Reply to 'Comment on "Angstrom-scale probing of paramagnetic centers location in nanodiamonds by 3He NMR at low temperatures"' by A. Shames, V. Osipov and A. Panich, Phys. Chem. Chem. Phys. 2018, 20, DOI.

Shames et al. made a comment on our article (DOI: 10.1039/C7CP05898E) stating that their experience in EPR studies of detonation nanodiamonds suggests the existence of two main types of paramagnetic center in detonation nanodiamonds which questions our results. In this reply we provide insights into why there is only one main type of paramagnetic centers detected in nanodiamonds used in this work, which validates the correctness of the proposed original method to determine the distances between paramagnetic centers and nanoparticle surfaces by 3He NMR.

Angstrom-scale probing of paramagnetic centers location in nanodiamonds by 3He NMR at low temperatures.

In this article a method to assess the location of paramagnetic centers in nanodiamonds was proposed. The nuclear magnetic relaxation of adsorbed 3He used as a probe in this method was studied at temperatures of 1.5-4.2 K and magnetic fields of 100-600 mT. A strong influence of the paramagnetic centers of the sample on the 3He nuclear spin relaxation time T1 was found. Preplating the nanodiamond surface with adsorbed nitrogen layers allowed us to vary the distance from 3He nuclei to paramagnetic centers in a controlled way and to determine their location using a simple model. The observed T1 minima in temperature dependences are well described within the frame of the suggested model and consistent with the concentration of paramagnetic centers determined by electron paramagnetic resonance. The average distance found from the paramagnetic centers to the nanodiamond surface (0.5 ± 0.1 nm) confirms the well-known statement that paramagnetic centers in this type of nanodiamond are located in the carbon shell. The proposed method can be applied to detailed studies of nano-materials at low temperatures.