Adsorption is the accumulation of atoms, molecules, or ions at the surface of a solid or liquid as the result of physical or chemical forces. It differs from absorption, in that an adsorbed substance remains at the surface while an absorbed substance spreads throughout the absorbing material. An adsorbed substance is termed an adsorbate while the material on which adsorption occurs is the substrate. The release of an adsorbate is termed desorption.

Chemists make a distinction between chemical adsorption, or chemisorption, characterized by the formation of chemical bonds with the substrate, and physical adsorption or physisorption, which results from the van der Waals force. Chemisorption plays an essential role in corrosion, heterogeneous catalysis, and electrochemistry. Physisorption is a factor to be dealt with in the design of vacuum systems and is also used as a tool to study highly irregular surfaces. Further distinctions can be drawn between localized...