Spin S=1 centers: a universal type of paramagnetic defects in nanodiamonds of dynamic synthesis
Résumé
Intrinsic paramagnetic defects in similar to 5 nm sized nanodiamonds, produced by various dynamic synthesis (DySND) techniques (detonation, shock-wave, pulsed laser ablation of solid carbon containing targets), have been studied by multi-frequency electron paramagnetic resonance (EPR). X-band (9-10 GHz) EPR spectra of DySND, in addition to the main intensive singlet Lorentzian-like EPR signal, reveal a low intensity doublet pattern within the half-field (HF) region (g similar to 4). On transferring spectra to the Q-band (34 GHz) the shape of the HF pattern changes and splitting between doublet components is reduced from 10.4 to 2.6 mT. The HF patterns observed are attributed to the `forbidden' Delta M-S = 2 transitions between the Zeeman levels of some spin-triplet (S = 1) centers. The model of two triplet centers with g similar to 2.003 and zero-field splitting parameters D-1 = 0.095 cm(-1) (TR1) and D-2 = 0.030 cm(-1) (TR2) satisfactorily describes experimental results at both microwave frequencies. The spin-triplet-type defects are observed in a wide variety of DySND samples irrespective of industrial supplier, cooling and carbon soot refinement methods, initial purity, disintegration, or subsequent targeted chemical modification. This indicates that the intrinsic defects with S = 1 in DySND systems are of universal origin.