Single crystal diamond produced by chemical vapor deposition (CVD) at very high growth rates (up to 150 m/h) has been successfully annealed without graphitization at temperatures up to 2200°C and pressures <300 torr. Crystals were annealed in a hydrogen environment by using microwave plasma techniques for periods of time ranging from a fraction of minute to a few hours. This low-pressure/high-temperature (LPHT) annealing enhances the optical properties of this high-growth rate CVD single crystal diamond. Significant decreases are observed in UV, visible, and infrared absorption and photoluminescence spectra. The decrease in optical absorption after the LPHT annealing arises from the changes in defect structure associated with hydrogen incorporation during CVD growth. There is a decrease in sharp line spectral features indicating a reduction in nitrogen-vacancy-hydrogen (NVH ؊ ) defects. These measurements indicate an increase in relative concentration of nitrogen-vacancy (NV) centers in nitrogencontaining LPHT-annealed diamond as compared with as-grown CVD material. The large overall changes in optical properties and the specific types of alterations in defect structure induced by this facile LPHT processing of high-growth rate single-crystal CVD diamond will be useful in the creation of diamond for a variety of scientific and technological applications. microwave plasma ͉ hydrogen ͉ vacancy ͉ nitrogen

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A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of ±250 °C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H2/CH4/N2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 μm/h. The source of N2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV–visible absorption spectroscopies.

A general method to map strain with parts per million (ppm) resolution in single-crystal wafers and plates is demonstrated. An x-ray technique has been used to obtain separate maps of strain and tilt across synthetic diamond growth sectors. Data consisting of rocking curve maps obtained with a charge coupled device detector were analyzed. The strain results image the growth sectors and reveal a strain pileup near the sector boundaries. The diamond was yellow to the eye due to nitrogen impurities. Not only the topography of the strain map, but also the strain magnitudes, are consistent with the strain arising from nitrogen impurities. High strain resolution in the ppm range is needed to observe these effects.