## 3 Results
### Fundamental Characteristics of CYTOP NP Deposition
#### 3.1.2 Influence of Laser Processing Parameters on the NP Deposition  
The morphology of the deposited NPs on the glass also changed depending on laser processing parameters, such as the number of pulses and the pulse energy. Figure 4a shows SEM images of the deposited NPs on the glass when the number of pulses was varied from 1 to 10,000. The lower SEM images show enlarged views of the upper images. In this experiment, the pulse energy and the CYTOP-glass distance were kept constant at 5 \(\upmu\)J/pulse and 100 \(\upmu\)m, respectively (note that, in this experiment, a glass slide was placed horizontally above the CYTOP substrate, as shown in Figure 1).  
As shown in Figure 4a, fibrous network structures composed of NP aggregates were formed on the glass surface, and the pores in the network structures became narrower with an increasing number of pulses. We also conducted the NP deposition at a greater CYTOP-glass slide distance for comparison. Figure 4b shows overall (left) and enlarged (upper right) SEM images, a histogram of the NP sizes (middle) obtained from the enlarged SEM, and an AFM image (right) of the glass surface after 10,000 pulse irradiations at a CYTOP-glass distance of 4000 \(\upmu\)m. It can be seen from the images that NPs were distributed fairly uniformly on the glass slide. The average diameter of the NPs was 26.3 nm, with a standard deviation of \(\pm\) 8.6 nm. The NPs were highly monodisperse and close-packed to form a monolayer structure. The surface roughness of the monolayer structure was 18.9 \(\pm\) 1.37 nm.  
Figure 3: (**a**) SEM images of deposited NPs with different CYTOP-glass slide distances. (**b**) NP size as a function of the CYTOP-glass slide distance.  
Figure 2: Schematic of the NP deposition process at various CYTOP–glass distances.  
Table 1 shows a summary of the glass morphologies after the fs laser irradiation with different CYTOP-glass distances and different numbers of pulses. The pulse energy was maintained at 5 uJ/pulse. As shown in Table 1, when the CYTOP-glass distance was less than 1000 \(\upmu\)m, network structures tended to deposit on the glass slide. With increasing distance, the monolayer structure was more likely to be formed. Thus, the CYTOP-glass slide distance strongly influenced the morphology of the NP-deposited glass.  
In addition, we investigated the glass surface after NP deposition at various pulse energies from 3.0 to 8.0 uJ/pulse, as shown in the SEM images in Figure 5. Enlarged views of the deposited NPs are shown at the bottom. The number of pulses and the CYTOP-glass distance was kept constant at 1000 pulses and 100 \(\upmu\)m, respectively.  
The images in Figure 5 show that, when the pulse energy was less than 5 uJ/pulse, the network structures of NP aggregates gradually formed closed-rings and bridges and became dense with increasing pulse energy. By contrast, when the pulse energy was 8 uJ/pulse, agglomerates composed of melted NP aggregates were deposited onto the glass slide.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Distance [\(\upmu\)m]**No. of Pulses** & **1** & **500** & **1000** & **3000** & **10,000** \\ \hline
100 & \(\upmu\)m & \(\upmu\)m & \(\upmu\)m & \(\upmu\)m \\
1000 & \(\times\) & \(\upmu\)m & \(\upmu\)m & \(\upmu\)m \\
4000 & \(\times\) & \(\times\) & \(\times\) & \(\upmu\)m \\
10,000 & \(\times\) & \(\times\) & \(\times\) & \(\upmu\)m \\ \hline \hline \end{tabular}
\end{table}
Table 1: Effect of the CYTOP–glass distance and the number of pulses on the glass morphology.  
Figure 4: (**a**) SEM images of NPs deposited with different numbers of pulses. Enlarged views are shown at the bottom. The CYTOP-glass distance was 100 \(\upmu\)m. (**b**) Low-magnification (left) and enlarged (inset) SEM images, size distribution histogram (middle), and an atomic force microscopy (AFM) image (right) of NPs deposited at a CYTOP-glass distance of 4000 \(\upmu\)m. The number of pulses was 10,000.