This paper presents a method for predicting the selectivity of silicon epitaxy by linking it to the reversibility of precursor adsorption and silicon condensation. Reversible adsorption enables long-range lateral gas-phase diffusion of precursor species, while reversible condensation permits chemical vapor transport of silicon, both of which suppress nucleation on the mask. The degree of reversibility is quantified by the ratio of the net deposition flux to the equilibrium desorption flux, the latter estimated from thermodynamic equilibrium calculations assuming a fast surface reaction. Analysis of published experimental data reveals that the transition from non-selective to selective deposition occurs at a net deposition flux to equilibrium desorption flux ratio of ≈10−2. This threshold coincides with the reactive sticking coefficient of SiCl2, the dominant silicon species in chloride-based processes, indicating that reversible condensation is the necessary condition for selectivity. The proposed equilibrium-based flux ratio thus provides a quantitative criterion for assessing selective-area epitaxy.

The multilayer thermite material Al/CuO is an outstanding representative of metastable intermolecular composites characterized by excellent energy and combustible properties. However, the combustion of such a material is accompanied by intensive release of gas and spraying products. In this work, it is demonstrated that in a certain thickness range (2-3μm) of the multilayer thermite material (Al/CuO)nformed on the surface of Sitall substrates, the reaction products remain on the surface of the substrate in the form of composite entities, in some cases resembling ladybugs. By means of high-speed video shooting from different angles, the propagation velocity of the combustion front was measured and the intensity of gas release was visually assessed depending on the thickness of the multilayer structure (Al/CuO)n. The spraying products effect becomes significant for multilayer structures (Al/CuO)40with a total thickness of 4μm. It was found that the propagation velocity of the combustion front increases with the thickness of the multilayer structure (Al/CuO)nuntil the effect of spraying products intensifies. The morphology and composition of the combustion products of multilayer structures were studied using scanning electron microscopy in combination with focused ion beam and energy-dispersive x-ray spectroscopy. In particular, it was found that in many cases, the composite entities are hollow inside and consist of an aluminum oxide framework, rounded fuses of metallic copper, and fragments of unreacted film multilayers. As a result of the analysis of experimental data, two combustion modes of multilayer thermocomposite materials on a substrate were described depending on the temperature of the combustion front, which are related to the thickness of the multilayer structure.

This paper reports on the formation and study of Ag-Nb-N-O/TiO2 nanowires (NWs) for photocatalytic reduction of CO2. Firstly, the Ag-Nb-N-O thin film was grown by simultaneous magnetron sputtering of Ag and Nb targets in an atmosphere of Ar and N2. Subsequently, the Ag-Nb-N-O thin film was coated with TiO2 NWs, which were presynthesized by a hydrothermal method and then annealed at 500 degrees C. Before photocatalytic tests, the Ag-Nb-NO/TiO2 NW samples were subjected to heat treatment at 350 degrees C. A morphology of the fresh and 350 degrees C-annealed Ag-Nb-N-O/TiO2 NWs was comprehensively studied by SEM, TEM, EDXS, and XRD. Heating was found to facilitate the extrusion of Ag particles from the bulk of the Ag-Nb-N-O film to its surface. In addition, the heat treatment led to partial evaporation of silver and its further redeposition on the surface of TiO2 NWs in the form of Ag nanoparticles. The Ag-Nb-N-O/TiO2 NWs subjected to the 350 degrees C heating possessed a remarkable photocatalytic activity in the synthesis of methanol from CO2, which was 3 times over that of the pure TiO2 NWs. This is associated with the contribution of localized surface plasmon resonance of Ag particles to generation of the charge carriers. Moreover, we demonstrate that LSPR-induced heating of Ag nanoparticles, confirmed by IR imaging, plays a crucial role in charge carrier separation. The thermoelectromotive force generated by the temperature gradient facilitates electron transfer from TiO2 to Ag, thereby improving CO2 reduction efficiency. Additionally, we revealed that an external electric field enables an improvement of the Ag-Nb-N-O/TiO2 NW photocatalytic activity providing an additional increase in the methanol yield by 60 %.

During reactive magnetron sputtering in a chemically active gas environment, the formation of a chemical compound on the target surface changes its sputtering rate. As a result, a significant change in the composition of the film being formed occurs in the narrow pressure range of the chemically active gas. In order for the process cycle to be highly reproducible, it is necessary to clearly understand the processes occurring during sputtering and ensure a high level of control of the chemically active gas. In this paper, the process of the formation of Mo–Si–N–O thin films by reactive magnetron sputtering, which are used as phase-shifting layers of phototemplates, is studied. A theoretical and experimental approach is presented for predicting and controlling the composition of multicomponent thin films formed by reactive sputtering using two separate targets in a chemically active gas environment. The experimental results of changes in the composition of Mo–Si–N–O thin films depending on the nitrogen pressure during the simultaneous reactive magnetron sputtering of two targets, molybdenum and silicon, are presented. The changes in the composition of the Mo–Si–N–O films are modeled, taking into account the kinetic theory of gases, geometric characteristics of vacuum magnetron sputtering equipment, and simple physical and chemical assumptions. It is established that the key factor determining the composition of a thin film is the process of the nitridation of targets, which leads to a sharp change in their sputtering rate.

Enhancing the photosensitivity of titanium dioxide TiO2 by shifting the absorption spectrum to the long-wavelength region of the solar spectrum is a critical task. This problem can be solved by the modification of TiO2, e.g., by the formation of heterostructures with another semiconductor material. In this work, the development of a technique for the formation of photoactive TiO2–ZnO composite layers using electrophoretic deposition is presented. The results of studying the photosensitivity of TiO2 and TiO2–ZnO samples on a silicon substrate coated with carbon nanotubes are given. The formation of TiO2–ZnO composite layers by electrophoretic deposition is carried out using stabilizing additives: sodium lauryl sulfate and hydroxypropylcellulose. As a result layers of TiO2–ZnO/carbon nanotube composite material are obtained; their morphology is studied by scanning electron microscopy (SEM). It is demonstrated that the addition of 50 wt

The study of the structural and electrophysical properties of piezoelectrics is an important task for the creation of efficient piezoelectric nanogenerators designed to increase the autonomy of electronic devices. Barium titanate BaTiO3 is one of the promising materials for creating nanogenerators. Special sample preparation is required to study its properties. In this study, the results of studying the electrical properties of an individual BaTiO3 nanowire attached to the substrate surface using atomic force microscopy are presented. The BaTiO3 nanowires are formed by two-stage hydrothermal synthesis using titanium dioxide TiO2 as a precursor and sodium titanate as an intermediate compound. The surface morphology and phase composition of BaTiO3 nanowires are studied using a scanning electron microscope and X-ray diffraction. A technique for fixing an individual BaTiO3 nanowire on a conductive substrate for studying the piezoelectric characteristics using an atomic force microscope (AFM) is presented. The BaTiO3 nanowires obtained have a tetragonal phase with the average length of 14 μm and a diameter of 330 nm. The internal voltage of the nanowire is –0.45 V and the piezoelectric coefficient d33 is 5.2 pm/V. The resulting data confirm the possibility of applying BaTiO3 nanowires in nanogenerators and MEMS devices.

We report on a novel approach for the encapsulation of vital antibacterial protein lysozyme between two graphene-containing films on a solid substrate composed of silver nanoparticles on porous silicon (Ag/PSi) possessing surface-enhanced Raman scattering (SERS) activity. SERS- spectra of 10 nM lysozyme were collected and compared for the graphene-free Ag/PSi, the graphene-coated Ag/PSi, and the graphene sandwich with lysozyme on Ag/PSi. The spectral regions with characteristic bands of the protein were subjected to quantitative/qualitative analysis. The findings revealed that the bottom graphene layer facilitated a more ordered orientation of protein molecules, augmented the Raman signal due to graphene-induced charge transfer, and dissipated heat generated by plasmonic nanoparticles/laser. The top graphene layer additionally reduced the temperature effect on the protein by several degrees, which was verified by computer modeling. Thus, it was demonstrated that the graphene sandwich enabled recording of SERS-spectra of the protein with the slightly changed secondary structure. Moreover, the graphene coating resulted in more protein Raman bands compared to that of the uncoated Ag/PSi. Therefore, the encapsulation of lysozyme within the graphene sandwich on a plasmonic substrate reduces its thermal carbonization, enabling the reliable analysis of proteins by SERS- spectroscopy at concentrations that are clinically relevant.

Wide band gap (WBG) oxide and metal nanocomposites can possess bifunctionality from combining tightly coupled nanoobjects with different physicochemical properties. Adjusting synthesis conditions tunes these properties through modulating the process–morphology–function relationship. However, the controllable synthesis of such nanocomposites and their related applications are still underexplored. Here, we present a novel process flow to synthesize crystalline ZnO nanosheaves dotted with silver nanoparticles. The uniqueness of our strategy lies in the use of a silver mask for vertical growth of ZnO nanosheaves and thermal evaporating/dewetting Ag film to form a photocatalytic/plasmonic heterostructure. Upon combining a huge specific surface area and nanocrystallinity of ZnO nanosheaves, we enabled its surface-enhanced Raman scattering (SERS)-activity free of plasmonic components, yet their Ag modification resulted in improving detection limit in relation to Ellman’s reagent. Ag/ZnO nanosheaves showed dramatic photocatalytic activity to clean SERS-active surface. The systematic approach to synthesize Ag/ZnO heterostructure holds great promise in practical applications associated with interest in both photocatalytic and plasmonic properties.

The present study investigates the photocatalytic properties of hydrothermally synthesized TiO2 nanowires (NWs) for CO2 reduction in H2O vapor. It has been demonstrated that TiO2 NWs, thermally treated at 500–700 °C, demonstrate an almost tenfold higher yield of products compared to the known commercial powder TiO2 P25. It has been found that the best material is a combination of anatase, TiO2-B and rutile. The product yield increases with increasing heat treatment temperature of TiO2 NWs. This is associated with an increase in the degree of crystallinity of the material. It is shown that the best product yield of the CO2 reduction in H2O vapor is achieved when the TiO2 NW photocatalyst is heated to 100 °C.

Understanding the formation and evolution of arrays of metallic nanoparticles is a very important task as they are increasingly used in various devices. In this work, we used HRTEM mode for continuous in-situ observations of the evolution of Ag and Au nanoparticle arrays with an average size of similar to 4 nm, formed on the surface of amorphous carbon by vacuum-thermal evaporation, under the influence of a microscope electron beam without any other energetic influence. Our studies show that electron beam exposure induces a process of nanoparticle coalescence for Au and simultaneous coalescence and vaporization for Ag. As a result, the evolution of Ag and Au nanoparticle arrays has different mechanisms. In the case of Ag, the aggregation of nanoparticles occurs through the gas phase by the Ostwald ripening mechanism. In the case of Au, it was found that the aggregation of nanoparticles depends on their mutual crystalline orientation, resulting in the realization of mechanisms through bridge formation or through jumping. The influence of the crystalline orientation of the nanoparticles on the coalescence mechanism was confirmed by molecular dynamics simulations. MD simulations revealed that it is most favorable for coalescence if the densely packed planes of neighboring nanoparticles have a perpendicular arrangement in space.

In this work, we propose an original approach for rapid and easy conversion of a thin Ag-Nb-N-O film into surface enhanced Raman scattering (SERS) active substrate. The initial Ag-Nb-N-O substrate has a long shelf life because silver particles are prevalently accumulated inside the film and possess resistivity to degradation. An activation of the substrate is carried out just before the SERS-measurements by a 15-second microwave heating the Ag-NbN-O film at 800 W, which facilitates immediate extrusion of internal silver to the surface. This leads to the formation of a dense array of Ag particles that show an improved SERS-activity. We compare SERS-activity of the initial and microwave-treated Ag-Nb-N-O films with that of a control substrate based on Ag nanoparticles grown on the SiO2 surface. Both initial and control substrates are aged in a moist air for 60 days before the SERSmeasurements. An intensity of the SERS-signal from 10-5 M 5,5 '-Dithiobis(2-nitrobenzoic acid) or DTNB on the activated Ag-Nb-N-O film is approx. 270 higher than that on the control Ag nanoparticles. The TEM and EDS studies of the initial Ag-Nb-N-O film prove its stability to sulfidization while the control Ag nanoparticles are found to bind to sulfur from the moist air.

For the solution of the problem of energy storage, new and more efficient functional electrode materials for electrochemical devices such as supercapacitors and their formation technologies are being developed. In particular, using the method of electrolyte-free electrophoretic codeposition, a composite material of carbon nanotubes (CNTs)/RuO2·xH2O with high specific capacitance and power values can be obtained. In this study, the optimal composition of a 50-mL suspension for electrophoretic deposition (EPD) is determined by sedimentation analysis. It is demonstrated that in the course of the iodoform reaction with acetone, I2 (20 mg) ensures the saturation of particle surfaces with protons and their deposition on the cathode, thus replacing the electrolytes that introduce impurities into the final coating. It is established that the presence of a dispersing agent (5 mg of hydroxypropyl cellulose) is required in the suspension to maintain stability. The possibility of removing hydroxypropyl cellulose during annealing in air at a temperature of about 260°C is studied and confirmed by the methods of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Composite material, processed in this way and obtained from a suspension containing double-walled CNTs and RuO2·xH2O, equal to 2 and 10 mg, respectively, has a capacity of 21.5 and 8.6 mF/cm2 at cyclic sweep rates of 10 and 100 mV/s, respectively. It is established that elevated temperatures and prolonged heat treatment lead to a deterioration in the electrochemical characteristics due to the degradation of RuO2·xH2O and the CNTs.

Silver is one of the most promising nanomaterials for plasmonic applications, but it has become clear that the shape and internal symmetry of nanoparticles can significantly affect the scattering and absorption of light waves. Therefore, for the use of silver nanoclusters in plasmonic applications, it is very important to determine the conditions of stability of the structure and form of Ag nanoparticles. To this end high-resolution electron microscopy was used to examine initial and annealed arrays of silver nanoparticles with diameters ranging from 0.8 to 9.4 nm, formed on a carbon substrate by vacuum thermal evaporation. It was found that small Ag nanoparticles (D < 3.0 nm) have almost perfect FCC structure, while nanoparticles of larger diameter unexpectedly have predominantly icosahedral or decahedral facets. To explain this contradiction from the perspective of standard crystallographic theory, molecular dynamics simulations using the TB-SMA potential were conducted to study the stability limits of structural modifications of silver nanoclusters of similar diameters, and possible atomic rearrangement mechanisms that could lead to such experimental results were found. Based on the results of the computer analysis, conclusions were drawn about the technological possibilities of creating the desired crystal structure of Ag nanoparticles when preparing SERS substrates.

Currently, there is a growing demand for miniaturized power supplies, including planar supercapacitors, whose principle of operation is based on fast redox reactions. This circumstance stimulates investigations of composite structures made of high-surface-area carbon-based materials and transition-metal compounds. In this paper, we report the results of studying coatings based on few-layer graphite nanoflakes FLGN/Ni(OH) 2 and their oxidized form OFLGN/Ni(OH) 2 , obtained by repeated electrophoretic deposition. These coatings are used in prototype parallel-plate (3D) and planar supercapacitors. A processing route using a 450-nm laser for pattern scribing is developed for the latter. It is shown that, by regulating the nickel-ion-source proportion in the suspension from 0.04 to 0.64 g/L, one can control the physical properties of the composite at the deposition stage. The composite’s physical properties are studied by cyclic voltammetry, scanning microscopy, and elemental analysis. The peak capacity values are obtained for samples with the minimum concentration (0.04 g/L); they turn out to be 1.51 and 1.31 F/g for the FLGN-containing samples and 1.86 and 1.29 F/g for the OFLGN-containing samples of bulk and planar supercapacitors, respectively.

We propose an approach to identify points on a timeline of Ag wet electroless deposition on macroporous silicon (macro-PS) that correspond to formation of Ag particles possessing prominent surface-enhanced Raman scattering (SERS) activity. This approach is measuring a surface potential of macro-PS, which sharply decreases at the moment of nearly complete saturating the Si skeleton surface with Ag particles of diameter below 60 nm favorable for an intensive surface plasmon resonance. The most intensive SERS-spectra of 5,5'-dithio-bis-[2-nitrobenzoic acid] (DTNB) were collected on macro-PS covered with Ag particles for 20 min. Considering breaking S-S bonds of DTNB in presence of Ag, which leads to chemisorption of monomolecular TNB layer on the surface of Ag structures, we claim 2 x 10(-9) M TNB detection limit. Lower concentration at 10(-10) M resulted in absence of SERS-spectra in some spots showing that the analyte was adsorbed unevenly. The analytical enhancement factor was calculated as similar to 0.7 x 10(7).

The NQ21 peptide has relatively recently attracted attention in the biomedical sphere due to its prospects for facilitating the engineering of the HIV1 vaccine and ELISA test. Today, there is still a need for a reliable and fast methodology that reveals the secondary structure of this analyte at the low concentrations conventionally used in vaccines and immunological assays. The present research determined the differences between the surface-enhanced Raman scattering (SERS) spectra of NQ21 peptide molecules adsorbed on solid SERS-active substrates depending on their geometry and composition. The ultimate goal of our research was to propose an algorithm and SERS-active material for structural analysis of peptides. Phosphate buffer solutions of the 30 µg/mL NQ21 peptide at different pH levels were used for the SERS measurements, with silver particles on mesoporous silicon and gold-coated “nanovoids” in macroporous silicon. The SERS analysis of the NQ21 peptide was carried out by collecting the SERS spectra maps. The map assessment with an originally developed algorithm resulted in defining the effect of the substrate on the secondary structure of the analyte molecules. Silver particles are recommended for peptide detection if it is not urgent to precisely reveal all the characteristic bands, because they provide greater enhancement but are accompanied by analyte destruction. If the goal is to carefully study the secondary structure and composition of the peptide, it is better to use SERS-active gold-coated “nanovoids”. Objective results can be obtained by collecting at least three 15 × 15 maps of the SERS spectra of a given peptide on substrates from different batches.

This study demonstrates the ability to control the properties of TiO2–CuOx composite layers for photocatalytic applications by using a simple electrophoretic deposition method from isopropanol-based suspension. To obtain uniform layers with a controlled composition, the surfactant sodium lauryl sulfate was used, which influenced the electrophoretic mobility of the particles and the morphology of the deposited layers. The TiO2–CuOx composite layers with different CuOx contents (1.5, 5.5, and 11 wt.%) were obtained. It is shown that the optical band gap measured by UV–VIS–NIR diffuse reflectance spectra. When CuOx is added to TiO2, two absorption edges corresponding to TiO2 and CuOx are observed, indicating a broadening of the photosensitivity range of the material relative to pure TiO2. An open-circuit potential study shows that by changing the amount of CuOx in the composite material, one can control the ratio of free charge carriers (n and p) and, therefore, the catalytic properties of the material. As a result, the TiO2–CuOx composite layers have enhanced photocatalytic activity compared to the pure TiO2 layer: methanol yield grows with increasing CuOx content during CO2 photoreduction.

TiO2 is one of the most common photocatalysts at the moment. One-dimensional TiO2, which has a high specific surface area, is of particular interest. The properties of such nanowires will largely depend on the phase composition, which affects the width of the optical band gap. This paper presents the results of a study of the photocatalytic activity of TiO2 nanowires depending on the phase composition using the reduction of CO2 to methane and methanol as an example. The formation of TiO2 nanowires was carried out using a hydrothermal synthesis method from a commercial TiO2 powder. After synthesis, the nanowires were thermally treated in air to obtain nanowires with different phase compositions. The morphology and phase composition of TiO2 nanowires were studied. The resulting nanowires had a size of about 8 μm and a diameter of about 330 nm.

For the first time, it was demonstrated that the catalytic properties of semiconductors can be activated using an external electric field only. More particularly, the TiO2 and Fe2O3 were found to produce noticeable amounts of carbon monoxide from carbon dioxide – water vapor gas mixture under the electric field with the strength in the 104 V/cm range. The reported process, i.e. the activation of semiconductors using the electric field is more efficient than the utilization of UV–vis radiation in terms of energy efficiency and amount of products formed.