N. A. Kiselev

Carbon nanotubes from polyethylene precursors: Structure and structural changes caused by thermal and chemical treatment revealed by HREM

High resolution electron microscopy (HREM) reveals that carbon nanotubes obtained by heating a polyethylene precursor in the presence of catalytic Ni particles have a structure consisting of stacked conical carbon layers. Two main types of nanotube structures were identified. When the conical angle along the tubes is in the range 16–35 °, “bamboo”-shaped nanotubes are observed, characterized by open carbon edges (OEs) that were assumed to terminate in hydrogen. When the conical angle is in the range 75–85 °, a “fish-bone”-type structure is observed. Following heat treatment in the temperature range 1200–2800 °C, the catalytic Ni particles were removed and the hydrogen content reduced. As a result, the neighboring OEs were linked together, revealed in the HREM by the formation of loops along both the external tube sides and also the insides of the inner channels. Chemically, the pre-heat treated tubes could withstand bromination, but were completely destroyed by treatment with hot concentrated HNO3. Treatment of the pre-heat treated tubes with molten V2O5 revealed no penetration of this material between the OEs along the external wall or into the inner channel. The microstructure of the catalytic Ni particles, present at the tips of the pre-heat treated nanotubes, was also investigated. Outer polycrystalline layers consisting of Ni3C and probably NiO were observed near the periphery of terminal Ni particles not covered with graphitic layers and also near that of open regions of partially covered particles.

The structure of 1D CuI crystals inside SWNTs.

Nanocomposites consisting of one‐dimensional CuI crystals inside single‐walled carbon nanotubes were obtained using the capillary technique. high‐resolution transmission electron microscopy investigations of the atomic structure of the encapsulated 1D CuI crystals revealed two types of 1D CuI crystals with growth direction <001> and relative to the bulk hexagonal CuI structure. Atomic structure models were proposed based on the high‐resolution transmission electron microscopy images. According to the proposed models and image simulations, the main contrast in the 1D crystal images arises from the iodine atoms whereas copper atoms, with lower atomic number giving lower contrast, are thought to be statistically distributed.

One-Dimensional Crystals inside Single-Walled Carbon Nanotubes: Growth, Structure and Electronic Properties

Single-walled carbon nanotubes (SWNTs) discovered in 1993 are currently among the most exciting and promising nanostructures (Bethune et al., 1993; Iijima & Ichihashi, 1993). They arouse huge interest due to their unique atomic structure, outstanding chemical and electronic properties (thermal and electric conductivity), as well as mechanical characteristics (high values of Youngs modulus, tensile and compressive strengths, high cracking resistance etc.). SWNTs possess the maximum geometric anisotropy factors among the nanostructures known so far. The unique properties of carbon nanotubes (CNTs) are governed not only by their unusual tubular structure, but also by the fact that they are virtually devoid of any structural defects (Dresselhaus et al., 1995; Iijima, 1991; Saito et al., 1992). As a result, CNTs are of a great importance for development of nanoelectronics elements (logical gates, memory devices, emitters, and nanowires), nanoelectromechanical systems, nanocomposite fillers (aimed at increasing strength and functionality of bulk materials), probe tips for scanning probe microscopy etc. One of the major areas of SWNTs technological application has been the development of a new generation of field-effect transistors (Tans et al., 1998). The electronic properties of defect-free SWNTs are extremely sensitive to the nanotube’s geometric structure (Avouris et al., 2007; Saito et al., 1992), which depends to a great extent on the chiral vector; this may be regarded both as an advantage and a serious drawback of this material. So far, no efficient methods have been developed for the preparation and isolation of SWNTs with a desired chirality (Hou et al., 2008; Odom et al., 2000). For this reason, many attempts have been undertaken to develop methods that would allow separating the array of SWNTs into semiconducting and metallic nanotubes and/or modify the electronic properties of SWNTs without their separation by chirality (Chaturvedi et al., 2008; Eliseev et al., 2009a; Monthioux et al., 2006). Modification of nanotubes allows direct adjustment of their electronic properties. One of the simplest ways to controlled modification of the SWNTs is filling of the nanotube channels

The behaviour of 1D CuI crystal@SWNT nanocomposite under electron irradiation

Nanocomposite 1D CuI crystal@SWNT was obtained by the growth of CuI nanocrystals inside single walled carbon nanotubes (SWNTs) using the capillary technique. High resolution transmission electron microscopy (HRTEM) investigation of the atomic structure of 1D CuI crystals revealed two types of 1D CuI crystals: with growth direction and relative to the bulk hexagonal CuI stucture. EM images were recorded and atomic models of the structure were proposed. According to the proposed models and image simulations, the main contrast in the 1D crystal images arises from the iodine atoms. In this paper the 1D CuI crystal@SWNT nanocomposite behavior determined mainly by the influence of the electron beam was investigated and it is shown that the 1D CuI nanocrystals can oscillate and rotate inside the nanotube channel under a 100kV electron beam. The oscillations occur within an exposure time of 25 s. With longer exposure time of ∼90 s, the 1D crystal gradually decreases in length, sometimes moving inside...

Size-Dependent Structure Relations between Nanotubes and Encapsulated Nanocrystals

The structural organization of compounds in a confined space of nanometer-scale cavities is of fundamental importance for understanding the basic principles for atomic structure design at the nanolevel. Here, we explore size-dependent structure relations between one-dimensional PbTe nanocrystals and carbon nanotube containers in the diameter range of 2.0-1.25 nm using high-resolution transmission electron microscopy and ab initio calculations. Upon decrease of the confining volume, one-dimensional crystals reveal gradual thinning, with the structure being cut from the bulk in either a <110> or a <100> growth direction until a certain limit of ∼1.3 nm. This corresponds to the situation when a stoichiometric (uncharged) crystal does not fit into the cavity dimensions. As a result of the in-tube charge compensation, one-dimensional superstructures with nanometer-scale atomic density modulations are formed by a periodic addition of peripheral extra atoms to the main motif. Structural changes in the crystallographic configuration of the composites entail the redistribution of charge density on single-walled carbon nanotube walls and the possible appearance of the electron density wave. The variation of the potential attains 0.4 eV, corresponding to charge density fluctuations of 0.14 e/atom.

A compact X-ray tube with a field emitter based on carbon nanotubes

A compact X-ray tube with a field emitter based on carbon nanotubes is developed. Over a long time interval, the X-ray tube maintains an anode current of 300 μA, an anode voltage of 10 kV, and the stable characteristics of the field emitter.

HRTEM of 1DSnTe@SWNT nanocomposite located on thin layers of graphite

The method for imaging of highly sensitive nanostructures unstable under electron beam irradiation is introduced. To reduce charge and thermally generated beam damage, highly conductive multilayered graphene or thin graphite layers were used as supports for nanostructures. Well‐defined crystalline structure of graphite layers enables image reconstruction by Fourier filtering and allows maintaining high quality of images. The approach was tested for imaging of highly sensitive quasi one‐dimensional SnTe nanocrystals hosted inside single‐walled carbon nanotubes. Relying on the filtered images and the image simulation, the structure of one‐dimensional SnTe was established as a chain of fcc NaCl type unit cells, connected by the [001] edges with <110> direction coinciding with nanotube axis.

Characterization of SWCNT products manufactured in Russia and the prospects for their industrial application

Single-wall carbon nanotubes (SWCNTs) are of the greatest interest for application in materials used for various purposes due to all of their unique properties. However, the practical use of SWCNTs has, until quite recently, been limited by the absence of a cheap industrial process for manufacturing them. Currently, a technology for the synthesis of SWCNTs from hydrocarbon raw materials providing the initial SWCNTs product of a sufficiently high quality has been developed in Russia for the first time in world history. In this work, the results of the characterization of the SWCNT products available in the Russian market are presented and the most promising directions among the technical applications of the materials and products on the basis of SWCNTs are highlighted.

Field emission from carbon layers containing very long and sparse nanotubes∕nanofilaments

Field-emission characteristics of carbon layers with very long (up to several mm) and sparse nanotubes (nanofilaments) have been investigated. For such layers field emission current of 10μA is registered at very low average electric field Eav=0.16V∕μm and the values of the field amplification coefficient β reach 45 000. It has been found that, at electric fields corresponding to the onset of the field emission, the emitting nanotubes are stretched towards the anode. At high emission currents (exceeding 30–50μA), one or several luminous filaments have been observed in the gap between the sample and the anode. These luminous filaments are carbon nanotubes (nanofilaments) heated by the emission current.

Properties of Field Electron Emitter Based on Carbon Nanotubes Installed in the Small-Sized X-Ray Tube

A small-sized X-ray tube with a carbon nanotube planar field electron emitter has been manufactured and tested. Field electron emitter was grown by the chemical vapor deposition (CVD) method on a nickel substrate. During long time tests (more than 50 hours) the X-ray tube has demonstrated stable characteristics of the emitter current in the dc mode. Relative emission current fluctuations were about 0.3% at the emitter emission current equal to 550 μA.