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The article describes the features of photoluminescence (PL) of silicon and carbon nanocolloids prepared by us using known approaches. In the course of the study, Si and C nanoparticles (NPs) were dispersed in non-polar and polar liquids, respectively, in order to study their photoluminescent properties as a function of temperature. For a number of samples, a bathochromic shift in the position of the PL maximum was observed, as well as a change in the PL intensity depending on the solvent and temperature. The latter opens up prospects for applications of PL thermometry, for example, for mapping the temperature distribution. We calculated the temperature coefficients of changes in the PL intensity as a function of temperature, and in addition, we found that the relatively important temperature sensitivity is associated not only with the internal properties of Si NPs and C NPs, but also, to a large extent, with the mechanisms of the Forster resonant energy transfer in non-polar liquids. The latter is probably realized between particles of different sizes and significantly depends on the change in the viscosity of the liquid with decreasing temperature, which prevents the chaotic movement of NPs and their aggregates in the solution. Presumably, the resonant transfer of Forster energy between Si particles can be the reason that then interactions at short distances between particles of different sizes are possible, in the cases when the NP size distribution is relatively large. Therefore, based on the foregoing, the main directions for improvement should be the development of unified Si NPs and C NPs to clarify the recorded effect and increase the sensitivity in luminescence thermometry using the required type of colloidal solutions and solvent for the respective NPs. The information presented in the article is of interest since it forms the basis for understanding the observed effects during the analysis of experimental data using the available literature sources.

We present results on the photothermal (PT) and heat conductive properties of nanogranular silicon (Si) films synthesized by evaporation of colloidal droplets (drop-casting) of 100 ± 50 nm-sized crystalline Si nanoparticles (NP) deposited on glass substrates. Simulations of the absorbed light intensity and photo-induced temperature distribution across the Si NP films were carried out by using the Finite difference time domain (FDTD) and finite element mesh (FEM) modeling and the obtained data were compared with the local temperatures measured by micro-Raman spectroscopy and then was used for determining the heat conductivities k in the films of various thicknesses. The cubic-to-hexagonal phase transition in Si NP films caused by laser-induced heating was found to be heavily influenced by the film thickness and heat-conductive properties of glass substrate, on which the films were deposited. The k values in drop-casted Si nanogranular films were found to be in the range of lowest k of other types of nanostructurely voided Si films due to enhanced phonon scattering across inherently voided topology, weak NP-NP and NP-substrate interface bonding within nanogranular Si films.

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.

У статті ми описуємо особливості будови гібридних наноструктур вуглець-кремній (Si@C). Вихідні кремнієві наночастинки (Si НЧ) були отримані кислотним травленням із порошкоподібного силумінового (80 % Al – 20 % Si) сплаву. Для приготування гібридних наноструктур Si@C було запропоновано використання стандартних термічних та хімічних методів. Рекомендований підхід передбачає обробку окисленої поверхні Si НЧ полівінілпіролідоном, як сполукою-попередником, що містить вуглець; отриманий продукт слід піддавати подальшій карбонізації. Для запобігання значного спікання компонентів, Si НЧ, оброблені полівінілпіролідоном, поміщали в піч з киплячим шаром і прожарювали при 400 та 500 °C в атмосфері аргону протягом 4 годин. За даними атомно-силової мікроскопії, скануючої електронної мікроскопії, трансмісійної електронної мікроскопії (ТЕМ) та скануючої трансмісійної електронної мікроскопії з висококутовою кільцевою діаграмою темного поля (СТЕМ-ВКДТП), ми отримали інтерфейс Si@C та відповідні Si/C гетероструктури. Використовуючи зображення TEM та СТЕМ-ВКДТП, ми виявили, що 2D вуглецеві наноструктури утворюються на структурованій поверхні нанокремнію, як на підкладці. Згідно візуалізації модифікованого інтерфейсу, вуглецеві НЧ є аморфними та напіваморфними наноструктурами. Вуглецеві НЧ, інтерфейс Si@C та відповідні Si/C гетероструктури гібридів Si@C можуть бути перспективними як зонди для розробки нових сенсорних пристроїв. Сенсорні відгуки датчиків на гібридній основі Si@C на пари аміаку, метанолу та етанолу вимірювали при кімнатній температурі та порівнювали. Слід зазначити, що датчики на гібридній основі мають високу чутливість та вибірковість до 10 мд. аміаку, на відміну від реакції на 1000 мд. парів метанолу та етанолу. Запропоновані гібриди мають великий потенціал щодо використання в адсорбційних напівпровідникових газових датчиках для визначення аналітів у парах з використанням нановуглецю, зв’язаного з кремнієм, у гібридних наноструктурах в якості зонду. In this paper, we describe the design features of carbon-silicon (Si@C) hybrid nanostructures. Initial silicon nanoparticles (Si NPs) were prepared by acid etching from powdered (80 % Al – 20 % Si) silumin alloy. For preparing Si@C hybrid nanostructures, the use of standard thermal and chemical methods was proposed. The recommended approach involves treatment of the oxidized surface of Si NPs with polyvinylpyrrolidone as a carbon-containing precursor compound. The resulting product should be subjected to further carbonization. To prevent significant sintering of the components, Si NPs treated with polyvinylpyrrolidone were placed in a fluidized bed furnace and calcined at 400 and 500 °C in an argon atmosphere for 4 h. According to the data of atomic force microscopy, scanning electron microscopy, transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, we obtained the Si@C interface and the corresponding Si/C heterostructures. By using TEM and HAADF-STEM imaging, we found that 2D carbon nanostructures are formed on the structured nanosilicon surface as on the substrate. According to the visualization of the modified interface, carbon NPs are amorphous and semi-amorphous nanostructures. Carbon NPs, the Si@C interface, and the corresponding Si/C heterostructures of Si@C hybrids can be prospective as probes for the development of new sensor devices. Sensing responses of Si@C hybrid-based sensors to ammonia, methanol and ethanol vapors were measured at room temperature and compared. Notably, hybrid-based sensors are highly sensitive with a selectivity of up to 10 ppm of ammonia, contrasting to the response to 1,000 ppm of methanol and ethanol vapors. The proposed hybrids have great potential to be used in adsorption semiconductor gas sensors to determine analytes in vapors using nanocarbon bonded to silicon in hybrid nanostructures as a probe.

Hydrogen generation rate is one of the most important parameters which must be considered for the development of engineering solutions in the field of hydrogen energy applications. In this paper, the kinetics of hydrogen generation from oxidation of hydrogenated porous silicon nanopowders in water are analyzed in detail. The splitting of the Si-H bonds of the nanopowders and water molecules during the oxidation reaction results in powerful hydrogen generation. The described technology is shown to be perfectly tunable and allows us to manage the kinetics by: (i) varying size distribution and porosity of silicon nanoparticles, (ii) chemical composition of oxidizing solutions, (iii) ambient temperature. In particular, hydrogen release below 0 &deg, C is one of the significant advantages of such a technological way of performing hydrogen generation.

Multiple enhancement of the Raman scattering efficiency is observed in porous-silicon-based one-dimensional photonic bandgap (PBG) structures with tunable reflection and dispersion under excitation at 1.06 µm. The experimental results are explained as being due to the resonant increase in the effective Raman susceptibility at light wavelengths close to the PBG edges. This effect is discussed in view of possible applications in the Raman spectroscopy of molecules embedded in porous media as well as in the Raman laser based on silicon. Copyright c � 2011 John Wiley & Sons, Ltd.

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.

Semiconductor–insulator–semiconductor heterojunction solar cells were prepared using atomic layer deposition (ALD) technique. The silicon surface was treated with oxygen and hydrogen plasma in different orders before dielectric layer deposition. A plasma-enhanced ALD process was applied to deposit dielectric Al2O3 on the plasma pretreated n-type Si(100) substrate. Aluminum doped zinc oxide (Al:ZnO or AZO) was deposited by thermal ALD and serves as transparent conductive oxide. Based on transmission electron microscopy studies the presence of thin silicon oxide (SiOx) layer was detected at the Si/Al2O3 interface. The SiOx formation depends on the initial growth behavior of Al2O3 and has significant influence on solar cell parameters. The authors demonstrate that a hydrogen plasma pretreatment and a precursor dose step repetition of a single precursor improve the initial growth behavior of Al2O3 and avoid the SiOx generation. Furthermore, it improves the solar cell performance, which indicates a change of t...