MPCVD growth of C-13-enriched diamond single crystals with nitrogen addition

摘要

This study describes the growth of C-13-enriched (100)-oriented diamond single crystals by the MPCVD (microwave plasma chemical vapour deposition) process. All crystals are at least 6 x 6 mm(2) in area and 0.5-1.0 mm in thickness. The samples with nominal C-13 percentages (R = [C-13] [C-13 + C-12]) of 0.011 (natural abundance), 0.10, 0.21, 0.24 and 034 were obtained by controlling the flow of the carbon-13 and carbon-12 methane feed gases. To obtain thicker and near -colourless quality C-13-enriched diamond, 190 ppm of nitrogen was added into the gas mixture. The shift towards lower frequency in the Raman peak positions and decrease in the thermal conductivities of the near -colourless crystals with increasing C-13 percentages are similar to previous studies of isotopically-controlled diamond grown with no nitrogen additive. The images of the structural defects associated with C-13-enrichment obtained by spatially-resolved X-ray rocking curve measurement show distinct patterned structures that runs parallel to the < 100 > direction. Moreover, the broadening in the line width of the nuclear magnetic resonance (NMR) peak from sp(3) C-13 correlates with increasing R. We also expand the study by injecting 500 ppm of nitrogen. Higher nitrogen concentration leads to the formation of brown crystals. The brown crystals show far greater C-13 NMR peak intensity than the near-colourless. This suggests that paramagnetic nitrogen impurities in the brown crystals hasten the spin-lattice relaxation time of the C-13 nuclear spin that resulted in higher intensity. The isotopic splitting observed for the localized vibrational mode of the NVH0 defect in brown crystals is attributed to the co-existence of both the C-13 (3114.2 cm(-1)) and C-12 (3123.5 cm(-1)). Unlike the isotopic splitting observed for NVH0 defect, the peak position of the NS defect shifts towards lower frequency as R increases. Not only have we demonstrate the growth of bigger isotopically-controlled diamond single crystals, the results shown here have provided a framework to further investigate the interplay between C-13 atoms and nitrogen impurity. (C) 2015 Elsevier B.V. All rights reserved.