Germanium (Ge) nanowires were fabricated by electrochemical deposition on titanium‐coated silicon substrate. Arrays of nanowires with different mean diameters were obtained using indium nanoparticles of various sizes as centers of nucleation. Raman spectroscopy was used to establish the structural properties of nanowires under different laser excitation intensities. Cycles of measurements with different intensities demonstrated irreversible changes in the structure. Initial study with minimal excitation intensity of 3 W/cm2 displayed that the spectra are descriptive of amorphous Ge. Further study at increased intensities led to the transformation of Raman spectra to the shapes that can be attributed to crystalline Ge. Detailed analysis of spectra shapes for samples with different mean diameters of Ge nanowires after exposure to high intensity laser radiation allows to estimate the fraction of the crystalline phase in Ge nanowires. The spectra of a sample irradiated by He–Ne laser were compared with thermally annealed sample in a vacuum at 150 °C. A similar shape of the obtained spectra indicates on the thermal nature of the effect, which leads to a change in the observed structural properties. This change under even slight heating can be explained by thermal isolation of nanowires from the substrate.

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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.

Abstract. Metal-assisted silicon etching in the HF/H2O2/H2O solution with silver ions as a catalyst was investigated. It is found that geometric parameters of layers of nanostructured silicon are determined by the silver-catalyst concentration. A spontaneous stop of the etching process at low Ag+ ion concentration is explained by formation of insoluble Ag2SiO3.

This study is devoted to the confinement effects on freezing and melting in electrochemical systems containing nanomaterial electrodes and liquid electrolytes. The melting of nanoparticles formed upon freezing of liquids confined in pores of disordered nanostructured n-type silicon has been studied by low-temperature differential scanning calorimetry. Experimental results obtained for deionized water, an aqueous solution of potassium sulfate, and n-decane are presented. A model is proposed for predicting the melting point of nanoparticles formed during freezing of liquids inside the pores of a disordered nanostructured material. The model is based on the classical thermodynamic concept of the phase transition temperature dependence on the particle size. It takes into account the issues arising when a liquid is dispersed in a matrix of another material: the effect of mechanical stress resulted from the difference in the thermal linear expansion coefficients at a temperature gradient, the effect of the volumetric liquid content in the matrix, the presence of a nonfreezing liquid layer inside the pores, and the effect of wettability of the matrix with the liquid. Model calculations for water and n-decane confined in nanostructured silicon matrix have been carried out considering the volumetric liquid content. The results obtained have been compared with the differential scanning calorimetry data.

Germanium nanowires fabricated by the electrochemical liquid–liquid–solid deposition from water solutions on titanium coated silicon substrate were studied by Raman spectroscopy in order to estimate the heating effect of exciting radiation. The Stokes to anti‐Stokes ratio was determined for crystalline Ge wafer and for nanowires with different mean diameters at two different excitation wavelengths. It was demonstrated that local heating by exciting laser radiation can lead to an increase in temperature sufficiently high for crystallization of initially amorphous Ge nanowires. The results presented may be of great use for fabricating devices, such as metal ion batteries or thermoelectric elements, based on Ge nanowire.

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