Presentation on theme: "Alejandro López Bezanilla"— Presentation transcript:
1 Alejandro López Bezanilla Effect of the Chemical Functionalization on Charge Transport in Carbon-based materials at the Mesoscopic ScaleAlejandro López BezanillaInstitut des Nanosciences et Cryogénie (INAC)CEA Grenoble, FranceExaminers:· Prof. Mark Casida (UJF) Président du Jury· Prof. Juan José Sáenz (UAM) Rapporteur· Prof. Alain Rochefort (EPM) Rapporteur· Dr. Xavier Blase (CNRS)· Dr. Pablo Ordejón (CIN2)Encadrants:· Dr. Stephan Roche (CEA) Encadrant· Dr. Pascale Maldivi (CEA) Co-encadrante (Grenoble)· Dr. Vincent Derycke (CEA) Co-encadrant (Saclay)
2 ChimTronique Transversal axes Saclay (S. Palacin) Grenoble (R. Baptist)
3 Outline → Motivations → Electronic properties of CNTs and GNRs · Functionalization→ Decimation method· Green´s function technique→ Results· Functionalized nanotubes·Functionalized nanoribbons·Edge defects in nanoribbons
4 Carbon atom Hybrid Molecular Orbitals Cohesion Electronic properties in the vicinity of EFValence electron orbitals:~ 2D (sp2)Grapheneinteractions between pz orbitals (bonds/bands )~ 3D (sp3)Diamond
5 -effective model2 atoms/ cellnearest neighbor orbital overlap12
7 if we alter these properties ? SummarizingWhat would it happenif we alter these properties ?
8 → Selective electrical signals of molecular adsorption events. Bio-, photo-sensors→ Selective electrical signals of molecular adsorption events.→ Protein interaction.→ Virus detection.Zhou et al. Nano Letters 9, 1028 (2009)
9 e- Bio-, photo-sensors Photoactive molecules: Phtalocyanine …→ Transmission after photoactive molecule functionalization.→ Properties of the linker.hve-Left leadRight lead300 nmS. Campideli et al.J. Am. Chem. Soc. 2008, 130, 11503
10 Towards graphene nanoribbon transistor Using top-down lithography to fabricate GNRs…· Ribbons down to ~ 10 nm widthP. Kim et al (Columbia Univ. USA)E. Dujardin (CEMES, France)Ph. Avouris et al. (IBM, USA)· MOSFETs : clean GNR-FET with ~ 3nm are necessary !!!W 2 nm !X. Li et al., Science 319, 1229 (2008)X. Wang et al., PRL 100, (2008)
11 Functionalizing graphene 2D Graphene and Graphene ribbonsGoal: how to create or enlarge energy/conduction band gapsA graphene-based electrochemical switch(M. Lemme & A. Geim)Controlled electrochemical modification of graphene such that its conductance changes bymore than six orders of magnitude (reversible bipolar switching devices).:: Chemical reaction of graphene with hydrogen (H+) and hydroxyl (OH-), which are catalytically generated from water molecules in the sub-stochiometric silicon oxide gate dielectric. The reactive species attach to graphene making it nonconductive but the process can subsequently be reversed by short current pulses that cause rapid local annealing.
12 Hybrid Carbon Based Materials Is sp2 bondingbroken/preserved?
13 sp2 vs sp3 functionalization CH2 chemisoptionsp2sp3Zigzagnanotube axisArmchairnanotubeaxis
14 sp2 vs sp3 functionalization Phenyl chemisoptionTube axis
15 Electronic states sp3 sp2 LDoS (0.6 eV) Energy bands 2 phenyls carbene XΓXΓcarbene2 phenylscarbene
16 SIESTA: an ab initio approach → Efficient tool for first-principles calculations (geometrical relaxation,…)→ Local atomic-like orbitals basis set:· no coupling beyond a cutoff distance,· sparse Hamiltonian.→ No fittings, no adjustable parameters.s-orbitalp-orbitalsp-hybrid orbital
17 Description of the system Building block→ SWCNT (10,10)Size : ~ 500 atoms→ phenyl groups1.3 nm3 nm
18 Transport formalisms Kubo-Greenwood Landauer-Büttiker Order N method : only Hamiltonian - Vector productsallows big systems simulationsNo contactsIntrinsic propertiesQuantum diffusion mechanismMean free path, scattering time, mobilityOrder power N method :inversion of Hamiltonian limites size of systems simulationsAccuracyTransmission and reflexion probabilityLocalization length, conductance
19 Problem definition & Decimation technique Problem statementProblem definition&Decimation technique
20 Problem definition Channel Non-interacting electrons LeftleadRightleadChannelNon-interacting electronsScattering free leads (perfect electrodes)No backscattering at lead - reservoir interfaceIncident electrons are in thermal equilibrium with reservoirs
21 Problem definition Nanotubes Left lead Right lead channel Nanoribbons
22 Conductance from Green´s function Fisher and Lee relation for transmission:T(E) = Tr [ ΓLGC ΓRGC ](r)(a)Σ LΣ RHC~where:ΓL,R = i [ Σ L,R - Σ L,R ](r)(a)~GC = [ E- HC - Σ L- Σ R ] - 1S. Fisher and P.A. Lee, Phys. Rev. Lett., 23, 6851 (1981)Datta, Electronic transport in mesoscopic system, Cambidge (1995)
48 Conclusions Decimation technique Carbon Nanotubes Graphene Nanoribbons → Full ab initio transport studies: SIESTA +TB_SimCarbon Nanotubes→ Chemical modification leads to diffusive transport→ sp2 vs sp3 functionalizationGraphene Nanoribbons→ sp3 defects induce backscattering→ Mind the radicals! → Benzenoid edge defects are not critical in electronic transport properties
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