In a world first, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have captured an image showing the internal orbits, or spatial distribution, of particles in an exciton—a goal that had eluded scientists for almost a century.
Excitons are excited states of matter found within semiconductors.
Excitons are formed when semiconductors absorb photons of light, which causes negatively charged electrons to jump from a lower energy level to a higher energy level. This leaves behind positively charged empty spaces, called holes, in the lower energy level. The oppositely charged electrons and holes attract and they start to orbit each other, which creates the excitons. Excitons are crucially important within semiconductors, but so far, scientists have only been able to detect and measure them in limited ways. One issue lies with their fragility: it takes relatively little energy to break the exciton apart into free electrons and holes. Furthermore, they are fleeting in nature so in some materials, excitons are extinguished in about a few thousandths of a billionth of a second after they form, when the excited electrons “fall” back into the holes.
The researchers first generated excitons by sending a laser pulse of light at a two-dimensional semiconductor—a recently discovered class of materials that are only a few atoms in thickness and harbor more robust excitons.
After the excitons were formed, the team used a laser beam with ultra-high energy photons to break apart the excitons and kick the electrons right out of the material, into the vacuum space within an electron microscope.
Ultimately, the team succeeded in measuring the exciton’s wavefunction, which gives the probability of where the electron is likely to be located around the hole. (Phys.org, OIST)
The work has been published in Science Advances.
