A Novel strategy to enhance micro/nano-tribological properties of DLC film by combining micro-pattern and thin ionic liquids film

Both of surface topography and chemical composition play important roles in affecting the adhesive force and friction force in micro/nano-electromechanical systems (M/NEMS). Two effective approaches of reducing adhesion and friction of contacting interfaces are to create patterned surface and lower surface energy, which are especially beneficial for M/NEMS production yield and product reliability. Diamond-like carbon (DLC) films with high hardness, low friction coefficient and good wear resistance have aroused particular interest as protective film. Also, ionic liquids (ILs) display better tribological properties than that of conventional lubricants, such as PFPE and X-1P. In this article, we present a novel method to fabricate the micro-patterned DLC-IL films by combination of by combination of inductively coupled plasma (ICP) etching method, magnetron sputtering technology and dip-coating method. DLC films with different packing density micro-grooves were prepared by controlling the photolithography design. The morphologies and surface chemical states of DLC and DLC-IL films were characterized by atomic force microscope (AFM), XPS and Raman. The adhesion and friction on the as-prepared DLC and DLC-IL films were studied by colloidal probe mounted on AFM cantilever in contact mode. The microtribological behaviors of the DLC and DLC-IL films were evaluated by UMT-3 tribometer in a ball-on-plate reciprocating mode. The experimental results showed that adhesive force and friction force of the DLC films with micro-grooves reduced effectively with increase of groove area density and incorporation of thin ILs film. The corresponding synergetic anti-adhesion and friction reduction mechanisms of surface pattern and chemical modification were discussed and clarified with emphasis. The lowered adhesion and friction force were attributed to two factors including (1) the reduced real area of contact between DLC films and colloidal tip; (2) incorporation of thin ILs films to avoid direct contact between DLC films and colloidal tip, which facilitating the sliding of colloidal tip on DLC films.