KINETICS OF SURFACE ALLOY FORMATION - CU(100)-C(2X2)PD

The kinetics of formation of the Cu(100)-c(2×2)Pd surface alloy is studied by adsorption of 1/2 ML of Pd on Cu(100) at 100 K followed by rapid heating up to selected anneal temperatures between 248 and 276 K. The domain-growth process is monitored via low-energy electron diffraction (LEED), Auger-electron spectroscopy, work-function measurements, and hydrogen thermal desorption. The initial stage of alloy formation, during which a considerable fraction of adsorbed Pd atoms replaces Cu atoms located in the first substrate layer, is found to be rapid and short. The subsequent late stages are slow. In the latter case, beam-profile measurements are consistent with self-similar domain growth. The corresponding analysis of the LEED peak intensity indicates that the growth law for the average domain radius has a power-law form with an exponent of 1/8. The scaling arguments presented show that such a low value of the growth exponent can really occur if the Pd-Cu ordering of the Allen-Cahn type is limited by dissolution of Pd islands occurring via the Lifshits-Slyozov scenario. The activation energy for diffusion in the domain-growth regime is estimated to be 0.4 eV. © 1994 The American Physical Society.