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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.

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.

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.

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.

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.

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.

Surface electronic properties of the native-oxide-covered and sulfide-passivated InN grown on the Si(111) substrate were studied by photoemission spectroscopy induced by synchrotron radiation, as well as by photoluminescence and atomic-force microscopy. It was found that the treatment of the native-oxide-covered InN surface with the solution of ammonium sulfide in 2-propanol results in the increase of the surface band bending by 0.7–0.8 eV. Sulfide passivation causes increase in the photoluminescence intensity of InN, as well as the appearance of the photovoltage induced by illumination with red light, which is the evidence of the reduction of the surface recombination velocity due to sulfide passivation. These improved electronic properties remain stable for at least 20 months of the exposure in air.

The site-controlled selective area growth of N-polar GaN nanorods (NR) was developed by plasma-assisted MBE (PA MBE) on micro-cone-patterned sapphire substrates (µ-CPSS) by using a two-stage growth process. A GaN nucleation layer grown by migration enhanced epitaxy provides the best selectivity for nucleation of NRs on the apexes of 3.5-µm-diameter cones, whereas the subsequent growth of 1-μm-high NRs with a constant diameter of about 100 nm proceeds by standard high-temperature PA MBE at nitrogen-rich conditions. These results are explained by anisotropy of the surface energy for GaN of different polarity and crystal orientation. The InGaN single quantum wells inserted in the GaN NRs grown on the µ-CPSS demonstrate photoluminescence at 510 nm with a spatially periodic variation of its intensity with a period of ∼6 µm equal to that of the substrate patterning profile.

Multilayer (Mg/NbOx)82 nanostructures with different thickness of Mg layers and the constant thickness of NbOx layers have been prepared. The samples were obtained by ion-beam sputtering of metal and ceramic target and multiple consecutive depositions of NbOx and Mg layers onto substrates. The multilayering of the samples was confirmed by X-ray small-angle reflectometry. The thickness of one bilayer (magnesium layer + niobium oxide layer) was determined based on the small-angle data. The thickness of one bilayer in the studied structures was varied from 2.2 nm to 6.2 nm. Despite the separated deposition the magnesium layer's surface in the (Mg/NbOx)82 nanostructures was partially oxidized. The electric percolation transition was observed in the (Mg/NbOx)82 nanostructures at increase of the Mg layers thickness. At small bilayer thicknesses (less than 4.5 nm) the Mg phase is the partially oxidized nanogranules and the charge transfer in such samples is carried out by electron tunneling between the nanogranules. At larger bilayer thickness, the multilayer samples exhibit usual metallic conductivity.

The 5D0 – 7Fn fluorescence of Eu3+ ions in Y2O3 thin films grown on Al2O3 substrates was studied. The films were produced by laser molecular beam epitaxy. The spectral lines revealed small inhomogeneous broadening which evidences for small distortions of cubic lattice. The measurements of the fluorescence lifetimes provided an indication of photon density of states and local field effects due to a nearby dielectric interface on radiative transitions in impurity ions in thin crystalline films.

The work is devoted to the study of p-GaN: Mg epitaxial layers grown by the ammonia MBE technique. We find that the conductivity of GaN layers doped with Mg does not change with a postgrowth heat treatment. Formation of Mg3N2 nanocrystallites on GaN surface during epitaxial growth of the GaN layer with a high magnesium doping level was detected by the RHEED technique for the first time. It was shown that the Mg3N2 nanocrystallites formation competes with the acceptor states formation process. It has been proposed that the growth temperature can be applied as an additional “tuning” mechanism which affects the Mg incorporation into the growing GaN:Mg layers.

We report on Ga 2 O 3 deposition on c-plane sapphire substrates by hydride vapour phase epitaxy using metallic gallium, hydrogen chloride and dry air as precursors. High deposition rate up to 250 µm/h has been realized. As confirmed by X-ray diffraction and micro-Raman measurements, produced films consisted of pure monoclinic β-Ga 2 O 3 phase and were (−201) oriented. The full width at half maximum (FWHM) for (−201) rocking curve was decreasing with increasing GaCl flow. The narrowest FWHM of 20 arcmin has been detected.

Background Severe traumatic brain injury (STBI) is almost always accompanied by movement disorders. The use of electroencephalography (EEG), supplemented by mathematical analysis, in combination with functional magnetic resonance imaging (fMRI) expands the possibilities of studying brain neuroplasticity as a basis for compensation post-traumatic motor disorders. Material and methods Multichannel EEG and fMRI 3T during passive motor test (hand finger clenching by experimenter) were performed in 28 patients with STBI and 17 healthy subjects. The most detailed spectral-coherent analysis of spatial EEG changes was performed in 10 patients with varying degrees of hemiparesis, but similar to the norm fMRI response. Results It was revealed that individual EEG restructurings in a passive motor test in patients with STBI are characterized by significant variability and the inclusion of the brain regions not typical for the norm. Secondary statistical analysis showed that the topography of EEG coherence changes shows the greatest correlation with the degree of hemiparesis: increased reactivity of the frontal-central areas in the ipsilateral hemisphere relative movement with mild hemiparesis and the inclusion of both hemispheres as the motor disorders increase. Localization of these changes is similar to the topography of the fronto-pontine, parietotemporo-pontine and occipito-mesencephalic motor tracts cortical projections. Conclusions This results demonstrate a greater sensitivity of EEG responses to the degree of motor defect compared with hemodynamic (fMRI). They confirm our hypothesis put forward earlier on the possible participation of the extra-pyramidal system in compensating for the post-traumatic motor defect. Supported by RFFI 18-013-00355 .

Severe traumatic brain injury (STBI) is nearly always comes with movement disorders. Objectives Comparison of cerebral structural-functional control of movement’s opportunity and implementation in healthy volunteers and patients with various degrees of hemiparesis after STBI. Methods Observation groups: 28 patients with SOBI (main) and 17 healthy volunteers (control). 3T fMRI recorded at rest and passive right hand finger clenching (by experimenter). Individual and group analysis of Sensorimotor resting-state network and motor fMRI responses was carried out by FSL software (ICA algorithm), SPM8 and CONN. Topography and volume activated brain regions as well as brain connectivity between them were determined. Results At STBI in the majority cases without hemiparesis or with its mild degree, neuroanatomy of the rest-state sensorimotor network and “passive” motor fMRI response are close to normal. However with an increase of hemiparesis expression we have seen an asymmetric reduction of sensorimotor resting-state network and more diffuse “passive” fMRI response - with activation of nonspecific to movement brain structures: frontal and temporal cortex, cerebellar vermis and others. Discussion A comparison of the passive movement’s functional anatomy in STBI with motor system topographic anatomy indicates a variability in movement disorders compensation mechanisms based on the possible inclusion of different “functional doublers”, such as fronto-pontinus conduction tract as well as occipito–temporopontinus. This hypothesis confirmed by comparative analysis of brain connectivity within different neuroanatomical motor tracts in healthy volunteers and patients with STBI. Conclusions The retrieved data can be useful to develop individualized neurorehabilitation programs of post-traumatic motor disorders. Supported by RFFI 115-36-01038.

Radiation-produced defects in doped and nominally undoped n-GaN with charge carrier concentrations in a range of 4 × 10 16 cm -3 to about 2 × 10 18 cm -3 are investigated. Layers of n-GaN are irradiated with fast electrons at 0.9 MeV, 60 Co gamma rays and protons at 150 keV. The production rates of radiation defects in n-GaN are estimated and compared with literature data. Annealing processes of radiation defects in n-GaN in the temperature range 100-700 °C are also discussed. The annealing behavior appears to be complicated. Two temperature intervals, from T= 100 to 400°C and from T = 500 to 700°C, are characteristic for modification and annealing processes of radiation-produced defects in n-GaN.

Formation and annealing of radiation-induced defects in doped and nominally undoped n-GaN are investigated by means of electrical measurements and Raman spectroscopy. The production rate of defects turned out to be dependent on the dopant concentration. This suggests that at least one kind of native defects is involved in impurity–defect interactions at room temperature. Two prominent stages of defect annealing are revealed. The annealing processes at T ≥100°C are associated with mobile native defects. A considerable fraction of radiation defects is still present in the materials after annealing to T ≥750°C.

We present the results of a detailed study of the first and second-order Raman scattering in wurtzite GaN and AlN at room and liquid helium temperatures. A complete group-theory analysis of phonon symmetry and optical selection rules permitted us to assign the observed features in the second-order Raman spectra to combinations of phonons at the Γ, K, and M points of the Brillouin zone. The joint treatment of these results with lattice dynamical calculations based on phenomenological interatomic potential model allowed us to obtain the reliable data on phonon dispersion curves in bulk GaN and AlN.

The results of Raman spectra studies on cubic GaN epitaxial layers grown on (0 0 1)GaAs and GaP substrates are presented. A distinct feature observed at the low-frequency edge of the LO phonon line in the backscattering spectra is shown to be due to the upper surface polariton mode. Our studies reveal high sensitivity of the surface polariton mode to the doping level and quality of the GaN–substrate interface.

We present the results of Raman experiments on cubic GaN epitaxial layers grown on (0 0 1) GaAs substrates. A distinct line observed at the low-frequency edge of the LO phonon in the backscattering spectra is shown to be due to the upper surface polariton mode. We show that the high transparency of the layer results in a weak efficiency of scattering by the lower polariton mode and strong increase of the scattering in backward configuration. The research reveals a high sensitivity of the surface polariton mode to the film thickness, doping level and quality of the GaN GaAs interface.