Search

The structure, morphology, and chemical state of composites based on arrays of multiwalled carbon nanotubes and tin oxide (SnOx/MWCNT) obtained using the method of magnetron sputtering were studied using the scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and near edge X-ray absorption fine structure methods. It has been shown that porous layers with a defective structure containing Sn(II) and Sn(IV) oxides along with tin metal were formed on the surface of the MWCNT, which were transformed into crystalline Sn(IV) oxide with a tetragonal lattice at a temperature of ~550°C. The special characteristics of the oxidation and crystallization of the composite components depending on the modes of thermal treatment have been studied. It has been demonstrated that varying the modes of thermal treatment enabled nanostructured materials to be formed that differed significantly in structure, morphology, and composition. It has been hypothesized that the special aspects of the transformation of the composite structure in the process of thermal treatment were determined by the presence of contact of the MWCNT surface with atmosphere.

The structure of individual multi-wall carbon nanotubes exposed to irradiation by a argon ions and electron flux, as well as subsequent heat processing in an inert medium has been studied using transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that irradiation with argon ions and electrons leads to the formation of defects in the structure of carbon nanotubes, changes in the interlayer distance in the walls of nanotubes, and the fixing of functional oxygen-containing groups on their surface. Annealing of pre-irradiated nanotubes in an inert atmosphere causes a partial restoration of the multi-wall carbon nanotube structure. At the same time, in the case of irradiation with argon ions, the nanotube structure is being recovered and the oxygen concentration decreases. In the case of electron irradiation after annealing, extended multi-vacancy defects occur, on which functional groups containing a double chemical bond of carbon and oxygen (C=O) are formed. Using calculations carried out within the framework of density functional theory, the coupling energy values and optimized geometry for various configurations of vacancy clusters in the graphene plane have been obtained.

Adding an oxidizing agent to a solution of hydrofluoric acid significantly changes the process of electrochemical etching, because allows to accelerate the dissolution of electron silicon. In this work, we studied the formation process and morphology of macropores in high-resistance n-Si depending on the concentration of HCl in the HF: C2 H5 OH electrolyte. It is shown that the presence of HCl leads to a more uniform pore diameter distribution both at the surface and in the layer depth, and the increase in etching rate. With an increase in HCl concentration, a narrower pore diameter distribution is observed; the main pores near the surface approximate in size to the pores in the depth of the porous layer. The results are explained by the action of HCl as an oxidant.

The composites based on manganese oxide (MnO2–х), copper oxide (CuO) and yttrium oxide (Y2 O3) are obtained. The gas response and selectivity of multicomponent composites to toxic and hazardous gases are found. Enhanced gas response of MnO2–х/CuO composite to hydrogen sulfide and methylcyan are observed as compared with as-grown manganese oxide. Doping of MnO2–x by yttrium oxide instead of copper oxide leads to changes gas-sensing properties of the composite to hydrogen sulfide, formaldehyde and sulfur dioxide. The presence of copper and yttrium oxides in MnO2–x increases the response to ethyl alcohol vapors.

Multilayer integrated porous membranes are obtained in a monolithic frame containing two types of porous silicon: macroporous silicon with pore diameters up to 10 μm and channel silicon with channel diameters from 100 to 300 nm. A laboratory technology is proposed for preparing macroporous/channel silicon two-layer structures with the use of high-resistance n-Si substrates (1 Ω cm). The pore-formation mechanism and its effect on the morphology of porous layers for electrolytes using formic acid and ammonium hydroxide are discussed.

The features of pore formation during photoanodization in electrolytes based on ammonium fluoride are studied depending on illumination, pH, current density. When comparing electrolytes with different pH (acidic and alkaline), a decrease in the pore diameter is observed at the same illumination and current densities in alkaline HF: NH4 OH solutions at a relatively equal etching rate in depth. In dilute HF: NH4 OH: H2 O under low illumination, there is a direct dissolution of silicon with the formation of a «starlike» pore morphology and a branching tendency. In the case of a concentrated solution of HF: NH4 OH 1: 4 branching is observed with increasing current density

The structure of multi-walled carbon nanotubes exposed to a pulsed high-power ion beam is investigated using the methods of Raman spectroscopy and transmission electron microscopy. It has been shown that irradiation with an ion beam generates significant defects in the structure of nanotubes. With an increase in the number of pulses, processes associated with the annealing of defects in the internal structure of the samples are observed. Electron microscopy data make it possible to distinguish two types of defects leading to a decrease in the interlayer distance of the carbon nanotube wall

Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g−1) compared to the as-prepared nanotubes (13 F·g−1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.

A method for estimating the electrical conductivity of individual carbon nanotubes (CNT), based on modeling of experimental image profiles that are obtained using electrostatic force microscopy (EFM), is proposed. As a result of the profile modeling, the voltage between the tip and CNT was determined as the parameter that characterizes the conductivity of an individual nanotube. A positive correlation between this voltage and the conductivity of individual CNTs was found.

The influence of irradiation by pulsed ion beam on the morphology, structure, and chemical composition of a composite based on multiwalled carbon nanotubes (MWCNTs) and tin dioxide (SnO2-x@MWCNTs) was investigated. It has been established that irradiation of the composite by pulsed ion beam leads to the formation of Sn/SnOx core-shell nanoparticles, which adhere to the surface of the MWCNTs. The “core” is metallic Sn and the “shell” is amorphous SnOx. A uniform distribution of Sn/SnOx nanoparticles on the surface of the MWCNTs was noted, and the maximal concentration of tin in both volume and surface layer was achieved by triple irradiation with an energy density of 0.5 J/cm2. This composite exhibited good electrochemical performance as an anode material for lithium-ion batteries, delivering 1494 mA h g−1 as a first discharge capacity and 634 mA h g−1 discharge capacity (72% capacity retention) after 30 cycles of charge/discharge.

The morphology, structure, and electrophysical characteristics of multiwall carbon nanotubes (MWCNTs), as affected by defects induced by ion bombardment, are studied using Raman spectroscopy and scanning and transmission electron microscopies. Annealing in an inert atmosphere results in partial recovery of the nanotube structure: the nanotube walls contain regions of recovered graphene structure and regions plagued with extended defects that result in corrugation of graphene layers comprising the walls of MWCNTs. These structural alterations result in a marked decrease in conductivity of the processed MWCNTs.

Changes in the local atomic and electronic structure and the chemical state of the surface of multiwalled carbon nanotubes (MWCNTs) irradiated with continuous and pulsed ion beams are studied using transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy. It is demonstrated that changes in the structure and the chemical state of MWCNTs under continuous irradiation with argon ions are attributable to the radiation-induced defect formation. When a pulsed carbon–proton beam is used, thermal effects exert a considerable influence on the structure of carbon nanotubes. The obtained results suggest that continuous and pulsed ion beams are suitable for targeted functionalization of physical and chemical properties of MWCNTs.

The structure and properties of the individual multi-walled carbon nanotubes (MWCNT) subjected to He:O plasma treatment (250 W) have been studied by means of SEM and IR-spectroscopy. It is shown that plasma treatment causes formation of extended defects and oxidation of graphene layers in the MWCNT`s walls. In this case, rounded craters up to 50 nm in size are formed on the surface of the nanotubes. The increment of treatment time leads to formation of graphene belts. The results of numerical modeling indicate the possibility of multivacancy defects formation in the structure of graphene planes by means of carbon atoms substitution.

In this work, we studied the morphology, structure, and electrochemical properties of supercapacitors formed based on undoped and nitrogen-doped multi-walled carbon nanotubes (MWCNTs, N-MWCNTs). It was shown that doping with nitrogen leads to an increase in the specific surface area of MWCNTs due to the formation of structural defects and functional groups. Using scanning electron microscopy, it was shown that the electrodes formed on the basis of undoped and doped MWCNTs have a porous structure, which ensures the penetration of electrolyte into the volume of the electrodes. A comparative analysis of the electrochemical characteristics of the electrodes of supercapacitors in the traditionally used acidic electrolyte H2SO4 is carried out. Using cyclic voltammetry, it was shown that the high specific capacitance of an N-MWCNTs electrode at low sweep speeds is due to Faraday processes involving structural defects, functional oxygen-containing and nitrogen-containing groups on the surface of the nanotubes.

The physicochemical processes of the formation of through channels in heavily doped n-Si (0.01 Ohm · cm) in organic electrolytes of various compositions were studied. The conditions of the formation of multilayer structures consisting of mesoporous and macroporous layers with through channels with diameters of 20-90 nm, thicknesses from 20 to 360 µm and channel density about 1010 cm-2 are considered. Integrated membranes were formed on the obtained structures and their gas transmission was studied.

The effect of ion irradiation and thermal annealing on electrophysical properties of the layers of multi-walled carbon nanotubes (MWCNT) have been studied. The structure of MWCNT subjected to ion and thermal treatment has been studied using transmission electron microscopy and the electrical resistance of MWCNT layers before and after treatments has been measured. The data obtained show that generation of the structural defects in MWCNT's walls and thermal reconstruction of the defects make it possible to control the electrophysical properties of MWCNT layers.

The effect of ion irradiation and thermal annealing on electrophysical properties of multi-walled carbon nanotube (MWCNT) network have been studied. The morphology and structure of MWCNT networks have been studied by means of SEM and Raman spectroscopy. It is shown that irradiation causes formation of defects in the structure of MWCNT. Annealing leads to partial recovery of the structure of MWCNT. Electrophysical measurements indicate an effect of internal structure transformation on the resistance of MWCNT networks. The increment of the resistance of MWCNT networks after treatments is observed. It is shown that the combination of ion irradiation and thermal annealing effectively manage the electrophysical properties of MWCNT networks.

This work is devoted to the study of new functional nanocomposite materials for supercapacitor electrodes based on layers of porous silicon (PS), carbon nanotubes (CNTs) and tin oxide with a high specific surface area, uniform distribution of components, and stability during cycling. Methods for producing consolidated layers of carbon nanotubes on a developed surface of porous silicon have been developed and optimized. Nanocomposites have been created by uniformly applying a metal oxide component to the layers of carbon nanotubes/porous silicon (CNT/PS). Structural and electrochemical characteristics of electrodes based on CNT/PS and SnOx/CNT/PS have been studied.

Nanostructures based on multi-walled carbon nanotubes (MWCNT) and zinc oxides (ZnO) and indium (In2O3) were obtained and studied. The morphology and elemental composition of MWCNT/ZnO and MWCNT/ZnO/In2O3 nanostructures were investigated by scanning electron microscopy (SEM). The gas response of the layers and individual MWCNT, MWCNT/ZnO, MWCNT/ZnO/In2O3 nanostructures to nitrogen dioxide (NO2), ammonia (NH3), ethanol vapor (C2H5OH) and acetone vapor ((CH3)2CO) was determined. Enhanced gas selectivity of the obtained nanostructures in comparison to the ZnO and ZnO/In2O3 layers was achieved.

Методами рентгеноэлектронной спектроскопии и сканирующей электронной микроскопии исследована морфология, структура и состав композитов на основе многостенных углеродных нанотрубок и оксида олова, сформированных с применением двух различных методов для осаждения оксида олова: метода химического газофазного осаждения и метода магнетронного распыления. Полученные данные позволили изучить особенности дефектообразования и изменения химического состояния углерода в стенках многостенных углеродных нанотрубок в процессе формирования композитов, а также исследовать тип взаимодействия оксида олова с внешними стенками углеродных нанотрубок на межфазных интерфейсах композитов, сформированных различными методами. Авторы выражают благодарность к. х. н. Стенькину Ю. А., Росликову В. Е. за проведение синтеза исходных МУНТ и композитов методом магнетронного распыления, а также Д. А. Смирнову и администрации российско-германского канала синхротронного накопителя BESSY II (Берлин, Германия) за помощь в проведении измерений методами XPS и XANES. Авторы благодарят руководство ОмЦКП СО РАН за предоставление оборудования для исследования образцов методами SEM и EDX. Работа выполнена по государственному заданию ОНЦ СО РАН в соответствии с Программой фундаментальных научных исследований государственных академий наук на 2013-2020 годы по направлению II.9, проект № II.9.2.1 (номер госрегистрации в системе ЕГИСУ НИОКТР АААА-А17-117041210227-8), а также при частичной поддержке гранта РФФИ № 18-32-00233 мол_а, в части анализа композитов методом SEM.

A technique for determination of the dielectric constant of individual hemoglobin molecules is presented. It is based on modeling the profiles of their images obtained using electrostatic force microscopy. The obtained values of the static dielectric constant are in agreement with the known literature data. The proposed method can be adapted to determine the dielectric characteristics of individual molecules of various proteins.

A new method for the synthesis of porous crystalline tin-dioxide (SnO2) layers from composites on the basis of multiwalled carbon nanotubes (MWCNTs) and nonstoichiometric amorphous tin oxide (MWCNT/SnO x ) is proposed. An MWCN/SnO x composite layer produced by magnetron sputtering is annealed in air atmosphere at 500°C for 30 min. A homogeneous porous layer comprised of crystalline SnO2 spherical particles with a size of about 0.1 μm is obtained as a result. In the process of annealing, nearly all the amount of carbon is removed in the form of gaseous oxides (only a small amount remains in the upper part of the porous SnO2 layer). The structural defectiveness of nanotube walls, which increases because of the magnetron deposition of tin, plays a crucial role in the carbon oxidation and destruction of MWCNTs.

Methods of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES) were used to investigate the influence of irradiation by argon ions of multi-walled carbon nanotubes (MWCNTs) on the composites SnO 2-x /MWCNTs formation. It has been shown that irradiation of the MWCNTs leads to the formation of structural defects and oxygen-containing groups in the walls of carbon nanotubes. The presence of the latest in MWCNTs walls leads to chemical interaction of the tin oxide with the surface of MWCNTs through formation of chemical Sn O C bonds at the interfaces “Tin oxide-MWCNTs” at synthesis of the composite by CVD method. It has been established that the crystalline structure of the tin oxide clusters forming on surface of MWCNTs depends essentially on the defectiveness in the structure of the outer walls of carbon nanotubes.

Data on the distribution of iron in nitrogen-containing multiwall carbon nanotubes (N-MWCNTs) and changes in its chemical state and concentration under different parameters of irradiation by a pulsed ion beam are obtained by methods of transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersion analysis. It is shown that the irradiation of N-MWCNTs with an energy density of 0.5 J/cm2 lead to the formation, on their lateral surfaces, of structures with a size of 2–10 nm, consisting of metallic iron encapsulated in a carbon shell. An increase in the energy density to 1–1.5 J/cm2 leads to a substantial removal of iron clusters from the tips of carbon nanotubes and a reduction in the amount of iron in the bulk of the N-MWCNT layer.

Using the methods of X-ray photoelectron (XPS) and X-ray absorption near edge structure (XANES) spectroscopies with synchrotron radiation, data on changes in the electronic structure and chemical composition of nitrogen-containing multiwalled carbon nanotubes (N-MWCNTs) upon their exposure to the radiation of argon ions with an energy of 5 keV are obtained. It is found that the exposure leads to an increase in the degree of defectiveness of the N-MWCNTs structure and to the carbon oxidation with formation of various oxygen-containing groups (C–OH, C=O/COOH, C–O–C/O–C–O, and CO3). The presence of carbon–oxygen bonds on the surface of carbon nanotubes is associated with the formation of radiation defects. It is shown that an increase in the fraction of nitrogen atoms present in the substituting configuration in the N-MWCNTs wall structure due to the irradiation does not give rise to an increase in the density of the occupied states near the Fermi level against the background of an increase in the degree of structure defectiveness, carbon oxidation, and a decrease in the total nitrogen concentration. The obtained results show that the irradiation of N-MWCNTs with argon ions allows one to successfully functionalize their surface.

Laser technologies that are used for the development of sensor elements for Remotely Operated Vehicles (ROVs) are presented, as well as the latest developments in underwater robotics where laser spectroscopy methods are applied to environmental monitoring. A submersible laser spectrometer unit intended for studying Raman scattering and laser-induced fluorescence (LIF) spectra is presented. The spectrometer was developed as an element of an ROV sensor system for remote detection and measurements of organic matter concentrations in sea water and underwater objects. The results of environmental tests of the submersible LIF spectrometer in various marine areas, including the Arctic, are described.

The complex methods of transmission electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used to investigate the changes in the morphology, phase composition, and electronic structure of the composite SnO 2−x /nitrogen-doped multiwalled carbon nanotubes (SnO 2−x /N-MWCNTs) irradiated with the pulsed ion beam of nanosecond duration. The irradiation of the composite SnO 2−x /N-MWCNTs leads to the formation of nanoparticles with the core–shell structure on the surface of CNTs with a sharp interfacial boundary. It has been established that the “core” is a metal tin (Sn 0 ) with a typical size of 5–35 nm, and the “shell” is a thin amorphous layer (2–6 nm) consisting of nonstoichiometric tin oxide with a low oxygen content. The “core–shell” structure Sn SnO x is formed due to the process of heating and evaporation of SnO 2−x under the effect of the ion beam, followed by vapor deposition on the surface of carbon nanotubes.

The electric conductivity of individual multiwalled carbon nanotubes (CNTs) doped with nitrogen has been studied in as-synthesized, heat-treated, and argon-ion-irradiated states by the method of electrostatic force microscopy (EFM). Modelling of transverse cross-section profiles of EFM images were used to determine the potential difference across the probe tip–CNT gap (U tip-CNT), which is a parameter related to the conductivity of CNTs. A strong correlation between the specific volume conductivity of a CNT layer and average U tip-CNT value has been found for all types of samples. It is established that a change in the conductivity of N-doped CNTs upon thermal annealing and argon-ion irradiation is caused by modification of the composition and/or concentration of defects in CNT walls.

The oxidation of mesoporous silicon in a double-layer “macroporous silicon–mesoporous silicon” structure is studied. The morphology and dielectric properties of the buried insulating layer are investigated using electron microscopy, ellipsometry, and electrical measurements. Specific defects (so-called spikes) are revealed between the oxidized macropore walls in macroporous silicon and the oxidation crossing fronts in mesoporous silicon. It is found that, at an initial porosity of mesoporous silicon of 60%, three-stage thermal oxidation leads to the formation of buried silicon-dioxide layers with an electric-field breakdown strength of Ebr ~ 104–105 V/cm. Multilayered “porous silicon-on-insulator” structures are shown to be promising for integrated chemical micro- and nanosensors.

In this paper, we investigate the activation of the surface of multi-walled carbon nanotubes by irradiating them with a beam of argon ions with an energy of 5 keV during the formation of composites with tin oxide (SnOx/MWCNTs) by the method of gas-phase chemical deposition. The analysis of the structure and chemical state of the formed composites was carried out using synchrotron radiation using X-ray photoelectron spectroscopy (XPS) and X-ray adsorption spectroscopy (XANES) methods. The results obtained showed that the preliminary treatment of MWCNTs with argon ions leads to the formation of oxygen-containing functional groups on their surface, which act as interfacial interaction centers during the subsequent formation of the composite. It has been shown that subsequent heat treatment allows one to partially restore the crystal structure of the walls of carbon nanotubes and optimize the crystal structure of tin oxide in the composite

The morphological changes of the two-layer structures consisting of the upper macroporous layer and the buried mesoporous layer as a result of high-temperature annealing in oxygen, were investigated. The formation of pass-through pores in the layer of mesoporous silicon during the oxidation process at a sufficiently high porosity of the initial layer was found. The processes that presumably lead to the detected morphological changes are considered. A method for the formation of gas-permeated membranes consisting of oxidized macroporous silicon and a layer of buried silicon oxide having pass-through pores is presented. The gas transmission of the obtained membrane was investigated. Partial passage of nitrogen dioxide through the membrane was recorded.

The structure and properties of individual MWCNTs subjected to electron irradiation and thermal annealing in an inert atmosphere of Ar have been investigated by means of transmission electron microscopy, Raman spectroscopy, and electrophysical methods. It is shown that electron irradiation generates point defects and it changes the interlayer distance in the MWCNTs` walls. Thermal annealing in an inert atmosphere leads to a partial restoration of the MWCNTs` structure. At the same time, the large-scale defects are observed in the nanotube walls, due to which the MWCNTs acquire a `zigzag` form. Consecutive ionic and thermal treatments determine the MWCNTs` electrophysical properties and could be used as a method for conductivity manipulation.