PhysOrg reports scientists have discovered that silicon with high concentrations of metals like copper, nickel and iron, can exhibit the strange property of "retrograde melting", which means it melts as it cools down. The discovery may be useful in lowering the production cost of some silicon-based chips and solar cells.
The material, a compound of silicon, copper, nickel and iron, "melts" (actually turning from a solid to a slush-like mix of solid and liquid material) as it cools below 900 degrees Celsius, whereas silicon ordinarily melts at 1414 degrees C. The much lower temperatures make it possible to observe the behavior of the material during melting, based on specialized X-ray fluorescence microprobe technology using a synchrotron -- a type of particle accelerator -- as a source.
The findings could be useful in lowering the cost of manufacturing some silicon-based devices, especially those in which tiny amounts of impurities can significantly reduce performance. In the material that Buonassisi and his researchers studied, impurities tend to migrate to the liquid portion, leaving regions of purer silicon behind. This could make it possible to produce some silicon-based devices, such as solar cells, using a less pure, and therefore less expensive, grade of silicon that would be purified during the manufacturing process.