Families of carbon nanotubes: Graphyne-based nanotubes (original) (raw)
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New families of carbon nanotubes
2002
Fundamentally new families of carbon single walled nanotubes are proposed. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphite-based nanotubes by the introduction of yne groups. Similarly to ordinary nanotubes, arm-chair, zig-zag, and chiral graphyne nanotubes are possible. Electronic properties, predicted using tight-binding and ab initio density functional methods, show a rich variety of metallic and semiconducting behaviors. * Corresponding author: galvao@ifi.unicamp.br FAX: +551937885376 The early report of carbon nanotubes by Iijima [1] generated an enormous amount of research activity. New and exciting phenomena have been observed [2], including field emission [3], quantum conductance [4], superconductivity [5], and higher thermal conductivity than diamond [6]
ISRN Nanotechnology, 2012
We examined the graphene and carbon nanotubes in 5 groups according to their structural and electronic properties by using ab initio density functional theory: zigzag (metallic and semiconducting), chiral (metallic and semiconducting), and armchair (metallic). We studied the structural and electronic properties of the 3D supercell graphene and isolated SWCNTs. So, we reported comprehensively the graphene and SWCNTs that consist of zigzag (6, 0) and (7, 0), chiral (6, 2) and (6, 3), and armchair (7, 7). We obtained the energy band graphics, band gaps, charge density, and density of state for these structures. We compared the band structure and density of state of graphene and SWCNTs and examined the effect of rolling for nanotubes. Finally, we investigated the charge density that consists of the 2D contour lines and 3D surface in the XY plane.
Using large-scale DFT calculations, we investigate the structural and electronic properties of both armchair and zigzag graphdiyne nanotubes as a function of size. To provide insight into these properties, we present new detailed calculations of the structural relaxation energy, effective electron/hole mass, and size-scaling of the bandgap as a function of size and chirality using accurate screened-exchange DFT calculations. These calculations provide a systematic evaluation of the structural and electronic properties of the largest graphdiyne nanotubes to date, up to 1296 atoms and 23328 basis functions. Our calculations show that zigzag graphdiyne nanotubes (GDNTs) are structurally more stable compared to armchair GDNTs of the same size. Furthermore, these large-scale calculations allow us to present simple analytical formulas to guide future experimental efforts for estimating the fundamental bandgaps of these unique nanotubes as a function of chirality and diameter. While the bandgaps for both the armchair and zigzag GDNTs can be tuned as a function of size, the conductivity in each of these two different chiralities is markedly different. Zigzag GDNTs have wider valence and conduction bands and are expected to have a higher electron-and hole-mobility than their armchair counterparts.
Exciton effect in new generation of carbon nanotubes: graphdiyne nanotubes
Journal of Molecular Modeling, 2020
Graphdiyne-based nanotubes (GDNTs) are a novel type of carbon nanotubes. While conventional carbon nanotubes (CNTs) are generated by rolling graphene sheets, GDNTs are generated by rolling sheets that are similar to graphene but where the edges are elongated by the introduction of additional acetylene bonds between vertices (C 6 aromatic rings). Such nanotubes are predicted to have many useful practical applications, but a thorough understanding of the relationship between their structure and their physical properties is still missing. We present a theoretical study of the electronic and optical properties of GDNTs. The structural, electronic, and optical properties of GDNTs with different diameters (i.e., 2-10 additional acetylene bonds) have been studied systematically by using density function theory (DFT) and self-consistent charge density functional tight-binding (SCC-DFTB) and by solving the Bethe-Salpeter equation (BSE), with and without considering the electron-hole interactions. The results indicate that the GDNTs are semiconductors with the direct band gap in close range, which is beneficial for photoelectronic devices and applications. Moreover, the absorption spectra of the GDNTs with different edge structures, (armchair, and zigzag) revealed little differences between the optical spectra of armchair and zigzag GDNTs, which could mean that fine separation between those structures (a process that is likely difficult and expensive in practice) will not be necessary. Importantly, the nanotubes were highly stable based on their cohesive energies, and their exciton binding energies were as large as about~1 eV. From a methodological point of view, SCC-DFTB was found to be in agreement with more elaborate DFT calculations for most systems.
Accounts of Chemical Research, 2013
I n this Account, we discuss the chemistry of graphitic materials with particular reference to three reactions studied by our research group: (1) aryl radical addition, from diazonium precursors, (2) DielsÀAlder pericyclic reactions, and (3) organometallic complexation with transition metals. We provide a unified treatment of these reactions in terms of the degenerate valence and conduction bands of graphene at the Dirac point and the relationship of their orbital coefficients to the HOMO and LUMO of benzene and to the Clar structures of graphene. In the case of the aryl radical addition and the DielsÀAlder reactions, there is full rehybridization of the derivatized carbon atoms in graphene from sp 2 to sp 3 , which removes these carbon atoms from conjugation and from the electronic band structure of graphene (referred to as destructive rehybridization). The radical addition process requires an electron transfer step followed by the formation of a σ-bond and the creation of a π-radical in the graphene lattice, and thus, there is the potential for unequal degrees of functionalization in the A and B sublattices and the possibility of ferromagnetism and superparamagnetism in the reaction products. With regard to metal functionalization, we distinguish four limiting cases: (a) weak physisorption, (b) ionic chemisorption, in which there is charge transfer to the graphitic structure and preservation of the conjugation and band structure, (c) covalent chemisorption, in which there is strong rehybridization of the graphitic band structure, and (d) covalent chemisorption with formation of an organometallic hexahapto-metal bond that largely preserves the graphitic band structure (constructive rehybridization). The constructive rehybridization that accompanies the formation of bis-hexahapto-metal bonds, such as those in (η 6-SWNT)Cr(η 6-SWNT), interconnects adjacent graphitic surfaces and significantly reduces the internanotube junction resistance in single-walled carbon nanotube (SWNT) networks. The conversion of sp 2 hybridized carbon atoms to sp 3 can introduce a band gap into graphene, influence the electronic scattering, and create dielectric regions in a graphene wafer. However, the organometallic hexahapto (η 6) functionalization of the two-dimensional (2D) graphene π-surface with transition metals provides a new way to modify graphitic structures that does not saturate the functionalized carbon atoms and, by preserving their structural integrity, maintains the delocalization in these extended periodic π-electron systems and offers the possibility of threedimensional (3D) interconnections between adjacent graphene sheets. These structures may find applications in interconnects, 3D-electronics, organometallic catalysis, atomic spintronics and in the fabrication of new electronic materials.
Electronic Properties of Graphite and Single Walled Carbon Nanotubes-A DFT Study
2010
Abstract Density functional theory has been used to model graphite and single walled carbon nanotube. The results indicate that three dimensional graphite is a semi metal and two dimensional graphite is a semiconductor with zero gap. Density of states and band structure plots indicate that carbon nanotubes with chirality (10, 10),(9, 0) are metallic and (10, 0) tube is semiconducting.
Accounts of Chemical Research
I n this Account, we discuss the chemistry of graphitic materials with particular reference to three reactions studied by our research group: (1) aryl radical addition, from diazonium precursors, (2) DielsÀAlder pericyclic reactions, and (3) organometallic complexation with transition metals. We provide a unified treatment of these reactions in terms of the degenerate valence and conduction bands of graphene at the Dirac point and the relationship of their orbital coefficients to the HOMO and LUMO of benzene and to the Clar structures of graphene.
2003
We perform density functional theory calculations on a series of armchair and zigzag nanotubes of diameters less than 1nm using the all-electron Full-Potential(-Linearised)-Augmented-Plane-Wave (FPLAPW) method. Emphasis is laid on the effects of curvature, the electron beam orientation and the inclusion of the core-hole on the carbon electron energy loss K-edge. The electron energy loss near-edge spectra of all the studied tubes show strong curvature effects compared to that of flat graphene. The curvature induced π − σ hybridisation is shown to have a more drastic effect on the electronic properties of zigzag tubes than on those of armchair tubes. We show that the core-hole effect must be accounted for in order to correctly reproduce electron energy loss measurements. We also find that, the energy loss near edge spectra of these carbon systems are dominantly dipole selected and that they can be expressed simply as a proportionality with the local momentum projected density of states, thus portraying the weak energy dependence of the transition matrix elements. Compared to graphite, the ELNES of carbon nanotubes show a reduced anisotropy. I. INTRODUCTION Since the discovery of carbon nanotubes by Iijima [1] in 1991, much effort has been devoted experimentally [2, 3, 4, 5] and theoretically [6, 7, 8] to study this new material. The one dimensional character of single wall nanotubes (SWNT's) enables them to exhibit very interesting physical properties due to the quantum confinement of electrons in a one dimensional lattice. Remarkable optical, thermoelectric, mechanical and electronic properties can be expected. Doping or intercalation [9, 10, 11, 12, 13, 14, 15, 16, 17], structural defects [18, 19] and pressure effects [20] are known to enrich these properties. Resonant Raman spectroscopy and optical absorption spectroscopy [21, 22, 23, 24] have been widely used to describe the electronic structure of isolated and ropes of nanotubes. Scanning tunneling microscopy [19, 25] has also been used to detect the Van Hove spikes of SWNT's. Most of the theoretical studies are based on the application of the Born-von Karman boundary conditions to the two dimensional graphene sheet [7, 26] in a zonefolding technique and the all-valence tight-binding method [6, 26, 27]. This graphene zone-folding approach is known to be inaccurate to describe the unoccupied density of states (DOS) [28] a few eV's beyond the Fermi level. Density functional theory (DFT) calculations [28, 29] have also been carried out but very few calculations [29] probing core-loss spectra are available. Electron energy loss spectrum (EELS) and X-ray absorption spectroscopy (XAS) measurements are available but their theoretical interpretation is often limited to the site and angular momentum projected local density of states (LDOS). This interpretation does not account for transition matrix elements which are known to be important and sensitive to the momentum transfer direction for anisotropic