09-Jul-2015 - Forschungszentrum Jülich GmbH

Researchers Develop Ultrahigh-Resolution 3D Microscopy Technique for Electric Fields

Down to the Quantum Dot

Using a single molecule as a sensor, scientists in Jülich have successfully imaged electric potential fields with unrivalled precision. The ultrahigh-resolution images provide information on the distribution of charges in the electron shells of single molecules and even atoms. The 3D technique is also contact-free. The first results achieved using "scanning quantum dot microscopy" have been published in the current issue of Physical Review Letters. The related publication was chosen as the Editor's suggestion and selected as a Viewpoint in the science portal Physics. The technique is relevant for diverse scientific fields including investigations into biomolecules and semiconductor materials.

"Our method is the first to image electric fields near the surface of a sample quantitatively with atomic precision on the sub-nanometre scale," says Dr. Ruslan Temirov from Forschungszentrum Jülich. Such electric fields surround all nanostructures like an aura. Their properties provide information, for instance, on the distribution of charges in atoms or molecules.

For their measurements, the Jülich researchers used an atomic force microscope. This functions a bit like a record player: a tip moves across the sample and pieces together a complete image of the surface. To image electric fields up until now, scientists have used the entire front part of the scanning tip as a Kelvin probe. But the large size difference between the tip and the sample causes resolution difficulties – if we were to imagine that a single atom was the same size as a head of a pin, then the tip of the microscope would be as large as the Empire State Building.

Single molecule as a sensor

In order to improve resolution and sensitivity, the scientists in Jülich attached a single molecule as a quantum dot to the tip of the microscope. Quantum dots are tiny structures, measuring no more than a few nanometres across, which due to quantum confinement can only assume certain, discrete states comparable to the energy level of a single atom.

The molecule at the tip of the microscope functions like a beam balance, which tilts to one side or the other. A shift in one direction or the other corresponds to the presence or absence of an additional electron, which either jumps from the tip to the molecule or does not. The "molecular" balance does not compare weights but rather two electric fields that act on the mobile electron of the molecular sensor: the first is the field of a nanostructure being measured, and the second is a field surrounding the tip of the microscope, which carries a voltage.

"The voltage at the tip is varied until equilibrium is achieved. If we know what voltage has been applied, we can determine the field of the sample at the position of the molecule," explains Dr. Christian Wagner, a member of Temirov’s Young Investigators group at Jülich’s Peter Grünberg Institute (PGI-3). "Because the whole molecular balance is so small, comprising only 38 atoms, we can create a very sharp image of the electric field of the sample. It’s a bit like a camera with very small pixels."

Universally applicable

A patent is pending for the method, which is particularly suitable for measuring rough surfaces, for example those of semiconductor structures for electronic devices or folded biomolecules. "In contrast to many other forms of scanning probe microscopy, scanning quantum dot microscopy can even work at a distance of several nanometres. In the nanoworld, this is quite a considerable distance," says Christian Wagner. Until now, the technique developed in Jülich has only been applied in high vacuum and at low temperatures: essential prerequisites to carefully attach the single molecule to the tip of the microscope.

"In principle, variations that would work at room temperature are conceivable," believes the physicist. Other forms of quantum dots could be used as a sensor in place of the molecule, such as those that can be realized with semiconductor materials: one example would be quantum dots made of nanocrystals like those already being used in fundamental research.

Facts, background information, dossiers

  • Forschungszentrum Jülich
  • scanning quantum do…

More about Forschungszentrum Jülich

  • News

    Synapses as a model: solid-state memory in neuromorphic circuits

    They are many times faster than flash memory and require significantly less energy: memristive memory cells could revolutionize the energy efficiency of neuromorphic computers. In these computers, which are modeled on the way the human brain works, memristive cells function like artificial ... more

    Alzheimer’s Research: New Insights into the Formation of Toxic Protein Clumps

    Small aggregates of proteins known as Aβ oligomers are suspected as the main cause for the development of Alzheimer’s disease. However, it is not yet clear where and under what conditions these toxic aggregates form. Researchers from Heinrich Heine University Düsseldorf and Forschungszentru ... more

    Increasing the Activity of Catalysts

    A layer as thin as a single atom makes a huge difference: On the surface of an electrode, it doubles the amount of water split in an electrolysis system without increasing the energy requirements. Thus, the ultrathin layer also doubles the amount of hydrogen produced without increasing cost ... more

  • q&more articles

    Macromolecular environments influence proteins

    The high-intensity interaction of proteins with other macromolecules can cause signifi cant changes to protein properties such as translational mobility, for example, or their conformational states. Accordingly, the study of proteins in macromolecular environments that typically very closel ... more

    Caffeine Kick

    Caffeine is the most widely consumed psychoactive substance worldwide. It supplies the active ingredient in beverages such as coffee, tea and energy drinks. Caffeine can focus vigilance and attention, reduce drowsiness and enhance the ability to perform cognitive functions. Its neurobiologi ... more

  • Authors

    Prof. Dr. Jörg Fitter

    Jörg Fitter studied physics at the University of Hamburg. After completing his doctoral studies at FU Berlin, he worked in neutron scattering and molecular biophysics at the Hahn Meitner Institute in Berlin and Jülich Research Center. He completed his habilitation in physical biology at Hei ... more

    Dr. David Elmenhorst

    studied medicine in Aachen before receiving his doctorate in sleep research from the German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt, DLR) in Cologne. During 2008/2009, he was a visiting researcher at the Brain Imaging Centre in Canada’s Montreal Neurological Institute an ... more

    Prof. Dr. Andreas Bauer

    studied medicine and philosophy in Aachen, Cologne and Düsseldorf, where he received his doctorate in the field of neuroreceptor autoradiography. After specialist medical training at Cologne University Hospital he completed his habilitation in neurology at the University of Düsseldorf. Sinc ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by: