Alexander Panich - Academia.edu (original) (raw)
Papers by Alexander Panich
Applied Magnetic Resonance
We have experimentally and theoretically investigated multicomponent 1H nuclear magnetic resonanc... more We have experimentally and theoretically investigated multicomponent 1H nuclear magnetic resonance (NMR) echo decays in a-Si:H films containing anisotropic nanopores, in which randomly moving hydrogen molecules are entrapped. The experimental results are interpreted within the framework of the previously developed theory, in which a nanoporous material is represented as a set of nanopores containing liquid or gas, and the relaxation rate is determined by the dipole–dipole spin interaction, considering the restricted motion of molecules inside the pores. Previously, such characteristics of a nanostructure as the average volume of pores and their orientation distribution were determined from the angular dependences of the spin–spin and spin–lattice relaxation times. We propose a new approach to the analysis of the NMR signal, the main advantage of which is the possibility of obtaining nanostructure parameters from a single decay of the echo signal. In this case, there is no need to an...
Journal of Magnetic Resonance
Diamond and Related Materials, 2008
XPS, EPR and NMR studies of the ozone-treated nanodiamond (NDO) are presented. Based on the spect... more XPS, EPR and NMR studies of the ozone-treated nanodiamond (NDO) are presented. Based on the spectra, the nature of the surface chemical functional groups, which were formed as a result of the ozone reaction with the pristine DND surface in the soot, is discussed.
Diamond and Related Materials, 2011
Nuclear spin–lattice relaxation measurement is an effective tool for studying electronic structur... more Nuclear spin–lattice relaxation measurement is an effective tool for studying electronic structure and magnetic properties of nanosized compounds. The present work deals with the effect of oxygen molecules, adsorbed onto the surface of carbon nanoparticles – in which the number of surface atoms is comparable with that in the sample's volume – on nuclear spin–lattice relaxation rate of the carbon
Diamond and Related Materials, 2007
We report about the electron paramagnetic resonance and nuclear magnetic resonance signals in bul... more We report about the electron paramagnetic resonance and nuclear magnetic resonance signals in bulk and thin film-type ultrananocrystalline diamond with and without nitrogen. The localization and nature of defects for powder and compact film samples were analyzed. From the analysis of spin-lattice and spin-spin relaxation times, we have found that spin states sit in sp 2 enriched region belonging to the grain boundaries.
Diamond and Related Materials, 2007
Diamond and Related Materials, 2012
ABSTRACT We review recent nuclear spin–lattice relaxation studies of carbon nanomaterials, such a... more ABSTRACT We review recent nuclear spin–lattice relaxation studies of carbon nanomaterials, such as nanodiamonds, carbon onions, activated carbon fibers, graphene and carbon nanoscrolls. We show that a significant reduction in the relaxation time in nanoparticles compared with that in the bulk compounds and a stretched exponential magnetization recovery are caused by the interaction of nuclear spins with unpaired electron spins of paramagnetic defects, which creates an effective channel for the nuclear relaxation. We present a theoretical approach for such kind of relaxation in static and magic angle spinning regimes and explain a difference in the data received in these regimes. We also extend our approach for the case of additional contributions to the relaxation resulting from interaction of nuclear spin with conduction electrons and with adsorbed paramagnetic oxygen molecules. The developed approach allows correct interpreting of the NMR relaxation data and receiving useful information on properties of nanomaterials from the NMR measurements.
Diamond and Related Materials, 2012
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
The Journal of …, 2011
This work examines several polycrystalline diamond samples for their potential as polarizing agen... more This work examines several polycrystalline diamond samples for their potential as polarizing agents for dynamic nuclear polarization (DNP) in NMR. Diamond samples of various origin and particle sizes ranging from a few nanometers to micrometers were examined by EPR, solid-state NMR and DNP techniques. A correlation was found between the size of the diamond particles and the electron spinÀlattice relaxation time, the 13 C nuclear spinÀlattice relaxation times in room temperature magic-angle-spinning experiments, and the ability of the diamond carbons to be hyperpolarized by irradiating unpaired electrons of inherent defects by microwaves at cryogenic temperatures. As the size of the diamond particles approaches that of bulk diamond, both electron and nuclear relaxation times become longer. NMR signal enhancement through DNP was found to be very efficient only for these larger size diamond samples. The reasons and implications of these results are briefly discussed, in the light of these EPR, DNP, and NMR observations. * Due to the estimation method in use (continuous saturation and fitting by eq 1) the error bars for the short relaxation times listed above may reach 30% of the values presented.
The Journal of …, 2009
... with a known amount of paramagnetic defects, N s = (6.3 ± 0.5) × 10 19 spins/g.(22). ... Furt... more ... with a known amount of paramagnetic defects, N s = (6.3 ± 0.5) × 10 19 spins/g.(22). ... Furthermore, the intense peak around δ = 36 ppm is asymmetric and could, in principle, be deconvoluted into ... The narrow line having a chemical shift of δ = 36.1 ± 0.3 ppm and a line width of Δν ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1993
ABSTRACT
Chemical Physics Letters, 1997
The CF bonding and localization effects in fluorine-intercalated graphite CxF with 3.8 ⩽ x ⩽ 6.5... more The CF bonding and localization effects in fluorine-intercalated graphite CxF with 3.8 ⩽ x ⩽ 6.5 have been studied by 19F NMR. An analysis of 19F shielding measured in our experiment and of data taken from the literature shows that the changing character of the CF bond occurs for x < 3 whereas the change in conductivity occurs for x in the range from 3 to 6. We suggest that the drop in conductivity for fluorine concentrations above that corresponding to σmax is caused by a percolation mechanism rather than by the change in bond length.
X-ray structural analysis, nuclear magnetic resonance, optical spectroscopy and second harmonic g... more X-ray structural analysis, nuclear magnetic resonance, optical spectroscopy and second harmonic generation were used to characterize the new nonlinear crystals LiInS2 and LiInSe2 which possess maximum band gap (3.59 and 2.86 eV at 300 K, respectively) among ternary chalcogenides. As grown crystals are only slightly colored while color change after annealing is due to native point defects.
Applied Spectroscopy, 1996
High resolution in the NMR spectra of diffusing molecules in graphite intercalation compounds, ze... more High resolution in the NMR spectra of diffusing molecules in graphite intercalation compounds, zeolites, crystalline solvates, and hydrates is achieved because of the selective motional averaging of the intermolecular dipole-dipole interactions. An analysis of such spectra yields information about molecular motion and arrangement, as well as chemical shift anisotropy.
Applied Magnetic Resonance, 2004
We review the nuclear magnetic resonance (NMR) studies of the indirect nuclear exchange coupling ... more We review the nuclear magnetic resonance (NMR) studies of the indirect nuclear exchange coupling and electronic structure of the chain and layered semiconductors TI(I)M(III)X 2 (M = TI, Ga, In, X = Se, S, Te) and some other low-dimensional Tl-contained semiconducting compounds. Both univalent and trivalent TI atoms in these compounds show essential chemical shielding anisotropy despite their formal sphe¡ symmetric 5dt~ 2 and 5d t~ electron configurations. Sucia a behavior results from the sp-hyb¡ of the TI electron wave functions. Strong exchange coupling among the spins of TP + and M 3+ ions, which reside in neighboring chains or layers, is observed. Such coupling is realized due to the overlap of the TP + and M ~+ electron wave functions across the intervening chalcogen atom. This overlap is the important mechanism in the formation of the valence and conduction bands and determines the electronic structure and properties of the compounds. The long-range indirect nuclear exehange coupling vŸ a chalcogen atom is an analog of the Kramers mechanism of electron spin exchange via a nonmagnetic b¡ ion. Recent photoemission spectroscopy studies and band-structure calculations of several aforementioned compounds have confirmed the NMR results on the interch• and interlayer overlap.
Applied Magnetic Resonance, 2004
The influence of thermal molecular motions on spin echo decay in pure nuclear quadrupole resonanc... more The influence of thermal molecular motions on spin echo decay in pure nuclear quadrupole resonance (NQR) is considered. Our calculations show that the Hahn echo decay is caused by dipole-dipole interaction of the nuclear spins and is strongly affected by molecular mobility that can lead to the shortening of the echo decay with increased temperatare. Slow molecular motion yields ah exponential ~.3 time dependence, while fast motion yields an exponential decay. The outlined theory allows us to explain ah unusual shortening of the "CI NQR echo decay on heating in thiourea-C2Cl ~ inclusion compound.
Applied Magnetic Resonance, 2009
We report on electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) study of deto... more 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 Cu 2?-related components. Applying the same annealing process to the cobalt-modified samples leads to broadening of the singlet line, reduction of Co 2? 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. 13 C nuclear spin-lattice relaxation rate R 1 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 Cu 2? and Co 2? complexes at the DND surface and their interaction with the carbon nuclear spins, both directly and via a coupling of Cu 2? and Co 2? electrons with those of the broken bonds. The aforementioned annealing of the Cu-and Co-DND results in an
Applied Magnetic Resonance, 2013
We report on electron paramagnetic resonance and nuclear magnetic resonance study of graphene oxi... more We report on electron paramagnetic resonance and nuclear magnetic resonance study of graphene oxide produced by the Hummers method. We show that this compound reveals isolated Mn 2? ions, which originate from potassium permanganate used in the process of the sample preparation. These ions are likely anchored to the graphene oxide planes and contribute to the 1 H and 13 C spin-lattice relaxation.
Applied Magnetic Resonance
We have experimentally and theoretically investigated multicomponent 1H nuclear magnetic resonanc... more We have experimentally and theoretically investigated multicomponent 1H nuclear magnetic resonance (NMR) echo decays in a-Si:H films containing anisotropic nanopores, in which randomly moving hydrogen molecules are entrapped. The experimental results are interpreted within the framework of the previously developed theory, in which a nanoporous material is represented as a set of nanopores containing liquid or gas, and the relaxation rate is determined by the dipole–dipole spin interaction, considering the restricted motion of molecules inside the pores. Previously, such characteristics of a nanostructure as the average volume of pores and their orientation distribution were determined from the angular dependences of the spin–spin and spin–lattice relaxation times. We propose a new approach to the analysis of the NMR signal, the main advantage of which is the possibility of obtaining nanostructure parameters from a single decay of the echo signal. In this case, there is no need to an...
Journal of Magnetic Resonance
Diamond and Related Materials, 2008
XPS, EPR and NMR studies of the ozone-treated nanodiamond (NDO) are presented. Based on the spect... more XPS, EPR and NMR studies of the ozone-treated nanodiamond (NDO) are presented. Based on the spectra, the nature of the surface chemical functional groups, which were formed as a result of the ozone reaction with the pristine DND surface in the soot, is discussed.
Diamond and Related Materials, 2011
Nuclear spin–lattice relaxation measurement is an effective tool for studying electronic structur... more Nuclear spin–lattice relaxation measurement is an effective tool for studying electronic structure and magnetic properties of nanosized compounds. The present work deals with the effect of oxygen molecules, adsorbed onto the surface of carbon nanoparticles – in which the number of surface atoms is comparable with that in the sample's volume – on nuclear spin–lattice relaxation rate of the carbon
Diamond and Related Materials, 2007
We report about the electron paramagnetic resonance and nuclear magnetic resonance signals in bul... more We report about the electron paramagnetic resonance and nuclear magnetic resonance signals in bulk and thin film-type ultrananocrystalline diamond with and without nitrogen. The localization and nature of defects for powder and compact film samples were analyzed. From the analysis of spin-lattice and spin-spin relaxation times, we have found that spin states sit in sp 2 enriched region belonging to the grain boundaries.
Diamond and Related Materials, 2007
Diamond and Related Materials, 2012
ABSTRACT We review recent nuclear spin–lattice relaxation studies of carbon nanomaterials, such a... more ABSTRACT We review recent nuclear spin–lattice relaxation studies of carbon nanomaterials, such as nanodiamonds, carbon onions, activated carbon fibers, graphene and carbon nanoscrolls. We show that a significant reduction in the relaxation time in nanoparticles compared with that in the bulk compounds and a stretched exponential magnetization recovery are caused by the interaction of nuclear spins with unpaired electron spins of paramagnetic defects, which creates an effective channel for the nuclear relaxation. We present a theoretical approach for such kind of relaxation in static and magic angle spinning regimes and explain a difference in the data received in these regimes. We also extend our approach for the case of additional contributions to the relaxation resulting from interaction of nuclear spin with conduction electrons and with adsorbed paramagnetic oxygen molecules. The developed approach allows correct interpreting of the NMR relaxation data and receiving useful information on properties of nanomaterials from the NMR measurements.
Diamond and Related Materials, 2012
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
The Journal of …, 2011
This work examines several polycrystalline diamond samples for their potential as polarizing agen... more This work examines several polycrystalline diamond samples for their potential as polarizing agents for dynamic nuclear polarization (DNP) in NMR. Diamond samples of various origin and particle sizes ranging from a few nanometers to micrometers were examined by EPR, solid-state NMR and DNP techniques. A correlation was found between the size of the diamond particles and the electron spinÀlattice relaxation time, the 13 C nuclear spinÀlattice relaxation times in room temperature magic-angle-spinning experiments, and the ability of the diamond carbons to be hyperpolarized by irradiating unpaired electrons of inherent defects by microwaves at cryogenic temperatures. As the size of the diamond particles approaches that of bulk diamond, both electron and nuclear relaxation times become longer. NMR signal enhancement through DNP was found to be very efficient only for these larger size diamond samples. The reasons and implications of these results are briefly discussed, in the light of these EPR, DNP, and NMR observations. * Due to the estimation method in use (continuous saturation and fitting by eq 1) the error bars for the short relaxation times listed above may reach 30% of the values presented.
The Journal of …, 2009
... with a known amount of paramagnetic defects, N s = (6.3 ± 0.5) × 10 19 spins/g.(22). ... Furt... more ... with a known amount of paramagnetic defects, N s = (6.3 ± 0.5) × 10 19 spins/g.(22). ... Furthermore, the intense peak around δ = 36 ppm is asymmetric and could, in principle, be deconvoluted into ... The narrow line having a chemical shift of δ = 36.1 ± 0.3 ppm and a line width of Δν ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1993
ABSTRACT
Chemical Physics Letters, 1997
The CF bonding and localization effects in fluorine-intercalated graphite CxF with 3.8 ⩽ x ⩽ 6.5... more The CF bonding and localization effects in fluorine-intercalated graphite CxF with 3.8 ⩽ x ⩽ 6.5 have been studied by 19F NMR. An analysis of 19F shielding measured in our experiment and of data taken from the literature shows that the changing character of the CF bond occurs for x < 3 whereas the change in conductivity occurs for x in the range from 3 to 6. We suggest that the drop in conductivity for fluorine concentrations above that corresponding to σmax is caused by a percolation mechanism rather than by the change in bond length.
X-ray structural analysis, nuclear magnetic resonance, optical spectroscopy and second harmonic g... more X-ray structural analysis, nuclear magnetic resonance, optical spectroscopy and second harmonic generation were used to characterize the new nonlinear crystals LiInS2 and LiInSe2 which possess maximum band gap (3.59 and 2.86 eV at 300 K, respectively) among ternary chalcogenides. As grown crystals are only slightly colored while color change after annealing is due to native point defects.
Applied Spectroscopy, 1996
High resolution in the NMR spectra of diffusing molecules in graphite intercalation compounds, ze... more High resolution in the NMR spectra of diffusing molecules in graphite intercalation compounds, zeolites, crystalline solvates, and hydrates is achieved because of the selective motional averaging of the intermolecular dipole-dipole interactions. An analysis of such spectra yields information about molecular motion and arrangement, as well as chemical shift anisotropy.
Applied Magnetic Resonance, 2004
We review the nuclear magnetic resonance (NMR) studies of the indirect nuclear exchange coupling ... more We review the nuclear magnetic resonance (NMR) studies of the indirect nuclear exchange coupling and electronic structure of the chain and layered semiconductors TI(I)M(III)X 2 (M = TI, Ga, In, X = Se, S, Te) and some other low-dimensional Tl-contained semiconducting compounds. Both univalent and trivalent TI atoms in these compounds show essential chemical shielding anisotropy despite their formal sphe¡ symmetric 5dt~ 2 and 5d t~ electron configurations. Sucia a behavior results from the sp-hyb¡ of the TI electron wave functions. Strong exchange coupling among the spins of TP + and M 3+ ions, which reside in neighboring chains or layers, is observed. Such coupling is realized due to the overlap of the TP + and M ~+ electron wave functions across the intervening chalcogen atom. This overlap is the important mechanism in the formation of the valence and conduction bands and determines the electronic structure and properties of the compounds. The long-range indirect nuclear exehange coupling vŸ a chalcogen atom is an analog of the Kramers mechanism of electron spin exchange via a nonmagnetic b¡ ion. Recent photoemission spectroscopy studies and band-structure calculations of several aforementioned compounds have confirmed the NMR results on the interch• and interlayer overlap.
Applied Magnetic Resonance, 2004
The influence of thermal molecular motions on spin echo decay in pure nuclear quadrupole resonanc... more The influence of thermal molecular motions on spin echo decay in pure nuclear quadrupole resonance (NQR) is considered. Our calculations show that the Hahn echo decay is caused by dipole-dipole interaction of the nuclear spins and is strongly affected by molecular mobility that can lead to the shortening of the echo decay with increased temperatare. Slow molecular motion yields ah exponential ~.3 time dependence, while fast motion yields an exponential decay. The outlined theory allows us to explain ah unusual shortening of the "CI NQR echo decay on heating in thiourea-C2Cl ~ inclusion compound.
Applied Magnetic Resonance, 2009
We report on electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) study of deto... more 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 Cu 2?-related components. Applying the same annealing process to the cobalt-modified samples leads to broadening of the singlet line, reduction of Co 2? 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. 13 C nuclear spin-lattice relaxation rate R 1 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 Cu 2? and Co 2? complexes at the DND surface and their interaction with the carbon nuclear spins, both directly and via a coupling of Cu 2? and Co 2? electrons with those of the broken bonds. The aforementioned annealing of the Cu-and Co-DND results in an
Applied Magnetic Resonance, 2013
We report on electron paramagnetic resonance and nuclear magnetic resonance study of graphene oxi... more We report on electron paramagnetic resonance and nuclear magnetic resonance study of graphene oxide produced by the Hummers method. We show that this compound reveals isolated Mn 2? ions, which originate from potassium permanganate used in the process of the sample preparation. These ions are likely anchored to the graphene oxide planes and contribute to the 1 H and 13 C spin-lattice relaxation.