The utilization of graphene on silicon carbide (SiC) substrates holds substantial promise for advancements in spintronics and nanoelectronics. Furthermore, incorporating magnetic metals provides an optimal framework for probing fundamental physical phenomena. The approach to developing such systems is in situ intercalation of graphene with magnetic metals. Herein, the electronic structure is analyzed and the magnetic properties of the system are synthesized by the thermal decomposition of 6H‐SiC(0001) surface and subsequent intercalation of graphene with cobalt (Co) and iron (Fe) atoms. X‐ray photoemission spectroscopy and low‐energy electron diffraction are employed to control the synthesis and metal intercalation processes. The morphological characteristics of the synthesized system are studied by means of atomic force microscopy. The findings derived from magneto‐optic Kerr effect measurements reveal a homogeneous ferromagnetic ordering at room temperature. Angle‐resolved photoemission spectroscopy is used to ascertain the impact of intercalation on graphene's electronic structure. The results of this study are essential for the development of graphene‐based spintronics and nanoelectronic devices as well as for fundamental studies in magnetic graphene systems.

Iron chalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase segregation, where superconducting clusters form at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase segregation. We studied temperature dependences of the photoelectron spectra of Se 3d, Fe 3p, and the valence band at temperatures above and below T-c approximate to 27 K of the compound (K0.8Na0.2)(0.8)Fe1.8Se2 with substitution of alkali metal atoms. A strong temperature dependence was found for both the valence band and the core levels: we observed a significant broadening of the spectra, which monotonically decreased with increasing sample temperature under cyclical temperature change. We believe that this broadening is associated with the appearance of volume charges in the dielectric matrix, leading to the band bending. Moreover, the shape of the potential that arises under the surface of this compound was restored, and an estimate was obtained for the relative amount of the superconducting phase. These results will help to better understand the physical processes occurring in this compound.

Mixed copper-containing pyrochlores Bi 2 Co 1/2 Cu 1/2 Ta 2 O 9 +Delta , Bi 2 Ni 1/2 Cu 1/2 Ta 2 O 9 +Delta , Bi 2 Co 1/3 Cu 1/3 Ni 1/3 Ta 2 O 9 +Delta (sp.gr. Fd-3 m ) were synthesized by the solid-phase reaction method. The surface composition and chemical state of transition element atoms in pyrochlores were characterized by XPS, NEXAFS spectroscopy. According to the XPS spectra, bismuth and tantalum cations have an effective charge of + 3 and +(5- delta ). The NEXAFS Cu2p spectra of pyrochlores are shown to represent a superposition with the CuO and Cu2O 2 O spectra in terms of the main spectral characteristics. This indicates a variable Cu ion content in oxide pyrochlores in the form of Cu(I,II) ions.

Two series of the bismuth tantalate pyrochlore samples, codoped with Mg,Mn and Zn,Mn, were synthesized via solid-phase reaction. It was established that the Bi2Mg(Zn)xMn1−xTa2O9.5−Δ (x = 0.3; 0.5; 0.7) samples contain the main phase of cubic pyrochlore (sp. gr. Fd-3m) and an admixture of triclinic BiTaO4 (sp. gr. P-1). In both sets, the amount of BiTaO4 is proportional to the amount of manganese doping, however, zinc-containing samples have a higher level of impurities than magnesium-containing ones. The unit cell parameter of the Zn,Mn codoped bismuth tantalate phase increases with an increasing content of zinc ions in the samples from 10.4895(5) (x = 0.3) to 10.5325(5) Å (x = 0.7). The unit cell parameter of Mg,Mn codoped bismuth tantalate pyrochlores increases uniformly with an increasing index x(Mg) from 10.4970(8) at x = 0.3 to 10.5248(8) Å at x = 0.7, according to the Vegard rule. The NEXAFS and XPS data showed that the ions were found to have oxidation states of Bi(+3), Ta(+5), Zn(+2) and Mg(+2). In the Ta 4f XPS spectrum of both series of samples, a low energy shift of the absorption band characteristic of tantalum ions with an effective charge of (+5-δ) was observed. The XPS spectra of Bi4f7/2 and Bi4f5/2 also show a shift of bands towards lower energies which is attributed to the presence of some low-charge ions of transition elements in the bismuth position. The NEXAFS spectroscopy data showed that manganese ions in both series of samples have predominantly 2+ and 3+ oxidation states. XPS data indicate that in zinc-containing preparations the proportion of oxidized manganese ions is higher than in magnesium-containing ones.

New intercalation compounds CrxZrSe2 were synthesized and thoroughly studied. Cr atoms were found to occupy the positions both tetrahedrally and octahedrally coordinated by the Se atoms in the interlayer gap. The magnetic properties and electrical resistivity were studied in the temperature ranges of 2.4-300 K and 80-340 K, respectively. The compounds change their behavior from semiconducting (x = 0.1) to metallic (x > 0.1). The magnetic interaction strongly depends on the Cr content and temperature. The spin-glass state with antiferromagnetic interaction exists at T < T-crit for CrxZrSe2 with x <= 0.2, while at x >= 0.3 ferromagnetic contribution arises as well. The single crystals of CrxZrSe2 were grown to study the electronic structure of the materials. A combination of the X-ray photoelectron spectroscopy (including that across Cr 2p-3d and Zr 3p-4d resonance) and X-ray absorption spectroscopy methods allowed to propose the location of the Cr 3d-states in the Se 3p-Zr 4d energy gap.

Cubic pyrochlore of the composition Bi2Co0.5Cr0.5Nb2O9+triangle (sp. gr. Fd-3m, a = 10.4838(8) angstrom) was synthesized in several stages using a solid-phase reaction from oxide precursors at a final temperature of 1050 degrees & Scy;. Using NEXAFS spectroscopy data, the electronic state of cobalt and chromium ions during the synthesis process was studied. It has been established that before the formation of phase- pure pyrochlore, Cr(III) ions are converted to Cr(VI), and then again to Cr(III); Cobalt ions Co(III) are reduced to Co(II). NEXAFS Cr2p spectra of ceramics synthesized at 650 degrees & Scy;, according to the main characteristics of the spectrum, coincide with the spectrum of K2Cr2O7 and indicate the chromium content in the oxide ceramics in the form of tetrahedral CrO42- ions, and according to the nature of the Co2p spectrum, cobalt ions are in the Co(II) state and Co(III). In the composition of pyrochlore Bi2Co0.5Cr0.5Nb2O9+triangle, synthesized at 1050 degrees & Scy;, cobalt and chromium appear predominantly in the form of Co(II) and Cr(III) ions. Analysis of phase transformations showed that changes in the oxidation state of transition element ions and the color of ceramics are associated with the formation of intermediate synthesis products.

Iron chalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase segregation, where superconducting clusters form at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase segregation. We studied temperature dependences of the photoelectron spectra of Se 3d, Fe 3p, and the valence band at temperatures above and below T_c≈ 27 K of the compound (K _0.8 Na _0.2 ) _0.8 Fe _1.8 Se _2 with substitution of alkali metal atoms. A strong temperature dependence was found for both the valence band and the core levels: we observed a significant broadening of the spectra, which monotonically decreased with increasing sample temperature under cyclical temperature change. We believe that this broadening is associated with the appearance of volume charges in the dielectric matrix, leading to the band bending. Moreover, the shape of the potential that arises under the surface of this compound was restored, and an estimate was obtained for the relative amount of the superconducting phase. These results will help to better understand the physical processes occurring in this compound.

According to X-ray powder phase analysis, Bi(2)Mg(x)Mn(1-x)Ta2O(9.5-triangle) (x=0.3;0.5;0.7) samples synthesized using ceramic technology contain the main phase of cubic pyrochlore (space group Fd-3m) and the impurity phase BiTaO4 4 of the triclinic modification (sp. Gr. P-1), the content of which is proportional to the degree of doping with manganese. The unit cell parameter of the pyrochlore phase increases uniformly with increasing index x(Mg) from 10.4970(8) at x=0.3 to 10.5248(8) angstrom (x=0.7), obeying the Vegard rule. The electronic state of all ions included in Bi(2)Mg(x)Mn(1-x)Ta2O(9.5-triangle )was studied using X-ray spectroscopy. According to NEXAFS and XPS data, it was established that doping with magnesium does not change the oxidation state of bismuth and tantalum in pyrochlore. Meanwhile, in the Ta4f(-), Bi4f(7/2 ) and Bi4(f5/2) spectra of the samples, an energy shift of the absorption bands towards lower energies is observed, which is typical for bismuth and tantalum ions with an effective charge of (+3-delta) and (+5-delta), caused by the distribution of manganese(II) and magnesium(II) ions in the position of bismuth and tantalum. According to NEXAFS and XPS spectroscopy, manganese ions in the samples have oxidation states predominantly +2 and +3, the proportion of which increases with increasing manganese content in the samples.

The results of studying the electronic structure of transition-metal oxides TiO2 and MoO2 with a rutile-type crystal structure are presented. The electronic structure is studied theoretically within the framework of the linearized augmented-plane-wave method using the Wien2k software package. The band structure, and the total and partial densities of electronic states are calculated. Based on the filling of energy bands with electrons, an explanation is given for the different types of electrical conductivity of TiO2 and MoO2. The valence band and subvalent states of commercial TiO2 and MoO2 samples in the form of powders at two different excitation energies of 120 and 1486.6 eV are studied using X-ray photoelectron spectroscopy. Based on calculations, the observed features of the structure of the experimentally recorded spectra are interpreted.

The physico-chemical state specificity of the epitaxially formed five tin monolayers interface with a thin silicon buffer layer, and the transformation of the epitaxial structure as a result of in-situ thermal annealing from silicon atoms charge state of point of view are studied. A high-resolution X-ray photoelectron spectroscopy was applied using a high intensity synchrotron radiation. The possibility of oxygen atoms diffusion is shown to the silicon buffer layer during storage of structures in laboratory conditions. High-temperature ultrahigh vacuum annealing causes a phase rearrangement of such structures surface layers, which is accompanied by redistribution of oxygen atoms to the epitaxial silicon buffer, and the formation of the thin SiO2 layer at the tin-silicon interface.

Iron dichalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase separation, in which superconducting clusters are formed at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase separation. We studied the temperature dependences of the photoelectron spectra of Se 3d, Fe 3p and the valence band at temperatures above and below Tc ≈ 27 K of the compound (K0.8Na0.2)0.8Fe1.8Se2 with a unique substitution of alkali metal atoms. A strong temperature dependence of both the valence band and core levels was discovered: we observed a strong broadening of the spectra, which monotonically decreased with increasing sample temperature, while the temperature changes were cyclic. We believe that this broadening is associated with the appearance of space charges in the dielectric matrix, which leads to band bending. Moreover, the shape of the potential arising under the surface of a given compound was reconstructed, and an estimate was obtained for the relative amount of the superconducting phase. The results obtained will help to better understand the physical processes occurring in this compound.

A cubic pyrochlore with the composition Bi1.865Co1/2Fe1/2Ta2O9+Δ (space group Fd-3m, a = 10.5013(8) Å) was synthesized from oxide precursors using solid-phase reactions. These ceramics are characterized by a porous microstructure formed by randomly oriented grains of an elongated shape with a longitudinal size of 0.5–1 µm. The electronic state of cobalt and iron ions in oxide ceramics was studied by NEXAFS and XPS spectroscopy. The parameters of the XPS spectra of Bi4f, Bi5d, Ta4f, Co2p, and Fe2p ionization thresholds for a complex pyrochlore were compared with the parameters of the corresponding oxides of the transition elements. The energy position of the XPS-Ta4f and -Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) oxide by 0.75 eV. According to XPS spectroscopy, bismuth and tantalum cations have the corresponding effective charge of +3 and +(5-δ). The NEXAFS-Fe2p spectrum of ceramics coincides with the spectrum of Fe2O3 in its main spectrum characteristics and indicates the content of iron ions in the oxide ceramics in the form of octahedral Fe(III) ions, and according to the character of the Co2p spectrum, cobalt ions are predominantly in the Co(II) state.

The analysis of the results on the study of erosion products of tungsten-containing elements of a thermonuclear reactor first wall by spectroscopic and other methods is carried out, combined with a brief comparison of studies of carbon erosion products in the form of carbon-deuterium films CD x ( x ~ 0.5) from the T-10 tokamak with graphite walls and mixed films CH x –Me (with impurities Me = W, Fe, etc.) from a high-current plasma accelerator QSPA-T with hydrogen plasma, performed using similar methods. Examples of other unique modern experiments with tungsten and carbon in Russia and abroad are also considered, including in situ diagnostic methods of erosion products, and additionally are presented three new spectra of CD x and CH x –Me films. The relevance and interconnection of research on the topic “the first wall carbon–metal materials” is dictated by the construction of the JT-60SA fusion reactor in support of the ITER and DEMO project, which will operate for the first ten years with the first wall and divertor made of carbon fiber composites, followed by a transition to metal walls. It is shown that the technique for studying CD x films has a universal character, and a number of presented new methods for erosion research of tungsten-containing materials complement and enhance it. As shown, spectroscopic methods for the comparative research of tungsten and carbon erosion products on the surface and in the bulk of the material, including new methods and physical results, make it possible to identify associated problems and prepare practical recommendations for the safe operation of thermonuclear devices.

The effect of Fe and Mg-codoping on the crystal structure, optical and dielectric properties of bismuth tantalate-based pyrochlores has been studied. Samples of Bi2MgxFe1−xTa2O9.5−Δ (x ≤ 0.7) are characterized by a porous dendrite-like microstructure. Fe,Mg-codoped bismuth tantalate pyrochlores are thermally stable up to a temperature of 1140 °C (x = 1). The Bi2Mg0.5Fe0.5Ta2O9.5−Δ thermal expansion coefficient increases uniformly and weakly from 3.6 to 9.3 × 10−6 °C−1 (30–1050 °C). The unit cell parameter of solid solutions increases uniformly from 10.5009(1) Å (x = 0.3) up to 10.5225(7) Å (x = 0.7). The structural parameters of disordered pyrochlore are determined by the Rietveld method (sp. gr. Fd3¯m:2 (227), Z = 8). According to near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy data, ions in solid solutions are in the charge states Bi (+3), Mg (+2), Fe (+3), Ta (+5-δ). The Mössbauer spectrum is represented by a symmetric doublet with parameters IS = 0.365 ± 0.0020 mm/s, QS = 0.604 ± 0.034 mm/s, related to Fe3+ ions in regular axial octahedral positions. The samples exhibit the properties of dielectrics. The permittivity and the tangent of dielectric losses at 20 °C increases with the growth of iron content in the samples in the range of 28.5–30.5 and 0.001 (1 MHz). The width of the band gap of the obtained materials for direct allowed electronic transitions is in the range of 2.16(5)–2.41(5) eV. The studied samples satisfy the condition of efficient conversion of solar energy into an electrical one and are promising as catalysts and light-absorbing elements for solar panels.

The effect of Zn-doping on the phase composition and optical properties of the Bi2ZnxFe1-xTa2O9.5-Δ (x = 0.3, 0.5, 0.7) was studied. XRD data showed that the samples crystallize in the structural type of pyrochlore (sp. gr.Fd-3m). For all the samples, an admixture of bismuth orthotantalate β-BiTaO4 triclinic modification up to 22.5 wt.% is observed. The content of β-BiTaO4 increases with zinc doping. The unit cell parameter of the pyrochlore phase rises from 10.4878 (x = 0.3) to 10.5154 Å (x = 0.7). The samples are characterized by a porous microstructure with indistinct grain boundaries. Zinc oxide has a sintering effect on ceramics. The charge state of the ions in Bi2ZnxFe1-xTa2O9.5-Δ was investigated by X-ray spectroscopy. NEXAFS and XPS data show that zinc doping does not change the oxidation degree of iron and bismuth ions in pyrochlore. The ions are in the charge states Bi(+3), Fe(+3), Zn(+2). In the Ta4fspectrum, an energy shift of the absorption band towards lower energies by ΔE = 0.5 eV is observed, which is typical for tantalum ions with an effective charge of (+5-δ). With the increase of x(Zn), the Bi 4f7/2 and Bi 4f5/2 bands are observed to shift to lower energies due to the distribution of some Zn(II) ions in the bismuth position.

Представленная работа посвящена изучению распределения элементов химического состава поликристаллических образцов феррита бария составов BaFe12-xTixO19 и BaFe12-xMnxO19. Исследуемые образцы ферритов получены методом твердофазного синтеза при температуре 1400 °С из стехиометрических смесей оксидов и карбонатов. Методом рентгеновской дифракции показано, что все исследуемые образцы имеют одну кристаллическую фазу, характерную структуре гексаферрита M-типа. Методом дифференциально-сканирующей калориметрии определены значения температуры Кюри. Показано, что замещение железа атомами Ti и Mn приводит к уменьшению температуры магнитного фазового перехода. Методами рентгеноспектрального анализа и рентгеновской фотоэлектронной спектроскопии установлены различия в атомном составе объёма и поверхности изучаемых ферритов. Показано, что барий способен проявлять поверхностную сегрегацию. Обнаружено, что замещение железа марганцем в структуре гексаферрита бария приводит к поверхностной сегрегации бария, в то время как замещение титаном препятствует ей.

The Bi1.6Cr0.8Ta1.6O7 +/-Delta pyrochlore was synthesized by the solid-phase method (sp. gr. Fd-3m:2, 10.45523(3) angstrom, Z = 8). The thermal stability of the pyrochlore in air up to 1140 degrees C has been established. With increasing temperature (30-1200 degrees C), the unit cell parameter and the thermal expansion coefficient increase isotropically, although weakly from 10.4413 to 10.5255 angstrom and 4.6 x 10-6 to 9.2 x 10-6 degrees C -1. The electron spin resonance spectrum of the Bi1.6Cr0.8Ta1.6O7 +/-Delta contains an intense Lorentz-shaped band (g-2.05) with a width of Delta BPP-160 mT. According to X-ray absorption fine structure and X-ray photoelectron spectroscopy, the ions are in the charge states Bi(+3), Ta(+5-delta), Cr(+3). The sample contains shallow traps with a depth of 0.39 eV and deep traps with an energy of 1.7 eV. At temperatures above 400 degrees C, ion transfer begins to dominate, which is revealed in a decrease in the conductivity activation energy to 0.78 eV.

The joint intercalation of Co and Fe atoms under a graphene buffer layer synthesized on a SiC(0001) single crystal has been studied. Intercalation has been performed by means of the alternating deposition of ultrathin Fe and Co metal films on the substrate heated to 450°C with the subsequent heating to 600°C in 15 min. It has been shown that Co and Fe atoms under these conditions are intercalated under graphene, forming compounds with silicon and with each other. The existence of a magnetic order in the system up to room temperature has been demonstrated using a superconducting quantum interferometer. A possible stoichiometry of the formed alloys has been analyzed using data on the shape and magnitude of hysteresis loops. In addition, it has been found that Fe and Co in the system exposed to the atmosphere are not oxidized. Thus, graphene protects the formed system. This study makes contribution to the investigation of graphene in contact with magnetic metals and promotes its application in spintronic and nanoelectronic devices.

Distribution of chemical elements in polycrystalline BaFe 12– x Ti x O 19 and BaFe 12– x Mn x O 19 barium ferrite samples is studied. The samples are prepared by solid-phase synthesis at 1400 °C from stoichiometric mixtures of oxides and carbonates. The XRD data indicate that all the studied samples have one crystalline phase characteristic of the M-type hexaferrite structure. The Curie temperatures are determined by differential scanning calorimetry. It is shown that replacing iron with Ti and Mn atoms diminishes the temperature of magnetic phase transition. The difference in bulk and surface atomic composition between the studied ferrites are established by XRD and XPS. It is shown that barium can exhibit surface segregation. The replacement of iron by manganese in the barium hexaferrite structure leads to surface segregation of barium, while the replacement by titanium hinders the segregation.