## 3 Results and Discussion
### The PE Characteristics during Wavelength (Photon Energy) Scan Against Scratching Environments
Using the \(\alpha\) values shown in Figure 6 in Reference [11], we calculated the ratios of \(\alpha\) values, both at 760 and 25 \({}^{\circ}\)C and at 340 and 25 \({}^{\circ}\)C; the ratio for the former was \(\alpha_{760}/\alpha_{25}=6.3\) and that for the latter \(\alpha_{340}/\alpha_{25}=2.2\). For comparison, we calculated the ratio of \(\alpha A\) values at 339 and 25 \({}^{\circ}\)C obtained in the present experiment (Figure 11a). In the cases of acetone and air, the ratio values were \(\alpha A_{339}/\alpha A_{25}=6.7\) for acetone and \(\alpha A_{339}/\alpha A_{25}=4.1\) for air. This indicates that the increase in the \(\alpha\) values from 25 to 339 \({}^{\circ}\)C for the present scratched iron samples was considerably greater than that for the nickel: \(\alpha_{340}/\alpha_{25}=2.2\). This difference may be related to the surface cleaning of the nickel and the surface scratching of the iron samples. We consider the PE process. Firstly, the electrons can be photo-excited from the valence band of the metal, becoming hot electrons before being transported through the overlayer to the outer surface. The overlayer is considered to consist of a mixed trilayer of Fe\({}_{\mathrm{x}}\)O, Fe\({}_{\mathrm{3}}\)O\({}_{4}\), and FeOOH, as mentioned above. Regarding the overlayer suffering electron-electron scattering during the transport, we examined whether the amount of surface elements present in the overlayer can affect the \(\alpha A\), causing a change in the ability of the electrons to emit. We used XPS intensities of Fe 2\(p\), Fe 3\(p\), and O 1\(s\). Figure 13 shows the plots of the \(\alpha A\) values against XPS Fe 2\(p\), Fe 3\(p\), and O 1\(s\) intensities at 25, 200, and 339 \({}^{\circ}\)C, respectively. In Figure 13a-c, it is seen that, with increasing temperature, the data points of \(\alpha A\) values tended to shift to the higher values of XPS Fe 2\(p\), Fe 3\(p\), and O 1\(s\) intensities, and the level of \(\alpha A\) values also became higher. We paid attention to the slope of the approximately straight lines plotted in Figure 13. The \(\alpha A\) values  
Figure 12: Plots of the activation energies, \(\Delta E_{\alpha\mathrm{A}}\) (**a**) and \(\Delta E_{\mathrm{NT}}\) (**b**), obtained from the wavelength scan against the scratching environments. values at 200 and 339 \({}^{\circ}\)C tended to increase with increasing XPS Fe 2\(p\), Fe 3\(p\), and O 1\(s\) intensities, with a much steeper gradient at 339 \({}^{\circ}\)C. Therefore, it seems that the increase in the amount of iron and oxygen atoms enhances the \(\alpha A\). In Table 5, we examine how the acceptor number of the environment molecules can be related to the activation energies obtained from the PE characteristics data during temperature and wavelength scans and from the XPS data. Here, it should be noted that the scratching environments are rearranged in decreasing order of the acceptor number. The results given in Table 5 are featured as follows: (1) the activation energies of \(\Delta E_{\text{O 1s}}\), \(\Delta E_{\text{O 2}}\), and \(\Delta E_{\text{O 1 sPEAK}}\) for air are remarkably higher than those for other environments, and this trend is analogous to that of \(\Delta E_{\text{aUp1}}\). This indicates that the surface oxygen species in the case of air are more strongly bound on the surface, such that increased thermal energy is required to grow the oxide layer, which leads to an increase in the PE in the Up1 temperature scan; (2) for the environments from water to benzene, the decreasing order of the acceptor number is in good agreement with the decreasing order of \(\Delta E_{\text{aUp1}}\). This means that the molecule of liquid environments with higher acceptor number, meaning higher Lewis acidity or electrophilicity of a solvent, produces higher \(\Delta E_{\text{aUp1}}\).