Fig. 3: Interface functionalization.

a Schematic diagram of the interface functionalization process. Scanning electron microscopy (SEM) images of microfiber surfaces with (b) MoS₂, (c) GO, (d) MoS₂-GO, e GO-MoS₂, and (f) GO-MoS₂-Au. (The position outlined by the dotted line in (f) was the structure model of Au@Ag₂S in the FDTD simulation.) AFM height profiles of microfiber surfaces with (g) GO, (h) MoS₂, and (i) GO-MoS₂-Au. (Due to the limitations of AFM resolution, microfibers could not be used in (g, h, i). Instead, the same processed optical fibers with a diameter of 125 μm were used for measurement. The results can provide a reference for the thickness of the surface layer on the microfiber). j Wavelength shifts recorded by the sensor with the GO-MoS₂-Au interface during the interface functionalization process. k Raman spectra of microfiber surfaces with various interfaces. l FDTD map and corresponding intensities of the optical microfiber surfaces with GO, MoS₂, GO-MoS₂, MoS₂-GO, and GO-MoS₂-Au interfaces. (Inset: the unit and structures of the simulated microfiber. The thickness of each layer was based on the height information obtained from the AFM results: GO was 3 nm; MoS₂ was 5 nm; Au@Ag₂S was 15 nm). m Schematic diagram of evanescent field enhancement induced by the plasmon effect. n Transverse electric field amplitude distributions of the HE₁₂ mode of bent microfibers with various interfaces calculated via numerical mode simulation software. (Simulation model: the thickness of GO was 3 nm, refractive index was 3.5388 ref. ⁵¹; the thickness of MoS₂ was 5 nm, refractive index was 3.9257 ref. ⁵². For Au@Ag₂S, since its surface occupied area was only 6.33%, and the surrounding was water, its thickness was 15 nm, refractive index was 1.3639 [1.8205 ref. ⁵³ ×6.33% + 1.3330_{(refractive index of water)}×(1–6.33%)]. We idealized the coatings as being uniform.) o Bulk refractive index sensitivities of the microfiber with the GO-MoS₂-Au interface and the fiber without an interface