Unusual stress behaviour of La₂O₃- and CeO₂-doped diamond-like carbon nanofilms

Abstract

Diamond-like carbon (DLC) and seven kinds of La₂O₃- and CeO₂-doped DLC composite nanofilms were deposited by unbalanced magnetron sputtering. Raman spectra show that these deposited films have the obvious characteristics of amorphous DLC films. X-ray photoelectron spectroscopy confirms that the La₂O₃ and CeO₂ are formed within the DLC films. Combining the C1s spectrum and Raman spectra, the DLC amorphous structure is not changed with the doping of La₂O₃ and CeO₂. Auger electron spectroscopy exhibits that La, Ce, O and C elements distribute uniformly along the depth direction, and they diffuse into the substrate at the interface between the substrate and film. Residual compressive stress of pure DLC films is 0.9 GPa, and those of La₂O₃ and CeO₂ doped DLC films are lower than 0.25 GPa. The residual stress of seven kinds of rare earth oxides doped DLC films reduces to lower than 1/3 of that of pure DLC films. When the composite concentration of rare earth oxides is less than or equal to 9%, the residual compressive stress is in the range of 0.01–0.02 GPa, which is 1/90–1/45 of that of pure DLC films, indicating unusual stress behaviour.

Keywords:

• La₂O₃
• CeO₂
• DLC
• residual compressive stress

Acknowledgements

The authors appreciate the financial support from the Key Project of National Natural Science Foundation of China (Grant No. 50535020), the Natural Science Foundation of Liaoning Province of China (Grant No. 20071083), and the National Natural Science Foundation of China (Grant Nos. 50575034, and 50675029).