Physicists “aged” quantum crystals

(ORDO NEWS) — Scientists from the Moscow Institute of Physics and Technology and the Institute for Problems of Chemical Physics of the Russian Academy of Sciences have proposed a simple and convenient way to obtain quantum dots of a certain size using chemical aging. This will help experimental physicists to obtain quantum dots of the required size much easier, easier and cheaper.

Colloidal quantum dots are nanoscale crystals whose properties – the frequency of absorbed or emitted electromagnetic waves – depend on size. They are used for the manufacture of solar panels, televisions, fire detectors.

At the Laboratory of Photonics of Quantum-Dimensional Structures of the Moscow Institute of Physics and Technology, colloidal quantum dots of lead sulfide are being studied. The standard process for their synthesis is carried out by mixing, under certain conditions, two precursor substances containing sulfur and lead. With the help of special equipment and chemical reagents, this process is controlled, obtaining quantum dots of a certain size. However, this method is complex, expensive, and not all point sizes can be obtained with it.

“If physicists needed quantum dots, and they did not have their own equipment to obtain them, they used to have to fork out heavily for custom-made synthesis or order from foreign catalogs. In addition, not all outlet sizes can be purchased or ordered. We were looking for a way that would make it possible to obtain quantum dots of lead sulfide of the required size and, therefore, the necessary properties as simply and cheaply as possible, without additional equipment and special skills,” says Ivan Shukhov, deputy head of the laboratory of photonics of quantum-dimensional structures at MIPT.

Experimenting with various substances, the researchers found that in the presence of a mixture of oleic acid and oleylamine, the spectrum of quantum dots changes. Further examination using electron microscopy showed that in the presence of this mixture, the standard synthesis proceeds in the opposite direction. Sulfur and lead atoms “run away” back into the solution, while quantum dots “age” and become smaller. At the same time, their size distribution is preserved. In other words, the same quantum dots are obtained as before exposure to the mixture, only smaller. Accordingly, their properties are also different. Research results published in the journal Materials Today Chemistry…

Aging of crystals is a generally accepted term that implies a stable change in the characteristics of materials over time
Oleic acid and oleylamine are separately used in standard quantum dot synthesis. However, it was the simultaneous use and interaction of these two substances that made the controlled aging of crystals possible.

“We have proposed a solution thanks to which experimenters, having quantum dots of 10 nanometers in size, can age them tomorrow to 8 nanometers, the day after tomorrow – to 6 nanometers, and so on. At the same time, their absorption will change from 2 microns to 1.8 microns during the first aging and to 1.5 microns during the second. That is, from one can within a very short time and with the help of very simple operations it becomes possible to obtain colloidal quantum dots of the required size and properties, – comments Vladimir Razumov, head of the laboratory of photonics of quantum-dimensional structures at the Moscow Institute of Physics and Technology. – Our result will allow, for example, physicists, who have only test tubes from special equipment, to obtain from one available sample different samples of these colloidal quantum dots – of different sizes. Experimenters only need to wait a certain amount of time.

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