Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Supercomputer unravels structures in DVD materials

10.01.2011
First model of rapid phase change in storage material

Although 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, researchers from Jülich, 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)


Model of crystallization of AIST alloy in a DVD.
Upper left: a laser pulse (hv arrow) causes motion of the central antimony atom (left), which then exchanges its bonds to two neighbours.
Upper right: The green vector sum of the three short red bonds changes.
Below: A sequence of such processes leads from the amorphous (left) to the crystalline form (right). Illustration: Forschungszentrum Jülich

Information is stored 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 Jülich, 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 Jülich 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.

The phase change in AIST alloys proceeds from the outside of the bit, where it adjoins the crystalline surroundings, towards its interior. In Nature Materials, the team explains this using a "bond exchange model", where the local environment in the amorphous bit is changed by small movements of an antimony atom (see figure). A sequence of many such steps results in reorientation (crystallization), without requiring empty regions or large motions. The antimony atoms, stimulated by the laser pulse, have simply exchanged the strengths of the bonds to two neighbours, hence the name „bond exchange" model.

The team had clarified the phase transition in GST materials in earlier work (DOI: 10.1103/PhysRevB.80.020201). Here the amorphous bit crystallizes via nucleation, i.e. small crystallites formed in the interior grow rapidly until they covered the whole bit. The speed of the transition can be explained by observing that amorphous and crystalline phases contain the same structural units, "„ABAB" rings. These four-membered rings contain two germanium or antimony atoms (A) and two tellurium atoms (B) and can rearrange in the available empty space without breaking many atomic bonds.

The calculation of the structure of amorphous AIST is the largest yet performed in this area of research, with simulations of 640 atoms over the comparatively long time of several hundred picoseconds. Some 4000 processors of the Jülich supercomputer JUGENE were used for over four months in order to obtain the necessary precision. In addition to sheer computing power, however, experience in scientific computing and the simulation of condensed matter is essential. Jones notes: "Forschungszentrum Jülich is one of the few places where all these aspects come together."

The deeper theoretical understanding of the processes involved in writing and erasing a DVD should aid the development of phase change storage media with longer life, larger capacity, or shorter access times.

More information on Jülich solid-state research
http://www.fz-juelich.de/iff/
Homepage of Nature Materials:
http://www.nature.com/nmat/index.html
Further information on the topic at:
http://www.fz-juelich.de/portal/index.php?cmd=show&mid=715&index=163
Contact:
Dr. Robert Jones
Tel.: +49 2461 61-4202
r.jones@fz-juelich.de
Press contact:
Kosta Schinarakis
Tel.: +49 2461 61­4771
k.schinarakis@fz-juelich.de
Forschungszentrum Jülich…
pursues cutting-edge interdisciplinary research addressing pressing issues facing society today while at the same time developing key technologies for tomorrow. Research focuses on the areas of health, energy and environment, and information technology. The cooperation of the researchers at Jülich is characterized by outstanding expertise and infrastructure in physics, materials science, nanotechnology, and supercomputing. With a staff of about 4 600, Jülich – a member of the Helmholtz Association – is one of the largest research centres in Europe.

Dr. Robert Jones | EurekAlert!
Further information:
http://www.fz-juelich.de

More articles from Physics and Astronomy:

nachricht Light-emitting bubbles captured in the wild
28.02.2017 | Georg-August-Universität Göttingen

nachricht Scientists reach back in time to discover some of the most power-packed galaxies
28.02.2017 | Clemson University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Light-emitting bubbles captured in the wild

28.02.2017 | Physics and Astronomy

Triboelectric nanogenerators boost mass spectrometry performance

28.02.2017 | Materials Sciences

Calculating recharge of groundwater more precisely

28.02.2017 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>