A. M. Panich

Nuclear magnetic resonance study of fluorine–graphite intercalation compounds and graphite fluorides

Abstract In this paper, we review the NMR investigations of graphite fluorides and fluorine–graphite intercalation compounds. The latter compounds are now considered a unique family of graphite intercalation compounds (GICs) which exhibits a behavior that is strikingly different from all other known GICs. The study of the origin of semimetal–metal and metal-insulator transformations, localization effects and C–F bonding in fluorine–graphite intercalation compound, as well as the studies of the structure, bonding, molecular dynamics and phase transitions in intercalated graphite fluorides are presented. Critical review of 13 C and 19 F chemical shifts is done, and the nature of C–F bond in fluorine–graphite intercalation compounds and graphite fluorides is discussed. The NMR data are compared with the results of other spectroscopic methods, X-ray and conductivity measurements. The reviewed NMR data provide an atomic level rationale for understanding of physical properties of fluorine–graphite intercalation compounds and graphite fluorides.

Electronic properties and phase transitions in low-dimensional semiconductors

We present the first review of the current state of the literature on electronic properties and phase transitions in TlX and TlMX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi- and photoconductivity, nonlinear effects in their I–V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of TlX and TlMX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor–metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. The electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.

Nuclear Magnetic Resonance Studies of Nanodiamonds

This critical review examines the Nuclear Magnetic Resonance (NMR) studies of diamond nanoparticles that have been carried out for the past decade. Investigations of purified nanodiamonds and those with chemically modified surfaces are reviewed in detail. These findings are discussed together with results obtained by other methods. For the non-experts in magnetic resonance, the basic principles of NMR experiments and an introduction to the interpretation of the NMR parameters in carbon nanostructures are given.

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...

Nanodiamond graphitization: a magnetic resonance study.

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. (1)H, (13)C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp(2) carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions.

19F NMR study of CF bonding and localization effects in fluorine-intercalated graphite

Abstract The CF bonding and localization effects in fluorine-intercalated graphite C x F with 3.8 ⩽ x ⩽ 6.5 have been studied by 19 F NMR. An analysis of 19 F shielding measured in our experiment and of data taken from the literature shows that the changing character of the CF bond occurs for x x in the range from 3 to 6. We suggest that the drop in conductivity for fluorine concentrations above that corresponding to σ max is caused by a percolation mechanism rather than by the change in bond length.

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.

Nuclear magnetic resonance study of fluorine-graphite intercalation compounds

To study the origin of semimetal-metal and metal-insulator transformations, localization effects and C-F bonding in fluorine-intercalated graphite and NMR investigations have been carried out for a wide range of fluorine content, . Fluorine spectra for small fluorine content, x > 8, are attributed to mobile fluorine acceptor species which are responsible for the increase of electric conductivity in the dilute compound. When increasing the fluorine content to corresponding to the maximum electric conductivity, covalent C-F bonds start to occur. The number of these bonds grows with fluorine content resulting in a decrease in conductivity which is caused by a percolation mechanism rather than by a change in bond length. A difference in chemical shift for fluorine-intercalated graphite and covalent graphite fluoride has been observed and is attributed to different C-F bonding in these compounds.

A magnetic resonance study of MoS2 fullerene-like nanoparticles

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS(2) nanoparticles. Spectra of bulk 2H-MoS(2) samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS(2) reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS(2) exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS(2) ones.