题目：新能源材料的人工设计与模拟计算系列之二
报告人：郑家新，王辉
时间：2013年3月21日 下午15：00-17：00
地点：北京大学深圳研究生院 G栋205室

题目（一）：石墨烯的能隙调控，界面性质，与器件模拟
报告人：郑家新   (北京大学前沿交叉学科研究院)
报告摘要：
   石墨烯具有极高的载流子迁移率，可以用于制备快速切换的晶体管。但由于石墨烯本身是零能隙的，并不适合做有效的室温场效应管，所以打开一个可控的能隙并保持较高的迁移率是石墨烯走向器件应用的关键。和逻辑器件相比，射频器件不需要较大的开关比，石墨烯射频器件应用最近引起了世界广泛的研究兴趣。在本报告中，我首先介绍我们通过第一性原理方法设计将单层石墨烯夹于双层硼氮片之间这种三明治结构，实现能隙的打开和连续可调，同时理论模拟出其场效应行为。其次介绍我们采用第一性量子输运模拟方法，预言了短沟道石墨烯场效应管的优越的射频性能。因为石墨烯的器件应用需要与金属电极接触，最后介绍我们对双层和三层石墨烯与金属接触的界面性质的系统研究工作。
 
题目（二）：Structural and electronic origin of novel-highly magnetostrictive Fe-Ga alloy
报告人：Hui Wang  Shenyang National Laboratory of Materials Science,Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110016, CHINA
报告摘要：
Magnetostrictive materials exhibiting large magneto-elastic coupling and fast mechanical response have great potential in micor-/nano-sonar, sensor, actuator and energy transducer applications. Rare earth and transition metal intermetallic alloys Terfenol-D (Tb0.3Dy0.7Fe2) are well known for their giant magnetostriction up to a few thousands ppm (μm) which have been used in practical applications in the past few decades. Heusler shape memory alloys (Ni2MnGa) exhibit large strains up to 60 mm that is mainly stemmed from magnetic-field-induced martensitic phase transition. However, besides the lack of rare-earth element and highly applied external magnetic field, their applications have been limited owing to their mechanical brittleness in nature. Therefore, the exploration of new class of materials combined high magnetostriction, excellent ductility and low-cost is indeed needed.

As one of the Fe-based magnetostrictive materials, Fe1-xGax alloy exhibits desirable mechanical properties and large tetragonal magnetostriction under lower magnetic field (~100 Oe), which make this binary alloys an intriguing candidate for sonar, sensor and actuator applications. However, the magnetostriction of Fe1-xGax alloy is still not large enough (3/2λ001 = 400 ppm) comparing with Terfenol-D and Ni2MnGa alloys, few practical applications have been reported so far. Therefore, in this report we will demonstrate density functional theory (DFT) and molecular dynamical (MD) studies on Fe-Ga alloy and try to give basic understandings of its fundamental mechanism and predictions on how to further improve its magnetostriction for future practical applications.