▎ 摘　　要

Few-layer vertical graphene (VG) was prepared on arrayed carbon nanotubes (CNTs) without a catalyst by using radio frequency sputtering deposition and microwave plasma enhanced chemical vapor deposition, and the field emission (FE) performance of VG-CNT composites was tested and optimized. The FE performance is found to be strongly dependent on the heights (but not the actual heights) and densities of CNTs, the shapes of VG, and the diameters of VG-CNT composites. The optimal shapes for FE are demonstrated to be CNTs with middle densities and small diameters and VG with high densities and small sizes. The optimal FE performance from our large area VG-CNT composites is found to have a low threshold field of 1.28 V/mu m (at 10 mA/cm(2)), a high maximum emission current density of 87.63 mA/cm(2) (4.28 times higher than that from our previously prepared graphene-CNT composites), and excellent stability at an extremely high mean emission current density of 36.28 mA/cm(2) over a period of 50 h, far better than those of pristine CNTs, pure VG, and shape non-optimized VG-CNT composites. (C) 2017 Elsevier B.V. All rights reserved.