AlGaN-based quantum well (QW) heterostructures grown by plasma-assisted molecular beam epitaxy on c-Al2O3 substrates have been studied. The high-temperature (785 °C) synthesis of AlN buffer layer nucleated by a migration-enhanced epitaxy and including several ultrathin GaN interlayers was the optimum approach for lowering the threading dislocations density down to 108–109 cm−2. High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) has revealed the step-like roughness of the AlN/Al2O3 interface. Also, the formation of Al-rich barriers induced by temperature-modulated epitaxy and the spontaneous compositional disordering have been found in the AlxGa1−xN (x > 0.6) barrier layers. The origin of these phenomena and their influence on parameters of the mid-UV stimulated emission observed in the QW heterostructures were discussed. The fine structure of the QWs formed by a submonolayer digital alloying technique has been displayed by HAADF STEM, and optical properties of the QW structures were studied by temperature- and time-dependent photoluminescence spectroscopy.

AlGaN-based SQW heterostructures grown by plasma-assisted molecular beam epitaxy on c-Al2O3 substrates have been studied with high resolution transmission electron microscopy (HR TEM), photoluminescence spectroscopy and x-ray diffraction. The high-temperature (780°C) synthesis of the AlN buffer layer nucleated on c-Al2O3 by a migration enhanced epitaxy and including several ultra-thin GaN interlayers grown under moderate N-rich conditions was shown to be the optimum approach for lowering the threading dislocations density down to 108-109 cm-2. HR TEM study has confirmed the fine structure of single quantum wells (SQW) formed by a sub-monolayer digital alloying technique and revealed different kinds of compositional inhomogeneities in the AlxGa1-xN barrier layers of the heterostructures, including the formation of Al-rich barriers induced by the temperature-modulated epitaxy and the spontaneous compositional disordering along the growth axis for x=0.6-0.7. The influence of these phenomena on the parameters of the mid-UV stimulated emission observed in the SQW structures has been studied as well.

Stressor-controlled epitaxy has been proposed as an efficient method of CdSe quantum dot fabrication. The studies are performed on a type-II CdSe/BeTe system, where CdTe and BeSe inteface bonds play a role of intrinsic stressors. Predeposition of ~0.2 ML CdTe stressor ( Δ a/a= +15%), corresponding to a local maximum of RHEED specular spot intensity, appears to induce variation of stress field across the BeTe surface, caused by alternating regions with CdTe and BeSe bonds. It results in preferential nucleation of regularly arranged CdSe QDs at the BeSe sites with the following vertical chess-ordering in the CdSe/BeTe multilayers. The structures demonstrate bright up to RT PL in the 1.9-2.1 eV range and strong in-plane PL anisotropy related to non-equivalent bottom and top CdSe QD interfaces having estimated from x-ray diffraction total concentrations of CdTe and BeSe bonds of 0.3-0.4 and 0.6-0.7 ML, respectively.

A series of crystalline isomorphic solid solutions of Yttrium-Lutetium Aluminum Garnets (Y1−cLuc)3Al5O12 (c = 0 – 1) has been studied. The measurements of dielectric loss (DL) tangent tgδ has been performed at electromagnetic wavelengths 1 – 0.6 mm and temperature T = 300 K. The results obtained has been compared with longitudinal acoustic waves (AW) attenuation data for frequencies f = 1 – 9.4 GHz, T = 4.2 – 300 K and with theory. The correlation between the DL and the AW attenuation is observed. The dependencies of DL (at T = 300 K) and AW attenuation (at T > 77 K) on concentration c are qualitatively identical in the whole interval c = 0 – 1. From comparison with theory it follows that the observed DL is due to the two-phonon intrinsic lattice loss. It is caused by the lattice anharmonicity as well as the AW attenuation at not too low temperatures. Also the prediction for concentration dependence of DL at very low temperatures is discussed that follows from comparison with the results of “heat pulse” propagation experiments for the same samples at T = 2 K and theory.

To immobilize a high sulfate radioactive wastes a system Na2O-A12O3-P2O5-SO3 has been chosen as one where glasses have a relatively low melting points and good chemical durability. Glasses within partial system 44 Na2O, 20 A12O3 (36-x) P2O5 x SO3 have been prepared at 1000 °C. A possibility of assimilation up to 12 mole % of SO3 has been established. The basic properties of sulfate-containing glasses as density, microhardness, thermal expansion coefficient, transformation and deformation temperatures, viscosity, electric resistivity, leach rate of ions and diffusion coefficients of 22Na, 35S, 90Sr and 137Cs have been measured. Glass structure by infrared and EPR spectroscopies has been investigated.