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The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive intercalation of iron and silicon atoms into the graphene. Experiments are carried out in situ in ultrahigh vacuum. The elemental composition and chemical state of the surface of prepared samples and their atomic structure are determined by low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy using synchrotron radiation. The thickness of deposited iron and silicon layers varies in the range of 0.1–2 nm, and the sample annealing temperature is varied from room temperature to 600°C. We show that intercalation of silicon into the graphene/Fe/SiC system leads to the formation of a layer of Fe–Si solid solution coated with the surface silicide Fe3Si. The films are effectively protected by graphene from exposure to ambient environment, which opens possibilities for their practical application.

The process of formation of cobalt silicides near the graphene-silicon carbide interface by intercalation of single-layer graphene grown on the 4H- and 6H-SiC(0001) polytypes with cobalt and silicon is studied. The experiments were carried out in situ in ultrahigh vacuum. The analysis of the samples is performed by high-energy-resolution photoelectron spectroscopy using synchrotron radiation, low-energy electron diffraction, and also Raman spectroscopy, atomic-force and kelvin-probe microscopies. The thicknesses of the deposited cobalt and silicon layers is varied to 2 nm, and the sample temperature, from room temperature to 1000°C. Co and Si atoms deposited on heated samples is found to penetrate under graphene and are localized between the buffer layer and the substrate, which leads to a transformation of the buffer layer into additional graphene layer. It is shown that the result of intercalation of the system with cobalt and silicon is the formation under two-layer graphene of a Co–Si solid solution and silicide CoSi coated by the surface Co3Si phase. It is shown that the thickness and the composition of the formed silicide films can be changed by varying the amount of the intercalated material and the order of their depositions.

In this paper, we studied cobalt intercalation of single-layer graphene grown on the 4H-SiC(0001) polytype. The experiments were carried out in situ under ultrahigh vacuum conditions by high energy resolution photoelectron spectroscopy using synchrotron radiation and low energy electron diffraction. The nominal thicknesses of the deposited cobalt layers varied in the range of 0.2–5 nm, while the sample temperature was varied from room temperature to 800°C. Unlike Fe films, the annealing of Co films deposited on graphene at room temperature is shown to not intercalate graphene by cobalt. The formation of the graphene–cobalt–SiC intercalation system was detected upon deposition of Co atoms on samples heated to temperatures of above ~400°C. Cobalt films with a thickness up to 2 nm under graphene are formed using this method, and they are shown to be magnetized along the surface at thicknesses of greater than 1.3 nm. Graphene intercalation by cobalt was found to be accompanied by the chemical interaction of Co atoms with silicon carbide leading to the synthesis of cobalt silicides. At temperatures of above 500°C, the growth of cobalt films under graphene is limited by the diffusion of Co atoms into the bulk of silicon carbide.

The ab initio calculations of the magnetic anisotropy of thin (to six monolayers) nickel films and iron films with unusual fcc structures formed upon intercalation of graphene with Fe atoms are presented. The data have been obtained for both the pure-surface films and the films coated with graphene. The density functional theory and the pseudopotential method are used to calculate the magnetic moments of atoms of all the layers and to determine the total energies of the structures with different orientations of magnetic moments of iron and nickel atoms with respect to the film surface. A strong influence of graphene on the magnetic properties contacting iron films is demonstrated.

Intercalation of the graphene-cobalt system with silicon was investigated experimentally. The ab initio calculation of the electronic structure of a low-dimensional graphene-silicon-cobalt system was carried out using the density functional theory. The most advantageous positions of intercalated Si atoms are determined. It is shown that the introduction of silicon under graphene leads to a sharp decrease in the interaction of carbon atoms with the substrate.

In the present study the evolution of the electronic structure of the graphene/Fe/Ni(111) interface with increasing number of intercalated iron atoms is investigated. The Eσ(k) dependences and full and partial densities of states are calculated within density functional theory. It is shown that an increase in the number of iron layers does not affect the electronic structure, but greatly affects the magnetic properties of the interface.

The intercalation of iron under a graphene monolayer grown on 4H-SiC(0001) is studied. The experiments have been carried out in situ under conditions of ultrahigh vacuum by low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and near carbon K-edge X-ray absorption spectroscopy. The deposited iron film thicknesses have been varied within 0.1–2 nm and the sample temperatures from room temperature to 700°C. It is shown that the intercalation process begins at temperatures higher than ~350°C. In this case, it is found that intercalated iron atoms are localized not only between graphene and a buffer layer coating SiC, but also under the buffer layer itself. The optimal conditions of the intercalation are realized in the range 400–500°C, because, at higher temperatures, the system becomes unstable due to the chemical interaction of the intercalated iron with silicon carbide. The inertness of the intercalated films to action of oxygen is demonstrated.

Ab initio calculations of the electron spectrum of the graphene–cobalt–nickel system were performed in the slope of the spin density functional theory (SDFT). Dispersion curves Eσn(k) are presented; they were used to determine partial and total densities of valence electron states, and also magnetic moments of all atoms in the supercell. Energy position of the “Dirac cone” defined by pz states in graphene is shown to depend only slightly on the number of Co layers intercalated into the gap between the cobalt and graphene layers.

The intercalation of cobalt under a graphene monolayer grown on a Ni(111) single crystal film is studied. The experiments are conducted in ultrahigh vacuum. Samples are characterized in situ by low energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and magnetic linear dichroism in photoemission of Co 3p electrons. New data are obtained on the evolution of the atomic and electronic structure and magnetic properties of the system with increasing thickness of the intercalated cobalt layer in the range up to 2 nm. It is shown that a pseudomorphic epitaxial film of Co(111) having magnetization perpendicular to the surface is formed under the grapheme layer during intercalation in an anomalously wide range of thicknesses.

The ab initio calculations of the electronic structure of low-dimensional graphene–iron–nickel and graphene–silicon–iron systems were carried out using the density functional theory. For the graphene–Fe–Ni(111) system, band structures for different spin projections and total densities of valence electrons are determined. The energy position of the Dirac cone caused by the p z states of graphene depends weakly on the number of iron layers intercalated into the interlayer gap between nickel and graphene. For the graphene–Si–Fe(111) system, the most advantageous positions of silicon atoms on iron are determined. The intercalation of silicon under graphene leads to a sharp decrease in the interaction of carbon atoms with the substrate and largely restores the electronic properties of free graphene.

A new method for synthesis of graphene-protected iron silicides has been tested, which consists in formation of graphene on Ni(111) followed by two-step intercalation of the system with Fe and Si. Characterization of the samples was performed in situ by low-energy electron diffraction, angular-resolved photoelectron spectroscopy, core-level photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in photoemission of Fe 3p electrons. It is shown, that at 400 °C the intercalation of graphene/Ni(111) with iron occurs in a range up to 14 ML. The graphene layer strongly interacts with the topmost Fe atoms and stabilizes the fcc structure of the film. The in-plane ferromagnetic ordering of the film has a threshold nature and arises after the intercalation of 5 ML Fe due to the thickness-driven spin reorientation transition. Subsequent intercalation of graphene/Fe/Ni(111) with Si leads to the formation of the inhomogeneous system consisted of intercalated and nonintercalated areas. The intercalated islands coalesce at 2 ML Si when a Fe-Si solid solution covered with the Fe3Si surface silicide is formed. The Fe3Si silicide is ferromagnetic and has an ordered (√3 × √3)R30° structure. The graphene layer is weakly electronically coupled to the silicide phase keeping its remarkable properties ready for use.

The silicon intercalation under single-layer graphene formed on the surface of an epitaxial Co(0001) film was investigated. The experiments were performed under conditions of ultra-high vacuum. The thickness of silicon films was varied within the range of up to 1 nm, and the temperature of their annealing was 500°C. The characterization of the samples was carried out in situ by the methods of low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and magnetic linear dichroism in photoemission of Co 3p electrons. New data were obtained on the evolution of the atomic and electronic structure, as well as on the magnetic properties of the system with an increase in the amount of intercalated silicon. It was shown that the intercalation under a graphene layer is accompanied by the synthesis of surface silicide Co2Si and a solid solution of silicon in cobalt.

Intercalation of graphene formed on silicon carbide surface with iron, cobalt and silicon has been used to form the graphene/silicides/SiC interfaces. The experiments were carried out in situ in ultrahigh vacuum conditions. The elemental composition and chemical state of the sample surfaces, as well as their atomic structure, were controlled by high-energy-resolution photoelectron spectroscopy and low-energy electron diffraction. The nominal thicknesses of the deposited iron, cobalt and silicon layers varied in the range of 2-20 Å, and the temperature of the sample annealing was changed from room temperature to 600°C. It is shown, that the intercalation of graphene/Fe/SiC with Si leads to the formation of Fe-Si solid solution layer covered with surface silicide Fe3Si, while intercalation of graphene/Co/SiC with Si results in the formation of a Co-Si solid solution and CoSi silicide covered with Co3Si surface phase. The obtained silicide layers are reliably protected by graphene, making it compatible for nanoscale applications at ambient conditions.

Ultrathin (∼2 nm) films of Co 2 FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ . Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF 2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3 p and Co 3 p electrons. The study shows that the synthesis of the Co 2 FeSi ferromagnetic alloy occurs in the temperature range of 200–400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF 2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

The magnetic linear dichroism (MLD) effect in photoemission of Mn 3p electrons was used to study magnetic properties of Mn films (to 2.5 nm thick) grown on the Si(111)-(7 × 7) surface at room temperature and manganese silicide films grown by solid-phase epitaxy. The experiments were performed using linearly polarized light with a photon energy of 130 eV, incident at an angle of 30° to the sample surface. Photoelectron spectra were measured in a narrow solid angle focused along the normal to the surface for two opposite sample magnetization directions in the surface plane, perpendicular to the polarization vector of the light wave. It was shown that the MLD effect characteristic of films with high-temperature ferromagnetism appears after depositing ∼2 nm Mn. The formation of manganese silicides upon annealings of the sample with deposited 2.5 nm Mn results in the disappearance of the MLD effect.

The initial stages of the growth of manganese films on the Si(111)7 × 7 surface at room temperature and reactions of solid-phase synthesis of manganese silicides, which occur during annealing these films in the temperature range up to 600°C, have been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. It has been shown that the deposition of manganese on the silicon surface leads to the formation of interfacial manganese silicide and a film of the silicon solid solution in manganese. The growth of a metallic manganese film begins after the deposition of ∼6 A Mn. The segregation of silicon is observed in the coverage range of 17 A Mn. The annealing of the sample with a coverage of 25 A Mn in the temperature range of 200–400°C leads to the formation of a Mn-Si solid solution and manganese monosilicide. A further increase in the temperature to 600°C results in the transformation of MnSi into the semiconductor silicide MnSi1.7.

The processes that occur in ultrathin (up to 1 nm) Fe and Co layers during deposition onto the Si(100)2 × 1 surface in various sequences and during annealing of the formed structures to a temperature of 400°C are studied. The elemental and chemical compositions of the films are analyzed by in situ high-resolution X-ray photoelectron spectroscopy using synchrotron radiation, and their magnetic properties are determined using the magnetic linear dichroism effect in the angular distribution of Fe 3p and Co 3p electrons. It is shown that, when iron is first deposited, the formed structure consists of the layers of FeSi, Fe3Si, Co-Si solid solution, and metallic cobalt with segregated silicon. The structure formed in the alternative case consists of the layers of CoSi, Co-Si solid solution, Co, Fe-Si solid solution, and Fe partly covered by silicon. All layers (apart from FeSi, CoSi) form general magnetic systems characterized by ferromagnetic ordering. Annealing of the structures at temperatures above 130dgC (for the Co/Fe/Si system) and ∼200°C (for Fe/Co/Si) leads to the formation of nonmagnetic binary and ternary silicides (FexCo1 − xSi, FexCo2 − xSi).

The solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface coated at room temperature by a 2-nm-thick manganese film has been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. The dynamics of variation of the phase composition and electronic structure of the near-surface region with increasing sample annealing temperature to 600°C, has been revealed. It has been shown that, under these conditions, a solid solution of silicon in manganese, metallic manganese monosilicide MnSi, and semiconductor silicide MnSi1.7 are successively formed on the silicon surface. The films of both silicides are not continuous, with the fraction of the substrate surface occupied by them decreasing with increasing annealing temperature. The binding energies of the Si 2p and Mn 3p electrons in the compounds synthesized have been determined.

Initial growth stages of manganese films on the Si(100)2 × 1 surface at room temperature have been investigated using high-energy-resolution photoelectron spectroscopy, and the dynamics of the variation in their phase composition and electronic structure with the coverage growth has been revealed. It has been shown that the interfacial manganese silicide and the film of the solid solution of silicon in manganese are sequentially formed under these conditions on the silicon surface. The growth of the metal manganese film starts after the deposition of ∼0.9 nm Mn. Segregation of silicon on the film surface is observed in the range of coverages up to 1.6 nm Mn.

Subthreshold photoelectron emission was observed to emerge from palladium nanoclusters formed on pyrographite surface under irradiation by photons in the energy range 3.1–6.5 eV. The average size of the palladium nanoclusters on the pyrographite surface was 50–80 nm, and the average height, 2–4 nm. Besides conventional photoemission from states below the Fermi level, photoelectron emission was observed at the energies of photons irradiating the surface 0.9 eV below the work function of the Pd surface. It is assumed that this emission is stimulated by direct electron transitions from Pd states below the Fermi level to the unfilled electron surface states formed in the Coulomb potential of image forces (image states) and, subsequently, into vacuum. This phenomenon is assumed to originate from the contact spot field generated above the surface which is nonuniform in work function. This assumption is supported by the calculations presented in the paper.

The formation of the Co/Si(110)16 × 2 interface and its magnetic properties are studied by high-energy-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism in the photoemission of core electrons. It is shown that a cobalt coating less than 7 A thick deposited on the silicon surface at room temperature results in the formation of an ultrathin (1.7 A) interfacial cobalt silicide layer and a layer of silicon-cobalt solid solution. The ferromagnetic ordering of the interface is observed at an evaporation dose corresponding to 6–7 A in which case a cobalt metal film begins to grow on the solid solution layer. During 300°C-annealing of the sample covered by a nanometer-thick cobalt layer, the metal film gradually disappears and four silicide phases arise: metastable ferromagnetic silicide Co3Si and three stable nonmagnetic silicides (Co2Si, CoSi, and CoSi2).

The formation of a silicon-iron (Si/Fe) interface has been studied in situ by the method of high-resolution photoelectron spectroscopy using synchrotron radiation. The experiments were performed under ultrahigh vacuum conditions (at a residual pressure of 3 × 10−10 Torr) in a range of Si coating thicknesses within 0.04–0.45 nm. It is established that the process begins with the formation of a FeSi silicide and Fe-Si solid solution on the iron substrate surface. As the Si coating thickness increases, the solid solution converts into ferromagnetic (Fe3Si) and nonmagnetic (FeSi) silicides. It is shown that thermostimulated solid-state reactions leading to the transformation of FeSi and Fe3Si silicides into a semiconducting β-FeSi2 silicide start at a temperature close to 600°C.

Investigations of electrons excited into image states (IS) of Pd clusters and their interaction with adsorbed hydrogen using photoelectron (PE) spectroscopy with synchrotron radiation is presented. Pd clusters were deposited on pyrolytic graphite surfaces which were used as inert substrates. PE spectra measured for Pd clusters at low photon energies show additional peaks at energies of ~ 4.7 and 5.25 eV that corresponds to Pd image states at energies E IS − E vac ≈ − 0.75 ± 0.1 eV and E IS − E vac ≈ − 0.2 ± 0.1 eV. After hydrogen adsorption on graphite with Pd clusters the H-induced features: positive peaks at energy − 2 eV, − 3.5 eV, − 7 eV and a small negative peak at − 4.6 eV, were observed in the valence band spectra of Pd below E F . While the peaks at − 3.5 eV and − 2 eV are the result of the formation of H-induced states in the SBZ the − 7 eV peak is due to strong interaction of Pd clusters with hydrogen producing a H―Pd bonding adsorbate state. It is proposed that a charge transfer from IS2 to Pd-H bond dominates over the H − anion neutralization via transfer of excess charge from H − to IS1.

Formation of the Si/Co interface and its magnetic properties have been studied by high-resolution photoelectron spectroscopy with synchrotron radiation. The experiments have been performed in situ in superhigh vacuum (5 × 10−10 Torr) with coating thicknesses up to 2 nm. It has been found that, in the initial stage of silicon deposition on the surface of polycrystalline cobalt maintained at room temperature, ultrathin layers of the Co3Si, Co2Si, CoSi, and CoSi2 silicides are formed. The three last phases are nonmagnetic, and their formation gives rise to fast decay of magnetic linear dichroism in photoemission of Co 3p electrons. At deposition doses in excess of ∼0.4 nm Si, a film of amorphous silicon grows on the sample surface. It has been established that the Si/Co interphase boundary is stable at temperatures up to ∼250°C and that further heating of the sample brings about escape of amorphous silicon from the sample surface and initiates processes involving silicide formation.

We have studied the UV reduction process of thin graphene oxide films, deposited on silicon substrate from ethanol suspension. Chemical structure of obtained material was analyzed by XPS method. TEM images showed holes formation during reduction process, that are connected into network. Films with observed structure have great variety of possible future applications, such as gas-sensors and different organic/nonorganic nanocompisites.

The initial stages of Heusler alloy (Co2FeSi) thin film growth by reactive epitaxy on the Si(100)2 × 1 surface are studied, and formation conditions for this alloy are found. At a substrate temperature of lower than, or equal to, 180°C, an island film of ternary Co-Fe-Si film grows on the surface. The silicon content in this film is lower than in the compound to be synthesized. The film becomes continuous when its thickness exceeds 1.2 nm. It is shown that post-growth annealing at 240°C can raise the silicon content in the film and be conducive to obtaining Heusler alloy of a desired composition. In situ measurements of the films show that ferromagnetic ordering in them has a threshold and shows up at the coalescence growth stage of the Co-Fe-Si island alloy.

The phase composition, electronic structure, and magnetic properties of ultrathin cobalt films (no thicker than 20 A) applied on a Si(111)7 × 7 surface at room temperature are studied by high-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism. It is shown that, as the cobalt thickness increases, first interface cobalt silicide and then an island (discontinuous) film of silicon-in-cobalt solid solution form on the silicon surface. A metal cobalt film starts growing after the deposition of a ∼7-A-thick Co layer. It is found that the ferromagnetic ordering of the system, which is characterized by surface magnetization, sets in after the deposition of a ∼6-A-Co layer at the stage of Co-Si solid solution formation.

The phase composition, electronic structure, and magnetic properties of ultrathin layers of iron and iron silicides formed upon deposition of 1- to 25-A-thick Fe film on an atomically clean vicinal surface Si(100) at room temperature have been investigated using high-resolution photoelectron spectroscopy with synchrotron radiation and the magnetic linear dichroism in Fe 3p electron photoemission. It has been demonstrated that the phases involved (Fe-Si solid solution, the Fe3Si silicide, the iron film) are formed in the same order as in iron deposition on the Si(100) singular face; in this particular case, the segregation of silicon on the iron film is noticeably enhanced. It has been established that the ferromagnetic ordering of the films in the plane of the sample surface follows a threshold character and sets in after a 7-A-thick film has been deposited during the stage of growth of the Fe3Si silicide. A further deposition brings about an increase in the remanent magnetization of the film, which reaches saturation at coverages of about 20 — ricated exhibits magnetic anisotropy with the easy magnetization axis aligned with the substrate steps.

The initial stages of the growth of cobalt films on the Si(100)2 × 1 surface and the dynamics of variation in their phase composition, electronic structure, and magnetic properties with a coverage increasing in the range 1–20 A resolution photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in Co 3p electron photoemission. It has been shown that a film of metallic cobalt starts to grow at a coverage of ∼7 A. This process is preceded by the stages involving the formation of the interface cobalt silicide and the Co-Si solid solution. It has also been demonstrated that, at coverages below 15 A, the sample surface is coated by segregated silicon. The ferromagnetic ordering of the film in the surface plane has been found to follow a threshold character and set in at a coverage of ∼6 A. A further increase in the coverage in the range 8–16 A is accompanied by a slower increase in the remanence of the film.

The effect of cold rolling, polishing, and thermal annealing conditions on the atomic structure and surface geometry of platinum foils has been studied. The surface morphology has been analyzed using low-energy electron diffraction, atomic force microscopy, and scanning tunneling microscopy. The chemical composition of the surface has been evaluated by Auger electron spectroscopy. It has been demonstrated that a variation in the conditions used for the preparation of the samples makes it possible to produce surfaces with different degrees of perfection from atomically smooth to rippled, fractal, and diffraction-disordered surfaces.

The phase composition, electronic structure, and magnetic properties of nanostructures formed upon deposition of iron on the surface of the Si(556) vicinal face coated by a submonolayer silver film with a √3×√3-Ag structure have been studied using high-energy-resolution photoelectron spectroscopy and analysis of magnetic linear dichroism in photoemission of Fe 3p electrons. The effective thickness of the deposited iron layer is varied from 1 to 25 A. It has been shown that a 1- to 2-A Fe coverage leads to the formation of a metastable iron silicide thin layer with a CsCl-type structure on the surface of the sample. A further deposition of Fe (up to ≈7 A) brings about the formation of chains consisting of nonmagnetic islands of the Fe—Si solid solution on this layer, which are oriented along the steps of the substrate. A ferromagnetic alignment of the system along the surface of the sample appears only at coverages of approximately 10 A, when larger (≈100 nm) iron islands start to grow on the solid solution layer.

The solid-phase epitaxy of iron silicide on the Si(111) surface coated with a native oxide layer is studied by high-resolution photoelectron spectroscopy using synchrotron radiation and by atomic force microscopy. The iron deposition dose changes up to 1 nm, and the annealing temperature changes up to 500°C. At room temperature, the native oxide layer is shown to be impermeable to Fe atoms and an iron film grows on the sample surface. An increase in the annealing temperature to ∼100°C results in a change in the film morphology, increasing its heterogeneity. As the annealing temperature increases to ∼250°C, Fe and Si atoms diffuse through the oxide layer and undergo a solid-phase reaction. As a result, stable iron monosilicide ɛ-FeSi forms.

The interaction of cobalt atoms with a Si(111)7 × 7 surface subjected to in situ oxidation in an oxygen atmosphere at a pressure of 10−5 Pa, an exposure of 20 L, and a temperature of 500°C is studied by high-decomposition (100 meV) photoelectron spectroscopy using synchrotron radiation. This surface treatment is shown to form an oxide film, which has a complex composition, occupies about 80% of the substrate surface, and has a thickness of ∼6 A. At room temperature and a coverage of up to six monolayers, cobalt atoms are found to migrate to free (unoxidized) silicon surface spots rather than being adsorbed on the formed oxide layer. In these spots, a thin layer of cobalt disilicide first forms and a Co-Si solid solution then grows on it. Some cobalt atoms penetrate under the oxide layer and form a three-component Co-Si-O interfacial phase and a metastable cobalt disilicide with a CsCl-type structure at the SiO x -Si interface.

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 A). 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 A). In the coverage range of 3.4–4.3 A the solid solution transforms into Fe3Si. However, the in-plane ferromagnetic ordering of the silicide occurs only at 6.8 A Fe that demonstrates the thickness dependence of the magnetic properties of Fe3Si. The subsequent sample annealing to 150°C transforms Fe3Si to e-FeSi, leading to the disappearance of ferromagnetic behavior.

The early stages of iron silicide formation in the Fe/SiOx/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 SiOx/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 initial stages of iron silicide growth on the Si(1 0 0)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 � C. Our results support the existence of three stages in the Fe deposition on Si(1 0 0) 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 5 ML. The solid-phase reaction was found to depend on the deposited metal dose. At 5 ML, the reaction begins at 60 � C, and the solid-phase synthesis leads to the formation of only metastable silicides (FeSi with the CsCl-type structure, c-FeSi2 and a-FeSi2). A specific feature of this process is Si segregation on the silicide films. At a thickness of 15 ML and more, we observed only stable phases, namely, Fe3Si, e-FeSi and b-FeSi2. � 2007 Elsevier B.V. All rights reserved.

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 2p 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 e-FeSi, metastable disilicide γ-FeSi2, and disilicide β-FeSi2. The temperature ranges of existence of these phases were determined. Silicon was found to segregate on the γ-FeSi2 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 2p 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 SiOx/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.

The interaction of cobalt atoms with an oxidized Si(1 0 0)2 × 1 surface was studied by photoelectron spectroscopy with synchrotron radiation at room and elevated temperatures. The SiO x layer grown in situ on the crystal surface was ∼0.3 nm thick, and the amount of deposited cobalt was varied within eight atomic layers. It was found that Co atoms could penetrate under the SiO x 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 SiO x layer at ∼250 °C, producing cobalt disilicide with a stable CaF 2 -type of structure.

Core-level photoelectron spectroscopy with synchrotron radiation (hv = 140 eV) has been applied to study the variation in the Si+ charge state in silicon films deposited on the W(100) surface after thermal annealing of the substrate. The purpose of this study is to check the mechanism responsible for the sharp increase in the yield of Na+ ions in electron-stimulated desorption from a sodium layer adsorbed on the Si/W(100) surface after high-temperature annealing. The evolution of the W 4f7/2 and Si 2p photoelectron spectra and the valence band photoemission spectra is investigated for two silicon coverages (1 and 3 ML) on the W(100) surface in the temperature range 300

Cobalt adsorption and condensation on the Si(1 0 0)2 × 1 surface as well as solid-phase reaction of CoSi 2 formation have been studied by high-resolution photoelectron spectroscopy with synchrotron radiation. We have measured the Si 2p and valence-band spectra after the Co deposition from a submonolayer coverage to 6 ML thickness and a subsequent annealing to 600 °C. Room temperature Co adsorption results in the loss of the initial surface reconstruction, and the chemisorbed Co atoms appear to be embedded into the upper layer of Si(1 0 0); however, no stable CoSi 2 was observed. With further metal deposition, a discontinuous solid solution Co Si film was formed and the dissolved Si concentration decreased with the distance from the crystal surface. The formation of cobalt disilicide was found to occur in the range of 250–400 °C.

The initial stages of the growth of cobalt disilicide (CoSi2) on a 2×1 reconstructed Si(100) surface in the presence of oxygen have been studied for the first time by method of high-resolution photoelectron spectroscopy. The evolution of the electron structure of the sample surface was traced in the course of silicon oxidation, cobalt deposition, and subsequent thermal annealing. It is established that cobalt atoms penetrate to the oxide-silicon interface even at room temperature. This phenomenon favors the formation of an epitaxial CoSi2 layer with improved morphology.

Recent studies of the atomic structure of the single-crystal silicon surface (both clean and covered by adsorbates) that are performed by high-resolution core-level photoelectron spectroscopy using synchrotron radiation are reviewed. The physical principles of the method, experimental techniques, the spectrum processing procedure, and the procedure of determining the energy shifts of the core levels in the subsurface layer are outlined. Emphasis is placed on the surface modes of silicon 2p spectra, which are observed for the main types of silicon surface reconstruction (Si(111)-7×7 and Si(100)-2×1), and on a correlation between these modes and the atomic structure of the (111) and (100) surfaces. Also, particular attention is given to the studies of the Ge/Si system, which is viewed as a promising material of nanoelectronics, as well as to those concerned with metal and gas adsorption on basic (low-index) silicon faces. These studies clearly demonstrate that core-level photoelectron spectroscopy provides extremely detailed information on the structure of adsorbed layers and on the adsorption-stimulated reconstruction of the substrate surface.

Solid-phase formation of ultrathin CoSi2 layers on Si(100)2×1 was studied using high-resolution (∼140 meV) photoelectron spectroscopy with synchrotron radiation (hν=130 eV). The evolution of Si 2p spectra was recorded both under deposition of cobalt on the surface of samples maintained at room temperature and in the course of their subsequent annealing. It was shown that Co adsorption on Si(100)2×1 is accompanied by a loss of reconstruction of the original silicon surface while not bringing about the formation of a stable CoSi2-like phase. As the amount of deposited cobalt continues to increase (up to six monolayers), a discontinuous film of the Co-Si solid solution begins to grow on the silicon surface coated by chemisorbed cobalt. The solid-phase reaction of CoSi2 formation starts at a temperature close to 250°C and ends after the samples have been annealed to ∼350°C.

We have studied the room-temperature adsorption of cobalt in the range of submonolayer coverages on a reconstructed Si(100)2×1 surface. The measurements were performed by methods of high-resolution (∼140 meV) photoelectron spectroscopy using synchrotron radiation (hν=130 eV). An analysis of changes in the Si 2p line shape in the course of cobalt deposition showed that the metal adsorption leads to the loss of the initial substrate surface reconstruction. The results are interpreted using a model whereby adatoms arriving at the silicon surface are incorporated into the uppermost atomic monolayer, occupying positions between four Si atoms and forming rows parallel to the 〈110〉 directions in the substrate.

The growth of cobalt disilicide on the Si(100) surface by reactive epitaxy at T=350°C was studied within the 10–40 ML cobalt coverage range. A new method of mapping the atomic structure of the surface layer by inelastically scattered medium-energy electrons was employed. The films thus formed were shown to consist of CoSi2(221) grains of four azimuthal orientations turned by 90° with respect to one another. This domain structure originates from substrate surface faceting by (111) planes, a process occurring during silicide formation. B-oriented CoSi2(111) layers grow epitaxially on (111) facets.

The binding energies of Si 2p and Co 3p core-shell electrons in four stable cobalt silicides (Co3Si, Co2Si, CoSi, and CoSi2) have been determined by high-resolution photoelectron spectroscopy using synchrotron radiation. The silicides were formed by solid-state epitaxy under identical conditions on Si(100), Si(110), and Si(111) faces of silicon single crystals.