Figure 1
Core-satellite nanoassemblies on an optical interference substrate and their mechanism for SERS enhancement. (a) Schematic representation of 60 nm-30 nm core-satellite AuNP assemblies on an optical interference substrate composed of a silica spacer (silica thickness: w) and silicon reflector and (b) the SERS enhancement mechanism through phase control of the light. When the laser beam hits the substrate, reflection occurs at the air-silica and the silica-silicon interfaces. The reflected light from the silica-silicon interface and the incident wave create a phase-matched condition for the interference at the location of hot spots (near field) and excite the molecular vibrations. This results in emitting Raman photons coherent with excitation, which also undergo the near field enhancement at hot spots. Ei: incident wave and Er1 and Er2: reflected waves from the top and bottom interfaces of the silica spacer. Note, this is a schematic representation of the optical interference of the reflections from air-silica and silica-silicon interfaces mediated by the NPs. (c) Scanning electron microscopy (SEM) image of 60 nm-30 nm core-satellite AuNP assemblies fabricated on a 110 nm silica-coated silicon substrate through a two-step self-assembly method that involves the electrostatic self-assembly of DNA-modified core NPs onto the positively charged silica surface and DNA-directed self-assembly of the complementary DNA modified satellite NPs onto the cores, and (d) statistical analysis of the number of satellite NPs surrounding each core NP.
