Studies of Diamond-Like Carbon Coatings for Protection of Optical Components

Ion-deposited diamond-like carbon is a promising candidate for thin protective coatings for optical components. Our recent studies have been directed to ascertaining several key properties of the coating, and verifying its protective nature. Tests performed on coated discs of CaF2 indicated improved resistance to environmental attack by acids, bases, and solvents. Hermeticity was corroberated by comparing the effects of HF-acid on coated and uncoated surfaces. The tenacity to substrates such as glass and CaF2 was demonstrated by the difficulty to remove the coating with standard techniques, such as exposure to HF and water. Also, a marked decrease in abrasion was found (by measuring forward optical scatter) for the coated portion of a disc. Optical measurements performed on these coated discs indicated that the coating neither significantly decreased transmission as measured from 2 to 6 microns, nor induced visible scatter. High resolution scanning and transmission electron micrograph studies indicate that the films are partly amorphous with a partial ordering of carbon atoms; while Raman studies indicated both graphite as well as microcrystalline diamond-type behavior. ESCA studies indicated a C to CaF2 gradient throughout the coating indicative of ion implantation. Thickness determinations were made by substrate dissolution and surface profile measurements.