## 3 Results and Discussion
### Effects of Fe\({}_{x}\)O Layer and Hydroxyl Groups at the Surface Overlayer on PE  
We hypothesized why the baseline of the PE intensity gradually increases with increasing temperature, as observed in the glow curve during the Up1 temperature scan for air in Figure 1 in Reference [6]. We examined the chemical structure of the overlayer. From the spectra of Fe \(2p\) (Figure 1) and Fe \(3p\) (Figure 2), it is seen to be the film structure of the iron oxide layer that is mainly responsible for TAPE because of the weakness of the metal signal. Firstly, we pay attention to the XPS intensity of the O\({}^{2-}\) component because of its strong contribution to the PE. Figure 16a,b shows the plots of the XPS intensity ratio of O\({}^{2-}\)/Fe \(2p\) and of O\({}^{2-}\)/Fe \(3p\) at 25, 200, and 339 \({}^{\circ}\)C in different environments, respectively. In Figure 16a,b, it is seen that, generally, the XPS intensity ratios of O\({}^{2-}\)/Fe \(2p\) and of O\({}^{2-}\)/Fe \(3p\) are nearly constant at each temperature in the different environments, but they increase greatly with increasing temperatures. For example, we consider the XPS intensity ratio of O\({}^{2-}\)/Fe \(3p\) for acetone, which showed values of 2.206 at 25 \({}^{\circ}\)C, 2.902 at 200 \({}^{\circ}\)C, and 3.386 at 339 \({}^{\circ}\)C, as shown in Figure 16b. Using these XPS intensity ratios and the sensitivity factor of 2.9 (O 1s) and 1.54 (Fe \(3p\)) in the XPS measurement, these XPS intensity ratios were converted to the atomic ratio of O/Fe, i.e., 2.206 \(\times\) 1.54/2.9 = 1.171 (25 \({}^{\circ}\)C), 2.902 \(\times\) 1.54/2.9 = 1.541 (200 \({}^{\circ}\)C), and 3.386 \(\times\) 1.54/2.9 = 1.798 (339 \({}^{\circ}\)C). For the atomic ratio of Fe/O, the values of 0.85 (25 \({}^{\circ}\)C), 0.65 (200 \({}^{\circ}\)C), and 0.56 (339 \({}^{\circ}\)C) were obtained. In the same way, using the XPS intensity ratio of O\({}^{2-}\)/Fe \(2p\) in Figure 16a and the sensitivity factor of 2.9 (O 1s) and 10.5 (Fe \(2p\)), the atomic ratios of Fe/O for acetone were obtained as 0.80 (25 \({}^{\circ}\)C), 0.60 (200 \({}^{\circ}\)C), and 0.52 (339 \({}^{\circ}\)C). Thus, the Fe/O atomic ratios obtained from the XPS data given in Figure 16a,b had almost the same values. Interestingly, the atomic ratio of Fe/O gradually decreased with increasing temperature. The atomic ratios of Fe/O at 200 and 339 \({}^{\circ}\)C were found to become much smaller than that (Fe/O = 0.75) of the stoichiometric oxide of Fe\({}_{3}\)O\({}_{4}\), which is assigned as the main oxide component. This means that the scratched surface was oxygen-rich. As shown in Figure 11a,b, for all environments,  
Figure 15: Activation energies of the PE quantum yield (emitted electrons/photon), \(\Delta E_{Y}\), obtained at wavelengths of 200, 210, 220, and 230 nm during the wavelength scan at 25, 200, and 339 \({}^{\circ}\)C, together with those of the electron photoemission probability (\(\Delta E_{aA}\)) for all environments. The values of \(\Delta E_{Y}\) come from the mean values of the scan data at two wavelengths, and the values of \(\Delta E_{aA}\) are from Table 2 in Reference [7]. the PE characteristics such as \(\alpha A\) and \(N_{\rm T}\) at 200 and 339 \({}^{\circ}\)C tended to increase in the arrangement order of the environments, and the XPS O 1s intensity also approximately increased in the same order of the environments (Figure 4c). Therefore, since the electrical conductivity of a p-type semiconductor of non-stoichiometric oxides is known to increase upon oxidation, the scratched surface can be said to have the property of a p-type semiconductor. It is well known that, although wustite (ferrous oxide) has an ideal (stoichiometric) formula, FeO, its actual stoichiometry is closer to Fe\({}_{\rm x}\)O with 0.833 \(<\) x \(<\) 0.957, where, for every three \"missing\" Fe\({}^{2+}\) ions, the crystal contains two Fe\({}^{3+}\) ions to balance the charge [12].