Controlling the diameters and field emission properties of vertically aligned carbon nanotubes synthesized by thermal chemical vapor deposition

We report here the synthesis of vertically well-aligned carbon nanotubes and the effect of catalytic metal layer on the diameter of grown, carbon nanotubes and the field emission characteristics of them. The carbon nanotubes were grown by thermal chemical vapor deposition at temperatures below 900 degreesC on Fe metal catalytic layer, deposited by sputtering process on a Si substrate and pretreated by heat and NH3 gas. We found that the thickness of metal layers could be an important parameter in controlling the diameters of carbon nanotubes. With varying the thickness of the metal layers the grain sizes of them also vary so that the diameters of the nanotubes could be controlled. Field emission measurement has been made on the carbon nanotubes field emitters at room temperature in a vacuum chamber below 10(-6) Torr. Our vertically aligned carbon nanotube field emitter of the smallest diameter emits a current density about 10 mA/cm(2) at 7.2 V/mum. The field emission property of the carbon nanotubes shows strong dependence on the nanotube diameters as expected.