STRUCTURES OF ULTRA-THIN FE OVERLAYERS ON A RH(001) SURFACE

The structures of ultra-thin Fe overlayers grown on a Rh(001) surface have been investigated by low energy electron diffraction (LEED) and angle-resolved Auger electron spectroscopy (ARAES) for film coverages of 0-20 ML and in a wide temperature range of 100-1300 K. Deposition at 350 K formed a pseudomorphic (1 x 1) fcc (001) structure of Fe for film thicknesses of 1-5 ML. New subspots due to a (2 square-root 2 x square-root 2)R45-degrees superstructure appeared at 6 ML and became streaky at 8 ML. The main spots then splitted into four in the respective [110] direction corresponding to four faceted planes above 10 ML. The facet structure was observed in a wide coverage range of 10-20 ML. It is confirmed by ARAES that Fe films have an fcc structure over the whole coverage range. The deviation from the pseudomorphic structure above 6 ML is interpreted to be caused by the lattice mismatch (5.7%) between Fe and Rh in the fcc structure. Annealing of these Fe films up to 1300 K caused sequential LEED patterns of (1 x 1) with a high background (1-5 ML) or streaky along the [100] direction (6-8 ML), c(2 x 2) and finally the (1 x 1) structure. From the change in Auger intensities the c(2 x 2) structure observed above 1100 K corresponding to a surface Fe coverage of 0.5 remained after the desorption of Fe overlayers.