超洁净石墨烯薄膜的制备方法

Synthesis of Superclean Graphene

化学气相沉积(Chemical vapor deposition,CVD)法制备的石墨烯薄膜具有质量高、可控性好、可放大等优点,近年来受到了学术界和工业界的广泛关注。然而,近期研究结果表明,在高温CVD生长石墨烯的过程中,伴随着许多副反应,这些副反应会导致石墨烯薄膜表面沉积大量的无定形碳污染物,造成石墨烯薄膜的"本征污染"现象。同时,这些污染物的存在会导致转移后的石墨烯薄膜表面更脏,对石墨烯材料和器件的性能带来严重影响。这也是CVD石墨烯薄膜的性能一直无法媲美机械剥离石墨烯的重要原因之一。事实上,超洁净生长方法制备得到的超洁净石墨烯薄膜在诸多指标上都给出了目前文献报道的最好结果,代表着石墨烯薄膜材料制备技术的发展前沿。本文首先对CVD法制备石墨烯过程中表面污染物的形成机理进行分析,然后综述了超洁净石墨烯薄膜的制备方法,并列举了超洁净石墨烯薄膜的优异性质。最后,总结并展望了超洁净石墨烯未来可能的发展方向和规模化制备面临的机遇与挑战。

Graphene has attracted enormous interest in both academic and industrial fields, owing to its unique, extraordinary properties and significant potential applications. Various methods have been developed to synthesize high-quality graphene, among which chemical vapor deposition(CVD) has emerged as the most encouraging for scalable graphene film production with promising quality, controllability, and uniformity. However, a gap still exists between ideal graphene, having remarkable properties, and the currently available CVD-derived graphene films. To close this gap, numerous studies in the past decade have been devoted to decreasing defect density, grain boundaries, and wrinkles, and increasing the controllability of layer thickness and doping of graphene. Significant recent advances in this regard were the discovery of the inevitable contamination of graphene surface during high-temperature CVD growth and the synthesis of superclean graphene, representing a new growth frontier in CVD graphene research. Surface contamination of graphene is a major hurdle in probing its intrinsic properties, and strongly hinders its applications, for instance, in electrical and photonic devices. In this review, we aim to provide comprehensive knowledge on the inevitable contamination of CVD graphene and current synthesis strategies for preparing superclean graphene films, and an outlook for the future mass production of high-quality superclean graphene films. First, we focus on surface contamination formation, e.g. amorphous carbon, during the high-temperature CVD growth process of graphene. After introducing evidence to confirm the origin of surface contamination, the formation mechanism of the amorphous carbon is thoroughly discussed. Meanwhile, the influence of the intrinsic cleanness of graphene on the peeling and transfer quality is also revealed. Second, we summarize the state-of-the-art superclean growth strategies and classify them into direct-growth approaches and post-growth treatment approaches. For the former, modification of the CVD gas-phase reactions, for example, using metal-vapor-assisted methods or cold-wall CVD, is effective in inhibiting the formation of amorphous carbon. For the latter, both chemical and physical cleaning methods are employed to eliminate amorphous carbon without damaging the graphene, e.g. selective etching of as-formed amorphous carbon using CO2, and removal of amorphous carbon from the graphene surface using a lint roller based on interfacial force control. Third, we summarize the outstanding electrical, optical, and thermal properties of superclean graphene. Superclean graphene exhibits high carrier mobility, low contact resistance, high transparency, and high thermal conductivity, further highlighting the significance of superclean graphene growth. Finally, future opportunities and challenges for the industrial production of high-quality superclean graphene are discussed.