Diamond and diamondlike coatings : preparation, properties and application

Diamond is the hardest and the best heat conducting material known, transparent in the visible and infrared (IR), except from 2.5 to about 6.5 $\mu$m wavelength) with a high refractive index (2.4), very high electrical resistivity (> 10$^{20}$ ohm cm), exceptional chemical inertnes and high thermal stability. Due to its unique properties, the diamond has attracted attention of men over centuries. For the same reason researchers allover the world have tried to synthesize diamond. One of the main obstacles in synthesizing diamond arises from the fact that it is thermodynamically stable only at high pressures (Fig. 1) [37], so that it exists under normal conditions only as a metastable phase. Although due to kinetic reasons diamond remains unchanged at lower temperatures, at about 1500 $^{\circ}$C in an inert atmosphere begins its transformation into the stable modification-graphite. Since the first successful attempts to synthesize diamond - those in Sweden [62,63] and USA [20], the laboratoryexperiments have been turned into an advanced industry. In the industrial process a suitable carbon source (graphite) is brought to the thermodynamically correct region in the presence of a solvent/catalyst (one of the group VIII transition metals) whereby the diamond synthesis results. In recent decades it has proved possible to produce virtually pure carbon films with properties similar to those of diamond by deposition from a gas phase at low pressures, using methods which provide activated, high energy species in the gasphase. However, the films exhibited marked differences in their optical, electrical, mechanical and other characteristics, depending on the method and conditions of preparation used. This diversity of properties is a consequence of the ability of carbon atom to form different strong carbon-carbon chemical bonds. The nature of the bond formed is determined by the type of hybridization of valence electrons (sp$^{1}$, sp$^{2}$, sp$^{3}$) (Fig. 2), [...