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A new way to shape the atomic structure of a material with ultrafast laser light

The figure shows how the atomic structure of tin selenium, a crystalline substance that can convert heat into electricity, changes when exposed to heat or ultrafast laser light. The structure in the middle is room temperature. When heated (left), from this point of view, the upper and lower atoms move slightly to the left, and some of the other atoms move slightly. Scientists thought that exposing a material to ultrafast laser light would do much the same thing. Instead, the atom has shifted in a new way (right). LCLS, SLAC’s X-ray free electron laser, allows researchers to see for the first time the movement and structural distortions of these atoms, opening new avenues for adjusting materials with light. Credits: Yijing Huang / Stanford University

Thermoelectric materials convert heat into electricity and vice versa, and their atomic structure is closely related to how well they work.


Currently, researchers are investigating the atomic structure of tin selenide, which is a highly efficient thermoelectric material. Laser light.. This result opens up new ways to improve the structure of thermoelectrics and many other materials by creating materials with dramatic new properties that may not exist in nature. ..

“It’s very important for this class of material because its functional properties are structurally related,” said Yijing Huang, a graduate student at Stanford University who played an important role in the experiments at the SLAC National Accelerator Laboratory at the Department of Energy. Says. “By changing the nature of the light you put in, you can adjust the nature of the material you make.”

Experiments were conducted on SLAC’s Linac Coherent Light Source (LCLS), an X-ray free electron laser.The result is today Physical Review X Highlighted by a special collection dedicated to ultra-fast science.

Heat vs. light

Because thermoelectric converts waste heat For electricity, they are considered a form of green energy. Thermoelectric generators have powered Apollo’s lunar landing project, and researchers have sought ways to use them to convert the heat of the human body into electricity and charge gadgets. Doing the opposite creates a temperature gradient that can be used to cool the wine in a refrigerator with no moving parts.

Tin selenide is considered one of the most promising Thermoelectric material Grow as an individual crystal, Relatively cheap and easy to manufacture. Unlike many other thermoelectric materials, tin selenide is lead-free and is a much more efficient heat exchanger. It is relatively easy to make because it is composed of regular cube-like crystals that resemble rock salt.

To investigate how these crystals react to light, the team struck tin selenide with a powerful pulse of near-infrared laser light to change its structure. The light excited the electrons in the atoms of the sample, shifting some positions of those atoms and distorting their placement.

Researchers then used pulses of X-ray laser light from LCLS to track and measure the movement of these atoms and the resulting changes in their crystal structure. This is fast enough to capture the changes that occur in just one millionth of a second.

A new way to shape the atomic structure of a material with ultrafast laser light

This figure of SLAC’s X-ray free electron laser experimental data shows how atoms of a thermoelectric material called tin selenide moved from room temperature when exposed to ultrafast laser light. Shown (red arrow). The purple circle represents the selenium atom and the green circle represents the tin atom. This result was surprising because scientists believed that heat and light had the same effect. This study shows a new way for light to shape the structure and related properties of materials. Credits: Yijing Huang / Stanford University

“To reconstruct the place where atoms are moving, we need the ultrafast pulses and atomic resolution provided by LCLS,” said research co-author SLAC and Stanford professor and director of the Stanford PULSE Institute. David Reis said. “Without it, we would have made a mistake.”

Amazing results

This result was totally unexpected, and when fans told other members of the team what they saw in the experiment, they had a hard time believing in her.

One proven way to change the atomic structure of Tin selenide Is to add heat. This changes the material in a predictable way and actually improves the performance of this particular material. With conventional knowledge, shining a laser beam gives almost the same result as heating.

Mariano Trigo, a SLAC staff scientist and researcher at SLAC’s Stanford Institute for Materials and Energy Science (SIMES), said:

“But after almost two years of discussion, I Ching finally convinced the other members of the team that they were pushing the material towards a completely different structure. This result was when they were excited. I think it’s against most people’s intuition about what happens to them. Electronic For higher energy levels. “

A theoretical calculation by Shan Yang, a graduate student at Duke University, confirmed that this interpretation of the experimental data was correct.

“This article and its classes are certainly very interesting because it’s a system where small changes can lead to very different results,” Reis said. “But the ability to create entirely new structures with light, that is, structures that do not know how to make them in other ways, is probably more universal.”

He added that one area where it might be useful is a decade-old quest to create superconductors (materials that conduct electricity without loss) that operate at temperatures close to room temperature.


Converting Materials with Light: Research could lead to ultra-fast light-based computers, etc.


For more information:
Yijing Huang et al, Observation of New Lattice Instability in Ultrafast Photoexcited SnSe, Physical Review X (2022). DOI: 10.1103 / PhysRevX.12.011029

Quote: Https: //phys.org/news/2022-02-material-atomic-ultrafast-laser.html for materials with ultrafast laser light (February 14, 2022) acquired on February 14, 2022. A new way to form an atomic structure

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A new way to shape the atomic structure of a material with ultrafast laser light

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