Nuclear Magnetic Resonance Study of Ultrananocrystalline Diamonds

TL;DR

This study uses NMR techniques to analyze the structure and surface chemistry of ultrananocrystalline diamond particles, revealing a diamond core with a fullerene-like shell and paramagnetic centers at the core-shell interface.

Contribution

It provides detailed NMR characterization of UNCD, identifying the core-shell structure and the location of paramagnetic centers, advancing understanding of UNCD surface chemistry.

Findings

UNCD particles have a diamond core with a sp2-carbon shell.

Paramagnetic centers are mainly at the core-shell interface.

Significant increase in spin-lattice relaxation rate compared to natural diamond.

Abstract

We report on a nuclear magnetic resonance (NMR) study of ultrananocrystalline diamond (UNCD) materials produced by detonation technique. Analysis of the 13C and 1H NMR spectra, spin-spin and spin-lattice relaxation times in purified UNCD samples is presented. Our measurements show that UNCD particles consist of a diamond core that is partially covered by a sp2-carbon fullerene-like shell. The uncovered part of outer diamond surface comprises a number of hydrocarbon groups that saturate the dangling bonds. Our findings are discussed along with recent calculations of the UNCD structure. Significant increase in the spin-lattice relaxation rate (in comparison with that of natural diamond), as well as stretched exponential character of the magnetization recovery, are attributed to the interaction of nuclear spins with paramagnetic centers which are likely fabrication-driven dangling bonds with unpaired electrons. We show that these centers are located mainly at the interface between the diamond core and shell.