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Scientists measure near-perfect results in low-cost semiconductors



The light emitted by the nearest artist's "quantum dots" that they absorb. Credit: Ella Marushchenko

Small, easy-to-produce particles, called quantum dots, can soon become more expensive single-crystal semiconductor locations in advanced electronics in solar collectors, camera sensors, and medical imaging tools. Although quantum dots began to penetrate the consumer market ̵

1; in the form of quantum-point televisions – they are hampered by long-lasting uncertainty about their quality. Now, the new measurement technique developed by Stanford University researchers can ultimately eliminate these doubts.


"Traditional semiconductors are separate crystals grown under vacuum under special conditions. We can produce it in large quantities, in a flask, in a laboratory, and we have shown that they are as good as the best single crystals, ”said David Hanifi, Stanford Chemistry Graduate and author of the co-author of this work, published on March 19th. Science .

Scientists have focused on how the quantum dots revitalize the light they absorb by the quality of semiconductors. While previous attempts to find out the effectiveness of a quantum dot have referred to high performance, this is the first measurement method that allows you to show reliably that you can compete with individual crystals.

This is Alberto Salleo, prof. materials science and engineering Stanford and Paul Alivisatos, professor of nanotechnology and nanotechnology at Samsung University, Berkeley University, California. Alivisatos emphasized how measuring techniques can create new technologies and materials that require the efficiency of our semiconductors.

"These materials are so effective that the existing measurements could not measure how good it is. It's a huge leap forward," said Alivisato. "It may ever allow programs that require materials that have a high luminescence efficiency well above 99%, most of which have not yet been invented."

The expensive production facility from 99 to 100 the advantage of quantum dots. Even before this work, there were signs that quantum dots could approach some of the best crystals. They are also very adaptable. Changing their size alters the wavelength they emit, which is a useful feature for color programs such as Biological Samples, TVs, or computer monitors. to do the work of one big, perfect single crystal of them. Making so many of these quantum points means more opportunities for someone to grow wrong, more opportunities for a defect that can hinder productivity. Methods for measuring the quality of quantum dots previously proposed by other semiconductors emit more than 99 percent of the light they absorb, but this was not enough to answer their questions about their possible defects. To do this, scientists needed a method of measuring these particles accurately

"We want to measure 99.9-99.999 percent. Emission efficiency, because if semiconductors are able to restore light, every photon that you absorb can make a really interesting science and make devices that did not exist before, ”said Hanifi.

The technique of scientists was to check the amount of heat generated by the exhausted quantum points, not just the light emission, because excessive heat is a sign of inefficient emissions. This method, commonly used for other materials, has never been applied to quantum dot measurement in this way and was 100 times more accurate than others previously. They found that quantum dot groups reliably spread about 99.6 percent. The light they absorb (with a possible 0.2 percent error in any direction), which is similar to the best single crystal emissions

. a film with many possible defects is as good as the best semiconductor, said Salleo, co-author of this document.

Conversely, results of concern indicate that quantum dots are extremely resistant to defects. Measuring Technique is also the first to firmly determine how different quantum dot structures are comparable to each other – most likely to emit quantitative points with exactly eight atomic layers of a specific coating material, which is the highest quality indicator. The shape of these points should lead to the design of new light-emitting materials, said Alivisatos

Completely New Technologies

This study is a collection of projects under the Department of Energy. Energy Frontier Research Center, called photonics within thermodynamic limits. The center, led by Jennifer Dionne, Associate Professor of Materials Science and Engineering at Stanford, aims to create optical materials – materials that affect light flow – with the highest possible efficiency

The next step in this project is another step towards more accurate measurements. If researchers can find that these substances reach 99.999 percent. With greater efficiency, it provides the opportunity for technologies that we have never seen before. This may include new luminous dyes that improve our ability to look at biology on atomic scale, fluorescent cooling, and fluorescent solar concentrators that allow a relatively small amount of solar cell energy to come from a large area of ​​solar radiation. All of this is said to be the spin-off stage that they have already set, which can lead to more rapid pulse research and application.

"People working in these quantum dot materials have been thinking for more than a decade that points can be as effective as single crystal materials," Hanif said.


Learn More:
More stable light comes from intentionally "broken" quantum points

More information:
David A. Hanif et al., Re-describing the luminescence of unity in quantum points with a photothermal threshold quantum yield, Science (2019). DOI: 10.1126 / science.aat3803

Journal Reference:
Science

Submitted by:
Stanford University


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