Very small, easy-to-produce particles, called quantum dots, may soon take more expensive single crystalline semiconductors in advanced electronics found in solar panels, camera sensors and tools in medical imaging. Even the quantum dots have begun to enter the consumer market-in the form of quantum TV dots-they have been hampered by long uncertainty about their quality. Now, a new measurement method developed by researchers at Stanford University can completely dissolve the doubts.
"Traditional semiconductors are single crystals, grown in vacuum under special conditions. These we can do in large numbers, in flask, in a lab and we show them as good of the best crystal, "said David Hanifi, a graduate Stanford chemistry student and co-lead author of the paper written on this work, published on March 1
Researchers are focused on how well the quantities of dots re-start the light they absorb, the magnificent measure of semiconductor quality. While previous attempts to find out the sum of dot efficiency hinted at high performance, this is the first measurement method to confidently show they can compete with the same crystal.
This work is the result of a collaboration between the labs of Alberto Salleo, professor of materials at Stanford's science and engineering, and Paul Alivisatos, the Samsung Distinguished Professor of Nanoscience and Nanotechnology at the University of California, Berkeley , a pioneer in quantum dot research and senior author of the paper. Alivisatos emphasized how the measurement method can lead to the development of new technologies and materials that need knowledge of the efficiency of our semiconductors at a careful level.
"These materials are so good that existing measurements can not be quantifying how well they are. They are a giant leap forward," says Alivisatos. "Deploying applications may require someday with luminescence materials that are over 99 percent, most of them not invented yet."
Between 99 and 100
for expensive apparel equipment is not the only advantage of the whole point. Even before this work, there are signs that quantum dots can come in or exceed the performance of some of the best crystals. They are also customizable. Changing their size changes the amount of light they emit, a useful feature for color-based applications such as tagging biological samples, televisions or computer monitors.
Despite the positive qualities, the small size of quantum points means they can take billions to do the work of a large, perfect single crystal. Doing so many dots altogether means more opportunities for something to grow incorrectly, more opportunities for a defect that can withstand performance. Methods that measure the quality of other semiconductors previously suggested dots totally emitting 99 percent of the light they sucked but not enough to answer questions about their potential for defects. To do so, researchers need a measurement technique that is better suited to accurately study these particles.
"We want to measure the efficiency of the kingdom out of 99.9 to 99.999 percent because, if the semiconductor can re-capture as every photon, you can make science really fun and make devices that do not exist before , "said Hanifi.
Methods of researchers involved checking for excess heat produced by energized quantum dots, rather than just light emission analysis because excessive heat is a signature of poor emission. This method, commonly used for other materials, has never been applied to measure quantum dots in this way and is 100 times more accurate than others used in the past. They found that groups of trustworthy quantum dots were released about 99.6 percent of the light they absorbed (with potential error of 0.2 percent in either direction), which is comparable to the best single-crystal emissions.
"It's amazing that a movie with many potential defects is as good as the most perfect semiconductor you can do," says Salleo, co-author of the paper.
Contrary to concerns, the results indicate that the dots of the sum are a wonderful disability. The measurement method is also the first to resolve firmly how different dot dots are different from each other-dots totally specific with eight atomic layers of a special coating material which emit the fastest, an indicator of superior quality. The shape of the dots should be the design guide for new light-emitting materials, according to Alivisatos.
This research is part of a collection of projects within a funded Department of Energy Energy Frontier Research Center, called Photonics on Thermodynamic Limits. Led by Jennifer Dionne, professor of materials at Stanford's science and engineering, the center's aim is to create optical materials-materials that affect the flow of light-with the highest possible efficiency.
The next step in this project is to make even more accurate measurements. If researchers determine that these materials have achieved efficiencies at or above 99.999 percent, which opens the possibility for technologies we have not seen before. These may include new glowing dyes to enhance our ability to look at biology on the atomic scale, luminescent cooling and luminescent solar concentrators, allowing a relatively small range of solar cells to take energy from a large area of solar radiation. All this is said, the measurements they have established are a milestone of their own, it is likely to encourage a more immediate help in quantum research and dots.
"People who work on quantum dots are thought for over a decade that dots can be as effective as single crystal materials," Hanifi says, "and now we are there is evidence. "
A more stable light comes from deliberately & # 39; squashed & # 39; dot total
David A. Hanifi et al, Determines the near-unity of luminescence in quantum dots with a photothermal threshold of total yield, Science (2019). DOI: 10.1126 / science.aat3803