基于二维晶体－铁电／铁磁异质结的新型电子器件

Graphene and 2D crystals will remain as a hype-active and exciting research area for the following decade. The exploration of new 2D materials and the innovations in device concepts will bring not only disruptive development in technologies but also breakthroughs in fundamental research. For examples, graphene-boron nitride superlattices show recursive mimibands in quantum Hall effects (Hofstadter's butterfly), and transition metal dichalcogenide-graphene heterojunctions show extremely high photovoltaic quantum efficiency. Besides such van der Waals heterojunctions formed by different types of 2D crystals, there are also scarce efforts in developing heterostructures of 2D crystals and functional materials..This proposal is focusing on novel electronic devices based on 2D crystal-ferroelectric/ferromagnetic heterostructures. Using ferroelectric dipoles and/or magnetic proximity effect, we can non-invasively modify the physical properties of 2D crystals, and thus explore new device concepts and functionalities. In particular, we will develop flexible 2D crystal-ferroelectric touch panels and non-volatile memory with high performance, and use ferroelectric polymer gating to create atomically thin p-n junctions with one monolayer of 2D crystals and to study the quantum Hall effect of graphene under localized strong electric dipoles. The combinations of 2D crystals and ferromagnetic substrates may be promising in developing novel electron spin-based electronic devices, such as spin Hall magnetoresistance devices and spin-wave Seebeck effect devices. The development of 2D crystal-ferromagnetic electronic devices will also allow us to study fundamental physics, such as the scattering and relaxation mechanism of electron spins in graphene, and the magnetic proximity effect on an atomic layer.

石墨烯和二维晶体将是未来数十年科学研究的热点方向。新的二维材料的制备和器件结构的创新不仅会带来电子器件应用上的“破坏性”(disruptive)发展,而且往往伴随着革命性的基础物理实验上的突破。二维晶体当前研究的一个重点是不同的二维材料形成的异质结,但是二维晶体和功能材料的异质结研究并没有得到很大发展。.本课题的研究方向是基于二维晶体-铁电/铁磁异质结结构的新型电子器件。通过异质结的构造,用铁电和铁磁材料来调控二维晶体本身的物性,从而实现新的电子器件结构原型以及研究新奇的二维维度下的凝聚态物理现象。铁电聚合物可以在二维材料内引入非挥发性的超高掺杂，结合其高透光和可弯曲性，可以做柔性的触摸屏和非挥发性存储器。通过控制铁电极化有序度，可以研究石墨烯在局域化的极强电偶极子影响下的量子化行为。二维晶体－铁磁异质结可以用来研究基于电子自旋的新型电子器件，并以此来研究自旋的散射和近场交换机制。

本项目的申请构想为构筑石墨烯/二维晶体和功能材料的异质结，用铁磁和铁电等功能材料的物性来调控二维晶体本身的性质,从而实现新的电子器件结构原型以及研究新奇的二维维度下的凝聚态物理现象。自2015年本项目开展以来，新的二维晶体和功能材料概念层出不穷，如拓扑概念的兴起和外尔半金属的发现；从2017年开始，传统铁磁和铁电功能材料也发现存在异常丰富的二维范德瓦尔斯晶体的形式。.针对这些新的研究热点和趋势，本课题不仅按照项目申请书的内容展开，并对研究进程中发现的一些有趣的点深入展开，进而取得了一定的亮点成果: 一种新的制备二维主族元素化合物异质结的方法；而且及时调整了研究内容，在新的二维铁磁、铁电和多铁共存晶体的发现与物性，二维磁性拓扑半金属，以及石墨烯/多铁隧穿器件等方向做出了非常有新意的工作。