Mechanical properties of tungsten doped amorphous hydrogenated carbon films prepared by tungsten plasma immersion ion implantation

Tungsten doped amorphous carbon films are produced on silicon (100) wafers by post implantation of tungsten ions into the a-C:H films prepared by plasma immersion ion implantation and deposition (PIII&D). The film structures are evaluated by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, and Raman spectroscopy. The surface morphology is investigated by atomic force microscopy. The mechanical properties of the films including hardness and friction coefficients of the W-implanted layer are determined by nanoindentation and nanoscratch tests. The peak concentration of tungsten reaches 27 at.% and the formation of W-C nanocrystallites is observed. The W-C nanocrystallites and C-C bondings are found to change gradually with depth. The hardness which is slightly improved after W ion implantation is affected by the W-C strengthening phase, C-C structure, and compressive stress. Owing to energetic ion bombardment, the friction coefficient is reduced on the surface of the W-implanted layer and also increases gradually towards the bulk a-C:H film. The structural continuity enables the film to remain intact during the scratch test.