The effect of sodium adsorption on a gold film deposited on a tungsten substrate was studied. The deposition of Na atoms onto a thin film of gold on tungsten leads to a change in the spectra of the valence band and the core levels of gold and tungsten. An analysis of the spectra showed that the sodium atoms in the surface layer are in a neutral state, and the diffusion of sodium atoms deep into the gold film leads to the formation of the NaxAuy intermetallic compound. Heating a gold film with the formed NaxAuy intermetallic compound at a temperature 640 K leads to partial desorption of sodium and gold atoms from the surface layer of the NaxAuy intermetallic compound.

The electronic structure of a gold film deposited on W was studied during the adsorption of sodium atoms. An analysis of the photoemission spectra from the valence band and core levels of Au 4f and Na 2p upon synchrotron excitation in the photon energy range of 80–600 eV showed that Na adsorption leads to the formation of NaxAuy intermetallic compounds of various stoichiometry under the Na monolayer.

Photoelectron spectroscopy was used to study the electronic structure in situ in an ultrahigh vacuum before and after the adsorption of sodium atoms on the surface of tungsten oxidized at an oxygen pressure of 1 Torr and a temperature of 950 K. The photoemission spectra from the valence band and the W 4f, O 2s, and Na 2p core states were studied under synchrotron excitation in the photon energy range 80-600 eV. It is found that a tungsten oxide film is formed containing various tungsten oxides with an oxidation state of 6+ to 4+. The deposition of a 1.1 monolayer of sodium atoms on the surface of oxidized tungsten leads to the reduction of the W6+ states to W4+ and the reaction with oxygen in the hydroxyl composition, which is reflected in the change in the spectrum of the W 4f and O 2s core states. It is shown that the cathodoluminescence spectrum is associated with the luminescence of tungsten oxide. Keywords: adsorption, sodium, tungsten oxides, photoelectron spectroscopy, cathodoluminescence.

Photoelectron spectroscopy was used to study the electronic structure in situ in an ultrahigh vacuum before and after the adsorption of sodium atoms on the surface of tungsten oxidized at an oxygen pressure of 1 Torr and a temperature of 950 K. The photoemission spectra from the valence band and the W 4f, O 2s, and Na 2p core states were studied under synchrotron excitation in the photon energy range 80–600 eV. It is found that a tungsten oxide film is formed which contains various tungsten oxides with an oxidation state of 6+ to 4+. The deposition of a 1.1 monolayer of sodium atoms on the surface of oxidized tungsten leads to the reduction of the W6+ states to W4+ and the reaction with oxygen in the hydroxyl composition, which is reflected in the change in the spectrum of the W 4f and O 2s core states. It is shown that the cathodoluminescence spectrum is associated with the luminescence of tungsten oxide.

The electronic structure of thermally oxidized tungsten used as an emitter in thermal ionization of organic molecules is studied. Tungsten foil was thermally oxidized at oxygen pressure 1 Torr and temperature 950 K. The photoemission spectra from the valence band and O 2s and W 4f core levels are studied under synchrotron excitation with the photon energies 100 ÷ 600 eV. It is shown that thermal oxidation of tungsten leads to the formation in the W near-surface region various tungsten oxides with an oxidation state from 6+ to 4+. In this case, mainly tungsten oxides with an oxidation state of 6+ are formed on the surface, the proportion of which gradually decreases with distance from the surface with an increase in tungsten oxides with an oxidation state of 4+.

Using the method of photoelectron spectroscopy, an in situ study in ultrahigh vacuum of the electronic structure of a clean surface of tungsten oxidized at an oxygen pressure of 1 Torr and temperature of 1000 K was carried out. The spectra of photoemission from the valence band and core levels O 1s, O 2s, W 4f under synchrotron excitation in the photon energy range 80  600 eV are studied. It was found that a semiconductor film of tungsten oxide is formed, which contains various tungsten oxides with an oxidation state of 6+ to 4+. On the surface, mainly tungsten oxides with an oxidation state of 6+ are formed, the proportion of which gradually decreases with distance from the surface with an increase in tungsten oxides with an oxidation state of 4+.

Laser beam patterning is used to prepare field emission cathodes from the arrays of vertically aligned carbon nanotubes (CNTs). Field emission properties of the cathodes are measured in a technical vacuum of similar to 10(-2) Pa. A stable current of similar to 500 mu A from a 1 cm(2) cathode is preserved after a long-term testing for three hours under applied voltage of similar to 1.1 V/mu m. A degradation mechanism of CNT cathodes is considered and reasons of increased cathode stability are proposed.

We study the in-situ growth of a nanocomposite material consisting of a thin CuPcF4 film and multiphase/multidimensional indium nanoparticles, self-organizing on the surface and in the bulk, at various stages of thermal deposition of metal on an organic film under ultrahigh vacuum conditions. The analysis of high-resolution transmission electron microscopy (HR-TEM) images provided valuable information about the evolution of morphology, size, density, and distribution of indium nanoparticles upon indium deposition. These 2D/3D ultra-small nano-objects turned out to have not only body-centered tetragonal (bct) crystal structure, typical for bulk indium, but also unusual face-centered cubic (fcc) one. Using a synchrotron facility, the study of the electronic structure of the hybrid nanocomposite on variable stages of metal deposition was performed by XPS and NEXAFS. Core-level spectra related to the organics indicated reasonably weak chemical interaction of indium with CuPcF4 molecules, which is not the case for a number of metal/organic semiconductor systems, while valence band spectra have shown a considerable change of the material electronic properties. The energy level diagrams, derived from the experiment, can be applied for the creation of new prototypes of metal-organic memory devices.

Here, the synthesis of holey carbonylated (C-ny) graphene derivative and its application for gas sensing is demonstrated. The carbonylation of graphene oxide leads to the 3-fold increase in the concentration of carbonyl groups' up to 9 at.% with a substantial elimination of other oxygen functionalities. Such a chemical modification is accompanied by the perforation of the graphene layer with the appearance of matrices of nanoscale holes, leading to corrugation of the layer and its sectioning into localized domains of the is-conjugated network. Combined with the predominant presence of carbonyls, granting the specificity in gas molecules adsorption, these features result in the enhanced gas sensing properties of Cny graphene at room temperature with a selective response to NH3. Opposite chemiresistive response towards ammonia when compared to other analytes, such as ethanol, acetone, CO2, is demonstrated for the C-ny graphene layer both in humid and dry air background. Moreover, a selective discrimination of all of the studied analytes is further approached by employing a vector signal generated by C-ny multi electrode chip. Comparing the experimental results with the calculations performed in framework of density functional theory, we clarify the effect of partial charge transfer caused by water and ammonia adsorption on the chemiresistive response. (C) 2020 Elsevier Ltd. All rights reserved.

The electronic structure of an ultra-thin molybdenum oxide film obtained by oxidation of molybdenum at an oxygen pressure of 1 Torr and the effect of adsorption of sodium atoms Na on its electronic structure are studied by ultra-vacuum photoelectron spectroscopy in ultrahigh vacuum. Photoemission spectra from the valence band and core levels of O 2s, Mo 3d Mo 3p, and Na 1p are studied, upon synchrotron excitation in the photon energy range 80 − 600 eV. It is shown that in the formed oxide film, molybdenum is in two states: Mo6+ and Mo4+. On the surface of the oxide, oxygen is induced both in the composition of the oxides and in hydroxyl. It was shown that MoO3 is formed on the surface, and MoO2 at a distance from the surface. The deposition of Na atoms leads to intercalation of the molybdenum oxide 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.

DSC and calorimetric studies of multi-walled carbon nanotubes (MWCNTs) with average diameters in the range 7, 9 and 18 nm were carried out. MWCNTs were obtained by the CVD method. The kinetic processes in MWCNTs were studied from room temperature to 550 degrees C in a nitrogen flow using differential scanning calorimetry (DSC) on a Perkin - Elmer - 8000. It was found that exo- and endothermic peaks are not observed on the DSC curves after water evaporation. This indicates that all studied MWCNTs have a small number of defects, functional groups, and other impurities. The heat capacity of MWCNTs was measured by the relaxation method in the temperature range from 2 to 275 K by using PPMS. In the temperature dependences of the specific heat were observed that for MWCNTs with the decrease of the temperature below 20 K the curves shift to lower values with an increase the average diameter. The main result was that at temperatures below 45 K with the decreasing of the nanotubes diameter the ratio of heat capacity of nanotubes to the heat capacity of graphite increases. The perfection of structure and low amount of the defects, functional groups and impurity contamination for MWCNTs were demonstrated in the comparison of the XPS and NEXAFS spectra for these nanotubes with CVD prepared nanotubes (18 nm) after mechanical and chemical functionalization.

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 Fe 3 Si, while intercalation of graphene/Co/SiC with Si results in the formation of a Co-Si solid solution and CoSi silicide covered with Co 3 Si surface phase. The obtained silicide layers are reliably protected by graphene, making it compatible for nanoscale applications at ambient conditions.

The structural and some other characteristics of quasi-freestanding single-layer graphene obtained by annealing of the buffer layer in the flow of hydrogen are studied in comparison with those of conventional epitaxial graphene. The high structural quality and good lateral uniformity of the thus-obtained graphene film are checked and confirmed by the use of such techniques as Raman spectroscopy, atomic force, and Kelvin probe force microscopies. The confirmation of its single-layer and freestanding character is obtained via the analysis of respective data of X-ray photoelectron spectroscopy.

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.

The electronic structure of an ultra-thin molybdenum oxide film obtained by oxidation of molybdenum at an oxygen pressure of 1 Torr and the effect of adsorption of sodium atoms on its electronic structure are studied by photoelectron spectroscopy. Photoemission spectra from the valence band and core levels of O 2s, Mo 3d, Mo 3p, and Na 1p are studied upon synchrotron excitation in the photon energy range 80–600 eV. It is shown that in the formed oxide film, molybdenum is in two states: Mo6+ and Mo4+. On the surface of the oxide, oxygen is induced both in the composition of the oxides and in hydroxyl. It was shown that MoO3 is formed on the surface, and MoO2 at a distance from the surface. The deposition of Na atoms leads to intercalation of the molybdenum oxide layer.

Electronic structure of molybdenum oxides obtained by the oxidation of molybdenum at an oxygen pressure of 1 Torr (thin film) and air (thick film) was studied. It was shown that a thick oxide film is formed from MoO3 oxide, and a thin film from a mixture of MoO3 and MoO2 oxides, which is reflected in the form of valence band spectra. Oxygen on the surface belongs both in molybdenum oxide and in the hydroxyl group, which is associated with dissociative adsorption of water during the oxidation of molybdenum in air for a thick film.

We studied the electronic structure of gold nanoparticles deposited on a tungsten surface before and after the deposition of sodium atoms with subsequent heating at T = 630 K by in situ photoelectron spectroscopy in ultrahigh vacuum. The photoemission spectra from the valence band and core levels of Au 4f and Na 2p were studied upon synchrotron excitation in the photon energy range of 80–600 eV. The changes in the spectra of the valence band and core levels of Au 4f and Na 2p are associated with a change in the surface topography caused by the deposition of sodium atoms and heating, which led to an increase in the surface area by several times. The surface topography and cathodoluminescence of a layer of gold nanoparticles deposited on a tungsten surface are studied.