Interatomic force interaction in an i-AlCuFe quasicrystal

Partial spectra of thermal vibrations of Al, Cu, and Fe atoms in an icosahedral quasicrystal have been obtained by the isotopic-contrast method in inelastic neutron scattering. Joint analysis of these results and the published data on the atomic and electronic structures of the icosahedral i-AlCuFe quasicrystal has been performed. A physical model of the quasicrystal structure is proposed that is in agreement with the existing experimental data and qualitatively describes the peculiarities of interatomic interaction.     

Partial spectra of atomic thermal vibrations in decagonal and icosahedral quasicrystals

The atomic dynamics of an Al-Ni-Fe decagonal quasicrystal and an Al-Cu-Fe icosahedral quasicrystal are investigated experimentally using the isotopic contrast method in inelastic neutron scattering. The partial spectra of thermal vibrations of copper, nickel, iron, and aluminum atoms in the decagonal and icosahedral quasicrystals are reconstructed directly from the experimental data without recourse to model concepts. The limiting energies and positions of the main features in the partial spectra of atomic thermal vibrations in decagonal and icosahedral quasicrystals are determined. It is established that, in the quasicrystals under investigation, the copper and nickel atoms are bound more weakly than the iron atoms and that the partial vibrational spectrum of aluminum atoms in the quasicrystals is considerably harder than the spectrum of pure metallic aluminum.     

Specific heat of nanostructured superconducting tin in magnetic fields

Specific heat of tin nanoparticles, which are embedded in porous glass with average pore size ～7 nm, has been investigated in the low-temperature region in magnetic fields up to 2 T. The temperatures of the transition into the superconducting state in various magnetic fields have been determined for tin nanostructured in porous glass. The H _c -T _c phase diagram has been constructed. The upper critical field has been evaluated and the electronic specific heat coefficient and the Debye temperature have been refined. These results have been discussed within the structural model of tin nanoparticles in porous glass.     

MBE-grown Si: Er light-emitting structures: Effect of implantation and annealing on the luminescence properties

Features appearing in the photo-and electroluminescence spectra of light-emitting structures based on MBE-grown Si: Er layers are studied. The luminescence properties of Si layers implanted by Er and O ions were used as a reference. The temperature quenching of the photoluminescence intensity of Er-containing centers in MBE-grown and implanted layers can be approximated adequately by the same functional relationships with equal activation energies but with preexponential factors differing by more than two orders of magnitude. It is shown that the electroluminescence of Er³⁺ ions can be increased by additional coimplantation of erbium and oxygen ions into MBE-grown light-emitting diode structures and subsequent annealing. After this treatment, the Er-containing centers continue to dominate the luminescence spectrum.     

New possibilities in crystal morphology

Two new morphological phenomena are predicted in crystals: meniscus disappearance and meniscus fixation. Helium crystals are the most convenient objects for their observation. The text was submitted by the authors in English.     

Synthesis of Adamantyl-substituted Keto Esters

Russian Journal of Organic Chemistry -     

Reduction of Ohmic Losses in the Cavities of Low-Power Terahertz Gyrotrons

Radiophysics and Quantum Electronics - In the gyrotrons designed for the terahertz frequency range, the issue of primary interest is to ensure stable single-mode generation during operation at...     

Wideband Windows for Millimeter- and Submillimeter-Wave Vacuum Devices

Radiophysics and Quantum Electronics - We present the results of a theoretical calculation and an experimental study of double-sided antireflective processing of a dielectric plate by creating a...     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Fast quasi-optical phase shifter based on the effect of induced photo conductivity in silicon

We study, both numerically and experimentally, a microwave commutator (phase shifter), whose active element comprises a metal plane mirror with a semiconductor plate on it. Phase shifting of the reflected microwave beam is attained by creating a conducting layer in the semiconductor by a laser with quantum energy approximately equal to the forbidden band width. Using a disk of high-purity silicon and a titatnium-sapphire pulsed laser, we study experimentally a 180° phase shifter operated with a Gaussian wave beam at a frequency of 30 GHz. Efficient phase shifting of the wave beam over a time of several nanoseconds is shown at a low power level.