X-ray photoelectron study of the effect of concentration and activity of metal-containing carbon nanostructures on polymer modification

The effect of the concentration and activity of metal-containing carbon nanostructures on the modification of polymethyl methacrylate is studied by X-ray photoelectron spectroscopy using an X-ray electron magnetic spectrometer. It is shown that at a nanostructure concentration in the range of 10^?2–10^?3% the structure of the nanomodified acrylic resin is significantly altered, adapting to the structure of the nanoform. This results in a change in the optical properties of the polymer. The change in the polymer structure is controlled by the C1s-spectrum shape. The increasing activity of nanostructures after functionalization leads to an increase in the degree of polymer-structure modification.     

Investigation of Ag-TiO2 nanostructures photocatalytic properties prepared by modified dip coating method

In this article, titanium dioxide and silver nanostructures were deposited on glass substrates using modified sol–gel methods and dip-coating technique. The films were characterised chemically and physically using different techniques (TLC, UV–Vis and XRD) and tested for environmental applications regarding degradation of aromatic hydrocarbons. The photocatalytic activity of the TiO₂ nanostructures is tested with different small concentrations of phenol in water and reaction mechanisms discussed. Considerable enhancement is observed in the photodegradation activity of Ag-modified (3 wt.%) TiO₂ compared to unmodified TiO₂ nanostructures for phenol concentrations within the pseudo-first-order Langmuir–Hinshelwood (LH) model for reaction kinetics. The pseudo-first-order global degradation rate constant increased from <0.005 min^?1 for TiO₂ to 0.013 min^?1 for 3 mol% Ag-modified TiO₂. The enhancement is attributed to the incorporation of Ag which promotes the generation of reactive oxygen species and increases the carrier recombination life-time. In addition, Ag has been observed to extend the absorption to the visible region by its surface plasmon resonances and to suppress the anatase–rutile phase transformation. Moreover, TiO₂ grain size prepared was found to be 10 nm which maximises the active surface area. For phenol initial concentrations as low as 0.0002 M, saturation trend in the degradation process occurred at 0.00014 M and the reaction rate can be fitted with half-order LH kinetics.     

Heating of dye-doped microparticles filled with aggregated metal-containing nanostructures by optical radiation

It is found that localizing hot spots inside a resonance microparticle doped with a dye and filled with nanosized metal particles strongly affects heating of these particles and of the entire microparticle. If hot spots lie in the resonance region in the dark or illuminated hemisphere of the microparticle, the microsphere is heated considerably faster. Hot spots in the dark hemisphere of the microparticle may be heated to a maximal temperature sooner than the resonance region in the dark hemisphere.     

Emissivity of powders prepared from nanoporous carbon

Powders prepared from nanoporous carbon are promising for creating cold emitters, which are essential to the development of reliable next-generation monitors. The results of an experimental study of the temperature and time dependences of the emission current from nanoporous carbon coatings are reported. It is shown that the stable emission may last at least 20 h under continuous operation if the emission current density does not exceed 0.6 mA/cm² at room temperature and an accelerating field strength of 800–1200 V/mm. The highest values of the unstable-in-time current density vary from 2.5 to 3.2 mA/cm².     

Electronic transport study of PbSe pellets prepared from self-assembled 2D-PbSe nanostructures

This work presents a study of the electronic transport properties of PbSe pellets fabricated starting of PbSe nanostructures that exhibited a flake-like 2D morphology, which were synthesized by the co-precipitation method. Seebeck coefficient measurements revealed that the PbSe sample displays n-type conductivity, a maximum Seebeck coefficient of −512.6 μV/K around 380 K, and that the carriers scattering is dominated by acoustic and optical phonons. The Fermi level dependence on the temperature and the band gap energy are also reported. Interestingly, size-dependent confinement effects due probably to the reminiscent PbSe 2D character could be evidenced.     

Investigation of carbon microspheres prepared by solid-phase pyrolysis of metal-free phthalocyanine

By using solid-phase pyrolysis of metal-free phthalocyanine (H₂C₃₂N₈H₁₆) we have prepared carbon microspheres with a mean diameter from 2–3.5 μm and sufficiently narrow size distribution. The elemental composition, structure and morphology of samples were studied by scanning electron microscopy, energy-dispersive X-ray microanalysis, and X-ray diffraction. A strong electron paramagnetism was revealed in microspheres.     

Carbon nanotubes and nanostructures grown from diamond-like carbon and polyethylene

We report a simple way to synthesize carbon nanotubes and nanostructures from the solid phase. Vacuum annealing of diamond-like carbon (DLC) films or polyethylene mixed with catalyst in argon atmosphere leads to the formation of nanotubes and nanostructures. High-resolution transmission electron microscopy studies reveal highly graphitized multi-walled nanotubes (MWNTs) or amorphous fibre-like structures, depending on the catalyst amount. This synthesis process may give a new approach to understanding the phase transition of different carbon allotropes into nanotubes or nanostructures. Received: 3 July 2001 / Accepted: 3 July 2001 / Published online: 2 October 2001     

Electron field emission from amorphous carbon with N-doped nanostructures pyrolyzed from polyaniline

Carbon-based materials have been of great interest due to their potential application in cold cathodes for field emission displays and other vacuum microelectronic devices. Pyrolyzed polyaniline (PPANI) with N-doped nanostructures was prepared by pyrolysis of polyaniline at high temperature of 900 °C. The morphologies and microstructures were investigated by scanning electron microscopy, transmission electron microscopy, AFM, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that there were sp²C-N and sp³C-N bonds between the nitrogen and the carbon atoms in the nanostructures of the PPANI obtained. The electron field emission investigations showed that the turn-on field and effective work function ?_e of PPANI were 1.7 V/μm and 0.010 eV which were lower than N-doped amorphous carbon films obtained by other methods.     

Irradiation-induced magnetism in carbon nanostructures

Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.     

Superconductivity in hydrogenated carbon nanostructures

We present an application of density functional theory for superconductors to superconductivity in hydrogenated carbon nanotubes and fullerane (hydrogenated fullerene). We show that these systems are chemically similar to graphane (hydrogenated graphene) and like graphane, upon hole doping, develop a strong electron phonon coupling. This could lead to superconducting states with critical temperatures approaching 100 K, however this possibility depends crucially on if and how metallization is achieved.     

Photoluminescence from heterogeneous SiGe/Si nanostructures prepared via a two-step approach strategy

A two-step approach of preparation for SiGe/Si heterogeneous nanostructures, which combined with ultra-high vacuum chemical deposition and electrochemical anodization techniques, is demonstrated. Uniformly distributed nanostructures with a quite uniform distribution of size and morphology are obtained. A strong room-temperature photoluminescence from the nanostructures was observed with a narrow full-width at half-maximum of around 110 meV. The possible origins of the two main peaks at around 1.6 and 1.8 eV have been discussed in detail. The two-step approach is proved to be a promising method to fabricate new Si-based optoelectronic materials.     

Study of the angular and polarization structures of radiation scattered by monolayers of metal-containing nanostructures during their oxidation

The angular and polarization scattering characteristics of copper, nickel, and palladium monolayers composed of quasi-monodisperse nanograins 2–5 nm in size, as well as aggregates and chains of these nanograins, have been investigated during oxidation of monolayers with different packing densities of particles in a monolayer. On the basis of the experimental data, a number of integral scattering characteristics of monolayers of different metals and the angular dependences of the scattering matrix elements for laser wavelengths in the visible range have been calculated and analyzed. It is demonstrated that the polarization properties of the angular structure and the scattering matrix elements depend strongly on the degree of order of the structures and the presence of chains in monolayers of metal-containing nanostructures. Oxidation of nanostructures leads to the chaotic distribution of metal cores in a nanostructure. It is shown that scattering from nanostructures is more sensitive to oxidation in comparison with absorption. A nonlinear concentration dependence of scattering intensity was observed for copper nanostructures on a quartz substrate near the plasma resonance (at 633 nm) of all structures under study and at 440 nm for nanostructures on a silicon substrate (i.e., at the wavelength corresponding to strong absorption in silicon).     

Surface enhanced Raman spectroscopy of carbon nanostructures

Surface enhanced Raman scattering (SERS) of diamond nanocrystals and fullerene was investigated. Ag and Au films were used as SERS-active agent. In the first series of experiments SERS were prepared with sputtered island metals on the nanoparticles surfaces. In the second one the nanoparticles were positioned on silver surface using laser acceleration method. SERS is a powerful method to analyze the light accelerated nanoparticles patterning for their spatial distribution and structure. The enhancement in Raman spectral intensity of graphite-like phases and blinking effect are observed. Additional bands due to selective enhancement from cluster surface with different arrangement are generated. For SERS of diamond crystal phase as well as for fullerenes the characteristic shift and asymmetry of Raman bands are also observed. The investigation can be of interest both for the understanding of carbon nanostructures’ physics and for their applications, especially for bio-detection, as well as for the studying of SERS mechanism.     

Willmore energy for joining of carbon nanostructures

Numerous types of carbon nanostructure have been found experimentally, including nanotubes, fullerenes and nanocones. These structures have applications in various nanoscale devices and the joining of these structures may lead to further new configurations with more remarkable properties and applications. The join profile between different carbon nanostructures in a symmetric configuration may be modelled using the calculus of variations. In previous studies, carbon nanostructures were assumed to deform according to perfect elasticity, thus the elastic energy, depending only on the axial curvature, was used to determine the join profile consisting of a finite number of discrete bonds. However, one could argue that the relevant energy should also involve the rotational curvature, especially when its size is comparable to the axial curvature. In this paper, we use the Willmore energy, a natural generalisation of the elastic energy that depends on both the axial and rotational curvatures. Catenoids are absolute minimisers of this energy and pieces of these may be used to join various nanostructures. We focus on the cases of joining a fullerene to a nanotube and joining two fullerenes along a common axis. By comparing our results with the earlier work, we find that both energies give similar joining profiles. Further work on other configurations may reveal which energy provides a better model.     

Mechanisms of postsynthesis doping of boron nitride nanostructures with carbon from first-principles simulations

Electron-beam-mediated postsynthesis doping of boron-nitride nanostructures with carbon atoms [Nature (London) 464, 571 (2010); J. Am. Chem. Soc. 132, 13?692 (2010)] was recently demonstrated, thus opening a new way to control the electronic properties of these systems. Using density-functional theory static and dynamic calculations, we show that the substitution process is governed not only by the response of such systems to irradiation, but also by the energetics of the atomic configurations, especially when the system is electrically charged. We suggest using spatially localized electron irradiation for making carbon islands and ribbons embedded into BN sheets. We further study the magnetic and electronic properties of such hybrid nanostructures and show that triangular carbon islands embedded into BN sheets possess magnetic moments, which can be switched on and off by electrically charging the structure.     

Methane conversion into hydrogen and carbon nanostructures

Methane pyrolysis in an ac electric arc is implemented: CH4 - C+2H2. The synthesized nanostructure carbon material is analyzed using a transmission electron microscope. It is shown that a catalyst enables carbon conversion into carbon nanotubes.     

Study of carbon nanostructures obtained by pyrolytic synthesis

The structure and phase composition of a carbon nanomaterial obtained by the thermal decomposition of toluene-ferrocene mixtures are studied by Mössbauer spectroscopy, high-resolution electron microscopy, and x-ray diffraction. Variations in the structural state of the catalyst and in the quantitative yield of the nanomaterial are analyzed as functions of the synthesis time.     

Spin polarization in carbon nanostructures with disclinations

We performed ab initio calculations, using density functional theory, to study spin polarization in carbon nanostructures with disclinations. The results indicate that compounds with positive and negative Gaussian curvature may exhibit a net magnetic moment in the ground state. Additionally, we can conclude that, carbon compounds that display an odd number of pentagons and heptagons, present polarization in the ground state.     

Interfaces between nanostructures and stepwise creep in highly oriented polymers

A comparative laser-interferometric study of steady creep in oriented ultrahigh-molecular-weight polyethylene films differing in the structure of interfaces between nanosized structural units has been carried out to gain a better understanding of the creep mechanism in oriented polymer materials. In contrast to conventional methods, laser interferometry permits measurement of creep rates from very small strain increments (0.3 μm) to within 1%. This technique made it possible to detect the stepwise nature of plastic deformation in creep. The data obtained suggest that the creep rate and its periodic changes are controlled by the structure of the interfaces, and that the plastic deformation itself occurs to a considerable extent through shear of nanosized structural units relative to one another by an “acceleration-deceleration” type. It is proposed that the “deceleration” phase is due to a glide resistance created by some “stoppers” having either physical or chemical nature, which become destroyed and reappear again in the course of creep. Fiz. Tverd. Tela (St. Petersburg) 41, 1788–1791 (October 1999)