Microscopic theory of surface-enhanced Raman scattering in noble-metal nanoparticles

Abstract

We present a microscopic model for surface-enhanced Raman scattering (SERS) from molecules adsorbed on small noble-metal nanoparticles. In the absence of direct overlap of molecular orbitals and electronic states in the metal, the main enhancement source is the strong electric field of the surface plasmon resonance in a nanoparticle acting on a molecule near the surface. In small particles, the electromagnetic enhancement is strongly modified by quantum-size effects. We show that, in nanometer-sized particles, SERS magnitude is determined by a competition between several quantum-size effects such as the Landau damping of surface plasmon resonance and reduced screening near the nanoparticle surface. Using time-dependent local density approximation, we calculate spatial distribution of local fields near the surface and enhancement factor for different nanoparticles sizes.

Landau damping of surface plasmons in metal nanostructures

“…While, within TDLDA, the Kohn-Sham wave functions are directly determined by the (self-consistent) confining potential, the local fields are, instead, defined solely by the induced charge density via the (screened) Coulomb potential and, therefore, depend on the confining potential indirectly. Hence, the deviation of E n from its classical behavior across the interface is determined by the electron density spillover over the classical (hard wall) boundary [73], and, therefore, is largely independent of the system overall shape. Furthermore, recent TDLDA studies of relatively large (up to 10 nm) nanoparticles revealed [55,56] that the main impact on plasmon linewidth comes precisely from the electron density tail and dielectric environment, implying that it is the plasmon local field near the interface, rather than electron wave functions, that chiefly determines the plasmon decay rate magnitude in real structures.…”

Quantum theory of the electromagnetic response of metal nanofilms

“…Physically, the behavior illustrated in Fig. 1 can be understood as the result of electron spillover 31,32 (in the case of F-type boundary condition) or as the combined action of the finite charge density of the jellium and of the uncertainty principle (in the case of B-or R-type boundary conditions).…”

Nonlocal Effects on Surface Enhanced Raman Scattering From Bimetallic Coated Nanoparticles

“…Now, SERS is playing an important role in surface science, spectroscopy, and detection [5] due to the high sensibility of detection with molecular identification capabilities [6,7]. It was believed that the mechanisms for the SERS enhancement include the chemical adsorption of the metal interface [8], quantum effects [9], and the electromagnetic (EM) field enhancement at the position of the single-molecule near metal nanoparticles [10][11][12][13][14].…”