X-raying a DVD
Little is known about the detailed structural changes that take place when data are stored and retrieved
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.
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