Influence of the Chemical Modification of the Nanodiamond Surface on Electron Paramagnetic Resonance/Electron-Nuclear Double Resonance Spectra of Intrinsic Nitrogen Defects

Abstract

A high-frequency/high-magnetic field (94 GHz/3.3 T) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) study of monocrystalline nanodiamonds (ND) is carried out. Influence of the hydrogen and fluorine modification of the ND surface on EPR and ENDOR signals from the superficial and bulk paramagnetic centers is observed. The effect shows that the ND bulk paramagnetic centers could serve as the intrinsic probe of ND surface modification despite deep localization, shielding from the environment and two-layered surface of the diamond nanoparticle.

Electronic g-Tensor Calculations for Dangling Bonds in Nanodiamonds

“…Unfortunately, a direct comparison between the theoretical and experimental results is not straightforward because of two essential reasons. First, different production and purification procedures applied to NDs result in differently functionalized surfaces, and, unless explicitly stated as in the works of Yavkin et al or Panich et al , it is hardly possible to trace the specific surface functionalization that was present during the EPR experiment. Second, experimental measurements provide an average value of Δ g̅ for an ensemble of NDs that constitute a sample, while our data are obtained for single nanoparticles.…”

“…The total energy differences, on the other hand, are not similar either, as the highest ΔE value for hydroxylated ND is 17.2 kcal/mol [DB(O23−H23)], while the analogous value for aminated ND is almost twice as large33.8 kcal/mol [DB(H39−N20−H40)]. In addition, these numbers are vastly higher than those seen for C 35 36 [DB(H39−N20−H40)] reveals that, with respect to the structure of pure C , they are located on the geometrically equivalent C atoms. In addition, even more might be said at this point: on the basis of their geometric positions, DBs in hydroxylated and aminated NDs can be divided into the same three groups consisting of twelve DBs as in the case of hydrogenated and fluorinated NDs.…”

“…In addition, let us make another assumption that formation of DBs occurs in a random statistical manner, which might be reasonable if one takes into account how NDs are usually obtainedby applying milling, grinding, or pulverizing techniques. 8 36 , respectively. Among these numbers, only 528 ppm of C 35 (OH) 36 appears to agree with the experimental value, while others are slightly too low.…”

“…)36 (including the lowest energy DB), the total energy differences do not exceed 7.9 kcal/mol; for another twelve DBs, the range of ΔE is 11.2−19.1 kcal/mol, and for the last twelve DBs, the ΔE values fall within 26.2−33.8 kcal/mol. The most important part of this observation is that every DB in a particular group is located on the geometrically equivalent C atom of C 35 , indicating that the first, second, and third groups, respectively, correspond to DB(H33/F33), DB(H28/F28), and DB(H23/F23) type of DBs met while investigating C 35 H 36 and C 35 F 36 .…”

“…11 Concerning hydrogenated NDs, we have expanded our previous work 12 by including octahedrally shaped C 165 H 100 among the modeled systems, while for fluorinated NDs, octahedral C 84 F 64 and C 165 F 100 , as well as cubic C 54 F 48 and tetrahedral C 51 F 52 , were newly added. Hydroxylated and aminated NDs were fully investigated for the first time, but due to the substantially increased amount of calculations, we have confined ourselves to the smallest models C 35 (OH) 36 and C 35 (NH 2 ) 36 of the most common octahedral shape. 13 In addition, the simultaneous presence of several DBs in hydrogenated and fluorinated NDs was analyzed and a comparison of the obtained results to the available experimental data was presented.…”