When a crystal is subjected to a periodic potential, under certain circumstances it can adjust itself to follow the periodicity of the potential, resulting in a commensurate state. Of particular ...interest are topological defects between the two commensurate phases, such as solitons and domain walls. Here we report a commensurate-incommensurate transition for graphene on top of hexagonal boron nitride (hBN). Depending on the rotation angle between the lattices of the two crystals, graphene can either stretch to adapt to a slightly different hBN periodicity (for small angles, resulting in a commensurate state) or exhibit little adjustment (the incommensurate state). In the commensurate state, areas with matching lattice constants are separated by domain walls that accumulate the generated strain. Such soliton-like objects are not only of significant fundamental interest, but their presence could also explain recent experiments where electronic and optical properties of graphene-hBN heterostructures were observed to be considerably altered.
The strong suppression of equilibrium magnetic tunneling in a graphene/hBN/graphene heterostructure caused by the Coulomb correlation gap in the tunneling density of states has been found. Comparison ...has shown that the suppression of the equilibrium tunneling conductivity
in a high magnetic field with a decrease in the temperature and the dependence of the observed gap width Δ on the filling factor of Landau levels ν are qualitatively similar to the respective results of similar experiments in GaAs heterostructures and has confirmed our hypothesis concerning the nature of the effect. However, the determined gap width Δ is much larger than those measured in all previous works in semiconductor heterostructures probably because the cyclotron energy in graphene is much higher than that in GaAs in the region of low Landau levels.
One-dimensional quasi-periodic nanogratings with spacings in the range from 160 to 600 nm are written on a dry or wet titanium surface exposed to linearly polarized femtosecond IR and UV laser pulses ...with different surface energy densities. The topological properties of the obtained surface nanostructures are studied by scanning electron microscopy. Despite the observation of many harmonics of the one-dimensional surface relief in its Fourier spectra, a weak decreasing dependence of the first-harmonic wavenumber (nanograting spacing) on the laser fluence is found. Studies of the instantaneous optical characteristics of the material during laser irradiation by measuring the reflection of laser pump pulses and their simulation based on the Drude model taking into account the dominant interband absorption allowed us to estimate the length of the excited surface electromagnetic (plasmon-polariton) wave for different excitation conditions. This wavelength is quantitatively consistent with the corresponding nanograting spacings of the first harmonic of the relief of the dry and wet titanium surfaces. It is shown that the dependence of the first-harmonic nanograting spacing on the laser fluence is determined by a change in the instantaneous optical characteristics of the material and the saturation of the interband absorption along with the increasing role of intraband transitions. Three new methods are proposed for writing separate subwave surface nanogratings or their sets by femtosecond laser pulses using the near-threshold nanostructuring, the forced adjustment of the optical characteristics of the material or selecting the spectral range of laser radiation, and also by selecting an adjacent dielectric.
Tunneling and magnetic tunneling are investigated in graphene/
h
-BN/graphene van der Waals heterosystems. Two new types of systems are found, in which negative differential conductivity regions are ...implemented due to resonant tunneling through defect levels in the
h
-BN barrier, and current caused by their presence is generated.
One-dimensional quasiperiodic structures whose period is much smaller than the wavelength of exciting radiation have been obtained on a titanium surface under the multipulse action of linearly ...polarized femtosecond laser radiation with various surface energy densities. As the radiation energy density increases, the one-dimensional surface nanorelief oriented perpendicularly to the radiation polarization evolves from quasiperiodic ablation nanogrooves to regular lattices with subwave periods (100–400 nm). In contrast to the preceding works for various metals, the period of lattices for titanium decreases with increasing energy density. The formation of the indicated surface nanostructures is explained by the interference of the electric fields of incident laser radiation and a surface electromagnetic wave excited by this radiation, because the length of the surface electromagnetic wave for titanium with significant interband absorption decreases with an increase in the electron excitation of the material.
Resonant tunneling through defect levels in the
h
-BN barrier of van-der-Waals heterostructures is investigated. The effect of multiplication of the tunneling resonances through these levels due to ...the effect of a high degree of imperfection of the structure of the neighboring graphene layer formed intentionally by its processing in plasma is found. Various mechanisms of such an effect are discussed.
Plankton communities are very important for the functioning of aquatic ecosystems 1, 2. Phytoplankton is the dominant primary producer in the aquatic environment, from which most food webs begin, and ...which produces oxygen necessary for aquatic organisms 3. Indicators of phytoplankton development are used to assess the ecological state of water bodies 4. By quickly responding to changes in the aquatic environment, phytoplankton can serve as an indicator of the state of the entire ecosystem.
Objective
—A comparative analysis of the state of phytoplankton in two lakes experiencing anthropogenic pressure and located on the island territory of the Solovetsky archipelago and on the mainland of the Arkhangelsk oblast in the Northern Dvina River basin. Lake Bannoe (Gagarye) is located on the territory of Solovetsky village. Previously, a leather processing plant and a bathing facility of the monastery were located on its shore. Now there are buildings of the Solovetsky branch of the Arkhangelsk experimental algae plant. Lake Kholmovskoye is located in the Primorsky district of the Arkhangelsk oblast, 18 km from the city of Arkhangelsk. On the western shore of the lake is the village of Kholm and summer cottages. From the side of Lake Kholmovskoye, the village of Kholm is surrounded by an artificially dug ditch, into which all household drains flow. On the northern shore are former household premises. An operating cage trout farm is located in the water area of the lake, which is a source of additional organic matter entering the lake waters.
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