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:5/27/2016)... ... May 27, 2016 , ... Doctors in Italy, Japan, ... studies on the BRCA-1 associated protein (BAP1) gene and its link to malignant mesothelioma. ... Click here to read the full article now. , The studies analyzed for ...
(Date:5/27/2016)... At present, the Biotech sphere is ... know that volatility is what makes this industry interesting to ... Pharmaceuticals Corp. (NASDAQ: SNTA ), CTI BioPharma Corp. ... LPTN ), and Heat Biologics Inc. (NASDAQ: HTBX ... alerts for these stocks at: http://www.activewallst.com/register/ ...
(Date:5/26/2016)... New Jersey and READING, ... Indegene ( http://www.indegene.com ), a leading ... to life science, pharmaceutical and healthcare organisations and ... of innovative scientific support throughout the product lifecycle, ... with the launch of IntraScience.      ...
(Date:5/26/2016)... Despite the volatility that continues to ... Today,s pre-market research on ActiveWallSt.com directs the investor community,s focus ... RDUS ), Cerus Corp. (NASDAQ: CERS ), ... Prime Therapeutics Inc. (NASDAQ: FPRX ). Register with ... http://www.activewallst.com/ On Wednesday, shares in ...
Breaking Biology Technology:
(Date:3/21/2016)... , March 22, 2016 ... recognition with passcodes for superior security   ... a leading provider of secure digital communications services, today ... biometric technology and offer enterprise customers, particularly those in ... facial recognition and voice authentication within a mobile app, ...
(Date:3/15/2016)... , March 15, 2016 --> ... published by Transparency Market Research "Digital Door Lock Systems Market ... 2015 - 2023," the global digital door lock systems market ... in 2014 and is forecast to grow at a CAGR ... micro, small and medium enterprises (MSMEs) across the world and ...
(Date:3/14/2016)... , Allemagne, March 14, 2016 ... http://www.apimages.com ) - --> - Renvoi : ... - --> --> ... solutions biométriques, fournit de nouveaux lecteurs d,empreintes digitales ... LF10 de DERMALOG sera utilisé pour produire des ...
Breaking Biology News(10 mins):