A simple method to control the diameter of carbon nanotubes and the effect of the diameter in field emission

We developed a simple method to control the diameter of carbon nanotubes (CNTs) and studied the effect of the diameter of CNTs in field emission. We fabricated Fe nanoparticle arrays of uniform size by filling Fe ion solution in the pores of the anodic aluminum oxide membrane bonded to a silicon wafer. Then we used them as catalysts to fabricate CNTs at a high temperature of 950 °C. The diameter of the nanoparticles could be controlled by changing the concentration of Fe ion solutions and consequently that of CNTs from 5 to 20 nm. Coating the Si wafers with gold greatly increased the field emission. The CNTs showed a good field emission property of a low turn-on field (1.8 V/μm), very high current density (94 mA/cm2) and long-term stability (5 h for 10% degradation of current density from 1 mA/cm2). Decreasing the diameter of the CNTs increased the field emission, while the field emission stability was almost unaffected by the diameter and length.