We investigate self-assembled nanoislands in heteroepitaxial GeSi systems by means of atomic force microscopy and micro-Raman scattering techniques. We show that the surface diffusion of Si atoms from the substrate to the islands is strongly enhanced when the temperature increases, giving rise to a wider stability range of pyramid-shaped volumes.

Formation of Si nanocrystals in amorphous Si-metallic Sn film structures has been studied experimentally, by using the Auger spectroscopy, electron microscopy, and Raman scattering methods. The results are analyzed in comparison with recent results on the crystallization of tin-doped amorphous Si. A mechanism of silicon transformation from the amorphous to the nanocrystalline state in the eutectic layer at the Si-Sn interface is proposed. The mechanism essence consists in a cyclic repetition of the processes of formation and decay of the Si-Sn solution. The application aspect of this mechanism for the fabrication of nanosilicon films used in solar cells is discussed. K e y w o r d s: silicon, nanocrystals, thin films, metal-induced crystallization, tin, solar cell.

Using methods of the scanning electron microscopy, Raman scattering of light(RS), and electron paramagnetic resonance (EPR), consistent research of the local structure and magnetic features of different types of raw coal samples from Donetsk basin is carried out. It is established that the ratio of the main peak intensities of RS spectrum D and G is inversely related to the volatile substance amount Vdaf in the coal samples. The study of the kinetic behavior of the EPR line width in hydrogen, oxygen, and methane sorption-desorption processes in each coal sample helped determine that the diffusion coefficient value for hydrogen in coal at room temperature is equal to DН = (2 ÷ 7) × 10−5 cm2/s. It is demonstrated that the oxygen diffusion occurs with time according to two different exponential laws with diffusion coefficients DO,1 = 5 × 10−6 cm2/s and DO,2 = 5.5 × 10−7 cm2/s, respectively. The smaller coefficient corresponds to the diffusion caused by the hopping process. Finally, it is established that the anthracite is a unique type of coal which does not possess the ability “to conserve” the significant EPR line width after oxygen pumping out from the samples.

Porous silicon carbide ͑SiC͒ ceramics are produced using carbon matrices derived from natural wood. Such material is especially promising as it is environmentally friendly with attractive physical properties, including a high level of biocompatibility, chemical inertness, and mechanical strength. We have developed a forced impregnation process with further synthesis of SiC using natural wood as well as a variety of industrial carbon materials and compared the properties of these ceramics. The structure and composition of the materials obtained were investigated by Raman scattering spectroscopy. The hardness of the samples was estimated using the Vickers technique. It was shown that the phase composition and mechanical properties of synthesized SiC ceramics can be effectively controlled by the initial Si contents and temperature of the synthesis process. A large variety of options are demonstrated for materials development taking into account an optimal porosity selection for various practical applications.

Abstract