Measurement of the distribution of site enhancements in surface-enhanced raman scattering

Abstract

On nanotextured noble-metal surfaces, surface-enhanced Raman scattering (SERS) is observed, where Raman scattering is enhanced by a factor, Ḡ, that is frequently about one million, but underlying the factor Ḡ is a broad distribution of local enhancement factors, η. We have measured this distribution for benzenethiolate molecules on a 330-nanometer silver-coated nanosphere lattice using incident light of wavelength 532 nanometers. A series of laser pulses with increasing electric fields burned away molecules at sites with progressively decreasing electromagnetic enhancement factors. The enhancement distribution P(η)dη was found to be a power law proportional to (η)-1.75, with minimum and maximum values of 2.8 × 104 and 4.1 × 1010, respectively. The hottest sites (η > 109) account for just 63 in 1,000,000 of the total but contribute 24% to the overall SERS intensity.