EPITAXIAL-GROWTH OF MAGNESIUM ON RU(0001)

The type of growth and the local geometry of magnesium adsorbed on Ru(0001) were investigated by low-energy electron diffraction (LEED), work-function measurements, and thermal-desorption spectroscopy. Despite the large initial dipole moment of 4.5 D the LEED pattern revealed a hexagonal superstructure even at low global Mg coverage (theta(Mg)) greater-than-or-equal-to 0.05) with local coverage theta(Mg)=0.65 indicating island growth. In contrast to most alkali-metal/metal systems, where liquidlike adlayers are formed for coverages lower than 0.25, the repulsive dipole-dipole interaction is overcompensated by the overlap of wave functions due to the existence of two valence electrons. During completion of the first monolayer (theta(Mg)=0.75) the hexagonal superstructure is slightly compressed along the high-symmetry directions of the Ru substrate. This compression is completed when the Mg-Mg distance reaches the corresponding bulk value. Further deposition of Mg leads to a multilayer growth (most likely layer by layer). For such an epitaxially grown, 9-ML thick Mg film on Ru(0001), a LEED structural analysis was performed which revealed Mg bulklike values for the interlayer spacings.