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It has been established that adhesion can be promoted by the incorporation of intermediate carbide forming layers between the substrate and the diamond films. For example the incorporation of a 20 nM layer of titanium between gallium arsenide crystals and diamond films promotes adhesion whereas the deposition of diamond directly on GaAs results in delamination of the film.lt has not yet been physical properties that are either identical to or very close to that of natural diamond crystals. This attribute, in combination with the ability to deposit diamond films over large areas and on complex shapes, makes this technology a very important one for hard coating, machining and tribological applications. Th ability to vary the ratios of diamond to graphite bonding in the material offers a further

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Figure 6. Surface structure of a silicon carbide tool before and after diamond coating. The Raman spectrum shows that the film is primarily composed of diamond bonded material.

degree of freedom in tailoring the material with particular properties and end applications in mind.

In order to fully exploit the superior physical properties of diamond films several research , engineering and scaling issues have to be addressed. Some of the main ones are as follows:

■ An improved understanding of the plasma chemistry of hydrocarbon - hydrogen mixtures is required to establish a firm foundation for the fundamenital mechanismsat work in the process.

• The influence of the substrate material needs to be better understood. Current understanding is based largely on empirical observations.

• The factors that determine the nucleation and growth characteristics of these films on various substrates have to be studied and quantified.

• The mechanisms governing the growth rate of diamond films have to be understood, controlled and applied to the solution of practical problems.

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Figure 7. The smooth morphology of a diamond film on sapphire. The uncoated film is shown in the top micrograph. The Raman spectrum indicates that the film is a two phase material containing both diamond and graphite.

• The all important issue of scaling, equipment development and the establishment of manufacturing technology for specific applications has yet to be addressed.

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