▎ 摘　　要

The initial stages of graphene chemical vapor deposition at very low pressures (<10(-5) Torr) were investigated. The growth of large graphene domains (similar to up to 100 mu m) at very high rates (up to 3 mu m(2) s(-1)) has been achieved in a cold-wall reactor using a liquid carbon precursor. For high temperature growth (>900 degrees C), graphene grain shape and symmetry were found to depend on the underlying symmetry of the Cu crystal, whereas for lower temperatures (<900 degrees C), mostly rounded grains are observed. The temperature dependence of graphene nucleation density was determined, displaying two thermally activated regimes, with activation energy values of 6 +/- 1eV for temperatures ranging from 900 degrees C to 960 degrees C and 9 +/- 1 eV for temperatures above 960 degrees C. The comparison of such dependence with the temperature dependence of Cu surface self-diffusion suggests that graphene growth at high temperatures and low pressures is strongly influenced by copper surface rearrangement. We propose a model that incorporates Cu surface self-diffusion as an essential process to explain the orientation correlation between graphene and Cu crystals, and which can clarify the difference generally observed between graphene domain shapes in atmospheric-pressure and low-pressure chemical vapor deposition. (C) 2014 AIP Publishing LLC.