Search

This work is aimed at studying the effect of saturated stearic acid (SA) under in vitro culture conditions on the embryos of the domestic cat (Felis silvestris catus) and at estimating how a change in the composition of intracellular lipids is reflected in the results of cryopreservation. The addition of SA to the culture medium had no effect on the development of cat embryos in vitro before cryopreservation. There were also no changes by the total amount of lipids in the embryos after the effect of SA. Meanwhile, the degree of lipid unsaturation was reduced in the embryos after in vitro cultivation with SA. Moreover, the temperature of lipid phase transition onset (T*) was higher in the embryos exposed to the effect of SA as compared with the control. A decrease in the efficiency of embryo cryopreservation during the cultivation with SA was associated with a decrease in the degree of unsaturation of intracellular lipids and a increase in T *. The results can be important for the conservation of genetic resources of the species from the subfamily Felinae. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a progressive age-related neurodegenerative pathology of the central nervous system, characterized by a selective loss of dopaminergic neurons of the nigrostriatal pathway and the presence of specific inclusions (Lewy bodies) in dopaminergic neurons. To study the mechanisms of this pathology and to search for possible ways for its correction, genetic mouse models of PD have been designed. Transgenic mice of the B6.Cg-Tg(Prnp-SNCA*A53T)23Mkle/J strain (hereinafter referred to as B6.Cg-Tg), one of such models, carry the A53T mutation in the human alpha-synuclein gene. The aim of this work was to study the locomotor activity and the level of anxiety, as well as the density of neurons in the brain of male B6.Cg-Tg mice aged six months. Sex- and age-matched wild type C57BL/6J mice were used as controls. The obtained results demonstrate that B6.Cg-Tg mice are characterized by a high locomotor activity and low anxiety. In addition, they demonstrate a selective decrease in the density of neurons in the subventricular zone and substantia nigra, as well as in the hippocampal CA1, CA3, CA4 regions and the granular layer of the dentate gyrus. Thus, B6.Cg-Tg mice at the age of six months only partially match the key pathophysiological hallmarks of PD, such as a reduced neuronal density in the substantia nigra and hippocampal CA1 and CA3 regions. Meanwhile, these mice have neither bradykinesia nor high levels of anxiety. [ABSTRACT FROM AUTHOR]

This work is the first attempt to study the effect of such an assisted reproductive technology (ART) as in vitro culture of preimplantation embryos on social behavior of offspring, using BTBR (BTBR T+Itpr3tf/J) mice as an idiopathic model of autism. C57BL/6J mice were used as controls. Social behavior was investigated in the adult offspring of mice obtained either by natural conception (C57BL/6J and BTBR groups) or after in vitro culture and embryo transfer (ET) of appropriate mouse strains to pseudopregnant C57BL/6J females (ET-C57BL/6J and ET-BTBR groups). The BTBR mice demonstrated reduced levels of social recognition and motivation compared to C57BL/6J mice. However, ET-C57BL/6J and ET-BTBR females demonstrated a decreased interest in a novel partner (stranger) compared to naturally conceived controls of the same sex, as revealed in a social recognition session of this test. Thus, in vitro culture of embryo affects social recognition in the offspring of C57BL/6J and BTBR mice, but in females only. [ABSTRACT FROM AUTHOR]

Diamond is an important material for electrical and electronic devices. Because the diamond is in contact with the metal in these applications, it becomes necessary to study the metal–diamond interaction and the structure of the interface, in particular, at elevated temperatures. In this work, we study the interaction of the (100) and (111) surfaces of a synthetic diamond single crystal with spattered titanium and molybdenum films. Atomic force microscopy reveals a uniform coating of titanium and the formation of flattened molybdenum nanoparticles. A thin titanium film is completely oxidized upon contact with air and passes from the oxidized state to the carbide state upon annealing in an ultrahigh vacuum at 800 °C. Molybdenum interacts with the (111) diamond surface already at 500 °C, which leads to the carbidization of its nanoparticles and catalytic graphitization of the diamond surface. This process is much slower on the (100) diamond surface; sp2-hybridized carbon is formed on the diamond and the top of molybdenum carbide nanoparticles, only when the annealing temperature is raised to 800 °C. The conductivity of the resulting sample is improved when compared to the Ti-coated diamond substrates and the Mo-coated (111) substrate annealed at 800 °C. The presented results could be useful for the development of graphene-on-diamond electronics. [ABSTRACT FROM AUTHOR]

The role of lipids in mammalian preimplantation development is a fundamental problem of modern embryology. This is especially topical for early development in Carnivora and some other mammals, the species whose oocytes and early embryos are lipid-rich. One of the promising approaches to improve cryotolerance in lipid-rich embryos is to modify their lipidome in vitro. This work aimed at studying the effects of linoleic acid (LA) on the domestic cat embryos during in vitro development and to evaluate how the change in lipid content affects the cryopreservation results. In-vitro-derived embryos were cultured with 400 µM LA for 66 h and randomly distributed between three groups: (1) for the evaluation the lipid amount in embryos and the stage of development, (2) for the estimation of the unsaturation degree in the intracellular lipids and the starting temperature of the lipid phase transition (Т*), and (3) for the cryopreservation by programmed freezing. The rate of in vitro development was not affected in the LA-exposed noncryopreseved embryos. Nile Red staining did not reveal changes in the lipid amount in the LA-treated embryos. However, Raman measurements showed that lipid unsaturation degree was higher in embryos after in vitro culture with LA. In the LA-treated embryos, T* was lower, and the rate of blastocyst development was higher after cryopreservation as compared with controls; this indicates a higher rate of development of such embryos with a modified lipid composition. Thus, the exposure to LA in vitro led to the increase of lipid unsaturation degree and decrease of the T* in cat embryos, which affected their development after cryopreservation. [ABSTRACT FROM AUTHOR]

Arrays of aligned carbon nanotubes (CNTs) are anisotropic nanomaterials possessing a high length-to-diameter aspect ratio, channels passing through the array, and mechanical strength along with flexibility. The arrays are produced in one step using aerosol-assisted catalytic chemical vapor deposition (CCVD), where a mixture of carbon and metal sources is fed into the hot zone of the reactor. Metal nanoparticles catalyze the growth of CNTs and, during synthesis, are partially captured into the internal cavity of CNTs. In this work, we considered various stages of multi-walled CNT (MWCNT) growth on silicon substrates from a ferrocene–toluene mixture and estimated the amount of iron in the array. The study showed that although the mixture of precursors supplies evenly to the reactor, the iron content in the upper part of the array is lower and increases toward the substrate. The size of carbon-encapsulated iron-based nanoparticles is 20–30 nm, and, according to X-ray diffraction data, most of them are iron carbide Fe3C. The reasons for the gradient distribution of iron nanoparticles in MWCNT arrays were considered, and the possibilities of controlling their distribution were evaluated. [ABSTRACT FROM AUTHOR]

Herein, the filling of single‐walled carbon nanotubes (SWCNTs) with sulfur is performed, and the magnetic properties of the formed nanomaterials are studied. Encapsulation of sulfur species results in the appearance of a specific magnetic ordering in the system due to the formation of nanoscopic grains composed of sulfur and residual catalytic Fe nanoparticles contained in the SWCNTs. The magnetic character of the obtained 1D nanostructures is studied using superconducting quantum interference device (SQUID) magnetometer and a sequential ferromagnetic–antiferromagnetic ordering in the material is revealed. Magnetic and optical properties are strongly dependent on the synthesis protocols. A significant Raman intensity increase related to the encapsulated nanostructures is obtained when filling is performed at high‐pressure high‐temperature conditions. Simultaneously, the magnetic susceptibility gets strongly reduced for high‐pressure filling, which is related to the escape of iron particles from the nanotube interior, and the magnetic properties of the material are governed by a weak ferromagnetic ordering of Fe–S structures remained inside SWCNTs. Sulfur encapsulation provides the new route for controlling the magnetic properties in 1D nanomaterials that pave the way for advanced magneto‐optical applications. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and theoretical study of the electronic structure of the fluorinated fullerene C60F36. UV photoemission spectroscopy (UPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy have been used for probing the density of electronic states in the valence and conduction bands of the compound. An assignment of spectral features was carried out using the results of ab initio B3LYP ground-state calculations of the electronic structure of C60F36. The sample of C60F36 is a mixture of three isomers. The calculations of the density of occupied states of these isomers revealed only a small effect of the π-system organization on the UPS profile. It was demonstrated that the CK-edge NEXAFS spectrum of the fluorinated fullerene can be successfully modeled using the (Z+1) approach properly treating the core hole impact on the spectral profile. [ABSTRACT FROM AUTHOR]

Graphene derivatives are promising sensor materials due to their high surface area available for molecule adsorption and conductivity changes under the adsorbate impact. The selectivity of such materials can be tuned through the attaching of certain functional groups preferably interacting with the defined gases. In the present work, we compare the reactivity of graphene oxide, oxyfluorinated graphene, and fluorinated graphene toward gaseous NOx molecules. The interaction of the molecules with the graphene‐based films was monitored by in situ X‐ray photoelectron and near‐edge X‐ray absorption fine structure spectroscopy measurements. The spectra before and after exposure of the films to a gaseous NOx mixture detected equal concentrations of adsorbed NO2 and NO species on graphene oxide, the preferable interaction of oxyfluorinated graphene with NO2 and the absence of the adsorbed molecules on the fluorinated graphene surface. These results are useful for the development of selective graphene‐based gas sensors. [ABSTRACT FROM AUTHOR]

An interaction of graphene with gaseous molecules increases substantially with grafting of functional groups to its surface. However, in the efficient sensors, such interaction should not be too strong to provide an easy desorption of molecules. Here, we reveal an influence of fluorine and hydroxyl species on the graphene surface on the restorable adsorption of ammonia and nitrogen dioxide, taken as model gases having a different donor/acceptor property. Conductive films of few-layered fluorinated graphene and oxyfluorinated graphene were produced using a one-step process of the exfoliation and partial reduction of corresponding graphite derivatives. The films showed a similar sensitivity on exposure to NH 3 and NO 2 , while the fluorinated graphene-based sensor had much better recovery after a simple argon purging at room temperature. Density functional theory calculations revealed that NO 2 and NH 3 molecules are adsorbed on fluorine and oxygen from a hydroxyl group as well as bare carbon atoms located near the functionalized carbon. The strongest adsorption energy was obtained for an oxyfluorinated graphene–NH 3 system due to short N⋯H(O) contacts. Our results show that fluorinated graphene is more perspective for gas sensing as compared to oxygenated graphene due to its higher chemical stability and weaker interactions with the adsorbed molecules. [ABSTRACT FROM AUTHOR]

Few-layer graphene materials have been produced by decomposition of fluorinated graphite intercalated with acetonitrile (CH3CN) or isopropylamine ((CH3)2CHNH2) in the conditions of thermal shock. Electronic structure of the samples before and after exfoliation was studied using near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy. Analysis of the spectroscopic data revealed the same set of nitrogen species in both exfoliation products that indicates decomposition of the intercalated molecules to the atomic state. Most of the nitrogen atoms were incorporated at the edges of graphene layers in pyridinic and protonated nitrogen forms. A difference in the electrochemical performance of the graphene materials was related with the exfoliation degree and the defect density in the graphene layers. Schematic representation of a process of thermal exfoliation of acetonitrile-intercalated fluorinated graphite. [ABSTRACT FROM AUTHOR]

We show that irradiation of room-temperature fluorinated graphite of C 2 F composition by electron beam with a kinetic energy of 500 eV detaches the fluorine atoms from two or three top layers. The dielectric property of C 2 F prevents effective penetration of the beam in depth of the sample, and electrons are accumulated between the interior layers. Comparative study of the initial C 2 F sample and that after irradiation by means of X-ray photoelectron, X-ray absorption near edge structure, Raman and reflection optical spectroscopy detects a partial recovering of the π-bonds which increases the surface conductivity by more than three orders. The mechanism responsible for removal of fluorine atoms from dielectric matrix under electron irradiation is proposed and substantiated by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

A heating of graphite oxide in concentrated sulfuric acid results in partial removal of oxygen and formation of polyatomic vacancy defects in graphene layers. The boundaries of the defects are decorated by oxygen-containing groups, the number of which can be significantly reduced with the sample annealing in an inert atmosphere. It is shown that initial and annealed perforated graphite (PG) samples interact with gaseous thionylchloride at room temperature. X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy find negatively charged chlorine and covalently bonded chlorine in the initial PG and only the latter chlorine form in the annealed PG. According to the reference data and our quantum-chemical calculations, graphene donates charge to the adsorbed chlorine atoms, while covalent chlorine bonding occurs at vacancy edges. Two chemical states of chlorine detected by XPS in perforated graphene after exposure to SOCl2. [ABSTRACT FROM AUTHOR]

Fluorinated graphite intercalation compounds (FGICs) with acetonitrile C2F x · yCH3CN ( x = 0.92, 0.69, and 0.49) have been synthesized using a gaseous mixture of BrF3 and Br2 at room temperature and subsequent replacement of the reaction medium components on acetonitrile by isopiestic method. The change in functional composition and electronic structure of FGICs under annealing at 250-260 °C was studied by infrared, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) methods. Analysis of the data revealed interaction of acetonitrile with a C2F x matrix. The X-ray spectra detected formation of new nitrogen species attributed to two-coordinated and mono hydrogenated three-coordinated atoms. Mechanism of nitrogen incorporation in the fluorinated graphene layers was proposed. Schematic structure of graphite fluoride C2F x intercalated with acetonitrile and NEXAFS N K-edge spectrum of C2F0.69 · 0.137CH3CN before and after annealing at 250 °C. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) properties of CdS nanoparticles were studied depending on spacing between the nanoparticles and carbon nanotube (CNT) surface. Using a chemical bath deposition procedure the nanoparticles were grown directly on CNT arrays or arrays covered by a polystyrene layer. The polymer thickness was changed by varying the polystyrene concentration in a solution and the duration of CNT immersing. Transmission electron microscopy and atomic force microscopy were used for estimation of CdS nanoparticle size. An increase in the separation between CdS and CNTs was found to enhance the PL intensity and contribute to the exciton lifetime. PL spectra of CdS nanoparticles grown on a CNT surface and polystyrene layer coating the CNTs. [ABSTRACT FROM AUTHOR]

The heating of graphite oxide in concentrated sulfuric acid results in partial removal of oxygen and formation of holes with a size of ∼2 nm. The Raman scattering shows that the distance between the holes decreases with the time of processing while the temperature of the acid has no crucial effect on the defectiveness of a graphene layer. The functional composition of the reduced graphite oxide samples is studied by IR and X-ray photoelectron spectroscopy. From the spectral analyses the longer the treatment, the larger the amount of oxygen removed from the graphite oxide. It is found that the edges of the holes are decorated with hydroxyl, carbonyl, and carboxyl groups and hydrogen. An increase in the temperature promotes formation of carboxyl groups. The influence of oxygenated groups and holes on the supercapacitor performance of reduced graphite oxide samples is checked using cyclic voltammetry measurements in an acidic electrolyte. Specific capacitance of samples depending on temperature and time of graphite oxide treatment by concentrated H2SO4. The scan rate of the potential was 5 mV s−1. [ABSTRACT FROM AUTHOR]

CdS nanoparticles have been grown on multiwalled carbon nanotubes (CNTs) using a chemical bath deposition. Transmission electron microscopy and Raman spectroscopy revealed that crystalline ordering of nanoparticles depends on the duration of synthesis. Moreover, X-ray photoelectron spectroscopy showed that the surface of CdS nanoparticles contains ammonia used as a complexing agent in the reaction. Application of voltage to the substrate with array of aligned CNTs resulted in luminescence of CdS nanoparticles. Efficiency of the electroluminescence depends on the CdS crystallinity and size. Large well-crystallized nanoparticles give bright spots on the cathode image, while the glow from smaller, poor ordered nanocrystalls is strongly scattered. [ABSTRACT FROM AUTHOR]

Perforation of graphite is carried out by treating the graphite oxide with a boiling mineral acid H2SO4 or H3PO4. High-resolution transmission electron microscopy shows formation of a large number of vacancy defects (holes) in the graphene sheets, which are caused more likely by the CO2 liberation during the reduction process. The characteristic size of the holes is about 2 nm. The obtained materials are comparatively examined by X-ray diffraction, Raman and IR-absorption spectroscopy, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. It is found that the products obtained using a strong acid H2SO4 and a weak acid H3PO4 are different in the concentration and electronic state of oxygen and the mean distance between defects. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) was electrochemically deposited onto aligned carbon nanotube (CNT) arrays during 500 and 2500 sec. The electronic state of nitrogen in the composites was investigated by near-edge X-ray absorption fine structure spectroscopy. The N K-edge spectra revealed that mainly emeraldine base was developed in the former composite, while emeraldine was highly protonated in the latter composite. Electrochemical measurements showed that the CNT/PANI composites have significantly better performance than the non-coated nanotubes. The higher specific capacity in the composite obtained during the shorter time was related with the thinner PANI layer deposited on the CNT surface. [ABSTRACT FROM AUTHOR]

Molybdenum(VI) sulfide deposited on the surface of thermally exfoliated graphite has been reduced at 1273 K in dynamic vacuum conditions. High resolution transmission electron microscopy showed formation of layered particles with an average diameter of 20 nm which, using the Fourier analysis of images, were attributed to Mo3S4 phase. Graphite surface more likely promotes the transformation of MoS3 to Mo3S4 because the unsupported particles occurred in the sample have the MoS2 structure. [ABSTRACT FROM AUTHOR]

Arrays of aligned multi-walled nitrogen-doped carbon (CNx) nanotubes were synthesized by the catalytic chemical vapor deposition method using acetonitrile and a mixture of acetonitrile and toluene taken in equal ratio as sources for nanotube growth. The structure of arrays was investigated by means of scanning electron microscopy (SEM) and angle-resolved X-ray absorption spectroscopy near the CK- and NK-edges. The width of angular distribution of CNx nanotubes in the arrays was determined from the Fourier analysis of SEM images, and the ordering of graphitic layers of nanotubes was evaluated from angular dependence of the π*/σ*-intensity ratio near the CK-edge. It was shown that relative intensity of π*-resonance corresponding to N2 molecules embedded into CNx nanotubes can be used as a marker for definition of the deviation of straight CNx nanotubes from a normal direction. [ABSTRACT FROM AUTHOR]

The impedance of polystyrene-onion-like-carbon (PS-OLC) composites in the low-frequency (10–50 kHz) range has been studied as a function of the OLC weight fraction in the material. The composites were fabricated by rolling of PS filled with OLC powder obtained through the annealing of detonation nanodiamonds at 2140 K. The homogeneity of OLC distribution in the PS matrix has been studied as dependent on the number of rolling stages. It is established that the percolation threshold in PS-OLC composites is achieved at an OLC content of 35–40 wt %. [ABSTRACT FROM AUTHOR]

The properties of materials containing carbon nanotubes depend on the degree of alignment and the internal structure of nanotubes. It is shown that the degree of misorientation of carbon nanotubes in samples can be evaluated from the measurements of the angular dependences of the carbon X-ray emission and carbon X-ray absorption spectra. The CK α emission and CK X-ray absorption spectra of the array of multiwalled carbon nanotubes synthesized by catalytic thermolysis of a mixture of fullerene and ferrocene are measured. A comparison of the calculated model dependences of the relative intensities of the π and σ bands in the spectra with the experimental results makes it possible to evaluate the degree of misorientation of nanotubes in the sample and their internal texture. [ABSTRACT FROM AUTHOR]

Angular-resolved X-ray absorption spectra were measured for pyrolytic graphite samples of various quality. A new approach to determining the misorientation of graphite grains in polycrystalline samples is proposed, which is based on calculations of the angular dependence of the relative intensity of a peak corresponding to the π* state for a normal distribution of grains. The experimental values are used to construct theoretical angular dependences using partial densities of the π* and σ* states determined from the nonempirical calculations for graphite. [ABSTRACT FROM AUTHOR]

Nitrogen‐doped carbon nanotubes have been synthesized by thermal decomposition of acetonitrile vapor over Ni/Co catalysts with varied ratio of metals. X‐ray photoelectron spectroscopy revealed that nitrogen atoms are embedded into tube walls in two different forms at least: (1) three‐coordinated nitrogen and (2) pyridinic‐like nitrogen. The ratio between these forms depends on the catalyst composition. Electronic structure of nitrogen‐doped carbon nanotubes was examined by means of photoemission, X‐ray photoelectron, X‐ray emission and X‐ray absorption spectroscopy. Field electron emission characteristics of samples produced were correlated with nitrogen content. The experimental data was interpreted using results of quantum‐chemical semiempirical AM1 calculations on models of nitrogen‐containing carbon tubes. Incorporation of three‐coordinated nitrogen was found from calculation of the models using the transfer matrix approximation to improve the current‐voltage characteristics of carbon nanotubes. [ABSTRACT FROM AUTHOR]

The electronic structure of tetragonal and rhombohedral polymers of the C60 fullerene is investigated using x-ray emission spectroscopy. It is found that, compared to the C60 molecular crystals, the formation of intermolecular covalent bonds in two-dimensional layers of the C60 fullerene polymers leads to a broadening of the maxima in the C K α x-ray emission spectra, a decrease in the density of high-energy states, and an increase in the width of the valence band of the polymer. The experimental data are interpreted by analyzing the results of the calculations performed within the density functional theory for the C60 fullerene cage forming eight and twelve covalent bonds. It is shown that the electronic interactions between C60 molecules in the polymerized layers are provided by two types of molecular orbitals located at energies 0.5–3.0 and ∼5.0 eV below the energy of the Fermi level. [ABSTRACT FROM AUTHOR]

The electronic state of nanodiamond/graphite interfaces in samples prepared by annealing of nanodiamonds (ND) at 1150-1600 K has been probed using X-ray fluorescence spectroscopy and field-emission measurements. Comparison between[C]Ka spectra of ND before and after annealing revealed an enhancement of density of high-energy occupied states in the products. A quantum-chemical calculation using a carbon model showed that the observed states could originate from the electrons of dangling bonds produced by peeling of a graphitic shell from the (111) surface of a diamond particle. The developed graphitic layers screen the weakly bonding electrons, which results in a lowering of the efficiency of field-electron emission from the samples with an increase of annealing temperature. [ABSTRACT FROM AUTHOR]

The electronic structure of samples produced by nanodiamond annealing has been examined using ultra-soft X-ray emission and X-ray absorption spectroscopy. Analysis of spectra of diamond/graphite composites showed that carbon atoms constituting the nanoparticles are at least in three states: diamond-like state, graphitic-like state and interface carbon, characterized by high electron localization. Comparison between theoretical spectra of the models and experimental spectra suggested the latter states correspond to three-coordinated carbon atoms from diamond surface. [ABSTRACT FROM AUTHOR]

CNx nanotubes have been prepared by acetonitrile decomposition over Ni, Co and Ni/Co catalysts. X-ray photoelectron spectroscopy study on the samples revealed a change of nitrogen concentration and shape of N 1s line with variation of the catalyst used. Quantum-chemical calculations on tube fragments showed the energy of N 1s level depends on the atomic structure of carbon tube and kind of incorporated nitrogen. The largest binding energies were found to be characteristic of three-coordinated nitrogen atoms doping the zigzag and chiral carbon nanotubes. [ABSTRACT FROM AUTHOR]

The angular dependence of the intensity of CKα radiation measured from a film of oriented carbon nanotubes shows an increase in the yield of x-ray fluorescence along the growth direction of the nanotubes. The angular distribution of the intensity of scattered x rays is close in magnitude to the angular distribution of the directivity of nanotubes in the film that is determined by analyzing an electron-microscope image. To explain the propagation of radiation along the nanotubes, two mechanisms are proposed on the basis of reflection from inner walls of a tube (channeling) and an anomalous dispersion of CKα photons in the carbon medium. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current–voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes. © 2004 MAIK “Nauka/Interperiodica”. [ABSTRACT FROM AUTHOR]

Nitrogen-containing carbon nanotubes are synthesized using a gas-phase reaction. The synthesis of nitrogen-doped carbon nanotubes from 100 to 500 Å in diameter is accomplished through pyrolysis of acetonitrile (CH[sub 3]CN) at a temperature of 800°C. Cobalt and nickel metallic particles formed upon thermal decomposition of a mixture of maleate salts are used as catalysts. The materials synthesized are investigated by scanning and transmission electron microscopy. Analysis of the x-ray photoelectron spectra demonstrates that the content of nitrogen atoms in three nonequivalent charge states is approximately equal to 3%. A comparison of the CK[sub α] x-ray fluorescence spectrum of the carbon nanotubes synthesized through electric-arc evaporation of graphite and the x-ray fluorescence spectrum of the nitrogen-containing carbon nanotubes prepared by catalytic decomposition of acetonitrile indicates that, in the latter case, the spectrum contains a certain contribution from the sp³ states of carbon atoms. The temperature dependences of the electrical conductivity for different types of multi-walled carbon nanotubes are compared. The difference observed in the temperature dependences of the electrical conductivity is associated with the presence of additional scattering centers in nitrogen-containing carbon nanotubes. [ABSTRACT FROM AUTHOR]

Formic acid is a liquid organic hydrogen carrier from which hydrogen can be released together with CO 2 by catalytic decomposition. The development of supported Ni catalysts for H 2 production is important. Here, the effects of Ni state/dispersion are considered. For this purpose, three samples were prepared with about 3 wt% Ni deposited on porous N-doped carbon. The first sample contained predominantly Ni nanoparticles (∼2 nm), the second contained Ni clusters (<1 nm), and the third – single-atom Ni sites. The catalysts showed close activity in the gas-phase reaction. However, a minimum apparent activation energy of 105 kJ/mol and a maximum selectivity towards H 2 production of 99% were achieved for the single-atom Ni catalyst. The nature of its single-atom sites was established to correspond to Ni-N 4 and Ni-O 4 , which showed greater stability under the conditions of the catalytic reaction. [Display omitted] • Ni catalysts (∼3 wt%) were synthesized by decomposition of Ni(AcO) 2 on N-doped carbon support. • Reducing atmosphere promotes the formation of a Ni catalyst with nanoparticles (∼2 nm). • Inert atmosphere provides the formation of a single-atom Ni catalyst with Ni-N 4 and Ni-O 4 sites. • Single-atom Ni sites are stable under reaction conditions and provide 99% selectivity. • The activation energy of the H 2 production from formic acid decreases with decreasing Ni size. [ABSTRACT FROM AUTHOR]

• Templated carbon was synthesized using calcium tartrate and ethanol precursors. • Pyrolysis of calcium tartrate produced CaO template with surface carbon deposit. • Carbon deposit acted as a pattern for the growth of graphitic layers from ethanol. • Iron doping of calcium tartrate induced small mesopores in carbon materials. • The largest fraction of small mesopores was obtained at 0.2 at% iron doping. • Small mesopores provided a good performance of carbon materials in electrochemical capacitors. Porous carbon (PC) materials with a large specific surface area and high volume of mesopores were produced using iron-doped calcium tartrate (CaTr) as a template precursor and ethanol as a carbon source. The iron doping concentration was varied from 0.2 to 1.6 at%. Template precursor was decomposed in argon at 800 °C, the formed template nanoparticles were immediately used for chemical vapor deposition (CVD) of ethanol, and after the synthesis, they were removed by HCl treatment. It was shown that the template consisted of CaO nanoparticles 5–20 nm in size with oxidized carbon layers on the surface. The incorporation of iron into CaTr promoted graphitization of the carbon layers and led to formation of iron oxide nanoparticles 3–4 nm in size. These nanoparticles served as a replica for small mesopores in the graphitic layers obtained in the ethanol CVD process. PC materials grown on the templates with an iron doping 0.2–0.4 at% were enriched with small mesopores, and due to this, they had a surface area of 907–931 m2 g−1 and pore volume of 3.3 cm3 g−1. These materials showed the highest specific capacitances of 280–230 F g−1 at 2 mV s−1 in 1 M H 2 SO 4 electrolyte and a good rate capability. [ABSTRACT FROM AUTHOR]

The study examines the effect of in vitro cultivation of mouse embryos for 48 h with 200 µM linoleic acid (LA) on their viability after vitrification. Fluorescence microscopy of DAPI-stained embryos showed increased fragmentation of nuclei in case of exposure to LA without cryopreservation and a significant decrease in the number of cells in vitrified embryos 24 h after their thawing. Thus, in vitro cultivation with LA reduces the viability of mouse embryos after vitrification. [ABSTRACT FROM AUTHOR]

• A sandwich-type electrochemical cell with graphene working electrode is elaborated. • Phosphoric acid impregnated fluorinated graphene film works as solid electrolyte. • Electrical double layer formation at electrolyte/electrode interface is studied. • Charge transfer estimated from valence band XPS spectra is 0.02e per carbon atom. • Ion adsorption at graphene electrode splits C 1s levels and shifts the Fermi level. Here, we use in situ X-ray photoelectron spectroscopy (XPS) to investigate electrochemical processes at the graphene surface. As a model system, we design a sandwich-type electrochemical cell consisting of working graphene electrode separated from back by a fluorinated graphene (FG) film impregnated with a phosphoric acid electrolyte. Migration of the ions to the graphene electrode under applied potential causes a change of the observed concentration of carbon and phosphorus in the electrochemical cell as compared to the non-charged state. This fact allows revealing the process of electrical double layer formation at the graphene/FG-separator interface. The observed changes in the binding energies of elements composing electrolyte and graphene electrode are related with a shift of the Fermi level due to the charge transfer from the adsorbed ions. [ABSTRACT FROM AUTHOR]

It is demonstrated that the CK[sub α] x-ray fluorescence spectra of carbon nanotubes synthesized by electric-arc evaporation of graphite and the spectra of carbon nanotubes produced using catalytic decomposition of hydrocarbons differ in the intensity of the short-wavelength lines. In order to interpret the obtained data, the electronic structures of perfect and defect-containing nanotubes are calculated in the framework of the tightbinding method with optimized parameters. The density of localized states that correspond to the observed increase in the intensity of the fluorescence spectrum of catalytic nanotubes can be obtained in the case when 15-20% of the total number of carbon atoms are absent in the carbon network. It is shown that defects of this type can bring about a decrease in the band gap of the nanotubes. [ABSTRACT FROM AUTHOR]

The valence electronic structure of rhombohedrally polymerized C[sub 60], synthesized at 6 GPa and 725 °C, has been studied using x-ray emission spectroscopy. The C Kα spectrum of the polymer was found to differ from that of the C[sub 60] fullerite especially in the high-energy region. The observed spectra were compared to densities of states, calculated using a tight-binding approximation for three two-dimensional hexagonal C[sub 60] networks, distinguished by the nature of intermolecular bonding. Theoretical spectra of the polymers agree well with experiment and indicate that changes in the valence band of C[sub 60] upon polymerization are mainly due to the formation of intermolecular bonds, and only to a negligible degree due to a distortion of the C[sub 60] cage. Rotation of C[sub 60] within the hexagonal layer changes dramatically the electronic properties of the polymer from a semiconducting behavior for the structure with 66/66 connections to a metallic behavior for a layer containing C[sub 60] molecules that are linked through 56/65 bonds. The occurrence of the latter configuration may explain the observed metalliclike in-plane conductivity of the rhombohedral phase of C[sub 60]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This work reviews current advances in cryobanking gametes and preimplantation embryos for members of the order Carnivora. Problems specific to the application of current reproductive technologies to vulnerable and endangered carnivoran species are also discussed. In particular, cryopreservation of Carnivora species' oocytes and embryos is complicated by the abundance of lipid droplets in them. The review focuses on Felidae, Canidae, Mustelidae, and Ursidae because the most experience has been gained in these families in using the achievements of reproductive biology to preserve the genetic resources of nondomesticated species, including endangered ones. For comparison, studies on domesticated members of these families are reviewed: the cat, the dog, and the domestic ferret. Specific features of reproductive biological of the four families are taken into account. [ABSTRACT FROM AUTHOR]

Annealing and pressing are useful for improvement of the structural ordering of graphitic materials. Depending on the processing conditions, this may cause a gain or deteriorate the performances of graphitic anodes in batteries. In the present work, we study the effect of hot pressing on the interaction of multilayer holey graphene (HG) material with lithium ions. The initial HG sample with the holes of about 0.6–2 nm was pressured at 100 bar and room temperature, 600 °C, and 800 °C or at 500 bar and 800 °C. The analysis of the samples using X‐ray diffraction detected an increase in the thickness of graphene stacks after pressing. Electrochemical tests revealed the best performance for the HG sample produced at 100 bar and 600 °C. A rise of the temperature and pressure reduces the contribution from cross‐plane diffusion of lithium ions in the HG capacity. The authors found optimal values of temperature (600 °C) and static pressure (100 bar) for improvement of the rate capability of multilayer holey graphene (HG) in Li‐ion batteries. The hot pressing of the HG material in vacuum compacts the layers and flakes thus promoting diffusion of Li‐ions through the holes in graphene planes. [ABSTRACT FROM AUTHOR]

Ab initio calculations of dielectric function and electron energy loss (EEL) function of periodically rippled armchair-edged graphene were performed in the framework of the random-phase approximation. The bending of graphene was found to remove restrictions on the electron transitions being forbidden in the flat graphene for certain light polarization. As a result, new peaks appear in the optical absorption spectrum and EEL spectrum of rippled graphene. Energy position, intensity, and width of the peaks are sensitive to the height of out-of-plane graphene bending that can be used in construction of graphene-based materials with variable transparency window. [ABSTRACT FROM AUTHOR]

Effect of Ar+ ion irradiation on the structure of pristine and fluorinated single-wall carbon nanotubes (SWCNTs) was examined using transmission electron microscopy (TEM), Raman, and x-ray photoelectron spectroscopy (XPS). The TEM analysis revealed retention of tubular structures in both irradiated samples while Raman spectroscopy and XPS data indicated a partial destruction of nanotubes and formation of oxygen-containing groups on the nanotube surface. From similarity of electronic states of carbon in the irradiated pristine and fluorinated SWCNTs observed by XPS, it was suggested that defluorination of nanotubes proceeded with breaking of C-F bonds. [ABSTRACT FROM AUTHOR]

Lithium adsorption on high-surface-area porous carbon (PC) nanomaterials provides superior electrochemical energy storage performance dominated by capacitive behavior. In this study, we demonstrate the influence of structural defects in the graphene lattice on the bonding character of adsorbed lithium. Thermally evaporated lithium was deposited in vacuum on the surface of as-grown graphene-like PC and PC annealed at 400 °C. Changes in the electronic states of carbon were studied experimentally using surface-sensitive X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS data in combination with density functional theory calculations revealed the dative interactions between lithium sp2 hybridized states and carbon π*-type orbitals. Corrugated defective layers of graphene provide lithium with new bonding configurations, shorter distances, and stronger orbital overlapping, resulting in significant charge transfer between carbon and lithium. PC annealing heals defects, and as a result, the amount of lithium on the surface decreases. This conclusion was supported by electrochemical studies of as-grown and annealed PC in lithium-ion batteries. The former nanomaterial showed higher capacity values at all applied current densities. The results demonstrate that the lithium storage in carbon-based electrodes can be improved by introducing defects into the graphene layers. [ABSTRACT FROM AUTHOR]

Graphene materials including porous few-layered graphenes are under focus of scientific community today. The great attention towards them is caused by their remarkable properties. Here, we use two different fluorinated graphite intercalation compounds with different fluorine content in their matrices to prepare thermally exfoliated fluorinated graphites and to investigate them in terms of their structural, spectroscopic and electrochemical properties as materials for use in supercapacitors. A higher temperature of low-fluorinated graphenes preparation resulted in higher exfoliation degree and higher gravimetric capacitance in supercapacitor appliances. More dramatic leap of gravimetric capacitance was observed after a treatment in a concentrated acid mixture of graphene material samples prepared at the highest temperature of thermolysis with highest exposition time. [ABSTRACT FROM AUTHOR]

The magnetic susceptibility χ as of pristine and brominated arc-produced sample of multiwall carbon nanotubes (MWNTs) so single crystal graphite (SCG) was measured from 4.5 to 400 K. An additional contribution Δχ(T) to diamagnetic susceptibility χ(T) of carbon materials was found at T<50 K for all samples. It is shown that Δχ(T) are dominated by quantum correction to χ for interaction electrons (interaction effects, IE). The IE shows a crossover from two-dimensional to three-dimensional at B=5.5 T for MWNTs and always three-dimensional for SCG. The effective interaction between electrons for interior layers as MWNTs so SCG are repulsion and the electron–electron interaction λc was estimated to be λc∼0.26 for MWNTs and λc∼0.06 for SCG. [Copyright &y& Elsevier]