W-incorporated diamond-like carbon (W-C:H) films were fabricated by a hybrid beams system consisting of a DC magnetron sputtering and a linear ion source. The W concentration (1.08~31.74 at.%) in the film was controlled by varying the sputtering current. The cross-sectional topography, composition, and microstructure of the W-C:H films were investigated by SEM, XPS, TEM, and Raman spectroscopy. The mechanical and tribological properties of the films as a function of W concentration were evaluated by a stress-tester, nanoindentation, and ball-on-disk tribometer, respectively. The results showed that films mainly exhibited the feature of amorphous carbon when W concentration of the films was less than 4.38 at.%, where the incorporated W atoms would be bonded with C atoms and resulted in the formation of nanoparticles. The W-C:H film with 4.38 at.% W concentration showed a minimum value of residual compressive stress, a higher hardness, and better tribological properties. Beyond this W concentration range, both the residual stress and mechanical properties were deteriorated due to the growth of tungsten carbide nanoparticles in the carbon matrix. 1. Introduction Diamond-like carbon film (DLC) is a metastable form of amorphous carbon with a certain dominant sp3 bonding. Due to its unique properties such as high hardness, low friction coefficient, good chemical inertness, and the optical transparency in a wide range of VIS-IR, DLC film has been used as protective coatings in many industrial fields [1]. However, high residual stress is the major drawback of DLC films for its wider practical application [2–6]. Immense amounts of concrete research have shown that the incorporation of metal elements, such as Mo, Cu, Al, Cr, and W, is one of the good methods to decrease the internal stress of DLC films [7–12]. As one of the doped metal elements, W-incorporated DLC films (W-C:H) have been received considerable attention both in scientific research and industrial fields of carbon based materials [13–19]. The properties and structure of W-C:H films prepared by the process combining reactive magnetron sputtering with plasma source ion implantation were reported by Baba and coworkers [20]. Takeno et al. [21] investigated the electrical properties and structure of W-C:H films prepared by radio frequency plasma enhanced chemical vapor deposition, and a resistive superconducting transition was discovered in their report. Wang et al. [22] reported a rapid increase and a gradual decrease in the residual stress of DLC films prepared by end-Hall-type ion gun with increasing
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