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19 results on '"Vul’, A. Ya."'

1. Size Effect in Electron Paramagnetic Resonance Spectra of Impurity Centers in Diamond Nanoparticles

Author

Zegrya, G. G., Samosvat, D. M., Osipov, V. Yu., Vul', A. Ya., and Shames, A. I.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The evolution of the polycrystalline pattern of electron paramagnetic resonance (EPR) spectra of intrinsic and induced paramagnetic centers in an ensemble of submicrometer diamond particles on diminishing average particle size is considered. Recent experimental data unambiguously demonstrate consistent reduction and then zeroing of typical hyperfine pattern from P1 centers on approaching a certain particle size and below it. These changes are accompanied by appearance and strengthening of new structureless signals. In small particles the electron wave function of a surface paramagnetic center is delocalized over the whole nanoparticle. In result the electron spin "experiences" the average field of all surrounding nuclei, which is zero. At the same time, the paramagnetic centers localized in the bulk of a nanoparticle are also cut off the hyperfine interaction due to the electron spin diffusion. Thus, upon the nanodiamond particle size decreases the hyperfine related features of the polycrystalline EPR spectrum become weaker and the spectrum appear to be structureless.

Published
2019

4. Nuclear Magnetic Resonance Study of Ultrananocrystalline Diamonds

Author

Panich, A. M., Shames, A. I., Vieth, H. -M., Osawa, E., Takahashi, M., and Vul, A. Ya.

Subjects
Condensed Matter - Materials Science
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., Comment: 25 pages, 7 figures

Published
2007
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14. Raman characterization and UV optical absorption studies of surface plasmonresonance in multishell nanographite

Author

Osipov, V. Yu., Baranov, A. V., Ermakov, V. A., Makarova, Tatiana, Chungong, L. F., Shames, A. I., Takai, K., Enoki, T, Kaburagi, Y, Endo, M, Vul', A. Ya., Osipov, V. Yu., Baranov, A. V., Ermakov, V. A., Makarova, Tatiana, Chungong, L. F., Shames, A. I., Takai, K., Enoki, T, Kaburagi, Y, Endo, M, and Vul', A. Ya.

Abstract

Nanographite (NG) particles were produced by annealing of superpurified detonation nanodiamonds (grain size ~ 5 nm) at 1600 °C. The aim of this research was to provide Raman characterization of nanographites obtained and to investigate characteristic features of UV optical absorption in NG suspensions caused by the excitation of surface plasmon resonance (SPR) and its dependence on disorder and defectiveness of graphene shells during their transformation. The 1-st and 2-nd order Raman spectra of the NG samples excited at 514 nm were analyzed. Two different approaches applied for evaluation of the in-plane NG crystallite sizes by using the D- and G-band intensities ratio gave quite different results (~ 3.5 nm and ~ 5.5 nm) reflecting, most likely, a complicated NG structure. The changes in both intensity and position of SPR absorption peak for water suspension of NG particles may originate in structural imperfections and/or changes in aggregation of NG particles.

Published
2011
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17. Electronic properties and applications of ultrananocrystalline diamond

Author

Gruen, D. M., Shenderova, O. A., Vul’, A. Ya., Williams, Oliver Aneurin, Zimmermann, T., Kubovic, M., Denisenko, A., Kohn, E., Jackman, R. B., Gruen, D. M., Shenderova, O. A., Vul’, A. Ya., Williams, Oliver Aneurin, Zimmermann, T., Kubovic, M., Denisenko, A., Kohn, E., and Jackman, R. B.

Abstract

Ultrananocrystalline diamond (UNCD) is a 3–5 nm grain size material with many of the properties of diamond. Whilst intrinsic UNCD films display a mild p-type characteristic with high resistivity, the addition of nitrogen to the gas phase during deposition renders the material n-type with low resistivity and activation energy. Hall effect measurements as a function of temperature show that this conductivity mechanism is semi - metallic, with the carrier concentration decreasing very gradually with decreasing temperature. Increasing the nitrogen content in the gas phase during deposition results in higher carrier concentrations in the deposited films and lower activation energies. The carrier mobilities of the films are limited by the grain size of the films. A prototype heterostructure diode is demonstrated, combining single crystal and ultrananocrystalline diamond.

18. Nanodiamonds intercalated with metals: structure and diamond-graphite phase transitions

Author

Aleksensky, A.E., Baidakova, M.V., Yagovkina, M.A., Siklitsky, V.I., Vul', A. Ya, Naramoto, H., and Lavrentiev, V.I.

Subjects
*X-ray diffraction, *CONSTITUTION of matter, *SCANNING electron microscopy, *HYDROGEN
Abstract

We used X-ray diffraction, small-angle X-ray scattering, and scanning electron microscopy (SEM) to study the diamond graphite phase transition in detonation nanodiamond (ND) intercalated with Cu, Ni, Co and Fe for the first time. The study has been made before and after annealing in hydrogen and argon. The SEM data obtained support the idea of the hierarchic structure of ND with a size of primary cluster of about 5 nm. There are several levels of aggregation of primary clusters. We have shown that all the samples of ND are surface fractals. It means the structure can be characterized by three parameters: coherent scattering region (CSR), the size of scatterer A and fractal dimensionality D.The transition degree was identified by X-ray diffractometry from the peaks of bulk nanographite. Scanning electron microscopy was used to determine the sizes of metallic and carbon aggregates. We have found from the CRS, A and D data that the intercalation does not practically change the diamond core at annealing in hydrogen and its size is similar to that reported earlier. However the changes of the scatterer size and fractal dimensionality depend on type of intercalated metals in hydrogen annealing. [Copyright &y& Elsevier]

Published
2004
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19. Colloids of detonation nanodiamond particles for advanced applications.

Author

Shvidchenko AV, Eidelman ED, Vul' AY, Kuznetsov NM, Stolyarova DY, Belousov SI, and Chvalun SN

Abstract

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., (Copyright © 2019. Published by Elsevier B.V.)

Published
2019
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