Excitons are bonded pairs of electrons and holes in a solid, which, in principle, can be used in
Holes are the absence of an electron, and therefore theycarry a charge opposite to the electron. Opposite charges attract, and electrons and holes bond together to form excitons, which can then move through the material.
Keshav Dani, first author of the study and professor who heads the department of femtosecond spectroscopy
In ordinary semiconductors, excitons are extinguishedin about a few billionths of a second. In addition, they can be “fragile”, which makes them difficult to study. But about ten years ago, scientists discovered two-dimensional semiconductors: excitons are more stable in them.
Strong excitons give these materialstruly unique properties, which is why a lot of research has been carried out around the world using two-dimensional semiconductors in order to create new optoelectronic devices. However, these works were seriously hampered by insufficient technical equipment.
Scientists have long known that only one typeexcitons, called bright excitons, can interact with light. But there are other, so-called dark excitons, that have not been seen until now. To visualize dark excitons, scientists modified a powerful technique that had previously been primarily used to study single, unbound electrons.
The research team suggested:If a beam of light containing photons of high enough energy is used to strike excitons in a semiconductor material, the photon energy will destroy the excitons and knock electrons out of the material. By measuring the direction in which the electrons fly out of the material, it will be possible to determine the initial momentum of the electrons when they were part of the excitons. Thanks to this method, scientists will be able not only to see, but also to distinguish bright excitons from dark ones.
As a result, it turned out that darkThere are more excitons in a semiconductor than light excitons. And under certain conditions, light excitons can become dark and vice versa. Now scientists want to create stable excitons, which they believe can give materials unique properties.
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