Nitrogen inclusion in vertically aligned carbon nanotubes (v-CNTs) was performed in situ and in ultra-high vacuum by nitrogen ion implantation and evaluated by X-ray photoelectron spectromicroscopy. ...The creation of defects induced by the ions drives the formation of different nitrogen species (pyridinic, pyrrolic, and graphitic) at the CNT surface. While nitrogen implantation in CNT sidewalls has results similar to implantation in graphene, where mainly nitrogen sp2 bonding configuration occurs, we observed a different behaviour at the CNT tips, where nitrogen incorporation is also more efficient. A large amount of pyrrolic nitrogen is observed at the CNT tips compared to the amount at the CNT sidewalls for the same ion implantation parameters. This indicates a different reactivity of the CNT tips where the presence of natural defects may be involved in different nitrogen bonding formations between carbon and nitrogen with respect to the CNT sidewalls.
The interaction between evaporated gold and pristine or oxygen plasma treated multi-walled carbon nanotubes (MWCNTs) is investigated. Experimental and theoretical results indicate that gold ...nucleation occurs at defect sites, whether initially present or introduced by oxygen plasma treatment. Uniform gold cluster dispersion is observed on plasma treated carbon nanotubes (CNTs) and associated with the presence of uniformly dispersed oxidized vacancy centres on the CNT surface.
Organic nanoparticles of cholesterol and retinol have been synthesized in various AOT (Aerosol OT; sodium bis(2-ethylhexyl) sulfosuccinate)/heptane/water microemulsions by direct precipitation of the ...active principle in the aqueous cores. The nanoparticles are observed by transmission electron microscopy (TEM) using the adsorption of a contrasting agent, such as iodine vapor. The size of the nanoparticles can be influenced, in principle, by the concentration of the organic molecules and the diameter of the water cores, which is related to the ratio R = H2O/surfactant. The particles remain stable for several months. The average diameter of the cholesterol nanoparticles varies between 3.0 and 7.0 nm, while that of retinol varies between 4.0 and 10 nm. The average size of the cholesterol nanoparticles does not change much either as a function of the ratio R or as a function of the concentration of cholesterol. The constant size of the nanoparticles can be explained by the thermodynamic stabilization of a preferential size of the particles. Chloroform is used to carry the active principle into the aqueous cores. Retinol molecules form J-complexes composed of two or three molecules, as detected by UV−visible spectroscopy.
Multi-wall carbon nanotubes (MWCNTs) were exposed to a CF4 rf-plasma. X-ray photoelectron spectroscopy analysis shows that the treatment effectively grafts fluorine atoms onto the MWCNTs. The ...fluorine atomic concentration and the nature of the C-F bond (semi-ionic or covalent) can be tuned by varying the exposure time. Ultraviolet photoelectron spectroscopy analysis confirms that the valence electronic states are altered by the grafting of fluorine atoms. Characterization with high-resolution transmission electron microscopy reveals that while the plasma treatment does not induce significant etching impact on the CNT-surface, it does increase the number of active sites for gold cluster formation.
Multi-wall carbon nanotubes (MWCNTs) were decorated with metal clusters by thermal evaporation. Transmission electron microscopy (TEM) shows that the nature and extent of metal coverage can be varied ...by plasma treating the MWCNT surface. The metal clusters on oxygen plasma treated arc-discharge MWCNTs have a more dense distribution than the clusters evaporated on as-synthesized arc-discharge MWCNTs. In contrast, the plasma treatment did not affect the cluster distribution on CVD MWCNTs. Analyses of the valence band and the core levels by X-ray photoelectron spectroscopy suggest poor charge transfer between gold clusters and MWCNTs; on the contrary suggest good charge transfer between Ni clusters and MWCNTs.
Neuronal communication is tightly regulated by presynaptic signaling, thereby temporarily and locally secreting one or more transmitters in order to exert propagation or modulation of network ...activity. In the last 2 decades our insight into the molecular regulation of presynaptic transmitter vesicle traffic and fusion has exponentionally grown due to the identification of specific functional interactions between presynaptic proteins involved in these processes. In addition, a plethora of extracellular and intracellular messengers regulate neurotransmitter release, occasionally leading to short- or long-term adaptations of the synapse to altered environmental signals. Important in this respect is the ability of various nerve terminals to diverge their output by differentiation in secretion of co-localized transmitters. This divergence in presynaptic signaling may converge in the postsynaptic target neuron or spread to neighbouring cells. In this review differential presynaptic signaling mechanisms will be related to their potential divergent roles in transmitter release.
The effect of the oxygen plasma treatment on the electronic states of multi-wall carbon nanotubes (MWCNTs) is analyzed by X-ray photoemission measurements (XPS) and UPS, both using synchrotron ...radiation. It is found that the plasma treatment effectively grafts oxygen at the CNT-surface. Thereafter, the interaction between evaporated Pd and pristine or oxygen plasma-treated MWCNTs is investigated. Pd is found to nucleate at defective sites, whether initially present or introduced by oxygen plasma treatment. The plasma treatment induced a uniform dispersion of Pd clusters at the CNT-surface. The absence of additional features in the Pd 3d and C 1s core levels spectra testifies that no Pd–C bond is formed. The shift of the Pd 3d core level towards high-binding energy for the smallest clusters is attributed to the Coulomb energy of the charged final state.
We have investigated the nature of the interaction between samarium (Sm) and pentacene, and the energy level alignment at the resulting interfaces. The valence electronic structure of in situ ...prepared samples, i.e., pentacene evaporated onto Sm surfaces and vice versa, was investigated with ultraviolet photoelectron spectroscopy. Pentacene appears to physisorb on the metal surface. Sm also appears to interact weakly when evaporated on the organic material, forming clusters at low coverage. Indications of a valence change of Sm upon evolution from clusters to metallic film are found. The highest occupied molecular orbital of pentacene is measured at 1.85 eV below the metal Fermi level E F for both evaporation sequences. Estimating the energy of the lowest unoccupied molecular orbital of pentacene using the transport gap, we obtain a barrier of only 0.35 eV for the injection of electrons from the metal into the organic material.
Understanding the modification of the graphene's electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on ...SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants' concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors.
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