Electron field emission from an isolated carbon nanotube ͑CNT͒ was performed in situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1-60 m. The threshold field required for an emission current of 100 nA was seen to decrease from a value of 42 V m −1 at an anode to CNT tip separation of 1 m, asymptotically, to approach 4 V m −1 at a separation of 60 m. It is proposed that at low D, the electric field enhancement factor ͑␤͒ reduces as the anode electrode approaches the CNT mimicking a parallel plate configuration. Under "far field" conditions, where D Ͼ 3 h, where h is the CNT height, the CNT enhancement factor is no longer dependant on D, as shown by the asymptotic behavior of the threshold field, and is purely a factor of the CNT height and radius. For each CNT to tip separation, measured emission current data together with the threshold field and enhancement, are consistent with a Fowler-Nordheim analysis for the far field conditions, and dispels the need for a novel emission mechanism to explain the results as has been proposed recently. Since the identification of carbon nanotubes 1 ͑CNT͒, there has been sustained research academically and industrially into numerous potential applications.2-7 Much effort has been invested in the study of their application for electron sources by the process of electron field emission, 7-9 leading to the fabrication of possible next generation flat panel displays.10 Carbon nanotubes are promising candidates for cold cathode electron field emitters due to their electrical properties, chemical inertness, tensile strength, and high aspect ratio, which enable them to alter the local electric field around the tip due to a field enhancement factor, often denoted by ␤. It is important, therefore, in designing and fabricating field emission displays or future cold cathode sources, to understand fully the emission properties and characteristics of not just arrays and mats of CNT, but of individual CNTs. To date, various studies have been performed on field emission from a single CNT.11-13 Measurements of field emission often attempts to quantify the behavior in terms of the applied electric field and the local electric field at the tip, via ␤. For an emitter not operating in the high current space charge regime, the local electric field required for emission should not be a function of the electrode separation, D, and one would expect that measurements of the applied threshold field not to be dependent on the relative separation of the electrodes, with the applied electric field given simply as V / D, where V is the applied potential difference. In this letter, we report that the position of the anode electrode in field emission from a single CNT is important, and furthermore that redefining the manner in which the applied field is described gives rise to a better understanding of the CNTs field emission properties.Multiwalled carbon nanotubes were synthesized by a plasma arc discharge between two graphite electrodes. The subsequent carb...

We demonstrate control of ZnO nanorod density for self-organized growth on ZnO buffer layers on Si by varying Zn supersaturation during the initial growth phase, thereby altering the competition between 2D and 1D growth modes. Higher initial supersaturation favours nanorods of diameter <200 nm with micron-sized bases, resulting in low density nanorod arrays; nanorods grown with lower initial supersaturation have diameters <200 nm along their entire length, yielding higher density arrays. Field emission and imaging studies reveal field enhancement factors of >1000, attributed to sharp facet edges, and indicate that lower density arrays have more uniform emission due to a reduction in screening effects.

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We report the electron field emission characteristics of functionalised single walled carbon nanotube -polymer composites produced by solution processing. We show that excellent electron emission can be obtained by using as little as 0.7% volume fraction of nanotubes in the composite. Furthermore by tailoring the nanotube concentration and type of polymer, improvements in the charge transfer through the composite can be obtained. The synthesis of well dispersed randomly oriented nanotube -polymer composites by solution processing allows the development of carbon nanotube based large area cathodes produced using a scaleable technology. The relative insensitivity of the cathode's field emission characteristics to the electrical conductivity of the composite is also discussed.

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