卷 165, 编号 4 (2024)

Within the density functional theory method, an analysis of the process of recombinative desorption of hydrogen atoms located on the surface and in the near-surface layers of tungsten W(100) is conducted. A mechanism for the growth of clusters of adsorbed hydrogen atoms on the tungsten surface is proposed. The calculation of activation energies for desorption processes for various configurations of adsorbed hydrogen atoms is performed. The dependence of the recombinative desorption activation energy on the local environment is shown. The lowest activation energy for recombinative desorption ε_des ≈ 0.9–1.0 eV is achieved for a pair of H atoms, where one belongs to a cluster of hydrogen atoms adsorbed on the surface, and the other emerges from the subsurface layers of W(100).

The nature of thermal radiation from a layer of dense gas in local thermodynamic equilibrium with radiation is considered. The radiation spectrum of a gas layer containing a mixture of molecular gases and microparticles consists of a large number (hundreds and thousands) of peaks that rise above the pedestal corresponding to microparticle radiation. Changes in partial radiation fluxes with varying concentration of one of the active components are investigated. Information on molecular radiation parameters contained in the HITRAN database is of great importance for the analysis and calculations. It is shown that the model of a homogeneous atmosphere with spectrum averaging for one or all components is unreliable when analyzing radiation flux changes resulting from concentration changes of one of the radiating components. This model is only convenient for estimating integral parameters of gas radiation. The dense cloud model assumes that radiation in different directions of the layer is determined by different spatial regions that do not affect each other, and also assumes a sharp boundary for dispersed phase radiation. This model works better with increasing optical thickness of the layer relative to molecular components. The accuracy and capabilities of the dense cloud model are demonstrated by calculations of radiation fluxes generated by the standard atmosphere in the absorption bands of carbon dioxide molecules. A fundamental difference is shown between radiation flux changes from an optically dense gas layer with varying temperature when changing the concentration of an active component for single-component and multi-component systems. In a single-component gas, the change in partial radiation flux due to concentration changes of the radiating component is proportional to the temperature gradient, while in a multi-component gas, the change in partial radiation flux of a given component is almost compensated by reverse changes due to absorption by other components. A five-fold error in climate models for global temperature change due to changes in atmospheric carbon dioxide concentration is shown, as these models neglect the absorption of additional carbon dioxide radiation by water molecules and clouds. Additionally, the presented algorithms can serve as a basis for creating radiation amplifiers in the laser transition region for carbon dioxide with wavelengths near 9.5 μm and 10.6 μm. These amplifiers are suitable for monitoring combustion sources on Earth’s surface from satellites, as well as engines and power plants using fuel combustion. The sensitivity of these laser amplifiers exceeds that of modern thermal imagers by orders of magnitude, and the specified spectral lines of laser transitions for amplification fall within the atmospheric transparency window.

In the production of SERS substrates, two main approaches are used to form an array of plasmonic nanoparticles: photolithography and chemical methods, each having its advantages and disadvantages. Another possible method is thermal evaporation in vacuum, which was chosen for analysis through computer modeling. For this purpose, molecular dynamic simulation of crystallization processes of binary Ag–Au nanoparticles array was used, allowing smooth adjustment of the plasmon resonance wavelength. Three arrays of Ag–Au nanoparticles with diameter 2.0, 4.0 and 6.0 nm of various target compositions from Ag₉₀Au₁₀ to Ag₅₀Au₅₀ were created and subjected to cooling procedure from melt with different rates of thermal energy removal. During the modeling of Ag–Au nanoparticles internal structure formation, conclusions were drawn about the dependence of these processes on target composition, size, and level of thermal exposure. Based on the obtained patterns, adjustments to the technological process of creating SERS substrates using binary Ag–Au nanoparticles were proposed.

We investigate the magnetic response of thin NiI2 flakes for temperatures above 80 K. Since no magnetic ordering is expected for bulk NiI2, we observe clear paramagnetic response for massive NiI2 single crystals. In contrast, thin NiI2 flakes show well-defined ferromagnetic hysteresis loop within ±2 kOe field range. The value of the response does not scale with the sample mass, ferromagnetic hysteresis can be seen for any flake orientation in the external field, so it originates from the sample surface, possibly, due to the anisotropic exchange (Kitaev interaction). The observed ferromagnetism is weakly sensitive to temperature up to 300 K. If a flake is multiply exposed to air, ferromagnetic hysteresis is accompanied by the periodic modulation of the magnetization curves, which is usually a fingerprint of the multiferroic state. While NiI2 flakes can not be considered as multiferroics above 80 K, surface degradation due to the crystallohydrate formation decreases the symmetry of NiI2 surface, which produces the surface ferroelectric polarization in addition to the described above ferromagnetic one.

The sequential scheme for solving various electrostatic problems involving a macroscopic body of arbitrary shape by the method of eigenfunctions is presented. The basic properties of eigenfunctions – regular solutions of the Laplace equation – outside, inside and on the surface of the body are considered. Under the assumption of completeness of the system of eigenfunctions on the body surface, a general solution for the electrostatic Green’s function is found and the solution of Dirichlet and Neumann boundary value problems, both external and internal, is performed.

The generation of a powerful laser-induced shock wave in solid matter with a long period of stationary propagation of a flat front at extremely high pressure transfer from a low-density radiation absorber of a terawatt laser pulse to solid matter has been experimentally substantiated. The experiments were performed with flat targets containing an aluminum layer of various shapes and a laser radiation absorber layer made of porous material with a density of 0.01–0.025 g/cm³. The targets were irradiated with second-harmonic Ndlaser pulses with an intensity of 10¹³–5•10¹³ W/cm². Stationary propagation of flat shock waves in the aluminum layer was recorded at a velocity of 20–30 km/s for more than 1 ns with a near-maximum pressure increase from 3–3.5 Mbar in the absorber layer to 7–10 Mbar in the aluminum layer. The result significantly advances the possibilities of precise control over the spatial-temporal dynamics of shock waves in studies of the equation of state of matter.

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