Li-salt functionalised carbon nanotubes as low work function field emitters

Abstract

Carbon nanotubes have excellent field emission (FE) properties. The work function (WF) of materials plays a crucial role in their FE properties. From the well known Fowler-Nordheim equation, it is evident that reducing the WF should result in an exponential increase in current density at a given electric field. Therefore, for cold cathode applications it is desirable to minimize the emitter WF without compromising the cathode stability towards oxidation. We have recently shown that the WF of acid-oxidized multiwall carbon nanotubes (o-MWNT) can be reduced by exchanging acidic surface groups with alkali metal cations. In this paper, we report a method for applying o-MWNT onto carbon fibre (CF) fabric from solution and an improvement in the FE properties after converting carboxylic groups to the carboxylate salt of lithium via cation exchange. It is envisaged that this technique could be applied to a wide range of nanotube emitters to reduce the WF and improve the FE properties.