报告题目：Phase-change memory materials under high pressure
报告人：Ming Xu （徐明）
 
报告时间：2015年12月30日（星期三）14：00
报告地点：M255
 
摘要：
The binary phase change memories, which take advantage of the resistive contrast between the amorphous and the crystalline phases, will eventually give way to the high-capacity multi-state memories, in which both phases can reach various resistive states. Recent studies demonstrated that these multiple resistive states can be achieved in crystalline phase change materials (PCMs), by manipulating the vacancies in Ge-Sb-Te (GST) system and controlling the disorder with different annealing temperatures. In lieu of the heat treatment, our large-scale ab initio molecular dynamics (AIMD) simulations show that pressure can also tune the disorder in crystalline PCMs. Our models contain 1008 atoms of rocksalt-like GeSb2Te4 with random distribution of vacancies, and the AIMD simulations were performed at various temperatures and pressures for about 100 ps. We observed that, by lowering the migration energy for the anti-site hopping (e.g., Te ions jump to the Ge/Sb layers and Sb ions hop to the Te layers), the high pressure increases the compositional disorder due to the accumulation of these anti-site ions, resulting in some localized electronic states near the bottom of the conduction band. On the other hand, the disorder leads to the unorienteddisplacement of the anti-site ions, distorting and destabilizing the lattice near them. The disorder-induced electron localization triggered by pressure will pave the way for the understanding and development of the multi-state memory devices. And the random distortion of lattices due to the compositional disorder offers a new mechanism that may contribute to the amorphization of crystalline PCMs at high pressure.
 
个人简介：
徐明，德国亚琛工业大学博士后研究人员，洪堡学者。曾在复旦大学获得学士和硕士学位，并在美国约翰霍普金斯大学获得博士学位。曾先后师从著名材料学家马恩教授，著名相变存储权威Matthias Wuttig教授对相变材料进行多年深入的研究。首次利用第一性原理精确的确定了玻璃态的相变材料结构，首次利用压力对玻璃态和晶态的相变材料的结构和性质进行调节。成果发表在Physical Review Letters，PNAS，Advanced Science等权威期刊上。
 
联系人：尚大山 副研究员 （9088）