Credit: © 2006 AIP

Because of their remarkable mechanical strength and ability to carry large currents, carbon nanotubes (CNT) are being studied extensively for use as cold cathode field emission tips. The major technical issue in CNT field emitter research, however, is the development of a method for the mass production of vertically aligned CNT structures that have a large current-carrying capacity. The emission from single CNT tips is currently only in the microampere range.

Now, Yang Wei and colleagues1 from Tsinghua University in Beijing, China have developed ‘superaligned’ multiwalled CNT (MWNT) yarn emitters with current densities exceeding 100 A cm-2, which is an enhancement of more than 105 compared with CNT emitters reported to date. The superaligned yarns were produced by growing MWNT arrays on silicon substrates by low-pressure chemical vapour deposition. After an ethanol rinse, tight fibres, tens of micrometres in diameter and several centimetres in length, were obtained. MWNT yarns with diameters of 50 µm were then mechanically cut to 1 cm in length and attached lengthwise to copper bases with silver paste.

The yarn emitters can be mass produced and the dimensions of the tips readily defined by mechanical cutting, thus making this procedure efficient and highly reproducible. The CNT emitters were used to induce fluorescence in a green pixel tube, which is one of many potential applications of this technology.