The influence of the lanthanide cation type and calcination temperature on the crystal, local, and electronic structures of both individual and high-entropy (HE) Ln chromates/chromites (Ln = La - Yb, and Y) prepared by a coprecipitation is studied by using synchrotron X-ray diffraction, X-ray absorption fine structure spectroscopy, Raman and Fourier transform infrared spectroscopies, scanning electron microscopy with energy-dispersive Xray spectroscopy, simultaneous thermal analysis, and inductively coupled plasma atomic emission spectroscopy. Calcination of X-ray amorphous precursors at 550 degrees C resulted in the formation of individual LnCrO4 chromates with monoclinic (sp. gr. P21/n for Ln = La) or tetragonal (sp. gr. I41/amd for Ln = Sm - Yb, Y) structure. The PrCrO4 and NdCrO4 samples were a mixture of monoclinic and tetragonal phases. The HE LnCrO4 chromates were characterized by tetragonal structure regardless of the Ln3+ cation type involved. A further increase in temperature >= 650 degrees C led to the formation of Ln chromites having the orthorhombic symmetry (sp. gr. Pnma for LaCrO3, sp. gr. Pbnm for individual Ln = Pr - Yb, Y, and HE chromites). For all synthesized LnCrO3 samples, the lattice parameters, unit cell volumes, Cr-O-Cr bond angles, average Ln-O distances diminish with decreasing the Ln3+ cation radius. On the contrary, the octahedral distortions within CrO6 units increase with decreasing the Ln3+ cation radius. An analysis of the electronic structure showed the presence of an oxidation state (3+) for both Ln and Cr cations in all synthesized precursors and Ln chromites, and Cr5+ for Ln chromates. The local environment of the Ln3+ and Cr3+ cations in HE Ln chromites is close to that of similar ions in individual compounds. The local environment of the La3+ cation in La-containing compounds differs significantly from that of Ln3+ cations in other Ln chromites (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Yb, Y).

Methods of synthesis and modification of nanostructures are one of the most important directions in the study of transition metal dichalcogenides (TMDCs). The present work is devoted to a new field of TMDC nanoparticles synthesis from a bulk crystal using a femtosecond laser ablation in liquid. Tungsten disulfide TMDC is a promising material for resonant nanoantennas and photothermal therapy due to the combination of excitonic transition in the transparency window of biological tissues and its high refractive index (n>4) in the visible range. In this work the peculiarities of WSe2 laser ablation are studied. The influence of experimental synthesis parameters (specific solvent choice, distance between the focus point and the crystal surface) on nanoparticle crystallinity and size is shown. The influence of nanoparticle crystallinity on the excitonic response behavior in the extinction spectra of colloids is investigated. Additionally, the application of WSe2 nanoparticles as a SERS-active material is discussed. This study opens new possibilities for the practical use of WSe2 nanoparticles in photothermal applications and Raman spectroscopy.

Hexagonal boron nitride (hBN) has recently been shown to host native defects exhibiting optically detected magnetic resonance (ODMR) with applications in nanoscale magnetic sensing and imaging. To advance these applications, deposition methods to create wafer-scale hBN films with controlled thicknesses are desirable, but a systematic study of the ODMR properties of the resultant films is lacking. Here we perform ODMR measurements of thin films (3-2000nm thick) grown via three different methods: metal-organic chemical vapour deposition (MOCVD), chemical vapour deposition (CVD), and molecular beam epitaxy (MBE). We find that they all exhibit an ODMR response, including the thinnest 3nm film, albeit with different characteristics. The best volume-normalised magnetic sensitivity obtained is 30uT/sqrt(Hz um^3). We study the effect of growth temperature on a series of MOCVD samples grown under otherwise fixed conditions and find 800-900C to be an optimum range for magnetic sensitivity, with a significant improvement (up to two orders of magnitude) from post-growth annealing. This work provides a useful baseline for the magnetic sensitivity of hBN thin films deposited via standard methods and informs the feasibility of future sensing applications.

Owing to their atomically thin nature, structural defects in two-dimensional materials often play a dominating role in their electronic and optical properties. Here, we grow epitaxial GaSe monolayers on graphene/SiC by molecular beam epitaxy and characterise the layers by in situ scanning tunnelling microscopy and angle-resolved photoemission spectroscopy extracted from k-resolved photoemission electron microscopy mapping. We identify an electric dipole at the GaSe/graphene interface, with electrons accumulating on the GaSe, that cannot be compensated by p-type doping through the creation of defects formed by annealing in ultrahigh vacuum. Additionally, we demonstrate that both as-grown and defective GaSe layers are remarkably resilient to oxidation in a pure O2 environment, and chemisorption of O2 molecules on the surface can effectively electronically neutralise the doping in the layer. This work demonstrates the robust interlayer interaction in the GaSe/graphene van der Waals heterostructure and the role of defects on the doping for nanoelectronics.

Thanks to their record high refractive index and giant optical anisotropy, van der Waals (vdW) materials have accelerated the development of nanophotonics. However, traditional high refractive index materials, such as titanium dioxide (TiO2), still dominate in the most important visible range. This is due to the current lack of transparent vdW materials across the entire visible spectrum. In this context, we propose that germanium disulfide (GeS2) could offer a significant breakthrough. With its high refractive index, negligible losses, and biaxial optical anisotropy across the whole visible range, GeS2 has the potential to complement TiO2 and close the application gap of vdW materials in the visible spectrum. The addition of GeS2 could have a profound impact on the design of van der Waals nanophotonic circuits for any operation wavelength from ultraviolet to infrared, emphasizing the significance of the potential impact of GeS2 on the field of nanophotonics.

We report hyperspectral imaging in the UV-C spectral domain in epitaxial monolayers of hexagonal boron nitride (hBN). Under quasi-resonant laser excitation, the UV-C emission of monolayer hBN consists in resonant Raman scattering and photoluminescence, which appear to be spatially uncorrelated. Systematic measurements as a function of the excitation energy bring evidence of a photoluminescence singlet at similar to 6.045 eV. The spatial variations of the photoluminescence energy are found to be around similar to 10 meV, revealing that the inhomogeneous broadening is lower than the average photoluminescence linewidth of similar to 25 meV, a value close to the radiative limit in monolayer hBN. Our methodology provides an accurate framework for assessing the opto-electronic properties of hBN in the prospect of scalable hBN-based devices fabricated by epitaxy.

Chirality is probably the most mysterious among all symmetry transformations. Very readily broken in biological systems, it is practically absent in naturally occurring inorganic materials and is very challenging to create artificially. Chiral optical wavefronts are often used for the identification, control and discrimination of left- and right-handed biological and other molecules. Thus, it is crucially important to create materials capable of chiral interaction with light, which would allow one to assign arbitrary chiral properties to a light field. In this paper, we utilized van der Waals technology to assemble helical homostructures with chiral properties (e. g. circular dichroism). Because of the large range of van der Waals materials available such helical homostructures can be assigned with very flexible optical properties. We demonstrate our approach by creating helical homostructures based on multilayer As_2S_3, which offers the most pronounced chiral properties even in thin structures due to its strong biaxial optically anisotropy. Our work showcases that the chirality of an electromagnetic system may emerge at an intermediate level between the molecular and the mesoscopic one due to the tailored arrangement of non-chiral layers of van der Waals crystals and without additional patterning.

Nature is abundant in material platforms with anisotropic permittivities arising from symmetry reduction that feature a variety of extraordinary optical effects. Principal optical axes are essential characteristics for these effects that define light-matter interaction. Their orientation – an orthogonal Cartesian basis that diagonalizes the permittivity tensor, is often assumed stationary. Here, we show that the low-symmetry triclinic crystalline structure of van der Waals rhenium disulfide and rhenium diselenide is characterized by wandering principal optical axes in the space-wavelength domain with above π/2 degree of rotation for in-plane components. In turn, this leads to wavelength-switchable propagation directions of their waveguide modes. The physical origin of wandering principal optical axes is explained using a multi-exciton phenomenological model and ab initio calculations. We envision that the wandering principal optical axes of the investigated low-symmetry triclinic van der Waals crystals offer a platform for unexplored anisotropic phenomena and nanophotonic applications.

van der Waals topological insulators, characterized by their high-index dielectric response, offer a promising materials platform for nanophotonics. Among these materials, Bi2Te3 has one of the highest refractive indices and extinction coefficients. However, the precise determination of Bi2Te3 optical properties remains challenging owing to its complicated physical model, which includes an oxide layer, topological conducting states, and optical anisotropy. Here, we resolve this problem and develop an accurate optical model for Bi2Te3 in a broad (450-1500 nm) spectral range. Our study shows that an oxide layer plays a major role in optical model for these wavelengths, while the influence of topological conducting states and optical anisotropy is minimal. Our model allows us to obtain accurate Bi2Te3 optical constants and demonstrate their use in biosensors, thermal theranostics, and topological phase singularities. Moreover, we observe a polarization transition of topological phase singularity for Bi2Se3, which opens a new direction for the development of topological phase effects. Therefore, our results open new avenues for photonic applications of Bi2Te3 optical properties.

Abstract Graphene placed on hexagonal boron nitride (hBN) has received significant interest due to its excellent electrical performance and physics phenomena, such as superlattice Dirac points. Direct molecular beam epitaxy growth of graphene on hBN offers an alternative fabrication route for hBN/graphene devices. Here, we investigate the electronic transport of moiré field effect transistors (FETs) in which the conducting channel is monolayer graphene grown on hexagonal boron nitride by high temperature molecular beam epitaxy (HT-MBE). Alignment between hBN and HT-MBE graphene crystal lattices gives rise to a moiré-fringed hexagonal superlattice pattern. Its electronic band structure takes the form of a “Hofstadter butterfly”. When a strong magnetic field B is applied perpendicular to the graphene layer, the electrical conductance displays magneto-oscillations, periodic in B −1, over a wide range of gate voltages and temperatures up to 350 K. We attribute this behaviour to the quantisation of electronic charge and magnetic flux within each unit cell of the superlattice, which gives rise to so-called Brown-Zak oscillations, previously reported only in high-mobility exfoliated graphene. Thus, this HT-MBE graphene/hBN heterostructure provides a platform for observation of room temperature quantum effects and device applications.

Two-dimensional semiconductors (2DSEM) based on van der Waals crystals offer important avenues for nanotechnologies beyond the constraints of Moore's law and traditional semiconductors, such as silicon (Si). However, their application necessitates precise engineering of material properties and scalable manufacturing processes. The ability to oxidize Si to form silicon dioxide (SiO2) was crucial for the adoption of Si in modern technologies. Here, we report on the thermal oxidation of the 2DSEM gallium selenide (GaSe). The nanometer-thick layers are grown by molecular beam epitaxy on transparent sapphire (Al2O3) and feature a centro-symmetric polymorph of GaSe. Thermal annealing of the layers in an oxygen-rich environment promotes the chemical transformation and full conversion of GaSe into a thin layer of crystalline Ga2O3, paralleled by the formation of coherent Ga2O3/Al2O3 interfaces. Versatile functionalities are demonstrated in photon sensors based on GaSe and Ga2O3, ranging from electrical insulation to unfiltered deep ultraviolet optoelectronics, unlocking the technological potential of GaSe nanostructures and their amorphous and crystalline oxides.

2D semiconductors can drive advances in quantum science and technologies. However, they should be free of any contamination; also, the crystallographic ordering and coupling of adjacent layers and their electronic properties should be well-controlled, tunable, and scalable. Here, these challenges are addressed by a new approach, which combines molecular beam epitaxy and in situ band engineering in ultra-high vacuum of semiconducting gallium selenide (GaSe) on graphene. In situ studies by electron diffraction, scanning probe microscopy, and angle-resolved photoelectron spectroscopy reveal that atomically-thin layers of GaSe align in the layer plane with the underlying lattice of graphene. The GaSe/graphene heterostructure, referred to as 2semgraphene, features a centrosymmetric (group symmetry D3d) polymorph of GaSe, a charge dipole at the GaSe/graphene interface, and a band structure tunable by the layer thickness. The newly-developed, scalable 2semgraphene is used in optical sensors that exploit the photoactive GaSe layer and the built-in potential at its interface with the graphene channel. This proof of concept has the potential for further advances and device architectures that exploit 2semgraphene as a functional building block. A new approach to epitaxy and in situ band engineering of 2D semiconductors on graphene is presented. Atomically-thin layers of centro-symmetric gallium selenide (GaSe) form a high-quality, scalable interface with graphene, referred to as 2semgraphene. This provides a building block for optical sensors that exploit the photoactive GaSe layer and the charge dipole at its interface with the graphene channel. image

Обсуждаются возможности спектроскопии комбинационного рассеяния (КР) света для диагностики растительных масел и биологически активных добавок (БАД) на основе полиненасыщенных жирных кислот семейства омега‑3 (ПНЖК ω‑3). Показано, что по спектрам КР можно определять йодное число растительных масел, форму и относительное общее содержание ПНЖК ω‑3, а также соотношение массовых долей эйкозапентаеновой (ЭПК) и докозагексаеновой (ДГК) кислот в БАД Омега‑3. Обсуждаются возможности применения метода главных компонент для диагностики БАД Омега‑3 по спектрам КР.

The synthesis and detailed study of six series of high-entropy complex oxides containing lanthanides (Ln) and transition metals with the general formula Ln(2)M(2)O(7) (Ln = La-Yb, and Y; M = Ti, Zr, and Ce) with the number of different Ln cations not less than six in each case are reported. The influence of synthesis conditions (types of the Ln(3+) and M4+ cations, calcination temperature) used in the synthesis via either coprecipitation or sol-gel method on the crystal and local structures of target materials is comprehensively surveyed. The studies were carried out using a combination of long- (s-XRD), medium- (Raman, FT-IR, SEM-EDS) and short-range (XAFS) sensitive techniques, as well as AES-ICP and STA. It was established that the ratio of the cation radii gamma = (r) over bar (3+)(Ln)/(r) over bar (4+)(M) is the main factor that determines the type of initially formed crystal structure. In the boundary region (gamma similar to 1.42-1.47), the average radius of lanthanide cation ((r) over bar (3+)(Ln)), along with the (r) over bar (3+)(Ln)/(r) over bar (4+)(M) ratio, also plays a significant role in the type of the resulting crystal structure of the high-entropy lanthanide complex oxides. The presence of inhomogeneity in the distribution of elements in precursors significantly affects the phase composition of the resulting high-entropy oxides. An increase in the calcination temperature promotes not only the occurrence of subsequent phase transitions, but also an increase in the single-phase nature of the resulting high-entropy complex rare-earth oxides. At the same time, the cations included in the composition retain some independence, despite the fact that they occupy one crystallographic position in the resulting crystal structure.

The relevance of the research is caused by the need to evaluate the content of polycyclic aromatic hydrocarbons (PAHs) formed during coal combustion. The object of the study is street dust of Mezhdurechensk (Kemerovo region). The purpose of the work is to assess the level of accumulation of the polyarenes. The subject is the determination of the 14 polyarenes content. Methodology and methods are as follows: the samples are selected according to the standard methodology of the areal network. The analysis has been carried out by chromatography-mass spectrometry. The following results are obtained: The average total PAH content is 2 148±364 mkg/kg, a maximum value is 4 011 mkg/kg and a minimum – 401 mkg/kg. The content of heavy PAHs (1 432±163 mkg/kg) is twice as high as the content of light PAHs (716±202 mkg/kg) and the percentage of benz(a)pyrene is 17,0–33,8 %, which is typical for territories where fuel is burned. The distribution of PAHs by granulometric fractions has showed the fairly uniform accumulation of PAHs in small (50–20 microns) and medium (100–50 microns) fractions and their predominance compared with large (1 000–100 microns) fractions: 43,5, 37,22, 19,63 % accordingly. The amount of PAHs expressed in equivalents of the most dangerous carcinogen benz(a)pyrene is 570±140 mkg/kg, and exceeded the MPC (20 mkg/kg) by an average of 28,5 times. The contribution of benz(a)pyrene to the total toxicity is 91 %. The authors conclude that the main sources of PAHs are their emission during coal combustion, their direct presence in coals, and to a lesser extent – the loss of petroleum products during transport.

The emergence of van der Waals (vdW) materials resulted in the discovery of their giant optical, mechanical, and electronic anisotropic properties, immediately enabling countless novel phenomena and applications. Such success inspired an intensive search for the highest possible anisotropic properties among vdW materials. Furthermore, the identification of the most promising among the huge family of vdW materials is a challenging quest requiring innovative approaches. Here, we suggest an easy-to-use method for such a survey based on the crystallographic geometrical perspective of vdW materials followed by their optical characterization. Using our approach, we found As 2 S 3 as a highly anisotropic vdW material. It demonstrates rare giant in-plane optical anisotropy, high refractive index and transparency in the visible range, overcoming the century-long record set by rutile. Given these benefits, As 2 S 3 opens a pathway towards next-generation nanophotonics as demonstrated by an ultrathin true zero-order quarter-wave plate that combines classical and the Fabry-Perot optical phase accumulations. Hence, our approach provides an effective and easy-to-use method to find vdW materials with the utmost anisotropic properties.

Thanks to their record high refractive index and giant optical anisotropy, van der Waals (vdW) materials have accelerated the development of nanophotonics. However, traditional high refractive index materials, such as titanium dioxide (TiO2), still dominate in the most important visible range. This is due to the current lack of transparent vdW materials across the entire visible spectrum. In this context, we propose that germanium disulfide (GeS2) could offer a significant breakthrough. With its high refractive index, negligible losses, and biaxial optical anisotropy across the whole visible range, GeS2 has the potential to complement TiO2 and close the application gap of vdW materials in the visible spectrum. The addition of GeS2 could have a profound impact on the design of van der Waals nanophotonic circuits for any operation wavelength from ultraviolet to infrared, emphasizing the significance of the potential impact of GeS2 on the field of nanophotonics.

The possibility of synthesizing layers of the medium-temperature thermoelectric CrSi2 by hot pressing of the initial components (Cr and Si) has been investigated. The phase composition of samples obtained by hot pressing of Cr and Si before and after annealing in the region of their contact boundary has been investigated by X-ray analysis. It is shown that, under certain conditions, low-temperature synthesis of a CrSi2 layer with a thickness of 50 to 300 μm is possible at the interface between Cr and Si. The synthesis occurs at a temperature significantly lower than that given in the phase diagram, which opens up new technological possibilities for obtaining the CrSi2 compound. Keywords: thermoelectrics, chromium disilicide, phase interface, X-ray phase analysis.

Perfection of technologies along with extreme diagnostic potential cause high clinical and anatomical effect of surgical intervention for vitreoretinal pathology. However final functional result is not always comparable with the prognostic expectations. Having the knowledge about the changes of the eye tissue at retinal pathology and their interrelation with the stages of healing in response to the operative trauma, it is possible to carry out timely preventive activity to optimize the healing process. Up to date the recognized method of treatment of resistant macular edema and increasing of visual acuity in patients is intravitreal injection of corticosteroids. However, their application is limited both in acute and distant period due to a wide range of side effects. Therefore, the problem of inhibition and complex treatment of traumatic effects on the retina in the course of surgical treatment remains topical. A promising direction in solving this problem is the study of the influence of sulfated glycosaminoglycans (sGAG) on the inflammatory response and repair processes of vitreomacular and retinal interface structures. The purpose of this study was to summarize the experience of experimental studies of the effect of sGAG preparations on pathological processes of various tissues to create a substrate for further studies of their application in the field of vitreomacular and retinal interfaces.

The development of technology for integrating optical metaresonators with two-dimensional and layered van der Waals (vdW) materials opens up broad prospects for the creation of subdiffraction concentrators of electromagnetic energy, surface-emitting lasers, laser displays, and highly efficient nonlinear converters. In this work, we develop a straightforward strategy for the design and fabrication of surface-emitting laser devices based on few-layer transition metal dichalcogenides placed on the dielectric metasurfaces in the regime of quasi-trapped mode excitation. We optimize the parameters of MoTe2 flake and Si metasurface to achieve a positive feedback and to observe the lasing, resulting from their integration, with the predicted characteristics. Promising potential for the development of vdW-metalaser platform is associated with the possibility of simple polarization control of lasing regimes by employing the features of the bianisotropic response of the metasurface's building blocks.