"All matter consists of positively charged atomic nuclei and negatively charged electrons," explains Professor Dr.-Ing. Rolf Findeisen from the Institute of Automation Technology at the University of Magdeburg. "These generate electrical potentials. Using conventional methods, until now it has been barely possible to measure these very weak fields, which are responsible for many of the characteristics and functionalities of materials."
With the newly developed Scanning Quantum Dot Microscopy, a single molecule, known as a quantum dot, is mounted on the tip of the needle of a scanning force microscope. This tip travels, like the needle of a record player, over the sample with the molecule at temperatures close to absolute zero and thus, step by step creates a coherent representation of the surface.
Together with his doctoral student, Michael Maiworm, Professor Rolf Findeisen developed a controller for the innovative microscope method - an algorithm that controls the scanning process. This makes the accurate, but until now extremely long-winded measurement of potentials at molecular resolution possible in just a few minutes. "With the new controller we can now easily scan the entire surface of a molecule, as with a normal scanning force microscope," says Christian Wagner from the Jülich Research Center. This enables us to produce high-resolution images of the potential, which previously appeared unattainable.
"There are many possible uses for this new, unusually precise and fast microscopy technique," continues Michael Maiworm, who largely developed the controller as part of his dissertation supervised by Professor Findeisen. "They range from fundamental physical questions to semiconductor electronics - where even a single atom can be critical for functionality - and molecular chemical reactors to the characterization of biomolecules such as our DNA or biological surfaces."
The work is a part of the cooperation between Magdeburg and Jülich, which examines the targeted and automated manipulation of objects at nano level. In this connection the molecular tip has a dual function: it is simultaneously both a measuring probe and a tool. This opens up the possibility of, in future, being able to create nanostructures via 3D printing. It is conceivable, for example, that it might be possible to produce electrical circuits consisting of individual molecules or sensors of molecular dimension and resolution.
Quantitative imaging of electric surface potentials with single-atom sensitivity
Christian Wagner, Matthew. F. B. Green, Michael Maiworm, Philipp Leinen, Taner Esat, Nicola Ferri, Niklas Friedrich, Rolf Findeisen, Alexandre Tkatchenko, Ruslan Temirov, F. Stefan Tautz Nature Materials (published online 10 June 2019), DOI: 10.1038/s41563-019-0382-8