3D hollow carbon nanotetrapods synthesized by three-step vapor phase transport

In this work, novel 3D hollow carbon nanotetrapod structures are synthesized by all-vapor-phase process and its electrical properties are studied for electron field emission applications. The fabrication involves three main stages conducted sequentially in a single tube furnace, including in situ ZnO nanotetrapod synthesis, carbon chemical vapor deposition with acetylene/hydrogen (C2H2/H2) mixture and vapor-phase ZnO etching. The effects of C2H2/H2 gas flow composition, synthesis time and temperature on structural morphology of 3D carbon nanostructures and growth mechanisms are systematically investigated. The optimal condition that yields unique 3D hollow carbon nanotetrapod structures includes synthesis time of 3 min, temperature of 700 °C, C2H2 flow rate of 3 sccm, H2 flow rate of 24 sccm for 40-mm-tube-inner diameter. Insufficient synthesis time or C2H2 flow rate, excessive H2 flow rate and non-optimal temperature leads to very thin and distorted carbon nanotetrapod structures while excessive time or C2H2 flow rate entails 3D solid carbon nanotetrapod structures. For electrical properties, the nanostructures exhibit decreasing electrical conductivity and improved emission performances with decreasing synthesis time or C2H2 flow rates and increasing H2 flow rate. The optimal 3D hollow carbon nanostructure offers excellent field-emission performances with low turn-on electric field of 1.2 V/μm and high field-enhancement factor of ∼7620.