Surface enhancement factors for Ag and Au surfaces relative to Pt surfacesfor monolayers of thiophenol

Raman signal intensities from the 997 cm(-1) ring breathing mode of thiophe nol monolayers adsorbed at Ag, Au, and Pt surfaces were employed for determ ination of absolute surface enhancement factors (SEFs). Unlike previous est imations of SEFs, these SEFs are determined by referencing the surface-enha nced Raman scattering (SERS) intensities to the unenhanced Raman scattering at Pt surfaces. The surfaces studied include those commonly prepared in a laboratory ambient and those prepared in vacuum. Surfaces prepared in ambie nt include polycrystalline Ag electrochemically roughened by an oxidation-r eduction cycle (ORC), mechanically polished (MP) polycrystalline Ag, chemic ally polished (CP) polycrystalline Ag, Ag (111), MP polycrystalline Au, and MP polycrystalline Pt. vacuum environment surfaces include coldly deposite d Ag films (cold Ag) and room temperature-deposited (RT) "thick" Ag films. Each of these thiophenol/metal systems was sampled with an excitation wavel ength (lambda(ex)) of 514.5 nm; MP Au surfaces were also studied with lambd a(ex) of 720 nm. SEFs of 2.0 x 10(4) for ORC Ag, 5.3 x 10(3) for MP Ag, 160 for cold Ag, 64 for MP Au-720 (lambda(ex) = 720 nm), 69 for Ag (111), 39 f or CP Ag, 7.9 for RT "thick" Ag, and 2.2 for MP Au-514.5 (lambda(ex) = 514. 5 mn) are observed relative to the SEF of MP Pt, which is assigned as 1. Fo r practical purposes, the significance of the magnitudes of these SEFs is d iscussed in terms of estimated surface Raman limits of detection (LODs).