XPS, Raman scattering and SEM were used to study effect of DC bias voltages (0-400 V) on the synthesis of high nitrogen content of carbon nitride (CNx) films. Maximal N/C ratio up to 0.81 was first obtained at the bias voltage of 250 V, and the maximal fraction of sp(3) CN bond inside the film was up to 40%. Either too high or too low bias voltages would result in decrease of nitrogen content inside the CNx films. Typical G and D bands were identified. Intensities of G and D bands showed periodic development following an increase of bias voltages. Several groups of nanoscale particles were observed at the pulsed bias voltage of 5 kV. Each group of particles appeared sunflower type of distribution where the biggest (85 nm) particle at the center was surrounded by many small sizes (35 nm) of CN particles. (c) 2006 Elsevier B.V. All rights reserved.