fig3

Figure 3. Vacancy-induced strain for 2D materials. (A) Schematic of MoS₂ basal plane irradiated with helium ions; (B) HAADF-STEM image of MoS₂ showing different types of vacancies; (C) Enlarged image of HADDF-STEM revealing the atomic structure in single layer MoS₂ near the vacancy site; (A-C): quoted with permission from Yang et al.^[38]; (D) 2D structure model for LDH monolayer with V_O; (E) Schematic diagram illustrating the in-plane compressive strain induced by V_O in LDH nanosheets; (D-E): quoted with permission from Zhao et al.^[68]; (F) Schematic illustrating the alternant domain of WVs and SVs in WS₂; (G) Raman spectrum for WV domains. Inset shows the frequency shifts for $$ E_{2 g}^{1} $$ and A_1g modes; (F-G): quoted with permission from Jeong et al.^[73]. HAADF-STEM: high-angle annular dark field scanning transmission electron microscopy; LDH: layered double hydroxide; SVs: S vacancies; WVs: W vacancies; 2D: two-dimensional.