## 3 Results and Discussion
### Enhanced Subsurface Deformation of FS upon Indentation and Nanowear
In the case of nanowear, however, the friction force at the sliding interface is decreased slightly (Figure 4), but the surface nanowear and subsurface densification of FS increases with the treated H\({}_{2}\)O\({}_{2}\) concentration (Figures 4 and 6). Since the shear stress that propagates into the subsurface is the direct source of the friction-induced subsurface densification [42], the stress that diffuses into the subsurface must increase. This finding implies that the magnitude of the friction force at the sliding interface is not a good descriptor for the surface nanowear and subsurface densification of glass caused by friction [44], because the friction force is dissipated at the sliding interface, while the surface nanowear and indentation damage of FS is governed by mechanochemical reactions [35; 37; 38] and the subsurface densification of FS is governed by stress that diffuses into the subsurface region [42; 44]. This is consistent with the literature finding that the selective transfer phenomenon can effectively control dislocation movement and thus affects surface wear and damage [45]. In addition, the damage of the FS surface caused by indentation and nanowear increases with H\({}_{2}\)O\({}_{2}\) solution (Figures 3 and 4), accompanying the increased subsurface damage (Figures 5 and 6). Similar trends of the evolution of surface damage with subsurface damage have also been found on borosilicate glass in scratching [46] and wear tests [44]. Generally, the pile-up formation around the nanoindentation or nanoscratch is identified as the direct evidence for the shear flow during the nanoindentation or nanoscratch processes [41]. In the present study, there is no pile-up around the Vickers indentation mark on the FS surface (Figure 3). However, a tiny pile-up formation can be found on the annealed indentation mark on the FS surface, indicating there is some shear flow during the indentation process (Figure 5). The calculated shear flow volume of various FS surfaces is not zero according to [PERSON]'s methods (Figure 5). This means the presence of shear flow on the glass surface cannot be simply elucidated from the pile-up formation on pristine indentation topography [47]. The results obtained in the current study imply that even with surface hydroxylation by H\({}_{2}\)O\({}_{2}\) solutions, the surface and subsurface damage of FS can be altered significantly. The nanohardness, nanowear, and subsurface deformation following nanoindentation and nanoscratching of the FS surface in ambient conditions are slightly different than those in previous publications [23; 33; 40; 41], which may due to the slight difference in surface water  
Figure 6: (**a**) AFM image and (**b**) cross\(-\)section line profiles of various FS surfaces after sub-\(T_{g}\) annealing treatment. (**c**) Densified volume and shear flow volume of various FS surfaces during nanowear tests. (**d**) Recovery ratio of various FS surfaces. adsorption on FS surfaces. As the surface chemistry of FS is slightly altered, the water film thickness adsorbed on the FS surface is changed (Table 1), and the contact damage of the FS surface following indentation and nanowear is changed significantly since the mechanochemical reactions involving water play a critical role in the surface damage behavior of the FS surface [8; 9; 35; 36; 37]. These findings indicate that the hydrophilicity of the FS surface after various treatments or cleaning procedures should be paid more attention because it can significantly affect the contact damage behaviors.