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Whispering-gallery-mode disk optical nanocavities with an enhancement factor up to 100 can be fabricated from bulk transition metal dichalcogenides having an indirect bandgap using scanning probe lithography.

In this work, we experimentally investigate the effects of electric bias on the degradation of few-layer MoS2 back-gated field-effect transistors in ambient air. The devices were fabricated using mechanically exfoliated MoS2 flakes, which were transferred to a Si/SiO2 substrate by a PDMS-based transfer. We report an accelerated electric bias-induced degradation of the devices under investigation and used optical and scanning electron microscopy (SEM) to monitor changes of the morphology of the MoS2 channel. In particular, we found a linear dependency of the degradation on the electric field between the Ti/Au source and drain contacts. In addition, we identify four regions in which morphological changes occur, of which the edges of the MoS2 channel are most affected.

Sulfur treatment causes essential modification of the shape of the band potentials at the n-InP(100) surface, accompanied by photoluminescence enhancement.

An analysis of the operational conditions for utilizing a small-volume blast furnace (BF) both in metallurgical production and processing of resulting wastes is carried out. Micro blast furnaces can be recommended for integrated waste processing in metallurgical production and coal benefication due to the small effective height of the furnace (no more than 10–12 m) reducing the strength requirements of products following compacting operations for obtaining pellets or briquettes. On the example of a complex equipped with a 70 m3 micro-blast furnace, the application of carbon-containing pellets obtained from metallurgical production and coal benefication sludges was shown to result in reduced unit costs for the production of 1 ton of cast iron. However, for stable furnace operation, it is necessary to resolve outstanding problems involved in the preparation of ferrous wastes for the subsequent manufacture of carbon-containing pellets.

International audience; The electronic structure of α-V 2 O 5 , γ-V 2 O 5 and γ-MeV 2 O 5 (Me = Li, Na) bronzes is studied by quantum-chemical calculations completed by spectroscopic experiments. The calculations are performed using G 0 W 0 method with DFT+U self-consistent wavefunction as an initial approximation. The electronic band gap E g = 2.89 eV calculated for α-V 2 O 5 is found to be in a fair agreement with available experimental data. The strategy was then applied to studying the electronic structure of the γ-V 2 O 5 phase

We report the results of systematic experimental and theoretical studies of structural and dynamical properties of short-period GaN/AlN superlattices. The multilayer structures with the thicknesses of the constituent layers varying from two to several monolayers are grown using the submonolayer digital molecular beam epitaxy technique. In the framework of density functional theory, the lattice dynamics properties of the superlattices are studied. Good agreement between the experiment and theory is found, which made it possible to establish unambiguously a relationship between the features observed in the Raman spectra and the microscopic nature of the acoustic and optical phonon modes. The results obtained enhance the capabilities of Raman spectroscopy as a fast and non-destructive characterization method of short-period GaN/AlN superlattices and can be used to optimize growth process parameters for the fabrication of structurally perfect low-dimensional heterostructures.

In this work a comprehensive study is presented for the analysis of epitaxial graphene layers using Raman spectroscopy. A wide range of graphene types is covered, from defective/polycrystalline single layer graphene to multilayer graphene with low defect density. On this basis the influence of strain type, Fermi level and number of layers on the Raman spectrum of graphene is investigated. A detailed view on the 2 D / G dispersion and the respective slopes of uniaxially and biaxially strained graphene is given and its implications on the asymmetry of the G peak analyzed. A linear dependency of the phonon mode asymmetry on uniaxial strain is presented in addition to the known Fermi level dependence. Additional impacts on the asymmetry are found to be arising from the defect density and transfer doping of adsorbates. The discovered transfer doping mechanism is contrary to pure phonon excitation through excitons and exhibits increasing asymmetry with increasing Fermi level. A new characteristic correlation between the 2 D mode line width and the inverse I(D)/I(G) ratio is introduced that allows the determination of the strain type and layer number and explains the difference between Raman line widths of monolayer graphene on different substrates.

Raman spectroscopy is used to evaluate the structural perfection of epitaxial graphene films before and after deposition of a Ni layer to their surface by magnetron sputtering. Two deposition modes with different gas pressures and deposition times are investigated. It is found that Ni deposition under low pressure combined with long deposition time does not lead to the separation of graphene/Ni film. On the other hand, higher pressure and shorter deposition time results in successful but uncontrollable exfoliation of graphene together with the Ni film. The results obtained will serve as the basis for the optimization of Ni deposition modes, in order to achieve complete exfoliation of the graphene film from the SiC substrate without damaging the graphene layer.

Hybrid structures consisting of emitting carbon nanodots bound to the surface of monodisperse spherical silica particles, which function as microresonators, are synthesized. The carbon nanodots are deposited onto the particle surface through controllable coagulation in three different solvents: ammonia, hydrochloric acid, and glycerol. In photoluminescence spectra of hybrid structures, throughout the entire range of carbon nanodot emission, which extends from UV to near IR, we observe the presence of intensive narrow bands related to emission of the nanodots in the whispering gallery modes of a spherical microresonator. All the observed bands are identified by comparing the spectral positions of whispering gallery modes calculated using the transfer matrix method for spherical waves to the experimental data.

A relativistic version of a composite ab initio treatment of molecular spectroscopy and thermochemistry is developed, focusing on high-accuracy description of the properties of actinide (An) containing species. It is based on combining the calculation results at levels of theory with sufficiently full account of electron correlation, e.g., at the CCSDT(Q) level, but tackling only scalar relativity, with those obtained from more rigorous four-component relativistic calculations with the Dirac–Coulomb Hamiltonian. High accuracy achievable via this approach is revealed taking the examples of thorium and americium monoxide molecules. The errors in ab initio values for the bond length re, vibrational frequency ωe, and atomization energy D0 of the ThO molecule did not exceed 0.001 Å, 2.5 cm–1, and 0.5 kcal/mol, respectively. The composite numerical values for the first ionization potentials of the AmO molecule and the Am atom deviate from the experimental data just by 0.03 eV and 1 cm–1, respectively. For the first time, the proposed approach enabled high-accuracy evaluation of the molecular constants re, ωe and D0 for AmO and AmO+, as well as the second and third ionization potentials of the Am atom. The calculation results are indicative of a minor actinide contraction of the An–O bonds on going through the molecular series ThO → UO → AmO: the bond length in AmO is by 0.0073 Å shorter than that in ThO. The re(An–O) value is shown to be linearly dependent on the actinide atomic number in the periodic table. The results obtained may be used as benchmarks for parametrizing and calibrating the DFT functionals designed for treating An-containing molecules.

The buffer layer samples grown on the Si-face of the 4H- and 6H-SiC substrates were heated in a hydrogen flow at different temperatures (600–900 °C) and heating times (40–60 min) in order t...

Spectral and nonlinear optical properties of InAs nanowires synthesized via molecular beam epitaxy suspended in isopropanol are studied in this work at room temperature. The absorption spectra with a characteristic maximum at a wavelength of 235 nm, as well as the Raman spectra in a range of 180–280 cm–1, are obtained. The nonlinear transmittance of InAs nanowires with diameters less than the exciton Bohr radius was firstly investigated by a two-photon excitation in the transparent region (λ = 468 nm). The effect of cumulative bleaching, the manifestation of which is associated with the dynamic Stark effect, was discovered.

The results of studies of nominally undoped epitaxial p-GaSb layers grown by metal–organic vapor-phase epitaxy at a ratio TMSb/TEGa in the range from 1 to 50 are reported. At the ratio TMSb/TEGa = 50, GaSb epitaxial layers, whose resistivity is 400 Ω cm, are produced. It is shown that, for such layers, the crystal quality assessed by several methods remains comparable to the quality of n-GaSb substrates used for the growth of nominally undoped GaSb layers.

Systematic studies of the effect of the electron concentration on the Raman spectra of single-layer graphene films have been carried out. The samples were grown by thermal destruction of the Si-face of the 4H-SiC substrate. Analysis of the results led us to the conclusion that for the correct estimation of the electron concentration and strain values in graphene using Raman spectroscopy data it is necessary to take into account the value of the Fermi velocity in the graphene layer. This conclusion is valid for graphene on any other substrate as well, since the Fermi velocity in graphene depends on the dielectric constant of the substrate.

We report the results of systematic Raman spectroscopy studies of AlxGa1 –xN (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric conditions and growth fluxes. The high-intensity asymmetric low-frequency peak obeying Bose statistics is discovered in Raman spectra of the layers grown by temperature-modulated epitaxy at strongly Ga-enriched conditions. Theoretical model is developed to explain the origin and the high intensity of the observed low-frequency peak, which is attributed to the presence of excessive metallic gallium in AlGaN layers and can be explained by vibrations of gallium clusters with a diameter of ~1 nm. The nature of the low-frequency peak is similar to that of the boson peak in glasses, which occupies the same frequency range in Raman spectra. We demonstrate the capabilities of Raman spectroscopy as an express and non-destructive technique for optimization of growth conditions of AlGaN layers to achieve simultaneously the atomically-smooth droplet-free surface morphology and the high structural quality.

We present an extensive theoretical and experimental study to identify the effect on the Raman spectrum due to interface interdiffusion between GaN and AlN layers in short-period GaN/AlN superlattices (SLs). The Raman spectra for SLs with sharp interfaces and with different degree of interface diffusion are simulated by ab initio calculations and within the framework of the random-element isodisplacement model. The comparison of the results of theoretical calculations and experimental data obtained on PA MBE and MOVPE grown SLs, showed that the bands related to A1(LO) confined phonons are very sensitive to the degree of interface diffusion. As a result, a correlation between the Raman spectra in the range of A1(LO) confined phonons and the interface quality in SLs is obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy.

Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (VB−). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating VB− centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the VB− centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the VB− spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the VB− spin embedded in the hBN as a probe.

Monodisperse spherical nanoporous silicon (np-Si) particles of submicrometer size are fabricated with mesoporous silica particles as a template. Silicon is synthesized within the mesopores of monodisperse silica particles by the thermal decomposition of monosilane. Then, the template material (a-SiO2) is removed by wet etching. The particles obtained have a small root-mean-square size scatter (no more than 10%) and large specific surface area (250 m2 g–1) and pore volume (0.5 cm3 g–1). It is shown that np-Si particles exhibit photoluminescence in the visible and near-IR (infrared) spectral ranges.

The results of studies of the structural and optical properties of two-dimensional GaSe layers grown by molecular-beam epitaxy on GaAs(001) and GaAs(112) substrates using a valve cracking cell for the Se source are reported. The influence of the MBE growth parameters (the substrate temperature, Ga flux intensity, Se/Ga incident flux ratio) on the surface morphology of the layers is studied. By means of transmission electron microscopy, electron diffraction technique, and Raman spectroscopy, it is shown that the structure of the GaSe layers corresponds to the γ-GaSe polytype. From X-ray diffraction analysis, it is established that there exist α-Ga2Se3 inclusions in the GaSe layers grown under conditions of high enrichment of the growth surface with Se.

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.

Spherical micro-mesoporous silicon (mSi) particles were fabricated by thermal decomposition of monosilane (SiH4) within the mesopores of monodisperse silica particles (MSP) and subsequent etching out of the template material. The thermal destruction of SiH4 occurs within the whole pore volume uniformly because in the thermal chemical vapor deposition method we developed, the limiting stage of the process in which MSP pores are filled with silicon is the reaction in which monosilane is decomposed, rather than its diffusion within template mesopores. The porosity of the mSi particles synthesized can be varied without changes in the shape and outer diameter of the particles by varying the parameters of the technological process of silane decomposition. The particles have large Brunauer-Emmett-Teller specific surface area (250–350 m2 g−1) and pore volume (0.3–0.5 cm3 g−1). For the first time the obtained submicron spherical porous silicon particles are monodisperse with a size scatter not exceeding 10%, which provides the identity of their hydrodynamic and adsorption properties so important for biomedical applications. We introduced the cytostatic drug doxorubicin (DOX) into mSi pores by the physical adsorption method. It was shown that DOX is desorbed from the mSi pores and penetrates into K-562 cancer cells, with local DOX concentration maxima observed in the intracellular space. The cytotoxicity of the mSi and mSi/DOX particles was studied, and the inhibition capacities of the cancer-cell proliferation by doxorubicin adsorbed by mSi particles and a DOX solution were compared in vitro. It was shown that the half-maximal inhibitory concentration (IC50) is four times lower under the action of DOX-loaded mSi particles as compared with free doxorubicin.

Multigraphene films have been for the first time obtained on the surface of quartz glass via carbonization of polyimide Langmuir–Blodgett films. The Raman spectra of the films show bands G and D and a broad band at 2300–3200 cm–1, which are characteristic of graphite-like films. The transmission electron microscopy demonstrated that the films are constituted by “stacks” of layers spaced by 0.36 nm. The surface resistance of the 5-nm-thick films was 1.2 ± 0.2 kΩ, and the transmittance was 87% at λ = 550 nm. The transmittance was 97% in the IR part of the spectrum and 70–80% in the UV part.

The electric, piezoelectric, and optical properties of colloidally synthesized CsPbBr3 nanocrystals (NCs) are studied by combined scanning probe microscopy and optical spectrometry. It is found that the CsPbBr3 NCs have a cubic shape with an edge length of 10 nm. When deposited on a substrate, these NCs gather into faceted agglomerates up to several hundred nanometers in size. It is shown that the photoluminescence spectra contain, in addition to the main narrow edge-luminescence line (2.47 eV), two additional broad defect lines lying 40 and 200 meV lower than the main line. The NC agglomerates have a low surface potential (~20–30 mV) and contain a small amount of charges. It is shown that piezoelectric modulus d33 of CsPbBr3 NC agglomerates does not exceed 1 pm/V.

We investigated the growth of III-N/graphene heterostructures as a single process in a MOVPE reactor. Raman spectra revealed that graphene can be successfully deposited on sapphire substrate by propane pyrolysis if temperature exceeds 1060 °C and hydrogen is used as a carrier gas. GaN epitaxial layers and heterostructures on such graphene using both high-temperature AlN buffer layer and low-temperature GaN nucleation layer was demonstrated. Analysis of surface morphology and X-Ray diffraction curves indicate that GaN quality depends on graphene thickness. Use of copper electroplated Ni-based contact layer combined with thermal shock allows exfoliation of large-area III-N LED structures from sapphire.

The structural and electronic characteristics of epitaxial graphene films grown by thermal decomposition of the Si face of a semi-insulating 4H-SiC substrate in an argon environment have been studied by a large set of analytical techniques. It is shown that the results of a complex study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high-quality single-layer graphene films. The charge-carrier concentration in the graphene layer was within 7 × 1011–1 × 1012 cm–2, and the maximum mobility of electrons at room temperature approached 6000 cm2/(V s).

Transition metal oxyborates M3(BO3)2 (M = Mn, Co, Ni) belong to a group of materials with the kotoite structure and many of them demonstrate complex magnetic behavior as a result of competing interactions between magnetic ions in nonequivalent crystallographic positions. In this paper, we report results of the detailed infrared and Raman spectroscopic studies of a Co3(BO3)2 single crystal. Most of the phonons are observed and identified. Unusually large phonon shifts, in comparison to isostructural compound Ni3(BO3)2, were registered in the low- and mid-infrared frequency range (100–700 cm−1) of the spectra. The experimental findings are supported by the ab initio simulations of the lattice dynamics, which allow us to propose the normal-mode assignments. We argue that the large phonon shift between cobalt and nickel compounds are associated with changes of force constants induced by the changes of M–O bond lengths within the two types of octahedral MO6 groups. In addition to the first-order Raman scattering, intense second-order Raman scattering was detected due to the resonant enhancement regime. Furthermore, we performed the single crystal XRD experiments which did not show any detected evidences of magneto-structural phase transition previously observed in Ni3(BO3)2.

The electron lens in the Fermilab Integrable Optics Test Accelerator (IOTA) will enable new research in nonlinear integrable optics, space-charge compensation, electron cooling, and the stability of intense beams. This research addresses scientific questions on high-brightness beams and operational challenges of high-power accelerators for nuclear and particle physics. We review the roles that electron lenses play in this field and the physical principles behind their applications. The design criteria and specifications for the IOTA storage ring and electron lens are then discussed. We conclude with a description of the components of the apparatus.

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

Despite the importance of experimental confirmation, the ability of wide range of brain mapping methods to discover brain cognitive architectures in most studies can’t be evaluated directly. Only in rare cases, when due to medical need, it is possible to conduct experiments during neurosurgical operations, is it possible to assess the accuracy of certain approaches. In this paper we evaluate, how well we can reveal brain cognitive architectures structure by established and novel approaches based on fMRI data, with special focus on resting-state fMRI, and how well these findings match Direct Cortical Stimulation mapping data, which is a gold standard in neurosurgery. We illustrate our approach on three representative examples with different motor and cognitive architectures mapping. We found a significant correspondence between predicted maps and intraoperative data for both brain networks. This indicates that resting-state fMRI could be used as an additional source of information for neurosurgical planning, though its applicability to exploring and describing the whole variety of brain architectures for research purposes should be investigated in future.

GaInP microdisks contained InP/GaInP quantum dots having lateral size ∼150 nm and 1-5 μm−2 were investigated with help of microphotoluminescence technique. Experiments carried out in confocal, time-resolved and low-temperature modes. Comparison of results allowed to conclude that overlap of quantum dot emission area with whispering gallery mode antinode results in faster luminescence lifetime (Purcell effect). Whispering gallery mode lasing was detected. Obtained threshold power values were following 6 µW (Q=4500, T=8.5 K) and 0.4 µW (Q=7400, T=80 K).

In this work, we demonstrate the possibility of using local anodic oxidation (LAO) for fabricating optical devices based on thin transition metal dichalcogenides (TMDC) layers. By LAO we fabricated an optical cavity from 6-layered MoSe2 flake transferred on Si/Au substrate. Optical properties were investigated by measuring microphotoluminescence. The cavity exhibits three order of magnitude enhancement of the flake's photoluminescence, which is only one order of magnitude lower than the monolayer on a SiO2 substrate. Here we show that LAO is a high-precision lithography method suitable for fabricating optoelectronic devices made of thin TMDC layers.

Multilayer (Ni/ZrO2)45 nanostructures are obtained by the simultaneous sputtering of two Ni and ZrO2 targets and the deposition of material on moving substrates. The multilayer nature of the obtained samples was confirmed by small-angle X-ray reflectometry. It has been established that with a change in the thickness of nickel layers (from 1.5 to 10.8 nm), their morphology changes from discrete to continuous. A change in the morphology of nickel layers radically changes the electrical and magnetoresistive properties of multilayer nanostructures. Magnetoresistive effect is observed in the multilayer structures with discreet nickel layers.

The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp and dσ/d cos(θ), and the total cross-sections in a limited phase-space in momentum and scattering angle (p > 300 MeV/c and θ ≤ 45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement., Journal of High Energy Physics, 2020 (10), ISSN:1126-6708, ISSN:1029-8479

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40 σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions., Physical Review Letters, 124 (16), ISSN:0031-9007, ISSN:1079-7114

A nanocomposite in the form of monodisperse spherical mesoporous silica particles (mSiO2) filled with GaN:Eu3+ is synthesized by the template method. The method is based on the capillary impregnation of pores of mSiO2 particles with a melt of crystal hydrates of gallium and europium (0.22 wt %) nitrates, followed by thermal decomposition and ammonia treatment. It is shown that nanocomposite particles contain hexagonal GaN:Eu3+, are of spherical shape, monodisperse and do not coalesce with each other. The photoluminescence spectra of the mSiO2/GaN:Eu3+ particles show a group of lines characteristic of intracenter transitions in Eu3+.

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.

Results of the studies of the properties of single-crystalline bulk β-Ga2O3 grown from the melt are presented. High chemical purity and phase uniformity of the grown material are demonstrated. Raman spectroscopy studies confirmed low energies of optical phonons in β-Ga2O3, which makes it a promising material for laser optics applications.

We studied electrical transport in transistors fabricated on a surface of high quality epitaxial graphene with density of defects as low as 5·1010 cm−2 and observed quasistatic hysteresis with a time constant in a scale of hours. This constant is in a few orders of magnitude greater than the constant previously reported in CVD graphene. The hysteresis observed here can be described as a shift of ∼+2V of the Dirac point measured during a gate voltage increase from the position of the Dirac point measured during a gate voltage decrease. This hysteresis can be characterized as a nonvolatile quasistatic state memory effect in which the state of the gated graphene is determined by its initial state prior to entering the hysteretic region. Due to this effect the difference in resistance of the gated graphene measured in the hysteretic region at the same applied voltages can be as high as 70%. The observed effect can be explained by assuming that charge carriers in graphene and oppositely charged molecular ions from the solution form quasistable interfacial complexes at the graphene interface. These complexes likely preserve the initial state by preventing charge carriers in graphene from discharging in the hysteretic region.

The effect of atomic aluminum deposited onto sapphire substrates with different nitridation levels on the quality of AlN layers grown by ammonia molecular-beam epitaxy is investigated. The nitridation of sapphire with the formation of ~1 monolayer of AlN is shown to ensure the growth of layers with a smoother surface and better crystal quality than in the case of the formation of a nitrided AlN layer with a thickness of ~2 monolayers. It is demonstrated that the change in the duration of exposure of nitrided substrates to the atomic aluminum flux does not significantly affect the parameters of subsequent AlN layers.

We report on the thorough investigation of light emitting diodes (LEDs) made of core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) in the outer shell, which are grown on patterned substrates by metal-organic vapor phase epitaxy. The multi-bands emission of the LEDs covers nearly the whole visible region, including UV, blue, green, and orange ranges. The intensity of each emission is strongly dependent on the current density, however the LEDs demonstrate a rather low color saturation. Based on transmission electron microscopy data and comparing them with electroluminescence and photoluminescence spectra measured at different excitation powers and temperatures, we could identify the spatial origination of each of the emission bands. We show that their wavelengths and intensities are governed by different thicknesses of the QWs grown on different crystal facets of the NRs as well as corresponding polarization-induced electric fields. Also the InGaN incorporation strongly varies along the NRs, increasing at their tips and corners, which provides the red shift of emission. With increasing the current, the different QW regions are activated successively from the NR tips to the side-walls, resulting in different LED colors. Our findings can be used as a guideline to design effectively emitting multi-color NR-LEDs.

An upgrade of the long baseline neutrino experiment T2K near detector ND280 is currently being designed. The upgrade program includes the development a new highly granular fully active scintillator neutrino detector as a neutrino target. The baseline concept of the detector represents an array of about 2 × 1 0 6 small scintillator cubes each of 1 cm 3 . The 3D signal readout from each cube is provided by three orthogonal 1.0 mm Kuraray Y11 multiclad WLS fibers read out by SiPMs. A small prototype of the detector assembled of 125 cubes was tested in a beam of charged particles as well as with cosmic muons. Obtained parameters of the prototype are reported in this paper.