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 New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>