## 3 Results and Discussion
### Activation Energies Obtained by Arrhenius Plots of the XPS Characteristics  
We think that the PE can be greatly influenced by the structure of the iron oxide film, through which the electrons excited from metal base transfer to the outer surface. In order to quantitatively estimate the action of the film, we employed Arrhenius plots of the XPS data for the different environments. Table 4 lists the Arrhenius activation energies obtained by plotting the logarithm of the XPS data at 25, 200, and 339 \({}^{\circ}\)C against the reciprocal of the temperature in Kelvin, 1/T, for the samples scratched in the environments. For example, the Arrhenius equation for XPS Fe \(2p\) intensity was represented by \(I_{\rm Fe2p}=I_{\rm Fe2p0}\exp(-\Delta E_{\rm Fe2p})/k_{\rm B}T\), where \(\Delta E_{\rm Fe2p}\) is the activation energy, \(I_{\rm Fe2p}\) is the XPS Fe \(2p\) intensity, and \(I_{\rm Fe2p0}\) is the pre-exponential factor. The procedure to obtain the activation energy from the PE data during the wavelength scan is illustrated in Reference [7]. The XPS data examined were as follows: (1) the XPS intensity of Fe \(2p\), Fe \(3p\), O \(1s\), and \(C\) \(1s\); (2) the XPS intensity of O\({}^{2-}\), OH\({}^{-}\), and H\({}_{2}\)O components of the O \(1s\) spectrum; (3) the ratios of XPS O\({}^{2-}\) intensity/XPS Fe \(2p\) intensity and of XPS O\({}^{2-}\) intensity/XPS Fe \(3p\) intensity, which are described later; (4) the maximum peak intensity in the Fe \(2p\), Fe \(3p\), and O \(1s\) XPS spectra. We think that the activation energy obtained here represents the energy required for the formation or growth process of the above-mentioned species to thermally occur at the surface. The activation energies listed were obtained from Arrhenius plots of approximately straight lines with \(R^{2}\geq 0.82\). Although the activation energy values were not necessarily obtained in all the experiments, the following results listed in Table 4 are featured: (1) the value of \(\Delta E_{\rm O1s}\) was nearly twice as much as that of \(\Delta E_{\rm Fe2p}\) and \(\Delta E_{\rm Fe3p}\), indicating that the formation of surface oxygen species required more energy than that of surface iron species; (2) the value of \(\Delta E_{\rm O1s}\) for air was considerably higher than that for other environments. This finding can be associated with the highest value of \(\Delta E_{\rm AuUp1}\) for air, leading to the weakest PE intensity appearing in the glow curve, and the negative value of MSG, as shown in Table 2 and Figures 13 and 14 in Reference [5]; (3) interestingly, the \(\Delta E_{\rm C1s}\) for methanol, ethanol, and acetone had a negative value, which means that the growth process of carbon materials at the surface was exothermic, as described in Reference [7]; (4) the values of \(\Delta E_{\rm O2-/Fe2p}\) and \(\Delta E_{\rm O2-/Fe3p}\) relating to the formation of the non-stoichiometric oxide structure were almost independent of the environments, except for water, and the averages were 0.035 eV and 0.031 eV, respectively. If the film which has a non-stoichiometric oxide structure is generated at the surface, such a magnitude of energy may be required; (5) the average of the \(\Delta E_{\rm O2}\)\({}^{-}\) values was 0.48 eV and was considerably higher than that of \(\Delta E_{\rm OH}\)\({}^{-}\) (0.025 eV). The values of \(\Delta E_{\rm O2}\)\({}^{-}\) (0.072 eV) for water were much higher than that for other environments. This suggests that, in the case of water, it is difficult to produce O\({}^{2-}\) species. Furthermore, it is seen that the values of \(\Delta E_{\rm O2}\)\({}^{-}\) and \(\Delta E_{\rm OH}\)\({}^{-}\) were almost the same for benzene and acetone; that is, the values of \(\Delta E_{\rm O2}\)\({}^{-}\) were 0.027 eV (benzene) and 0.032 eV (acetone) and those of \(\Delta E_{\rm OH}\)\({}^{-}\) were 0.029 eV (benzene) and 0.032 eV (acetone).