In advanced electronic products found in solar panels, camera sensors, and medical imaging tools, tiny, easy-to-produce particles called quantum dots may soon replace more expensive single-crystal semiconductors. Although quantum dots have begun to enter the consumer market in the form of quantum dot TVs, there has been uncertainty about the quality of quantum dot TVs for a long time, hindering their development. Now, a new measurement technique developed by researchers at Stanford University may eventually eliminate these doubts.
Traditional single crystal semiconductors are grown under special conditions in a vacuum. We can manufacture these crystals in large quantities in Frask's laboratory, and we have proven that they are as good as the best single crystals, says David Hanifi, a chemistry graduate student at Stanford University.
The researchers focused on how effectively quantum dots re-emit the light they absorb, which is an indicator of the quality of semiconductors. Although previous research on the efficiency of quantum dots implies the high performance of quantum dots, this is the first measurement method to confidently prove that quantum dots can compete with single crystals.
The result of this work is a collaborating laboratory Alberto Salleo Professor of Materials Science and Engineering at Stanford University and Paul Alivisatos Samsung Distinguished Professor of Nanoscience and Nanotechnology, a senior author of the pioneering research paper at the University of California Berkeley Quantum Dots. Alivisatos emphasized how measurement technology can lead the development of new technologies and new materials, and these new technologies and new materials require us to understand the efficiency of semiconductors to a large extent.
Between 99 and 100
Being able to abandon expensive manufacturing equipment is not the only advantage of quantum dots. Even before this work, there are signs that the performance of quantum dots can approach or exceed some of the best crystals. They are also highly customizable, and changing their size will change the wavelength of the light they emit, which is a useful feature for color-based applications, such as labeling biological samples, televisions, or computer monitors.
Despite these advantages, the small size of quantum dots means that billions of quantum dots may be required to complete the work of a large, perfect single crystal. Making so many such quantum dots means that there are more opportunities to cause something to grow abnormally, and it also means that there are more opportunities for defects that may hinder performance. Previous techniques for measuring the quality of other semiconductors have shown that quantum dots emit more than 99% of the light they absorb, but this is not enough to answer questions about their potential defects. To do this, researchers need a measurement technique that is more suitable for accurately evaluating these particles.
Hanifi said that we want to measure the emission efficiency in the range of 99.9% to 99.999%, because if semiconductors can re-emit like every photon they absorb, you can make equipment that has never been seen before.
The researchers' technique includes examining the residual heat generated by the excited quantum dots, rather than just evaluating the light emission, because the residual heat is a sign of inefficient emission. This technique, which is commonly used in other materials, has never been used to measure quantum dots in this way, and it is 100 times more accurate than other materials in the past. They found that a group of quantum dots can reliably emit 99.6% of the light they absorb (with a potential error of 0.2% in any direction), which is comparable to the best single crystal radiation.
Contrary to people's concerns, the results show that quantum dots have amazing fault tolerance. This measurement technology is also the first method that can firmly resolve the comparison between different quantum dot structures. Quantum dots have precise 8 atomic layers. A special coating material can emit light at the fastest speed. This is a An indicator of excellent quality. Alivisatos said that the shape of these dots should guide the design of new luminescent materials.
Brand new technology
This research is part of a series of projects in a department of the Energy Frontier Research Center funded by energy, which is called thermodynamic limit photonics. The center is led by Jennifer Dionne, associate professor of materials science and engineering at Stanford University. Its goal is to create optical materials that can affect the flow of light with the highest efficiency.
The next step of the project is to develop more accurate measurement methods. If researchers can determine that the efficiency of these materials reaches or exceeds 99.999%, it opens up possibilities for technologies we have never seen before. These may include new luminescent dyes to enhance our ability to study biology on an atomic scale, luminescent cooling and luminescent solar concentrators, which allows a relatively small group of solar cells to absorb energy from large areas of solar radiation. Nonetheless, the measurement methods they have established are a milestone of their own and may encourage more direct advancement of quantum dot research and applications.
Hanifi said that people working on quantum dot materials have believed that quantum dots can be as efficient as single crystal materials, and now we finally have evidence.
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