Ultra-low-threshold field emission from conjugated polymers

Field-emission displays contain materials that emit electrons when charged to a low (negative) potential; the electrons excite light emission from phosphor screens. These devices have the potential to provide hat-panel visual displays with good picture quality at low power consumption and low cost(1). Field-emission devices at present use arrays of microfabricated tips as the emitting cathodes, but a potentially cheaper and simpler alternative is to use a thin-film cathode. This requires the identification of materials that will emit an appreciable electron current at low applied fields. Nitrogen-doped, chemical-vapour-deposited diamond films(2) and amorphous carbon films(3) have been explored for this purpose. The low electron affinity(4), wide bandgap and excellent transport properties(5) of some conducting organic polymers suggest that they might also provide good cathode materials. Here we demonstrate that this is so, reporting held emission from thin films of regioregular poly(3-octylthiophene) deposited on n-doped silicon, with indium tin oxide as the anode. The threshold fields that we measure for electron emission from these films are the lowest yet reported for any carbon-based material.