Non-destructive silicon quantification in low-level Si-doped diamond-like carbon films

Abstract

Diamond-like carbon (DLC) films offer exceptional mechanical and chemical properties but face limitations in adhesion and thermal stability, which restrict their broader applications. Current characterization methods for silicon-doped DLC films rely on destructive techniques, which pose challenges for industrial quality control. We investigate the effects of low-level silicon doping on the microstructure and optical properties of DLC while developing a non-destructive quantification method. Films were synthesized by co-deposition combining pulsed filtered cathodic vacuum arc and RF magnetron sputtering. Silicon incorporation was controlled by varying RF power up to 30 W. Characterization employed X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and spectroscopic ellipsometry, yielding silicon concentrations of 1.55 at.% to 4.64 at.% as determined by XPS. Microstructural analysis reveals C–Si bond formation and strengthened tetrahedral bonding networks with reduced graphitic clusters upon silicon doping. Wavelength-averaged optical properties show systematic decreases in both extinction coefficient and refractive index with increasing silicon content. Spectroscopic ellipsometry combined with Bruggeman effective-medium approximation modeling achieved a strong linear correlation (R2 = 0.97) with XPS-measured silicon concentrations. This non-destructive quantification at sub-5 at.% silicon levels, beyond the sensitivity range of conventional destructive techniques, offers a practical route to industrial-scale quality control of Si‒DLC films.