4. Atomic surface structures

At the atomic scale, a surface can exhibit structural states unknown in the bulk structure. Two main phenomena are known in surface crystallography: relaxation and reconstruction. In addition, particular ordered or disordered states are likely to occur in surface layers. Their origins can be diverse: they are, for example, linked to the presence of structural defects (steps, gaps...), to segregation in the case of alloys, or to the adsorption of foreign atoms (surfactants...).

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