单晶金属衬底上多层石墨烯的可控生长进展

Progress in Controllable Growth of Multilayer Graphene on Single Crystal Metal Substrate

石墨烯作为一种理想的二维材料,具有机械性能好、电阻率低、热导率高等优点,受到人们的广泛关注。特别地,通过调控石墨烯层数可以改变石墨烯的电学性质,如带隙可调、半导体性质、特殊量子行为等,拓展石墨烯在柔性透明电极、高温超导、高性能传感等领域的应用。目前,人们已对金属衬底上高质量单层石墨烯的制备做了很多研究,发现当单层石墨烯覆盖金属衬底时,衬底将失去催化活性,使得高质量多层石墨烯的可控生长变得非常困难。为了制备多层石墨烯,研究人员已经探索了多种生长方法。总结了单晶金属衬底上多层石墨烯两种常见的生长模式,即表面成核控制的层层往上生长和偏析成核控制的层层往下生长,表面成核控制生长包括气源分子束外延、等离子体化学气相沉积等,偏析成核控制生长包括合金衬底偏析、单质金属衬底偏析等。针对多层石墨烯的各种生长方法,分别从成核密度、晶畴尺寸、层厚均匀性等方面进行了分析总结。最后,对该领域的发展趋势进行了展望,有助于为多层石墨烯的可控生长提供新的解决方案,促进多层石墨烯的发展与应用。

As an ideal two-dimensional material,graphene has attracted extensive attention due to its advantages of excellent mechanical properties,low resistivity and high thermal conductivity.In particular,the electrical properties of graphene can be changed by adjusting the number of graphene layers,such as adjustable band gap,semiconductor properties,special quantum behavior,etc.So as to expand the application of graphene in flexible transparent electrodes,high temperature superconductivity,high-performance sensing and other fields.At present,many studies have been done on the preparation of high-quality monolayer of graphene on metal substrates.It is found that when monolayer graphene covers metal substrate,the substrate loses its catalytic activity,making the controllable growth of high-quality multilayer graphene very difficult.In order to prepare multilayer graphene,researchers have explored a variety of growth methods.Two common growth modes of multilayer graphene on single crystal metal substrate are summarized here:layer by layer up growth controlled by surface nucleation and layer by layer down growth controlled by segregation nucleation.For substrates with low carbon solubility or high carbon solubility but low actual carbon amount,the multilayer graphene grows mainly in a layer by layer up mode.Corresponding to the layer by layer up growth mode is surface nucleation controlled growth,such as using gas source molecular beam epitaxy,double temperature region chemical vapor deposition,plasma enhance chemical vapor deposition,metal assisted catalysis and other means to provide additional carbon free radicals for the continuous growth of multilayer graphene.The advantage of surface nucleation to control growth is that there are abundant means and adequate supply of carbon sources,which could form graphene of large size with different layer thickness theoretically.The disadvantage is that the controllability of nucleation density and orientation of multilayer graphene is weak,which is easy to cause small domain size and poor uniformity of graphene.In addition to substrate surface reaction growth,the gas phase reaction during CVD growth also affects the types,transfer and adsorption of carbon free radicals,thus having a profound impact on the cleanliness,growth rate and quality of graphene.Corresponding to the layer by layer down growth mode is segregation nucleation controlled growth,the alloy or elemental metal substrate with high carbon solubility is used to dissolve carbon at high temperature,and carbon segregation is controlled to grow multilayer graphene at cooling process.The advantage of segregation control growth is mainly solid phase reaction,which is not easily affected by adverse factors in the gas phase,carbon dissolution and segregation are more controllable,and the growth quality is higher.The disadvantages are that limited substrates type and long growth cycle.It is necessary to accurately control parameters such as the carbon dissolution amount,cooling rate and so on to grow large and uniform multilayer graphene with controllable layer thickness.In order to maximize the application potential of multilayer graphene in the field of electronics,the requirements of multilayer graphene for quality,performance,cost and scale will be higher in the future,focusing on the following aspects:1)Large-area uniform graphene preparation with controllable layer thickness;2)Control of stacking structure between layers of graphene;3)Low-cost,large-scale production of multilayer graphene.This paper is helpful to provide a new solution for the controllable growth of multilayer graphene and promote the development and application of multilayer graphene.