Structure and residual stress evolution of Ti/Al, Cr/Al or W/Al co-doped amorphous carbon nanocomposite films: Insights from ab initio calculations

Abstract

Here, we selected Ti, Cr, and W as the representative metal elements to composite with Al atom in order to generate co-doped amorphous carbon (a-C) films using ab initio calculations. Results show that compared with the pure and mono-doped cases, the Ti/Al, Cr/Al, or W/Al co-doped a-C films exhibit a general tendency of stress reduction. Particularly, it is noted that with the co-doping of Ti (1.56at.%)/Al (1.56at.%), Cr (1.56at.%)/Al (4.69at.%), or W (1.56at.%)/Al (1.56at.%), the residual stress is reduced by 83%, 78.9%, and 90.6%, respectively, without deteriorating the mechanical properties. Structural analysis reveals that the co-doping of Ti/Al, Cr/Al, or W/Al brings the critical and significant relaxation of distorted C–C bond lengths, as well as the formation of a weak covalent interaction for Ti–C, Cr–C, and W–C bonds and the ionic interaction for Al–C bonds, which account for the giant residual stress reduction. Consequently, by the synergistic effect of small amounts of soft ductile weak-carbide-forming metals and hard-carbide ones, it provides the theoretical guidance and desirable strategy to design and fabricate the a-C films with low residual stress and other novel performance/functions.