Cracking the code: Researchers uncover a ‘new synthetic frontier’ for quantum dots
A class of semiconductor nanocrystals known as quantum dots is expanding the frontiers of pure science while also eagerly pursuing practical applications such as lasers, quantum QLED televisions and displays, solar cells, medical devices, and other electronics. Masu.
A new technique for growing these microscopic crystals, published in this week’s Science journal, not only uncovers a new, more efficient way to construct useful types of quantum dots, but also opens the door for future research. It has also opened up a whole group of new chemicals for exploration by researchers. .
“We’re excited to see how researchers around the world can use this technology to prepare previously unimaginable nanocrystals,” said lead author and former Ph.D. at the Tarapin Institute at the University of California. said researcher Justin Ondry.
The team, which included researchers from the University of Chicago, the University of California, Berkeley, Northwestern University, the University of Colorado Boulder, and Argonne National Laboratory, literally replaced the organic solvents typically used to create nanocrystals with molten salts. achieved these remarkable results. Superheated sodium chloride, the type you sprinkle on baked potatoes.
“Sodium chloride is not a liquid in the head, but suppose you heat it to an unusual temperature such that it becomes a liquid. It looks like a liquid. It has a viscosity similar to water and is colorless. The only problem ‘These liquids are used as vehicles for colloid synthesis,’ said Dmitri Tarapin, a professor in the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) and Department of Chemistry, that no one had thought of.
Why salt?
Quantum dots are one of the better-known nanocrystals, not only for their wide range of commercial applications, but also for the recent 2023 Nobel Prize in Chemistry awarded to the team that discovered them.
“If there’s any material in the nanoworld that has had an impact on society in terms of applications, it’s quantum dots,” said study co-author Eran Rabbani, a professor at the University of California, Berkeley.
But much of the previous research on quantum dots, including the Nobel Prize work, involved dots grown using a combination of elements from groups 2 and 6 of the periodic table, Rabbani said. said. These are called “II-VI” (two-six) materials.
More promising materials for quantum dots are found elsewhere on the periodic table.
Materials from Groups 3 and 5 of the periodic table (III-V materials) are used in the most efficient solar cells, the brightest LEDs, the most powerful semiconductor lasers, and the fastest electronic devices. Although they potentially make good quantum dots, it has been impossible to use them to grow nanocrystals in solution, with a few exceptions. The temperatures required to produce these materials were too high for known organic solvents.
Molten salts can handle heat, making it possible to obtain materials that were previously inaccessible.
“This clear advance in molten salt synthesis by Professor Tarapin’s group opens up for the first time many materials for which colloidal synthesis was not previously possible,” said co-author Richard D.・Mr. Schaller stated. Northwestern University. “The use of many of these newly available materials has enabled fundamental and applied advances to be made, while creating entirely new synthetic frontiers available to the community.”
quantum era
One reason researchers synthesizing nanocrystals overlooked molten salts was because of their strong polarity, said University of Chicago graduate student Zirui Zhou, second author of the new paper.
The positively charged ions and negatively charged ions of salt have a strong attraction to each other. Because something as small as a nanocrystal has a small surface charge, the researchers reasoned that the charge would be too weak to push back the salt ions as they were pulled in. The growing crystals will be crushed before forming a stable material.
Or so previous researchers thought.
“This is an amazing observation,” Zhou said. “This is very inconsistent with what scientists traditionally think about these systems.”
New technology could mean better, faster quantum computers or new building blocks for classical computers, but for many of the research teams, the really exciting part is finding new It’s about developing materials.
“Many periods in human history are defined by the materials available to humans, such as the Bronze Age and the Iron Age,” Ondry says. “With this work, we have unlocked the ability to synthesize more than a dozen new nanocrystal compositions that will enable future technologies.”
Further information: Justin C. Ondry et al., Molten inorganic salt reduction route enables colloidal synthesis of III-V semiconductor nanocrystals, Science (2024). DOI: 10.1126/science.ado7088
Provided by University of Chicago
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