▎ 摘　　要

The graphene has several unique characteristics and many applications in all fields. Some of these characteristics are the quantum Hall effect at room temperature, the ambipolar field effect, the optical properties, the high electron mobility and the best electronic properties. The ability of fabricating large-area monolayer graphene is hindering its application. In this paper the effects of growth time on the quality of graphene synthesized by low-pressure chemical vapour deposition (LPCVD) has been investigated. Large-area monolayer graphene is synthesized on polycrystalline Cu foil (similar to 1 cm(2)) by controlled experiment LPCVD at different growth times (30, 60, 120 and 150 s). The synthesized graphene was characterized using Raman spectroscopy and scanning electron microscopy (SEM). The Raman spectrum showed a I (G) /I (2D) similar to 0.2 ratio which indicates that all samples are single-layer graphene and the SEM images demonstrate that the domain size increases when the growth time increases. The growth mechanism of LPCVD of graphene on Cu and the mechanisms governing the Raman scattering process in the films are also discussed. The control over the grain size of synthesized graphene by adjusting the growth time (achieved in this work), provides useful insights for understanding the growth mechanism of LPCVD of graphene and for optimization of the growth process to further improve the quality of graphene. Finally, with analyses of all investigations we found that the quality and the large-area of monolayer graphene improved by increasing the growth time and it is very important consequence for all those who do research on graphene.