Atmospheric Pressure Chemical Vapor Deposition Growth of High-Quality Single-Crystal AB-Stacked Bilayer Graphene

High-quality single-crystal AB-stacked bilayer graphene (AB-BLG) is highly desired because of its unique electronic properties and potential applications. However, its growth is still unsatisfactory owing to the coexistence of BLG and/or multilayer graphene. Here, high-quality AB-BLG single crystals is synthesized with size of approximate to 30 mu m on liquid Cu by chemical vapor deposition. The morphology and uniformity are characterized by optical micrographs and Raman spectroscopy. The crystal quality is evaluated by transmission electron microscopy, such as selected area electron diffraction and high-resolution imaging. The high-quality graphene layers and morphology can be regulated by tuning the oxidation degree of liquid Cu. Growth mechanism researches show that the small hexagonal graphene layer underneath the large graphene layer, forming an "inverted wedding cake" structure. Meanwhile, growth process studies by carbon isotope labeling technique in conjunction with atomic force microscope image of growth substrates with different oxidation degrees indicated that the roughness of the growth substrate can significantly affect the nucleation and growth of graphene. Appropriate roughness of liquid Cu by tuning the oxidation degree through Ar/O2 (the Ar/O2 volume ratio is 95%/5%) annealing and H2 reduction can weaken the interaction between the top graphene layer and substrate, benefiting the growth of AB-BLG single crystals.