Processing and characterisation of diamondlike carbon films

Abstract

In nature, carbon has two crystalline allotropes, diamond and graphite, with vastly different properties. However, through chemical or physical vapour deposition (CVD or PVD) a third state, diamondlike carbon (DLC), can be synthesised at low temperatures. There are two kinds of DLC films, one with a relatively large amount (up to 50 at.-%) of hydrogen which is thus named hydrogenated DLC, or a-C: H, and the other essentially without hydrogen inclusion which is thus named non-hydrogenated DLC or a-C (amorphous carbon). There are two basic ways to synthesise a DLCcoating: one is to dissociate a hydrocarbon gas (methane, ethylene, butane, etc.), and the other is by sputtering of a graphite target. Unbalanced magnetron sputtering, arc ion plating, and microwave, cathodic arc, and plasma assisted CVD are examples of suitable processes. The advantages and limitations of these processing methods are discussed. Methods which are often used to characterise DLC coatings are briefly described; advantages, limitations, and important influences on results are also outlined, with emphasis on Raman, infrared, electron energy loss, and NMR spectroscopy.