Magnetic resonance study of detonation nanodiamonds with surface chemically modified by transition metal ions

A. M. Panich, A. I. Shames, O. Medvedev, V. Yu Osipov, A. E. Aleksenskiy, A. Ya Vul'

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37 Scopus citations

Abstract

We report on electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) study of detonation nanodiamonds (DND) with the surface modified by copper and cobalt ions. The EMR spectrum of the pure DND sample shows an intense singlet originating from broken carbon bonds, while the spectra of copper- and cobalt-modified samples reveal additional signals with g > 2 and pronounced hyperfine structure (for copper). Increase in the Cu/Co concentration causes an increase of the corresponding EMR signals and broadening of the intense carbon-inherited singlet line. Subsequent annealing of the copper-modified samples in a hydrogen gas stream at 550 and 900°C causes narrowing of the singlet line and reduction of the Cu2+-related components. Applying the same annealing process to the cobalt-modified samples leads to broadening of the singlet line, reduction of Co2+ component and appearance of new intense low-field signals. NMR data correlate well with the EMR findings and yield information on interactions and locations of transition metal ions. 13C nuclear spin-lattice relaxation rate R1 in pure DND is driven by the interaction of nuclear spins with unpaired electron spins of broken bonds. Chemical modification of the DND surface by Cu and Co causes an increase in the relaxation rate, revealing appearance of paramagnetic Cu2+ And Co2+ complexes at the DND surface and their interaction with the carbon nuclear spins, both directly and via a coupling of Cu2+ and Co2+ electrons with those of the broken bonds. The aforementioned annealing of the Cu- and Co-DND results in an inverse process, i.e., a reduction of the relaxation rate, indicating that these complexes are destroyed and metal ions presumably join each other forming copper and cobalt nanoclusters. In the case of Co the nanoclusters are ferromagnetic, which results in the noticeable broadening of the 13C NMR lines.

Original languageEnglish
Pages (from-to)317-329
Number of pages13
JournalApplied Magnetic Resonance
Volume36
Issue number2-4
DOIs
StatePublished - 30 Oct 2009

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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