Initial stages of growth of Fe on Cu3Au(001) at low temperature:: Formation of 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 nonconventional growth mode. Indeed, the analysis of rocking curves, carried out through two independent methods, gives clear evidence of the formation of small islands 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 coalescence. At coalescence of the first bilayer, growth evolves through nucleation of the third layer. Experimental data rule out interface disruption at deposition. A possible connection of the bilayer growth with recent studies on the influence of electron confinement on the growth morphology is proposed. Thermal treatments significantly affect the morphology of bilayer islands. In particular, annealing at room temperature induces an aggregation of islands. After annealing at 400 K a striking reassembling of the islands, which become three layers thick, is observed.