Transparent carbon films: Comparison of properties between ion- and plasma-deposition processes

Optical, electrical, and mechanical measurements were made on transparent carbon films prepared by two different techniques: Ion sputtering of graphite with argon ion co-bombardment and rf plasma decomposition of hydrocarbon compounds. A comparison between the properties of films deposited by each technique is presented. The films deposited by the plasma process were more transparent, had a lower refractive index, and showed less mechanical stress than the sputtered films. They were softer and electrically less stable than the ion-sputtered films. Both processes produced films having very low charge density and high resistivity. The simplicity of the plasma process and the ability to cover larger areas makes it the preferred process for the protective coating of optical surfaces on a production basis.