## 3 Results and Discussion
Thus, nanoplate films were successfully formed on the surface with the nanoplates unlikely to overlap with each other and thus be well organized in a monolayer on the silicon surface. Silver nanoparticles with spherical and irregular shapes did start to appear on the surface after 8 h of immersion in the nanoplate solution. The irregular shapes were readily observed in 14 h and 22 h exposure time samples. It should be noted that for these samples, the distribution of triangular nanoplate shapes on the surface is still higher than the distribution of irregular shapes on surface. The formation of irregular shapes with increasing exposure times is likely related to the increasing coverage of nanoplates on the surface. This increased density means that it is possible that the nanoplates begin to coalesce when the neighboring particles get close to each other [39]. From the measurement of triangular nanoplate sizes, we calculated that the ratio of irregular to triangular shapes is 20:80 for both samples. Figure 4: FESEM images of triangular silver nanoplate thin films formed after varying exposure times of (**a**) 30 min, (**b**) 1 h, (**c**) 2 h, (**d**) 8 h, (**e**) 14 h, and (**f**) 22 h. Scale bar is 100 nm. The size of the particles on the surface was analyzed using the same approach as the 15 min sample and the analysis results are plotted in Figure 5 and given in Table 1. Importantly, the average edge length of triangular nanoplates for different exposure times did not change. However, the count of  
Figure 5: The edge length of triangular nanoplates on the surface for different exposure times. The edge length of 25 means the size of the nanoplates was from 20 to 30 nm, 35 from 30 to 40 nm, and 45 from 40 to 50 nm. Figure 6: Optical absorbance for silver nanoplate films formed after the various exposure times of (**a**) 15 min, (**b**) 30 min, (**c**) 1 h, (**d**) 2 h, (**e**) 8 h, (**f**) 14 h, and (**g**) 22 h.  
triangular nanoplates increased with exposure time, showing the density of nanoplates on surface increases with exposure time. The optical properties of the silver nanoplate films formed after different exposure times were studied by observing their absorbance spectra, which are presented in Figure 6. In the suspension there were three clear peaks at 330 nm, 550 nm, and 660 nm (see Figure 1). The signal from the substrate-bound nanoplate films is much weaker, as expected, as the optical characterization was done on the thin silver nanoplate films instead of the concentrated nanoplates in the suspension. However, for the sample with the highest coverage (produced after 22 h of substrate exposure), a broad surface plasmon at 660 nm was observed along with two shoulders at 330 nm and 550 nm. These peaks align closely with the spectrum of the suspension, further confirming the presence of the nanoplates on the substrate. Additionally, the intensity of the absorbance increased with increasing exposure time due to the increasing coverage of the nanoplates, as revealed by the SEM images. \begin{table}
\begin{tabular}{c c c} \hline
**Exposure** & **Edge Length of** & **Coverage of Nanoplates on** \\
**Times** & **Nanoplates (nm)** & **the Surfaces (Counts/\(\upmu\)m)** \\ \hline
15 min & 25.05 \(\pm\) 7.37 & 79 \\
30 min & 25.59 \(\pm\) 9.72 & 103 \\
1 h & 26.21 \(\pm\) 8.40 & 248 \\
2 h & 24.37 \(\pm\) 7.37 & 202 \\
8 h & 27.47 \(\pm\) 6.68 & 534 \\
14 h & 25.24 \(\pm\) 7.49 & 423 \\
22 h & 25.11 \(\pm\) 7.68 & 503 \\ \hline \end{tabular}
\end{table} 
Table 1: The measurement of the edge length and the coverage of triangular nanoplates on the surface for 15 min to 22 h samples of exposure times. Figure 7: The SERS spectrum of BPA on the silver nanoplate film (formed after 2 h exposure time) and Raman of BPA absorbed on a clean silicon surface. * are labels for the silicon peaks.