Fig. 1. Sketch map of the experimental setup for SERS examination of the ATNA substrate. Inset is (a₁) the mode intensity distribution and (a₂)−(a₄) the polarization examination results of the AVB.

Fig. 2. Fabrication and characterization of the ATNA substrates. (a)–(c) Sketch map of the fabrication process of the ATNA substrates; (d) SEM image of the Ag-coated PS nanosphere array with the diameter of PS nanospheres of D=300  nm; (e) SEM image of the Ag-coated PS nanospheres stripped from the silicon wafer using the slide glass; SEM images of the ATNA substrates fabricated using PS nanospheres with (f) D=300  nm, (g) 400 nm, and (h) 600 nm. (i) Reflection spectra of the ATNA substrates with D=300  nm (red curve), 400 nm (green curve), and 600 nm (violet curve).

Fig. 3. Calculation of the electric-field intensity enhancement factor of the ATNA substrates excited via the focused LPB and AVB. Transverse-electric-field intensity distributions of the focused (a) LPB and (b) AVB, under conditions of NA=0.8 and λ=633  nm. Sketch map of the ATNA substrates excited via (c) LPB and (d) AVB. Electric-field intensity distribution on the surface of ATNA substrates, with D=600  nm, excited via (e) LPB and (f) AVB. Electric-field intensity distribution on the surface of the ATNA substrates, with (g) D=300  nm and (h) 400 nm, excited via AVB.

Fig. 4. SERS sensitivity examination of the ATNA substrate with D=600  nm. (a) Raman spectra of R6G, with concentration from 10−8  M down to 10−12  M, absorbed on the surface of the ATNA substrates and excited via LPB. (b) Raman spectra of R6G, with concentration of 10−11  M, excited via AVB (blue curve) and LPB (red curve). (c) Raman spectra of R6G, with concentrations of 10−12  M and 10−13  M, excited via the focused AVB.

Fig. 5. SERS sensitivity examination of the ATNA substrate with D=400  nm. (a) Raman spectra of R6G, with concentration from 10−9  M down to 10−11  M, absorbed on ATNA substrate and excited via LPB. (b) Raman spectra of R6G, with concentrations of 10−11,10−12, and 10−13  M, excited via AVB.

Fig. 6. Examination of SERS uniformity and Raman enhancement factor of the ATNA substrate with D=600  nm. (a) Schematic diagram of Raman mapping excited via AVB; (b) Raman imaging within a square of 15  μm×15  μm using the characteristic peak of 1511  cm−1 [inset in (d)] of R6G with a concentration of 10−8  M; (c) histogram of the intensities of the 1511  cm−1 characteristic peak obtained along the white curve in (b); (d) Raman spectra of R6G with concentrations of 10−8  M (red curve) and 10−1  M (black curve) on the ATNA substrate and a glass slide, respectively.

Fig. 7. Examination of reproducibility of ATNA substrates excited via AVB. (a) Raman spectra of R6G with a concentration of 10−9  M obtained from five ANTA substrates with D=600  nm. (b) Histogram of intensities of the 1511  cm−1 characteristic peak shown in (a).