Surface-enhanced Raman scattering and fluorescence near metal nanoparticles

Abstract

We present a general model study of surface-enhanced resonant Raman scattering and fluorescence, focusing on the interplay between electromagnetic (EM) effects and the molecular dynamics as treated by a density matrix calculation. The model molecule has two electronic levels, is affected by radiative and non-radiative damping mechanisms, and a Franck-Condon mechanism yields electronvibration coupling. The coupling between the molecule and the electromagnetic field is enhanced by placing it between two Ag nanoparticles. The results show that the Raman scattering cross section can, for realistic parameter values, increase by some 10 orders of magnitude (to ∼ 10 −14 cm 2 ) compared with the free-space case. Also the fluorescence cross section grows with increasing EM enhancement, however, at a slower rate, and this increase eventually stalls when non-radiative decay processes become important. Finally, we find that anti-Stokes Raman scattering is possible with strong incident laser intensities, ∼ 1 mW/µm.

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

“…2,[64][65][66][67][68][69][70][71][72][73] The nonlocal hydrodynamical (NLHD) description has attracted considerable interest because of its numerical efficiency for arbitrarily-shaped objects 47,[74][75][76][77][78][79][80][81][82][83][84] and the possibility to obtain semi-analytical Example of the implementation of QCM in metallic gaps. In (a), a spatially inhomogeneous effective medium whose properties depend continuously on the separation distance is introduced in the gap between two metallic spheres.…”

Quantum Mechanical Description of Raman Scattering from Molecules in Plasmonic Cavities

“…1(b)), such as the length of a molecular bond, e.g., C=O. 21,22 These vibrations interact with the cavity photons through a nonlinear Hamiltonian, reminiscent of that found in optomechanical systems. 24 In this description, the large enhancement of the Raman scattering from a molecule in the plasmonic cavity occurs thanks to the significant shrinking of the effective mode volume of a single photon.…”

“…20 These results suggest that some experiments might have reached the regime where the quantum-mechanical nature of both the molecular vibrations and the plasmonic cavity emerges, 21 and call for an adequate theoretical description that goes beyond the classical treatment of the electric fields produced in plasmonic cavities. 1,22,23 In this work we address the underlying quantummechanical nature of Raman scattering processes by quantizing as bosonic excitations both the vibrations of the molecule and the electromagnetic field of a plasmonic cavity. The description of the vibrations through bosonic operators can be justified by considering the harmonic approximation to the energy landscape of the molecule along a generalized atomic coordinate ( Fig.…”

On the linear response and scattering of an interacting molecule-metal system

“…Shifting and finite lifetime of states appear rigorously and automatically within our approach and reveal an intricate coupling between molecule and metal not fully described by previous theories. Self-consistent incorporation of this quantum-molecular response into the continuum-electromagnetic scattering of the molecule-metal target is exploited to compute the localized surface-plasmon resonance wavelength shift with respect to the bare metal from first principles.Ever increasing experimental interest in a variety of plasmon-enhanced molecular spectroscopies has provided impetus for the development of a corresponding assortment of theoretical descriptions of these phenomena [1,2,3,4,5,6]. Linear molecular spectroscopies such as Raman and fluorescence have found their plasmonenhanced analogs in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence; both are now routinely realized in the extreme limit of singlemolecule detection; see, e.g., Refs.…”

“…Ever increasing experimental interest in a variety of plasmon-enhanced molecular spectroscopies has provided impetus for the development of a corresponding assortment of theoretical descriptions of these phenomena [1,2,3,4,5,6]. Linear molecular spectroscopies such as Raman and fluorescence have found their plasmonenhanced analogs in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence; both are now routinely realized in the extreme limit of singlemolecule detection; see, e.g., Refs.…”