Influence of the thermal power of a Fe atomic flux on the formation of Cu/Fe nanofilms on a Si(001) substrate

The growth of a Fe sublayer 1.5–14.0 monolayers (MLs) thick and a Cu film (about 5 MLs) on this sublayer is studied at a reduced temperature (1240$^\circ$C) and an elevated temperature (1400$^\circ$C) of a Fe source and at a reduced temperature (900$^\circ$C) of a Cu source. The films are examined by Auger electron spectroscopy, low-energy electron diffraction, and atomic force microscopy. As metal sources, thin Fe and Cu strips on a Ta foil are used. It is shown that a nonequilibrium 2D phase forms in the Fe-on-Si(001) film up to a thickness of 4–5 MLs. This phase appears as closely packed atomically smooth nanoislands. When the thickness of the film exceeds 4–5 MLs, the nonequilibrium Fe phase changes to the bulk (3D) phase of Fe and its silicide Fe$_x$ Si. At Fe source temperatures of 1240 and 1400$^\circ$C, the nonequilibrium phase consists of Fe with Si segregated on the Fe surface, and a Fe–Si mixture. Copper on the nonequilibrium Fe and Fe–Si phases grows, respectively, as a smooth layer Cu with Si segregated on the top and in the form of Cu–Fe and Cu–Si mixtures. Cu islands growing on the bulk Fe and Fe$_x$ Si phases have smaller and larger sizes, respectively.