Finding ways to routinely and reliably produce larger near-colorless and colorless single-crystal diamond needed for a variety of applications in science and technology is a major challenge. Microwave plasma assisted chemical vapor deposition (MPCVD) techniques have been refined to produce large, high-purity single crystal diamond anvils. Specifically multicarat single crystal diamond has been produced at high growth rate without annealing (around 50 µm/h) with low impurities content. UV–visible absorption, Raman/photoluminescence spectroscopy, cathodoluminescence, and confocal Raman imaging are used to characterize the diamond. The measurements show that the material has high optical quality and clarity without layers. The large intensity ratio of the second-order Raman peak to the fluorescence background is essential for high-pressure optical windows. The origin of the residual color is also examined.
The picture on the right shows a 2.4 carat single-crystal CVD diamond compared with 0.25 carat CVD diamond. Left images: Example of the evolution of CVD diamond single crystal starting with crystal 13.5 carat block to the 2.3 carat cut gem anvil.