New quantum dot microscope can display the electric potential of a single atom! A team of researchers in collaboration with Julich and Magdeburg Universities has developed a new method that can measure the electrical potential of a sample to atomic accuracy. Using traditional methods, it has until now been almost impossible to quantitatively record the electric potentials occurring in the vicinity of individual molecules or atoms. This new scanning quantum dot microscopy method, published in Nature Materials by Julich scientists at the Fürschenszentrum in Germany and partners from two other institutions, may open up new opportunities for chip manufacturing or the characterization of biomolecules such as DNA.
All matter is composed of positive nuclei and negative electrons, which generate electric potential fields that superimpose and compensate for each other even over short distances. Traditional methods do not allow quantitative measurements of these small-area fields, which determine the performance and functionality of many materials at the nanoscale. Almost all existing methods capable of imaging such potentials are based on the measurement of the force induced by the charge. However, these forces are difficult to distinguish from other forces occurring at the nanoscale, which hinders quantitative measurements. However, four years ago scientists from the Folsom Center discovered a method based on a completely different principle.
Scanning quantum dot microscopy attaches a single organic molecule (quantum dot) to the top of an atomic force microscope, and this molecule acts as a probe. The molecule is so small that we can attach a single electron from the tip of an atomic force microscope to the molecule in a controlled way. The researchers immediately recognized the promise of this approach and filed a patent application. However, practical applications are still a long way off. Initially, this was just a surprising effect with limited applicability. All that changes now, it is possible not only to visualize the electric fields of individual atoms and molecules, but also to quantify them precisely. This was confirmed by comparison with theoretical calculations performed by collaborators in Luxembourg.
In addition, a large area of ??the sample can be imaged to reveal various nanostructures simultaneously, and detailed images can be obtained in just an hour. The researchers spent several years studying this method and finally came up with a coherent theory. The reason for these very sharp images is an effect that keeps the tip of the microscope at a relatively large distance from the sample, about 2 to 3 nanometers - something that would be unimaginable with a regular atomic force microscope. In this case, it is important to know that all elements of a sample generate an electric field that affects the quantum dot and can therefore be measured. The tip of the microscope acts like a protective shield, suppressing damaging magnetic fields in distant areas of the sample.
The effect of the shielding electric field therefore decreases exponentially, and the quantum dots only detect the immediate surrounding area, and therefore the resolution is much higher than that of an ideal point detector. The Julich researchers credit their partners from the Otto von Guericke University Magdeburg with the speed of measuring the complete sample surface. Engineers there developed a controller that helps automate complex, repetitive sequences of scanning samples. An atomic force microscope works a bit like a tape recorder. The tip passes through the sample, stitching together a complete image of the surface. However, in previous work with scanning quantum dot microscopy, it was necessary to move to a separate location on the sample.
Measure one spectrum, move to the next position, measure another spectrum, and so on to combine these measurements into a single image. With the Magdeburg engineer's controller, it is now possible to scan the entire surface simply as with an ordinary atomic force microscope. It used to take 5-6 hours for one molecule, but now we can image an area of ??a sample containing hundreds of molecules in an hour. However, there are some disadvantages, and preparing metrics requires a lot of time and effort. The molecules that serve as measuring quantum dots must be attached to the tip beforehand, and this is only possible in a cryogenic vacuum. In contrast, ordinary atomic force microscopes can also work at room temperature and do not require a vacuum or complicated preparation.
However, Professor Stefan Tautz, Director of the Pacific Third Research Institute, is optimistic about this: This does not have to limit our options, the method is still innovative, and it is important for the first get excited about the project so it can show what it can really do. Quantum dot microscopy has many applications, and semiconductor electronics is pushing the boundaries of scale where a single atom can change functionality. Electrostatic interactions also play an important role in other functional materials such as catalysts. Characterization of biomolecules is another avenue. Due to the large distance between the tip and the sample, this method is also suitable for rough surfaces, such as the surface of DNA molecules, which have their own unique three-dimensional structure.