MG ON PD(111) - THE FORMATION OF LOCAL ORDER OBSERVED BY PHOTOELECTRON DIFFRACTION

We have studied the growth of Mg overlayers on Pd(111), a system with 16.6% misfit, by means of x-ray photoelectron diffraction. No long-range order is observed by low-energy electron diffraction. Pronounced forward-focusing maxima in Mg 1s emission indicate considerable short-range order. At coverages below 1 monolayer Mg is found to occupy fcc sites distributed over two layers. At higher coverages oriented clusters are formed, accommodating the misfit by alternatively occupying fcc and hcp sites. Comparison to single-scattering calculations suggests an average cluster size of less than 15 angstrom.