Researchers develop quantum dot microscope for measuring electric potentials of atoms

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Quantum Dots
Much like in an old tube television where a beam of electrons moves over a phosphor screen to create images, the new microscopy technique works by scanning a beam of electrons over a sample that has been coated with specially engineered quantum dots. (Credits - Wikimedia Commons)

A group of scientists from Jülich in collaboration with the University of Magdeburg has developed a new technique for measuring the electric potentials of a sample with accuracy to the atomic level. Using normal methods, it was almost impossible until now to measure the electric potentials which occur in the vicinity of individual molecules. The scanning quantum dot microscopy method, which was presented in the Nature Materials journal by researchers from Forschungszentrum Jülich in collaboration with other institutes, could open new possibilities in chip manufacturing or biomolecule characterization.

All matter consists of a positive nucleus of the atom and negative electrons. They generate electric potential fields which superpose and compensate the other, even at very small distances. Conventional methods do not allow for the measurements of these fields, that are responsible for many nanoscale properties and functions. Almost all the methods which are in use today are capable of imaging potentials which are based on the forces due to the electric charges. However, these forces are difficult to distinguish from other ones occurring at the nanoscale, that prevents measurements.

Researchers from Forschungszentrum Jülich, four years ago discovered a technique based on a different principle. Scanning quantum dot microscopy involves attachment of one organic molecule, quantum dot—to atomic microscope’s tip. This molecule acts as a  probe. Dr. Christian Wagner, lead researcher at the Controlled Mechanical Manipulation of Molecules group at Peter Grünberg Institute said that due to the small size of the molecule, individual electrons can be attached from atomic microscope’s tip to the molecule in a very controlled way.

Scientists recognized that this method can open up new avenues and hence filed a patent for it. But it could not be used in real experiments immediately. Initially, there were some limitations to its practical use. But now, the electric fields of individual atoms can be visualized and also precisely quantified. This was confirmed by comparing with theoretical calculations which were done by researchers at Luxembourg. Besides this, large areas of a sample can be imaged and the nanostructures can be displayed at once.

The researchers at Jülich spent a lot of time in investigating the technique and then developed a coherent theory for it. The very sharp images are possible due to the large separation from the sample which is permitted by the microscope tip, something beyond the ability of normal atomic force microscopes.

Engineers from Otto von Guericke University, Magdeburg developed a controller for automating the repeated sequence of scanning the sample. With the controller, now simply the whole surface can be scanned in an hour, whereas earlier it took 5-6 hours for a molecule. However, preparing the atomic dot takes lots of time but scientists are optimistic in overcoming this and applying it to challenging problems.

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