▎ 摘　　要

The direct growth of graphene at low temperatures on the desired dielectric substrate by plasma-enhanced chemical vapor deposition (PECVD) is significant for its electronic and optoelectronic applications. However, due to the high nucleation density, low-quality nanographene with small domain size is always grown, leading to a decline in their electrical performance. In this work, by effectively reducing the total nucleation density, high-quality large graphene crystals with hexagonal shape, 0.5 mu m size and uniform thickness were grown on the SiO2/Si substrate. The higher intensity ratio of Raman 2D peak to G peak (I-2D/I-G similar to 1.58) and the smaller intensity ratio of D peak to G peak (I-D/I-G similar to 1.15) for these crystals verify their much better quality than that of nanographene with an I-2D/I-G value of similar to 0.35 and an I-D/I-G value of similar to 1.57. In particular, the initial nucleation density in a given short growth time was first controlled to be low, less than 5 mu m(-2), and the subsequent multiple nucleation in the following long-time growth was suppressed under the optimized growth condition such as plasma power and growth temperature. This ensures a low total nucleation density all the time during growth, and thus facilitates the successful growth of large graphene crystals. This work will promote the study of low-temperature growth techniques of graphene on dielectric substrates, as well as the large-scale applications of graphene.