Synthesis of nanocrystalline diamond embedded diamond-like carbon films on untreated glass substrates at low temperature using (C2H2 + H2) gas composition in microwave plasma CVD

Abstract

Diamond-like carbon (DLC) films with well distinguished nanocrystalline diamond (NCD) grains embedded in the matrix are grown at ∼300 °C on glass substrates without any pre-treatment, using a specially-designed stainless-steel shadow-mask assembly creating diffuse secondary plasma that shields the growth zone from high energy ion bombardment. The effects of different compositions of the precursor gas, R = C2H2 / (C2H2 + H2), and gas pressure in the plasma at 500 W of microwave power demonstrate their significant influences on controlling the relative composition of the sp3 to sp2 hybridized carbon phases in the films. The maximum intensity ratio of IDia/IG (∼1.05) and IDia/ID (∼1.05) along with the corresponding minimum of ID/IG (∼1.0) appearing in the Raman spectrum at R = 0.33 and 25 Torr pressure, correlate a superior diamond-phase containing ∼55% sp3-hybridized carbon in the DLC network having high optical transmittance of ∼87% at 600 nm wavelength. A homogeneous microstructure with uniform distribution of the NCD grains of average size ∼10 nm and 〈111〉 crystallographic orientation, and smooth surface morphology with average roughness ∼2.1 nm is obtained in the optimum NCD embedded DLC film, the growth mechanism of which is discussed on the basis of parametric changes.