Fig. 1. Schematics of laser-induced chemical reduction for hierarchical silver micro-nanostructures by dielectric microsphere focusing. (a) Self-assembly of dielectric microspheres on the surface of PDMS film; (b)‒(c) dielectric microspheres were embedded into the uncured PDMS film; (d)‒(e) preparation of AgNPs/AgMRs/MS SERS substrates by laser-chemical reduction; (f) Raman detection

Fig. 2. Regulation of dielectric microsphere diameter (D) on the structure of AgNPs/AgMRs

Fig. 3. SEM micrographs of hierarchical silver micro-nanostructure surfaces under different photochemical parameters. (a) Evolution of hierarchical silver micro-nanostructure with CAgNO3∶CC6H5Na3O7 and irradiation time; (b) evolution of hierarchical silver nanostructure with laser irradiation power and irradiation time

Fig. 4. SERS performance of hierarchical AgNPs/AgMRs/MS hybrid structures. (a)‒(c) Regulation of the photochemical parameters CAgNO3∶CC6H5Na3O7, irradiation power, and microsphere diameter on Raman intensity of MB at 1624 cm^-1; (d)‒(g) Raman detection limit of MB, MG, 4-NBT, and CV on hierarchical AgNPs/AgMRs/MS hybrid structures SERS substrate; (h) repeatability of hierarchical AgNPs/AgMRs/MS hybrid structures; (i) histogram of intensity distribution of Raman characteristic peaks at 1396 cm^-1 and 1624 cm^-1 for MB molecules

Fig. 5. Raman detection limit of MB molecules on different substrates. (a) Si substrate; (b) PDMS substrate; (c) MS substrate; (d) PDMS/MS substrate; (e) AgNPs substrate; (f) AgNPs/MS substrate

Fig. 6. Numerical simulation of focusing effect and directional antenna effect of AgMRs/MS structure. (a) Optical field intensity distribution of the AgMRs/MS structure; (b) focused optical field intensity distribution curve of the AgMRs/MS structure; (c) optical field intensity distributions of directional antenna effect via the free space, MS and AgMRs/MS structures; (d) far-field emission polar plot of directional antenna effect via the free space, MS and AgMRs/MS structure

Table 1. Experimental and simulated characteristic size of AgMRs under dielectric microspheres with different diameters