Spot-profile Analysis

Whereas the spot positions carry information about the size of the surface unit cell, the shapes and widths of the spots, i.e. the spot profiles, are influenced by the long range arrangement and order of the unit cells at the surface. If vertical displacements (steps, facets) of the surface unit cells are involved, the spot profiles change as a function of electron energy. If all surface unit cells are in the same plane (within the transfer width of the LEED optics), the spot profile is constant with energy. 

Point defects, static disorder, and thermally induced displacements lead to an increase of the background intensity between the spots. Depending on the correlation between the scatters, the background is either homogeneous (no correlation) or 

Structured (correlation). If the coherently ordered surface areas (islands, domains) are smaller than the transfer width of the LEED system and at the same vertical height, the width of these areas. Aw, is directly related to the width of the LEED spots in fe-space, Afen  

This relationship is true for each direction parallel to the surface independently. It is particularly useful for determining the size of adsorbate islands which lead to extra superstructure spots. A good introduction (in German) to spot profile analysis is given by Henzler and Gopel [2.249]. 

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In the technique of spot-profile analysis LEED (SPA-LEED) [29, 30] intensity variations across LEED diffraction spots are measured. The technique provides information on both periodic and non-periodic arrangements of superstructure domains, terraces or facets, and strained regions. The interpretation of spot profiles is simplified due to the validity of the kinematic approximation, which is not the case for LEED I-V analysis. Deviations from simple structures resulting from defects produce characteristic modifications of the spot profile, so that a quantitative evaluation is possible. SPA-LEED has proven itself to be useful in the study of dynamic phenomena on surfaces such as phase transitions. Several examples of this capability are discussed in section 3 for Pb on Cu. 

SPA-LEED Spot profile analysis - low energy electron difiraction... 

SCH Scheithauer, U., Meyer, G., Henzler, M. A new LEED instrument for quantitative spot profile analysis Surf. Sci. 178 (1986) 441. 

SPALEED Spot-profile analysis low energy electron diffraction... 

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