ABSTRACT
Atoms at a metal surface exhibit unsaturated bonds that are available for fixing reactive species, atoms or molecules, present in the gas or liquid surrounding the surface. Such a reaction, when limited to one monolayer or a fraction of a monolayer, is known as an adsorption phenomenon or chemisorption. Similarly, atoms present in the bulk metal may diffuse toward and enrich the surface by so-called thermal segregation. Segregation may also occur by selective evaporation of the metal in vacuum or in an inert gas or by selective dissolution of the metal in a liquid phase (anodic segregation). Whatever the mechanism of surface enrichment, there is strong experimental evidence that the same structural and chemical states can be achieved by adsorption or segregation.
