## 3 Results and Discussion
### XPS Spectra and XPS Characteristics
This finding suggested that the appearance of the metallic component before the TPPE measurement may be related to the increase in the PE intensity, but the detail of the mechanism remained unclear. In the O1s peak shown in Figure 6, two components of Cu(OH)\({}_{2}\) and Cu\({}_{2}\)O appearing at higher and lower binding energies, respectively, were preferential, but the CuO component was negligible. Regarding CuO, the reaction of Cu\({}_{2}\)O + (1/2)O\({}_{2}\)\(\rightarrow\)CuO is considered to be unlikely because of the lack of O\({}_{2}\) in the present experiment. The two components were observed for every sample before the TPPE measurement, but after the TPPE measurement, in almost all cases, the lower binding energy component became more preferential than the higher binding component, although samples of 10-minute abrasion in H\({}_{2}\)O and ultrasonic cleaning in air both components were still preferential. This finding suggested that the change from the OH component (hydroxyl group) to the O\({}^{2-}\) component (oxide ion) partially occurred being accompanied by the desorption of H\({}_{2}\)O. Here, we suppose that this OH has a property of a radical, with the ability to attract electrons from the base metal through tunnelling followed by Auger emission, leading to the PE under light irradiation, although the mechanism of TPPE is not fully understood. We emphasize that this process becomes a key point in the increase in the TPPE intensity, as described later. It was examined for clarification how the Cu2p3/2 and the satellite peaks can be associated with the adsorption of oxygen. Here, the binding energies for the observed spectra are represented by real measured values in the experiment. In Figure 6, for a sample of 10-minute abrasion in H\({}_{2}\)O before the TPPE measurement, a sharp main Cu2p peak at 935 eV, which can be assigned to Cu and Cu\({}_{2}\)O, and a broad shoulder peak at 937 eV in the higher binding energy region of the main Cu2p peak, which may originate from Cu(OH)\({}_{2}\), were observed, and the satellite peak was clearly observed at 940-948 eV, which may be originated from Cu(OH)\({}_{2}\) because the satellite grew with the increase in the shoulder peak. On the other hand, for a sample of ultrasonic cleaning in H\({}_{2}\)O before the TPPE measurement shown in Figure 6, the sharp main peak was observed, but the satellite peak was very small. Similar behavior was observed for samples abraded in (CH\({}_{3}\))\({}_{2}\)CHOH and air before the TPPE measurement. In the case of samples abraded and ultrasonically cleaned in H\({}_{2}\)O, (CH\({}_{3}\))\({}_{2}\)CHOH, and air after the TPPE measurement, the satellite peak was very small, except for samples abraded in H\({}_{2}\)O and ultrasonically cleaned in CH\({}_{3}\)OH. For both types of samples abraded and ultrasonically cleaned in C\({}_{2}\)H\({}_{5}\)OH and C\({}_{3}\)H\({}_{7}\)OH before and after the TPPE measurement, the satellite peak was almost negligible. This finding may suggest that the TPPE observed for C\({}_{2}\)H\({}_{5}\)OH and C\({}_{3}\)H\({}_{7}\)OH has little relation to the Cu(OH)\({}_{2}\) component as the source of the satellite appearing in Cu2p peak. Finally, it is considered that the chemical structure of the metal surfaces before the TPPE measurement is composed of adsorbate (alcohols, H\({}_{2}\)O, and air)/Cu(OH)\({}_{2}\)/Cu\({}_{2}\)O/metallic Cu.