The results of ab initio calculations of the spin-polarized band structure of graphene on silicon carbide intercalated with cobalt and silicon atoms are presented. It is shown that metal and silicon atoms during intercalation are localized between the substrate and the buffer layer of carbon atoms. Initially, the cobalt layer is strongly coupled with the buffer layer. The subsequent intercalation of silicon and the formation of cobalt silicide leads to a transition from hybridized state to the formation of quasi-freestanding bilayer graphene on the surface of the system due to the transformation of the buffer layer to the second graphene layer.

The ab initio calculations have been performed for the spin-polarized band structure of graphene on silicon carbide intercalated with cobalt and silicon atoms. The cobalt and silicon atoms are shown to be localized during intercalation between the substrate and buffer layer of carbon atoms. The subsequent silicon intercalation and the formation of cobalt silicide lead to the transition from a strong hybridization to the formation of a quasi-free two-layer graphene on the system surface due to the transformation of the buffer layer to the second graphene layer.

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 4 H - and 6 H -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 Co 3 Si 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.

Исследован процесс формирования тонких пленок силицидов железа под графеном, выращенным на поверхности карбида кремния, путем последовательного интеркалирования графена атомами железа и кремния. Эксперименты проводились in situ в условиях сверхвысокого вакуума. Элементный состав и химическое состояние поверхности образцов, а также их атомная структура контролировались с помощью фотоэлектронной спектроскопии высокого энергетического разрешения с использованием синхротронного излучения и дифракции медленных электронов. Толщина нанесенных слоев железа и кремния варьировалась в диапазоне 0.1-2 nm, а температура отжига образцов изменялась от комнатной до 600oС. Показано, что интеркалирование системы графен/Fe/SiC кремнием приводит к образованию слоя твердого раствора Fe-Si, покрытого поверхностным силицидом Fe3Si. Полученные пленки надежно защищены графеном от воздействия окружающей среды, что открывает возможности для их практического применения. Ключевые слова: графен на карбиде кремния, железо, интеркалирование, силициды, фотоэлектронная спектроскопия.

One of the intriguing problems of modern magnetism is unravelling the non-equilibrium spin dynamics following laser excitation on the nanometer length scale. In this work the ultrafast magnetic behavior of thin Co/Pt multilayers is studied by resonant magnetic SAXS in transmission geometry. We have for the first time observed a very bright transient scattering from nanometer scale magnetic fluctuations.

Abstract The process of formation of cobalt silicides near the graphene-silicon carbide interface by intercalation of single-layer graphene grown on the 4 H - and 6 H -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 Co_3Si 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.

Graphene-based materials are of great interest for spintronics devices. In the present paper, the effect of intercalated iron on the electronic structure of the graphene/4H-SiC(0001) system has been studied in the frame of density functional theory. It is shown that the most energetically favorable position of intercalated Fe atoms corresponds to their location between the buffer layer and the top Si layer of the substrate. Insertion of Fe atoms into the system leads to the spin polarization of the electronic states of carbon. Another effect is that the buffer layer becomes flat and bilayer graphene forms in the system.

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.

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.

Intercalation synthesis of graphene-capped cobalt silicides has been studied in situ by core-level photoelectron spectroscopy with synchrotron radiation and low-energy electron diffraction. It is found that at 400 degrees C the intercalation of graphene/Ni(1 1 1) with cobalt takes place in a wide range of coverage up to 17 ML Co. Graphene is strongly coupled with the upper layer of Co atoms and stabilizes the fcc structure of the intercalated Co(1 1 1) film. Subsequent intercalation of graphene/Co/Ni(1 1 1) with silicon results in the formation of an ordered Co3Si surface phase of the (root 3 x root 3)R30 degrees structure and then of Co2Si silicide and Co-Si solid solution. Our experimental data and DFT calculations have shown that the coupling between the graphene layer and the surface silicide is rather weak and the properties of quasi-freestanding graphene are preserved.

AbstractIn this paper, we studied cobalt intercalation of single-layer graphene grown on the 4 H -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.

AbstractThe 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.

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.

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.

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 E σ n (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 p z 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.

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.

AbstractAb 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 E _σ n (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 p _ z 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.

AbstractThe intercalation of iron under a graphene monolayer grown on 4 H -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.