Synthesis and characterization of diamond-like carbon films for optical and mechanical applications

Abstract

Diamond-like carbon (DLC) films were directly deposited onto several substrates utilizing the ion beam deposition technique. By impacting high kinetic energy (1000 eV) of high molecular weight hydrocarbon ions onto the substrate, adherent, amorphous, high density and transparent DLC films were produced. Cross-sectional transmission electron microscopy demonstrates that the DLC films are homogeneous, free of pinholes and produce no damage to the silicon substrate. The hydrogen content of the DLC films is 30% and is free from other impurity contamination. These films are hard (Knoop hardness 1548 ± 200 kg mm -2), and resistant to organic solvents, mineral acids, extreme temperature cycling and moisture attack. The friction coefficient of the DLC films in the beginning of the experiment is 0.2, and then rapidly decreases to 0.1 with increasing sliding distance. An increase in humidity results in a slight increase in friction coefficient, but a significant decrease in wear factor. The optical band gap is 1.0 ± 0.1 eV and films are transparent in the IR region. The refractive index at 10.6 μm is 1.91 ± 0.02, and the absorption coefficient is 189 ± 10 cm -1. Raman spectra demonstrate that amorphous DLC films change to graphitic carbons upon rapid thermal annealing above 600 °C and also upon high ion energy with excess fluence and high power density laser irradiation by losing hydrogen in the films.