HfN x O y films are deposited by ion beam-assisted deposition on (100) silicon substrates at room temperature. According to X-ray diffraction analysis, at least two phases exist in HfN x O y film, and X-ray photoelectron spectroscopy results are in good agreement with these analysis. Both annealing and increasing assisting ion beam current increase the concentration of the β-Hf 7 O 8 N 4 phase in HfN x O y films. Field emission with low turn on field is reported. Field emission results suggest that the concentration of β-Hf 7 O 8 N 4 plays an important role in field emission properties. Hydrogen plasma treatment also enhances field emission properties. These results indicate that the HfN x O y film is an excellent material for field emitter.