We present the fabrication of vertically aligned cobalt nanowire arrays on planar surfaces as well as preliminary field-emission (FE) experiments using them as cold electron cathodes. These arrays are obtained by electrodeposition into nanoporous templates on Au/Ti/Si substrates at very low temperature (<100 °C). After the removal of the template, the arrays consist of statistically positioned vertical free-standing nanowires with high aspect ratios, uniform dimensions, and predetermined densities. The electron field-emission measurements show metallic and reproducible characteristics. Emission is found to be reasonably homogeneous over the whole sample area, and a current density of 1 mA/cm2 has been obtained. We show that the growth process permits us to predetermine the field amplification factor precisely, which is of primary importance for FE sources. A large variety of FE applications can be envisaged, including FE displays and microwave amplifiers.

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High current density (21A/cmZ) and high emitted current (210 m a ) from cold cathodes are needed for RF power applications. A dense vertically aligned nanofilament array is theoretically the best configuration. However a g d emitter shape uniformity and a high current per emitter are essential to attain such performances. Two different types of aligned nanofilament array have been studied: first, metallic Nanowires grown by electrodeposition into nanoporous templates at vely low temperature (T400"C) on a silicon wafer (see figure 1); second, carbon NanotubeslNanofibers (CNs) grown by catalytic plasma enhanced chemical vapour deposition (see figure 2). The fabrication process and the field emission properties of these two types of cathodes will be presented.Presently, the best results are obtained with CN cathodes. Arrays of 5.8 pm height and 50 nm diameter CNs exhibit geometrical enhancement factor (Mr) of 240+-7.5%. Moreover, currents close to 100 pA per emitter have been measured using a scanning anode field emission microscope. Due to these properties, 0.5 x 0.5 m d arrays emit a 2mA current corresponding to 0.8Aicmz, in DC mode. The same cathodes were tested at 1.5 GHz in a reentrant cavity experimental set-up, and exhibited 1.2 A/cm2 at this frequency.To our knowledge, that is the first report of a significant current at microwave frequency emitted from CN cathodes.The use of these cold cathodes in microwave triodes delivering 10 to 5oW at 30 GHz will be discussed for future telecommunication applications. Away of 2.1 pm height and 22 mn diameterAway of 5 pm heighi and 50 mn diameter CNsCobalt Nanowires