Structure, Optical and Mechanical Properties of Direct Current Magnetron Sputtered Carbon: Vanadium Nanocomposite Thin Films

The structure, the optical and the mechanical properties of carbon: vanadium nanocomposite thin films (∼1 at.% to 48 at.% V) grown by direct current magnetron sputtering at 110 °C are investigated using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, spectroscopic ellipsometry, and nano-indentation. At all compositions a phase separation into cubic vanadium carbide, VCx, (x ≤ 1) and carbon is observed, the structure of both phases changing continuously with the vanadium content. The film microstructure consists of statistically distributed spherical VCx particles in a carbon matrix at V concentrations of up to about 35 at.%, and at higher V concentrations of elongated, dendrite-like VCx nanocrystallites, which are separated by a carbon tissue phase. The microstructure hints to a transition from purely repeated nucleation dominated growth to a regime with competing repeated nucleation and surface diffusion. The optical properties are controlled by the phase composition of the films. The hardness is nearly independent of the composition, thus enabling the independent tuning of the absorption behavior at constant hardness.