Navigation Links
Nature of bonding determines thermal conductivity
Date:5/3/2011

Jlich/Aachen, 3 May 2011 - Optical data carriers such as DVDs, Blu-rays and CD-RWs store data in layers of so-called "phase change materials". In the future, these materials will enable the development of fast, non-volatile and energy-saving main memories. A prerequisite for this is a low thermal conductivity. Phase change materials display a surprisingly low thermal conductivity even in the crystalline state. This is described by an international research team including scientists from Jlich and Aachen in the latest edition of the respected journal Advanced Functional Materials (DOI: 10.1002/adfm.201002274). Their findings will facilitate a targeted search for materials with the desired properties.

Phase change materials are among the favourite candidates for developing a "universal memory", which is as fast as DRAM (dynamic RAM), has high storage density, is always ready for use and does not lose data even when inadvertently turned off. The data is stored in tiny areas of different electrical resistance, which are written to by heating with the aid of electric pulses. In doing so, the atomic ordering of the material and its electrical resistance is changed.

When heated, phase change materials switch from the unordered (amorphous) to the ordered (crystalline) state, which leads to a change in their physical properties. This feature has been exploited by industry for many years in optical data carriers such as DVDs, Blu-rays and CD-RWs. By means of a laser, the atomic structure and thus the optical properties are changed in minute areas of the discs. This allows bits to be written to the disc and be read out again by a laser.

"In order to produce energy-saving and tightly packed electronic memories, it is important when the data are written to the disc that the electrical resistance is significantly changed but that the energy remains as localized as possible," explains Dr. Raphal Hermann from the Jlich Centre for Neutron Science, who is also currently a visiting professor at the University of Lige. "Phase change materials are very well suited because they are poor conductors of heat not only in the unordered but also in the ordered state, in contrast to semiconductors, for example," adds Prof. Matthias Wuttig from RWTH Aachen University. As part of an international research team, Hermann and Wuttig are investigating the reasons for this surprising material behaviour on alloys of germanium, antimony and tellurium. With the aid of sophisticated scattering experiments at the European Synchrotron Radiation Facility (ESRF) in Grenoble, they demonstrated that the bonding conditions between the atoms in the crystalline state as well as deviations from the perfect lattice structure influence the transmission of these vibrations through the material and thus reduce its thermal conductivity.

"The starting point for our investigations was the observation by our Japanese colleagues that the amorphous material is harder than the crystalline," says Hermann. "This contradicted all assumptions, but the measured stronger bonding forces between the atoms in the amorphous state fitted the picture." The Jlich scientists investigated how the atoms in the specimens vibrate both locally in the atomic range and also over longer distances. "In the crystalline material, we found harder vibrations for the long-range order and better conductivity for sound than in amorphous material. This is normal and is related to an increase in the order. However, we were surprised by the results for short-range vibrations in the crystal. They were softer. The short-range order in crystalline material is therefore lower than in amorphous material. This is very unusual."

On the basis of all the experimental results, the Aachen research group headed by Wuttig developed a model to explain the apparent contradictions. "Normally, the propagation of sound waves in material correlates with the thermal conductivity. However, this is not the case with phase change materials. This is due to the fact that in the crystalline state atoms experience resonance bonding in other words, the bonding electrons are shared between several atomic pairs. In contrast, in amorphous material the atoms are covalently, that is more strongly and more locally, bonded. The crystalline material is therefore softer and the atoms vibrate more gently. In addition, there is more disorder in the local range. Both of these aspects impair the conductivity for heat carriers, which are partially of short wavelength, but not for the long-wavelength sound waves." The researchers assume that their findings will facilitate a targeted search for materials with the desired properties.


'/>"/>

Contact: Angela Wenzik
a.wenzik@fz-juelich.de
49-246-161-6048
Helmholtz Association of German Research Centres
Source:Eurekalert

Related biology technology :

1. DOE JGI Director Eddy Rubin highlights the genomics of plant-based biofuels in the journal Nature
2. Natures Premium(R) Brand First Fresh Pork in North America to Carry DNA TraceBack(R) Seal of Authenticity
3. James L. Wittliff, Ph.D., FACB, to Present Predicting Breast Cancer Outcome with Gene Expression Signatures on the Ziplex(R) System at the Association for Molecular Pathology Conference, October 30
4. Genetic clock makers at UC San Diego publish their timepiece in Nature
5. MySignatureBook Certified Compliant With SAFE-BioPharma Digital Standard(TM)
6. Webcast Alert: Regulus Therapeutics, Alnylam Pharmaceuticals and Isis Pharmaceuticals Announce New Nature Publication on miR-21 Conference Call
7. Nature Medicine study shows Peregrines bavituximab can cure lethal virus infections
8. Research Published in Nature Medicine Shows Disruption of Chemokine Interactions Inhibits Atherosclerosis in Mice
9. Data Published in Nature Cell Biology Reveal Novel Function of Drug Target EpCAM in Cancer Cell Signalling
10. Light-speed nanotech: Controlling the nature of graphene
11. Nature Reviews Publishes Article About Jennerexs Multi-Mechanistic Cancer Therapeutic
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:2/12/2016)... 12, 2016 Biocom, the association representing the ... group of San Diego companies to ... 2016 Precision Medicine Advocacy Fly-In. Biocom Fly-In participants had the ... Administration (FDA), the Centers for Medicare and Medicaid Services (CMS), ... Diego U.S. Representatives Susan Davis and Scott ...
(Date:2/12/2016)... 12, 2016 MedGenome,s Commitment ... Scientific Understanding of Complex Diseases Such as Cancer, ... --> --> MedGenome, ... and a leading provider of genomics research services ... to the GenomeAsia 100K consortium as a founding ...
(Date:2/11/2016)... Germany and GERMANTOWN, Maryland ... ; Frankfurt Prime Standard: QIA) today announced the introduction ... for gene expression profiling, expanding QIAGEN,s portfolio of Sample ... enable researchers to select from over 20,000 human genes ... interactions between genes, cellular phenotypes and disease processes. ...
(Date:2/11/2016)... New York, NY (PRWEB) , ... ... ... International (BPI), a business-to-business publication dedicated to delivering cutting-edge information focused on ... GE Healthcare Life Sciences to become a premier sponsor of the 2016 ...
Breaking Biology Technology:
(Date:2/3/2016)... , February 3, 2016 ... market research report "Automated Fingerprint Identification System Market by ... Search), Application (Banking & Finance, Government, Healthcare, and Transportation) ... MarketsandMarkets, the market is expected to be worth USD ... 21.0% between 2015 and 2020. The transformation and technology ...
(Date:2/3/2016)... , Feb. 3, 2016 ... the addition of the "Emotion Detection ... Machine Learning, and Others), Software Tools (Facial ... Areas, End Users,and Regions - Global forecast ... --> http://www.researchandmarkets.com/research/d8zjcd/emotion_detection ) has ...
(Date:2/2/2016)... This BCC Research report provides a ... the recent advances in high throughput ‘omic platforms ... forward. Includes forecast through 2019. Use ... opportunities that exist in the bioinformatic market. Analyze ... well as IT and bioinformatics service providers. Analyze ...
Breaking Biology News(10 mins):