It's the second most-abundant element in the Earth's crust as well as the key to modern technology – used in the integrated circuits that power such electronics as computers, mobile phones, and even some toasters and refrigerators. It's also used in compound form in building, ceramics, breast implants, and many other areas. And now the ubiquitous element may have a plethora of new applications, thanks to a team of Carnegie scientists who synthesized an allotrope (new/different physical form) with the chemical formula Si24.
The diamond-structured form of silicon normally used in technology applications has a semiconducting property called an indirect band gap, which differs from a direct band gap in that it requires an extra step to excite bound electrons into a free state so that they can participate in electrical conduction. Direct band gap semiconductors need only two entities to intersect; a photon imparts momentum on an electron. But indirect band gap semiconductors require a third entity – a lattice vibration called a phonon – because the minimum energy state of the conduction band and the maximum energy state of the valence band occur at different values of momentum.