Single Molecule Electronics

Kasper Moth-Poulsen, Chalmers University of Technology

September 2013

Kasper.moth-poulsen@chalmers.se

MCC075 Molecular Electronics

OutlineLecture 1

Background and MotivationExperimental Methods

Lecture 2 (Friday)

Molecular Design of Diodes, Switches etc.

Part 3

Self-assembly

What did we learn last time?

Statistics

“Contacting Individual Molecules Using Mechanically Controllable Break Junctions”Jan van Ruitenbeek, Lecture Notes in Physics 680, 253-271 (2005)

The Vision II: Aviram and Ratner

• “the molecular rectifier”

A. Aviram and M. A. Ratner, “Molecular Rectifiers” Chem. Phys. Lett. Vol. 29, pp. 277-283, 1974.

A. Aviram and M. A. Ratner, “Molecular Rectifiers” Chem. Phys. Lett. Vol. 29, pp. 277-283, 1974.

Solution Based Systems

Initially No electrodes directly involved

Rotaxanes

Fraser Stoddard and co-workers eg early work: Pure &App/. Chem.,Vol. 65, No. 11, pp. 2351-2359,1993.

Important factors for the single molecule systems

Molecular orbitals

InterfaceElectrodes

Nature Nanotech. 4 (9), 551-556, 2009

The chemical anchor point: controls the self-assembly and is of paramount importance for the nature of the electron transport

Nature Nanotech. 4 (9), 551-556, 2009

Nature Nanotech. 4 (9), 551-556, 2009

Importance of the chemical contacts

Nano Letters 8 (1) 1-5, 2008.

Nature Nanotech. 4 (9), 551-556, 2009.

Nano Letters 8 (1) 1-5, 2008.

Nature Nanotech. 4 (9), 551-556, 2009.

~1 GΩ range 0.2-1 MΩResistance

b ~0,63 Å-1 ~0,39 Å-1

Solid state device

STM measurement

Intermezzo: Chemistry 101

Orbitals in Carbon and Chemical Bonds

3.3 - 3.5 eV

2.5 - 2.8 eV

3.8 - 3.9 eV

nsat = 10

nsat = 9 nsat = 10nsat = 2

5.7 eV

2.3 eV 2.2 - 3.2 eV 1.4 - 1.8 eV

nsat = 20

Optical band gaps for ”infinite” polymers obtained by extrapolation of monodisperse oligomers

Calculation

Molecular Back-bone: does it matter?

Slide courtesy of prof. MB Nielsen, Univ. Copenhagen

Molecular Back-bone: does it matter?

Kushmerik, TS Mayer and co-workers J. Phys. Chem. B 2004, 108, 2827-2832

Molecular Back-bone: does it matter?

Tunnelling vs Hopping, where is the transition from small molecules to polymers?

Seong Ho Choi, BongSoo Kim, C. Daniel Frisbie, Science 2008

Hopping is temperature dependent

Tunnelling is NOT temperature dependent

Seong Ho Choi, BongSoo Kim, C. Daniel Frisbie, Science 2008

Tunnelling vs Hopping

Molecular Switches, 3 types

1) Conformation switches

2) Electronic switches

3) Translational switches

Conformational Switch

Emanuel Lörtscher, Jacob W. Ciszek, James Tour, and Heike Riel, Small 2006, 2, No. 8-9, 973 – 977

“Microfabricated Molecular Break Junction”

Switch

No-Switch

Emanuel Lörtscher, Jacob W. Ciszek, James Tour, and Heike Riel, Small 2006, 2, No. 8-9, 973 – 977

Ferdinan Evers and co-workers small 2009, 5, No. 19, 2218–2223

“Switching Driven by rotation in the central bond in the bipyridine unit, induced by alignment of the dipoles in the Nitro groups with the electric field”

Mayor, Wandlowski and co-workers Nano Lett. 2010, 10, 156-163

Conductivity vs torsion angle

Conductivity and torsion angle: detailed investigation

Molecular Switches, 3 types

1) Conformation switches

2) Electronic switches

3) Translational switches

SourceDrain

Tunnelin

g b

arr

ier

Tunnelin

g b

arr

ier

”Diamond plot”

3-terminal devices

Kubatkin et al. Nature 2003

3.3 - 3.5 eV

2.5 - 2.8 eV

3.8 - 3.9 eV

nsat = 10

nsat = 9 nsat = 10nsat = 2

5.7 eV

2.3 eV 2.2 - 3.2 eV 1.4 - 1.8 eV

nsat = 20

Optical band gaps for ”infinite” polymers obtained by extrapolation of monodisperse oligomers

Calculation

Electron delocalization via cross conjugation is less efficient than via linear conjugation

Molecular Back-bone: does it matter?

Slide courtesy of prof. MB Nielsen, Univ. Copenhagen

Cross-conjugation, where does it come from?

• It is all pz orbitals so why is the delocalization different?

So surprizing that the physists has come up with their own name for it:

“Quantum interference”

Chemist might say: we have known about it all the time:

ortho/para vs meta directing? Michael addition?

M. Mayor, H.B. Weber, J. Reichert, M. Albing, C. von Hänisch, D. Beckmann, M. Fischer, Angew. Chem. Int. Ed. 2003, 42, 5834-5838.

Position of the Anchor Groups

Smaller conductance(by 2 orders of magnitude)

para: linear conjugation

meta: cross conjugation

Switching via changes in electronic states: Cross Conjugation and Quantum Interference

dx.doi.org/10.1021/ja202471m |J. Am. Chem. Soc. XXXX, XXX, 000–000

Hummelen and Solomon

Synthesis and initial Charactarisation: Hummelen and co-workers Org. Lett., 2006, 8 (11), pp 2333–2336Transport and Thery „evidence of Quantum Interference” JACS ASAP 2011 dx.doi.org/10.1021/ja202471m

Brønsted-Nielsen and co-workers Org. Lett. 2006 Vol. 8, No. 6 1173-1176 J. Org. Chem, Vol. 73, No. 8, 2008

Ox

Red

D. Dulic , S. J. Van Der Molen , T. Kudernac , H. T. Jonkman ,J. J. D. de Jong , T. N. Bowden , J. van Esch , B. L. Feringa ,B. J. van Wees , Phys. Rev. Lett. 2003 , 91 , 207402 .

Conjugation/cross conjugation photoswitch

Molecular Switches

1) Conformation switches

2) Electronic switches

3) Translational switches

Dripling C60 for six weeks

Danilov/Kubatkin

D

Hedegård

Danilov and Kubatkin, NANO LETTERS Volume: 8 Issue: 8 Pages: 2393-2398

TPS

• We have discussed 3 types of switches, describe each type of Switch

How to Switch a Molecular Switch

• 1) thermal activation• 2) level allignment (gating)• 3) redox chemistry with reorganisation• 4) photoreaction• 5) magnetic switch

Kubatkin nature 2003

level allignment (gating)

Redox Switch

Redox Switch 2

Photo Switches

Photo Switch

Magnetic Switch

TPS

• Describe the different ways to activate switches

• 1) thermal activation• 2) level allignment (gating)• 3) redox chemistry with reorganisation• 4) photoreaction• 5) magnetic switch

“Molecular Trains: and organized molecular tranlational switch”

Molecular Machines

Fraser Stoddart and co-workers

SummaryMolecular Switches:

Conformational SwitchesElectronic SwitchesTranslational Switches

• 1) thermal activation• 2) level allignment (gating)• 3) redox chemistry with reorganisation• 4) photoreaction• 5) magnetic switch

Methods of contacting molecules• Scalability?• Tunability of a nanogap?• Single-molecule device possible?• Possible artifacts• Is gating possible?• For industry or for research?• How was it made?• How was the molecules designed?• What kind of switching?

5 min report (3 slides) + 1 A4 Written summarye-mail your presentation before oct 3 to

mkasper@chalmers.se

Seminar on Oct 5