Growth of diamond-like carbon films with significant nanocrystalline phases in a low-pressure high-density CH4 plasma in ICP-CVD: effect of negative dc substrate bias

• Single-step growth of DLC films with nanocrystal phase on glass, without diamond powder pre-treatment. • Inductively coupled low-pressure high electron-density (CH 4 + Ar) plasma used for the film deposition. • Optimum DLC film obtained at –40 V dc substrate bias, 450 °C, 900 W rf power and 25 sccm CH 4. • DLC film showed [I D /I G ] min ∼0.61 with [I Dia /I D ] max ∼1.09 in Raman and 64.28% of sp 3 C-C bonds in XPS data. • DLC film exhibited wide optical band gap ∼3.71 eV and <111> nanocrystal facets in the network. Working at relatively low-temperature and low-pressure, the development and optimization of diamond-like carbon (DLC) films with significant nanodiamond components on inexpensive glass substrates, without conventional pre-treatment by diamond powders, is the main objective of the present work. Using most familiar CH 4 -precursors diluted by Ar in a high-density-plasma triggered at high rf-power (900 W) in a planar inductively-coupled-plasma chemical vapour deposition (ICP-CVD) system, DLC thin-films are prepared via optimization in the flow rate of the precursor-gas at 30 mTorr (∼4 Pa) pressure and 450°C substrate temperature and, further by applying negative dc-bias to the substrates. The optimized samples obtained with negative substrate-bias possess good crystalline properties. From Raman results, the most crystalline sample is obtained with characteristic minimum I D /I G ratio reduced from 0.75 to 0.61, maximum I Dia /I D enhanced from 0.94 to 1.09, and the sp 3 hybridized C-C bonds increased from 44% to ∼64% at a substrate-bias of –40 V. The residual stress, and the optical band gap were calculated from Raman analysis. The optimized DLC film exhibits a high optical band gap (3.71 eV) as calculated from Tauc’s plot analysis of the UV-Vis data. The well-identified <111> crystallographic planes in the TEM micrograph demonstrate a significant fraction of nanocrystalline diamond component in the optimum DLC film.