Electronic g-tensors of nanodiamonds: Dependence on the size, shape, and surface functionalization

The electronic g-tensor dependence on the size, shape, and surface functionalization of nanodiamonds (NDs) is theoretically investigated by selecting dangling bonds and single substitutional nitrogen atoms as a main source of the unpaired electrons. The performed g-tensor calculations reveal that aforementioned paramagnetic impurities introduced into octahedrally shaped ND of C₈₄H₆₄ size behave in a very similar manner as those embedded into a smaller octahedral model of C₃₅H₃₆ size. Since cubic and tetrahedral NDs—C₅₄H₄₈ and C₅₁H₅₂—demonstrate a wider range of g-shift values than octahedral systems, the g-tensor dependence on different shapes can be considered as more pronounced. However, a different surface functionalization scheme, namely, fluorination, results in a much larger variation of the g-shifts, pointing to a significant impact the F atoms have on the local environment of the unpaired electrons in C₃₅F₃₆. A partial surface functionalization of C₃₅H₃₆ with benzoic acid and aniline groups indicates that, in some special cases, these linkers might induce a noticeable spin density redistribution which in turn substantially modifies the g-shift values of the system. Additional infrared (IR) spectra calculations show that some of paramagnetic defects in C₃₅H₃₆ and C₃₅F₃₆ possess clearly expressed signatures which could be useful while analyzing the experimental IR spectra of NDs.