Controllable Fabrication of Graphene and Related Two-Dimensional Materials on Liquid Metals via Chemical Vapor Deposition.

Due to the confinement of the charge, spin, and heat transport in the plane, graphene and related two-dimensional (2D) materials have been demonstrated to own many unique and excellent properties and witnessed many breakthroughs in physics. They show great application potential in many fields, especially for electronics and optoelectronics. However, a bottleneck to widespread applications is precise and reliable fabrication, in which the control of the layer number and domain assembly is the most basic and important since they directly determine the qualities and properties of 2D materials. The chemical vapor deposition (CVD) strategy was regarded as the frontrunner to achieve this target, and the design of the catalytic substrate is of great significance since it has the most direct influence on the catalysis and mass transfer, which can be the most essential elemental steps. In recent years, as compared to traditional solid metal catalysts, the emergence of liquid metal catalysts has brought a brand-new perspective and contributes to a huge change and optimization in the fabrication of 2D materials. On one hand, strictly self-limited growth behavior is discovered and is robust to the variation of the growth parameters. The atoms in the liquid metal tend to move intensely and arrange in an amorphous and isotropic way. The liquid surface is smooth and isotropic, and the vacancies in the fluidic liquid phase enable the embedding of heteroatoms. The phase transition from liquid to solid will facilitate the unique control of the mass-transfer path, which can trigger new growth mechanisms. On the other hand, the excellent rheological properties of liquid metals allow us to explore self-assembly of the 2D materials grown on the surface, which can activate new applications based on the derived collective properties, such as the integrated devices. Indeed, liquid metals show many unique behaviors in the catalytic growth and assembly of 2D materials. Thus, this Account aims to highlight the controllable fabrication of graphene and related 2D materials on liquid metals. By utilizing the phase transition of liquid metals, the segregation of precursors in the bulk can be controlled, leading to self-limited growth. By utilizing the fluidity of the liquid metals, 2D material crystals can achieve self-assembly on their surface, including oriented stitching, ordered assembly, and heterostacking, which enables the creation of new multilevel or hybrid structures, leading to property and function extension and even the emergence of new physics. Finally, the unique liquid characteristic of liquid metals can also offer us new ideas about the transfer process. By utilizing the shear transformation of liquid metals, the direct sliding transfer of 2D materials onto arbitrary substrates can be realized. The research concerning the self-limited growth, self-assembly, and sliding transfer of 2D materials on liquid metals is just raising the curtain on the behavioral study of 2D materials on liquid metals. We believe these primary technology developments revealed by liquid metals will establish a solid foundation for both fundamental research and practical application of 2D materials.