Study on particle size and field effect with sp2/sp3 ratio of hydrogenated diamond-like carbon

Abstract

Hydrogenated diamond-like carbon (HDLC) films were synthesized through a reactive gas-plasma process employing methane (CH4) and hydrogen (H2) as precursor gases on a silicon (100) wafer substrate, conducted at room temperature. The deposition process utilized a biased enhanced nucleation technique, varying the flow rate ratio of hydrogen and methane. The investigations revealed that increasing the methane flow rate led to a reduction in grain size and an augmented nucleation density of HDLC, as evidenced by contact-mode atomic force microscopy (AFM) images. This study demonstrated the effective control of diamond grain growth by introducing high-methane-concentration pulses during deposition. The field emission characteristics of HDLC samples were analyzed, revealing threshold fields of 12.2 V/μm for nanocrystalline films, 8.5 V/μm for subcrystalline films and 4.1 V/μm for microcrystalline films, corroborated by Raman spectra. Surface energy measurements indicated hydrophobic behavior in the samples. Notably, a decrease in the hydrogen/methane ratio was found to increase the sp2 character, which correlated with the emission field. AFM analysis of HDLC samples yielded surface roughness values ranging from 0.2 nm to approximately 0.01 nm, confirming the continuous, non-porous and smooth nature of the surfaces.