Fig. 2. Characterizations of the WOFN structure.

a Atomic force microscopy (AFM) image of a piece of WS₂ on a sapphire substrate. The thickness of the WS₂ film is ~0.6 nm, as shown in the inset. The scale-bar is 500 nm. b PL spectra of a transferred WS₂ film on a glass slide and silica OFN; 1–4 denote the different positions labeled in the inset, at which the spectra are collected. The red dashed boxes outline the positions of the transferred WS₂ on the WOFN and the residual WS₂ film on the glass substrate. The scale-bar corresponds to 20 μm. c Raman spectra of the sample from the positions in b. d Measured normalized transmission spectra of the WOFN and WS₂ on a silica substrate. The diameter of the OFN is ~800 nm, while the effective laminated length of WS₂ on the WOFN is ~60 μm. e Calculated transmission spectra with the same structure parameters as those in d. f PL spectra of the WOFN with different pump power values (at 532 nm). The inset shows the linear relationship between the PL intensity and the pump light power