Complex surface structures studied by low-energy electron diffraction

Structural results of complex surface structures determined by employing the method of low-energy electron on diffraction (LEED) are reviewed, LEED is the prime crystallographic technique in surface science, and its ranking among the surface crystallographic methods is comparable to x-ray diffraction for determining the structure of bulk materials. Various kinds of complexity are considered, starting with the atomic geometries of semiconductor surfaces which are heavily reconstructed exhibiting far-reaching relaxations down to deeper layers. A next class of systems are coadsorbate phases on metal surfaces whose complexity comes from the presence of various species. In this section also the structure of larger molecules on metal surfaces is discussed. In the last two chapters we concentrate on surfaces violating the two-dimensional translational symmetry. The simplest systems are incommensurate overlayers on metal surfaces. Each layer possesses translational symmetry, but the compound system breaks it. In a next step we also disregard the translational symmetry of each layer and focus on the structure of quasicrystal surfaces.