Bulletin of the Lebedev Physics Institute最新文献

We report the results of a study of a multispark discharge in deionized water (conductivity of no more than 0.1 μS/cm) with gas injection into the interelectrode space. Experiments are performed using a pulse generator with a storage capacitor energy of up to 1.6 J, a voltage up to 20 kV, and a pulse duration of 1.5‒2 μs. Active forms of oxygen and nitrogen formed in the liquid under the action of the discharge are quantitatively measured as functions of the time of exposure to the discharge and the type of the injected gas. The effect of the electrode material on the dynamics of the production of long-lived chemical compounds is analyzed.

X-ray absorption near-edge structure (XANES) spectroscopy based on synchrotron radiation is a dependable technique to obtain details on the structural properties of the complexes. Four physiologically significant copper (II) compounds are being studied through means of X-ray K-absorption spectroscopy. These complexes are: (1) Cu(L¹)₂Cl₂ ‧ 2H₂O, (2) Cu(L²)₂Cl₂ ‧ 2H₂O, (3) Cu(L¹)₂SO₄ ‧ 5H₂O and (4) Cu(L²)₂SO₄ ‧ 5H₂O, where L¹ = 5-chloro salicylaldehyde benzoyl hydrazone (sbh) and L² = 5-nitro sbh. We have obtained XANES spectra at the 2.5 GeV Cu K-Edge EXAFS beamline (BL-09), at Indus-2, RRCAT, Indore, India. From the position and type of absorbed X-ray discontinuities, information concerning the structural and chemical bonding of transition metal complexes has been discovered. Computer programs Origin and Athena have been used to analyze the XANES data. Numerous X-ray absorption features, such as chemical shift, edge width and shift of the Principal absorption maximum, have been found by the current analysis. The information on the chemical shift suggests that the complexes include copper in the +2-oxidation state.

The rhombohedral (R3) phase of molybdenum disulfide (MoS₂) is synthesized from elemental components at high temperatures and pressures. The crystal structure and lattice constants are determined by full-profile X-ray diffraction analysis of the synthesized powder. Scanning electron microscopy in combination with energy-dispersive X-ray microanalysis confirms the formation of layered crystals with the elemental composition of Mo and S in the ratio of 1 : 2. Luminescence spectra of the 3R-MoS₂ bilayer transferred onto a SiO₂/Si substrate demonstrate narrow emission lines characteristic of low-defect materials.

During the research of a complete stage sliding discharge on a surface of solid dielectric in atmospheric air in pulsed mode, an effect of self-organization of the discharge formation was found. With increase of pulse repetition rate, a change of the current flow pathway occurs. From the surface of a dielectric substrate, starting from a middle part of the discharge gap, the discharge channel shifts to surrounding gas volume. We explained this phenomenon by an accumulating ionization effect within gas volume due to the difference of vibrational relaxation time of oxygen, depending on temperature on dielectric substrate and within gas volume above the surface.

We report a study of the spectrum of the Cherenkov beam instability in a plasma dielectric waveguide. In the absence of plasma, the instability results from the induced Cherenkov radiation of many transverse slow electromagnetic modes of the waveguide. In the presence of plasma, the long-wavelength part of the spectrum is due to the excitation of a potential Langmuir wave, aperiodic self-modulation of the beam, and Cherenkov radiation of a surface plasma wave; the high-frequency part of the spectrum weakly depends on the presence of plasma in the waveguide.

We report the results of calibration of a two-channel scintillation spectrometer with a thickness of 0.5X₀ on the secondary electron beam of the Pakhra accelerator developed at the Lebedev Physical Institute of the Russian Academy of Sciences. Light signals in the spectrometer are registered with FEU-49 photoelectron multipliers. At an electron energy of E ≈ 30 MeV, the relative energy resolution of the sum of the signals from both channels is ~5%.

The effect of 532-nm pulsed laser radiation on properties of a single-crystal diamond film containing optically active SiV^‒ centers is studied using in-situ measurements of the photoluminescence spectra at a temperature of 77 K. It is shown that at a pulse duration of 500 ns, the threshold energy density at which the rearrangement of SiV^‒ centers is recorded is ~0.112 J/cm². The rearrangement leads to a decrease in the intensity of the zero-phonon emission line of SiV^‒ centers relative to the intensity of the Raman scattering signal on optical phonons of the diamond matrix. With an increase in the energy density of incident pulses to 0.540 J/cm², the luminescence quenching effect reaches saturation, and traces of ablation and/or graphitization are observed on the film surface. The found effects are explained by local heating of the diamond film due to the processes of three-photon absorption of light, in which the absorption coefficient sharply depends on the energy of incident pulses.

Reflection microscopy in the visible and near-infrared range is used to study optical properties of EuS₂ flakes. It is shown that for small flake areas, microreflection spectra can be adequately described by a model that combines the reflection of light from both the film‒substrate structure and the substrate. The indirect absorption edge (E_g = 0.83 eV) and the refractive index below the indirect absorption edge (n = 2.9) are determined from the microreflection spectra.

Explosive emission processes are of great importance in electrodynamic and accelerating structures exposed to high-power radio-frequency electromagnetic waves. These processes emerge due to the explosion of microprotrusions on the surface of electrodes. The paper presents the results of radiation magnetohydrodynamic calculations of the explosion of copper conductors under conditions similar to those that arise during the explosion of microprotrusions. This means that the current density is about 10⁹ A/cm². Quasi-stationary and radio-frequency explosion regimes are considered. It turns out that in both cases the maximum of the spectral distribution lies in the ultraviolet range. However, the radiation power that comes out of the conductor in the radio frequency regime is almost two orders of magnitude less than that in the quasi-stationary regime.

We report the results of a study of optoelectric properties of thin films consisting of titanium dioxide microscrolls doped colloidal systems containing linear carbon chains with anchor ends in the form of metal nanoparticles. The electric current generation in such films during irradiation with optical radiation is investigated. The presence of developed optoelectric properties due to the generated structure of the microscrolls is demonstrated. In the approximation of a Schottky photodiode, a model for calculating the photocurrent in the structures in question is proposed. The integral quantum efficiency is estimated and a conclusion is made that the considered samples are promising materials for solar cells.