A New, Simple and Versatile Strategy for the Synthesis of Short Segments of Zigzag-Type Carbon Nanotubes.

Short segments of zigzag single-walled carbon nanotubes (SWCNTs) were obtained from a calixarene scaffold by using a completely new, simple and expedited strategy that allowed fine-tuning of their diameters. This new approach also allows for functionalised short segments of zigzag SWCNTs to be obtained; a prerequisite towards their lengthening. These new SWCNT short segments/calixarene composites show interesting behaviour in solution.

S-Shaped Conformation of the Quaterthiophene Molecular Backbone in Two-Dimensional Bisterpyridine-Derivative Self-Assembled Nanoarchitecture.

The conformation and the two-dimensional self-assembly of 4'-(3',4″-dihexyloxy-5,2':5',2″:5″,2‴-quaterthien-2,5‴-diyl)-bis(2,2':6',2″-terpyridine) molecules are theoretically and experimentally investigated. This molecular building block forms a hydrogen-bonded chiral supramolecular nanoarchitecture on graphite at the solid/liquid interface. Scanning tunneling microscopy (STM) shows that the molecule adopts an S-shaped conformation in this structure.

Tailoring the structure of two-dimensional self-assembled nanoarchitectures based on ni(ii) -salen building blocks.

The synthesis of a series of Ni(II) -salen-based complexes with the general formula of [Ni(H2 L)] (H4 L=R(2) -N,N'-bis[R(1) -5-(4'-benzoic acid)salicylidene]; H4 L1: R(2) =2,3-diamino-2,3-dimethylbutane and R(1) =H; H4 L2: R(2) =1,2-diaminoethane and R(1) =tert-butyl and H4 L3: R(2) =1,2-diaminobenzene and R(1) =tert-butyl) is presented. Their electronic structure and self-assembly was studied. The organic ligands of the salen complexes are functionalized with peripheral carboxylic groups for driving molecular self-assembly through hydrogen bonding.

Effect of the chemical functionalization on charge transport in carbon nanotubes at the mesoscopic scale.

We present first-principles calculations of quantum transport in chemically functionalized metallic carbon nanotubes with lengths reaching the micrometer scale and random distributions of functional groups. Two typical cases are investigated, namely, a sp2-type bonding between carbene groups (CH2) and the nanotube sidewalls and a sp3-type bonding of nanotubes with paired phenyl groups. For similar molecular coverage density, charge transport is found to range from a quasi-ballistic-like to a strongly diffusive regime, with corresponding mean free paths changing by orders of magnitude depending on the nature of the chemical bonding.

Magnetically induced field effect in carbon nanotube devices.

Three-terminal devices with conduction channels formed by quasi-metallic carbon nanotubes (CNTs) are shown to operate as nanotube-based field-effect transistors under strong magnetic fields. The off-state conductance of the devices varies exponentially with the magnetic flux intensity. We extract the quasi-metallic CNT chirality as well as the characteristics of the Schottky barriers formed at the metal-nanotube contacts from the temperature-dependent magnetoconductance measurements.

Charge carriers in few-layer graphene films.

The nature of the charge carriers in 2D few-layer graphites (FLGs) has been recently questioned by transport measurements [K. S. Novoselov, Science 306, 666 (2004)10.

Probing the electronic properties of self-organized poly(3-dodecylthiophene) monolayers by two-dimensional scanning tunneling spectroscopy imaging at the single chain scale.

Regioregular poly(3-dodecylthiophene) films self-organized on highly oriented pyrolytic graphite have been investigated by scanning tunneling microscopy and two-dimensional scanning tunneling spectroscopy (STS). Simulated spectra in very good agreement with the experimental data have been obtained by a method combining ab initio and semiempirical approaches, which allows a careful discussion of the polymer electronic states. From the experimental data, with the support of modeling, it is shown that the STS spectra give a direct access to the polymer semiconducting band gap without noticeable charge-transfer effects from the substrate.

Electronic transport in carbon nanotubes with random coverage of physisorbed molecules.

The chemical sensitivity of electronic transport in carbon nanotubes under the physisorption of molecular species is investigated using a tight-binding scheme, parametrized by first-principles calculations. Such a computational method enables tackling of the complex electronic properties of chemically grafted conducting nanotubes. Our calculations demonstrate that the impact of physisorption on the transport regime critically depends on the HOMO-LUMO gap of the attached molecules.

Anomalous magnetotransport in chemically doped carbon nanotubes.

We report on anomalous magnetotransport features in chemically doped, weakly disordered carbon nanotubes. Under the application of a magnetic field parallel to the tube axis, hole conduction is shown to be strongly affected by impurity scattering with short mean free path and negative magnetoresistance, strongly different from electron conduction with much longer mean free path and positive magnetoresistance behavior.

Mesoscopic transport in chemically doped carbon nanotubes.

Electronic quantum transport is investigated in boron- and nitrogen-doped carbon nanotubes using tight-binding methods correlated to ab initio calculations. The present technique accurately accounts for both effects of dopants, namely, charge transfer and elastic scattering. Generic transport properties such as conduction mechanisms, mean-free paths, and conductance scalings are derived for various concentration of randomly distributed boron and nitrogen dopants.