N.A. Kiselev

Double-walled carbon nanotubes fabricated by a hydrogen arc discharge method

Abstract Double walled carbon nanotubes (DWNTs) were obtained by the arc discharge technique in an atmosphere of Ar and H 2 mixture (1:1/v:v) at 350 Torr. The catalyst was prepared from a mixture of Ni, Co, Fe and S powders heated in an inert gas atmosphere at 500°C for 1 h. High resolution electron microscopy (HREM) revealed that the dominant type of obtained nanotubes were DWNTs with outer diameter in the range of 1.9–5 nm and inner tube diameters in the range 1.1–4.2 nm. As a rule, the DWNT tubes form into bundles. Occasionally single walled nanotubes (SWNTs) were observed by HREM although Raman spectroscopy did not reveal the presence of significant quantities of these tubules in the bulk product.

Field electron emission from nanotube carbon layers grown by CVD process

Abstract We present the field emission characteristics of nanotube carbon layers grown by chemical vapor deposition process. In this process, products of thermal decomposition of polyethylene were used as the source of carbon. SEM and HREM investigations of manufactured layers showed that these layers consisted of randomly oriented conical layer carbon nanotubes (CLNTs). The diameter of nanotubes usually ranged from 20 up to 40xa0nm. The investigations of field electron emission were fulfilled at room and low (≈120xa0K) temperatures. The emission current of 0.1xa0nA arose at the average electric field E av =1.5–2.5 V/μm . The emission current of 100xa0μA (current density ≈10xa0mA/cm2) was observed at E av =4–4.5 V/μm . The value of field amplification coefficient β was equal to 1300–2000. The field emission characteristics replotted in Fowler–Nordheim coordinates were linear at room and low (≈120xa0K) temperatures for current variation of 5–6 orders of magnitude. The calculations of field amplification coefficient β were fulfilled for an array of aligned closed nanotubes. These calculations demonstrated strong dependence of β versus the distance between nanotubes and their height.

SEM and HREM study of the internal structure of nanotube rich carbon arc cathodic deposits

The structural components and the internal organization of carbon cathodic deposits fabricated using an arc with the conditions adjusted for the effective production of nanotubes have been characterized by transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and scanning electron microscopy (SEM). Typically, such deposits are columnar structures oriented along the growth direction. Three main components were observed: multiwalled nanotubes, multilayer polyhedral particles and curved graphitic formations. The measured distributions and relative quantities of the components depended on the deposition regimes. Column interiors were composed of a mixture of all these components, while the outer covering of the columns was formed predominantly of nanotubes. Multiwalled nanotubes formed a mesh-like arrangement around these columns and their growth surfaces, with smaller amounts of nanotubes present inside the columns. Nanotubes in various fragments of the deposits were mainly oriented at high angles to the deposit axes. In the column coverings, groups of tubes oriented at angles >45° to the axes were present with no sets of nanotubes or bundles aligned along the deposit axes seen. Finally, a mechanism of deposit formation is proposed in connection with the recorded data.

One-dimensional SnF2 single crystals in the inner channels of single-wall carbon nanotubes: II. Structure and nanocomposite construction modeling

A structural model of the nanocomposite consisting of one-dimensional (1D) α-SnF2 single crystals and single-wall carbon nanotubes (SWCNTs) is proposed. The main cationic motif is revealed in the structure of monoclinic modification: two-layer packing of tin cations along the [283] direction. Four theoretical structural projections of a 1D crystal on the plane parallel to the [283] direction are determined and described. A fragment of the α-SnF2 structure in an SWCNT (with a channel diameter of 1.02 nm) is calculated. High-resolution electron microscopy (HREM) images are modeled. These images correspond to the actually observed HREM patterns.

HREM of nanometric tips prepared from epitaxially grown silicon whiskers

Abstract Nanometric tips prepared from Si whiskers frown epitaxially by VLS techniques were investigated by HREM. Whiskers were grown on 0.23 × 2mm (111)Si ‘butt-ends’ of plate-shaped substrates oriented in using X-ray diffraction techniques. Since the tip ends are suitably thin, and in an appropriate orientation— —for lattice imaging, the HREM images which are obtained display facetting at the end of the tips. SEM images of the bases of tips removed mechanically from the substrate, and also two-beam diffraction contrast TEM images show that the cross-sections of the nanometric tips prepared by a one-stage process are equilateral triangles with truncated corners. This is also confirmed by observing changes in the lattice image contrast across tips, with the appearance of characteristic half-spacing contrast at specific thicknesses typical of wedge-shaped crystals. According to HREM, the lattice is defect-free. There are two versions of tip etching (two combinations of three [111] shape-making faces). The extreme ends of the tips are atomically sharp, with an apex cone angle of 18–24°. Tips prepared by a two-stage process are characterised by a thick base and thin ‘cylindrical’, needle-shaped part 50–200 nm in diameter and 6–20 μm long. The angle which forms the needle profile of the thin part with [ 1 ¯ 11 ] growth direction is 1.5–4°. Profile imaging of the thin part reveals small steps along [111]. The ends of these tips are also atomically sharp, and resemble those prepared by a one-step etching process.

Nucleation and growth of crystalline diamond particles on silicon tips

The data on the deposition, structure, and electric properties of crystalline diamond particles at silicon tips grown on single-crystal silicon substrates obtained over the last decade, mainly at the Institute of Crystallography of the Russian Academy of Sciences, have been reviewed. It is shown that silicon emitters coated with crystalline diamond are highly electrically stable. They are used to prepare long-life cathodoluminescence light sources.