Initial stages of growth of Fe on Cu3Au(001) at low temperature: Formationof two-layer-thick islands

A He diffraction study on the initial stages of growth of Fe on Cu3Au(001) at 140 K is presented. The measurements provide evidence of a nonconvention al growth mode. Indeed, the analysis of rocking curves, carried out through two independent methods, gives clear evidence of the formation of small is lands that present a singular height h = 3.18 +/- 0.05 Angstrom, typical of a bilayer structure. As growth proceeds the mean distance between bilayer islands remains essentially constant (similar to 25 Angstrom) until coalesc ence. At coalescence of the first bilayer, growth evolves through nucleatio n of the third layer. Experimental data rule out interface disruption at de position. A possible connection of the bilayer growth with recent studies o n the influence of electron confinement on the growth morphology is propose d. Thermal treatments significantly affect the morphology of bilayer island s. In particular, annealing at room temperature induces an aggregation of i slands. After annealing at 400 K a striking reassembling of the islands, wh ich become three layers thick, is observed.