Single Molecule Electronics Kasper Moth-Poulsen, Chalmers University of Technology September 2013 MCC075 Molecular Electronics

Outline Lecture 1 Background and Motivation Experimental 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, (2005)

The Vision II: Aviram and Ratner “the molecular rectifier” A. Aviram and M. A. Ratner, “Molecular Rectifiers” Chem. Phys. Lett. Vol. 29, pp , 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 ,1993.

Important factors for the single molecule systems Molecular orbitals Interface Electrodes Nature Nanotech. 4 (9), , 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), , 2009

Importance of the chemical contacts Nano Letters 8 (1) 1-5, Nature Nanotech. 4 (9), , 2009.

Nano Letters 8 (1) 1-5, Nature Nanotech. 4 (9), , ~1 GΩ range MΩ Resistance  ~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 n sat = 10 n sat = 9n sat = 10n sat = eV 2.3 eV 2.2  3.2 eV 1.4  1.8 eV n sat = 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,

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, Conductivity vs torsion angle Conductivity and torsion angle: detailed investigation

Molecular Switches, 3 types 1) Conformation switches 2) Electronic switches 3) Translational switches

Source Drain Tunneling barrier ”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 n sat = 10 n sat = 9n sat = 10n sat = eV 2.3 eV 2.2  3.2 eV 1.4  1.8 eV n sat = 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 p z 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, 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/ /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 2333–2336 Transport and Thery „evidence of Quantum Interference” JACS ASAP 2011 dx.doi.org/ /ja202471m Brønsted-Nielsen and co-workers Org. Lett Vol. 8, No 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, Conjugation/cross conjugation photoswitch

Molecular Switches 1) Conformation switches 2) Electronic switches 3) Translational switches

Dripling C 60 for six weeks Danilov/Kubatkin

 Hedegård

Danilov and Kubatkin, NANO LETTERS Volume: 8 Issue: 8 Pages:

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

Summary Molecular Switches: Conformational Switches Electronic Switches Translational 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 summary your presentation before oct 3 to Seminar on Oct 5