**2. Materials and Methods**

XRD has been measured using Cu-k<sup>α</sup> radiation. Accuracy of the XRD intensity is estimated to be approximately 10%, based on the variation of repeated measurements. Rutherford backscattering (RBS) has been performed with MeV He ions for evaluation of film thickness and composition. Similarly, accuracy of the RBS is estimated considering the variation of the repeated measurements. High-energy ion irradiation has been performed at room temperature and normal incidence. Irradiation of high-energy ion with lower incident charge than the equilibrium charge without carbon foil is often employed for the samples of XRD measurement; however, the effect of non-equilibrium charge incidence does not come into play because the length for attaining the equilibrium charge is much smaller than the film thickness, as described for each material in Section 3.

SiO<sup>2</sup> films have been grown by thermal oxidation of Si(001) at 1300 ◦C for 5 hr. According to XRD, the films are polycrystalline with diffraction peaks at ~21◦ , 22◦ , 31◦ , 33◦ , 36◦ and 69◦ , with very weak peak at 44◦ and 47◦ . The peaks at ~21◦ , 22◦ , 44◦ and 47◦ have been assigned to (100), (002), (004) and (202) diffraction of hexagonal-tridymite structure [70]. The strong peak at 69◦ is Si(004) and peak at 33◦ is possibly Si(002). Film thickness is ~1.5 µm and the composition is stoichiometric (O/Si = 2.0 ± 5%) by RBS of 1.8 MeV He. Film density is taken to be the same as that of amorphous-SiO<sup>2</sup> (a-SiO2), since it has been derived to be 2.26 gcm−<sup>3</sup> from XRD results, which is close to that of a-SiO<sup>2</sup> (2.2 gcm−<sup>3</sup> )

Pure ZnO films have been prepared on MgO (001) substrate by using a radio frequency magnetron sputtering (RFMS) deposition method with ZnO target, and it has been reported that the dominant growth orientation is (001) and (100) of hexagonal-wurtzite structure

depending on the substrate temperature of 350 ◦C and 500 ◦C during the film growth, respectively [71,77,78]. The composition is stoichiometric, i.e., O/Zn = 1.0 ± 0.05, and film thickness is ~100 nm by He RBS. Here, the density is taken to be 4.2 <sup>×</sup> <sup>10</sup><sup>22</sup> Zn cm−<sup>3</sup> (5.67 gcm−<sup>3</sup> ).

Preparation and characterization methods of Fe2O<sup>3</sup> films are described in [60]. Briefly, Fe2O<sup>3</sup> films have been prepared by deposition of Fe layers on SiO2-glass and C-plane cut Al2O<sup>3</sup> (C-Al2O3) substrates using a RFMS deposition method with Fe target (99.99%) and Ar gas, followed by oxidation at 500 ◦C for 2–5 hr in air. According to RBS of 1.4–1.8 MeV He ions, the composition is stoichiometric (O/Fe = 1.5 ± 0.1) and film thickness used in this study is ~100 nm. Here, the density of 3.96 <sup>×</sup> <sup>10</sup><sup>22</sup> Fe cm−<sup>3</sup> (5.25 gcm−<sup>3</sup> ) is employed. Diffraction peaks have been observed at ~33◦ and 36◦ , and crystalline structure has been identified as hexagonal Fe2O<sup>3</sup> (hematite or α-Fe2O3). These correspond to (104) and (110) diffraction planes.

TiN films have been prepared on SiO2-glass, C-plane cut Al2O<sup>3</sup> (C-Al2O3) and R-plane cut Al2O<sup>3</sup> (R-Al2O3) substrates at 600◦C using a RFMS deposition method with Ti target (99.5%) and high purity N<sup>2</sup> gas. RBS of 1.4–1.8 MeV He ions shows that the composition is stoichiometric (N/Ti = 1.0 ± 0.05) and that the film thickness used in this study is ~170 nm (deposition time of 1 hr). Here, the density of 5.25x10<sup>22</sup> Ti cm−<sup>3</sup> (5.4 gcm−<sup>3</sup> ) is employed. Diffraction peaks have been observed at 36.6◦ , 42.6◦ and ~77◦ on SiO<sup>2</sup> glass and C-Al2O3. Crystalline structure has been identified as a cubic structure and these correspond to (111), (200) and (222) diffractions [79]. Diffraction intensity of (111) is larger than that of (200) on SiO<sup>2</sup> glass, and diffraction of (111) on C-Al2O<sup>3</sup> is very intensive. TiN on R-Al2O<sup>3</sup> has preferential growth orientation of (220) of a cubic structure (diffraction angle at ~61◦ ). Sputtered atoms are collected in the carbon foil (100 nm) and the sputtered atoms are analyzed by RBS to obtain the sputtering yields [54] (carbon collector method).
