兹邀请光科系首届毕业生徐明博士（2001年入学复旦大学本科）作学术报告。徐明于2013年获得Johns Hopkins大学的博士，目前在德国WTH Aachen 大学从事博士后研究。他的报告题目是：相变存储材料结构基础以及压力对其电阻的调控。报告时间12月26日（星期五）上午9点，报告地点在电光源楼301会议室。
    附件是徐博士报告摘要与简历。

相变存储材料结构基础以及压力对其电阻的调控

徐明

I. Institute of physics (IA), RWTH Aachen University, 52056 Aachen, Germany

Abstract

Phase-change materials (PCMs) exist in at least two phases under the ambient condition. One is the amorphous state and another is crystalline phase. The distinct physical properties and the fast transformation between amorphous and crystalline phases render these materials the ability to store information. Regardless of the wide applications of PCMs, a fundamental question is yet to be solved: why GST presents so many useful features? Since the properties of a material are largely determined by its atomic structure, our first task is to fully understand the structure of the two functional phases: the amorphous and crystalline GSTs (a-GST and c-GST). High pressure is then applied to both phases to control the resistivity and ab initio molecular dynamics (AIMD) simulations are used to monitor the structural change.

Using the electron localization functions, we found that a-GST bears a right-angle local structure which is conflict with researchers’ previous notion that Ge should be in a tetrahedral environment. Such right-angle local structure can persist at low-to-medium pressure (under 8 GPa), accompanied by 4 orders of magnitude resistivity change.

The c-GST has a rocksalt (NaCl) structure, with Te occupy the anion sites and Ge/Sb/vacancies take the cation sites. Recent studies demonstrated that these multiple resistive states can be achieved in c-GST, by manipulating the vacancies and controlling the disorder with different annealing temperatures. In lieu of the heat treatment, our large-scale AIMD simulations show that pressure can also tune the disorder in crystalline c-GST. We observed that, by lowering the migration energy for the anti-site hopping, the high pressure increases the compositional disorder due to the accumulation of these anti-site atoms, resulting in some localized electronic states near the bottom of the conduction band. The disorder-induced electron localization triggered by pressure will pave the way for the understanding and development of the multi-state memory devices.

徐明简介：

Education

2008-2013        Ph.D.        Materials Science & Engineering,       Johns Hopkins University

2005-2008        M.S.         Optics,                                                       Fudan University, China

2001-2005        B.S.  Optical and Information Science,                 Fudan University, China       

Honors and Awards

2014-2015        Start-up funding for junior researchers               WTH Aachen University, Germany

2013-2015        Humboldt Postdoc Fellowship                             Germany

2008-2011        Samstag Fellowship                                             Johns Hopkins University, USA

2004                   Bursary Student                                                    University College Cork, Ireland

2002-2006        1^st class scholarship (3 times)                          Fudan University, China