In this work, the processes of disproportionation of solid-phase silicon monoxide, accompanied by the formation of nanocrystalline silicon precipitates in the medium of amorphous SiOx suboxide (initial composition SiO0.9), have been studied. Based on the data of X-ray diffraction analysis and transmission electron microscopy, the dynamics of changes in the amount, concentration and size of phase precipitates of silicon with an increase in the temperature of isochronous annealing from 800 °C to 1200 °C is traced. It was found that with a monotonic increase in the total mass of the precipitated silicon, the number of its crystallization centers per unit volume nonmonotonically depends on temperature. The activation energy of diffusion of silicon atoms in the SiOx matrix was determined to be Ea1= 1.64 eV, and the activation energy of their transfer from the formed precipitates to the growth medium of SiOx was Ea2 = 2.38 eV. Anisotropic deformation of silicon crystallites precipitated during the disproportionation of SiO has been revealed for the first time. This phenomenon is associated with the difference in the specific volumes of the separated phases and the anisotropy of the growth rate of silicon precipitates formed in a solid amorphous medium.

Dispersed composite materials based on silicon monoxide and carbon (SiO/C) were obtained as a result of heat treatment of a powder mixture consisting of 40 wt% SiO and 60 wt% CF0.8. Annealing was carried out in an argon atmosphere at temperatures 1000 − 1250°C. Using electron microscopy and Raman scattering, it was found that at Т>=1100°C, silicon carbide appears in the solid-phase product, including in the form of cubic nanowhiskers. Based on the data on the weight loss of the reaction mixture, the composition of the resulting products was calculated as a function of the annealing temperature. Anodes made of composites obtained at temperatures above 1100°C demonstrate a sharp drop in capacitance and Columbic efficiency. It is shown that the observed changes are caused not so much by the formation of SiC as by an increase in the oxygen content in the matrix surrounding the silicon precipitates, which were formed as a result of disproportionation of SiO. It was found that the optimal annealing temperature, which provides the highest values of capacity, the initial coulombic efficiency and the ability to operate at high speed current densities is Т =1150°С.

We present the results on the selective-area growth of GaN nanowires using a molecular beam epitaxy technique on patterned SiOx/Si substrates without any seed layers. The patterned SiOx/Si substrates were prepared by the simple microlens photolithography method. The influence of the substrate temperature on the morphological properties of GaN nanowires was investigated. The optimal growth parameters for the selective-area growth of GaN nanowires were experimentally determined.

The effect of annealing temperature in argon atmosphere on the ability of Si-C nanocomposites to reversibly insert lithium was investigated. It was found that the higher the annealing temperature during the formation of the composite, the lower is the capacitance of the electrode made from it. X-ray diffraction analysis and transmission electron microscopy reveal that the reason of the capacitance decrease is formation at T  1100°C of silicon carbide of cubic modification -SiC, inactive with respect to the formation of lithium alloys or intercalates.

When studying the processes of thermal carbonization of silicon monoxide in the presence of non-stoichiometric carbon monofluoride, it was found that increasing the annealing temperature of mixtures of SiO and CFx powders in a quasiclosed volume to 1000°C and higher leads to the release of whisker-like SiC nanocrystals. The studies showed that in parallel with the known crystallization of SiC nanowires as a result of the interaction of SiO vapors with carbon monoxide, previously undescribed interaction of CO with gas-phase silicon difluoride SiF2 takes part in their formation. At temperatures below 1200°C, this reaction is dominant, making the largest contribution to the yield of SiC nanowires.

We demonstrate the possibility of selective-area growth of ordered arrays of GaN nanowires by molecular beam epitaxy on SiOx/Si substrates patterned by photolithography with microspherical lenses without the preliminary formation of seed layers. The effect of the substrate temperature on the morphological properties of the obtained arrays of nanowitres is studied. The optimal growth parameters ensuring the selective-area growth of GaN nanowires are experimentally found.

A new method for formation of porous silicon-carbon nanocomposites is proposed. It is based on reduction of carbon monofluoride by silicon. The resulting composite materials consist of silicon nanoparticles enclosed in a carbon shell. The contacts of such particles ensure the flow of current through the arising carbon matrix. Density, porosity and resistivity on the composition of the Si-C tablets obtained by the proposed method are determined. The materials under the study are of interest for high-capacity negative electrodes of lithium-ion batteries.

Isochronous annealing of preliminarily compacted silicon nanopowder specimens is investigated. The density, structure, and conductivity of the material are determined as a function of sintering temperature. The electrochemical characteristics of anodes, which were sintered in the temperature range of 1100 to 1200°C, are studied using galvanostatic tests and cyclic voltammetry. It is found that the specimen, which was annealed at T = 1150°C, shows the best results. This specimen has a density of 1.60 g/cm 3 , a connected silicon framework, and an open-pore system.

AbstractThe technique of the electrochemical and photoelectrochemical etching of single-crystal silicon wafers commonly used to fabricate macroporous silicon layers is inefficient and costly. An alternative method for forming bulk macroporous silicon is the high-temperature sintering of Si powder. The process of nanopowder sintering preliminarily subjected to dry cold compression (without binding additives) is investigated. The properties of the sintered material, including its microstructure, density, and electrical conductivity, are studied at different annealing temperature and time. Techniques for changing the porosity of the sintered samples and for determining of the interior surface area are discussed.

The silicon anodes for lithium-ion batteries subjected to cyclic tests of variable duration are studied by electron microscopy, energy-dispersive X-ray analysis, and Raman scattering. It is shown that the discharge capacity of electrodes based on macroporous silicon degrade due to the fracture of silicon walls and the formation of a Si-Li amorphous phase. Both effects arise early on testing. The number of cracks and the degree of disorder of the silicon crystal lattice are found to grow with the number of lithiation cycles and be nonuniformly distributed along the height of the walls. Namely, lithium is incorporated largely into the upper part of the structure adjacent to the separator. The disorder degree of the crystal lattice in the lithiated anodes is compared with that in standard amorphous silicon by analysis of the Raman spectra.

Scientific and methodical fundamentals are developed for the technology of manufacturing of microstructured Si anodes based on macroporous silicon. The main technological processes include the electrochemical etching of single-crystal silicon wafers that allows obtaining an ordered lattice of cylindrical macropores with a cavity between the porous layer and support, anisotropic shaping, formation of a copper contact, and separation of the silicon structure from the support. Microstructures are manufactured in the form of a grid, columns, and zigzags with thin monodispersed walls of different crystallographic orientation. The possibility of repeated use of the Si support for anodic treatment and the manufacturing of several anodic structures from a single plate Si wafer is shown. The performed electrochemical tests demonstrate that the anodes manufactured according to the developed technology sustain hundreds of charge–discharge cycles.