Unlike relaxation, the phenomenon of reconstruction involves a change in the periodicity of the surface structure - the diagram below shows a surface, viewed from the side, which corresponds to an unreconstructed termination of the bulk structure. it is frequently observed on fcc(110) surfaces), but is much more prevalent on semiconductor surfaces. It occurs with many of the less stable metal surfaces (e.g. The reconstruction of surfaces is a much more readily observable effect, involving larger (yet still atomic scale) displacements of the surface atoms.
The magnitude of the contraction in the first layer spacing is generally small ( < 10 % )- compensating adjustments to other layer spacings may extend several layers into the solid. (Whether this is a reasonable model for bonding in a metal is open to question !) On the other hand, an atom at the unrelaxed surface suffers from an imbalance of forces and the surface layer of atoms may therefore be pulled in towards the second layer. If we use a localized model for the bonding in the solid then it is clear that an atom in the bulk is acted upon by a balanced, symmetrical set of forces. We can consider what might be the driving force for this process at the atomic level. The right picture shows the relaxed surface: the first layer of atoms is typically drawn in slightly towards the second layer (i.e. It involves adjustments in the layer spacings perpendicular to the surface, there is no change either in the periodicity parallel to the surface or to the symmetry of the surface.įigure (left) Unrelaxed Surface and (right) Relaxed Surface with \(d_\). Relaxation is a small and subtle rearrangement of the surface layers which may nevertheless be significant energetically, and seems to be commonplace for metal surfaces.
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