## 3 Results and Discussion
### Cross-Sectional Structures  
To investigate the embedded material in the pores in detail, cross-sectional observation was conducted. Figure 13a shows the backscattered electron (BSE) image of the cross-section of pores irradiated with a laser fluence of 0.5 J/cm\({}^{2}\), a scanning speed of 200 mm/s, a scan pitch of 8 \(\upmu\)m, and a pulse width of 256 fs. There was some clumping inside the pores, and the material was embedded to the deepest depth in all of the pores. The clumps were detected in a brighter color than the YSZ substrate, indicating that they may be heavier elements than zirconium, i.e., silver. To clarify the elemental component, the EDX mapping of each element is shown in Figure 13b. YSZ substrate consisted of zirconium (Zr) and yttrium (Y); however, it was not in the area of nanopores. It was found that the pores were filled with silver (Ag), and silver completely penetrated inside the pore. Outside the pore, i.e., the YSZ surface, had no bright silver peak, indicating the attached material on the surface was selectively removed by laser irradiation keeping the silver inside the pore. A small amount of carbon (C) was detected around the nanopore apertures. On the other hand, no carbon was observed in the area inside the pore where the clear silver peak was detected, indicating that the silver and the dispersant, PVP, were completely separated in the pore. In addition, almost no oxygen was detected inside the pores, and it could not be determined that the silver clumps were severely oxidized. Moreover, no elements other than the constituent elements (Zr, O, Ag, and C) were detected in the cross-sections, except for elements attributed to the Pt coating and the measurement device. Figure 11: Change in pore-embedded ratio with different laser fluences and scanning speeds. Elemental distribution in the depth direction of the sample was investigated by GDOES analysis. The sample was prepared by area irradiation with a laser fluence of 0.5 J/cm\({}^{2}\), a scanning speed of 200 mm/s, a scan pitch of 8 \(\upmu\)m, and a pulse width of 256 fs. Figure 14 shows the distribution of each chemical component with depth from the sample surface. After laser treatment, no significant changes with depth from the surface in the main components of YSZ such as zirconium (Zr), oxygen (O), and yttrium (Y) were observed (Figure 14a). This is considered to be an effect of ultrashort pulse irradiation. Femtosecond pulsed laser irradiation is characterized by its ability to suppress thermal effects on surrounding materials by irradiating high-intensity energy in an extremely short time. In addition, since the objective of this study was to remove the dried film on the surface and embed silver nanoparticles, a laser fluence extremely smaller than the ablation threshold of YSZ was used. Therefore, even though the laser irradiation removed the dried film on the surface, the resulting fluence is much higher than the ablation threshold of YSZ. Figure 12: Parameter map with a color map of the change in pore-embedded ratio irradiated with the pulse width of 256 fs. Figure 13: EDX analysis of the cross-section of the pores after embedding silver nanoparticles: (**a**) Backscattered electron (BSE) image, (**b**) elemental mapping images. film, which has a smaller ablation threshold than YSZ, the surface of the YSZ substrate itself did not melt. Hence, there is no risk of segregation of certain components such as yttria in the material, and as a result, the components in the original sample remained unchanged. After laser treatment, a small amount of carbon (C) was also detected and slightly increased at depths less than 200 nm, but almost zero in other areas.