26-Jan-2021 - Georg-August-Universität Göttingen

Crystal structures in super slow motion

Researchers first to succeed in filming a phase transition with extremely high spatial and temporal resolution

Laser beams can be used to change the properties of materials in an extremely precise way. This principle is already widely used in technologies such as rewritable DVDs. However, the underlying processes generally take place at such unimaginably fast speeds and at such a small scale that they have so far eluded direct observation. Researchers at the University of Göttingen and the Max Planck Institute (MPI) for Biophysical Chemistry in Göttingen have now managed to film, for the first time, the laser transformation of a crystal structure with nanometre resolution and in slow motion in an electron microscope.

The team, which includes Thomas Danz and Professor Claus Ropers, took advantage of an unusual property of a material made up of atomically thin layers of sulphur and tantalum atoms. At room temperature, its crystal structure is distorted into tiny wavelike structures - a "charge-density wave" is formed. At higher temperatures, a phase transition occurs in which the original microscopic waves suddenly disappear. The electrical conductivity also changes drastically, an interesting effect for nano-electronics.

In their experiments, the researchers induced this phase transition with short laser pulses and recorded a film of the charge-density wave reaction. "What we observe is the rapid formation and growth of tiny regions where the material was switched to the next phase," explains first author Thomas Danz from Göttingen University. "The Ultrafast Transmission Electron Microscope developed in Göttingen offers the highest time resolution for such imaging in the world today." The special feature of the experiment lies in a newly developed imaging technique, which is particularly sensitive to the specific changes observed in this phase transition. The Göttingen physicists use it to take images that are composed exclusively of electrons that have been scattered by the crystal's waviness.

Their cutting-edge approach allows the researchers to gain fundamental insights into light-induced structural changes. "We are already in a position to transfer our imaging technique to other crystal structures," says Professor Claus Ropers, leader of Nano-Optics and Ultrafast Dynamics at Göttingen University and Director at the MPI for Biophysical Chemistry. "In this way, we not only answer fundamental questions in solid-state physics, but also open up new perspectives for optically switchable materials in future, intelligent nano-electronics."

Facts, background information, dossiers
  • crystal structures
  • phase transitions
  • nanoelectronics
More about Uni Göttingen
  • News

    Research describes fundamental principle of enzyme catalysis

    It is well known in physics and chemistry that equal charges repel each other, while opposite charges attract. It was long assumed that this principle also applies when enzymes – the biological catalysts in all living organisms – form or break chemical bonds. It was thought that enzymes pla ... more

    Novel quantum effect discovered in naturally occurring graphene

    Usually, the electrical resistance of a material depends very much on its physical dimensions and fundamental properties. Under special circumstances, however, this resistance can adopt a fixed value that is independent of the basic material properties and “quantised” (meaning that it chang ... more

    How diphosphorus can be used for chemical reactions

    Chemical syntheses of new active ingredients or functional materials are based on the use of molecular building blocks. These must be simultaneously reactive but also stable enough to enable targeted incorporation into larger molecules. A research team from the University of Göttingen and t ... more

More about MPI für biophysikalische Chemie