Tip-Enhanced Raman Spectroscopy and Microscopy on Single Dye Molecules with 15 nm Resolution

Our recently developed approach of UHV-tip-enhanced Raman spectroscopy permits us to acquire Raman spectra of a few single brilliant cresyl blue (BCB) molecules and even a single one adsorbed on a Au(111) surface. This is substantiated by simultaneously recorded STM images. Furthermore, because of the reduced photobleaching in UHV, the time frame for spectral acquisition is sufficiently extended to allow tip-enhanced Raman imaging of a single BCB molecule with a lateral resolution of 15 nm.

Figure 1

STM images of five (a) and a single BCB molecule (d) adsorbed on Au(111), the corresponding height cross sections (b),(e) and the UHV-RR and UHV-TERR spectra (c),(f).

Figure 2

(a) TERS image in Raman mode ($568–572{\mathrm{cm}}^{-1}$) of a single BCB molecule on Au(111); (b) x- and y-cross sections of the Raman intensity through the center of the molecule.

Figure 3

STM image of BCB molecules adsorbed on step sites of a Au(111) sample; (b) topography profile along the arrow; (c) Raman intensity ($568–572{\mathrm{cm}}^{-1}$) profile along the arrow.

Figure 4

Series of 30 subsequent TERR spectra of a BCB monolayer on Au(111) (integration time: 1 s; laser power: 0.4 mW) recorded (a) in ultrahigh vacuum and (b) in a pure oxygen atmosphere; (c) time dependence of the TER band and background intensity at $570{\mathrm{cm}}^{-1}$ in the spectra.