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Cu3Au crystal is a model for the study of the order–disorder transition in binary metallic alloys. The ordered distribution of Au and Cu atoms in the bulk of this crystal is maintained up to Tc = 663 K where the order–disorder first order transition takes place. A number of methods was so far applied to theoretical and experimental determination of the dependence of long range order (LRO) parameter for the surface layer on the crystal temperature. It was found that, for the surface atomic layer, the order–disorder transition starts at T smaller than Tc and that it is the second-order transition. However, considerable disagreements can be found in quantitative results presented in particular papers.
Our goal is to apply the Directional Elastic Peak Electron Spectroscopy (DEPES) [1] in investigation of order–disorder transition in the surface atomic layers. As a first step, we have calculated the heights of particular DEPES maxima in the Single Scattering Cluster (SSC) approximation [2] for particular values of LRO parameter, for Cu3Au(001) clusters characterized by different inelastic mean free paths of electrons, effective Debye temperatures, and surface layer atomic structures (including composition, relaxation, and rippling). The most promising result seems to be the large sensitivity of calculated heights to changes of the rippling of Au atoms in the first atomic layer. We expect that fitting of our calculated heights to the measured ones will permit to determine the dependence of the surface layer LRO parameter on sample temperature and will give, for he first time, information about changes of the rippling mentioned above during the order–disorder transition.
References:
[1] S. Mróz, M. Nowicki, Surf. Sci. 297 (1993) 66.
[2] A. Stuck, M. Nowicki, S. Mróz, D. Naumowic, J. Osterwalder, Surf. Sci. 306 (1994) 21.
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