The BCN films were synthesized on Si (110) wafers by using dual ion beam sputtering deposition from boron carbide target. The influences of ion assist source energy and N-2 relative flow rate on the surface roughness, mechanical properties and chemical bonding structure of BCN films were investigated systematically. The surface roughness was measured using non-contact optical surface profilometer and the mechanical properties of BCN films were evaluated with nano-indenter. The BCN films were characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that the BCN films' surface roughness varied in the range of 5-15 nm, and their hardness and reduced elastic modulus fluctuated in the scope of 18-29 GPa and 192-229 GPa, respectively. When the BCN films' surface roughness varied in the range of 8-12 nm, the values of hardness and reduced elastic modulus were fluctuated slightly. The BCN films with the smoothest surface (R-a = 5 nm) and the highest hardness of 28 GPa were obtained at the ion assist source energy of 200 eV and the N-2 relative flow rate of 50%. The BCN films were amorphous and contained several bonding states such as B-N, B-C and C-N with B-C-N hybridization. (C) 2012 Elsevier B.V. All rights reserved.