On the magnetic properties of nanodiamonds: Electronic g-tensor calculations

Electronic g-Tensor Calculations for Dangling Bonds in Nanodiamonds

The electronic g-tensor calculations are performed for dangling bonds (DBs) introduced into nanodiamonds (NDs) with four different functional groups on their surfaces. For hydrogenated and fluorinated NDs, it is found that g-shifts of the latter vary in a much wider range, and the same is also true for the total energy differences between the highest and the lowest energy DBs. In addition, it is shown that the shape of NDs significantly impacts the energetics and g-shifts of DBs, whereas the influence of the size is much less pronounced, as is the influence of the presence of one DB in the vicinity of the other, resulting in no substantial change on their magnetic behavior. For hydroxylated and aminated NDs, it is demonstrated that the variation range of g-shifts is larger for the former, whereas the opposite is seen regarding the total energy differences. On the whole, some of the positions of DBs can be energetically very costly in these NDs; besides, the lowest energy DBs are irregular, that is, formed by OH- and NH₂-bonded C atoms, contrasting with hydrogenated and fluorinated NDs, for which irregular DBs are the most energetically unfavorable.

Computational study on the electronic g-tensors of hydrophilic and hydrophobic nanodiamonds interacting with water

Hydrogenated and hydroxylated nanodiamonds (NDs) are modeled by putting emphasis on the most common paramagnetic impurities-dangling bonds as well as single substitutional nitrogen atoms-and their interaction with water. It is shown that, despite its overall hydrophobicity, hydrogenated ND can become locally hydrophilic due to the introduced defects; therefore, water molecules may be attracted to the particular sites at its surface. To assess the direct influence of water on the magnetic behavior of NDs, the solvent-induced shift of the g-tensor was employed, indicating that for the same types of impurities, the impact the water has strongly depends on their positions in ND. In addition, water molecules at the locally hydrophilic sites of hydrogenated ND may influence the magnetic behavior of defects to the same extent as it may be influenced in the case of hydroxylated ND. Moreover, the overall hydrophilic nature of the latter does not necessarily guarantee that water, although being strongly attracted to the vicinity of impurity, will form a hydrogen bond network with a substantial impact on the local environment of the unpaired electron. The obtained data imply that in the context of the Overhauser effect, for which the solvent-induced shift of the g-tensor is proposed as a tool to reveal whether some NDs are more favorable for it to occur compared to the others, hydrogenated NDs should perform no worse than hydroxylated ones, despite only the local hydrophilicity of the former.

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.