Process for applying a carbonaceous coating onto a surface

摘要

The surface of a material is covered with a carbonaceous coating by vacuum deposition, the carbon in a substantially pure form originating from a hydrocarbon gas plasma. The surface to be coated is coupled to a source of direct current operating at a frequency of less than 500 kHz, at which the electrical impedance of the plasma does not vary appreciably during the deposition process. As the impedance of the plasma is substantially constant, the process is reliable and reproducible. It can be performed without dynamic control and without adjustment and it does not require any adapter of impedance between the source of alternating current and the vacuum chamber. It has been found that frequencies in the range 300-400 kHz with voltages of the order of 1 kV or more have given good results. The coatings obtained are intended chiefly for reducing the reflectivity of optical substrates. <IMAGE>