大型放射光施設 SPring-8

日時: 2009年12月9日(水) 13: 30-15: 00

場所: 普及棟大講堂

Speaker: J. Akola

Language: English

Affiliate: Nanoscience Center, Department of Physics, FI-40014 University of Jyv.skyl., Finland
Department of Physics, Tampere University of Technology, FI-33101 Tampere, Finland

Title: Density functional / molecular dynamics simulations of phase-change materials: characterization of amorphous phases

Abstract:
The technological applicability of phase-change materials (PCM) is based on the rapid amorphous-to-crystalline transition and subsequent changes in optical (and electrical) properties. The structure of the amorphous phase poses the main problem for scientists and is difficult to tackle both experimentally and theoretically. In this talk, I shall present theoretical results for the amorphous and disordered phases of PCMs which were obtained by performing massively-parallel density functional (DF) / molecular dynamics (MD) simulations on the IBM Blue Gene supercomputers in Forschungszentrum J.lich, Germany.
I shall first discuss the theoretical methods and their limitations, and especially in the context of DF methods and available exchange-correlation functionals. Tellurium is the basis of most PCMs, and it has turned out that elemental Te with an anomalous density maximum at the melting point provides a good example in this context. Among PCMs, we have studied most extensively the Ge₂Sb₂Te₅ alloy (GST-225, DVD-RAM), where a full melt-quench simulation has provided us a consistent view of the structural and electronical properties as well as the amorphous-to-crystalline transition. I also present results for two technologically important PCMs: Ge₈Sb₂Te₁₁ (GST-8,2,11, Blu-ray Disc) and Ag_3.5In_3.8Sb_75.0Te_17.7 (AIST, DVD±RW) alloys.

担当者: 小原真司
PHS: 3910
E-mail: kohara@spring8.or.jp