Electronic properties of carbon toroids

Single-chirality of single-walled carbon nanotubes (SWCNTs) through chromatography and its potential biological applications

Gel chromatography is used to separate single-chirality and selective-diameter SWCNTs. We also explore the use of photothermal therapy and biosensor applications based on single-chirality, selected-diameter, and unique geometric shape.

A Review of Geometry, Construction and Modelling for Carbon Nanotori

After the discovery of circular formations of single walled carbon nanotubes called fullerene crop circles, their structure has become one of the most researched amongst carbon nanostructures due to their particular interesting physical properties. Several experiments and simulations have been conducted to understand these intriguing objects, including their formation and their hidden characteristics. It is scientifically conceivable that these crop circles, nowadays referred to as carbon nanotori, can be formed by experimentally bending carbon nanotubes into ring shaped structures or by connecting several sections of carbon nanotubes. Toroidal carbon nanotubes are likely to have many applications, especially in electricity and magnetism. In this review, geometry, construction, modelling and possible applications are discussed and the existing known analytical expressions, as obtained from the Lennard-Jones potential and the continuum approximation, for their interaction energies with other nanostructures are summarised.

The Aharonov–Bohm effect in the carbon nanotube ring

The Aharonov–Bohm oscillations of the persistent current and the energy gap are investigated with consideration of the bond length dependent hopping parameters.

Symmetry groups associated with tilings on a flat torus

This work investigates symmetry and color symmetry properties of Kepler, Heesch and Laves tilings embedded on a flat torus and their geometric realizations as tilings on a round torus in Euclidean 3-space. The symmetry group of the tiling on the round torus is determined by analyzing relevant symmetries of the planar tiling that are transformed to axial symmetries of the three-dimensional tiling. The focus on studying tilings on a round torus is motivated by applications in the geometric modeling of nanotori and the determination of their symmetry groups.

Synthesis and non-covalent functionalization of carbon nanotubes rings: new nanomaterials with lectin affinity

We present a mild and practical carbon nanotubes rings (CNRs) synthesis from non-covalent functionalized and water-soluble linear single-wall carbon nanotubes. The hemi-micellar-supramolecular self-organization of lactose-based glycolipid 1 on the ring surface, followed by photo-polymerization of the diacetylenic function triggered by UV light afforded the first water-soluble and biocompatible CNRs. The obtained donut-like nanoconstructs expose a high density of lactose moieties on their surface, and are able to engage specific interactions with Arachis hypogea lectin similar to glycoconjugates on the cell membrane.

Giant orbital paramagnetism in toroidal carbon nanopeapods

The electronic structure and the magnetic response of toroidal carbon nanopeapods (TCNPs) are investigated within the sp(3) tight-binding formalism. It is found that in the presence of mirror symmetry, there exists a level crossing at the Fermi level in the energy spectrum of a TCNP, leading to giant orbital paramagnetism (GOP), in spite of the curvatures and hybridizations of the outer toroidal carbon nanotube (TCN). When the mirror symmetry is broken by rotating the inner C(60)s, however, two level crossings appear at the Fermi level, and the GOP changes into a very small diamagnetic response. The results reveal the GOP in a filled TCN, depending on the characteristics of the filling materials and temperature.

Persistent currents in a carbon nanotube torus encapsulated with a carbon ring

A toroidal carbon nanowire (TCNW) model is proposed for an ideal one-dimensional mesoscopic ring, consisting of a toroidal carbon nanotube (TCN) and an encapsulated carbon ring, of which the electronic structure and thus the persistent current (I(pc)) are investigated within the tight-binding formalism. The tube-ring interactions lead to a charge transfer from the inner ring to the outer TCN, and thus the Fermi level rises and the band overlaps in a certain flux range. In zigzag TCNWs with a metallic TCN, the actual magnetic response, the amplitude and the period of I(pc) in the primary carbon ring are concealed by those in the resultant TCNW; in zigzag TCNWs with a semiconducting TCN, I(pc) exhibits the same behavior as that in their primary carbon rings. The results show that I(pc) in the sample ring depends strongly on the surrounding environment and thus a semiconducting or insulating matrix may provide a desired environment for measuring persistent current in mesoscopic rings.

Effect of external fields on low-frequency optical properties of achiral carbon tori

By using the tight-binding model including the curvature effect, the low-frequency electronic and optical properties with perpendicular polarization under electric and magnetic fields are studied for achiral carbon tori. Electronic properties (state energies, energy gaps, state degeneracy and wavefunctions) are strongly modulated by varying the direction and the magnitude of electric fields. The perpendicular magnetic field further enhances modulations of the electronic states. The variation of state energies and wavefunctions with external fields could be directly reflected in optical properties such as the amplitude and the frequency of absorption spectra and the exhibition of new peaks. Additionally, dependences of the low-frequency absorption peaks on electric fields, with and without magnetic fields, are significantly sensitive to the toroidal geometry.

Large-area patterning of carbon nanotube ring arrays

Single-walled carbon nanotubes were assembled into large-area arrays of nanoscale rings on silicon via direct patterning with a self-assembled colloidal polystyrene sphere mask. Nanotubes from liquid suspension gathered at the base of each sphere in the mask to form rings, and the resulting arrays consisted of well-ordered nanotube rings with diameters of 203+/-21 nm and 97+/-14 nm for rings formed with 780 and 450 nm colloidal spheres, respectively. Ring heights were found to be 4.7+/-1.8 nm and 5.9+/-1.4 nm for 780 and 450 nm sphere masks, respectively. A first-order geometric model was proposed to account for the observed ring diameters. The approach presented demonstrates an efficient and straightforward path for patterning carbon nanotubes into well-defined surface distributions on various substrates with highly controlled and tunable dimensions.

Shape and complexity at the atomic scale: the case of layered nanomaterials

In nature there are numerous layered compounds, some of which could be curved so as to form fascinating nanoshapes with novel properties. Graphite is at present the main example of a very flexible layered structure, which is able to form cylinders (nanotubes) and cages (fullerenes), but there are others. While fullerenes possess positive curvature due to pentagonal rings of carbon, there are other structures which could include heptagonal or higher membered rings. In fact, fullerenes and nanotubes could display negative curvature, thus forming nanomaterials possessing unexpected electronic and mechanical properties. The effect of curvature in other nano-architectures, such as in boron nitride and metal dichalcogenides, is also discussed in this account. Electron irradiation is a tool able to increase the structural complexity of layered materials. In this context, we describe the coalescence of carbon nanotubes and C(60) molecules. The latter results now open up an alternative approach to producing and manipulating novel nanomaterials in the twenty-first century.

Sidewall Carboxylic Acid Functionalization of Single-Walled Carbon Nanotubes

The reactions of single-walled carbon nanotubes (SWNTs) with succinic or glutaric acid acyl peroxides in o-dichlorobenzene at 80-90 degrees C resulted in the addition of 2-carboxyethyl or 3-carboxypropyl groups, respectively, to the sidewalls of the SWNT. These acid-functionalized SWNTs were converted to acid chlorides by derivatization with SOCl(2) and then to amides with terminal diamines such as ethylenediamine, 4,4'-methylenebis(cyclohexylamine), and diethyltoluenediamine. The acid-functionalized SWNTs and the amide derivatives were characterized by a set of materials characterization methods including attenuated total reflectance (ATR) FTIR, Raman and solid state (13)C NMR spectroscopy, transmission electron microscopy (TEM), and thermal gravimetry-mass spectrometry (TG-MS). The degree of SWNT sidewall functionalization with the acid-terminated groups was estimated as 1 in 24 carbons on the basis of TG-MS data. In comparison with the pristine SWNTs, the acid-functionalized SWNTs show an improved solubility in polar solvents, for example, alcohols and water, which enables their processing for incorporation into polymer composite structures as well as for a variety of biomedical applications.