Mikhail V. Kuznetsov

Metastable phase diagram of Ti–Si–N(O) films (CSi<30 at.%)

Abstract Metastable ternary concentration diagram of phase formation in arc-deposited films Ti–Si–N(O) ( C Si T dep =300–500 K is presented in this paper along with comparison of the diagram with equilibrium isothermal cross-sections of Ti–Si–N and Ti–Si–O systems. At a temperature of 300 K and C Si >10–15 at.% a transition takes place from metastable supersaturated cubic solution TiSi x N y O z to amorphous state TiSi x N y O z . Intermediate bi-phase area (TiSi x N y O z + Ti 5 Si 3 (O,N) with heterogeneous structure, preceding forming an amorphous state, was found. In the context of the heterogeneous nucleation, kinetics of the deposition of the phases TiSi x N y O z , Ti 5 Si 3 (O,N) was analyzed. It was shown that heterogeneous microstructure of these films and concentration range (on silicon) of the forming bi-phase area is defined by energy parameters of growth kinetics of critical Ti 5 Si 3 (O,N) crystal nucleus. Applicable to the system Ti–Si–N(O) ( C Si x N y O z was considered. Amorphous structures in arc-condensed films of Ti–Si–N(O) (15 C Si x framework, and Ti–N(O) bonds are more preferable as compared to Si–N(O) bonds.

Large-Scale Sublattice Asymmetry in Pure and Boron-Doped Graphene.

The implementation of future graphene-based electronics is essentially restricted by the absence of a band gap in the electronic structure of graphene. Options of how to create a band gap in a reproducible and processing compatible manner are very limited at the moment. A promising approach for the graphene band gap engineering is to introduce a large-scale sublattice asymmetry. Using photoelectron diffraction and spectroscopy we have demonstrated a selective incorporation of boron impurities into only one of the two graphene sublattices. We have shown that in the well-oriented graphene on the Co(0001) surface the carbon atoms occupy two nonequivalent positions with respect to the Co lattice, namely top and hollow sites. Boron impurities embedded into the graphene lattice preferably occupy the hollow sites due to a site-specific interaction with the Co pattern. Our theoretical calculations predict that such boron-doped graphene possesses a band gap that can be precisely controlled by the dopant concentration. B-graphene with doping asymmetry is, thus, a novel material, which is worth considering as a good candidate for electronic applications.

Metastable TiSixNyOz films of B1-type structure prepared by the arc process

Abstract Metastable TiSi x N y O z films with the cubic B1-type structure were synthesized by arc deposition. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron microprobe analysis (EMA) methods were employed to study the composition and structure of the films as a function of the arc process parameters: working gas pressure, substrate temperature and potential. It was established that silicon atoms are introduced into the B1-type structure of TiN y O z films and are located in the non-metallic sublattice. The influence of the non-metallic sublattice non-stoichiometry and oxygen impurity content on the silicon concentration in the films was discussed on the basis of the experimental data obtained and the quantum chemical calculations performed.

Structure of epitaxial δ-NbN films deposited by cathode reactive sputtering

Abstract The low-temperature (298–673 K) growth and structure of epitaxial δ-NbN thin films (100–800 A) deposited by reactive sputtering on the (100) NaCl cleavage surface have been studied by transmission electron microscopy. The films have a parallel epitaxial orientation (100)NaCl ∥ (100)NbN and contain microtwin interlayers in the (111) planes. The micro twin content dependence on the background pressure as well as on deposition rate has been found. It has been concluded that microtwins form at the initial growth stage as a result of coalescence of islands of different orientations, (100) and (111), like condensed fcc metal films. The high density of block boundaries and the distortion of coherent growth with small film thicknesses ( h ≈ 100 A ) are attributed to the high activation energy of coalescence and recrystallization processes characteristic of refractory compounds.

Composition and submicron structure of chemically deposited Cu2Se-In2Se3 films

Films of substitutional solid solutions of the Cu2Se-In2Se3 system containing up to 7.5 at. % In have been obtained by chemical deposition from aqueous media. The composition, structure, and morphology of the films have been studied. Data of X-ray diffraction and X-ray photoelectron spectroscopy showed that copper in the solid solution occurs in a single-valence state (Cu+). The deposited layers possess a globular morphology and are nanostructured.

Chemical sensors based on a hydrochemically deposited lead sulfide film for the determination of lead in aqueous solutions

Chemical sensors for determining lead in aqueous solutions are developed based on hydrochemically deposited lead sulfide (PbS) films; their composition and surface morphology are studied. The sensors are sensitive to lead to 31.5–32.5 mV/pcPb with the limit of detection of the metal 1.5 × 10–8 M. The role of photoactivation and doping of films in increasing the sensitivity of the film sensor to lead is determined. The studied chemical sensors can be relatively easily regenerated by soaking in distilled water for 10–30 min; they have sufficiently high selectivity to lead in the presence of sodium, nickel, zinc, and cadmium salts in solution.

Modeling the Dynamics of Natural Forest Ecosystems in the Northeast of European Russia under Climate Change and Forest Fires

Abstract: The individual-based EFIMOD simulation model was used for regional-scale assessments of the dynamics of basic characteristics of the carbon and nitrogen balance in the forest ecosystems of north central Russia. Two forest strict nature reserves were chosen as case studies. Data from the National Forest Inventory were used for model initialization. Initial soil data were taken from a soil survey database containing data on soil organic matter and nitrogen content in the organic layer and mineral soil for different forest types and regions of European Russia. Standard meteorological data were used as climatic inputs. Two simulation scenarios (without disturbances and with forest fires) were coupled with 2 climatic ones (actual climate and the scenario of climate change). The main sources of uncertainty were analyzed and the model parameters were evaluated. A Monte Carlo procedure was applied for evaluation of the robustness of coefficients. Simulation results showed that the greatest carbon accumulation occurred in the scenario without disturbances. Fires resulted in significant losses in soil organic matter and tree biomass through direct and indirect carbon dioxide emissions. Simulated climate change led to an increased decomposition rate of soil organic matter and a related increase in the productivity of vegetation; however, for this region, the carbon balance was positive. This was primarily because young and middle-aged stands are prevalent in the region modeled. A full analysis would require analytical data on the possible dynamics of mature and over-mature forests in the same scenarios of climate change and forest fires.

Telescope Array search for EeV photons and neutrinos

We present the searches for photons and neutrinos with the 9 years of data of the Telescope Array surface detector (2008--2017). The both searches employ multivariate analysis with the classifier based on the Boosted Decision Tree. The diffuse flux limits for photons and down-going neutrinos are obtained for the primary energies greater than 1 EeV.

Structure and composition of chemically deposited In2S3 thin films

Nanostructured thin indium(III) sulfide thin films 285–756 nm thick are obtained via chemical deposition from aqueous solutions containing indium chloride, thioacetamide, tartaric acid, and hydroxylamine hydrochloride at temperatures of 343–368 K. Oxygen- and carbon-containing impurities, which are not observed in the film bulk (at a depth of 12 nm), are detected in the surface layers of the films. When the synthesis temperature increases, the layer morphology changes substantially and the crystallite size increases from 70 to 150 nm. Upon annealing at a temperature of 573 K, crystallite aggregates are fused and In2S3 films are enriched with 6 to 10 at % of oxygen.

Atomic structure of a 1T-TiSe2 surface layer from photoelectron and Auger electron holography data

A three-dimensional (3D) reconstruction of the atomic structure of the (100) surface of a 1T-TiSe2 layered dichalcogenide crystal has been performed from X-ray photoelectron and Auger electron diffraction data. The diffraction patterns of the emission of Auger electrons of Se(LMM) selenium and photoelectrons of Ti2p titanium have been considered as holographic diagrams. Being processed with the scattering pattern extraction algorithm using the maximum entropy method (SPEA-MEM), they provide individual 3D images of the nearest environment of selenium and titanium atoms in the TiSe2 lattice. Using reconstructed 3D images, the positions of 128 atoms in the 2 × 2 × 1.5-nm region of the surface layer of TiSe2 have been determined. The structure of the surface has a 1T polytype. Interatomic distances in the layer and van der Waals gap are larger than the respective parameters in the bulk of the crystal. It is assumed that titanium layers in two Se-Ti-Se upper surface structural units are displaced along the [001] axis. The structure of the surface layer can be described by a unit cell of the P3 space group with the parameters a = 3.85 Å and c = 14.4 Å.