*3.2. ZnO*

The XRD intensity at a diffraction angle of ~34◦ ((001) diffraction) and 32◦ ((100) diffraction) normalized to those of unirradiated ZnO films on the MgO substrate is shown in Figure 3 as a function of the ion fluence for 90 MeV Ni+10, 100 MeV Xe+14 and 200 MeV Xe+14 ion impact. It appears that the XRD intensity degradation is nearly independent of the diffraction planes. The XRD intensity degradation per unit fluence YXD is given in Table 3, together with sputtering yields [54], stopping powers and projected ranges (SRIM2013). The X-ray (Cu-kα) attenuation length LXA is obtained to be 36.6 µm [80] and the attenuation depth is 11 and 10 µm for the diffraction angle of ~34◦ and 32◦ , respectively; thus, the X-ray attenuation correction is unnecessary. It appears that the appropriate energy for the YXD vs. S<sup>e</sup> plot, E − Se`/2, where ` = a film thickness of ~100 nm, is nearly the same as E\* for sputtering, in which the energy loss of a carbon foil of 100 nm is considered. Similarly to the case of SiO2, the characteristic length (LEQ) is estimated to be 4.6, 4.4 and 4.2 nm for 90 MeV Ni+10, 100 MeV Xe+14 and 200 MeV Xe+14, respectively, from the empirical formula of the single-electron loss cross-section σ1L(10−<sup>16</sup> cm<sup>2</sup> ) of 0.52 (90 MeV Ni+10), 0.54 (100 MeV Xe+14) and 0.57 (200 MeV Xe+14) [83,84]. Here, σ1L = σ1L(Zn) + σ1L(O), and the ionization potential I<sup>P</sup> and Neff are described in Section 3.1. Again, LEQ is much smaller than the film thickness and the charge-state effect is insignificant.

**Figure 3.** XRD intensity normalized to as-deposited films of ZnO as a function of ion fluence for 90 MeV Ni (∆, +), 100 MeV Xe (o, x) and 200 MeV Xe () ions. Diffraction planes are (002) at ~34◦ (∆, o, ) and (100) at ~32◦ (+, x). Linear fit is indicated by dashed lines. An estimated error of XRD intensity is 10%.

**Table 3.** XRD data of ZnO films. Ion, incident energy (E in MeV), XRD intensity degradation (YXD), E\* = E − ∆E (energy loss in carbon foil of 100 nm) (MeV) and electronic (Se\*) and nuclear (Sn\*) stopping powers in keV/nm and projected range Rp\* (µm) at E\* calculated using SRIM2013. Sputtering yield Ysp from [54]. Sputtering yield by 100 keV Ne ion is also given.


Figure 4 shows the XRD intensity degradation YXD vs. electronic stopping power (Se) (SRIM2013 and TRIM1997) together with the sputtering yields Ysp vs. Se. Both YXD and Ysp follow the power-law fit and the exponent for YXD using TRIM1997 gives a slightly larger value than that using SRIM2013. The exponent of lattice disordering is nearly the same as that of sputtering. The change in the lattice parameter ∆`c appears to scatter, and roughly −0.2% and −0.1% with an estimated error of 0.1% are obtained for (100) and (002) diffractions by 100 MeV Xe at 10 <sup>×</sup> <sup>10</sup><sup>12</sup> cm−<sup>2</sup> , assuming that ∆`c is proportional to the ion fluence. <sup>∆</sup>`c is obtained at <sup>−</sup>0.3% for (002) diffraction by 200 MeV Xe at <sup>5</sup> <sup>×</sup> <sup>10</sup><sup>12</sup> cm−<sup>2</sup> , and no appreciable change in the lattice parameter is observed by 90 MeV Ni ions at <sup>40</sup> <sup>×</sup> <sup>10</sup><sup>12</sup> cm−<sup>2</sup> ; more data are desired.

**Figure 4.** XRD degradation per unit fluence YXD of polycrystalline ZnO film vs. electronic stopping power S<sup>e</sup> (TRIM1997 and SR2013). Power-law fit to YXD = (0.057Se) 1.32 (TRIM1997) (o, blue dotted line) and (0.0585 Se) 1.16 (SRIM2013) (+, black dotted line). Sputtering yield Ysp vs. S<sup>e</sup> (TRIM1997, ) and Se (SR2013, x) is also shown. Sputtering yield from [54]. Power-law fits to Ysp: (0.175 Se) 1.57 for both Se from TRIM1997 and SR2013 is indicated by green dotted line.
