Tunable field emission properties of carbon nanotube arrays by engineering Fe catalysts

High-quality carbon nanotube (CNT) arrays composed of nanotubes with different diameters and wall numbers were synthesized by water-assisted chemical vapor deposition (CVD) from engineered Fe catalysts. Interestingly, the distribution of nanotube diameter and wall number broadened over 2.5 times as the catalytic Fe thickness increased. The mean diameter and wall number of nanotubes increased monotonically with the Fe thickness, while the calculated CNT area density within an array dropped about 32 times. Field emission measurements revealed that the turn-on voltage for CNT arrays decreased from 3.5 to 2.5 V/µm with the increased catalytic Fe thickness. It was believed that the screening effect from the proximity of neighboring nanotubes has a dominant influence than the CNT diameter on the resulting turn-on voltage.