A. V. Gusel’nikov

Synthesis and structure of films consisting of carbon nanotubes oriented normally to the substrate

Films consisting of oriented carbon nanotubes (CNTs) are synthesized by thermal decomposition of a carboniferous compound + ferrocene mixture and studied by scanning electron microscopy. It is shown that the thickness and structure of the films depend on the synthesis conditions, specifically, on the way the reaction mixture is introduced. Multiple injection of the reaction mixture causes growth of multilayer CNT films, the number of layers in which equals the number of injections. The basic possibility of CNT continuous growth normally to the substrate surface is demonstrated. A mechanism behind the layered structure of the films consisting of oriented CNTs is suggested.

Effect of purification on the electron structure and field emission characteristics of a carbonaceous material containing single-wall carbon nanotubes

A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current-voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes.

Determination of the texture of arrays of aligned carbon nanotubes from the angular dependence of the X-ray emission and X-ray absorption spectra

The properties of materials containing carbon nanotubes depend on the degree of alignment and the internal structure of nanotubes. It is shown that the degree of misorientation of carbon nanotubes in samples can be evaluated from the measurements of the angular dependences of the carbon X-ray emission and carbon X-ray absorption spectra. The CKα emission and CK X-ray absorption spectra of the array of multiwalled carbon nanotubes synthesized by catalytic thermolysis of a mixture of fullerene and ferrocene are measured. A comparison of the calculated model dependences of the relative intensities of the π and σ bands in the spectra with the experimental results makes it possible to evaluate the degree of misorientation of nanotubes in the sample and their internal texture.

The field emission properties of carbon nanotubes and SiC whiskers synthesized over Ni particles deposited in ion tracks in SiO2

Carbon nanotubes (CNTs) and SiC whiskers are synthesized by the pyrolysis of acetonitrile vapor over Ni nanoparticles deposited in the pores obtained by etching heavy ion tracks in dielectric SiO2 layers on single crystal silicon substrates. The structures obtained are studied by scanning electron microscopy and Raman spectroscopy, and their field emission characteristics are measured. The formation of CNTs or SiC whiskers as a result of catalytic hydrocarbon pyrolysis is found to depend on the occupation of ion tracks by nickel clusters. It is shown that the threshold of electron emission appearance is 1 V/µm for both types of the samples and that differences in the shape of current-voltage characteristics are explained by differences in the electronic structure of CNTs and SiC whiskers.

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.

A Laboratory CVD Reactor for the Synthesis of Vertically Oriented Carbon Nanotube Arrays

The functional structure and the design of a CVD reactor for the synthesis of vertically oriented carbon nanotube (VOCNT) arrays on silicon substrates are described. To synthesize VOCNTs, various organic compounds, viz., toluene, cyclohexane, and acetonitrile, and their mixtures in the liquid state were tested under normal conditions.

The Automation of a CVD-Reactor for the Synthesis of Vertically Oriented Carbon Nanotube Arrays

The functional diagram and the automation system of a CVD-reactor for the synthesis of vertically oriented carbon nanotube arrays on silicon substrates are described. The system is intended predominantly for recording the physical parameters of the CVD-reactor in real time, generating the instructions for the operator on the selected synthesis-process flow, on-screen display of the selected parameters, and management of the automatic protection of the reactor units and assemblies against contingencies or unspecified actions of the operator. The structure of the system for data acquisition, visualization of synthesis variables, and the CVD process control that allows the synthesis of vertically oriented carbon nanotube arrays is presented.

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.

Effect of iron nanoparticles in the films of composite materials and carbon nanotubes on the angular dependence of X-ray emission

The angular dependences of X-ray emission were measured for a series of polymer film samples with different concentration of finely dispersed iron. X-ray fluorescence maximum was found to shift toward higher angles with increasing the iron concentration in a sample. The form of angular dependences of X-ray emission was calculated taking into account the particle absorption coefficients in a composite material for incident and emitted radiation. The experimental and theoretical dependences were compared to estimate the content of nanoparticles in the polymer composite and iron nanoparticles in the samples of oriented carbon nanotubes.