## 3 Results and Discussion
### Suppressed Mechanical Properties of FS Surfaces  
Figure 2 displays the nanohardness and reduced modulus of various FS surfaces measured with nanoindentation tests. Note that the maximum penetration depth of the indenter into the FS surface is 50 nm, and the nanohardness and reduced modulus are estimated by the average value between the penetration depth of 30 nm and 50 nm, because the obtained values in the near-surface (\(<\)30 nm) are mainly caused by the indentation-size effect [31]. The nanohardness and reduced modulus of the pristine FS surface are \(\sim\)10 GPa and \(\sim\)71 GPa, respectively, which are close to the values in previous publications [32; 33]. As the H\({}_{2}\)O\({}_{2}\) concentration increases, the nanohardness and reduced modulus of the FS surface begin to decrease, to \(\sim\)9.5 GPa and \(\sim\)68 GPa, respectively, as the H\({}_{2}\)O\({}_{2}\) concentration increases to 20%. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **Pristine** & **0\%** & **5\%** & **10\%** & **20\%** \\ \hline Water contact angle (\({}^{\circ}\)) & 66 & 66 & 63 & 60 & 58 \\ \hline Thickness of water (nm) & 0.42 & 0.42 & 0.46 & 0.50 & 0.52 \\ \hline \(F_{\text{c}}\) (nN) & 59.09 & 59.09 & 70.89 & 82.31 & 89.70 \\ \hline \(F_{\text{vdw}}\) (nN) & 13.03 & 13.03 & 11.79 & 10.84 & 10.33 \\ \hline Calculated \(F_{\text{a}}\) (nN) & 72.11 & 72.11 & 82.68 & 93.16 & 100.03 \\ \hline Measured \(F_{\text{a}}\) (nN) & 78.01 & 78.01 & 89.56 & 103.45 & 112.03 \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of the calculated and measured adhesion forces. Herein, the calculated adhesion forces were determined based on Ref [21]. The measured adhesion forces were tested on various FS surfaces before nanowwear tests. Not only are the nanomechanical properties of the FS surface affected, but also the macroscale mechanical response. The macroscale mechanical properties of the FS surface were analyzed with Vickers indentation, and AFM images of Vickers indentation imprints were obtained to further reveal the surface damage behavior of the FS surface, as shown in Figure 3. It was found that the Vickers hardness of the pristine FS surface is \(\sim\)7.1 GPa, which is close to the hardness value of the original FS surface reported in the previous investigations [33,34]. Note that the Vickers hardness of the FS surface is much smaller than the nanohardness (Figure 2); the discrepancy between the two hardness measures must due to the difference in penetration depth with the two methods, where the penetration depth of the indenter is calculated to be \(\sim\)0.8 \(\upmu\)m under an applied load of 0.1 N, which is much deeper than that in nanoindentation tests (Figure 2). As the concentration of the H\({}_{2}\)O\({}_{2}\) solution increases from 0% to 20%, the residual indentation depth (volume) of the FS surface increases from \(\sim\)0.37 \(\upmu\)m (\(\sim\)1.2 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{3}\)) to \(\sim\)0.5 \(\upmu\)m (\(\sim\)1.2 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{3}\)) (Figure 3b,c), and the corresponding Vickers hardness of the FS surface decreases from \(\sim\)7.0 GPa to \(\sim\)6.2 GPa (Figure 3d). This result indicates that the Vickers hardness of the FS surface decreases with the H\({}_{2}\)O\({}_{2}\) solution concentration, where the overall trend is similar to that in nanohardness (Figure 2). There are two possible reasons for the decrease in hardness of the FS surface after treatment in various H\({}_{2}\)O\({}_{2}\) solutions. First, after treatment with H\({}_{2}\)O\({}_{2}\) solutions, the FS surface becomes more hydrophilic and more water molecules can be adsorbed on the FS surface (Table 1); these water molecules are more susceptible to diffusing into the FS subsurface and facilitate the hydrolysis of the Si-O-Si network during the indentation process [8,35], causing more damage to the surface of FS, and thus reducing hardness (Figures 2 and 3).