It was revealed that sp3-sp2 rehybridization of carbon atoms on the facets of nanocrystalline paricles of detonation diamond under thermal treatment results in weakening the hardness of its primary ...agglomerates. That discloses a secret of the unusual high strength of industrial diamond agglomerates and allows obtaining hydrosol of individual diamond nanoparticles ranging of 4–5 nm. Details of sp3-sp2 rehybridization have been studied by number of complementary methods including TEM, AFM, XPS, Raman scattering, X-ray diffraction and dynamic light scattering. A model for complete explanation of the processes during the annealing and obtaining stable hydrosols of 4–5 nm DND particles with different ζ-potentials is suggested. The model reveals the new ways for obtaining nanodiamond sols in other solvents.
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Nanodiamond (ND) is one of the most attractive allotropic modification of carbon due to their unique physical and chemical properties. In the present review the current state of science and ...technology in the field of NDs is analyzed. ND can be used in various application and in different form e.g. as a dispersion phase in suspension, as a filler in composites, etc., so the sedimentation stability of ND in different media are under scrutiny. Thus, theoretical aspects of ND suspension coagulation mechanisms and the methods avoiding it were considered. The dependence of rheological behavior on particles modification was discussed as well. Various methods for the preparation and modification of NDs to obtain particles of various sizes on a nanometer scale with different physicochemical properties were reviewed. The area of practical application for NDs was considered on the example of polymer composites. The various manufacturing methods, mechanical properties and medical aspects for thermosetting, thermoplastic and elastomer ND composites were summarized.
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•The review presents current state of science in the field of nanodiamonds.•There are several methods for stabilizing of nanodiamond particles in various liquids.•The review contributes to a better understanding the nature of sol-gel transition in nanodiamond suspensions.•Composites filled with nanodiamonds exhibit improved mechanical properties.
We report on a novel approach that allows determining the spatially resolved nuclear spin–lattice relaxation times and NMR line widths in nanomaterials. The approach was applied to a newly ...synthesized nanomaterialdetonation nanodiamonds with manganese ions directly grafted to the surface of the nanodiamond particles. The interaction of the carbon nuclear spins with paramagnetic Mn2+ ions results in acceleration of nuclear spin–lattice relaxation and broadening of the 13C resonance line. Using spin dephasing experiments, we were able to determine the layer-by-layer contributions of the paramagnetic Mn2+ions to the spin–lattice relaxation time and line width of the carbon spins positioned at different depths from the diamond surface. Developed for nanodiamonds, this approach is more general and can be successfully applied to study the distribution of nuclear relaxation rates and line broadening and for mapping magnetic interactions inside various nanoparticles, being of practical use in various nanotechnologies.
We report on the first 1H NMR relaxation and magnetic resonance imaging (MRI) study of aqueous suspensions of detonation nanodiamond (DND) grafted by Gd(III) ions. In contrast to Gd(III)–ND ...conjugates implemented via organic species, Gd(III) ions were directly grafted to the surface of DND particles. Such Gd(III)-grafted DND particles significantly shorten spin–lattice (T 1) and spin–spin (T 2) relaxation times of water protons providing relaxivities of r 1 = 33.4 and r 2 = 332 mM–1 s–1, which considerably exceed most of those reported in the literature. It makes the Gd(III)-grafted DND complexes attractive for use as novel MRI contrast agents.
A remarkable observation that detonation of oxygen-deficient explosives in an inert medium produces ultra-fine diamond particles having diameters of 4–5 nm was made four decades ago, but this novel ...form of diamond has never been isolated in pure form thereafter. The reason for the difficulty was that the core aggregates having a diameter range of 100–200 nm are extremely tight and could not be broken up by any known method of de-aggregation. After a number of futile attempts, we were able to obtain primary particles by using the recently emerging technique of stirred-media milling with micron-sized ceramic beads. The milled aqueous slurry of nanodiamond gave a stable, thick and dark-coloured colloidal solution. After light sonication, dynamic light scattering measurements gave a sharp distribution in the single-digit nano-range, and HRTEM indicated separate particles having diameters of 4–5 nm, which agreed with the X-ray value of 4.4 nm for the primary particles. A model is presented for the core aggregates, which resembles the well-known grape-shaped ‘aggregate structure’ of the hardest type of carbon black.
The energy spectrum of deep impurity centers in wide-bandgap semiconductors (
E
g
> 2 eV) of mesoscopic sizes
R
⪢ λ
D
, where λ
D
is the de Broglie wavelength, at which the spectrum of free ...(uncoupled) charge carriers is not quantized, but the surface significantly affects physical processes in the bulk, has been theoretically considered. It has been shown that the binding energy of an electron on an impurity center near the surface of the crystal tends to zero. In this case, the wavefunction of the electron of the impurity center located in the surface region is delocalized; i.e., the energy of the impurity electron lies in the conduction band. The possible effect of such an energy overlap on effects observed in wide-bandgap mesoscopic semiconductors is discussed.
The experiments have shown qualitative changes in electron paramagnetic resonance (EPR) spectra with decreasing average size of diamond particles from 100 μm to 18 nm. The characteristic hyperfine ...splitting in the EPR spectrum due to the interaction of an unpaired electron of a neutral impurity (nitrogen atom) in the diamond lattice with its nuclei disappears, and the resulting EPR spectrum is a superposition of two singlet Lorentzian lines. The reason for the observed effect is the indirect exchange interaction of electrons localized on bulk impurity centers through electrons localized on surface dangling bonds. Such an interaction of electrons localized on bulk centers becomes possible due to the resonant energy transfer between them. The transfer is result of the exchange interaction with electrons of surface centers. It is shown, that the energy of the indirect exchange interaction depends on the size of the diamond particle; therefore, the effect can be observed only in the case when particle size is smaller than a critical value Rcr. The calculated value of the Rcr based on the suggested model fitted well with experimental data.
the results are presented for investigation of electrical conductivity of nano crystalline diamond (NCD) films with thickness of 0.5–0.6 microns grown on silicon Si(100) substrates by the CVD metho d ...using methane-hydrogen and methane-hydrogen-oxygen mixtures. By the metho d of heating in vacuum with using hydrogen analyzer AB-1, the concentration of hydrogen in the studied films was determined and the relationship between the content of hydrogen in the NCD film and its conductivity was estimated. It has been shown that high-temperature processing in vacuum at the temperature of 600°C leads to desorption of hydrogen from the films and to a significant increase in their resistance.
We report on EPR and 13C and 1H NMR studies of detonation nanodiamond particles with surface grafted by paramagnetic gadolinium ions obtained by ion exchange with hydrogen atoms of carboxyl groups ...through the reaction of aqueous nanodiamond suspension with an aqueous solution of gadolinium nitrate. Our findings give clear evidence that Gd3+ ions are chemically bound to the nanodiamond surface and interact with electron and nuclear spins of the diamond nanoparticle, which results in acceleration of electron and nuclear spin–lattice relaxations. A model of positioning of Gd3+ ions on the DND surface terminated by oxygen-containing groups is suggested. The distance between the Gd ion and nanodiamond surface is estimated by relaxation measurements as 0.32 nm. Biomedical applications of the studied nanomaterials are discussed.
Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements were done on nanodiamond samples fabricated by the detonation method and purified by acids. Comprehensive acid treatment ...leads to the reduction of EPR signals of magnetic impurities and revealing two weak and narrow EPR lines with
g
1
=
4.26, ▵
H
pp
=
2.9 mT and
g
2
=
4.00, ▵
H
pp
=
1.4 mT at
T
=
4 K, separated by the distance of 10.4 mT. The origin of this new doublet EPR signal observed in the well purified sample is discussed. The magnetic susceptibility behavior and doublet EPR signal (
g
∼
4) suggest the weak antiferromagnetically exchange coupling of
S
=
1/2 paramagnetic defects as well as the presence of isolated dimers with
S
=
1.
