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

Abstract

Diamond-like carbon (DLC) and seven kinds of La 2 O 3 -and CeO 2 -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 La 2 O 3 and CeO 2 are formed within the DLC films. Combining the C1s spectrum and Raman spectra, the DLC amorphous structure is not changed with the doping of La 2 O 3 and CeO 2 . 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 La 2 O 3 and CeO 2 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. IntroductionDiamond-like carbon (DLC) films have attracted much attention, due to their unique properties, such as high hardness, atomic level smoothness, low-friction coefficient, excellent abrasion resistance, negative electron affinity, chemical inertness, high-thermal conductivity and optical transparency [1,2]. However, residual compressive stress and low-adhesion strength limit their practical applications [3,4]. To reduce the residual stress and to enhance the adhesion strength of DLC films, doping transition metals into the DLC films, such as Ti, Mo, Cr, W, etc., has been widely used to improve their mechanical properties [5,6]. This kind of strategy utilizes the metallic affinity between the film and metallic substrate to enhance the adhesion strength, and forms carbide between the doping transition metal and carbon element as a pivotal site to reduce the residual stress and increase the tribological properties [7,8]. While this kind of method converts the amorphous structure with the doping of transition metals, the increase of adhesion strength effect is not available between the film and non-metallic substrate. The action mechanism of transition metals to the mechanical and tribological properties to the DLC

A novel approach of deposition for uniform diamond films on circular saw blades

“…The full width at half maximum (FWHM) of sample RB is the smallest at the lower side of location A (figure 4) and upper side of location B (figure 5) among the three samples, meaning the lowest crystalline defects and anisotropic stress distribution[30]. The broad peaks are observed for graphite G mode ranged from 1520 to 1580 cm −1 in figures 4 and 5[32,[39][40][41][42]. The peaks spanned from 1430 to 1480 cm −1 belong to trans-polyacetylene[32].…”