We have deposited niobium nitride thin films by ion beam assisted deposition and evaluated their properties from the viewpoint of a cathode material for vacuum microelectronics devices. Substrate temperature and ion-atom arrival rate ratio were selected as deposition parameters. The film properties of nitrogen composition, crystallinity, electric resistivity, work function and sputtering yield against a low-energy argon ion bombardment were investigated. It was found that polycrystalline films could be obtained at the substrate temperature higher than 500 degrees C, and the composition could be controlled by the ion-atom arrival rate ratio. The results also showed that the stoichiometric nitride film exhibited superior properties of a lower work function and a lower partial sputtering yield of niobium. The electron emission test also demonstrated a lower current fluctuation for the stoichiometric films. In summary, ion beam assisted deposition provided a low temperature process which could control the film properties suitable to a cathode material. (C) 1999 Elsevier Science B.V. All rights reserved.