Rashid Zhapakov

The study of the processes of low-temperature synthesis of one-dimensional particles, which are the basis for two- and three-dimensional structures, is relevant for materials science. The modified metal-stimulated electrochemical etching method made it possible to synthesize silicon nanowires with an average thickness of about 292.6 nm. Scanning electron microscopy has shown the formation of nanowires, flower-like structures, and clusters of matter after the deposition of zinc oxide on the porous surface. The hexagonal structure of ZnO crystallites was determined by X-ray diffraction spectroscopy. Studies of the initial sample by electron paramagnetic resonance (EPR) spectroscopy revealed a narrow signal in the center of the spectrum. The subtraction of the EPR spectra with a sequential increase in microwave power up to 8 mW shows the absence of saturation of the signal. This indicates an almost free flow of charges through the surface nanostructures under the influence of an external field. Heat treatment in an air atmosphere at 300 °C caused a significant increase in the intensity of the EPR spectrum. This led to an increase in the intensity of charge transfer through paramagnetic centers.

A hierarchical surface that includes objects with different sizes, as a result of creating local fields, initiates a large number of effects. Micropores in the composition of macropores, as well as nanoclusters of the substance, were detected by scanning electron and atomic force microscopies on the surface of ZnO/Por-Si samples. An identical fractal dimension for all levels of the hierarchy was determined for these structures, which is associated with the same response to external excitation. Photoluminescence studies have shown the presence of localized levels in the band gap, with the probability of capturing both electrons and holes, which ensures charge transitions between energy bands. Decomposition of the electron paramagnetic resonance (EPR) signal into components made it possible to determine the manifestations of various types of interaction between paramagnetic particles, including the hyperfine structure of the spectrum. The ordering of the structure of the substance as a result of sequential annealing in the range from 300 to 500 °C was revealed in the EPR spectrum. This fact, as well as photo- and gas sensitivity for all types of samples studied, confirms the prospects of using these structures as sensors.

The development of devices combining optical and electrical functions based on silicon-containing materials is one of the challenges in microelectronics. By plasma enhanced chemical vapor deposition synthesis and subsequent annealing, silicon nitride samples with both excess silicon and excess nitrogen were formed. The high concentration of Si-H and N-H bonds was determined by Raman spectroscopy in samples before annealing. By the transmission electron microscopy, it was determined that in addition to silicon nitride, silicon clusters were formed in the sample’s matrix. The photoluminescence spectra changed significantly for both types of samples during annealing in different gas atmospheres. Heat treatment of samples at 1100 °C after synthesis led to the disappearance of the PL spectrum, and after annealing at 800 °C, photoluminescence increases. It is noted that the highest intensity of photoluminescence was detected after annealing in the air atmosphere and the lowest in the nitrogen. The participation of N centers in recombination processes was confirmed by the method of electron paramagnetic resonance. The different mechanisms of particle interaction leading to photoluminescence and charge storage are considered. Thus, the conditions for the synthesis and annealing of silicon nitride layers are selected to obtain controlled luminescent properties in various spectral ranges.

The stability of structures to various influences determines the effectiveness of the sensors that are based on them. A modified method of metal-stimulated electrochemical etching and hydrothermal etching made it possible to synthesize the combined structure of silicon nanowires and ZnO crystallites. The hexagonal structure of zinc oxide crystallites was determined by the X-ray diffraction method. Several causes of radiative recombination have been identified in the photoluminescence spectra, and their nature is associated with the defective structure of zinc oxide. Electron paramagnetic resonance (EPR) spectroscopy studies have revealed energy-stable, uniformly distributed and low-dimensional nanostructures.

Determining the features of the formation of hierarchical structures based on the interactions of elementary particles is a promising area of research. The deposition of 20 and 25 layers of zinc oxide by spray pyrolysis on the Si surface with stepped porosity led to the formation of ZnO particles of various sizes. X-ray fluorescence spectroscopy revealed zinc-containing compounds in thin formed layers. The maximum photoluminescence intensity and peaks characteristic of nanosized zinc oxide were found for a sample with 25 film layers. The mechanism of nanocrystal formation includes the capture of charges on oxygen vacancies.

The formation of structures of different sizes on the surface of a single sample and the study of the mechanisms of their excitations and energy transitions is a promising area of research. ZnO/SiO₂/Si heterostructures were formed by two-stage electrochemical etching of silicon wafers and synthesizing zinc oxide nanoparticles using sol-gel technology. By scanning electron and atomic force microscopies, various pores and clusters were identified. The presence of five levels of surface hierarchy provided the synthesis of light-emitting particles with different properties. Light emission mechanisms are associated with the recombination of excitons and the hyperfine structure of charged particles trapped on oxygen vacancy.

Thin films of tin oxide and composite systems based on them have found the greatest applications in solar energy. The properties of oxides depend on the obtaining technology and following processes. The choice of the optimal solution maturation time influences the functional properties of the films. In this research, solutions with the adding different volume of concentrated aqueous solution of ammonia (NH4OH) per 100 ml of the system were prepared: 0.8 ml (pH=1.40), (pH=1.46) and 1.6 ml (pH=1.49). This enabled the study of the properties of films obtained from solutions of different acidity. The resistance of the films was measured in the 10 different parts of the films. In addition, the effect of the isothermal annealing time at 2500C on the structural and optical properties of the samples was investigated. As a result of this study, there was found the correlation between an increase in the duration of annealing and a decrease in the transparency of films obtained from the SnCl4/EtOH. The annealing at temperature 2500C within 6 hours led to a change in transparency of films from 93% (λ=550nm) to 88%. The further increase of the annealing duration up to 9 hours does not affect the transparency of films