Physicists photographed crystal structure transformation under laser pointer beam

Laser beams can be used to change the properties of materials in extremely precise ways. This principle has been widely used in technologies such as rewritable DVDs. However, the basic process is generally carried out at such an unimaginable speed and such a small scale that it has not been directly observed so far.

Researchers from the University of Göttingen and the Max Planck Institute for Biophysical Chemistry (MPI) in Göttingen have now successfully photographed the crystal structure with nanometer resolution and slow motion in an electron microscope for the first time. laser pointer conversion process. The results have been published in the “Science” magazine.

The team included Professors Thomas Danz and Claus Ropers, who took advantage of the unusual properties of a material composed of thin atomic layers of sulfur and tantalum atoms. At room temperature, its crystal structure is twisted into tiny wave-like structures-forming “charge density waves”. At higher temperatures, a phase change occurs, and the original microscopic waves suddenly disappear. Electrical conductivity will also change dramatically, which is an interesting effect for nanoelectronics. In the experiment, the researchers induced this phase transition with a short laser pulse and recorded the film that reacted with the charge density wave.

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The first author from the University of Göttingen explained: “What we have observed is the rapid formation and growth of a small area where the material is switched to the next phase. The ultrafast transmission electron microscope developed in Göttingen provides this imaging The highest time resolution in the world today.”

The particularity of this experiment lies in a newly developed imaging technique, which green laser pointer is particularly sensitive to the special changes observed in this phase transition. The images taken by physicists in Göttingen are entirely a collection of electrons scattered by crystal fluctuations. Their cutting-edge methods allow researchers to gain fundamental insights into light-induced structural changes.

Professor Claus Ropers, a leader in nano optics and ultrafast dynamics at the University of Göttingen and director of MPI in biophysical chemistry, said: “We have been able to transfer our imaging technology to other crystal structures. In this way, we not only answer The fundamental problems in solid-state physics have also opened up new prospects for optical switch materials in smart nanoelectronics in the future.”