Supercomputer unravels structures in DVD materials

Eventhough the storage of films and music on a DVD is part of our digital world, the physical basis of the storage mechanism is not understood in detail. In the current issue of the leading journal Nature Materials, scientists from J�lich, Finland, and Japan provide insight into the read and write processes in a DVD. This knowledge should enable improved storage materials to be developed. (DOI: 10.1038/NMAT2931).

Storage of information is done in a DVD in the form of microscopic bits (each less than 100 nanometres in size) in a thin layer of a polycrystalline alloy containing several elements. The bits can have a disordered, amorphous or an ordered, crystalline structure. The transition between the two phases lasts only a few nanoseconds and can be triggered by a laser pulse. Common alloys for storage materials such as DVD-RAMs or Blu-ray Discs contain germanium (Ge), antimony (Sb) und tellurium (Te) and are known as GST after the initials of the elements. The most popular alloys for DVD-RW are AIST alloys, which contain small amounts of silver (Ag) and indium (In) as well as antimony (Sb) and tellurium (Te).

"Both alloy families contain antimony and tellurium and appear to have much in common, but the phase change mechanisms are quite different", explains Dr. Robert Jones of Forschungszentrum J�lich, who has collaborated with an international team on the problem. In addition to experimental data and x-ray spectra from the Japanese synchrotron SPring-8, the world's most powerful x-ray source, the team used extensive simulations on the J�lich supercomputer JUGENE. The combination of experiment and simulations has enabled the structures of both phases to be determined for the first time and allowed the development of a model to explain the rapid phase change.........