Fig. 1. Principle of SNOM-TERS. (a1) Sketch map of SNOM-TERS platform. M: mirror, LL: laser line, A: attenuator, HWP: half-wave plate. Insets show the transverse mode intensity of fiber RVM (a2) and the corresponding transverse electric vector distribution examinations (a3–a5). (b) PFT bunded on the tuning fork to approach silicon substrate. (c) SEM image of PFT with a tip curvature radius of 20 nm. (d) Photograph of PFT achieving background-free tip hotspot with the fiber RVM internal illumination.

Fig. 2. Performance evaluation of SNOM-TERS platform. (a) Illustrations of the background-free tip hotspot approaching silicon substrate with tip-substrate distance of d. (b) Calculated electric-field intensity enhancement factor |E_tip/E₀|² of tip hotspot in the case of d=10 nm and λ=632.8 nm, with E_tip and E₀ being of electric field of tip hotspot and fiber RVM, respectively. (c) Shear-force topography of SWCNT dispersed on a silicon substrate and (d) the corresponding time-series of SNOM-TERS spectra of SWCNT with excitation power increasing from 0 mW to 0.12 mW. Star symbol indicated the position of tip hotspot, and integration time of spectrometer was 1 s. (e) Normalized SNOM-TERS spectrum of SWNT obtained from (d) at t=55 s. (f) Time-series of SNOM-TERS spectra of SWCNT with excitation power of 0.2 mW.

Fig. 3. Fingerprint information acquisition of glucose molecules. (a) Shear-force topography (15 μm×15 μm) of glucose molecules clustered on a hydrophilic silicon substrate and (b) a typical three-dimensional morphology distribution (5 μm×5 μm). (c) Height distribution of glucose molecule cluster obtained along a dashed white line in (b). (d) Far-filed Raman spectra of glucose molecules clustered on silicon (black curve) and hydrophilic silicon (red curve) substrates. Inset is an illustration of glucose molecules adsorbed efficiently on hydrophilic silicon, and the integration time of spectrometer was 20 s. (e) Time-series of SNOM-TERS spectra of glucose molecular cluster with excitation power increasing from 0.1 mW to 0.25 mW, and the integration time of spectrometer was 120 s. (f) SNOM-TERS spectrum with PFT approaching glucose molecules cluster and locating at the position indicated by star symbol in (b). Excitation power was 0.25 mW, and integration time of spectrometer was 120 s. (g) DFT-calculated Raman spectra of chain and D-(+)-glucose molecules (Method 1) with chemical structures of two types of glucose molecules being shown in Fig. S10.

Fig. 4. Vibrational modes identification of chain glucose molecules. Multi-peak Gaussian curve-fitting analysis of SNOM-TERS spectrum of chain glucose molecules within (a1–l1) twelve spectral windows and (a2–l2) corresponding DFT calculations.