Surface-Enhanced Raman Excitation Spectroscopy of a Single Rhodamine 6G Molecule

Abstract

The surface-enhanced Raman excitation profiles (REPs) of rhodamine 6G (R6G) on Ag surfaces are studied using a tunable optical parametric oscillator excitation source and versatile detection scheme. These experiments afford the ability to finely tune the excitation wavelength near the molecular resonance of R6G (i.e., approximately 500-575 nm) and perform wavelength-scanned surface-enhanced Raman excitation measurements of a single molecule. The ensemble-averaged surface-enhanced REPs are measured for collections of molecules on Ag island films. The relative contributions of the 0-0 and 0-1 vibronic transitions to the surface-enhanced REPs vary with vibrational frequency. These results highlight the role of excitation energy in determining the resonance Raman intensities for R6G on surface-enhancing nanostructures. Single-molecule measurements are obtained from individual molecules of R6G on Ag colloidal aggregates, where single-molecule junctions are located using the isotope-edited approach. Overall, single-molecule surface-enhanced REPs are narrow in comparison to the ensemble-averaged excitation profiles due to a reduction in inhomogeneous broadening. This work describes the first Raman excitation spectroscopy studies of a single molecule, revealing new information previously obscured by the ensemble.

Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy (SHINERS)

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Anion Stabilization in Electrostatic Environments

“…[6][7][8][9][10][11][12][13] A major challenge is that of understanding the interaction between extended metallic systems, such as surface metal gates or a nanoparticle, and an adsorbed molecule. From a theoretical standpoint, these two components are characterized by different lengthscales.…”

Simplified Sum-Over-States Approach for Predicting Resonance Raman Spectra. Application to Nucleic Acid Bases

“…10,11 The combination of surface enhancement with intramolecular excitations gives rise to surface-enhanced resonance Raman scattering (SERRS) which provides an extraordinary sensitivity, even to the level of single-molecule detection. [12][13][14] While theoretical descriptions of resonance Raman scattering has been developed early on by Shorygin and co-workers 2,15 and by Albrecht,16,17 calculations of resonance Raman scattering from medium-size and large molecules are not often routinely performed. Raman scattering is a second-order process and its cross sections are given by the Kramers-Heisenberg-Dirac (KHD) dispersion relation.…”