Yu. V. Fedoseeva

XANES Investigation of Pristine and Fluorinated Single-Walled Carbon Nanotubes Before and After Annealing

X-ray absorption near-edge structure (XANES) spectroscopy has been used for comparative investigation of the electronic structure of pristine and fluorinated single-walled carbon nanotubes (SWCNTs) before and after annealing. The SWCNTs were produced by catalytic chemical vapor deposition method and fluorinated using a gaseous mixture of BrF3 and Br2 at room temperature. The samples were annealed at 250°C for 0.5 hour directly in the vacuum chamber of the X-ray spectrometer. C K-edge XANES spectra showed increase in the π* resonance intensity after the treatment of as-produced and fluorinated SWCNTs that was attributed to the detachment of adsorbed molecules and defunctionalization of nanotubes with the heating. Furthermore, analysis of the spectra revealed the annealing of the SWCNT samples produces topological defects in the nanotube walls.

A comparative study of argon ion irradiated pristine and fluorinated single-wall carbon nanotubes

Effect of Ar(+) ion irradiation on the structure of pristine and fluorinated single-wall carbon nanotubes (SWCNTs) was examined using transmission electron microscopy (TEM), Raman, and x-ray photoelectron spectroscopy (XPS). The TEM analysis revealed retention of tubular structures in both irradiated samples while Raman spectroscopy and XPS data indicated a partial destruction of nanotubes and formation of oxygen-containing groups on the nanotube surface. From similarity of electronic states of carbon in the irradiated pristine and fluorinated SWCNTs observed by XPS, it was suggested that defluorination of nanotubes proceeded with breaking of C-F bonds.

Electromagnetic properties of phosphate composite materials with boron-containing carbon nanotubes

The possibility of developing electromagnetic composite materials based on unfired heat-resistant mechanically strong phosphate ceramics has been studied. Boron-containing multiwalled carbon nanotubes and onion-like particles (B-MWCNTs) synthesized by electric-arc evaporation of a graphite rod enriched with boron are used as a functional additive to the phosphate matrix. According to transmission electron microscopy, the average nanoparticle length is ∼100 nm. According to X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, the boron content in B-MWCNT walls is less than 1 at %, and substitution of carbon atoms with boron leads to the formation of acceptor states in the conduction band. An increase in the electromagnetic response of phosphate ceramics by ∼53 and ∼13–15% for 1.5 wt % B-MWCNT additive is detected in quasi-static and gigahertz ranges, respectively. It is assumed that a stronger effect can be achieved using longer B-MWCNTs than those formed under electric arc conditions.

X-ray spectroscopy study of lithiated graphite obtained by thermal deposition of lithium

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СKα XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.

Structure of carbon nanoparticles synthesized by adiabatic compression of acetylene and their application in supercapacitors

The work reports the study of the structure of carbon nanoparticles prepared by the pyrolysis of heliumdiluted acetylene under adiabatic compression in a piston reactor. At a pushing gas pressure of 0.5 MPa, 0.7 MPa, and 0.9 MPa the reaction gas was heated to temperatures of 400 °C, 600 °C, and 750 °C. By transmission electron microscopy it is found that carbon nanoparticles have a spherical shape and their size varies from 20 nm to 60 nm. The structural features of carbon nanoparticles are determined from the X-ray photoelectron spectroscopy data and the analysis of the near-edge X-ray absorption fine structure spectroscopy. Carbon nanoparticles prepared at a pushing gas pressure of 0.5 MPa have an amorphous structure and consist of hydrogenated carbon with impurities of polycyclic aromatic fragments. At a stronger compression ratio, carbon nanoparticles with a layered structure consisting mainly of sp2 hybridized carbon atoms are formed. The capacitance behavior and electrochemical impedance of carbon nanoparticle-based supercapacitors are compared.

Functional composition and electrochemical characteristics of oxidized nanosized carbon

The functional composition and electrochemical behavior of the samples of N121 oxidized nanosized technical carbon in aqueous electrolytes are studied. For oxidation a 30% aqueous hydrogen peroxide (H2O2) solution and 2% H2O2 with the addition of singlet oxygen or ozone were used. By means of X-ray photoelectron spectroscopy data and the analysis of the near edge X-ray absorption fine structure the features of the chemical structure of the samples are found. The oxygen concentration did not exceed 5 at.% in the samples. The analysis of cyclic voltammograms reveals that at low scan rates the specific capacitance of the material is determined by the functional composition of the surface. The sample oxidized by 30% H2O2 solution and containing the largest number of–OH and–COOH groups demonstrated the highest capacitance in 6M KOH and in 1М H2SO4 it was the sample with the highest concentration of C=O groups formed during the oxidation with singlet oxygen. The stability of carbon electrodes is studied in supercapacitor models.

An X-ray spectroscopy study of CdS nanoparticles formed by the Langmuir–Blodgett technique on the surface of carbon nanotube arrays

The composition and electronic structure of cadmium sulfide (CdS) nanoparticles formed by the Langmuir–Blodgett (LB) technique on clean silicon wafers and the surface of vertically aligned carbon nanotube (CNT) arrays are studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The samples were annealed in a vacuum at 175 °C and 225 °C to remove the organic matrix of the LB film. From the analysis of the XPS data the increased concentration of sulfate groups on the surface of CdS nanoparticles formed on CNTs and the electron density transfer from CdS to CNTs are determined. An increase in the LB film annealing temperature causes an increase in the degree of crystallinity and the CdS crystallite size and a decrease in the photoluminescence intensity of a CdS–CNT hybrid.

X-ray spectroscopic study of the electronic structure of boron carbonitride films obtained by chemical vapor deposition on Co/Si and CoO x /Si substrates

Boron carbonitride films are synthesized by chemical vapor deposition from a mixture of triethylamine borane and ammonia on a metallic or oxidized cobalt sublayer sprayed over Si(100) substrates. Scanning electron microscopy shows that the surface of a BCxNy/Co/Si sample has a homogeneous fine-grained structure; filamentous entities are found on the surface of the BCxNy/CoOx/Si sample. The electronic structure of the films is investigated by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). An analysis of the spectra shows that BCxNy films are composed of graphite and hexagonal boron nitride (h-BN) regions and complex BCxNyOz components with B-C, N-C, B-O, N-O, and C-O bonds. The deposition of the BCxNy film on the oxidized Co sublayer results in an increase in the number of C-O, N-O, B-O, and C-N bonds and a decrease of the graphite and h-BN components and in the number of C-B bonds. The XPS data are used to estimate the surface elemental composition of the BCxNy/CoOx/Si sample. It is found that the film consists of 66 at.% graphite component and 3 at.% h-BN; the proportion of complex C0.46B0.11N0.05O0.38 components is 31 at.%.