Giant Thermopower and Figure of

Merit in Single-Molecule Junctions Colin Lambert,

Lancaster University

.Lancaster

Manchester .

R. Nichols

S. Higgins

•Durham

M. Bryce

M. Turner

An idea !

.Lancaster

Destructive interference = power !

A different idea!

• Introduction to single-molecule electronics

• Hunting for Fano resonances and signatures of room-temperature quantum interference

• Geometric control of Fano resonances • Giant thermopower and figure of merit in single-

molecule devices induced by Fano resonances

Single-molecule

LEGO

Anchors

Linkers

N N

NN

Zn

Ar

Ar

N

N N

NN

Zn

Ar

Ar

N N

NN

Zn

Ar

Ar

N N

NN

Zn

Ar

Ar

N

N

Pt Ru Pt

Ph2P

PPh2

PPh2

Ph2PN N

L

L

L

L

1,3-butadiyne linked porphrin porphyrin tape oligo phenylene ethynylene (OPE)

metallopolyyne

N N

NN

Zn

Ar

Ar

N

N N

NN

Zn

Ar

Ar

N N

NN

Zn

Ar

Ar

N N

NN

Zn

Ar

Ar

N

N

Pt Ru Pt

Ph2P

PPh2

PPh2

Ph2PN N

L

L

L

L

1,3-butadiyne linked porphrin porphyrin tape oligo phenylene ethynylene (OPE)

metallopolyyne

Simple 1-d carbon chain = oligoynes

Anchors versus linkers:

Oligoynes

Examples with N=4 carbon

atoms in the chain

(ie n=2 triple bonds)

Amine

CN

Pyridine

Thiol

DHBT

Unfortunately oligoynes are

explosive, so cap the ends

M. Santiago, I. Grace,M. Bryce,

C. Wang, R. Jitchati, A. Batsanov,

S. Higgins, C.J. Lambert,

and R. Nichols,

JACS, S132 9157 (2010)

dihydrobenzo[b]-thiophenyl (DHBT)

Comparison with experiment

Pyridine

thiol

Amine

CN

DHBT

Lo

g G

/G0

Slopes = 0.1 – 0.3 per angstrom

Si-based single-molecule

electronics

8.5 nm SiO2 layer

Si (111)

Polysilicon

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(A)(B)

Gap (~10nm)

Source

Drain Gate

Tunnel Barrier Receptor

Molecular Backbone

I-V characteristics

0 2 4 6

Voltage (V)

0

0.002

0.004

0.006

0.008

0.01

Curr

ent

(nA

)

280K

Measurements in the

absence of molecules

(low leakage currents)

Measurements in the

presence of molecules

Ashwell, et al ACS Nano 4, 7401 (2010)

Also : Angew. Chemie, 50, 8722 (2011)

Molecular wires used in silicon devices

In situ reaction of an amino-terminated molecular linker with

4-ethynylbenzaldehyde electrode-grafted molecules on

opposite sides of the nanogap

Functional units

Mach-Zehnder interferometers

N

N Zn

Ar

Ar

N

N

N

N

ZnAr

N

N

N

N

Zn

Ar

ArN

N

N

N

Zn

Ar

ArN

N

N

N

ZnAr

N

N

N

NZn

Ar

Ar

N

N

NN

N

N N

NS

S

Shielding units

Single-molecule sensing

Phys. Rev. Lett. 102, 086801 (2009)

Simulation of break-junctions Wenjing Hong, David Zsolt Manrique, Pavel Moreno García, Murat Gulcur, Artem Mishchenko,

Colin Lambert, Martin R. Bryce, and Thomas Wandlowski JACS 134, 2292 (2011)

Calculation of pulling curves Classical MD followed by DFT relaxation at each step.

(Morse potential between gold and anchor atom S)

Hunting for Fano resonances and

signatures of room-temperaure

quantum interference R= CH3(CH2)5O T. Wandlowski, V. Kaliginedi, G.P. Moreno; H. Valkenie, W. Hong, V. García-Suárez, P.

Buiter, J. Otten, J. Hummelen and C.J. Lambert, JACS 134 5262 (2012)

Comparison with experiment

The Fano resonance in more

detail

Removal of Fano resonance by

protonation H attached to O

ie O replaced by OH

Geometric control of Fano

resonances

PRB 79, 033405 2009

2

21

2

21

)ΓΓ(εE

Γ4ΓT

1T ε,EFor

4Γ)(

4ΓT,ΓΓΓWhen

22

2

21

E

Breit-Wigner resonances: a reminder

Width Г

Peak position ε

Typical effect of varying a thiol-

gold contact gap

Control of Breit-Wigner

resonances via ring rotation

Transmission coefficient for various

rotation angles between rings

mole

cule

angle

2 0

3 15

4 30

5 46

6 52

7 62

8 88

Control of ring rotations

Experiment; Colombia group: Nature 442, 904 (2006) Theory: Lancaster group, J. Phys.

Cond. Matt. 20, 022203 (2008)

Fano versus Breit-Wigner resonances

ΦHΨ 1

1Γ 2Γ

22)1

2

1

*

21

Γ(ΓεE

εE

Γ4ΓT

side group with eigenvalue ε1

backbone state, with a resonant energy ε Φ

Rotate side group with respect to wire backbone

Phys. Rev. B 74, 193306 (2006)

Control of the Fano resonances via side-

group rotations

Giant thermopower and figure of merit

induced by Fano resonances PRB 79, 033405 2009

Transmission coefficients for various

twist angles

Giant thermopower and figure of

merit in single-molecule devices PRB 79, 033405 2009

• electrical conductance G,

• thermopower S,

• Peltier coefficient Π,

• thermal conductance κ ,

• ZT=S2GT/κ

Moments of the “probability

distribution P(E)=T(E)[-df(E)/dE]”

-

Thermopower versus twist and

temperature

Figure of merit ZT

Collaborators and real workers

Molecular Synthesis

• M.R. Bryce (Durham)

• H. Anderson (Oxford)

Lancaster theory RAs and

PhDs

• V. Garcia-Suarez (now Oviedo)

• L. Oroszlany (now Budapest)

• I. Grace, S. Bailey, C. Finch, D.

Manrique, R. Sparks, D.

Visontai, T. Pope, K. Guillemot,

C. Peterfalvi

Transport measurements and/or

synthesis

• R. Nichols, S. Higgins (Liverpool)

•T. Wandlowskii (Berne)

•N. Agrait (Madrid)

•G. Ashwell (Bangor)

Theory

• J. Ferrer (Oviedo)

• J. Cserti (Budapest)

• J. Jefferson (QinetiQ)

Summary

• ‘Lego’ of single-molecule electronics: anchors, linkers, functional units, pendant groups, ............

• Fano resonances and quantum interference in a series of OPE-derivatives.

• Giant thermopower and figure of merit in single-molecule devices induced by Fano resonances

Experimental evidence of room temperature Fano resonances and quantum interference Beilstein J. Nanotech. 2011, 2, 699 Nature Nano. 2012, 7, 304; PRL. 2012, 109, 056801; Nano. Lett. 2012, 6, 1643; JACS 2012, 134, 5262;

transport

HS

H

)(

General problem

Eg Landauer

G=2e2/h T(EF)

Electron pumping

via Brouwer

formula

Torques and forces

Low – frequency

transport

Thermoelectrics

Ab initio self-consistent mean-

field transport

Spin and Molecular Electronics in Atomically - Generated Orbital Landscapes

Lancaster transport codes + SIESTA + non-equilibrium Greens functions (zero or finite bias; normal or

superconducting contacts; thermoelectrics; non-co-linear magnetism; NEMS)

Victor

Garcia

Porphyrin-based molecular wires

G. Sedghi, L. J. Esdaile, H. L. Anderson, V. M. García-Suárez, C.J.

Lambert, S. Martin, D. Bethell, S. J. Higgins and R. J. Nichols,

Nature Nano, 6 517 (2011)

Example: Planar trimer

(001) Au, with 7x7=49 atoms per layer. Total 588 atoms for trimer

SZ gold ; DZP molecule

Comparison between experiment

and theory

Nature Nano, 6 517 (2011)