▎ 摘　　要

A thin Al2O3 dielectric film was directly grown onto graphene layers without any surface treatment prior to H2O-based atomic layer deposition for the first time. The growth mechanism of Al2O3 dielectric film has been studied by changing the growth temperature and purge time. We found that the film morphology was influenced by the amount and distribution of physically adsorbed precursor molecules on the graphene, especially by physically adsorbed H2O molecules. Within an optimal temperature window, conformal and uniform Al2O3 thin films were obtained as confirmed by atomic force microscopy and transmission electron microscopy results. Raman spectroscopy revealed that no extra defects are generated in the graphene layers. Furthermore, the low leakage current and interface traps in dual-gated graphene field-effect transistors demonstrate the high-quality dielectric/graphene stack.