## 4 Conclusions  
Electron emission and surface charge transfer at real metal surfaces are considered to play a significant role in various problems in tribology, corrosion, adhesion, and so on. However, little is known about the behavior of electrons in the superficial overlayers. We quantitatively revealed the action of the overlayers on photoelectron emission (PE) from scratched iron surfaces. This layer is related to the process of the transport of electrons photo-excited from the metal inside to the surface, which corresponds to the second of [PERSON]'s three steps model for PE. We conducted the PE measurement as a function of temperature and light wavelength (photon energy) for samples scratched in seven different environments, using a modified Geiger counter with a heating system. As the observed PE output, we obtained the PE characteristics: Arrhenius activation energies for the PE quantum yields (the number of emitted electrons per incident photon of light) were obtained from the PE during temperature scan, and the electron photoemission probability was obtained from the PE during light wavelength scan, while the shape of the glow curves, representing the temperature dependence of PE intensity, strongly depended on the environments and indicated the presence of a baseline increasing with temperature. On the other hand, X-ray photoelectron spectroscopy (XPS) measurements of Fe 2\(p\), Fe 3\(p\), O 1\(s\), and C 1\(s\) core spectra for samples scratched in the environments after PE measurement at 25 \({}^{\circ}\)C and after cooling to 25 \({}^{\circ}\)C following PE measurement at 200 and 339 \({}^{\circ}\)C were performed. The total number of electrons counted in the XPS measurements of Fe 2\(p\), Fe 3\(p\), and O 1\(s\), called XPS intensity, greatly depended on the environments and the temperatures. As XPS characteristics of the overlayers, the following results were obtained: the XPS intensities for scratched surfaces and their temperature dependence, Arrhenius activation energies of XPS intensities of O 1\(s\) and the O\({}^{2-}\) component of O 1\(s\), and the temperature dependence of the XPS intensity ratio of O\({}^{2-}\)/Fe 3\(p\) and O\({}^{2-}\)/Fe 2\(p\), leading to the anticipation of Fe\({}_{\text{x}}\)O with a p-type semiconductor characteristic. In addition, the strength of acceptor number of the molecules of the liquid environments relating to acid\(-\)base interaction was used. The observed PE output was closely associated with the XPS characteristics of the overlayers.  
The connection of the thermal analysis of PE data for metal surfaces with that of XPS data clarified that the electron transfer at the surfaces in the PE can be strongly governed by the flow of hot electrons across the surface layers, including oxygen species. The contribution of the first process in [PERSON]'s three-step PE model, optical excitation, to the present PE was little. The findings related to the electron emission observed in the present study can be applied to better understand the charge transfer at various real surfaces. In future work, we will extend this study to other metals and semiconductor materials.  
[PERSON] conceived the study and designed the experiments, and wrote the paper; [PERSON] contributed to the analysis of the XPS and PE data; [PERSON] contributed to the setup of the PE measurement apparatus and a discussion on the research. All authors have read and agreed to the published version of the manuscript.  
The authors would like to thank the Ministry of Education, Culture, Sports, Science, and Technology for supporting this work through a grant in aid. They also gratefully acknowledge [PERSON], a former student of [PERSON], for performing the TAPE and XPS measurements.  
The authors declare no conflicts of interest.