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Understanding the phase-change mechanism of rewritable optical media

Nature Materials volume 3, pages 703–708 (2004)Cite this article

Abstract

Present-day multimedia strongly rely on rewritable phase-change optical memories. We demonstrate that, different from the current consensus, Ge2Sb2Te5, the material of choice in DVD-RAM, does not possess the rocksalt structure but more likely consists of well-defined rigid building blocks that are randomly oriented in space consistent with cubic symmetry. Laser-induced amorphization results in drastic shortening of covalent bonds and a decrease in the mean-square relative displacement, demonstrating a substantial increase in the degree of short-range ordering, in sharp contrast to the amorphization of typical covalently bonded solids. This novel order–disorder transition is due to an umbrella-flip of Ge atoms from an octahedral position into a tetrahedral position without rupture of strong covalent bonds. It is this unique two-state nature of the transformation that ensures fast DVD performance and repeatable switching over ten million cycles.

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Figure 1: Fourier-transformed EXAFS spectra for crystallized and laser-amorphized samples.
Figure 2: The crystal structure of laser-amorphized GST.
Figure 3: Raman scattering spectra for crystallized and re-amorphized Ge2Sb2Te5 layers.
Figure 4: Measured and simulated Ge-edge XANES spectra for GST for the crystalline and amorphous states.
Figure 5: Fragments of the local structure of GST around Ge atoms in the crystalline (left) and amorphous (right) states.

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Acknowledgements

The XAFS measurements were performed at beamlines 12C at the Photon Factory, Japan, and BL01B1 at SPring-8, Japan as parts of proposals 2001G332 and 2001B0099-NX, respectively. A.V.K. would like to thank A. S. Mishchenko for a useful discussion. A. I. F. acknowledges support by the US Department of Energy Grant No. DE-FG02- 03ER15477.

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Author notes

  1. Alexander V. Kolobov: On leave from: A. F. Ioffe Physico-Technical Institute, 26 Polytechnicheskaya St., 194021 St Petersburg, Russia

Authors and Affiliations

  1. Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8562, Japan

    Alexander V. Kolobov, Paul Fons & Junji Tominaga

  2. Department of Physics, Yeshiva University, 245 Lexington Avenue, New York, 10016, New York, USA

    Anatoly I. Frenkel

  3. Department of Physics, Box 351560, University of Washington, Seattle, 98195, Washington, USA

    Alexei L. Ankudinov

  4. SPring-8, Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo, 679-5198, Japan

    Tomoya Uruga

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  1. Alexander V. Kolobov
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Correspondence to Alexander V. Kolobov.

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Kolobov, A., Fons, P., Frenkel, A. et al. Understanding the phase-change mechanism of rewritable optical media. Nature Mater 3, 703–708 (2004). https://doi.org/10.1038/nmat1215

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