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An empirical model of the saltating aleurite and sand particle size distribution has been developed based on the measurements of the differential number concentrations in the size range from 30 to 330 μm using a size distribution approximation of the sum of two lognormal distributions. Approximations of the vertical profiles of distribution parameters have been derived for the layer from 0 to 15 cm. Vertical profiles of the modal size of the coarse particles in the saltation layer from 3 to 15 cm and in the surface air layer from 0.125 to 16 m are compared with measurements in the Aral region.

Vertical profiles of the total saltating particle concentration have been constructed for a range of wind speed changes in the surface layer of the atmosphere from 5.5 to 10.5 m/s, and the profiles of the concentration of aleurite (silt) and sandy particles according to measurements in a desertified area in the Astrakhan Region under conditions of quasi-continuous saltation have been found. In the saltation layer from 0 to 15 cm, the concentration of silty particles with a size of 47 μm decreases two times more slowly than the concentration of sand particles with a size of 156 μm. In the lower saltation layer about 9 cm thick, the logarithmic gradient of the total concentration does not depend on the wind speed, and in the upper saltation layer it changes from –0.40 to –0.21 cm–1 with an increase in the wind speed in the atmospheric surface layer from 5.5 to 10.5 m/s. It is shown that, in contrast to the lower saltation layer at heights of 11 and 15 cm, the dependences of the particle concentration on the wind speed turned out to be nonlinear. For the lower and upper layers of saltation, approximations of the concentration of saltation particles are obtained as a function of height, wind speed, and the threshold speed of saltation.

A Cu2ZnSnS4 (CZTS) thin film deposited on Mo contact film using direct current magnetron sputtering and sulfurized is studied. The morphological and structural investigations are focused on the interface between the CZTS film and the back Mo layer. The film is shown to be polycrystalline with an average grain size of 0.8 µm and of a high conductivity of the grain boundaries. It is also characterized by a suitable elemental composition with a noncritical deviation from the stoichiometry across the film depth. This results in the optical bandgap of 1.48 eV, which is optimal for solar cell absorbers. Raman spectra show low FWHMs of two A-symmetry dominant bands for CZTS thin film, which confirms a high quality of the crystal structure over a large area. At the same time, ZnS secondary phase is found on the film surface, while MoS2 is detected in the depth using a resonant excitation. The Raman mapping shows a non-uniform distribution of MoS2 along the interface between the CZTS film and the back Mo layer.

Size distributions of saltating aleurite and sand particles have been measured in a windsand flux in a desertified area in Astrakhan oblast. The distributions are approximated by a sum of lognormal distributions for the aleurite-sand and aleurite fractions. The threshold wind velocity for the total particle concentration is determined under conditions of nonintermittent saltation. It is found that the threshold velocity depends on the size of saltating particles. Empirical approximations of the total number concentration and differential particle concentration of aleurite and sand particles as functions of wind velocity are obtained.

Two-dimensional (2D) MoS2 possesses unique optical and electrical properties and has many practical applications in nano-optoelectronics. Raman spectroscopy allows readily identify monolayer of MoS2, but the unambiguous determination of the number of layers in a few-layer structure remains a challenging task. In this work, the modification of frequencies of the most intense bands arising from in-plane and out-of-plane vibrations in the spectra of mono- and few-layer MoS2 crystals is studied experimentally, using the Raman scattering technique, and systematically analyzed theoretically, considering the influence of the interlayer interaction as well as the anharmonic interactions within the layer. A good agreement between experimental spectra and theoretical simulations is demonstrated, which allows to estimate the thickness of few-layer MoS2 and also determine parameters of the interlayer and anharmonic interactions. Possible effects of Fermi resonance in 2D MoS2 and the corresponding frequency shift of fundamental modes are considered. The proposed theoretical approach can be used to analyze Raman spectra, estimate the interlayer interaction, anharmonism, and the number of layers for other 2D layered materials.

According to satellite monitoring data (MODIS/Terra), the spatial distribution of the aerosol optical depth (AOD) at a wavelength of 550 nm for the summer smog of 2007 over the North China Plain (NCP) and adjacent areas has been obtained. Areas over which the AOD is higher due to regional anthropogenic contamination sources near Beijing and Shanghai, as well as the smoke haze forming due to agricultural burning (the southwest part of the NCP), have been revealed. The similarity of optical and microphysical characteristics of aerosol in the smoke haze over the NCP and in the Russian territory has been found: (i) the decisive contribution to the optical characteristics of smoke aerosol is made by the fine mode and (ii) the attenuation spectra in the wavelength region 340–1020 nm are approximated (in logarithmic coordinates) by parabolas or fourth degree polynomials. The monitoring data at the AERONET Beijing site show that the single scattering albedo in the summer smog over the NCP is on average less (0.91) than in the smoke haze in the Russian territory (0.95–0.96). The radiative regimes of the atmosphere are significantly different: in the smog, the aerosol radiative forcing efficiency is lower approximately by 30% at the top of the atmosphere and higher by 30% at the bottom of the atmosphere than in the smoke haze.

Saltating particle aleurite mode is discovered in the windsand flux over desertified area. Approximation of the saltating particle distribution measured is received using two lognormal distribution functions. It is shown that aleurite and sand number concentration particles in the windsand flux depends on wind velocity in the surface layer in different way.

The saltating particle aleurite mode has been discovered in the wind–sand flux over a desertified area. The approximation of the measured saltating particle distribution was found using two lognormal distribution functions. In the wind–sand flux, the countable concentrations of aleurite and sand particles depend differently on the wind velocity in the atmospheric surface layer.

Using maximum aerosol optical depth (MAOD) spatial distribution formation technique the optically dense haze expansion scales in period from 15 to 31 July 2016 over Eurasia are estimated in during great Siberian smoke haze (SSH) with the area 16 mln km2 about, smog over the Northern China Plain (2 mln km2), dust haze in Takla Makan desert (0.8 mln km2) and hazes in India and Pakistan (1 mln km2 approximately). Empirical distribution function (EDF) MAOD is received which is approximated by linear function of MAOD logarithm. Aerosol optical depth (AOD) spatial distribution at wavelength 550 nm in SSH is analyzed. Total smoke aerosol mass assessment in SSH (3.2 mln tons) is evaluated. Smoke aerosol (SA) mass during maximum growth period from 22 July to 26 July 2016 over Siberia (50°-70°, 60°-120 °E) was equal 2 mln tons approximately. Aerosol index (AI) temporal variability is illustrated visually SA composition qualitative change in SSH during long-range transport. It is shown that AI variations are correlated with AOD variations. Aerosol radiative forcing (ARF) at the top and the bottom of the atmosphere over Siberia from 22 July to 26 July 2016 is estimated (average ARF are equal –68 and –98 W/m2). EDF AOD and EDF ARF at the top of the atmosphere are approximated by exponential and power function of AOD correspondingly.

The technique for constructing the spatial distribution of maximum aerosol optical depth (MAOD) has been used to estimate the optically dense haze expansion scales from July 15 to 31, 2016 (over an area of 20 million km2), including the record-scale Siberian smoke haze (SSH) with an area of around 16 million km2, smog over the Northern China Plain (around 2 million km2) and the adjacent offshore zones, a dust haze in the Taklamakan Desert (around 0.8 million km2), and hazes in India and Pakistan (almost 1 million km2). The empirical distribution function (EDF) of the MAOD is approximated by a linear function of the MAOD logarithm. The spatial distribution of aerosol optical depth (AOD) at a wavelength of 550 nm in the SSH has been analyzed. The total mass of smoke aerosol in the SSH has been estimated to be 3.2 million t, including around 2 million t over the territory of Siberia (50–70° N, 60–120° E) during the peak haze from July 22 to July 26, 2016. The qualitative composition of smoke aerosol in the SSH during its transport is illustrated through spatial and temporal variations in the aerosol index (AI). It is shown that AI variations are correlated with AOD variations. Aerosol radiative forcings (ARFs) at the upper and lower atmospheric boundaries over Siberia from July 22 to 26, 2016, have been estimated (with an average ARF of –68 and –98 W/m2). The EDFs of AOD and ARF at the upper atmospheric boundary have been approximated by exponential and power function of AOD, respectively.

We report a study of the photoconductivity mechanism and transport paths of photoexcited charge carriers in the GeSn/Ge/Si heterostructures. The dark conductivity was studied as a function of temperature, which allowed to identify of the presence of deep levels at EV+(100÷130) meV. We have established that point defects are the source of a band of electronic states and determine the photoconductivity response. The photocurrent dependencies on excitation intensity demonstrate that the main conduction occurs mainly through the Ge layer under low pumping and through the Si substrate under high one, since the GeSn top layer is much thinner has a much higher conductivity. This detailed understanding of the recombination processes is of critical importance for developing GeSn/Ge-based optoelectronic devices.

Automated instruments for measuring of (1) the dust aerosol particle concentrations and the dust aerosol particle size distribution function, (2) the vertical turbulent fluxes of the dust aerosol and (3) the electric characteristics of the windsand flux. The dust aerosol particle concentrations in the range from 0.5 to 5.0 mcm at heights 2 m and 20 cm were measured. The vertical turbulent fluxes and the uplift rate (reached 5 cm/s) of the dust aerosol were determined. Influence of the convective structures on the emission and turbulent fluxes of the dust aerosol was found. It was established that the average volume electric charge of the dust aerosol reached – 70 nC/m3 and the electric charge density at the surface did not exceed + 25 nC/m2 .

In(Ga)As quantum dots (QDs) are used in photonic and electronic devices with novel functionalities [1, 2, 3, 4, 5], advanced energy-efficient ‘green’ communication systems with ultra-large bit rate such as energy-efficient lasers [6, 7] and QD optical amplifiers [1], solar cells [8, 9, 10], single-photon emitters [11, 12, 13].

This paper reports the estimated scales of optically dense haze over Eurasia for the period from July 15 to July 31, 2016, including the Siberian smoky haze (with a smoke area of 16.3 million km2) over Siberia and European Russia, and also many countries of Europe, Kazakhstan, and other countries of Asia, the human-induced smog over the North Chinese Plain (about 2 million km2), dusty haze in the Takla-Makan Desert (about 0.8 million km2), and haze over India and Pakistan (approximately 1 million km2).

A four-channel photoelectric counter has been designed and manufactured for the measurements of saltating sand concentration fluctuations and size distribution function of particles with diameters >30 μm over desertified areas. The measurement results are given. It is shown that the vertical profile of the saltating sand concentration does not change on average in the altitude range from 3 to 7 cm over a desertified area in the neighborhood of the Volga. The distribution function of saltating sand particles over the desertified area is approximated with satisfactory accuracy by the lognormal distribution near the distribution maximum. Noticeable distinctions between the abovementioned distributions for large and small sand particles are observed.

Aleurite particle saltation trajectories have been calculated using the saltation dynamics model. Variability of the saltation trajectory parameters including of the height, range and particle flight time was analyzed. Saltation parameter dependencies from particle diameter and the friction velocity are approximated. Influence the lift-off velocity and the lift-off angle on the aleurite particle saltation trajectories was considered. Sliding coefficient dependencies from time during aleurite saltating particle transport were received for the various values of the particle diameter, friction velocity, lift-off velocity and lift-off angle.

We have characterized the large-scale smoke pollution of the European territory of Russia (ETR) and adjoining areas in July 2017, caused by long-range transport from forest-fire areas in Siberia, confirmed by calculations of ten-day back trajectories of air mass motion to the ETR urban area, spanning Archangelsk to Rostov-on-Don. The smoke-laden ETR area with an AOD > 0.3 (average value being 0.43 and maximal value being 2.5) on July 25, 2016, covered 5 million km2, and the total smoke mass was ~1.2 million tons. It is shown that the daily average mass concentration of aerosol with particle sizes less than 2.5 μm exceeded the corresponding maximum permissible concentration in the Moscow region during the period from July 24 to 27, 2016. The influence of local sources on aerosol and gas pollution of atmospheric air was estimated. The smoke haze in 2016 was found to be deficient in carbon monoxide as compared to smoke pollution in 2010. It is shown that the thermal and wind stratification in the atmospheric boundary layer markedly influenced the pollution level in the smoke-laden urban atmosphere. Smoke aerosol radiative effect was estimated. The average aerosol radiative forcings at the top and bottom of the atmosphere over ETR on July 25, 2016, were–29 and–53 W/m2, and extreme forcings reached–112 and–215 W/m2, respectively.

Atomically-thin MoS2 is a favorable material for flexible device and nano-optoelectronics application due to unique optical and photoelectrical properties related to the exciton and trion formation. These properties crucially depend on the flake structure, strains and surrounding environment. MoS2 flakes of hexagram (six-pointed star) shape grown by CVD on SiO2/Si are known to be polycrystalline, consisting of six rhomb-like single-crystals with grain boundaries and having uneven residual tensile strains. So, it is an attractive object for studying the influence of polycrystallinity and strains on the exciton and trion emission behavior. In this paper, the micro-photoluminescence (µ-PL) of a bi-layer MoS2 flake of hexagram shape is studied in comparison with a triangular flake of the same thickness and a similar size. The morphology, structural and optical properties are inspected, focusing on the impact of the flake polycrystallinity and residual tensile strains on the exciton and trion PL. It is shown that the hexagram flake possesses special spectral features: an increased exciton PL intensity and the band peak energy shifted towards higher energy at the boundaries between the constituent single-crystals. In contrast, the triangular flake demonstrates rather even spatial distribution of PL. The spectral differences between both the flakes and their parts are explained in terms of tensile strains appearing in MoS2 on SiO2/Si after the post-growth cooling. The tensile strains are shown to redshift all the spectral bands and reduce the A exciton contribution to the spectrum, thus increasing the spectral weight of the B exciton and trion bands.

Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies. It was shown that the use of the InGaAs buffer spectrally shifted the maximum of the QD PL band to 1.3 μm (telecommunication range) without a decrease in the yield. Photosensitivity for the metamorphic QDs was found to be higher than that in GaAs buffer while the photoresponses for both metamorphic and pseudomorphic buffer layers were similar. The mechanisms of PV and PC were discussed for both structures. The dissimilarities in properties of the studied structures are explained in terms of the different design. A critical influence of the defects on the photoelectrical properties of both structures was observed in the spectral range from 0.68 to 1.0 eV for contact configuration (ii), i.e., in the case of electrically active GaAs wafer. No effect of such defects on the photoelectric spectra was found for configuration (i), when the structures were contacted to the top and bottom buffers; only a 0.83 eV feature was observed in the photocurrent spectrum of pseudomorphic structure and interpreted to be related to defects close to InAs/GaAs QDs.

The influence of thickness on the structural parameters, off-stoichiometry and cation disorder in kesterite Cu2ZnSnSe4 films grown by flash deposition for solar cell absorbers is investigated employing X-ray diffraction, energy-dispersive X-ray and Raman spectroscopies. It is shown that the lattice parameters of Cu2ZnSnSe4 changed depending on film thickness: the 100 nm film turned out to be weakly stretched on the molybdenum-coated glass substrates, while, in the thicker films, the compressive deformation is defined. The causes of the changes in film structure are outlined. Raman spectra revealed secondary phases like Cu2SnSe3 detecting reduction of its fraction with an increment in thickness; also, the SnZn antisite defect fraction decreases. Simultaneously, the share of disordered kesterite phase associated with CuZn antisite defects rises with thickness. The obtained results can be useful for optimization of technological growth process.

Cu2ZnSnS4 (CZTS) thin films prepared by the spray pyrolysis method were studied. This deposition method does not require sophisticated technological setup and allows to easily varying different technological parameters, which is perspective in terms of mass application. Here we show how the variation of the substrate temperature and of the Cu/Zn stoichiometry ratio in the precursor solutions influence the optical and structural properties of CZTS film. The Raman spectra reveal that an increase in the substrate temperature and Cu content leads to a higher disorder of the crystal structure and to the secondary phase formation, in particular, Cu2-xS. In turn, the formation of secondary phases significantly affected the CZTS bandgap. We have found that the films with the substrate temperature 289 °C and the Cu/Zn stoichiometric ratio equal to 2.0 comprise a minimum content of secondary phases and having the best crystal structure.

Стаття присвячена актуальним питанням інвестування на фондових ринках. Розглянуто американський фондовий ринок з його основними біржами, котрі займають лідируючі позиції в світі фінансів. Звертуто увагу на те, що міжнародна фондова біржа формується за допомогою поєднання в єдину систему фондових ринків багатьох країн. Фондовий ринок забезпечує перенаправлення капіталу з однієї економічної сфери в іншу. А біржа, у свою чергу, надає необхідні умови для нормального функціонування ринку та його відповідної роботи. До головних функцій фондової біржі відносять: посередницьку, індикативну та регулятивну. Досліджено можливості вкладення коштів для тих інвесторів, які надають перевагу мінімальному рівню ризику, а також переваги роботи з цінними паперами великих надійних компаній з високим рівнем ліквідності та капіталізації, дивіденди за акціями яких виплачуються стабільно, результати діяльності компанії на них не впливають. Придбати або продати такі цінні папери можна в будь-який час. Структуровано вимоги до наведеного виду цінних паперів. Встановлено, що деякі проекти в певних сферах інвестування розраховані на короткострокову перспективу і швидко приносять дохід, а для інших розробляються довгострокові плани і кошти отримуються через десятки років, а також, що політичні обставини в світі та стрімкий розвиток технологій мають значний вплив на формування інвестиційних трендів. Запропоновано найбільш привабливі напрями вкладення коштів в світі, які останнім часом набувають популярності серед інвесторів. Їх увагу привертає сфера охорони здоров’я та медицини, а саме антивікове лікування та штучний інтелект. Поряд виступає технологічна сфера, яка розвивається швидкими темпами. Ще одна галузь, яка динамічно формується – аерокосмічна. Також порушено питання про актуальність інвестування в аграрний сектор України, тобто вітчизняні ринки мають великі перспективи.

InAs quantum dots are actively researched nanostructures for photonic and electronic devices. Metamorphic InAs/InGaAs quantum dot structures are III-V nanostructures with wider design possibilities as compared to the conventional pseudomorphic InAs/GaAs quantum dot structures. However, for photonic applications of these nanostructures, the effect of defect levels still needs in-depth investigation. We have focused on th e nfluence of electron traps of defects on photocurrent in plane of InAs/InxGa1-xAs quantum dot arrays with x = 0.15 or 0.31, grown by molecular beam epitaxy on GaAs substrates. The structures are studied by photocurrent and deep level thermally stimulated current spectroscopy together with HRTEM and theoretical modeling. The arrays are found to be photosensitive in the telecommunication ranges at 1.3 and 1.55 ?m, respectively. In the structures, a rich spectrum of electron trap levels of point defects EL6, EL7, EL8, EL9/M2, EL10/M1, M0 and three extended defects ED1/EL3, ED2/EL4, ED3/EL5 has been identified. Among them, new defect levels undiscovered earlier in InAs/InGaAs nanostructures has been detected, in particular, EL8 and M0. The found electron traps are shown to slow the time-dependent photocurrent at low temperatures. Besides a long-term kinetics due to trap charging, a prolonged photocurrent decrement versus time is measured under constant illumination. The decrement is interpreted to be related to a Coulomb screening/narrowing of the wetting layer conductivity channel of the array by the electrons captured in the quantum-dot-buffer interface, which is commonly assumed to have trap levels originated by the interdiffusion of the constituent atoms and from plastic strain relaxation. The decrement is well fitted by allometric exponents, which means many types of traps are involved in electron capturing. This study provides new findings into the mechanism of photoc urrent in plane of quantum dot layers, showing a crucial importance of growth-related interface defects of nanostructures on photoresponsivity at low temperatures.

В роботі здійснювалася модифікація поверхні поруватого кремнію водними розчинами нуклеїнових кислот та вивчався вплив такої модифікації на інтенсивність його фотолюмінесценції. Показано, що обробка поруватого кремнію водними розчинами нуклеїнових кислот призводить до зростання інтенсивності його фотолюмінесценції, причому для ДНК зміни є більшими ніж для РНК (гомополімер полі(А)). За допомогою інфрачервоної спектроскопії було виявлено, що в присутності нуклеїнових кислот на поверхні кремнію формується значно більша кількість зв’язків Si-O ніж в дистильованій воді. Встановлено, що концентрація молекулярного кисню в розчині ДНК слабо впливає на фотолюмінесценцію поруватого кремнію, в той час як опромінення оброблених розчинами ДНК зразків поруватого кремнію видимим світлом сприяє зростанню інтенсивності його фотолюмінесценції. Стимульований нуклеїновими кислотами ефект зростання фотолюмінесценції поруватого кремнію пояснюється потоншенням кремнієвого скелету, в результаті чого згідно з квантово-розмірною моделлю його фотолюмінесценції, ймовірність випромінювальних переходів зростає. Причиною цього може бути підсилення процесів розчинення і, особливо, окиснення кремнію в водному розчині нуклеїновими кислотами. Були запропоновані два шляхи впливу нуклеїнових кислот на зазначені процеси. По-перше, підсилення корозії поруватого кремнію поліаніонами, якими є нуклеїнові кислоти у водному розчині. По-друге, підвищена концентрація активних форм кисню в водних розчинах нуклеїнових кислот, генерація яких відбувається під впливом видимого світла. Останнє вважається основною причиною окислення поруватого кремнію. Представлені результати роботи можуть бути корисними для створення біосенсорів на основі поруватого кремнію. In this work, porous silicon surface was modified by aqueous solutions of nucleic acids and the effect of such modification on the porous silicon photoluminescence was studied. The treatment of porous silicon with the nucleic acid solutions was found to cause an increase in the photoluminescence intensity, the change being greater with DNA rather than RNA (homopolymer poly(A)). By means of infrared spectroscopy, it was found that the number of Si-O bonds at the silicon surface after treatment by nucleic acid solutions is much higher than that after treatment by distilled water. It is found that the porous silicon photoluminescence weakly depends on the concentration of the molecular oxygen in the DNA solution. At the same time, illumination of the DNA-treated porous silicon samples by the visible light enhances the porous silicon photoluminescence intensity. Nucleic acid stimulated increase in the porous silicon photoluminescence is attributed to thinning of the silicon skeleton, which, according to the quantum-size model of photoluminescence, leads to a radiative transition probability increase. The thinning could be related to enhancement of dissolution and, to a greater extent, to oxidation of porous silicon in aqueous solution by the nucleic acids. The effect of nucleic acids in aqueous solutions on the porous silicon modification was assumed to be twofold. Firstly, nucleic acids, being polyanions in aqueous solutions, can enhance the corrosion of porous silicon by water. Secondly, an increased concentration of reactive oxygen species is generated in aqueous solutions of nucleic acids under visible light illumination. The latter is supposed to be the main reason of porous silicon oxidation. The results of the work can be useful for the development of PSbased biosensors.

Metamorphic InAs/In0.15Ga0.85 As and InAs/In0.31Ga0.69 As quantum dot (QD) arrays are known to be photosensitive in the telecommunication ranges at 1.3 and 1.55 mu m, respectively; however, for photonic applications of these nanostructures, the effect of levels related to defects still needs in-depth investigation. We have focused on the influence of electron traps of defects on photocurrent (PC) in the plane of the QD array, studying by PC and deep level thermally stimulated current spectroscopy together with HRTEM and theoretical modeling. In the structures, a rich spectrum of electron trap levels of point defects EL6 (E-c - 0.37 eV), EL7 (0.29-0.30 eV), EL8 (0.27 eV), EL9/M2 (0.22-0.23 eV), EL10/M1 (0.16 eV), M0 (similar to 0.11 eV) and three extended defects ED1/EL3 (0.52-0.54), ED2/EL4 (0.47-0.48 eV), ED3/EL5 (0.42-0.43 eV) has been identified. Among them, new defect levels undiscovered earlier in InAs/InGaAs nanostructures has been detected, in particular, EL8 and M0. The found electron traps are shown to affect a time-dependent PC at low temperatures. Besides a long-term kinetics due to trap charging, a prolonged PC decrement versus time is measured under constant illumination. The decrement is interpreted to be related to a Coulomb screening of the conductivity channel by the electrons captured in the QD interface traps. The decrement is well fitted by allometric exponents, which means many types of traps involved in electron capturing. This study provides new findings into the mechanism of in-plane PC of QD arrays, showing a crucial importance of growth-related defects on photoresponsivity at low temperatures.

InAs/InGaAs heterostructures with quantum dots (QDs) have been studied for quite some time for light-emitting diodes operating from the near to the far infrared range. However, the room temperature QD emission is rather low, thus it is needed to look for improved structure designs allowing efficient enhancement of luminescence. In this work, we study the modification of photo- and thermo-electrical properties of InAs/In0.15Ga0.85As QD heterostructure, when introducing wide-bandgap In0.15Al0.85As confining barriers (CBs) at one or both sides of the QD layer. The structures demonstrate interband QD photoluminescence (PL) peaked at 1.2 μm measured from room temperature down to 10 K. The introduction of CBs allows to enhance the PL intensity by more than four orders of magnitude. The reason is a strong decrease of the thermal escape of both charge carriers confined in QDs and wetting layer, leading to a highly increased radiative recombination. The changes in optical transitions, involving quantum confinement states and defect-related levels, are studied by photocurrent (PC) measurements, also showing the expectable quenching of PC in the structures with CBs. The existing deep levels of defects are determined by thermally stimulated current spectroscopy. Having the same defect spectrum in all the studied structures, an increase in the defect density was detected near CBs at the QD layer. At low temperatures, defect traps in vicinity of the QDs layer caused the Coulomb screening of conductivity channel, that is studied by kinetics measurements in view of the CB introduction. The PC decrement under the constant illumination is theoretically explained by the screening. We confidently show that, despite of a slight increase in defects and PL blueshift in the QD structure with In0.15Al0.85As CBs, they can serve as improved active elements for energy-efficient QD lasers, single-photon emitters and optical amplifiers.

A technique is proposed for determining of the large-scale smoke aerosol fluxes using a wind field reanalysis data and the satellite monitoring data of the aerosol optical depths and the vertical profile of the attenuation coefficient. The directions of the long-range transport of the Siberian smoke haze fragments were determined in July 2016. The maximum large-scale mass fluxes and the total mass of the smoke aerosol during the transfer of air masses through the Ural meridian to the west (0.38*106 ton/day and 1.38*106 tons) and through the 115ºE meridian to the east (0.26*106 ton/day and 0.72*106 tons) were estimated.

According to measurement data on the desertified area in the Astrakhan oblast in the conditions of non-intermittent saltation, a strong influence of convective quasiperiodic structures with periods from 1.5 to 8 minutes on variations of the saltating particle concentrations are found. Statistical characteristics of the saltating particle concentrations variations are received. The vertical profile of the average particle concentration in the height range from 3 to 15 cm is obtained. An exponential approximation of the particle concentration profile with a logarithmic gradient of -0.32 cm−1 is proposed. It is shown that the average particle content in the saltation layer is 8.6 cm−2.

Molybdenum disulfide (MoS2) is one of the most interesting 2D materials. However, while monolayer MoS2 is well-explored, the few-layer flakes, also promising for flexible device and nano-optoelectronics application, remain less investigated. We study the variation of exciton and trion photoluminescence (PL) and structural properties of few-layer MoS2 grown on SiO2/Si by chemical vapor deposition. Scanning electron and atomic force microscopies show that most of the flakes have a triangular shape. The µ-PL spectra of the flakes show two broad bands associated to the A exciton overlapped by trion and B exciton. The light emission at room temperature redshifts when the number of layers increases, controlled by µ-Raman spectroscopy. In the temperature-dependent measurements from 80 to 290 K, the PL redshifts according to bandgap narrowing, while the intensity decreases due to the thermally activated nonradiative recombination related to the increase of the electron-phonon interaction. Exciton and trion bands are deconvoluted and their behaviors with temperature are studied by fitting the PL data with modelling equations. This allows to evaluate the spin-orbit splitting, quenching activation energy, trion effective size and other important parameters. These new findings are useful for the potential applications of few-layer MoS2 in nano-optoelectronics involving external modulation of optical properties.

InAs/GaAs quantum dot photodetector photoresponse spectra consist of quantum dot, wetting layer and GaAs components, however, they frequently contain features attributed to defect levels. In this study we focus on the origin of an unwanted negative photovoltage component in order to find a design allowing to eliminate these undesirable effects. Photoelectric properties of vertical InAs/GaAs quantum dot structures grown on semi-insulating (si) and n+-GaAs wafers are analyzed. It is found that the photoresponse drop above 1.37 eV in the photovoltage spectrum, observed with si-GaAs substrate, is originated from shallow defect levels in the unintentional space-charge area created at the interface between the substrate and n+-GaAs buffer. The intrinsic field in that area is opposite to the top pn junction, according to modelling calculations, and it reduces the photoelectric response. Photoelectric characterization of the heterostructure grown on n+-GaAs indicates that the utilization of n+-GaAs substrate helps to avoid this band bending and to eliminate its negative effects, increasing the total photoresponse.

Infrared photodetectors with In(Ga)As quantum dot (QD) active element functioning on interband and intersubband transitions are currently actively investigated, however, the vertical sensors were mostly reported. In the current study, a multilayer InGaAs/GaAs QD photodetector structure allowing the lateral photocurrent detection at normal incidence has been prepared depositing top contact. In order to have a comparison, a heterostructure with only a stack of InGaAs/GaAs wetting layers (WL) has been grown. In-depth photoelectrical characterization shows an effective broad-band photodetection related to the interband transitions between quantum-confined levels in QDs ranging from 1.03 to 1.38 eV (0.9-1.2 ?m) that covers much wider infrared range in comparison to that from WLs (1.27-1.38 eV). Photoluminescence spectroscopy confirms the existence of QD transitions, observed as intense QD emission which peaked at 1.12 eV (~1 ?m) redshifted in comparison to the WL structure. The mechanisms of photoconductivity are modelled and discussed, comparing both the structures. We also show that our QD stack has an order lower contribution from defects compared to similar QD structures investigated before. At the same time, our structures demonstrate appropriate device characteristics at room temperature, such as the wide dynamic range from 10 to 10 ?W cm and a high photoresponsivity up to 20 A W at low excitation intensities over 10-10 ?W cm, while at higher excitation intensities the responsivity is reduced, exhibiting a strong spectral dependence. Thereby, our results show that the grown multilayer InGaAs/GaAs QD heterostructure is of relevant interest for application in lateral QD photodetectors.

Down-converting “micromorph” silicon dioxide films with embedded silicon nanocrystals (nc-Si) covered by diamond-like carbon (DLC) are fabricated. DLC used as a radiation-protective, stabilizing and anti-reflection coating is found to modify optical and structural properties of nc-Si. The films are in detail characterized employing scanning electron microscopies, energy dispersive X-ray, Raman and FTIR spectroscopies. The existence of amorphous and nanocrystals phases in nc-Si/SiOx films has been confirmed using Raman spectroscopy. The impact of γ-irradiation on the DLC film was also shown. The main benefit is that photoluminescence (PL) spectrum of nc-Si/SiOx after deposition of DLC shifts in the infrared region close to the maximum of Si-based solar cells photoresponse with simultaneous PL enhancement by about 1.2 times. This effect has been explained by the passivation of non-radiative recombination centers in nc-Si/SiOx by H atoms. Studying the influence of γ-irradiation on the DLC coatings, the decrease of integral PL intensity of the structures due to the radiation damages of C-Hn bonds has been found. Moreover, γ-irradiation increases the disorder of C-Hn bonds in DLC as well as decreases the optical transmittance by ~20% in the range of 500 to 1100 nm, possibly, due to a weak graphitization of the films. The results show that nc-Si films with DLC as an antireflection, protection and down-converting coating might be considered as a perspective combination to improve the efficiency and degradation stability of solar cells.

Photoelectric properties of the metamorphic InAs/In x Ga1 − xAs quantum dot (QD) nanostructures were studied at room temperature, employing photoconductivity (PC) and photoluminescence spectroscopies, electrical measurements, and theoretical modeling. Four samples with different stoichiometry of In x Ga1 − xAs cladding layer have been grown: indium content x was 0.15, 0.24, 0.28, and 0.31. InAs/In0.15Ga0.85As QD structure was found to be photosensitive in the telecom range at 1.3 μm. As x increases, a redshift was observed for all the samples, the structure with x = 0.31 was found to be sensitive near 1.55 μm, i.e., at the third telecommunication window. Simultaneously, only a slight decrease in the QD PC was recorded for increasing x, thus confirming a good photoresponse comparable with the one of In0.15Ga0.75As structures and of GaAs-based QD nanostructures. Also, the PC reduction correlate with the similar reduction of photoluminescence intensity. By simulating theoretically the quantum energy system and carrier localization in QDs, we gained insight into the PC mechanism and were able to suggest reasons for the photocurrent reduction, by associating them with peculiar behavior of defects in such a type of structures. All this implies that metamorphic QDs with a high x are valid structures for optoelectronic infrared light-sensitive devices.

The bipolar effect of GaAs substrate and nearby layers on photovoltage of vertical metamorphic InAs/InGaAs in comparison with pseudomorphic (conventional) InAs/GaAs quantum dot (QD) structures were studied. Both metamorphic and pseudomorphic structures were grown by molecular beam epitaxy, using bottom contacts at either the grown n +-buffers or the GaAs substrate. The features related to QDs, wetting layers, and buffers have been identified in the photoelectric spectra of both the buffer-contacted structures, whereas the spectra of substrate-contacted samples showed the additional onset attributed to EL2 defect centers. The substrate-contacted samples demonstrated bipolar photovoltage; this was suggested to take place as a result of the competition between components related to QDs and their cladding layers with the substrate-related defects and deepest grown layer. No direct substrate effects were found in the spectra of the buffer-contacted structures. However, a notable negative influence of the n +-GaAs buffer layer on the photovoltage and photoconductivity signal was observed in the InAs/InGaAs structure. Analyzing the obtained results and the performed calculations, we have been able to provide insights on the design of metamorphic QD structures, which can be useful for the development of novel efficient photonic devices.

The optical permeability of rat head tissues, such as brain cortex, cranial bone and skin has been determined in the visible, near-infrared and short-wave infrared regions, aiming towards the trough-skull brain imaging.

Deep levels in metamorphic InAs/InxGa1-xAs quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x = 0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.