Raman spectroscopy of surfaces

Raman scattering has usually a very low efficiency. Therefore, during the first five decades after its discovery, Raman spectroscopic investigations of adsorbate-covered surfaces (except surfaces of highly porous samples) were out of reach. This changed in 1970s, when for molecules adsorbed on some surfaces, very large increase of the intensity of Raman spectrum (denoted as surface-enhanced Raman spectroscopy - SERS) was reported. In the past decade, two other very important achievements in surface Raman spectroscopy have been made: observation of SER spectrum of a single molecule and coupling of Raman spectroscope with the scanning probe microscope (STM or AFM) allowing a significant increase in the spatial resolution of Raman measurements in so-called tip-enhanced Raman spectroscopy (TERS). In the latter approach, fine tip made of a metal that supports surface plasmon resonances (such tip may be treated as a very local electromagnetic resonator) is brought at the nanometer distance above the surface, which induces large increase of the Raman scattering from molecules adsorbed at a Surface located underneath the tip. This short review presents an overview of the state of the art and further possible applications of Raman spectroscopy in surface analysis. We mainly focus on SERS and TERS. Future prospects in these fields are also discussed. (C) 2009 Elsevier B.V. All rights reserved.