Monitoring adsorption and desorption on a metal surface by optical non-resonant reflectivity changes

Abstract

A linear optical reflection technique is demonstrated as a simple and non-intrusive means for monitoring the adsorption and desorption of carbon monoxide on Cu(100). The non-resonant reflectivity change induced by CO adsorption on copper is of the order of −1%, allowing submonolayer sensitivity of 0.01 ML to be achieved. The induced reflectivity change exists over a broad frequency range, and is found to correlate linearly with the coverage in both the infrared ( λ=4.76 μm) and the visible ( λ=632.8 nm). CO adsorption is found to proceed with a constant sticking coefficient up to a coverage of 0.5 ML, after which Langmuir adsorption kinetics are followed. The changes in the adsorption kinetics correlate quantitatively with structural changes in the CO monolayer. This technique monitors the surface coverage directly, and is simple and inexpensive to implement. As an optical surface probe it allows time-resolved measurements and can be extended to high-pressure environments.