Alignment of Ni- and Co-related centres during the growth of high-pressure-high-temperature diamond

An extensive study of Co- and Ni-related centres in high-pressure synthetic diamond, using electron spin resonance, optical absorption and luminescence techniques, has revealed that most of these defects, in samples grown at low temperature (similar to1400degreesC), exhibit preferential alignment, i.e. a non-equal distribution over crystallographic ally equivalent orientations. Remarkably, this observation applies not only to defects assumed to involve only an Ni or a Co atom, but also to some Ni-N complexes. Annealing at T > 1600degreesC induces nitrogen mobility and the corresponding formation of numerous Ni-N-and Co-N-related centres. This annealing eventually destroys the preferential polarization of low-temperature centres.