Thin films of diamond are of interest for technological applications such as hard coatings, heat sinks in electronic devices and miniaturized vacuum diodes. They are typically produced by chemical vapour deposition, and the presence of atomic hydrogen has been considered crucial for the growth of the diamond crystals. Some studies have Claimed diamond film growth in a hydrogen-free environment, but questions remained about the growth conditions in those cases. Here we report the nucleation and growth of diamond by vapour deposition in a hydrogenfree, pure oxygen environment to form crystals that are heteroepitaxially aligned on a single-crystal sapphire substrate. In other words, we are able to achieve diamond growth under conditions where the oxidative 'etching' of carbon must compete with its deposition. By choosing a temperature range that results in preferential oxidation of non-diamond (graphitic) carbon species to that of diamond, we are able to achieve the accumulation of diamond.
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