ホーム > 広報活動 > イベント・セミナー > 2015年 > 第9回情報統合型研究交流会・一般公開シリーズ (6) - Nanosecond simulations of amorphous-to-crystalline transition by density functional theory - Prof. Jaakko Akola

第9回情報統合型研究交流会・一般公開シリーズ (6)
- Nanosecond simulations of amorphous-to-crystalline transition by density functional theory - Prof. Jaakko Akola

開催日: 2015.11.30 終了


第9回情報統合型研究交流会・一般公開シリーズ (6)

日 時

2015年11月30日(月) 15時00分~16時00分

場 所

物質・材料研究機構
千現地区 8階 特別応接室

講演者

Prof. Jaakko Akola
Department of Physics,
Tampere University of Technology, Tampre, Finland


講演概要

Title:
Nanosecond simulations of amorphous-to-crystalline transition by density functional theory
Abstract:
Phase-change (PC) materials are chalcogenide alloys that are ubiquitous in the world of rewritable optical storage media, familiar examples being digital versatile disc (DVD-RW) and Blu-ray Disc. Nanosized bits in a thin polycrystalline layer are switched reversibly and extremely rapidly between amorphous (a) and crystalline (c) states by laser irradiation or resistive heating, and the state can be identified by changes in resistivity or optical properties. The rate-limiting process in PC optical memories is the extremely rapid (nanosecond time scale) crystallization of nanosized amorphous “marks” in a polycrystalline layer. Our knowledge of the amorphous and ordered structures of Ge/Sb/Te and Ag/In/Sb/Te alloys has improved significantly in recent years and has led to plausible pictures for the transition between them. Nevertheless, the simulation of the actual crystallization process is complicated by the need to study large numbers of atoms over time scales that are difficult to attain, even with modern supercomputers. We have performed a series of density functional/ molecular dynamics (DF/MD) simulations on a sample of Ge2Sb2Te5 (GST-225) with 460 atoms. Simulations at 500 K, 600 K, and 700 K have been performed for up to 600 picoseconds in samples where crystallization was promoted by fixing the structure of a crystalline "seed", and for over 5 ns in four samples at 600 K without constraints. A comparison of the last four simulations shows a striking memory effect where crystallization is favored in an amorphous sample that had previously been crystallized.
[1] J. Kalikka, J. Akola, J. Larrucea, and R.O. Jones, Phys. Rev. B 86, 144113 
[2] J. Kalikka, J. Akola, and R.O. Jones, Phys. Rev. B 90, 184109 (2014).


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イベント・セミナーデータ

イベント・セミナー名
第9回情報統合型研究交流会・一般公開シリーズ (6)
- Nanosecond simulations of amorphous-to-crystalline transition by density functional theory - Prof. Jaakko Akola
会場
物質・材料研究機構
千現地区 8階特別応接室
開催日: 時間
2015.11.30
15:00-16:00
参加料
無料

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