Stratification of the Fe/Si(001)2$\times$1 interface by heat treatment of the wetting layer

The study was carried out by LEED, AES, EELS and AFM methods. Films of Fe/Si(001)2$\times$1 were obtained at substrate temperatures of 30$^\circ$C and source temperatures of 1250$^\circ$C. Wetting layer (WL) Fe on Si(001)2$\times$1 was formed by two-stage annealing at temperatures and thicknesses of 500$^\circ$C and 250$^\circ$C and 1 monolayer (ML) and 3 ML, respectively. Analysis and interpretation of the data obtained, taking into account possible reaction patterns, showed that after annealing at 1 ML thickness, the Fe composition corresponded to 2 ML Si/Fe. Further, at 2 ML, it changed to Fe/Si/Fe, at 3 ML, it changed to Fe–FeSi, and after annealing, to FeSi. At 4 ML, there was formation of FeSi/FeSi$_2$ film. And, further, at 7 ML and 10 ML, the composition of the films became Fe$_3$Si/FeSi$_2$ and, respectively, Fe/Fe$_3$Si/FeSi$_2$. At the same time, the upper Fe$_3$Si layers were coated with 0.6 ML and the Fe layers with 0.3 ML of segregated Si atoms, which number increased, after annealing at 250$^\circ$C, to 0.6 ML in the latter case. In the obtained Fe film, the size and average grain height were 10–20 nm and, respectively, $\sim$0.4 nm.