金属衬底上高质量大面积石墨烯的插层及其机制

Intercalation and its mechanism of high quality large area graphene on metal substrate

石墨烯作为一种新型二维材料,因其优异的性质,在科学和应用领域具有非常重要的意义.而其超高的载流子迁移率、室温量子霍尔效应等,使其在信息器件领域备受关注.如何获得高质量并且与当代硅基工艺兼容的石墨烯功能器件,是未来将石墨烯应用于电子学领域的关键.近年来,研究人员发展了一种在外延石墨烯和金属衬底之间实现硅插层的技术,将金属表面外延石墨烯高质量、大面积的特点与当代硅基工艺结合起来,实现了无需转移且无损地将高质量石墨烯置于半导体之上.通过系统的实验研究并结合理论计算,揭示了插层过程包含四个主要阶段:诱导产生缺陷、异质原子插层、石墨烯自我修复和异质原子扩散成膜,并证实了这一插层机制的普适性.拉曼和角分辨光电子能谱实验结果表明,插层后的石墨烯恢复了本征特性,接近自由状态.此外,还实现了多种单质元素的插层.不同种类的原子形成不同的插层结构,从而构成了多种石墨烯/插层异质结.这为调控石墨烯的性质提供了实验基础,也展现了该插层技术的普适性.

Graphene, a two-dimensional material with honeycomb lattice, has attracted great attention from the communities of fundamental research and industry, due to novel phenomena such as quantum Hall effect at room temperature, Berry phase, and Klein tunneling, and excellent properties including extremely high carrier mobility, high Young＇s modulus,high thermal conductivity and high flexibility. Some key issues hinder graphene from being used in electronics, including how to integrate it with Si, since Si based technology is widely used in modern microelectronics, and how to place high-quality large area graphene on semiconducting or insulating substrates. A well-known method of generating largearea and high-quality graphene is to epitaxially grow it on a single crystal metal substrate. However, due to the strong interaction between graphene and metal substrate, the intrinsic electronic structure is greatly changed and the conducting substrate also prevents it from being directly used in electronics. Recently, we have developed a technique,which intercalates silicon between epitaxial graphene and metal substrate such as Ru（0001） and Ir（111）. Experimental results from Raman, angle-resolved photoemission spectroscopy, and scanning tunneling spectroscopy confirm that the intercalation layer decouples the interaction between graphene and metal substrate, which results in the recovery of its intrinsic band structure. Furthermore, we can use this technique to intercalate thick Si beyond one layer and intercalate Si between graphene and metal film, which indicates the possibility of integrating both graphene and Si device and vast potential applications in industry by reducing its cost. Besides Si, many other metal elements including Hf, Pb, Pt,Pd, Ni, Co, Au, In, and Ce can also be intercalated between graphene and metal substrate, implying the universality of this technique. Considering the versatility of these elements, we can expect this intercalation technique to have wide applications in tuning graphene properties. We also investigate the intercalation mechanism in detail experimentally and theoretically, and find that the intercalation process is composed of four steps： creation of defects, migration of heteroatoms, self-repairing of graphene, and growth of intercalation layers. The intercalation of versatile elements with different structures by this technique provides a new route to the construction of graphene heterostructures, espectially van der Waals heterostructure such as graphene/silicene and graphene/hafnene, and also opens the way for placing graphene on insulating substrate for electronic applications if the intercalation layer can be oxidized by further oxygen intercalation.