Theoretical Study of the Electronic and Transport Properties of Lateral 2D–1D–2D Graphene–CNT–Graphene Structures

JETP Letters - The electronic and transport properties of new hybrid 2D–1D–2D structures of carbon atoms, which are graphene sheets continuously connected through a fragment of a...     

Simulation of molecular and electronic structure of polyhydrogenated (n,0)-tubulenes and their analogs intercalated with lithium

Molecular and electronic structure of four polyhydrogenated (n,0)-tubulenes, namely, [−C₂₄H₄−] _m (1), two isomers of composition [−C₂₈H₄−] _m (2 and3), and [−C₃₂H₄−] _m (4) withn benzene rings in the cross section (n=6, 7, 7, and 8, respectively), was simulated atm>1 (m is the number of repeating fragemnts). It was assumed that hydrogen atoms are attached to all carbon atoms lying on the two most distant elements of the cylinders of the corresponding tubulenes. The energy band structures of macromolecules1–4 and their Li-intercalated analogs [−C₂₄H₄Li−] _m (5) [−C₂₈H₄Li−] _m (two isomers,6 and7), and [−C₃₂H₄Li−] _m (8), containing one Li atom per repeating unit at each center, were obtained in the EHT approximation by the crystal orbital method. Geometric parameters of repeating units of structures1–8 were found after MNDO/PM3 optimization of the energies of hydrocarbon molecules C₇₂H₂₄, C₈₄H₂₆ (two geometric isomers), and C₉₆H₂₈, containing three repeating units of corresponding tubulenes1–4 each. The conductivity types of polyhydrogenated tubulenes1–4 are the same as those of their precursors, (6,0)-, (7,0)-, and (8,0)-tubulenes. Dispersion curves of systems5–8 are much the same as those of macromolecules1–4; however, electron energy spectra of5–8 possess metallic conductivity type and the positions of Fermi levels for these systems are higher than for compounds1–4. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2061–2067, November, 1999.     

Graphene-nanotube structures: Constitution and formation energy

A new class of carbon nanostructures is considered: covalently (or molecularly) bound graphene and carbon nanotube fragments. As found using semiempirical computations and molecular dynamics methods, the structures formed by bonding nanotube edge atoms to a planar segment of a graphene nanofragment or its edge atoms to nanotube atoms arranged at the element of cylinder and graphene nanoribbons attached to a nanotube by van der Waals forces along the nanotube are the most energetically stable systems.     

Formation of graphene quantum dots by “Planting” hydrogen atoms at a graphene nanoribbon

Different technological approaches for creating graphene quantum dots by the adsorption of hydrogen atoms are considered. The adsorption can occur both at convex portions of a distorted graphene nanoribbon and in the structure formed by two distorted graphene nanoribbon rows superimposed on each other at the places free from the ribbon crossings. It is shown that settlement of hydrogen atoms at convex portions of the nanoribbons is energetically favorable. This gives rise to the creation of insulating graphane (CH) nanodomains separating the conducting regions. As a result, a graphene quantum dot appears. The variation of the electron spectra of graphene quantum dots with the length of these graphane regions is discussed.     

Diboride bifullerenes and binanotubes

The structures and energy characteristics of a new class of nanotubes and fullerenes formed by binary layers of a trigonal network of metal atoms M and a graphite-like network of boron atoms are considered by the example of magnesium and zirconium diborides. It is shown that, contrary to the familiar carbon monolayer nanotubes, the dependence of the strain energy of diboride bitubulene on its diameter D deviates from the 1/D ² law because of the “crustlike” shape of a free fragment of the MB₂ bilayer, while bitubulenes with axis parallel to the M-M bonds have the optimum shape at a given diameter. Such bitubulenes are expected to be metallic because of the specific features of the band structure of bilayered diborides.     

Defect formation in a carbon onion upon irradiation with Ar ions

The interaction of an Ar ion with a C₆₀@C₂₄₀@C₅₄₀ carbon onion and an Ar ion beam with a C₆₀@C₂₄₀@C₅₄₀@C₉₆₀ carbon onion are studied by molecular dynamics. The energy threshold for the formation of a vacancy in a pentagon of the onion fullerene shell is examined in two temperature regimes (300 and 1000 K). The main types of defects formed in the onion structure at various incident ion energies are detected and described. It is shown that the pentagonal cycles with their nearest environment are the least stable regions in the carbon onion under irradiation. The results obtained provide direct confirmation of the possibility of formation of a diamond structure upon ion irradiation of carbon onions.     

Broken spin symmetry approach to chemical reactivity and magnetism of graphenium species

The basic problem of weak interaction between odd electrons in graphene and silicene is considered in the framework of the broken spin symmetry approach. This approach exhibits the peculiarities of the odd-electron behavior via both enhanced chemical reactivity and magnetism.     

Molecular and electronic structures of some trimers of polyhedral carbon clusters

Geometries and electronic structures of four crimped linear carbon clusters were modeled by the MNDO/PM3 method. Three of these clusters (C₁₈₀ clusters) are trimers ofI _h -C₆₀ fullene, which differ from each other by the mode of linkage of the monomers. The fourth cluster (C₁₇₂ pseudo-trimer) consists of two C₅₈ fragments of C₆₀ fullerene linked to each other through the C₅₆ cluster. The optimum geometric parameters, hieats of formation, and ionization potentials were calculated for the above-mentioned systems as well as for the corresponding C₁₂₀ and C₁₁₆ dimers. The possibility of extrapolation of the data on dimers and trimers to linear oligomers of the C₆₀ and C₅₆ clusters with a larger number of repeating fragments is discussed. The character of linkages of monomers was analyzed for the two trimers under consideriation, which have the most complex mode of binding of the C₆₀ fullerene molecule and its fragments, using the C₆₀H₂₀ and C₇₂H₂₄ molecules (whose carbon skeletons model the structures of these linkages) as examples. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–12, January, 1998.     

Edge-modified zigzag-shaped graphene nanoribbons: Structure and electronic properties

Control of the band gap of graphene nanoribbons is an important problem for the fabrication of effective radiation detectors and transducers operating in different frequency ranges. The periodic edge-modified zigzag-shaped graphene nanoribbon (GNR) provides two additional parameters for controlling the band gap of these structures, i.e., two GNR arms. The dependence of the band gap E _g on these parameters is investigated using the π-electron tight-binding method. For the considered nanoribbons, oscillations of the band gap E _g as a function of the nanoribbon width are observed not only in the case of armchair-edge graphene nanoribbons (as for conventional graphene nanoribbons) but also for zigzag GNR edges. It is shown that the change in the band gap E _g due to the variation in the length of one GNR arm is several times smaller than that due to the variation in the nanoribbon width, which provides the possibility for a smooth tuning of the band gap in the energy spectrum of the considered graphene nanoribbons.