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Precision control of Precision control of single molecule single molecule
electrical junctionselectrical junctions
Iain Grace & Colin Lambert
(b)
I0 Iw
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
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
(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.
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)
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
Theoretical tilt dependenceTheoretical tilt dependenceHollow site
Top site
Artificially shifted LUMO resonances
Surfaces of constant LDOSSurfaces of constant LDOS
Increasing the tilt angle alters the strength of the contact coupling
Molecule GeometryMolecule Geometry
Geometry A ~ α = 0
Geometry B ~ α = 60
Rings are free to rotate about the molecule axis
Rotational DependenceRotational DependenceRotate the whole molecule about its axis by an angle Φ
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.
