L. A. Chernozatonskii

Correlation between metal catalyst particle size and carbon nanotube growth

Abstract The dependence of carbon nanotube diameters upon the size of nickel catalyst particles supported on amorphous carbon films was studied. Nanotubes were catalytically grown at different temperatures to elucidate the effect of temperature. The transformation of nanotube-growth mechanism takes place in the range 700–800 °C as evident from particle size–nanotube diameter relations, tip particles and nanotube morphologies. At low temperature (700 °C), the nanotube growth is conducted through solid tip catalyst particles. At 800 °C, nanotubes grow via liquid catalyst particles by extrusion mode. Low-temperature tube diameters reproduce essential features of original particle size distribution. In contrast, high-temperature tubes exhibit universal Gauss-like diameter distribution irrespective of catalyst particle sizes.

ELECTRON FIELD EMISSION FROM NANOFILAMENT CARBON FILMS

Abstract Considerable field emission has been observed from the surface of nanofilament carbon structure films on various substrates (Si, quartz, glass): the density of emission current was up to 1 A/cm 2 while the electric field was about 100 V/μm. The ‘reconstruction’ and ‘inversion’ effects of field emission have also been observed on some structures after current breakdown.

Ballistic switching and rectification in single wall carbon nanotube Y junctions

Transport properties of various semiconducting zig-zag carbon nanotube Y junctions are studied for the investigations of rectification and switching. Our results indicate that such junctions, when symmetric, can support both ballistic rectification and/or the ballistic switching operating modes. Although structural symmetry of the Y junction is found to be a necessary condition for rectification, it may not be sufficient in all cases.

The superhard crystalline three-dimensional polymerized C60 phase

Abstract The profile analysis of the diffraction patterns, obtained for C 60 samples quenched from high pressure 13 GPa and temperature 670–820 K, yields proof of the formation of three-dimensional (3D) polymerized C 60 phase. The superhard phase manufactured after 13 GPa, 820 K treatment is characterized by common four-sided ring and (2+2) interfullerene cycloadditions in the layer, and (3+3) bondings between layers. The unit cell parameters of its body-centred orthorhombic Immm crystal structure refined by Rietveld program are equal to: a =0.867(4), b =0.881(1), and c =1.26(0) nm. Lattice dynamics simulation of 3D polymerized C 60 has shown that sound velocities, bulk modulus and broad bands in Raman spectra agree well with the measurements.

Two-dimensional semiconducting nanostructures based on single graphene sheets with lines of adsorbed hydrogen atoms

It is shown that lines of adsorbed hydrogen pair atoms divide the graphene sheet into strips and form hydrogen-based superlattice structures (2HG-SL). We show that the formation of 2HG-SL changes the electronic properties of graphene from semimetal to semiconductor. The electronic spectra of “zigzag” (n,0) 2HG-SL is similar to that of (n,0) carbon nanotubes and have a similar oscillation of band gap with n, but with nonzero minimal values. The composite dual-periodic (n,0)+(m,0) 2HG-SLs of zigzag strips are analyzed, with the conclusion that they may be treated as quasi-two-dimensional heterostructures.

Structure and properties of BeO nanotubes

The structure of a new non-carbon (beryllium oxide BeO) nanotube consisting of a rolled-up graphene sheet is proposed, and its physical properties are described. Ab initio calculations of the binding energy, the electronic band structure, the density of states, the dependence of the strain energy of the nanotube on the nanotube diameter D, and the Young’s modulus Y for BeO nanotubes of different diameters are performed in the framework of the density functional theory (DFT). From a comparison of the binding energies calculated for BeO nanotubes and crystalline BeO with a wurtzite structure, it is inferred that BeO nanotubes can be synthesized by a plasma-chemical reaction or through chemical vapor deposition. It is established that BeO nanotubes are polar dielectrics with a band gap of ∼5.0 eV and a stiffness comparable to that of the carbon nanotubes (the Young’s modulus of the BeO nanotubes YBeO is approximately equal to 0.7YC, where YC is the Young’s modulus of the carbon nanotubes). It is shown that, for a nanotube diameter D > 1 nm, the (n, n) armchair nanotubes are energetically more favorable than the (n, 0) zigzag nanotubes.

Field emitter arrays on nanotube carbon structure films

We present the finding of newly performed experiments of considerable field emission from the films consisting of nanotube carbon structures. Density of emission current was up to 1–3 A/cm2, while in 20–100 V/μm electric field it was 0.1–1 mA/mm2.

Diamond-like C2H nanolayer, diamane: Simulation of the structure and properties

We consider a new C2H nanostructure based on bilayer graphene transformed under the covalent bond of hydrogen atoms adsorbed on its external surface, as well as compounds of carbon atoms located opposite each other in neighboring layers. They constitute a “film” of the 〈111〉 diamond with a thickness of less than 1 nm, which is called diamane. The energy characteristics and electron spectra of diamane, graphene, and diamond are calculated using the density functional theory and are compared with each other. The effective Young’s moduli and destruction thresholds of diamane and graphene membranes are determined by the molecular dynamics method. It is shown that C2H diamane is more stable than CH graphane, its dielectric “gap” is narrower than the band gap of bulk diamond (by 0.8 eV) and graphane (by 0.3 eV), and is harder and more brittle than the latter.

The impact of edges and dopants on the work function of graphene nanostructures: The way to high electronic emission from pure carbon medium

The impact of the edges and the presence of dopants to the work function (WF) of graphene nanoribbons (GNR) and nanoflakes was studied by an ab initio approach. The strong dependence of the WF upon the GNR structure was found and a promising character for the field emission by the donor type impurities was observed. Basing on the predominant impact of the nanostructure edges to the emission properties, the small graphene flakes were investigated as a possible source for the electron emission. The obtained weak dependence of the low WF values of the graphene flakes on their size and shape allows to suggest that the pure carbon medium with high and uniform emission properties can be fabricated by todays technology.

Metal-semiconductor (semimetal) superlattices on a graphite sheet with vacancies

It has been found that periodically closely spaced vacancies on a graphite sheet cause a significant rearrangement of its electronic spectrum: metallic waveguides with a high density of states near the Fermi level are formed along the vacancy lines. In the direction perpendicular to these lines, the spectrum exhibits a semimetal or semiconductor character with a gap where a vacancy miniband is degenerated into impurity levels.