The connection between plasmon decay dynamics and the surface enhanced Raman spectroscopy background: Inelastic scattering from non-thermal and hot carriers

Abstract

Recent studies have established that the anti-Stokes Raman signal from plasmonic metal nanostructures can be used to determine the two separate temperatures that characterize carriers inside the metal-the temperature of photoexcited "hot carriers" and carriers that are thermalized with the metal lattice. However, the related signal in the Stokes spectral region has historically impeded surface enhanced Raman spectroscopy (SERS), as the vibrational peaks of adsorbed molecules are always accompanied by the broad background of the metal substrate. The fundamental source of the metal signal, and hence its contribution to the spectrum, has been unclear. Here, we outline a unified theoretical model that describes both the temperature dependent behavior and the broad spectral distribution. We suggest that the majority of the Raman signal is from inelastic scattering directly with non-thermal carriers that have been excited via damping of the surface plasmon. In addition, a significant spectral component (~ 1%) is due to a subpopulation of hot carriers in an elevated thermal distribution. We have performed temperature and power-dependent Raman experiments to show how a simple fitting procedure reveals the plasmon dephasing time, as well as the temperatures of the hot carriers and the metal lattice, in order to correlate these parameters with quantitative Raman analysis of chemical species adsorbed on metal surface.

Unveiling practical considerations for reliable and standardized SERS measurements: lessons from a comprehensive review of oblique angle deposition-fabricated silver nanorod array substrates

“…Intrinsic baselines may arise from fluorescence and Rayleigh scattering from the analyte molecules, particularly biomolecules, 225 as well as surface plasmon-induced mechanisms. 226–228 Extrinsic baselines include contributions from scattering or absorption by the SERS substrate, such as the morphology of nanostructures, environmental contamination molecules, background illumination, and instrument response.…”

Quantum Plasmonics in Sub-Atom-Thick Optical Slots

“…We hypothesize that these flares arise from transient subatomic slot modes created inside the larger NPoM nanogap. Since the slot modes enhance the penetration of light inside the metal (see below), they can enhance light emission (LE) which arises from hot-electron photoluminescence or electronic Raman scattering. − In both processes, light excites electrons near the Fermi energy to a higher state, from where they decay back to states on the parabolic s -band emitting red-shifted photons that give the flare (Figure a). In- and out-coupling of LE from the metal is enhanced by the local optical density of states and thus resonantly enhanced by the slot mode.…”

Probing electron and lattice dynamics by ultrafast electron microscopy: Principles and applications

“…Both electron relaxation/jumping and lattice vibrations accompanied by spatial variations can be transmitted at ultrafast speeds [52][53][54] (picosecond-femtosecond) within very small scales 55,56 (micronnanometer). When photons are absorbed by electrons, forming transferable charge carriers, the charge carrier will diffuse and relax [57][58][59][60] through both equilibrium and nonequilibrium paths, such as ballistic transport, 61,62 inelastic scattering, 63,64 and electron and phonon interactions. 18,33,65 The investigation of ultrafast carrier transfer on the nanoscale and profound changes in various physical parameters presents a formidable challenge for theoretical models.…”