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Researchers measure near-perfect results in low-cost semiconductors



The visualization of a close artist of quantum dots that emit light that they have absorbed. Regards: Ela Marushtenko
Small, easy to produce particles, called quantum dots, can soon take the place of the more expensive semiconductors of a single crystal in modern electronics found in solar panels, camera sensors and medical imaging. Although quantum points began to penetrate the consumer market ̵
1; in the form of quantum TVs – they were hampered by long-standing uncertainties about their quality. Now a new measurement technique developed by researchers at Stanford University can finally solve these doubts.
"Traditional semiconductors are single crystals vacuum-grown under special conditions, they can be made in large quantities, in a flask, in a laboratory, and we've proven to be as good as the best single crystals," says David Hanifie. , a graduate of Stanford Chemistry and a co-author of the article written for this work, published on March 15 in Science .

Researchers focused on how efficiently the quantum dots emit the light they are absorbing. indicator of semiconductor quality. While previous attempts to calculate quantum efficiency hinted at high performance, it is the first measurement method that confidently shows that they can compete with single crystals.

This work is the result of collaboration between Alberto Salleo's laboratories, Professor of Materials Science and Engineering at Stanford, and Paul Alivatos, the Honorary Professor of Nanosciences and Nanotechnology at the University of California, Berkeley, who pioneered quantum research points and senior author of the article. Avivicosos emphasizes that measurement techniques can lead to the development of new technologies and materials that require knowledge of the effectiveness of our semiconductors to a difficult extent.

"These materials are so effective that existing measurements are not able to determine how good they are. It's a giant leap forward," says Alizatos. "May one day allow applications that require materials with luminescence efficiency over 99 percent , most of which are not yet invented. "

Between 99 and 100

Ability to abandon the need for expensive production equipment is not the only advantage of quantum dots. , there were signs that quantum points could be They are also very adaptable, changing their size changes the wavelength of the light they emit, a useful function for color applications such as bioassay, television or computer monitors.

Despite these positive qualities, the small size of quantum points means it can take billions of them to do the work of a great, perfect monocrystal. Making so many of these quantum points means more chances for something that grows wrong, more chances for a defect that can interfere with performance. Techniques that measure the quality of other semiconductors preceding the quantum dots emit over 99% of the light they swallow, but this is not enough to answer questions about their potential for defects. To do this, researchers needed a more appropriate measurement technique, more suited to accurately assessing these particles.

"We want to measure the efficiency of emissions in the range from 99.9 to 99.999 percent because if the semiconductors can emit light as each photon they absorb, you can make a really fun science and make devices that did not exist before , "said Hanifi.

The researchers' technique involved testing for excess heat produced by quantum dots instead of evaluating only the light emission, as excess heat is signing an ineffective emission. This technique, often used for other materials, has never been used to measure quantum points in this way and is 100 times more precise than what others have used in the past. They found that groups of quantum points reliably emit about 99.6% of the absorbed light (with a potential error of 0.2% in each direction), which is comparable to the best emissions of a single crystal. the film with many potential defects is as good as the most perfect semiconductor you can do, says Salleo, who co-authored the article.

Contrary to concerns, the results show that the quantum points are strikingly defective. The technique of measurement is also the first to firmly decide how the different quantum dot structures compare with each other – quantum points with exactly eight atomic layers of special coating material emitted by the light as quickly as possible, the highest quality indicator.

All new technologies

This study is part of a collection of projects within the Energy Financing Department. Center for Energy Boundary Research, called Photodyna in Thermodynamic Limits. Led by Jennifer Dion, Associate Professor of Materials Science and Engineering at Stanford, the focus of the center is to create optical materials – materials that influence the light flow – with the highest possible efficiency.

The next step in this project is developing even more accurate measurements. If researchers can find that these materials reach 99,999% or more, this opens up the possibility of technologies we have never seen before. They can include new lighted dyes to improve our ability to view atomic scale biology, fluorescence cooling, and fluorescent solar concentrators that allow a relatively small number of solar cells to absorb energy from a large area of ​​solar radiation. All this is said, the measurements they have already established are a milestone for them, likely to encourage a more immediate impetus in the quantum points research and applications. A decade that points can be effective as one crystal, Hanifie said, and now we have proof.


See also:
More stable light comes from deliberately "crushed" quantum points

More Information:
David A. Hanifi et al., Redefining Nearly Uniform Luminescence at Quantum Dots with Photothermic Threshold of Quantum Yield, Science (2019). DOI: 10.1126 / science.aat3803

Journal Title:
science

Provided by:
Stanford University


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