## 3 Testing and Analysis
### Raman Scattering Spectroscopy and Raman Mapping  
The Thermo ScientificTM DXRTM 3 Raman spectrometer is used. The laser wavelength is 532 nm and the laser power is 100 MW. The integration time is set to 0.1 s and the resolution is set to 0.5. Objective magnification is 50\(\times\), and the slit size is 10 mm. Raman spectroscopy is a sensitive and effective technique used to detect the atomic vibrational modes in different kinds of materials [37]. Raman spectra were measured on ZnO, AgNPs/ZnO/Si, AuNPs/ZnO/Si, and CuNPs/ZnO/Si structures, and the results are shown in Figure 3.  
It can be seen from the figure that the Raman effect of the ZnO Raman substrate based on silver nanoarrays is stronger. SERS substrate activity was measured by the surface enhancement factor (_EF_) [38]. _EF_ refers to the ratio between the SERS signal of the target molecule on the substrate and the conventional Raman signal of these molecules when the number of molecules is the same, which can be expressed as  
\[EF=\frac{I_{surf}}{I_{bulk}}\times\frac{N_{bulk}}{N_{surf}}.\]  
According to the formula calculation, the calculation results of the surface enhancement factor are shown in Table 4. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **611 cm\({}^{-1}\)** & **Enhancement Factor** \\ \hline ZnO & 42.214 & 1 \\ CuNPs/ZnO/Si & 8642.916 & 2.04 \(\times\) 10\({}^{2}\) \\ AuNPs/ZnO/Si & 29,342.443 & 6.95 \(\times\) 10\({}^{2}\) \\ AgNPs/ZnO/Si & 592,145.872 & 1.40 \(\times\) 10\({}^{4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Enhancement calculation for the different noble metal substrate. Figure 3: Raman spectra of simple ZnO, AgNPs/ZnO/Si, AuNPs/ZnO/Si, and CuNPs/ZnO/Si structures. \begin{table}
\begin{tabular}{c c c} \hline \hline
**pH** & **Thickness (nm)** & **Diameter (nm)** \\ \hline
8.0 & 374 & 72.8 \\
9.0 & 522 & 63.9 \\
9.5 & 950 & 78.7 \\
10.0 & 1350 & 130.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Enhancement calculation for the different noble metal substrate. The nanowire in this picture was chosen for measure. The more the number of measurements points you select, the wider the range of measurements, and the more accurate the measurement is. These points were selected to represent the Raman image of the sample to be tested (Figure 4). The figure's majority of the parts are green, although some of parts are blue and yellow. It confirms that the surface of the sample is not very uniform. Some conditions in this experiment should be adjusted to make our samples more uniform. Figure 4 was shown pH 9.0 Raman map data. From the Figure 5, the nanowire is smooth, but not very uniform, so we can try other methods to make it better in future work. The enhancement Raman shift position is 1582 cm\({}^{-1}\). It is obvious that the nanostructure is clearer than the pH 9.0 samples. The surface uniformity of the Raman imaging map substantially improved compared to previous samples. The majority of the part is green, while a few parts are yellow and blue. This demonstrates that the homogeneity of the sample at pH 9.0 is higher in contrast to the homogeneity of the sample at pH 10.0. In future experiments, adjusting the pH appropriately to maintain it near pH 9.0 could enhance its uniformity. The samples are pH 10.0 on the Raman map data, and according to the demonstration of Figures 4-7, the uniformity of the film gradually deteriorated as the pH increased after pH exceeded 9. There are bumps on the surface of the film, which affect the quality of  
Figure 4: 1606 cm\({}^{-1}\) line Raman map, ZnO (pH9)/15 nm Cr/450 nm Ag nominal thickness (87 GLAD). Figure 5: Raman spectroscopy on the position (micrometres) = 8924 \(\upmu\)m, point #211.  
the overall film. Raman-enhanced signals are also weakening [38]. In these figures, the nanostructure is better than the pH 9.0 samples, although it is still not very perfect. In future work, we can try using sodium hydroxide to control the pH, as it might work better in uniform parts.