We have succeeded in synthesizing high-quality, large-size type IIa diamond crystals, measuring up to 12 mm in diameter or about 10 carats by the temperature gradient method under high pressure and high temperature (HPHT) of 5.5 GPa and 1300-1400 ^oC. The important points in the synthesis of the high-quality diamond crystals are the adequate selection and optimization of solvent metals and additives [1], the improvement of crystalline quality of seed crystal [2], and the high precious HPHT control over a prolonged time [3].

The derived high-quality diamond crystals have very few impurities (less than 0.1 ppm) and high crystalline quality (few crystal defects and little internal strain). X-ray topography found no crystal defects such as dislocations and stacking faults in the (001) growth sector of the large crystal grown on high-quality (001)-oriented seeds. Growth of crystals in which the (001) surface is dominant via advanced control of synthesis temperatures in the low-temperature region enabled us to produce diamond crystals free from crystal defects in large areas measuring 5 x 5 mm² or more [4]. The defect-free synthetic diamond will be valuable for a wide range of industrial and scientific applications such as optical windows, optical elements for synchrotron radiation, various high-sensitive detectors (sensors), substrates for high-quality CVD homoepitaxial diamonds, and so on. The excellent crystalline perfection of the high-quality synthetic diamond also permits us to comprehend the essential properties of diamond and to clarify the effects of the impurities and defects on the diamond properties.

REFERENCES

[1] H. Sumiya, S. Satoh, Diamond Relat. Mater., 5, 1359 (1996).

[2] H. Sumiya, N. Toda, Y. Nishibayashi, S. Satoh, J. Crystal growth, 178, 485 (1997).

[3] H. Sumiya, N. Toda, S. Satoh, J. Crystal Growth, 237-239, 1281 (2002).

[4] H. Sumiya, K. Tamasaku, Jpn. J. Appl. Phys., 51, 090102 (2012).

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