A rack-and-pinion device at the molecular scale

1. A rack-and-pinion device at the molecular scale Franco Chiaravalloti, Leo Gross, Karl-heinz Rieder, Sladjana M. Stojkovic, Andre Gourdon, Christian Joachim, and Francesca Moresco. Nature materials.2007, 6, 30-33. Tobe lab. Matsushita Minoru

2. Contents • Introduction Molecular Machines About Scanning Tunneling Microscope (STM) Purpose of This Work • Experiments • Results and Discussion • Conclusion

3. Introduction – Molecular Machines – “Molecular Machines” The molecule which has a function like various machines at molecular scale Driving force: External light, voltage or chemical conversions. Examples Rotor Axle Stator Legs Gimzewski, J. K. et al. Science1998, 281, 531. Van Delden, R. A. et al. Nature2005, 437, 1337. Access to one molecule but uncontrolled rotation. Observation by only indirect signatures. It is necessary to image and control a movement of a single molecule.

4. Introduction – About STM – STM can image and manipulate a single molecule. STM = Scanning Tunneling Microscope 走査型トンネル顕微鏡 Mechanism • Impressing vias voltage between tip and substrate Tip 探針 • Scanning with keeping tunneling current constant Tip Monolayer Substrate Surface • Tunneling current • Imaging information of height of tip The current which flowswhen this potential barrier is narrow.

5. Introduction – Purpose of This Work – Target MoleculeHB–NPB This molecule has six teeth like the ‘pinion’. A pyrimidine group A chemical ‘tag’ that can be detected by STM, provides an orientation axis to the molecule. tert-Butyl group The function of lifting the molecule to reduce the interaction of the aromatic parts with the substrate. The monolayer of HB–NPB molecules is like ‘rack-and-pinion device’. 単分子層 =

6. Experiments Condition of all presented experiments Substrate: Cu(111) surface cleaned with sputtering and annealing cyclesSelf-assemble monolayer: Made by subliming molecules onto the substrate at 480 K.STM experiment mode: Constant current mode Condition of STM experiments: Under ultrahigh vacuum (at a pressure of 10–10 mbar) At low temperature (7 K).

7. Results and Discussion – STM Images of Monolayer of HB–NPB – An STM image of an island border The pyrimidine group At ‘low’ voltage (47 mV) At ‘high’ voltage (2.2 V) Applying high voltage, the pyrimidine group can be observed as a maximum inside the molecule. This ‘tag’ indicates an orientation axis to the molecule.

8. Results and Discussion – Manipulation of One HB–NPB Molecule by STM – Manipulation of a single molecule on a surface The island border acts as a ‘rack’. The molecule as a ‘pinion’. The tip as the ‘pinion axis’. a) The tip approaches to the center of a molecule.b) Sufficient molecule-tip attractive force is maintained.c) A molecule moves on the surface by tip scanning.d-e) The tip is retracted back to where molecule-tip interaction is negligible and a molecule is left at a new position.

9. Results and Discussion – Manipulation of One HB–NPB Molecule by STM – These successive experimental images show the 60° rotation of the ‘pinion’ on its ‘rack’ (The white arrows show the orientations of the molecule).

10. Results and Discussion – Analysis of Rotation Movement of HB–NPB – There are two different directions in the manipulation, because of asymmetric shape of the ‘rack’. Not all successive manipulation make the 60° rotation of the ‘pinion’. Distributions of the rotation angles Step-down direction Step-up direction

11. Conclusion • Using a scanning tunneling microscope, a molecular ‘rack- and-pinion’ mechanism at work is observed at atomic-scale precision. • The piece-by-piece assembly of such device opens a new way of exploring the functioning of a molecular machines.