X-raying a DVD

Little is known about the detailed structural changes that take place when data are stored and retrieved - the read-write process - on an optical disc like a DVD. Now, researchers in Finland, Germany and Japan have used a synchrotron to study the materials used in DVDs.

The polycrystalline 'data' layer in DVD-RAM and Blu-Ray discs comprises several different materials including, commonly, germanium (Ge), antimony (Sb) and tellurium (Te), the so-called 'GST' elements. Rewritable DVDs (DVD-RW) use 'AIST' alloys, first developed by Ricoh in Japan and which contain small amounts of silver (Ag) and indium (In) as well as antimony and tellurium. The material as a whole can be a disordered, amorphous or an ordered, crystalline structure. Laser action lasting just nanoseconds triggers a transition between these two phases, recording or deleting bits of data.