Abstract
In relation to investigations of the surface composition of ordered alloys in the region of their critical temperature, the elemental concentrations of the top two atomic layers of a Au 3 Cu (001) alloy surface were determined with low energy ion scattering in the temperature range of 300–925 K. Up to 550 K the first layer consists only of Au atoms and the second layer of Cu atoms. Above this temperature desegregration occurs; from the temperature dependence a segregation enthalpy of 47 kJ/mole could be deduced. The segregation results in a contraction of the top layer distances compared to the bulk values. The segregation kinetics can be described as an exchange process between the top atomic layers with an activation energy of 0.2–0.3 eV. The temperature dependence of the surface concentration of this alloy is determined by the segregation process rather than by the bulk ordering phase transition.
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