Smart crystals guard surveillance cameras

17 Jun 2002

Small crystals of 'smart' materials embedded into a coating can make the surface change from transparent to reflective when bright light shines on it. This technology could protect sensitive optical equipment, such as surveillance cameras on satellites, from accidental damage or sabotage.

Lynn Boatner and colleagues at Oak Ridge National Laboratory in the US have patented this new material that contains nanoscale crystals of compounds such as vanadium oxides. They are embedded into an optically transparent host like aluminium oxide by ion implantation followed by thermal treatment. Intense light heats up the crystals, which causes them to undergo a rapid phase transition, changing the compound's resistivity by several orders of magnitude. The overall effect is a dramatic change from optically transparent to metallic, reflecting light from the surface. The particles absorb light over a fairly large range of wavelengths but work particularly well for longer wavelengths.

The nanocomposite material is more robust than other 'smart' materials because the crystals are an integral part of the surface. Boatner explained that these properties can be enhanced if the crystals are embedded into another crystalline material. The embedded crystals line up with the host crystal structure so that they all have the same orientation in the lattice. They can also be embedded into glasses.

Boatner also predicted applications in couplers and optical switches.

The team has made initial contacts with companies and is looking at device applications in electro-optics and magnetic storage.

SH