▎ 摘　　要

We study the metal-catalyst-free growth of uniform and continuous graphene films on different insulating substrates by microwave plasma-enhanced chemical vapor deposition (PECVD) with a gas mixture of C2H2, NH3, and H-2 at a relatively low temperature of 700-750 degrees C. Compared to growth using only C2H2 and H-2, the use of NH3 during synthesis is found to be beneficial, in transforming vertical graphene nano-walls into a layer-by-layer film, reducing the density of defects, and improving the graphene quality. The effect of different insulating substrates (including Al2O3 and SiO2) on the growth of graphene was studied under different growth temperatures, implying that the growth-temperature window and catalytic effect vary among insulators. The low activation energy barrier of Al2O3 proves it to be a more suitable substrate for the metal-catalyst-free growth of graphene at low temperature. These directly grown graphene films on insulators can be conveniently integrated into various electronic and optoelectronic applications avoiding any post-growth transfer processes.