Terahertz time-domain spectroscopy (THz-TDs) has been used to record the resonant frequencies of plasmon oscillations excited in samples of heterostructures with three InxGa1-xN/GaN quantum wells (QWs) by laser pulses with a duration of 130 fs in the temperature range from 90 to 170 K. Fast Fourier transform (FFT) of the time dependence of the electric field of THz-pulses made it possible to obtain the frequency spectra of the power and phase shift of THz-radiation, the interpretation of which made it possible to estimate the pulse relaxation time, mobility and effective mass of two-dimensional electron gas (2DEG) in the heterostructures. Using a series of frequency spectra of the power and phase shift of THz-radiation, the temperature dependences of the effective mass and relaxation time of the 2DEG pulse were obtained. Mobility value 2DEG obtained by the THz-TDs is in good agreement with the data of Hall measurements. Keywords: heterostructures, pulse relaxation time, 2DEG, terahertz radiation, terahertz spectroscopy.

The results of a comparative study of the optical properties of the thin films of zinc oxide ZnO, taking into account the influence of their copper doping, are presented. Using the experimental spectra of optical transmission, spectral dependences of the refractive and extinction index of the studied material, as well as components of complex dielectric permittivity constant, were calculated. The revealed features of the obtained dispersion curves are associated with the behavior of the impurity injected into the ZnO matrix. Keywords: zinc oxide, optical transmission, refractive index, dielectric permittivity.

The previously proposed model of dengling bonds of an organic macromolecule (MM) adsorbed on an ideal single-layer graphene (SLG) is generalized to the presence of structural defects in SLG: inclusions of two-layer or amorphous graphene. Analytical estimates of the charge transition between MM and the substrate and the adhesion energy are obtained. Keywords: macromolecule with dangling bonds, single- and bilayer graphene, amorphous graphene.

The results of a study of the optical and structural properties of wide-bandgap (x~0.7) layers in laser heterostructures based on CdxHg1-xTe solid solutions grown by molecular beam epitaxy on (013)GaAs substrates, as well as epitaxial films similar to these layers in chemical composition, are presented. It is shown that the position of the maximum of the photoluminescence spectrum and the nature of its temperature shift are related to the disordering of the composition of the solid solution. Shallow and deep acceptor levels were found in the bandgap. The possible influence of disordering and acceptor levels in laser structures on the energy spectrum of carriers is discussed. Keywords: CdHgTe, laser structures, photoluminescence, defects, structural properties.

Studies on the generation of terahertz (THz) radiation in p-n-heterostructures based on a-Si:H/c-Si upon their photoexcitation by a femtosecond titanium-sapphire laser with a wavelength of 800 nm are presented. The properties of observed THz radiation allow to explain its nature by excitation of fast photocurrent of nonequilibrium charge carriers created in the region of the potential barrier under femtosecond interband photoexcitation of the structure. The fast photocurrent, in turn, emits THz electromagnetic waves. The waveforms and amplitude spectra of the observed THz radiation reflect the dynamics of photoexcited charge carriers in the structures. The intensity of THz radiation observed in the studied p-n-heterostructures based on a-Si:H/c-Si is comparable to that generated in n-InAs crystals, which are widely used as emitters in systems of THz time-domain spectroscopy. Therefore, a-Si:H/c-Si p-n-heterostructures can be used as THz emitters for need of THz spectroscopy. Keywords: femtosecond laser photoexcitation, heterostructures, fast photocurrent, terahertz electromagnetic radiation.

The features of energy exchange during the contra-directional mixing of two linearly polarized light waves in a cubic photorefractive Bi12SiO20 piezocrystal of (001)-cut are analyzed. The dependences of the relative intensity of the signal wave on the azimuth of its polarization at the entrance to the crystal during mixing with the reference wave polarized in the plane of incidence are theoretically studied for various crystal orientation angles. The dependence of the relative intensity of the signal wave on the azimuth of its polarization is experimentally studied for the cases when the vector amplitudes of light waves propagating in the crystal are parallel and perpendicular to each other. The calculation is based on the numerical solution of the coupled waves equations with and without taking into account the self-diffraction of the light waves by the reflection holographic grating recorded in the crystal. Based on a comparison of theoretical and experimental data, the influence of self-diffraction on the mutual transformation of light waves during their contra-directional mixing is analyzed. The limits of applicability of the static grating and the dynamic grating approximations for solution of the coupled waves equations are determined. Keywords: Photorefractive crystal, reflection holographic grating, coupled wave equations, self-diffraction.

Spin pumping by traveling magnetostatic surface waves (MSSW) has been experimentally investigated in YIG|Pt structures made on the basis of 0.9, 4, 8, 14 and 18 μm thick YIG epitaxial films. It is found that at frequencies corresponding to the van Hove singularities in the density of states of the MSSW spectrum of the structure, the EMF value generated due to the inverse spin Hall effect increases. This increase is associated with an increase in the spin mixing conductance of the YIG|Pt interface due to an increase in the efficiency of electron-magnon scattering at the frequencies of van Hove singularities in the spin wave spectrum. Keywords: spintronics, spin transport, spin waves, magnon density of states.

In GdFeCo/Ir/GdFeCo heterostructures with amorphous GdFeCo layers, three critical points were found in the temperature dependences of the magnetization. In the neighborhood of 100 K, the temperature of compensation for the magnetizations of the Gd and FeCo sublattices is observed, which is found in the form of a magnetization minimum and does not depend on the magnetic field. As the temperature decreases, a sharp stepwise transition is observed, which corresponds to the switching of the mutual magnetization's orientation of the GdFeCo layers between their parallel and antiparallel configurations. This transition depends on the magnetic field in which the measurement is made. Its critical temperature shifts in the range of 70-300 K with a change in the field in the range of 0.5-5 T. At low temperatures <50 K, a transition to the spin glass state is observed, which is accompanied by a decrease in the magnetic moment to zero and disappears when the field is applied. Keywords: Compensation temperature, synthetic ferrimagnet, exchange interaction, magnetic anisotropy.

According to the impedance spectroscopy data, a significant frequency dispersion of the real and imaginary components of the permittivity was found in the intercalated AgxHfS2 samples. Using the modular formalism, the dielectric relaxation times were determined, which decrease in magnitude with an increase in the silver content in the samples. Their coincidence with the relaxation times determined from the frequency dependences of the imaginary parts of the complex impedance was shown. Keywords: Intercalates, impedance, hafnium disulfide, silver, dielectric permittivity, electrical module.

The energy spectra of ten isomers of trifluoromethyl derivatives of fullerenes C60(CF3)10 and C70(CF3)10 are calculated within the framework of the Hubbard model. Based on the obtained energy spectra, the optical absorption spectra of these compounds are modeled. The calculated optical absorption spectra are compared with the experimental spectra. Keywords: trifluoromethyl derivatives, fullerene, Hubbard model, energy spectrum, optical absorption spectrum.