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Fiche détaillée Thèses
Université Joseph-Fourier - Grenoble I (13/11/2009), Stephan Roche (Dir.)
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viva_final.ppt(12.5 MB)
Etude à partir des premiers principes de l'effet de la fonctionnalisation sur le transport de charge dans les systèmes à base de carbone à l'échelle mésoscopique.
Alejandro Lopez-Bezanilla1

A theoretical methodology and study of charge transport through GNRs, as well as in metallic and semiconducting CNTs, with randomly distributed functional groups covalently attached to the system surface is presented. By resorting to both first principles calculations, to obtain a suitable parametrization of the electronic structure, and a fully ab initio transport approach calculation to explore conduction regimes through large and disordered systems. The quantum transport modeling is based on the Green function formalism, combining an iterative scheme for the calculation of transmission coefficients with the Landauer formula for the coherent conductance. The results describe how the conductance of the hybrid systems is altered as a function of incident electron energy and molecules coverage density. Comparing two different types of functional groups, transport regimes are explored. Phenyls and hydroxyl groups induce a local orbital rehybridization of the CNTs and GNRs anchor carbon atoms from sp2-type to sp3-type yielding a localized transport regime. On the other hand, carbene groups do not disrupt the original sp2 network of armchair and small diameter zigzag CNTs which allows for good conductance preservation.
1 :  INAC - Institut Nanosciences et Cryogénie (ex DRFMC)
nanotubes – graphene – fonction Green – CNT GNR – transport electronic – decimation

First Principles Study of the Eect of Chemical Functionalization on Charge Transport in Carbon-Based Systems at the Mesoscopic Scale.
The chemical attachment of groups on single-walled carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) has attracted much attention as it provides an efficient way for tuning their electronic properties. These carbon based systems are being widely investigated as potential candidates for nanoelectronic interconnects and transistors. The control of electric current is, therefore, an important challenge in nanostructures engineering. I present a theoretical methodology and study of charge transport through GNRs, as well as in metallic and semiconducting CNTs, with randomly distributed functional groups covalently attached to the system surface. I resort to both first principles calculations, to obtain a suitable parametrization of the electronic structure, and a fully ab initio transport approach calculation to explore conduction regimes through large and disordered systems. The quantum transport modeling is based on the Green function formalism, combining an iterative scheme for the calculation of transmission coefficients with the Landauer formula for the coherent conductance. The results describe how the conductance of the hybrid systems is altered as a function of incident electron energy and molecules coverage density. Comparing two different types of functional groups, transport regimes are explored. Phenyls and hydroxyl groups induce a local orbital rehybridization of the CNTs and GNRs anchor carbon atoms from sp2-type to sp3-type yielding a localized transport regime. On the other hand, carbene groups do not disrupt the original sp2 network of armchair and small diameter zigzag CNTs which allows for good conductance preservation.

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