Crystallography by LEED: IV. Application of the iso-intensity map method to the Ni(100)-(11, 11)-S system

In the present study, we illustrate in the case of the $\text{Ni(001) and Ni(001)-(1}\text{1}\text{, 11)-S}$surfaces, the application of a procedure of surface analysis by LEED using iso-intensity maps for the specular beam together with a very fast LEED program based on the RFS method. This procedure has several advantages: first, iso-intensity maps prevent one from leaving out important experimental information. Second, the fast LEED program allows one to study a large number of beams previously selected from the maps for their particular interest, thus avoiding finding a wrong result, as could hapen if one looks only at a few beams. It comes out from this study that the adsorption distance $\text{d = 1.3}\text{A}\text{?}$ of the sulfur atoms is confirmed with the help of a cluster type superposition potential for the sulfur layer. The agreement between experiment and theory is generally excellent, except for a very strong experimental peak which is not well reproduced by calculation, whatever the changes in the physical or structural parameters. This has not been reported previously and is similar to what has been found by the same authors for the aluminium (001) surface.