Excellent field emission from carbon nanotubes grown by microwave-heated chemical vapor deposition

The growth of carbon nanotubes using a microwave-heated chemical vapor deposition system is reported. The material properties including morphology and emission behavior of carbon nanotubes were studied as a function of the Ni layer thickness, applied microwave power, and substrate types. It was found that the diameter and length of carbon nanotubes increase with the Ni layer thickness. The emission current density versus field characteristics of carbon nanotubes grown at 1000 W for 10 min show clearly two groups of characteristics marked off with the Ni thickness of 50 nm. The microwave power, which determines the resulting substrate temperature, also affects the adhesion, morphology, and emission property of carbon nanotubes. There is essentially no difference in the tube’s appearance for carbon nanotubes grown on different types of Si substrates, while carbon nanotubes grown on glass substrates are smaller and more uniform in diameter. A carbon nanotube emitter, grown at 900 W for 18 min on a p-type Si(100) coated with an 80-nm-thick Ni layer, has shown an excellent emission characteristic with extremely low turn-on and threshold fields, respectively, at 0.056 and 1.50 V/μm.