THE ACCURACY OF QUANTITATIVE LEED IN DETERMINING CHEMICAL-COMPOSITIONPROFILES OF SUBSTITUTIONALLY DISORDERED ALLOYS - A CASE-STUDY

We explore the accuracy of chemical composition profiles of substituti onally disordered alloys determined experimentally by LEED (low-energy electron diffraction) I(E) analysis. We analyst experimental I(E) spe ctra of pure Rh(111) for its known chemical composition by comparing t hem to calculations assuming a substitutionally disordered PtxRh1-x al loy surface. The layer concentrations known to be 100% Rh are reproduc ed with a maximum error of 8% when the Pendry R-factor (R-p) is employ ed. This error is considerably smaller than estimated by error bars de rived from the variance of R-p. We argue that the same accuracy can be expected for compositional depth profiles to be determined for alloys exhibiting weak chemical order and negligible lattice distortions suc h as PtxRh1-x. (C) 1998 Elsevier Science B.V. All rights reserved.