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electronics

Atoms-thick semiconductor layers stick like Post-its

Scientists have figured out how to make tiny individual films—each just a few atoms high—and stack them for use in new kinds of electronics.

Over the past half-century, scientists have shaved silicon films down to just a wisp of atoms in pursuit of smaller, faster electronics. For the next set of breakthroughs, though, they’ll need new ways to build even tinier and more powerful devices.

In a study that appears in Nature, researchers describe an innovative method to make stacks of thin, uniform layers of semiconductors just a few atoms thick which could expand capabilities for devices like solar cells and cell phones.

“When the material itself is just atoms thick, every little stray atom is a problem.”

Stacking thin layers of materials offers a range of possibilities for making electronic devices with unique properties. But manufacturing them is a delicate process, with little room for error, researchers say.

“The scale of the problem we’re looking at is, imagine trying to lay down a flat sheet of plastic wrap the size of Chicago without getting any air bubbles in it,” says Jiwoong Park, a professor of chemistry at the University of Chicago and at the Institute for Molecular Engineering and the James Franck Institute. “When the material itself is just atoms thick, every little stray atom is a problem.”

Today, these layers are “grown” instead of stacking them on top of one another. But that means the bottom layers are subjected to harsh growth conditions such as high temperatures while the new ones are added—a process that limits the materials with which to make them.

For the new process, Park’s team did something different. They made the films individually, then put them into a vacuum, peeled them off, and stuck them to one another, like Post-it notes.

This allowed scientists to make films that were connected with weak bonds instead of stronger covalent bonds—interfering less with the perfect surfaces between the layers.

“The films, vertically controlled at the atomic-level, are exceptionally high-quality over entire wafers,” says postdoctoral associate Kibum Kang, the study’s first author.

Graduate student Kan-Heng Lee, a co-first author of the study, then tested the films’ electrical properties by making them into devices and showed that their functions can be designed on the atomic scale, which could allow them to serve as the essential ingredient for future computer chips.

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The method opens up a myriad of possibilities for such films. They can be made on top of water or plastics; they can be made to detach by dipping them into water; and they can be carved or patterned with an ion beam.

Researchers are exploring the full range of what can be done with the method, which they said is simple and cost-effective.

“We expect this new method to accelerate the discovery of novel materials, as well as enabling large-scale manufacturing,” Park says.

Researchers from Cornell University are coauthors of the study. The US Air Force, the National Science Foundation, and the National Research Foundation of Korea funded the work.

Source: University of Chicago

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