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We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical techniques. Electron microscopy observations and electron diffraction patterns reveal that B doping considerably increases the length of carbon tubes and leads to a remarkable preferred zigzag chirality. These findings are corroborated by first-principles static add dynamical simulations which indicate that, in the zigzag geometry, B atoms act as a surfactant during growth, preventing tube closure. This mechanism does not extend to armchair tubes, suggesting a helicity selection during growth.

Publisher Summary This chapter introduces the main electronic features of CNTs and some general aspects of electronic conduction and transmission. The main experimental results obtained on the electrical resistivity of MWCNT and SWCNT and the very recent data relative to the thermopower of SWCNT bundles have also been presented. MWCNTs behave as an ultimate carbon fiber revealing specific 2D quantum transport features at low temperatures; weak localization and universal conductance fluctuations. At high temperature its electrical conductivity is described by means of the semiclassical models which were successful in describing graphite. At low temperature, they reveal 2D quantum transport features, one of them being observed in bulk carbons and graphites (weak localization), while the other can only be observed in a mesoscopic form (universal conductance fluctuations). Single-walled CNTs (SWCNTs) behave as pure quantum wires, which, if limited in length, reduce to quantum dots. Eeach type of CNT has its own features which are strongly dependent on the dimensionality of the electronic gas. The chapter also discusses the effect of intercalation on the electrical resistivity of SWCNT bundles and some potential applications.

General features of the energetics and electronic states of carbon nanotubes, containing pentagon-heptagon pair (5/7) topological defects in the hexagonal network of the zigzag configuration, are investigated within simple tight-binding models. This 5/7 pair defect on the nanotube structure is not only responsible for a change in nanotube diameter, but also governs the electronic behavior around the Fermi level. Furthermore, nanotubes having different helicities and different electronic properties can be connected using such a pair. Various configurations including one, two, and three 5/7 pairs are explored in order to understand the influence of several defects on the electronic properties of the system. Topological aspects associated with the presence of 5/7 pair defects in armchair and chiral nanotubes are also discussed.

We present a new technique aimed at preventing plane-wave based total energy and stress calculations from the effect of abrupt changes in basis set size. This s cheme relies on the interpolation of energy as a function of the number of plane waves, and on a scaling hypothesis that allows to perform the interpolation for a unique reference volume. From a theoretical point of view, the new method is compared to those already pr oposed in the literature, and its more rigorous derivation is emphasized. From a practical point of view, we illustrate the importance of the correction o n different materials (Si, BaTiO3, and He) corresponding to different types of b onding, and to different k-point samplings and cut-off energies. Then, we compare the different approaches for the calculation of the lattice par ameter, the bulk modulus, and its derivative versus pressure in bulk silicon., 41 pages, Revtex 3.0, 10 figures

Related Articles Quantized charge pumping through a carbon nanotube double quantum dot Appl. Phys. Lett. 100, 143104 (2012) Electrical characteristics of multiwalled carbon nanotube arrays and influence of pressure AIP Advances 2, 022103 (2012) Percolation threshold and electrical conductivity of a two-phase composite containing randomly oriented ellipsoidal inclusions J. Appl. Phys. 110, 123715 (2011) Tuning the electrical transport properties of double-walled carbon nanotubes by semiconductor and semi-metal filling J. Appl. Phys. 110, 123708 (2011) Electronic and transport properties of achiral carbon nanotubes with di-vacancy pairs J. Appl. Phys. 110, 113702 (2011)

Since the outstanding transport properties of graphene originate from its specific structure, modification at the atomic level of the graphene lattice is needed in order to change its electronic properties. Thus, topological defects play an important role in graphene and related structures. In this work, one-dimensional (1D) arrangement of topological defects in graphene are investigated within a density functional theory framework. These 1D extended lines of pentagons, heptagons and octagons are found to arise either from the reconstruction of divacancies, or from the epitaxial growth of graphene. The energetic stability and the electronic structure of different ideal extended lines of defects are calculated using a first-principles approach. Ab initio scanning tunneling microscopy (STM) images are predicted and compared to recent experiments on epitaxial graphene. Finally, local density of states and quantum transport calculations reveal that these extended lines of defects behave as quasi-1D metallic wires, suggesting their possible role as reactive tracks to anchor molecules or atoms for chemical or sensing applications.

The electronic properties of simple hexagonal graphite have been studied in the framework of the density-functional technique, using nonlocal ionic pseudopotentials and a large number of plane waves. This work leads to a first-step qualitative understanding of the electronic properties of nonperiodic structures such as pregraphitic and disordered carbons (turbostratic graphite), which are composed of periodic regions of simple hexagonal graphite surrounded by domains of the usual (Bernal) form of graphite. Particular attention has been paid to the comparison with the properties of the Bernal graphite. The valence charge density, the density of states, the band structure, as well as a description of the electronic energies at the Fermi level are provided. The latter is parametrized by a tight-binding model, and compared to the Slonczewski-Weiss-McClure model of Bernal graphite electronic energies. The Fermi surface is calculated and an exchange of hole and electron pockets between these two forms of graphite is observed. The behavior of electronic energies under pressure, and the associated deformation potentials, are also studied.

The band structure of graphite with the hypothetical simple hexagonal structure has been investigated near the Fermi energy, using a tight-binding approximation. Some general features of the structure of the π bands in the neighborhood of the zone edge are obtained and are expressed in terms of appropriate parameters. The Fermi surface is analyzed. The density of states and the resulting behavior near the Fermi level are compared to the results obtained for the Bernal structure (Slonczewski-Weiss-McClure model) and for the rhombohedral structure (Haering-McClure model). Possible application to disordered graphite (turbostratic) is also discussed.

The electronic properties of hexagonal graphite have been studied in the framework of the density-functional technique, using nonlocal ionic pseudopotentials and a large number of plane waves. The valence charge density and the density of states are presented, as well as the band structure and the charge-density contributions of some typical wave functions. The electronic energies, at the Fermi level, are parametrized by the Slonczewski-Weiss-McClure model, and compared with the parametrization of experimental data. The numerical accuracy of the calculation has been controlled, in order to provide a reliable comparison between theory and experiment. In particular, the agreement obtained in the framework of the density-functional theory for electronic energies at the Fermi level is surprisingly good.

The discovery of fullerenes (1) provided exciting insights into how architectures built from pure carbon units can result in new symmetries and structures with remarkable physical properties. Carbon nanotubes represent the most striking example (2). A carbon nanotube can be considered as the ultimate fiber, reflecting highly organized, near ideal sp2 bonded carbon structure. The organization of the hexagonal honeycomb carbon lattice into cylinders with helical arrangement of hexagonal arrays has created a very unusual macromolecular structure that is by far the most superior carbon fiber ever made.

Inductive coupled rf-plasma at 13.56 MHz was used to modify multiwalled carbon nanotubes (MWCNTs). This technique can be easily used to tailor the chemical composition of carbon nanotubes by attaching a wide variety of functional groups at their surface: oxygen-, nitrogen-, and fluorine-containing groups have been grafted. The influence of various plasma conditions (power, type of gas, treatment time, pressure, position of the CNT sample inside the chamber) on the functionalization of the MWCNT surface was analyzed by x-ray photoelectron spectroscopy. The results show that for too high oxygen plasma power, chemical etching occurs at the surface of the CNT, thus destroying its structure. On the other hand, for optimal values of the plasma parameters, functional groups (hydroxide, carbonyl, carboxyl, amine, fluorine, etc.) were found to bond to the CNT surface, suggesting that both the concentration and type of the functional groups are in close connection with the plasma conditions. These results were compared to interaction energies predicted by ab initio calculations for different functional groups under consideration, showing that functionalization by oxygen plasma produces mainly functional groups with lower interaction energy.

The synthesis of heteroepitaxial monocrystalline diamond films has been of technological and scientific interest for several decades. Using chemical vapor deposition techniques, polycrystalline diamond has been successfully grown on many substrates. However, iridium emerges in providing highly oriented films, significantly better than any other transition metals. In the present work we propose an ab initio density functional study of the interaction of diamond with different substrates used experimentally. The origin of iridium's specific behavior is investigated. The kinetics of carbon atoms in the substrate lattice is found to play a key role, determining the nucleation mechanisms and hence the quality of the final diamond film. (c) 2005 American Institute of Physics.

The orientational dependence of the interaction between two C-60 molecules is investigated using ab initio calculations. The binding energy, computed within density functional theory in the local density approximation, is substantially smaller than the one derived from the experimental heat of sublimation of fullerite, which calls into question the nature of inter-C-60 bonding. According to our calculations, the experimentally observed orientation with a C-60 presenting a hexagon-hexagon bond to a pentagonal face of the other C-60 is not really favored. Some other configurations are very close in energy and in fact a pentagon facing a pentagon and a hexagon facing a hexagon-hexagon bond are found to be slightly more favorable situations. Our results are compared to previous ones obtained either with previous empirical intermolecular potentials or to existing ab initio studies of crystalline C-60. In addition, the stacking of C-60 in a crystal and in a decahedral (C-60)(7) cluster is discussed. (C) 2005 American Institute of Physics.

International audience; We present a growth process relying on pulsed laser deposition for the elaboration of complex van der Waals heterostructures on large scales, at a 400°C CMOS-compatible temperature. Illustratively, we define a multilayer quantum well geometry through successive in situ growths, leading to WSe2 being encapsulated into WS2 layers. The structural constitution of the quantum well geometry is confirmed by Raman spectroscopy combined with transmission electron microscopy. The large-scale high homogeneity of the resulting 2D van der Waals heterostructure is also validated by macro-and microscale Raman mappings. We illustrate the benefit of this integrative in situ approach by showing the structural preservation of even the most fragile 2D layers once encapsulated in a van der Waals heterostructure. Finally, we fabricate a vertical tunneling device based on these large-scale layers and discuss the clear signature of electronic transport controlled by the quantum well configuration with ab initio calculations in support. The flexibility of this direct growth approach, with multilayer stacks being built in a single run, allows for the definition of complex 2D heterostructures barely accessible with usual exfoliation or transfer techniques of 2D materials. Reminiscent of the III−V semiconductors' successful exploitation, our approach unlocks virtually infinite combinations of large 2D material families in any complex van der Waals heterostructure design.

International audience; This work describes the design and synthesis of a π-conjugated telluro[3,2-β][1]-tellurophene-based synthon that, embodying pyridyl and haloaryl chalcogen-bonding acceptors, self-assembles into nanoribbons through chalcogen bonds. The ribbons π-stack in a multi-layered architecture both in single crystals and thin films. Theoretical studies of the electronic states of chalcogen-bonded material showed the presence of a local charge density between Te and N atoms. OTFT-based charge transport measurements showed hole-transport properties for this material. Its integration as a p-type semiconductor in multi-layered CuI-based light-emitting electrochemical cells (LECs) led to a 10-fold increase in stability (38 h vs. 3 h) compared to single-layered devices. Finally, using the reference tellurotellurophene congener bearing a C−H group instead of the pyridyl N atom, a herringbone solid-state assembly is formed without charge transport features, resulting in LECs with poor stabilities (

The increasing number of reports on regularly curved carbon nanotube‐type architectures makes it increasingly important to understand the structure of these nano‐objects, to predict their properties, and to get insight in the way they form. The present work attempts to explore some properties of regularly curved carbon nanotube by combining structural modeling, mechanical calculations, and experimental high‐resolution transmission electron microscopy (HRTEM) data.

Multi-layer graphene with rhombohedral ABC stacking is considered as a promising carbon phase possibly displaying correlated states like magnetism or high-T c superconductivity due to the occurrence of an ultraflat electronic surface band at the Fermi level. Despite Bernal graphite being the most stable form of graphite, three and four layers graphene samples with rhombohedral stacking can be synthesized. Recently, flakes of thickness up to 17 layers were tentatively attributed ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D two-phonon resonant Raman spectrum of Bernal graphite not completely theoretically understood. Here we provide a complete first principles description of the 2D Raman peak in three and four layer graphene for all possible stackings, as well as for bulk Bernal, rhombohedral and an alternation of Bernal and rhombohedral graphite, that can be seen as a periodic sequence of ABA and ABC trilayers. Calculations for several laser energies are performed and we give practical prescriptions are proposed to identify long range sequences of ABC multi-layer graphene flakes.; Les multicouches de graphène en empilement rhomboédrique sont considérés comme une phase prometteuse du carbone. Cela est due à la particularité de cette phase de pouvoir exhiber des états à forte corrélation électronique comme le magnétisme ou la supraconductivité à haute température critique. Ce qui est due, a son tour, à l’occurrence d’un état de surface avec une dispersion d’énergie électroniques quasi-nulle à proximité du niveau de Fermi. Malgré que le graphite Bernal soit la forme la plus stable du graphite, des échantillons a trois et quatre couches de graphène en empilement rhomboédrique ont pu être synthétisés. Plus récemment, des flocons d’épaisseur dépassant les 17 couches ont été isolés et provisoirement attribués à des séquences d’empilement rhomboédrique. Cette attribution à été faite via des expériences de spectroscopie Raman sous champ magnétique, bien que l’empreinte Raman des multicouche de graphène en empilement rhomboédrique est actuellement inconnue. Même le cas simple du spectre Raman résonnant à deux phonons (le pic 2D) du graphite Bernal n’est pas totalement compris. Dans ce travail de thèse, nous fournissons une description ab-initio complète du pic Raman 2D dans les systèmes de graphène à trois et quatre couches pour tous les empilements possibles, ainsi que pour le graphite Bernal, rhomboédrique et une alternance de graphite Bernal et rhomboédrique.