The initial stages of the formation of iron silicides in the Fe/Si(111)7 × 7 system in the course of solid-phase epitaxy are investigated using high-resolution photoelectron spectroscopy (∼100 meV) with synchrotron radiation. The spectra of the Si 2p core and valence-band electrons obtained after deposition of iron coverages of up to 28 monolayers on the surface of the sample and subsequent isochronous annealings at 650°C are measured and analyzed. It is shown that the first to form under Fe deposition is an ultrathin film of the metastable silicide FeSi with a CsCl-type structure, on which a layer of the Fe-Si solid solution with segregated silicon grows. At coverages in excess of 10 monolayers, an iron film grows on the surface of the sample. Annealing of a silicon crystal coated with a Fe layer leads to the sequential formation of two stable silicide phases, namely, the ɛ-FeSi and β-FeSi2 phases, in the near-surface region of the sample. It is found that the process of solid-phase synthesis of the ɛ-FeSi phase passes through the stage of transformation of the iron film into the Fe-Si solid solution.

High-resolution photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in Fe 3p core-level photoemission has been used to study both the initial stages of Fe/Si(111)7×7 and Fe/Si(100)2×1 interface formation and their ferromagnetic ordering. The correlation between the phase composition, electronic structure, and magnetic behavior of the interfaces has been established. It is shown that in-plane ferromagnetic ordering of the interfaces has a threshold nature and arises after the deposition of ∼7 Å Fe in both systems. However, the remanent magnetization of Fe/Si(111) is greater than that of Fe/Si(100) due to the difference in the chemistry of the phases being formed. In the former case, it was found that at room temperature an ultrathin metastable FeSi film with the CsCl structure grows at the first stage of Fe deposition on Si. At higher Fe coverages, a Si solid solution in iron, and later an Fe film, is found to develop on FeSi. The magnetic properties of the solid solution and the Fe film of ∼15 Å thick are quite similar. At the Fe/Si(100) interface, we observe the formation of iron-rich Fe3Si, in which the average magnetic moment of Fe atoms is markedly lower than that of the Fe film. Solid-phase reactions, starting at ∼100 °C in both systems, lead to a gradual conversion of ferromagnetic phases to the nonmagnetic ε-FeSi phase, which transforms to β-FeSi2 at temperatures above 600 °C.

The effect of magnetic linear dichroism in photoemission of Fe 3p electrons was used to investigate the magnetic properties of the Si(100)2 × 1 surface on which iron films up to 10 monolayers thick were deposited at room temperature under ultrahigh vacuum. The experiments were performed with linearly polarized light (at a photon energy of 135 eV) incident at an angle of 30° to the surface. The photoelectron spectra were measured in a narrow solid angle oriented along the normal to the sample surface for two opposite magnetization directions which were parallel to the surface plane and perpendicular to the polarization vector of the light wave. An analysis of the data obtained showed that the effect has a threshold character and appears after deposition of eight Fe monolayers, when the ferromagnetic silicide Fe3Si is formed on the surface.

The interplay between the phase composition, electronic structure, and magnetic properties of the Fe/Si(100)2×1 interface has been studied at the initial stages of its formation (at Fe doses up to 8 Å). The experiments were carried out in ultra high vacuum by using high-resolution photoelectron spectroscopy with synchrotron radiation. The interface magnetic properties were examined in terms of magnetic linear dichroism in angle-resolved Fe 3p core-level photoemission. It was found that at room temperature a disordered Fe–Si solid solution is formed at the first stage of Fe deposition (≤3.4 Å). In the coverage range of 3.4–4.3 Å the solid solution transforms into Fe3Si. However, the in-plane ferromagnetic ordering of the silicide occurs only at 6.8 Å Fe that demonstrates the thickness dependence of the magnetic properties of Fe3Si. The subsequent sample annealing to 150°C transforms Fe3Si to ε-FeSi, leading to the disappearance of ferromagnetic behavior.

The initial stages of iron silicide growth on the Si(100)2×1 surface during solid-phase synthesis were investigated by photoelectron spectroscopy using synchrotron radiation. The experiments were made on iron films of 1–50 monolayer (ML) thickness in the temperature range from room temperature to 750°С. Our results support the existence of three stages in the Fe deposition on Si(100) at room temperature, which include formation of the Fe–Si solid solution, Fe3Si silicide and an iron film. The critical Fe dose necessary for the solid solution to be transformed to the silicide is found to be 5ML. The solid-phase reaction was found to depend on the deposited metal dose. At 5ML, the reaction begins at 60°С, and the solid-phase synthesis leads to the formation of only metastable silicides (FeSi with the CsCl-type structure, γ-FeSi2 and α-FeSi2). A specific feature of this process is Si segregation on the silicide films. At a thickness of 15ML and more, we observed only stable phases, namely, Fe3Si, ε-FeSi and β-FeSi2.

The early stages of iron silicide formation in the Fe/SiO x /Si(100) ternary system during solid-phase epitaxy are studied by high-resolution (∼100 meV) photoelectron spectroscopy using synchrotron radiation. The spectra of core and valence electrons taken after a number of isochronous heat treatments of the samples at 750°C are analyzed. It is found that the solid-phase reaction between Fe and Si atoms proceeds in the vicinity of the SiO x /Si interface, which metal atoms reach when deposited on the sample surface at room temperature. Iron silicide starts forming at 60°C. Solid-phase synthesis is shown to proceed in two stages: the formation of the metastable FeSi interfacial phase with a CsCl-like structure and the formation of the stable β-FeSi2 phase. During annealing, structural modification of the silicon oxide occurs, which shows up in the growth of the Si+4 peaks and attenuation of the Si+2 peaks.

The interaction of cobalt atoms with an oxidized Si(100)2×1 surface was studied by photoelectron spectroscopy with synchrotron radiation at room and elevated temperatures. The SiOx layer grown in situ on the crystal surface was ∼0.3nm thick, and the amount of deposited cobalt was varied within eight atomic layers. It was found that Co atoms could penetrate under the SiOx layer even at room temperature in the initial growth. As the Co amount increased, a ternary Co–O–Si phase was formed at the interface, followed by a Co–Si solid solution. Silicide synthesis associated with the decomposition of these phases started under the SiOx layer at ∼250°C, producing cobalt disilicide with a stable CaF2-type of structure.

The solid-phase synthesis of iron silicides on the Si(100)2 × 1 surface with a 5-ML-thick iron film deposited at room temperature was studied by high-resolution photoelectron spectroscopy with the use of synchrotron radiation. Computer simulation of the measured Si 2 p spectra revealed the formation of silicides in this system already under annealing at a temperature of 60°C. The process of formation consists in successive syntheses of three iron silicide phases, more specifically, monosilicide ε-FeSi, metastable disilicide γ-FeSi 2 , and disilicide β-FeSi 2 . The temperature ranges of existence of these phases were determined. Silicon was found to segregate on the γ-FeSi 2 surface.

The room-temperature interaction of iron atoms with the oxidized Si(100)2×1 surface at a coverage from a submonolayer to four monolayers is studied by core-level photoelectron spectroscopy using synchrotron radiation. Computer simulation of the Si 2 p core electron spectra demonstrates that iron atoms penetrate beneath the silicon oxide even at room temperature. This process causes the initial silicon phases at the SiO x /Si interface to disappear; gives rise to a complex ternary phase involving Fe, O, and Si atoms; and favors the formation of a Fe-Si solid solution at the interface.

Interaction of iron atoms with the Si(100)-2 × 1 surface at room temperature is studied by core-level photoelectron spectroscopy using synchrotron radiation for Fe coverages ranging from a fraction of a monolayer to six monolayers. It is shown that the Fe/Si(100)-2 × 1 interface is chemically active: the Fe-Si solid solution forms early in deposition of iron on silicon. When the Fe coverage reaches four to five monolayers, the state of the system is changed and Fe3Si silicide arises.

The initial stages of oxidation of a Si(100)2 × 1 surface and the interaction of cobalt atoms with it were studied by core-level photoelectron spectroscopy. The study was carried out with cobalt coverages of up to 8 ML. Computer modeling of the spectra of photoexcited electrons revealed Co atom penetration under the silicon oxide layer, an effect observed even at room temperature. This process was shown to give rise to the disappearance of silicon interface phases at the oxide-layer-silicon boundary and to the formation of a more complex phase involving atoms of Co, O, and Si. After completion of the process, a Co-Si solid solution forms at the interface.