV Cu-irradiated magnetron-sputtering-deposited a-SiO\({}_{2}\). Exemplary fits of (**b**) unirradiated thermally grown a-SiO\({}_{2}\), (**d**) unirradiated a-SiO\({}_{2}\) prepared by magnetron sputtering deposition, and (**f**) a-SiO\({}_{2}\) irradiated by 18 MeV Cu to a fluence of \(3\times 10^{13}\) ions/cm\({}^{2}\).