Getting Complex Semiconductors To Arrange For Tuning Their Properties

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Researchers developed a way to effectively stack material layers on top of each other to create new materials with unique properties.

According to material scientists, stacking materials on top of each other can create new materials with entirely new properties. But the processes for stacking materials is tedious, not p[erfect, and not suited for large-scale production.

A team of researchers from SLAC National Accelerator Laboratory, led by Stanford Professor Hemamala Karunadasa, have developed a simpler and faster way to arrange the layers. They grew 2D layers of perovskites interleaved with thin layers of other materials in large crystals that assemble themselves.

“Rather than manipulating materials one layer at time,” said Karunadasa, who is an investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) at the Department of Energy’s SLAC National Accelerator Laboratory. “We’re just throwing the ions into a pot of water and letting the ions assemble the way they want to assemble. We can make grams of this stuff, and we know where the atoms are in the crystals. This level of precision allows me to know what the interfaces between the layers really look like, which is important for determining the material’s electronic structure—how its electrons behave.”

However, it is difficult to predict what arrangement can lead to certain unique properties. Moreover, the process earlier was very time consuming where layers are generally made by peeling films just one or two atoms thick, one at a time, from a bigger chunk of material. 

“The way they’re made has not been scalable and sometimes even difficult to reproduce from one batch to another,” Karunadasa said. “Peeling off layers that are just one or two atoms thick is specialized work; it is not something you and I can just go into the lab and do. These sheets are like a very flexible deck of cards; when you take one out, it can crumple or buckle. So it is hard to know the exact structure of the final stack. There is very little precedent for materials that look like the ones we created in this study.”

The team made six of the material with perovskite layers interleaved with metal halides or metal sulfides, and examined them with X-rays. In a particular case,  upon hitting the material with light, they found out that electrons mostly arranged in one type of layer and the holes mostly in the other. This is important because it allows you to tune those two environments to get the electronic behavior you want.

The research appeared in the journal Nature.


 

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