Chiral Vector Research Articles

Charge Transfer Structure–Reactivity Dependence of Fullerene–Single-Walled Carbon Nanotube Heterojunctions

Charge transfer at the interface between single-walled carbon nanotubes (SWCNTs) of distinct chiral vectors and fullerenes of various molecular weights is of interest both fundamentally and because of its importance in emerging photovoltaic and optoelectronic devices. One approach for generating isolated, discretized fullerene-SWCNT heterojunctions for spectroscopic investigation is to form an amphiphile, which is able to disperse the latter at the single-SWCNT level in aqueous solution. Herein, we synthesize a series of methanofullerene amphiphiles, including derivatives of C60, C70, and C84, and investigated their electron transfer with SWCNT of specific chirality, generating a structure-reactivity relationship. In the cases of two fullerene derivatives, lipid-C61-polyethylene glycol (PEG) and lipid-C71-PEG, band gap dependent, incomplete quenching was observed across all SWCNT species, indicating that the driving force for electron transfer is small. This is further supported by a variant of Marcus theory, which predicts that the energy offsets between the nanotube conduction bands and the C61 and C71 LUMO levels are less than the exciton binding energy in SWCNT. In contrast, upon interfacing nanotubes with C85 methanofullerene, a complete quenching of all semiconducting SWCNT is observed. This enhancement in quenching efficiency is consistent with the deeper LUMO level of C85 methanofullerene in comparison with the smaller fullerene adducts, and suggests its promise as for SWCNT-fullerene heterojunctions.

Bandgap opening by patterning graphene.

Owing to its remarkable electronic and transport properties, graphene has great potential of replacing silicon for next-generation electronics and optoelectronics; but its zero bandgap associated with Dirac fermions prevents such applications. Among numerous attempts to create semiconducting graphene, periodic patterning using defects, passivation, doping, nanoscale perforation, etc., is particularly promising and has been realized experimentally. However, despite extensive theoretical investigations, the precise role of periodic modulations on electronic structures of graphene remains elusive. Here we employ both the tight-binding modeling and first-principles electronic structure calculations to show that the appearance of bandgap in patterned graphene has a geometric symmetry origin. Thus the analytic rule of gap-opening by patterning graphene is derived, which indicates that if a modified graphene is a semiconductor, its two corresponding carbon nanotubes, whose chiral vectors equal graphene's supercell lattice vectors, are both semimetals.

Nonlinear softening and hardening nonlocal bending stiffness of an initially curved monolayer graphene

In the present article, the governing nonlinear nonlocal elastic equations are obtained for a monolayer graphene with an initial curvature and the related softening and hardening bending stiffness is analytically calculated. The effects of large deformation, initial curvature, discreteness and direction of chiral vector on the bending stiffness of the monolayer graphene are discussed in detail. A behavior more complex than previously reported in the literature emerges. It is found that the bending stiffness of graphene strongly depends on the initial configuration, showing not obvious maxima and minima, and suggesting the possibility of a smart tuning.

Universal Rule on Chirality‐Dependent Bandgaps in Graphene Antidot Lattices

Graphene with periodically patterned antidots has attracted intense research attention as it represents a facile route to open a bandgap for graphene electronics. However, not all graphene antidot lattices (GALs) can open a bandgap and a guiding rule is missing. Here, through systematic first-principles calculations, it is found that bandgaps in triangular GALs are surprisingly well defined by a chirality vector R = n a1 + ma2 connecting two neighboring antidots, where a1 and a2 are the basis vectors of graphene. The bandgap opens in the GALs with (n-m)mod3 = 0 but remains closed in those with (n-m)mod3 = ±1, reminiscent of the gap-chirality rule in carbon nanotubes. Remarkably, the gap value in GALs allows ample modulation by adjusting the length of chirality vectors, shape and size of the antidots. The gap-chirality relation in GALs stems from the chirality-dependent atomic structures of GALs as revealed by a super-atom model as well as Clar sextet analyses. This chirality-dependent bandgap is further shown to be a generic behavior in any parallelogram GAL and thus serves as an essential stepping stone for experimenters to realize graphene devices by antidot engineering.

The Universal Phase Space of AdS3 Gravity

We describe what can be called the "universal" phase space of AdS3 gravity, in which the moduli spaces of globally hyperbolic AdS spacetimes with compact spatial sections, as well as the moduli spaces of multi-black-hole spacetimes are realized as submanifolds. The universal phase space is parametrized by two copies of the Universal Teichm\"uller space T(1) and is obtained from the correspondence between maximal surfaces in AdS3 and quasisymmetric homeomorphisms of the unit circle. We also relate our parametrization to the Chern-Simons formulation of 2+1 gravity and, infinitesimally, to the holographic (Fefferman-Graham) description. In particular, we obtain a relation between the generators of quasiconformal deformations in each T(1) sector and the chiral Brown-Henneaux vector fields. We also relate the charges arising in the holographic description (such as the mass and angular momentum of an AdS3 spacetime) to the periods of the quadratic differentials arising via the Bers embedding of T(1)xT(1). Our construction also yields a symplectic map from T*T(1) to T(1)xT(1) generalizing the well-known Mess map in the compact spatial surface setting.

Functionalization of Single-Walled Carbon Nanotubes (SWNTs) with Stimuli- Responsive Dispersants

Copyright: © 2013 Zhao Y. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Carbon nanotubes (CNTs) have promised great opportunities for the development of next-generation materials science and technology, given their extraordinary mechanical and electronic properties. Ever since their first discovery in the early 1990s [1], carbon nanotubes have not only attracted enormous academic curiosity, but also fueled up extensive and continued pursuit of technological applications in numerous fields, such as field effect transistors, light emitting devices, photovoltaic materials, chemical sensors, actuators, and catalysis [2-4]. Carbon nanotubes belong to a unique family of carbon allotrope with a tubular shape, a diameter of 1-2 nm, and a length on the micron scale. Depending on the structure of layers, carbon nanotubes can be singlewalled and multiple-walled. Conceptually, a single-walled carbon nanotube can be perceived as being formed by wrapping a single layer of graphene sheet into a cylindrical structure. According to the different angles in which the graphene sheet is wrapped, the resulting tubes can be characterized as different types, such as “zigzag”, “armchair”, and “chiral”, defined by a chiral vector (Ch) and two indices (n,m) [5]. Typically, if m = 0, the SWNTs are called “zigzag” nanotubes, if n = m, they are “armchair”, and if otherwise, the SWNTs are categorized as “chiral”. Apart from chirality, SWNTs can also be simply divided into two electronic types, namely metallic and semiconducting, based on their electronic properties. Nanotubes with chiral indices n-m = 3x (x is an integer) are usually metallic, while others are semiconducting.

Metallic and Semiconducting Single-Walled Carbon Nanotubes: Differentiating Individual SWCNTs by Their Carbon 1s Spectra

The C 1s inner shell excitation spectra of individual metallic and semiconducting single-walled carbon nanotubes (SWCNTs) were measured using high-resolution electron energy loss spectroscopy in an aberration-corrected transmission electron microscope (TEM-EELS). On the basis of its diameter, the metallic SWCNT is most likely a (10,10) sample, whereas (11,12) and a number of other chiral vectors are consistent with the diameter of the semiconducting SWCNTs. The C 1s X-ray absorption spectra of the same electronically pure SWCNT materials were measured as individual bundles or agglomerations of bundles by scanning transmission X-ray microscopy. Spectral differences in the C 1s → π* transitions of metallic and semiconducting species, related to differences in the van Hove singularities in their unoccupied states, are observed by both methods. The fine structure of the C 1s → π* transitions is similar to that recently reported from nonspatially resolved X-ray absorption spectroscopy of ensemble samples of high-purity metallic and semiconducting SWCNTs. The quality of the TEM-EELS spectra of individual SWCNTs is such that the line shape can be used to identify if they are metallic or semiconducting, thereby opening up the possibility to interrogate the electronic state of single-SWCNT devices. A strong X-ray linear dichroism in the C 1s → π* band of both types of SWCNTs was observed.

Analysis of strained double-lightly doped MOSCNT using NEGF

The effects of uniaxial and torsional strains on the double-lightly doped MOSCNT (DLD-MOSCNT) performances are investigated, using the non-equilibrium Green function (NEGF) formalism in mode space approach. The Hamiltonian of the device is obtained by a tight-binding approximation assuming that only pz orbitals are contributing in carrier transport. In all simulation processes, one mode with the lowest subband is considered. DLD-MOSCNT has a small band-to-band tunneling and almost eliminates the ambipolar behavior of IDS–VGS characteristics because of the band engineering. We use a modified model to demonstrate the strain effects on such a low OFF-current device. The results show that the strain effects mainly depend on the chiral vector and diameter of CNT. The strain causes band gap and carrier velocity changes, which result in variation of ON- or OFF-current. In addition, the subthreshold swing of this device under uniaxial strain is calculated, which is about 61 mV/Dec for 2 % tensile strain in (16,0) and for −2 % compressive strain in (17,0). Under the uniaxial strain, in the case that the energy band gap increases, the variation of DIBL is very small.

Calculation of Cutting Lines of Single-Walled Carbon Nanotubes

Abstract. Carbon nanotubes (CNs) are hexagonally shaped arrangements of carbon atoms that have been rolled into tubes with outstanding properties. Carbon nanotubes are among the stiffest and strongest fibers known, and have remarkable electronic properties and many other unique characteristics. All properties of the carbon nanotubes are determined by its electronic structure. The main focus of this study has been to investigate the basic electronic band structure of carbon nanotubes and to understand the origin of the cutting lines. For this purposes brief introduction to the electronic properties of carbon nanotubes was given and then 3D electronic band structure was plotted. For different chirality vectors (n, m) 1D and 2D first Brillouin zones and cutting lines of SWNT were calculated and plotted. Key words: Single-walled carbon nanotube, Brillouin zone, Cutting line.

Anomalously interacting new extra vector bosons and their first LHC constraints

In this review phenomenological consequences of the Standard Model extension by means of new spin-1 chiral fields with the internal quantum numbers of the electroweak Higgs doublets are summarized. The prospects for resonance production and detection of the chiral vector $Z^*$ and $W^{*\pm}$ bosons at the LHC energies are considered. The $Z^*$ boson can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distributions in the same way as the well-known extra gauge $Z'$ bosons. However, the $Z^*$ bosons have unique signatures in transverse momentum, angular and pseudorapidity distributions of the final leptons, which allow one to distinguish them from other heavy neutral resonances. In 2010, with 40 pb$^{-1}$ of the LHC proton-proton data at the energy 7 TeV, the ATLAS detector was used to search for narrow resonances in the invariant mass spectrum of $e^+e^-$ and $\mu^+\mu^-$ final states and high-mass charged states decaying to a charged lepton and a neutrino. No statistically significant excess above the Standard Model expectation was observed. The exclusion mass limits of 1.15 TeV$/c^2$ and 1.35 TeV$/c^2$ were obtained for the chiral neutral $Z^*$ and charged $W^*$ bosons, respectively. These are the first direct limits on the $W^*$ and $Z^*$ boson production. For almost all currently considered exotic models the relevant signal is expected in the central dijet rapidity region. On the contrary, the chiral bosons do not contribute to this region but produce an excess of dijet events far away from it. For these bosons the appropriate kinematic restrictions lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump expected in the most exotic models.

A molecular dynamics simulation of water transport through C and SiC nanotubes: Application for desalination

In this work the conduction of ion-water solution through two discrete bundles of armchair carbon and silicon carbide nanotubes, as useful membranes for water desalination, is studied. In order that studies on different types of nanotubes be comparable, the chiral vectors of C and Si-C nanotubes are selected as (7,7) and (5,5), respectively, so that a similar volume of fluid is investigated flowing through two similar dimension membranes. Different hydrostatic pressures are applied and the flow rates of water and ions are calculated through molecular dynamics simulations. Consequently, according to conductance of water per each nanotube, per nanosecond, it is perceived that at lower pressures (below 150 MPa) the Si-C nanotubes seem to be more applicable, while higher hydrostatic pressures make carbon nanotube membranes more suitable for water desalination.

Non-peptidic cell-penetrating agents: synthesis of oligomeric chiral bicyclic guanidinium vectors

Polycationic oligo(chiral bicyclic guanidines) constitute useful non-peptidic penetrating agents for cell uptake and protein surface recognition. We report herein improved and selective procedures for the preparation of oligoguanidinium scaffolds linked through thioether bonds, with similar or different groups and functions at both ends of the chain. Two synthetic strategies were developed to obtain these compounds in relatively good yields from a common thioacetate precursor: generation of a disulfide intermediate or thiolate formation. Thus, tetraguanidinium intermediates 8 and 22 are best synthesized by the disulfide route, whereas hexamer 29, octamer 31, and trimer 37 arise from a combination of both the disulfide and the thioacetate routes. Finally, tetramer 28 can be readily obtained from either strategy.

Electron transfer kinetics at single-walled carbon nanotube paper: The role of band structure

The role of band structure of individual tubules from single-walled carbon nanotube paper in the electron transfer process was considered within Gerischer–Marcus theory using Raman scattering spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy data. A heterogeneous electron transfer rate of 1.06 × 10 − 3 cm s was observed for ferri/ferrocyanid. A position of the Raman radial breathing mode was used for determination of the chiral vectors of tubules being in resonance with excitation laser light of 1.17 eV. For these tubules, the calculated electron transfer rates are similar. It has been shown that nanotube electronic states away from the Fermi level contribute to the electron transfer kinetics due to the broad distribution of the redox states in electrolyte.

Glueball in a chiral linear sigma model with vector mesons

We present a two-flavour linear sigma model with global chiral symmetry and (axial-)vector mesons as well as an additional glueball degree of freedom. We study the structure of the well-established scalar resonances f0(1370) and f0(1500): by a fit to experimentally known decay widths we find that f0(1370) is predominantly a \bar{q}q state and f0(1500) is predominantly a glueball state. The overall phenomenology of these two resonances can be well described. Other assignments for our mixed quarkonium-glueball states are also tested, but turn out to be in worse agreement with the phenomenology. As a by-product of our analysis, the gluon condensate is determined.

Electronic and Optical Properties of Low-Dimensional B2CN Nanomaterials from First Principles

The structures and electronic and optical properties of B2CN sheet and single-walled B2CN nanotubes were investigated by the first-principles density functional calculations. By rolling up the planar low-energy B2CN nanosheets along various chiral vectors, four types of zigzag and armchair B2CN nanotubes were constructed. The present calculations show that the structural and electronic properties of B-rich B2CN nanotubes strongly depend on their sizes and chiralities. The zigzag and armchair B2CN nanotubes with the small diameter generally are semiconductors, and their band gaps decrease as the tube-radius increases. When the diameter of tubes is large enough, the four kinds of nanotubes may produce the electronic behavior transitions from semiconductor to metal. Owing to the electronic affinity difference among B, C, and N atoms, there are remarkable charge transfers from B to C and N atoms in B2CN nanostructures. The predicted dielectric and optical properties show that the zigzag and armchair B2CN nanotubes are the optical anisotropy with respect to light polarization, and their absorption spectra are sensitive to the chirality of tube.

Symmetry and Models of Double-Wall BN and TiO2Nanotubes with Hexagonal Morphology

The line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied for symmetry analysis of double-wall boron nitride and titania nanotubes (DW BN and TiO2 NTs) formed by rolling up the stoichiometric two-periodic (2D) slabs of hexagonal structure with the same or opposite orientation of translation and chiral vectors. We have considered the two sets of commensurate DW BN and TiO2 NTs with either armchair- or zigzag-type chiralities, i.e., (n1,n1)@(n2,n2) or (n1,0)@(n2,0), respectively. To establish the equilibrium interwall distances corresponding to the minima of energy, we have varied chiral indices n1 and n2 of the constituent single-wall (SW) nanotubes. To analyze the structural and electronic properties of hexagonal DW NTs, we have performed ab initio LCAO calculations using the hybrid Hartree–Fock/Kohn–Sham exchange-correlation functional PBE0 as implemented in CRYSTAL-09 code. The inversely stacked structure of zigzag-type DW BN NT, characterized by arrangement of positively and negatively charged rings in each atomic cross section (consisting of either B or N atoms, respectively), has been found to be energetically more preferable as compared to the straightly stacked structure containing nanotube rings consisting of the same type of atoms in cross sections, i.e., B(N) and B(N). In armchair-type DW BN NTs, each atomic ring contains the whole number of B–N bonds, which reduces the electrostatic interaction between both walls. On the other hand, main contribution to interwall bonding in DW TiO2 NTs is provided by interaction between the nearest oxygen and titanium ions of neighboring shells. The interaction between the walls results in a decrease of band gaps for double-wall NTs as compared to those for SW NTs, which is substantially larger for TiO2.

Symmetry and structure of SrTiO3 nanotubes

The full study of perovskite type nanotubes with square morphology is given for the first time. The line symmetry group L = ZP (a product of one axial point group P and one infinite cyclic group Z of generalized translations) of single-walled (SW) and double-walled (DW) SrTiO3 nanotubes (NT) is considered. The nanotube is defined by the square lattice translation vector L = l1a + l2b and chiral vector R = n1a + n2b, (l1, l2, n1 and n2 are integers). The nanotube of the chirality (n1,n2) is obtained by folding the (001) slabs of two- layers (with the layer group P4mm) and of three layers (with the layer group P4/mmm) in a way that the chiral vector R becomes circumference of the nanotube. Due to the orthogonality relation (RL) = 0, l1/l2 = −n2/n1 i.e. SW nanotubes with square morphology are commensurate for any rolling vector R(n1,n2). For SW (n,0) NTs the line symmetry groups belong to family 11 (T^Dnh) and are n/mmm or for even and odd n, respectively. For SW (n,n) NTs the line symmetry groups (2n)n/mcm belong to family 13 (T2n1 Dnh).The line symmetry group of a double-wall nanotube is found as intersection L2 = Z2P2 = (L ∩ L′) of the symmetry groups L and L′ of its single-wall constituents as earlier considered for DW CNTs. The symmetry group of DWNT (n,0)@M(n,0) belongs to the same family 11 (T^Dnh) as its SW constituents. The symmetry group of DWNT (n,n)@M(n,n) depends on the parity of M. For DW NTs with odd M, the line symmetry groups are the same as for their SW constituents and belong to family 13 (T2n1 Dnh). For even M, the rotations about screw axis of order 2n are changed by rotations around pure rotation axis of order n so that DW NT line symmetry groups belong to family 11 (T^Dnh). Commensurate STO DWNTs (n1,0)@(n2,0) and (n1, n1)@(n2, n2) belong to family 11 (T^Dnh) with n equal to the greatest common divisor of n1 and n2.

Unveiling Stability Criteria of DNA-Carbon Nanotubes Constructs by Scanning Tunneling Microscopy and Computational Modeling

We present a combined approach that relies on computational simulations and scanning tunneling microscopy (STM) measurements to reveal morphological properties and stability criteria of carbon nanotube-DNA (CNT-DNA) constructs. Application of STM allows direct observation of very stable CNT-DNA hybrid structures with the well-defined DNA wrapping angle of 63.4° and a coiling period of 3.3 nm. Using force field simulations, we determine how the DNA-CNT binding energy depends on the sequence and binding geometry of a single strand DNA. This dependence allows us to quantitatively characterize the stability of a hybrid structure with an optimal π-stacking between DNA nucleotides and the tube surface and better interpret STM data. Our simulations clearly demonstrate the existence of a very stable DNA binding geometry for (6,5) CNT as evidenced by the presence of a well-defined minimum in the binding energy as a function of an angle between DNA strand and the nanotube chiral vector. This novel approach demonstrates the feasibility of CNT-DNA geometry studies with subnanometer resolution and paves the way towards complete characterization of the structural and electronic properties of drug-delivering systems based on DNA-CNT hybrids as a function of DNA sequence and a nanotube chirality.

Ab Inito Study of Absorption Spectra in Ultra Small Diameter Single Walled Boron Nanotubes

We have investigated the absorption spectra in ultra small diameter single walled boron nanotubes for parallel and perpendicular polarized light as well as unpolarized light. In this paper we have studied absorption spectra for armchair (3,3),zigzag (5,0) and chiral (4,2) boron nanotubes containing 12, 20 and 56 atoms respectively. It is observed that absorption is highest for armchair followed by zigzag and chiral nanotubes. It is also found that absorption is higher for (3,3) and (5,0) nanotubes for perpendicular polarized light as compared to parallel polarized light, whereas chiral nanotube shows higher and wide range of absorption for parallel polarized light instead of perpendicular polarized light. We have compared our results with SWCNT and SWBNNT of same chiral vectors.

Using Clar sextets for two- and three-dimensional aromatic systems

After a brief history of the aromaticity concept, the use of Clar sextet circles is reviewed for explaining various aspects of planar aromatic systems (benzenoids, heterocycles) and of tridimensional carbon aggregates. When folding a graphene sheet for obtaining nanotubes, nanotori, or nanocones, the congruence of Clar sextet circles allows the classification of all such aggregates into two classes (congruent or incongruent) with marked differences in properties; this is in agreement with the well-known condition h - k ≡ 0 (mod 3), equivalent to congruence, in terms of the chiral vectors h and k for graphene sheets.