Field emission properties of vertically aligned gold nanowires of different aspect ratios and spatial distribution are presented. The nanowires were electrochemically deposited into the pores of etched ion-track polymer membranes. High emission site densities up to 5.7 10 5 cm −2 based on a controlled field enhancement of individual emitting sites were observed by means of field emission scanning microscopy. Local measurements reveal stable Fowler–Nordheim behavior of the emitters up to currents of 100 A. The integral emission of Au nanowires cathodes for device application is also discussed. © 2008 American Institute of Physics. Electron field emission FE from nanostructures has at-tracted much attention for vacuum nanoelectronic applica-tions, such as flat panel displays, x-ray and microwave tubes, and various sensors. 1,2 Besides carbon nanotubes CNTs, different semiconductors and metallic nanowires NWs have been investigated for this purpose. 3–6 Field enhancements from such nanostructures strongly depend on their morphol-ogy, spatial distribution, and interspacing. 7–10 Moreover, the dependence of field enhancement factor on the vacuum gap d has become an interesting topic of research to get an optimal performance of FE devices. 11 In this article, we present the FE properties of electro-chemically deposited Au NWs. This method is suitable for large scale synthesis of NWs with controlled lengths and aspect ratios. Cu and Ni NWs fabricated by this technique have shown rather uniform FE properties. 12,13 The morpholo-gies and FE properties of Au NWs were investigated by means of scanning electron microscopy SEM and field emission scanning microscope FESM. 14 FE maps, charac-terizations of individual emitting sites, as well as the integral FE results of NW cathodes are discussed here. Gold NWs were deposited electrochemically into the etched tracks of ion irradiated fluence 10 6 –10 7 cm −2 poly-carbonate foil, at GSI Darmstadt. The fabrication details are given elsewhere. 15 The vertically aligned and randomly distributed gold NWs are of lengths 6–15 m with a di-ameter 120– 265 nm of as shown in Fig. 1. The lengths and site densities of NWs, as estimated from SEM images, are listed in Table I. The NWs in all cases are free standing except for sample D, where NWs are agglomerated due to the bending of long wires, resulting in an increased effective spacing. The emission site density and current distribution of all samples were measured in the FESM at the pressure of 10 −9 mbar, using a tungsten anode of 5 m tip diameter. The regulated voltage scans for a constant current of 2 nA pro-vide electric field E-maps of the scanned areas, from which the potential emission site density NE max up to the given maximum field E max is determined. Such E-maps for samples A, C, D, and E in Fig. 2 show the distribution of freestanding and agglomerated NW emitting sites with a lateral resolution of 5–7 m. Resulting values of NE max for samples A, B, C, D, and E are 4 10 5 , 2.4 10 5 , 5.7 10 5 , 4.4 10 5 , and 5.6 10 5 emitters/ cm 2 at E max of 33, 43, 30, 17 and 20 V / m, respectively. It is interesting to find that in the best case up to 40% of the NWs are emitting sample A. The subsequently measured current I-maps at constant voltage reveal the real number of activated emitting sites at reason-able operating electric field E. NE values of 8 10 4 / cm −2 at 12 V / m, 2.6 10 4 / cm 2 at 25 V / m, and 10 5 , 3.4 10 4 , and 1.4 10 5 / cm 2 at 6 V / m have been obtained for samples A, B, C, D, and E Fig. 3a, respectively. All the above mentioned fields are macroscopic, while it is the lo-cally enhanced fields at the emission sites which govern the emission. The field enhancement is known to be dependent on the morphology as well as on the separation of the emitters. 7–10 In our samples, the separation of NW sites is 3–10 m and the wire lengths are 6 – 15 m. Since the NWs separation is much smaller than twice of their lengths, such configuration favors field-screening effect, as calculated for CNTs. 9,10 Comparing all the samples, sample D of agglom-erated NWs has maximum NW spacing and so the least screening effect, which results the lowest onset field of 4 V/ m for the strong emitters in the E-map Fig. 2c. Achieving much larger emitter number densities 10 5 cm −2 at 6 V / m compared to CNT cathodes with respect to the number of deposited nanostructures, makes Au NWs inter-esting for cold cathode applications. The FE properties of Au NWs were further investigated locally on randomly chosen emitting sites on FE maps for each sample. The measured I-E curves confirmed linear lnI / E 2 versus 1 / E dependence, as given in Fig. 3b and expected from Fowler–Nordheim FN theory. 16 The corre-sponding field enhancement factors were retrieved from these FN plots for the work function of 5 eV. In general, during initial increase of electric field, unstable emission was observed, probably due to adsorbates 17 or partial melting of NW tips caused by FE currents, 13 which tends to stabilize in the succeeding up and down cycles of E see Fig. 3b. The emitting sites on sample D possess the highest maximum current I max values among all the samples because of the agglomerated clusters of NWs. I max versus plot for sample D in Fig. 3c shows scattered maximum current values lying between 0.5– 100 A, which are on average hyperbolically related to the values. This might reflect enhanced heating