Enhanced Field Emission Performance of Hierarchical ZnO/Si Nanotrees with Spatially Branched Heteroassemblies

Silicon nanorods (SiNRs) with a large interspace and regularly aligned structure were fabricated by combining silver-catalyzed etching with a polysterene (PS) sphere template, then a hydrothermal reaction was utilized to synthesize large-scale ZnO nanowires (NWs) on Si nanorods. Compared with the as-prepared SiNRs and ZnO NWs, the high-density ZnO NWs on SiNRs have exhibited predominant field emission (FE) characteristics with a low turn-on field of 2.18 V/μm and a high field enhancement factor of ∼8100. The FE enhancement was attributed to highly crystallized ZnO NWs densely distributed on the surface of SiNRs, which can effectively increase emission site density, diminish screening effect, favor electron transfer due to band bending, and quickly transmit heat from the nanotrees to substrate. Our results indicate that ZnO/Si hierarchical structures might be an effective candidate for field emission cathode.