Rather than try to duplicate Nature's method, diamond could conceivably be produced if carbon atoms could be added one-at-a-time to an initial template, in such a way that a tetrahedrally bonded carbon network results (see Figure 5.1). These ideas led to experiments in which carbon-containing gases were heated under reduced pressure until the molecules broke apart, and then these fragments were condensed onto a nearby surface. Analysis showed that the thin film that resulted from this did, indeed, contain diamond. However, the rate of growth in these early experiments was low, and the films were impure, containing a large proportion of unwanted graphite. The breakthrough came in the late 1960s, when researchers in the USA discovered that the presence of atomic hydrogen during the deposition process would remove graphite from a surface much faster than diamond. This meant that the impure components were removed from the
Figure 5.1. In diamond, every carbon atom is bonded to four others in a strong, rigid tetrahedral structure.
growing film, leaving only pure diamond behind. This process became known as 'chemical vapour deposition' (CVD), since it involves a chemical reaction occurring within a vapour over a surface, leading to deposition of a thin coating onto that surface. Over the next few years more breakthroughs were made which allowed diamond films to be grown at significant rates on many useful materials. This series of discoveries stimulated world-wide interest in diamond CVD, in both academia and industry, which continues to the present day.
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