Two-faced liquid silicon
doi:10.1038/nindia.2011.72 Published online 19 May 2011
Researchers have found that liquid silicon can actually transform between two different 'phases' — one at low temperature and pressure and one at high temperature and pressure.
The liquid that exists at low temperatures and pressures has an atomic structure very close to the tetrahedral geometry of its crystal. At high temperatures, the liquid has substantially different structure. The finding has deeper implications for the mechanism of crystal formation.
Such novel phase transition has been proposed to exist between two forms of a liquid in a variety of substances such as water, silica and the technologically important element silicon. Experimental verification has been very difficult and computer simulations have played a very significant role in probing the existence of such a transition.
The similarity between these substances is that their atoms or molecules have loose packed energetically favorable arrangements.
Using computer simulations, a team of theoretical physicists from the Jawaharlal Nehru Centre for Advanced Scientific Research in Bengaluru investigated the possibility of such transition in case of silicon. They found clear evidence that a transition between two liquids exists with the associated critical point at negative pressures.
"A striking conclusion is that the phase behaviour of apparently diverse substances such as water and silicon are very similar. The presence of two liquid forms, under conditions in whichthe crystal is the stable form of the silicon, has consequences for mechanisms of crystal formation," says lead researcher Srikanth Sastry.
The finding may suggest novel avenues for making silicon in the crystal phase as well asdifferent forms of amorphous silicon. The possibility of the multiple liquid states into which silicon may transform, in addition to being in the crystal phase, may also have implications for device applications.
- Vasisht, V. V. et al. Liquid–liquid critical point in supercooled silicon. Nat. Phys. doi: 10.1038/NPHYS1993 (2011)