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A significant change in effective reflectance spectra of nanostructured porous silicon layers grown with different times of metal-assisted chemical etching is detected. The low reflectances at the level of 5–10% measured in the spectral range of 200–400 nm are explained by strong elastic scattering of light in combination with absorption in silicon nanostructures, while a reflectance increase in the range of 500–1800 nm, which is visually detected as a “white” layer appearance is associated with Mie scattering in silicon nanostructures with gradient porosity under conditions of weak optical absorption. The results obtained are discussed from the viewpoint of potential applications of “black” and “white” nanocrystalline silicon in photonics and sensorics.

International audience; In the present paper, we report on the investigation of thermal annealing (TA) effect on structural and optical properties of crystalline silicon nanowires produced by metal-assisted chemical etching approach. In particular, the impact of TA on nanowire length, relative volume and size distribution of voids is described in terms of Lifshitz-Slyozov-Wagner theory considering the TA induced Oswald ripening in the SiNW arrays. It was also found that TA leads to a decrease of the SiNWs total reflection in the wide UV-VIS-IR spectral range. The reported effects can be used for tuning of crystalline SiNWs arrays in view of their further applications in photonics related fields.

Hydrogen energy is one of the promising eco-friendly directions in the development of modern energy, and the production of hydrogen from water using a catalyst and solar energy is one of the simple and affordable methods for producing the necessary fuel. The search for suitable semiconductors for use as photocatalysts for water splitting into molecular hydrogen and oxygen is to be considered an urgent subject. The present work is devoted to a review of modern literature data on the preparation, description of the main physicochemical properties, and application of silicon nanostructures of various geometries as photocatalysts for hydrogen generation by splitting of water. In paper, we describe various methods for the preparation and synthesis of silicon nanomaterials with different geometries: silicon nanowires, silicon nanoparticles, silicon nanodots and porous structures. In addition, we consider the advantages and disadvantages of using heterojunction hybrid nanomaterials based ofn silicon nanostructures in photocatalytic processes to increase the efficiency of hydrogen evolution. Based on the data of published experimental and theoretical works, the mechanism of solar driven water splitting and the use of silicon nanostructures as a semiconductor catalyst is discussed. In conclusion, an assessment of the state of the problem of obtaining and studying the photocatalytic properties of silicon nanostructures is given.

This work has been done to identify quantitative criteria the degree of order and chaos morphology of porous layers consisting of silicon nanowire arrays. In order to fulfill the work, a method of using metal-assisted chemical etching has been utilized to produce nanowires. There has been done a work of digital processing of porous film images which were extracted by scanning electron microscope. Informational-entropic and Fourier analysis have been applied to quantitatively describe the degree of order and chaos in nanostructure distribution in the layers. Self-similarity of the layer morphology has been quantitatively described via its fractal dimensions by correlation method. The applied approach for image processing allows us to distinguish the morphological features of as-called "black" (more ordered) and "white" (less ordered) silicon layers, which are characterized by minimal and maximal optical reflection, respectively. From all of the methods of digital techniques that we have used the method for determining the conditional information of a chaotic set was proved to be the most informative.

A cheap and facile wet-chemical 'silver mirror' reaction approach has been proposed for the silicon nanowires (SiNWs), formed by the metal-assisted wet-chemical etching, decoration with silver nanoparticles (AgNPs). Scanning electron microscopy studies show that AgNPs can be deposited uniformly on the surface of SiNWs by the variation of AgNO3 concentration and reaction time. Adopting the reaction conditions, a homogenous AgNPs shell is formed around the silicon nanowires. The resultant AgNPs@SiNWs nanostructures show significantly (up to 40%) higher light absorption in the near-infrared range (up to 1500 nm) in comparison to SiNWs without AgNPs. This approach opens a new perspectives for a cheap and fast preparation of AgNP shells around SiNWs. Our observation supports that synthesized nanostructures might have promising application potential in near-infrared photodetectors or as photocatalysts.

The crystalline germanium nanostructures were obtained on a silicon surface by the chemical vapor deposition technique using a germanium (IV) iso-propoxide ([Ge(OiPr)4]) metalorganic precursor as a germanium source. As was observed, the one-dimensional (1D) germanium nanostructures on the silicon surface form without using a metal catalyst, meaning that the formation of 1D nanostructures is based not on a vapor–liquid–solid (VLS) growth mechanism, but on self-organization processes which take place on the silicon surfaces during the CVD process of germanium iso-propoxide pyrolysis. Our observation suggests that the non-catalytic growth of germanium nanocolumns is strongly dependent on the CVD process temperature. The germanium phase composition and morphology have been investigated by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), and high resolution scanning electron microscopy (HRSEM), respectively. Our results provide a new way to grow 1D germanium nanostructures without contamination by a catalyst, which the vapor–liquid–solid growth mechanism is known to cause, allowing for the application of such materials in micro- and optoelectronics.