## 3 Results and Discussion
### Material Phase Analysis  
To investigate the thermal damage of YSZ during the laser process, the material phase before and after laser irradiation was measured. Figure 15 presents the Raman spectra of the exposed YSZ surface after the removal of the surface dispersion film by various methods. A sample heated in an electric furnace to remove surface deposits instead of using a laser showed many characteristic peaks. Large monoclinic (m) peaks appeared between tetragonal (t) peaks compared to the unirradiated original YSZ surface [38], indicating that the phase transformation of YSZ from tetragonal to monoclinic phase progressed remark  
Figure 14: GDOES analysis of YSZ surface after embedding silver nanoparticles in the nanopores: (a) GDOES depth profile for each element, (b) magnified depth profile of Ag. ably during the heating process. When the dried film was removed by laser irradiation, the monoclinic peaks were not as distinct as those observed on the surface after electric furnace heating, whether femtosecond, picosecond, or nanosecond pulse widths were used. This result was not changed by changing the laser fluence of the femtosecond laser pulses. The samples after the surface treatment all showed a large leftward spectral increase of around 50 cm\({}^{-1}\). In the Raman analysis, when a strongly scattering material is measured, the low wavenumber side of the spectrum rises due to the effect of laser scattering. In this study, silver nanoparticles adhered to the surface after laser irradiation and heating in an electric furnace, which may have affected the spectral measurements. Although this spectral increase may have hidden the original zirconia peaks, it is clear that no significantly larger monoclinic peaks appeared compared to the furnace-heated surface. For quantitative analysis, the monoclinic volume ratio was calculated by the Raman intensity method [39]. The integrated intensity \(I\) of three peaks (147 cm\({}^{-1}\), 181 cm\({}^{-1}\), and 190 cm\({}^{-1}\)) from the baseline determined by connecting the minimum points of each peak was measured, and the monoclinic ratio \(V_{\rm m}\) was calculated by following the equation:  
\[V_{\rm m}=\frac{I_{\rm m}(181)+I_{\rm m}(190)}{2.07\times I_{\rm t}(147)+I_{\rm m }(181)+I_{\rm m}(190)} \tag{1}\]  
where the subscripts m and t identify the monoclinic and tetragonal phases, respectively. The monoclinic ratio of the furnace-heated surface was about 36%, while the other laser-irradiated surfaces had almost zero. On the other hand, our previous study has shown that the monoclinic ratio of the original YSZ surface was about 3%, and the pore-processed surface, which is shown as \"unirradiated\" in Figure 15, was about the same [29]. In general, the thermal effects during the process such as temperature change cause a tetragonal-to-monoclinic phase transformation of YSZ, degrading its mechanical material properties. YSZ has extremely high strength and toughness among ceramic materials and even zirconia-based ceramic materials due to the stress-induced toughening mechanism and is applied to products that require high strength and toughness such as dental materials, biomaterials, and mechanical parts. If the mechanical properties of the original YSZ are compromised due to a significant increase in the monoclinic phase on the YSZ surface during processing, the strength of the substrate itself will decrease even if silver is embedded in the YSZ surface, and the product life will be shortened due to  
Figure 15: Raman spectra of the before and after irradiated surface with different laser parameters, showing monoclinic (m) and tetragonal (t) peaks. damage from cracking. Furthermore, fracture on the surface can easily expose and release the silver embedded in the pores, which causes the loss functionalizing effect of the silver. Hence, an additional surface treatment method that prevents the increase of the monoclinic phase is required.