Alain Rochefort

Interaction of Substituted Aromatic Compounds with Graphene

We have modeled the adsorption of various substituted derivatives of benzene on a graphene sheet, using a first-principles density functional theory-local density approximation method. The presence of functional groups can significantly alter the overall magnitude of pi-pi interactions between the adsorbed molecules and graphene by giving rise to strong medium-range interactions involving pi-orbitals of the substituents. When the substituents can simultaneously permit the formation of hydrogen bonds between adsorbed molecules, it is possible to evaluate the relative contributions of hydrogen bonding and pi-based interactions to the overall adsorption. Adsorption of individual molecules and hydrogen-bonded aggregates reflects a hierarchical balance of the different interactions that determine the overall energy of adsorption.

Electrical and mechanical properties of distorted carbon nanotubes

We have calculated the effects of structural distortions of armchair carbon nanotubes on their electrical transport properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an increased electrical resistance. Electronic structure calculations show that these energy ranges contain localized states with significant

The effect of structural distortions on the electronic structure of carbon nanotubes

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Electronic and Transport Properties of Carbon Nano Peapods

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A Single Molecule Kondo Switch: Multistability of Tetracyanoethylene on Cu(111)

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Switching behavior of semiconducting carbon nanotubes under an external electric field

hybridization resulting from the increased curvature produced by bending. Our calculations of the contact resistance show that the large contact resistances observed for SWNTs are likely due to the weak coupling of the NT to the metal in side bonded NT-metal configurations.

Noncovalent bicomponent self-assemblies on a silicon surface.

We calculated the effects of structural distortions on the electronic structure of carbon nanotubes. The main effect of nanotube bending is an increased mixing of σ and π states. This mixing leads to an enhanced density-of-states in the valence band near the Fermi energy. While in a straight tube the states accessible for electrical conduction are essentially pure C(2pπ) states, they acquire significant C(2spσ) character upon bending. Bending also leads to a charge polarization of the C–C bonds in the deformed region reminiscent of interface dipole formation. Scattering of conduction electrons at the distorted regions may lead to electron localization.

Strongly reshaped organic-metal interfaces: tetracyanoethylene on Cu(100).

We theoretically studied the electronic and electrical properties of metallic and semiconducting nanotube peapods with encapsulated C 6 0 (C 6 0 @CNT) as a function of the carbon nanotube (CNT) diameter. For exothermic peapods (the CNT diameter>11.8 A), only minor changes, ascribed to a small structural deformation of the nanotube walls, were observed. These include a small electron charge transfer (less than 0.10 electron) from the CNT to the C 6 0 molecules and a poor mixing of the C 6 0 orbitals with those of the CNT. Decreasing the diameter of the nanotube leads to a modest increase of the charge density located between the C 6 0 s. More significant changes are obtained for endothermic peapods (CNT diameter<11.8 A). We observe a large electron charge transfer from C 6 0 to the tube, and a drastic change in electron transport characteristics and electronic structure. These results are discussed in terms of π-π interaction and C 6 0 symmetry breaking.

Tailoring the Photoluminescence Properties of Ionic Iridium Complexes

Single tetracyanoethyelene (TCNE) molecules on Cu(111) are reversibly switched among five states by applying voltage pulses with the tip of a scanning tunneling microscope. A pronounced Kondo resonance in tunneling spectroscopy indicates that one of the states is magnetic. Side bands of the Kondo resonance appear at energies which correspond to inter- and intramolecular vibrational modes. Density functional theory suggests that molecular deformation changes the occupancy in TCNEs molecular orbitals, thus producing the magnetic state.

States modulation in graphene nanoribbons through metal contacts.

We investigate theoretically the switching characteristics of semiconducting carbon nanotubes connected to gold electrodes under an external (gate) electric field. We find that the external introduction of holes is necessary to account for the experimental observations. We identify metal-induced gap states (MIGS) at the contacts and find that the MIGS of an undoped tube would not significantly affect the switching behavior, even for very short tube lengths. We also explore the miniaturization limits of nanotube transistors, and, on the basis of their switching ratio, we conclude that transistors with channels as short as 50 A would have adequate switching characteristics.