The atomic-scale structure of a surface is fundamental to understanding its various properties, be they electronic, magnetic, optical, chemical, or tribological. This chapter surveys the current state of knowledge of surface structure, and includes a discussion of the main methods employed to determine surface structure.

The temperature dependence of the first three interlayer distances of the Ag(111) surface was studied by low-energy electron diffraction (LEED) over the temperature range 128K to 723 K. The first three interlayer spacings and the effective Debye temperatures were extracted from the LEED analysis. At the lowest temperature, the first two interlayer spacings are slightly (0.5 %) contracted. All three interlayer spacings increase with temperature, finally reaching expansions relative to the bulk of about 0.8% at the highest temperature studied. The effective surface Debye temperature is lowest for the outermost layer, increasing toward the bulk value for successive layers.

Diffraction methods have provided the large majority of solved atomic-scale structures for both the bulk materials and their surfaces, mainly in the crystalline state. Crystallography by diffraction tends to filter out defects and focus on the periodic part of a structure. By adding contributions from very many unit cells, diffraction gives results that are, in effect, averaged over space and time. This is excellent for investigating stable states of solid matter as they occur in well-crystallized samples; some forms of disorder can also be analyzed reasonably well.