Characterization of boron-doped diamonds using ¹¹B high-resolution NMR at high magnetic fields

¹¹B static/magic-angle spinning (MAS) NMR experiments are applied to four different B-doped diamond samples prepared by either high-pressure and high-temperature (HPHT) or CVD methods with various starting materials. Application of MAS enhances the spectral resolution appreciably and differences of the four B-doped diamond samples are well reflected in the corresponding MAS spectra. From the comparison among the MAS spectra, and also their dependences on the magnetic-field and the pulse-flip angle, it is suggested that at least four kinds of boron including two kinds of impurities exist in B-doped diamond. We further examine ¹¹B spin-lattice relaxation times (T₁) for the four components and find that one of them is extremely short (ca. 500 ms) while others are in the range of several seconds. Relation between the component having the short T₁ and the super conducting transition temperature (T_c) value is suggested.