Quantitative SERS Measurements on Dielectric-Overcoated Silver-Island Films by Solution-Deposition Control of Surface Concentrations

A simple method to control the dosing of small adsorbate molecules onto solid surfaces from liquid solution is applied to quantitative surface-enhanced Raman scattering measurements on dielectric-overcoated silver-island films. The deposition method, based on substrate withdrawal from solution, is evaluated by measuring fluorescence (ex situ) and optical absorption (in situ) of dye molecules deposited onto glass surfaces. Control of adsorbate surface concentrations was accomplished by varying the withdrawal rate and the concentration of the dye in solution. The dosing method was used to study the dependence of the electromagnetic contribution to SERS enhancement on surface coverage of scatterer. The sensitivity enhancement was found to be constant for adsorbate coverages up to 60−80% of a monolayer. Beyond a full monolayer, SERS enhancement for additional molecules deposited onto the surface was found to drop significantly, by as much as 1 order of magnitude.