Factors influencing the enhancement of raman spectral intensity from a roughened silver surface: The adsorption and surface Raman scattering of 2-amino 5-nitro pyridine

Abstract

2-Amino 5-nitro pyridinc (ANP) adsorbs strongly at an electrochemically roughened silver surface and gives an intense surface-enhanced Raman (SER) spectrum which identifies the adsorbate as the [ANP] − ion [C 5H 4N 3O 2] −. Coulometric and spectrophotometric methods are used to provide an in situ measurement of the surface molecular concentration of this adsorbate. This is shown to be linearly dependent upon the anodic roughening charge transfer in 0.1 M KCl over the range 0–150 mC cm −2 for double-potential-step roughening cycles. A quantitative measure of the surface Raman enhancement factor for this adsorbate is obtained, and this is shown to reach a maximum of 1.5 × 10 4 for surface roughening involving the passage of 25 mC cm −2. For this amount of roughening or greater, it is concluded that the surface roughness further increases the total SER intensity by a factor of 10 or more due to the resulting high effective surface concentration of the adsorbate.