Design of thin DLC/TiO(2 )film interference coatings on glass screen protector using a neon-argon-based gas injection magnetron sputtering technique

This paper reports the results obtained from the deposition of diamond-like carbon (DLC) films on glass substrates by gas injection magnetron sputtering method. The conducted studies aimed to evaluate if the plasma discharge that is generated by varying the proportions of neon-argon (Ne-Ar) gases during pulsed injections (0%-100%) would promote the synthesis of DLC films with desirable sp(3) phase by means of electron impact-induced plasma interactions. The obtained DLC films showed the presence of sp(3) (C-C) hybridized bonds along the Gaussian distribution curve, which revealed that a maximum sp(3) content in the range of 32%-45% was obtained along the 40% injection of Ne gas, based on the analysis of the C1s core-level spectra and Raman spectroscopy. A 25% gain in hardness (H) and resistance to cracking (H-3/E-2) were also observed in the sp(3)-rich DLC sample (24.1 +/- 4 GPa and 0.29 +/- 0.04), thus promoting its use in various nanomechanical systems. The change in the sp(3)/sp(2) fraction ratio, demonstrated in this research, corresponded well to a calculated model of graded optical bandgap in the range from 0.53 to 3.01 eV. However, to further minimize the parasitic reflectance from a significant share of sp(2) (C=C) domains, thin titanium dioxide (TiO2) (8-36 nm) layers were deposited on the DLC surface, which provided maximum antireflective effect due to interference shift. A significant increase in visible-near-infrared transmittance (up to 87%) was observed as a result of such an interference in DLC/TIO2 bilayers. Our results have practical applications and aid in the design of functional nanocoating structures which are tremendously favored and required to improve the toughness of commercially available glass protectors in hostile environmental conditions.