V. Yu. Osipov

Optical properties of nanodiamond layers

Thin ultradisperse diamond (UDD) layers deposited from a water suspension are studied by optical and x-ray photoelectron spectroscopy (XPS). The effective band gap determined by the 104-cm−1 criterion for ozone-cleaned UDD is 3.5 eV. The broad structureless photoluminescence band (380–520 nm) is associated with radiative recombination through a system of continuously distributed energy levels in the band gap of diamond nanoclusters. The optical absorption of the material at 250–1000 nm originates from absorption on the disordered nanocluster surface containing threefold-coordinated carbon. The surface of UDD clusters subjected to acid cleaning contains nitrogen-oxygen complexes adsorbed in the form of NO3− nitrate ions. Annealing in a hydrogen atmosphere results in desorption of the nitrate ions from the cluster surface. The evolution of the oxygen (O1s) and nitrogen (N1s) lines in the XPS spectra under annealing of a UDD layer is studied comprehensively.

Proton magnetic resonance study of diamond nanoparticles decorated by transition metal ions

We report on a 1H NMR study of diamond nanoparticles decorated by copper and cobalt. Increase in the 1H relaxation rate under decoration results from the interactions of hydrogen nuclear spins of the surface hydrocarbon and hydroxyl groups with paramagnetic copper and cobalt ions. This finding reveals the appearance of paramagnetic Cu2+ or Co2+ ions on the detonation nanodiamond (DND) surface rather than as a separate phase, which is consistent with the 13C NMR data of the same samples. Our results shed light on the mechanism of ion incorporation. A topological model for relative position of paramagnetic Cu2+ or Co2+ ions and hydrogen atoms on the DND surface is suggested. An application of the studied nanomaterials in the field of biomedicine is discussed.

Structure and magnetic properties of detonation nanodiamond chemically modified by copper

We report on detailed study of detonation nanodiamonds (DNDs) whose surface has been chemically modified by copper with the aid of ion exchange in water DND suspension. High resolution transmission electron microscopy, Raman, IR, electron magnetic resonance (EMR), nuclear magnetic resonance (NMR), and superconducting quantum interference device techniques were used for the characterization of DND. Carboxyl groups, appearing on the surface of a nanodiamond particle during its synthesis and purification processes, provide an effective binding of divalent copper ions to the surface. The binding results from the ion exchange between metal cations and protons of surface carboxyl groups in water solutions. IR data evidence the presence of multiple COC groups in the dried copper-modified DND product. Both EMR and C13 NMR provide direct evidences of the appearance of isolated Cu2+ ions on the surface of the 5 nm nanodiamond particles. EMR spectra reveal well-pronounced hyperfine structure due to C63,65u nuclear...

Ultradisperse Diamond Cluster Aggregation Studied by Atomic Force Microscopy

The structure of ultradisperse diamond (UDD) conglomerates was studied by scanning atomic-force microscopy (AFM). The UDD layers were prepared from a detonation carbon obtained by synthesis in an aqueous medium. The finest details in the AFM images of UDD layers are of the order of 10 nm, which does not allow individual 4.5-nm diamond clusters to be distinguished. The UDD conglomerates deposited and dried on a silicon substrate surface, exhibit certain deformation and differ from the initial (apparently, spherical) shape. This may imply that cohesion between the UDD nanoparticles is comparable with their adhesion to the silicon substrate.

Magnetic Resonance Study of Nanodiamonds

Magnetic resonance techniques, namely Electron Paramagnetic Resonance (EPR) and solid state Nuclear Magnetic Resonance (NMR), are powerful non-destructive tools for studying electron-nuclear and crystalline structure, inherent electronic and magnetic properties and transformations in carbon-based nanomaterials. EPR allows to control purity of ultradispersed diamond (UDD) samples, to study the origin, location and spin-lattice relaxation of radical-type carbon-inherited paramagnetic centers (RPC) as well as their transformation during the process of temperature driven diamond-to-graphite conversion. Solid state NMR on 1H and 13C nuclei provide one with information on the crystalline quality, allows quantitative estimation of the number of different allotropic forms, and reveals electron-nuclear interactions within the UDD samples under study. Results of recent EPR and 13C NMR study of pure and transition metal doped UDD samples, obtained by detonation technique, are reported and discussed. In addition to characteristic EPR signals, originated form para- and ferromagnetic impurities and doping ions, the UDD samples show a high concentration of RPC (up to 1020 spin/gram), which are due to structural defects (dangling C-C bonds) on the diamond cluster surface. In-situ EPR sample’s vacuumization experiment in conjunction with precise SQUID magnetization measurements allowed concluding that each UDD particle carries a single spin (dangling bond) per each from 8 crystal (111) facets bounded the particle.

Size dependence of 13C nuclear spin-lattice relaxation in micro- and nanodiamonds.

Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved gHF1 = 4.26 and gHF2 = 4.00 signals. This feature is attributed to “forbidden” ΔMS = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D1 = 0.0950 ± 0.002 cm−1 and D2 = 0.030 ± 0.005 cm−1. Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-fie...

Optical properties of layers of ultradisperse diamond obtained from an aqueous suspension

The possibility of obtaining thin (1500–3000 Å) layers of ultradisperse diamond from an aqueous suspension is reported and the first results of studies of its optical properties are presented. It is deduced from an analysis of the optical absorption spectra of layers of ultradisperse diamond that the band gap of ultradisperse diamond is 2.06 eV. The luminescence spectra of ultradisperse diamond reveal a characteristic line with a peak at 363.7 nm.

Size-dependent Raman and SiV-center luminescence in polycrystalline nanodiamonds produced by shock wave synthesis

Size-dependent structural and luminescent properties of the diamond polycrystals produced by shock wave synthesis followed by grinding and separation into fractions of different polycrystal median sizes (25–1000 nm) are studied by comparative Raman and luminescence spectroscopy. The intense 738 nm narrow band luminescence of the SiV-centers are observed for all fractions. The SiV luminescence intensity has a maximum at the median size of about 180 nm that is controlled by competition between deactivation of the SiV-centers by defects in the diamond nanocrystal lattice and that controlled by nonradiative recombination centers in the volume of the intergranular layers.

Magnetic studies of a detonation nanodiamond with the surface modified by gadolinium ions

The diamond nanoparticle surface is modified with Gd(III) ions by ion exchange with carboxyl group protons during the reaction of nanodiamond hydrosol with an aqueous solution of gadolinium nitrate. The results of the study by electron paramagnetic resonance and static magnetization measurements at low temperatures confirm the attachment of gadolinium ions to the surface of the diamond particle ∼5 nm in size. A spatial model of the arrangement of ions, in which the ion is located away from the surface by no more than 0.4 nm, is proposed.