Final Report Summary - ATOMICSCALECIRCUIT (The next step in molecular electronics: Creation and investigation of a single-molecule circuit with atomic precision.)
Monoatomic and single-molecule wires [1] are seen as prospective elements of future molecular electronic devices. Their properties are commonly studied within mechanically-controlled [2] or scanning tunnelling microscope (STM) based [3] break junctions. These methods do, however, not permit insight into the geometric structure of the contacts at the atomic scale. Within this project we worked on an approach to use a low-temperature scanning tunnelling microscope (LT-STM) to (1) manufacture such a wire on the surface, and (2) lift the wire into an upright standing configuration to measure its electronic properties. To realize this goal we chose an approach that combines instrumental and software development. A first key component of our paradigm is the availability of atomic and/or molecular “building blocks” on an ultra-clean surface at low temperatures. This was achieved by constructing, calibrating and using a gold atom evaporator with precisely controllable rate attached to our LT-STM. The second key component of our paradigm is the on-surface assembly of such building blocks. As a model system we chose single Au atoms on a Au(111) single crystal surface. Using the STM we were able to assemble monoatomic Au chains on the surface. The third and most challenging component is the lifting of such surface-assembled structures into a vertical configuration using the STM tip. In systematic studies we came to the conclusion that simple, pre-programmed tip trajectories will not allow the lifting of these monoatomic wires. Instead, combined lateral and vertical tip motion on a very complex trajectory is required that explicitly takes the atomic structure of the surface into account. To respond to this challenge we developed in collaboration with our partners at the Forschungszentrum Jülich, Jülich (Germany) an integrated system combining a motion tracker [4] and a fast molecular dynamics simulation of the manipulation process that is capable of running while the experiment is performed. Thus, the simulation allows directly viewing the expected manipulation process including all atomic coordinates while the tip position is controlled directly by the hand of the experimenter using the motion tracker. This combination allows not only a very flexible try-and-error type of manipulation experiments but also to react directly on experimental measurements. This system thus goes far beyond state-of-the-art STM based manipulation. As such, our work can be seen as the next step in an attempt to join the reality of the experiment and the virtual reality of a computer simulation – in real time.
[1] Agraït, N., Yeyati, A. L. & van Ruitenbeek, J. M. Quantum properties of atomic-sized conductors. Phys. Rep. 377, 81–279 (2003).
[2] Xiang, D., Jeong, H., Lee, T. & Mayer, D. Mechanically controllable break junctions for molecular electronics. Adv. Mater. 25, 4845–67 (2013).
[3] Capozzi, B. et al. Tunable Charge Transport in Single-Molecule Junctions via Electrolytic Gating. Nano Lett. (2014). doi:10.1021/nl404459q
[4] M. F. B. Green, T. Esat, C. Wagner, P. Leinen, A. Grötsch, F. S. Tautz, and R. Temirov, Patterning a hydrogen-bonded molecular monolayer with a hand-controlled scanning probe microscope, Beilstein J. Nanotechnol (2014) DOI: 10.3762/bjnano.5.203
[1] Agraït, N., Yeyati, A. L. & van Ruitenbeek, J. M. Quantum properties of atomic-sized conductors. Phys. Rep. 377, 81–279 (2003).
[2] Xiang, D., Jeong, H., Lee, T. & Mayer, D. Mechanically controllable break junctions for molecular electronics. Adv. Mater. 25, 4845–67 (2013).
[3] Capozzi, B. et al. Tunable Charge Transport in Single-Molecule Junctions via Electrolytic Gating. Nano Lett. (2014). doi:10.1021/nl404459q
[4] M. F. B. Green, T. Esat, C. Wagner, P. Leinen, A. Grötsch, F. S. Tautz, and R. Temirov, Patterning a hydrogen-bonded molecular monolayer with a hand-controlled scanning probe microscope, Beilstein J. Nanotechnol (2014) DOI: 10.3762/bjnano.5.203