Surface Enhanced Raman Scattering Applied to Surface Chemical Kinetics

摘要

Surface enhanced Raman scattering (SERS), has the potential to be powerful tool in the study of surface chemical reaction processes. Sensitive to less than monolayer coverage even under ambient conditions, SERS has been used to obtain detailed surface reaction kinetics in only a few cases. The applications of SERS to study surface chemical reaction kinetics is presently limited because the enhancement mechanisms are reaction dependent. That is, the size and the number density of the surface roughness is dependent on the reaction parameters, such as delta H and temperature that are functions of time. For selected reactions, a partial solution exists if during the course of the reaction, surface reconstruction is confined to modification of the adatom structures. Electromagnetic enhancement, due to surface roughness of approx 20nm, is nearly constant in this case, and only the adatom enhancement mechanism is time dependent. The adatom concentration is also proportional to the background intensity due to electron-hole recombination in the metal substrate. Thus the adatom time dependence of the SERS spectra may be removed by normalization to the background in a spectral region without discrete SERS peaks. Applications to the decomposition of allynes, phosphonates, and NO2 on silver powders provide supportive evidence. Keywords: Reaction kinetics.