Elementary Processes at Surfaces I. Adsorption and Desorption

Adsorption/desorption phenomena have already been treated in Chap. 9 devoted to the structure of surfaces with adsorbates. In particular, the basic terms (for example, adsorbate, substrate, physisorption, chemisorption, coverage) have been introduced. However, there the final result of the adsorption/desorption process has been discussed, not the process itself. The latter is the subject of the present chapter, in which adsorption/desorption phenomena are treated within the kinetic approach. It resides in establishing the relationship between the rates of adsorption and desorption of atoms or molecules as a function of the external macroscopic variables, such as vapor pressure, temperature of the substrate and vapor, substrate surface structure, etc. Kinetics is an external manifestation of the atomic-scale dynamic processes occurring at the surface. Analysis of the kinetic data gives an insight into the atomic mechanisms involved in the adsorption and desorption. In particular, adsorption/desorption energetics (the height of energy barriers and the depth of energy wells) are commonly extracted from the experimental kinetic data.