Progress in research on ultra-low temperature controllable epitaxial growth of graphene

Figure 1. Schematic diagram of the principle of using a different carbon source molecule and corresponding London dispersive force to significantly reduce the epitaxial growth temperature of graphene

Previously, Ruoff's research team at the University of Texas at Austin used chemical vapor deposition (CVD) to successfully grow a large area of ​​single-layer graphene on copper foil substrates, making copper substrates the best choice for the growth of graphene. . Zhang Zhenyu's research team cooperated with Dr. Zhu Wenguang from the University of Tennessee in the United States (the latter as the “Thousands of Young People” program of the Central Organization Department, who has recently returned to HKUST in full time, using the first-principles-based density functional theory calculation to study graphite. The condensation behavior of carbon atoms in the initial stage of epitaxial growth of olefins on metal substrates, clarifying that copper as a catalytic substrate is superior to other metals because it is easier to nucleate everywhere (Phys. Rev. Lett. 104, 186101 (2010)) . Although this mechanism is beneficial to the growth of graphene, the nucleation process of "flowering everywhere" leads to a large number of grain boundaries, which seriously reduces the quality of graphene. In response to this problem, the team designed a suitable superstructure alloy surface, based on the "nucleation-growth" two-step kinetic approach, effectively inhibiting the formation of grain boundaries during growth, for high-quality preparation of large-scale Single crystal graphene provides a new idea (Phys. Rev. Lett. 109, 265507 (2012)). On the other hand, the conventional copper surface graphene growth based on a gaseous carbon source requires a high temperature of about 1000 °C. At this high temperature, not only the reaction energy consumption increases, but also it is difficult to effectively regulate the orderly growth of graphene. Recently, Zeng Changjun's research team took a different approach and used liquid benzene as a carbon source to reduce the growth temperature to 300 °C (ACS Nano 5, 3385–3390 (2011)). This is the lowest temperature in the world where graphene CVD has been reported.

The latest research by Dr. Jin-Ho Choi, a postdoctoral researcher of Zhang Zhenyu's research group, and the research team of Professor Zeng Changjun, have better understood the microscopic mechanism of graphene low temperature growth on metal substrates. Choi first theoretically predicts that London's dispersive force (mainly van der Waals force attraction) plays a decisive role in various subtle and competing chemical reactions in the growth of graphene: aromatic molecules have enhanced London dispersive power. Effectively prevents the desorption of adsorbed molecules from the surface and thereby promotes the necessary dehydrogenation reaction. Therefore, low-temperature growth of graphene can be achieved by using a larger aromatic molecule instead of a typical methane as a carbon source (see Figure 1).

The new experiment by Zeng Changjun's research team accurately validated this prediction and further expanded the applicable space of this mechanism. When a new, larger aromatic molecule (p-terphenyl) is used as the carbon source, a large-area high-quality single-layer graphene can be obtained at a temperature of 300 ° C or lower. The Raman spectrum, the light transmission spectrum, and the scanning tunneling microscope image clearly show that the graphene produced is a monolayer thickness. London dispersive force is caused by the ubiquitous transient dipole and is inherently ubiquitous; therefore, this work is of universal importance for the growth of surface nanostructures. The research results were published on May 31, 2013 under the title "Drastic reduction in the growth temperature of graphene on copper via enhanced London dispersion force" (Scientific Reports 3, 1925 (2013)).

The above research work was funded by the National Natural Science Foundation of China, the Chinese Academy of Sciences Foreign Youth Scientist Fund, the Korea Overseas Postdoctoral Fund, and the Ministry of Science and Technology.