Silicon-germanium alloy films were formed by electrochemical deposition of germanium into porous silicon matrices with thicknesses varying from 1.5 to 10 mu m followed by subsequent rapid thermal processing at 950 degrees C in an inert atmosphere. Study of the fabricated structures using SEM and Raman spectroscopy, as well as measurements of their electrical conductivity and thermoelectric properties revealed that the highest Seebeck coefficient (-505 mu V/K at 450 K) and Power Factor (1950 mu W/(m & sdot;K2) at 400 K) values were obtained when a 5 mu m-thick porous silicon was used as a structural matrix. Under such conditions, an optimal balance between electrical conductivity, structural disorder and electrical insulation from the substrate is achieved due to the presence of a residual porous underlayer, making it possible to maximize the film's thermoelectric performance. The obtained silicon-germanium alloy films are deemed suitable for the fabrication of both discrete and integrated thermoelectric devices based on monocrystalline silicon substrates.

Thermoelectric materials based on cobalt-containing SiGe alloy films were fabricated using monocrystalline silicon wafers with thin porous silicon layers electrochemically decorated with cobalt nanoparticles, filled germanium and subsequently subjected to rapid thermal processing. SEM, XRD, Raman spectroscopy and measurements of electrical conductivity and thermoelectric parameters revealed that an intermediate silicidization step involving thermal processing at 850 degrees C after cobalt deposition is crucial to maximize the resulting alloy's thermoelectric capabilities. The obtained silicidized SiGe:Co samples demonstrate a Seebeck coefficient of -450 mu V/K and an estimated figure-of-merit ZT value of up to 0.72 at 450 K due to the presence of crystalline cobalt silicides in the film. These results enable a new approach to the fabrication of thin film thermoelectric materials based on SiGe alloys.

Film structures based on Si1–xGex (0 < x < 1) solid solutions are currently obtained by chemical-vapor-deposition methods. For device application of the obtained structures, it is necessary to know the electrical properties of the material synthesized under different conditions. In this work, we carry out galvanomagnetic studies of the electrical conductivity in porous and solid Si1–xGex films, as well as the concentration and mobility of the majority charge carriers in them at a temperature of 30–300 K. It is shown that, as in pure silicon and germanium of comparable porosity, the electrical conductivity in the studied samples can be considered as in a medium with voids. It is established that the type of majority charge carriers in the alloy is determined by the type of silicon substrate used. This is practically important for creating both arms of a thermoelectric converter, which makes the method for producing Si1–xGex(0 < x < 1) alloy promising for device applications, in particular in thermoelectric converters and lithium-ion batteries.

Using photoluminescence and Raman spectroscopy, as well as high-resolution transmission microscopy and X-ray diffraction, germanium nanowires obtained by cathodic deposition from an aqueous solution of germanium dioxide were studied during their annealing by a laser at 720 °C under ambient conditions. It is established that the dynamics of Raman and photoluminescence spectra are related to the oxidation of wires during such annealing. The study showed that vacuum annealing of as-grown nanowires at 600 °C for 30 min suppresses laser high-temperature germanium oxidation. The observed effect is associated with the saturation of vacancies in the surface germanium suboxide with indium atoms used as a catalyst in the formation of nanowires.

It is common practice to use mesoporous layers, nanofibers, and nanospheres of titanium oxide of various chemical and phase compositions as electrodes for microbatteries. Studies of the properties of TiO2 nanotubes (TiO2 NT’s) have shown the relevance of using it as an anode electrode for sodium-ion batteries. In this paper a method for modifying TiO2 NT’s with the removal of the inner layer of nanotubes by etching in a mixture of sulfuric acid and hydrogen peroxide is proposed. It is demonstrated that the inner mesoporous layer of nanotubes hinders the embedding and extraction, respectively, of sodium ions into and from the structure of TiO2 NT’s. Cyclic voltammetry studies show that after the removal of the inner part of the nanotubes, anodic and cathodic peaks appear, which are responsible for the extraction and intercalation of sodium ions, respectively. It is established that sodium ions are not intercalated into the crystal lattice of the TiO2 NT’s sample after the etching of the inner layer, which indicates the reversibility of the ion introduction process. The studies have shown that TiO2 NT’s can be used as an anode electrode in ionic accumulators and microbatteries due to the electrochemical characteristics and the possibility of various modifications of the TiO2 NT’s array.

A variety of micro‐ and nanocomposite materials based on electrochemically‐acquired porous silicon are produced and evaluated in terms of their applicability to display technology. It is shown that porous silicon provides a versatile and well‐adjustable template for filling with other materials, which can outright change its electrophysical parameters. While, in terms of display applications, porous silicon layers are mostly prominent for their photohiminescence not akin to monocrystalline silicon, this property can be additionally enhanced by employing a variety of electrochemical techniques to form metal deposits of certain shapes.

Morphology and crystalline structure of silicon-germanium alloys formed by rapid thermal processing of germanium-filled porous silicon layers are evaluated. Two types of porous silicon are employed as matrices for electrochemical pore filling using GeO2 aqueous solutions and subsequently compared, the first one formed by electrochemical anodization and the second by silver-assisted chemical etching of monocrystalline silicon. The resulting alloys' structure and composition are investigated using scanning electron microscopy, energy -dispersive X-ray analysis, Raman spectroscopy and X-ray powder diffraction. It is shown that by varying the porosity of the initial matrix (by adjusting anodization current density for anodic porous silicon or changing silver deposition time for structures produced by metal-assisted etching) in the range from 55 to 75%, Si1-xGex alloys with germanium fractions of x = 0.31 to x = 0.83 can be formed, as indicated by Raman spectroscopy. It is concluded that composition-adjustable layers of silicon-germanium can be successfully formed on either type of porous silicon layer. While an increase in porosity generally leads to a decrease in silicon fractions in the alloy, the steepness of this effect varies heavily depending on the type of porous matrix used and should be considered independently for anodic porous silicon and silicon nanowires.

Continuous and porous films of Si _1-x Ge _x alloys with a germanium content of about 40 % and a thickness of 3–4 μ m formed on single-crystal silicon by electrochemical deposition into the porous silicon matrix with a subsequent rapid thermal annealing at a temperature of 950 ^∘ C have been investigated by the Raman scattering spectroscopy and scanning electron microscopy methods. Based on the spectra in the Stokes and anti-Stokes frequency bands with the use of the Boltzmann statistics and the Fourier thermal conductivity law, the film thermal conductivity coefficients have been determined; their values are 7–9 and 3–6 W/(m K) for the continuous and porous films, respectively. The low thermal conductivity of the porous film is explained by an additional phonon scattering at a developed surface of pores. The possibility of application of such films in thermoelectric converters is provided by the simplicity and scalability of the procedure of alloy producing and its low thermal conductivity

Photocatalysts based on the anodic single-walled titania nanotubes modified with metal nanoparticles (Au, Pd, Pt) were prepared and investigated. The metal nanoparticles sizes are in a range from 3 to 15 nm. The wall thickness of the nanotubes varied from 14 to 17 nm. It is established that photocatalysts with Au, Pd, Pt produce acetaldehyde during complete ethanol decomposition reaction. Additionally the formation of methane occurs in the TiO2 nanotubes with Pd and Au nanoparticles. We obtained firstly the multifunctional TiO2 nanotubes modified with Pd and Au nanoparticles for use both in air purification and in the production of hydrocarbon fuel precursors.

In this work, the effect of the electrolyte solution temperature on the morphology, phase composition, and photoelectrochemical properties of CuOx nanostructures were investigated. It has been shown that rising tem-peratures do not form the well-studied Cu(OH)2 nanorods, but CuO nanosheets 5-7 nm thick, layered on top of each other. The obtained copper oxide nanostructures possess the CuO crystal structure immediately after anodising. As the temperature of the electrolyte increases, the degree of light reflection decreases in the wavelength range from 190 to 1100 nm, with a maximum of 1.25%.

Сплошные и пористые плёнки сплавов Si1-xGex с содержанием германия около 40 % и толщиной 3-4 мкм, сформированные на монокристаллическом кремнии методом электрохимического осаждения германия в матрицу пористого кремния с последующим быстрым термическим отжигом при температуре 950 °C, исследованы методами спектроскопии комбинационного рассеяния света (КРС), оптической спектроскопии и сканирующей электронной микроскопии. На основе спектров, снятых в стоксовой и антистоксовой областях частот с использованием статистики Больцмана и закона теплопроводности Фурье, определены коэффициенты теплопроводности плёнок, которые составляют 7-9 и 3-6 Вт / (м ⋅ К) для сплошной и пористой плёнок соответственно. Низкая теплопроводность пористой плёнки объясняется дополнительнымфононным рассеянием на развитой поверхности пор. Перспективность применения таких плёнок в термоэлектрических преобразователях обеспечивается простотой и масштабируемостью способа изготовления сплава, а также его низкой теплопроводностью. Solid and porous films of the Si 1-xGex alloys with a germanium content of about 40% and a thickness of 3-4 μm, formed on single-crystal silicon by electrochemical deposition of germanium into a porous silicon matrix followed by rapid thermal annealing at a temperature of 950 °C, are studied by Raman spectroscopy, optical spectroscopy, and scanning electron microscopy. Based on the Raman spectra taken in the Stokes and anti-Stokes frequency regions, using Boltzmann statistics and the Fourier thermal conductivity law, the thermal conductivity of the films is determined, which is found to be 7-9 and 3-6 W/(m×K) for a continuous and porous film, respectively. The low thermal conductivity of the porous film is explained by additional phonon scattering from the developed pore surface. The prospect of using such films in thermoelectric converters is ensured by the simplicity and scalability of the method for manufacturing the alloy, as well as its low thermal conductivity.

Continuous and porous films of Si(1-x)Ge(x )alloys with a germanium content of about40%and a thickness of 3-4 mu m formed on single-crystal silicon by electrochemical deposition in to the porous silicon matrix with a subsequent rapid thermal annealing at a temperature of 950(degrees)Chave been investigated by the Raman scattering spectroscopy and scanning electron microscopy methods. Based on the spectra in the Stokes and anti-Stokes frequency bands with the use of the Boltzmann statistics and the Fourier thermal conductivity law, the film thermal conductivity coefficients have been determined; their values are 7-9 and 3-6 W/(m K) for the continuous and porous films, respectively. The low thermal conductivity of the porous film is explained by an additional phonon scattering at a developed surface of pores. The possibility of application of such films in thermoelectric converters is provided by the simplicity and scalability of the procedure of alloy producing and its low thermal conductivity

Morphology and crystalline structure of silicon-germanium alloys formed by rapid thermal processing of germanium-filled porous silicon layers are evaluated. Two types of porous matrices are used for electrochemical pore filling using GeO2 aqueous solutions and subsequently compared, the first one formed by electrochemical anodization and the second by metal-assisted chemical etching of monocrystalline silicon. The resulting alloys’ structure and composition are investigated using scanning electron-microscopy, Raman spectroscopy and X-ray powder diffraction. It is concluded that layers of silicon-germanium can be successfully formed on either type of porous layer, exhibiting some minor distinctions in uniformity but no major difference between the resulting alloys’ composition.

A method of germanium electrodeposition from a GeO2-based aqueous solution into the pore channels of anodic mesoporous silicon formed on n-type highly-doped (100) silicon wafers is described. The effect of deposition time, pore channel shape and preconditioning of porous silicon layers in hydrofluoric acid is evaluated. Recommendations are given in regards to the optimal parameter combinations to ensure uniform pore channel filling with germanium. The possibility of producing silicon-germanium alloys by subsequent rapid heat treatment of the germanium-filled porous silicon layers is established.

Titania (TiO2) is a widely used semiconductor for the photocatalytic decomposition of organic impurities in air, water and the conversion of CO2 into hydrocarbon fuel precursors. TiO2 in the form of nanotubes arrays is the most attractive for practical use because of the morphological advantages providing more favorable diffusion of photocatalytic reaction products and a low recombination rate of photogenerated electrons and holes. We have carried out a comparative study of the photocatalytic activity of gas-phase conversion of CO2 to hydrocarbon products and the defect properties of multi-walled and single-walled arrays of TiO2 nanotubes. Methanol and methane have been detected in the CO2 photoreduction process. The photocatalytic evolution rate of multi-walled TiO2 nanotubes is twice as fast for methane as for single-walled TiO2 nanotubes after four hours of irradiation and four times faster for methanol. The type and features of the structural defects have been investigated by EPR spectroscopy. For the first time, it has been shown that Ti3+/oxygen vacancy centers are mainly located inside the outer layer of nanotubes, while carbon dangling bonds have been observed directly on the surface of the inner layer. Carbon defects have been found to be the centers of adsorption and accumulation of photoinduced charge carriers. The results are entirely new; they clarify the role of different types of defects in the photocatalytic conversion of CO2 to hydrocarbon compounds and show good prospects for applying TiO2 nanotube arrays.

In this work, we propose a new, previously unpresented in the literature, approach to the formation of Si1-xGex films. This approach includes electrochemical processes of the formation of porous silicon, electrochemical deposition of low-melting metals and Ge. Post-heat treatment is made possible to synthesize film structures based on Si1-xGex solid solutions. Using this approach an alloy of the composition Si0.4Ge0.6 has been obtained at a lower formation temperature than predicted by the phase diagram for the Si-Ge system.

The effect of vacuum annealing (600 °C, 30 min) on the temperature stability against oxidation in air of germanium nanowires obtained by cathodic deposition from aqueous solutions of germanium oxide was studied by the method of photoluminescence in the visible range and Raman scattering. The stability was checked by laser annealing at temperatures above 1000 °C. It was shown that the evolution of photoluminescence and Raman peaks is associated with the formation of germanium oxide or suboxide upon laser annealing. Preliminary vacuum annealing of the sample significantly suppresses this process. The observed effect is associated with the formation of germanium oxide and the influence of indium atoms on this process.

Indium electrodeposition in-between silicon nanowire arrays fabricated by silver-assisted chemical etching of lightly-doped (100)-oriented silicon wafers is evaluated. It is concluded based on SEM and EDX analysis of indium’s distribution that, by utilizing pulsed-mode electrodeposition and maintaining a sufficiently low duty cycle value, indium particles can be formed exclusively at the very bottom of each consecutive pore on the residual silver particles left over from metal-assisted etching. This result differs significantly from irregular pore filling along with surface and subsurface deposition observed in the cases of continuous galvanostatic deposition regimes at prolonged durations or in the absence of residual silver particles. Bottommost fusible metal deposit localization, which is unattainable on porous silicon fabricated by electrochemical anodization, is presumed to be optimal for the growth of germanium crystallites inside the pores via the electrochemical liquid-liquid-solid approach and subsequent silicon-germanium alloy formation through thermal annealing.

The article presents comprehensive studies of the chemical composition and morphology of nanotubular anodic TiO2 layers at the first stages of the porous structure nucleation, by scanning electron microscopy (SEM), Auger spectroscopy (AES), time-of-flight secondary ion mass spectrometry (TOF.SIMS). Our goal was to show the profile distribution of chemical elements and reaction products at each of the initial stages of the anodic oxide growth in the ethylene glycol-based electrolyte containing fluoride, which will help expand the understanding of pore formation mechanism.