Scientists find 50nm conductive particle Steve BushUK and Dutch scientists have discovered the largest conductive particle yet. Called atrion (rhymes with prion), it consists of two electrons and a hole and is 50nm across– nuclei in typical semiconductors are 0.3nm apart, an electron is 10-22m acrossaccording to Toshiba.
The collaboration is between Toshiba Research Europe and the Universities of Cambridgeand Nijmegen. A trion, the biggest charged electrical particle so far discovered, can be formed when a laser creates an electron-hole pair in an electron-rich quantum well. The hole attracts a further electron and the electron-electron-hole triplet can be detected drifting in an electric field before it decays into an electron and a photon.
The two electrons attach to the hole in the semiconductor in much the same way aselectrons to the nucleus of an ion, said Toshiba. "It is a bit like a hydrogenion," said Dr Andrew Shields of Toshiba. "It forms when an electron joins anelectron-hole pair. The electron is more attracted to the hole than repelled by the otherelectron."
When a voltage is applied all three particles are found to move through thesemiconductor together.
"It is an exciton. We call it a charged exciton or trion. An electron-hole pair isa neutral exciton which does not move in a field," said Shields.
"It actually moves surprisingly quickly for such a large particle, only threetimes slower than an individual electron," said professor Michael Pepper, jointmanaging director at Toshiba.
The trion was made by shining a laser onto GaAs to make electron-hole pairs, thenadding another electron in a quantum well of a transistor structure, according to Shields.
The trion only lasts for about 1ns before one of the electrons falls into the hole, butbefore this happens, it can be moved a few micrometres indicating that is it indeedcharged, said Shields.
Previously it was thought that such a large particle would be fixed by imperfections inthe semiconductor, but the new findings have shown this is not the case.
Evidence for trion existence comes from the characteristic photon emitted oncombination - which differs from that emitted by recombination in a neutral exciton.
Shields said that trions could be used as temporary mobile photon stores in futuredevices, and that they can in principle be made entirely electrically.
"For instance, in the future it may be possible to use this phenomenon to makelight sources where we can modulate the output intensity or wavelength by moving thetrions around in the chip," he said.