Vapor-solid preparation of densely distributed and small-sized graphene nanoflakes on one-dimensional nanomaterials for low-field and highly stable field emission

Differently shaped two-dimensional (2-D) graphene nanoflakes (GNFs) were prepared on one-dimensional (1-D) carbon nanotubes (CNTs) and silicon nanowires (SiNWs) forming 2-D-1-D composites by using microwave plasma enhanced chemical vapor deposition. The GNFs are vertically aligned on 1-D nanomaterials with their sharp edges (less than 10 layers) unfolded outside and are rich in defects. GNF-CNT (or SiNW) composites with densely distributed and small-sized GNFs and not obviously thickened CNTs (or SiNWs) are found to have superior FE properties. The optimal FE performance obtained from the GNF-CNT composites shows a low threshold field of 1.54 V/μm and an extremely large maximum emission current density of 75.46 mA/cm2, far better than 1.77 V/μm and 27.90 mA/cm2 for the pristine CNTs, respectively. The FE improvement is ascribed to the significant increase of active emission sites and also the preservation of the high aspect ratio of CNTs. Furthermore, longtime (30 h) stable FE is achieved from GNF-CNT composites with optimal shapes at a high mean emission current density of 45.47 mA/cm2 and a low operation field of 1.766 V/μm, showing promising prospects in high-performance vacuum electronic device applications.