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Examination of complex surface structures

Lateral complexity is often a consequence of adsorbate induced reconstruction. Application of the tensor low energy electron diffraction (LEED) methodology has had a striking impact on surface reconstruction. The added precision and particularly the reliability with which adsorbate structures can be determined has greatly enhanced understanding of these systems. It is now clear that nearly every adsorbate system is accompanied by some sort of reconstruction of the substrate. This is particularly true of hydrogen.

Diffuse LEED (DLEED) experiments have proved a fruitful technique. Not only have they become part of the conventional analysis of surface structure, but they have stimulated the idea of electron holography at surfaces.

The problem of thermal vibrations at surfaces has proved a knotty one, but some progress has been made. Here the introduction of the concept of linear LEED will prove crucial. The assumption that diffraction from thermal vibrations of independent atoms adds linearly has been tested. This will greatly simplify the analysis of thermal data which is likely to prove complex: initial investigations of alkali adsorbates showed that simple models of thermal vibration in the adsorbate layer did not suffice to bring the data into the excellent agreement with experiment that is expected for clean surfaces with high Debye temperatures. Part of the blame lies in nonthermal effects such as distortion of the potential by dipole moment formation, but another source of problems which is being investigated is more complex structure to the thermal vibrations.

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