Fig. 1. (a) Schematic diagram showing the configuration of a L-GNP/S-GNP dimer linked with 1,6-hexanedithiol. (b) SEM and (c) TEM images of the dispersed GNP dimers. The insets show a magnified view of a typical GNP dimer. (d) DFM image of two isolated GNP assemblies. (e) SERS spectrum of 4-NTP measured from an isolated GNP dimer. (f) SERS image of the same assemblies shown in (d), constructed by using the intensity of the 1345 cm^–1 peak of 4-NTP in (e). (g) FDTD calculation showing the local electric field distribution of the GNP dimer at the X–Z plane. (h) Scattering spectrum of a single GNP dimer.