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Carbon nanotubeshave many advantages over conventional semiconductor and metal emitters for field emission displays (FEDs). However, the origin of the current saturation seen in carbon nanotubes at high fields is poorly understood. Here the effect of gas adsorbates on the field emission properties of patterned carbon nanotube arrays, such as the one shown in the Figure, is investigated.

We grew vertically aligned carbon nanotubes ͑CNTs͒ using microwave plasma-enhanced ͑MPE͒ and thermal chemical-vapor deposition ͑CVD͒ and characterized their field emission properties. We observe that the flickering and instability in the field emission are due to the metal particles present on the field-emission array ͑FEA͒ surface, particularly from the MPECVD-grown samples. The existence of metal particles is an obstacle to obtaining reliable emission properties. The emission properties of the CNT-FEA are studied as a function of gas-exposure time with hydrogen, nitrogen, and oxygen gases. Gas exposures affected turn-on voltage, hysteresis, and the slope of Fowler-Nordheim plots. We observe that the saturation of emission currents is attributed to gas adsorbates present on the surface of the FEA. Oxygen exposures induce more severe degradation on the field-emission properties than nitrogen, whereas emission properties are improved by hydrogen gas exposures that clean the surface of emitters. In addition, hydrogenation of carbon nanotubes has technical importance for activation of the CNT-FEA.

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Carbon nanotubes (CNTs) have been synthesized by ferrocene-catalyzed pyrolysis of toluene. The influences of the experimental conditions on the morphology and microstructure of the product have been analyzed. To find the proper temperature for synthesis of CNTs, the experiment was performed in a temperature range from 800 to 1100°C. From content variation of ferrocene and thiophene as the catalyst, morphological change of carbon nanotubes has been observed. Also, the influence of the gas ratio of hydrogen and argon on the nanotube samples was analyzed by scanning electron microscopy and transmission electron microscopy.