Evolution mechanism of nanocrystalline tungsten-carbon and effects on tungsten implanted amorphous hydrogenated carbon

Tungsten doped amorphous carbon films are prepared on silicon (100) by postimplantation of tungsten ions into pure amorphous hydrogenated carbon using the plasma immersion ion implantation technique. The peak concentration of tungsten reaches 27at.% and W–C nanocrystallites with largest diameters of ∼5nm are formed in the near surface region. Both the quantity and size of these nanocrystallites are observed to undergo unique transformation with increasing depths, enabling gradual release of the compressive stress and subsequently leading to better adhesion between the film and substrate. The film structures are evaluated by x-ray photoelectron spectroscopy and glancing angle x-ray diffraction, and high-resolution transmission microscopy is employed to investigate the structural transformation. The mechanical properties of the films including adhesion strength and hardness are determined by nanoindentation and nanoscratch tests. The formation of the nanocrystalline structures can be explained by ion implantation induced damage, chemical effects, and thermodynamics.