▎ 摘　　要

Recent studies show that, at the initial stage of chemical vapor deposition (CVD) of graphene, the isolated carbon monomers will form defective carbon clusters with pentagons that degrade the quality of synthesized graphene. To circumvent this problem, we demonstrate that high-quality centimeter-sized graphene sheets can be synthesized on Cu foils by a self-assembled approach from defect-free polycyclic aromatic hydrocarbons (PAHs) in a high vacuum (HV) chamber without hydrogen. Different molecular motifs, namely coronene, pentacene, and rubrene, can lead to significant difference in the quality of resulting graphene. For coronene, monolayer graphene flakes with an adequate quality can be achieved at a growth temperature as low as 550 degrees C. For the graphene obtained at 1000 degrees C, transport measurements performed on back-gated field-effect transistors (FETs) with large channel lengths (similar to 30 mu m) exhibit a carrier mobility up to similar to 5300 cm(2) V-1 s(-1) sat room temperature. The underlying growth mechanism, which mainly involves surface-mediated nucleation process of dehydrogenated PAHs rather than segregation or precipitation process of small carbon species decomposed from the precursors, has been systematically investigated through the first-principles calculations. Our findings pave the way for optimizing selection of solid carbon precursors and open up a new route for graphene synthesis.