Precision control of single molecule electrical junctions Iain Grace & Colin Lambert.
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Transcript of Precision control of single molecule electrical junctions Iain Grace & Colin Lambert.
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Precision control of Precision control of single molecule single molecule
electrical junctionselectrical junctions
Iain Grace & Colin Lambert
(b)
I0 Iw
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CollaboratorsCollaborators
University of LiverpoolUniversity of Liverpool• W. Haiss• R. Nicholls• R. Schiffron
Durham UniversityDurham University• C. Wang• M. Bryce• A. Batsanov
Smeagol teamSmeagol team• A. R. Rocha • S. Sanvito• V. Garcia Suarez• J. Ferrer• S. Bailey• C. Lambert
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Modelling of Molecular Electronics at Modelling of Molecular Electronics at LancasterLancaster
Controlling transport through single moleculesControlling transport through single molecules
Molecule Synthesis ~ Durham UniversityMolecule Synthesis ~ Durham University
•M. Bryce & C. Wang
O
O
O
O
R R
R RO O
O
O
O
O
R
R
R
R
S SNC CN
27 R = C6H13
HN
O
O
O
O
R R
R RO O
O
O
O
O
R
R
R
R
S SNC CN
28 R = C6H13
N N
Molecule CharacterizationMolecule Characterization• STM measurements• Cranfield ~ G. Ashwell, W. Tyrell• Liverpool ~ W. Haiss, R. Nicholls
Device fabrication ~ QinetiQDevice fabrication ~ QinetiQ Scalable technologyScalable technology
Gold contacts
Theory ~ Lancaster UniversityTheory ~ Lancaster University• I. Grace, T. Papadopolous, C. Finch• S. Sirichantaropass , V. Garcia Suarez• C. Lambert
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(b)
I0 Iw
Experimental Details ~ I(t) MethodExperimental Details ~ I(t) MethodX-Ray Crystallogaphy structure
Length ~ 2nm
IW ~ Measured current through the molecule
W. Haiss et al, Phys. Chem. Chem. Phys., 2004, 6, 4330.
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Tilting MoleculesTilting Molecules
No temperature dependence~ molecule is rigid~ for non-rigid molecules there is a strong temperature dependence
Theory on molecule tiltingTheory on molecule tiltingKornilovitch et al, PRB 64, 195413 (2001)Geng et al, App. Phys. Lett. 85, 5992 (2004)
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Theoretical ModellingTheoretical Modelling
Relax geometry of the isolated molecular wire ( SIESTA DFT code)
Extend the molecule to include surface layers of gold
Using SIESTA extract a tight binding Hamiltonian describing the extended
molecule
Compute zero-bias transport with a greens function scattering approach.
)(2 2
ETh
eG
Employ a simpler form of the SMEAGOL code~ developed to study very long molecules (10nm) efficiently
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Theoretical tilt dependenceTheoretical tilt dependenceHollow site
Top site
Artificially shifted LUMO resonances
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Surfaces of constant LDOSSurfaces of constant LDOS
Increasing the tilt angle alters the strength of the contact coupling
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Molecule GeometryMolecule Geometry
Geometry A ~ α = 0
Geometry B ~ α = 60
Rings are free to rotate about the molecule axis
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Rotational DependenceRotational DependenceRotate the whole molecule about its axis by an angle Φ
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ConclusionsConclusions
• Developed a theoretical method, based on the SMEAGOL code, to
compute efficiently the zero bias conductance of molecular wires.
• Good agreement with the measured magnitude of conductance.
• The behaviour of the tilt dependence of the conductance is determined by geometry of the molecule between the contacts.