Field-emission properties of vertically aligned carbon-nanotube array dependent on gas exposures and growth conditions

We grew vertically aligned carbon nanotubes (CNTs) using microwave plasma-e nhanced (MPE) and thermal chemical-vapor deposition (CVD) and characterized their field emission properties. We observe that the flickering and instab ility in the field emission are due to the metal particles present on the f ield-emission array (FEA) surface. particularly from the MPECVD-grown sampl es. The existence of metal particles is an obstacle to obtaining reliable e mission properties. The emission properties of the CNT-FEA are studied as a function of gas-exposure time with hydrogen, nitrogen, and oxygen gases. G as exposures affected turn-on voltage, hysteresis. and the slope of Fowler- Nordheirn plots. We observe that the saturation of emission currents is att ributed to gas adsorbates present on the surface of the FEA. Oxygen exposur es induce more severe degradation on the field-emission properties than nit rogen, whereas emission properties are improved by hydrogen gas exposures t hat clean the surface of emitters. In addition, hydrogenation of carbon nan otubes has technical importance for activation of the CNT-FEA. (C) 2001 Ame rican Vacuum Society.