Carbon Nanotube Based Bearing for Rotational Motions

We report the fabrication of a nanoelectromechanical system consisting of a plate rotating around a multiwalled nanotube bearing. The motion is possible thanks to the low intershell friction. Indeed, the nanotube has been engineered so that the sliding happens between different shells. The plate rotation is activated electrostatically with stator electrodes. The static friction force is estimated at $\approx 2\cdot10^{-15}$ N/\AA$^2$.Comment: 4 pages, 3 figure

Carbon nanotubes quench singlet oxygen generated by photosynthetic reaction centers

Photosensitizers may convert molecular oxygen into reactive oxygen species (ROS) including, e.g., singlet oxygen (1O2), superoxide anion (O2-•), and hydroxyl radicals (•OH), chemicals with extremely high cyto- and potential genotoxicity. Photodynamic ROS reactions are determinative in medical photodynamic therapy (cancer treatment with externally added photosensitizers) and in reactions damaging the photosynthetic apparatus of plants (via internal pigments). The primary events of photosynthesis take place in the chlorophyll containing reaction center protein complex (RC), where the energy of light is converted into chemical potential. 1O2 is formed by both bacterial bacteriochlorophylls and plant RC triplet chlorophylls in high light and if the quenching of 1O2 is impaired. In plant physiology, reducing the formation of the ROS and thus lessening photooxidative membrane damage (including the RC protein) and increasing the efficiency of the photochemical energy conversion is of special interest. Carbon nanotubes, in artificial systems, are also known to react with singlet oxygen. To investigate the possibility of 1O2 quenching by carbon nanotubes in a biological system, we studied the effect of carbon nanotubes on 1O2 photogenerated by photosynthetic RCs purified from purple bacteria. 1,3-Diphenylisobenzofuran (DPBF), a dye responding to oxidation by 1O2 with absorption decrease at 420nm was used to measure 1O2 concentrations. 1O2 was produced either from a photosensitizer (methylene blue) or from triplet photosynthetic RCs and the antioxidant capacity of carbon nanotubes was assessed. Less 1O2 was detected by DPBF in the presence of carbon nanotubes, suggesting that these are potential quenchers of this ROS. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Photocatalytic activity of N-TiO2 nanotubes decorated with CdS QD

The negative consequences of the modern world are environmental pollution. To decrease it, a lot of research is focused on finding solution for its remediation. Photoactive materials have ability to utilize solar energy for the degradation of organic and inorganic pollutants. Among different photoactive material TiO2 has advantages due to its non-toxicity, chemical stability and corrosion resistance. The aim of this study was to investigate the synergetic effect of nitrogen incorporation into crystal structure of TiO2 and deposition of CdS onto amelioration of the photocatalytic degradation of methylen orange compared to the pristine TiO2. For that purpose TiO2 nanotubes were obtained by anodization of titanium foil in HF containing electrolyte. To achieve crystal structure and at the same time to introduce nitrogen in TiO2, the samples were annealed in ammonia atmosphere at 450 °C, for different time of annealing. The highest amount of nitrogen was achieved for the shortest time of annealing (30 min). Beside that, it was observed that the highest level of interstitial nitrogen was also achieved for the shortest time of annealing. Further, CdS quantum dots (QDs) were deposited on the nitrogen doped TiO2 nanotubes via an ex-situ method (using binding reagent). According to the FESEM micrographs, a partial agglomeration of CdS QDs on some domaines on top of the nanotubes was observed. By performing the DRS, the improvement of the optical response after nitrogen doping and deposition of CdS was demonstrated. The sample with the highest amount of total nitrogen and interstitial nitrogen in combination with deposition CdS QDs exhibited the highest photocatalytic efficiency

The effect of disorder on the conduction electron spin resonance linewidth of the α and β phases of (BEDT-TTF)2I3

We present the electron spin resonance linewidth of α and β phases of the organic conductor di-bis (ethylenedithiolo) tetrathiafulvalene driiodide [(BEDT-TTF)2I3] disordered by fast electron irradiation. In the high temperature metallic phase the linewidth decreases in both phases with defect concentration in contrast to the predictions of the Elliott mechanism for spin relaxation in metals

Multiwalled carbon nanotubes produced by a continuous CVD method and their use in melt mixed composites with polycarbonate

In this study, two samples of multiwalled carbon nanotubes (MWNT) were synthesized by CVD of acetylene over Fe2Co catalysts supported by CaCO3 using different temperatures. The material produced at 660 °C (MWNT600) shows slightly better performance as evidenced by lower mean tube diameter and better conductivity as compared to the sample produced at 700 °C (MWNT700). In addition, it has a higher [O]:[C] ratio. Both materials were incorporated into polycarbonate using melt mixing using a small scale compounder. The results prove that these materials are very suitable for polymer composite applications as they show low electrical percolation concentration and good mechanical enhancement. The percolation threshold is as low as <0.875 wt% for MWNT660 and <1 wt% for MWNT700. MWNT700 showed slightly better dispersability as evidenced from light microscopy, SEM, and TEM. The effects in the stress-strain curves are similar in both composites, indicating a stress increase with MWNT incorporation

Some electronic properties of the organic superconductor &#946;-(BEDT-TTF )2I3

We report some results of magnetoresistance, magnetic susceptibility and magnetic anisotropy measurements on single crystals of the two dimensional organic superconductor &#946;L-(BEDT-TTF)2I3 from 4.2 to 300 K. From the c* magnetoresistivity we deduce a value of 0.5 meV for the tight binding transfer integral tc, and show that there is significant conductivity anisotropy (a factor 5) in the a-b plane at low temperatures. A short value of the relaxation time, 0.5 ps at 9 K, indicates that electron transport between planes is becoming incoherent, which may affect the superconducting transition temperature. The static spin susceptibility shows little enhancement relative to the specific heat. The magnetic anisotropy data give evidence for a temperature dependent conduction electron diamagnetism when the magnetic field is perpendicular to the conducting planes.Nous avons mesuré de 300 K à 4,2 K la magnétorésistance, la susceptibilité et l'anisotropie magnétique de monocristaux du supraconducteur organique bi-dimensionnel &#946;L-(BEDT-TTF)2I3. A partir de la magnétorésistance suivant c*, nous avons calculé une valeur de 0,5 meV pour l'intégrale de transfert tc dans un modèle de liaisons fortes. De plus, ces mesures indiquent que l'anisotropie de conductivité dans le plan a-b à basse température est d'un facteur cinq. La faible valeur du temps de relaxation (0,5 ps à 9 K) indique que le transport électronique entre plans devient incohérent, ce qui peut affecter la température de transition supraconductrice. La densité d'états dérivée de la susceptibilité de spin est en bon accord avec celle obtenue par chaleur spécifique. Lorsque le champ magnétique est dirigé perpendiculairement aux plans conducteurs, l'anisotropie magnétique provient en partie d'un diamagnétisme des électrons de conduction qui varie avec la température

Controlled positioning of carbon nanotubes by dielectrophoresis: Insights into the solvent and substrate role

We demonstrate the ability to precisely control the deposition of a defined number of carbon nanotubes (CNTs) from solution onto microfabricated electrodes using dielectrophoresis. The solvation shell around the CNTs, exhibiting a high dielectric constant which is possibly larger than the intrinsic dielectric constant of CNTs, is found to play a crucial role in electrophoretic processes. Substrate resistivity is also very important: The spatial repartition of the electric field between the substrate and the microelectrodes leads to deviations from the precise location of the CNTs. A recipe is given for the dielectrophoresis of CNTs which can be extended to other nanowires or nanotubes.status: publishe

Direct growth of carbon nanotubes on carbon fibers: Effect of the CVD parameters on the degradation of mechanical properties of carbon fibers

© 2014 Elsevier B.V. All rights reserved. Grafting carbon nanotubes (CNTs) directly on carbon fibers represents a promising approach in order to strengthen the weak interface between carbon fibers and polymer matrix in carbon fiber reinforced polymer composites (CFRCs). We have carried out direct growth of CNTs on carbon fibers by using two different catalytic chemical vapor deposition (CVD) processes, namely the conventional CVD process based on catalytic thermal decomposition of ethylene and the oxidative dehydrogenation reaction between acetylene and carbon dioxide. The effect of various CVD growth parameters, such as temperature, catalyst composition and process gas mixture, was for the first time systematically studied for both processes and correlated with the mechanical properties of carbon fibers derived from single-fiber tensile tests. The growth temperature was found to be the most critical parameter in the presence of catalyst particles and reactive gasses for both processes. The oxidative dehydrogenation reaction enabled decreasing CNT growth temperature as low as 500°C and succeeded to grow CNTs without degradation of carbon fiber's mechanical properties. The Weibull modulus even increased indicating partial healing of present defects during the CVD process. The new insights gained in this study open a way towards simple, highly reproducible and up-scalable process of grafting CNTs on carbon fibers without inducing any damages during the CVD process. This represents an important step towards CNT-reinforced CFRCs with higher damage resistance.status: publishe

Pressure effect on the magnetic susceptibility of low dimensional organic conductors &#945;-, &#946;-(BEDT-TTF)2I3 and (TMTSF)2X (X=ClO4, PF6, ReO4)

The pressure dependence of the static susceptibility of the &#945; and &#946; phases of (BEDT-TTF)2I3 and of (TMTSF)2X for X = CI04, PF6, Re04 was measured using a Faraday balance up to a pressure of 10 kbar. The fractional pressure dependence &#963; InXs/&#963;P is -2.0%/kbar and -3.3%/kbar for the &#945;- and &#946;-(BEDT-TTF)2I3 respectively and it is temperature independent. For (TMTSF)2X &#963;1nXs/&#963;P is about -3.0%/kbar at room temperature and increases to -4.8%/kbar on cooling. Both the magnitude and temperature dependence of the fractional pressure dependence in those two families are in contrast with the behaviour in TTF-TCNQ, where the magnitude is -8.%kbar and decreases with decreasing temperature