Electrical properties of transparent carbon nanotube networks prepared through different techniques

Ultra‐thin, optically transparent and electrically conducting films of pure carbon nanotubes (CNTs) are widely studied thanks to their promise for broad applications. In the present work, we study and compare different deposition techniques for the production of these networks: dip‐coating, spray‐coating, vacuum filtration and electrophoretic deposition on a quartz glass using single‐walled carbon nanotubes (SWCNTs) produced by the HiPCo method. In order to optimize the networks, besides the various deposition techniques we also investigate how the optical and electrical properties vary if the networks are fabricated from different CNTs, all synthesized by the CVD method: SWCNTs, DWCNTs and MWCNTs. As the main criteria for evaluating the quality of these CNT networks we measure the electrical surface resistance at a certain optical transmittance and correlate it to the morphology (homogeneity and roughness) of the networks. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of SOCl2 treatment on electrical and mechanical properties of single-wall carbon nanotube networks

Chemical modification by SOCl2 of an entangled network of purified single-wall carbon nanotubes, also known as 'bucky paper', is reported to profoundly change the electrical and mechanical properties of this system. Four-probe measurements indicate a conductivity increase by up to a factor of 5 at room temperature and an even more pronounced increase at lower temperatures. This chemical modification also improves the mechanical properties of SWNT networks. Whereas the pristine sample shows an overall semiconducting character, the modified material behaves as a metal. The effect of SOCl2 is studied in terms of chemical doping of the nanotube network. We identified the microscopic origin of these changes using SEM, XPS, NEXAFS, EDX, and Raman spectroscopy measurements and ab initio calculations. We interpret the SOCl2-induced conductivity increase by p-type doping of the pristine material. This conclusion is reached by electronic structure calculations, which indicate a Fermi level shift into the valence band, and is consistent with the temperature dependence of the thermopower.     

Analytic conditions for the existence of localized electron states in a linear chain with an arbitrary number of impurities

The effective Hamiltonian and the negative eigenvalue theorem are used to obtain an analytic formula for the integrated density of electron states in a linear chain with an arbitrary number of impurities within the tight binding approximation. From this formula, the analytic conditions for the existence of localized electron states lying above or below the band of states of host atoms are obtained. The way of obtaining the energies of localized states and the form of eigenvectors are also discussed.     

Interferometric investigation of an early stage of plasma expansion with the high-power laser system PALS

The results of interferometric investigation of early stage of plasma expansion carried out in the high-power laser system PALS are presented. The plasma was generated on planar solid Al and Mo targets, irradiated by iodine laser pulses with energies of 100 and 600 J in 0.4 ns at a wavelength of 1.315 μm. The interferometric investigation allowed to determine electron density distributions at chosen moments of the plasma expansion. On the basis of these distributions, information about dynamics and properties of expanding plasma was obtained. The effects of laser-target interaction, i.e., the diameter and the depth of craters as well as the crater shape, were investigated. This research was carried out within the framework of the project PALS/013 (reg. no. HPRI-CT-1999-00053).     

In Situ Migration Experiments at Äspö Hard Rock Laboratory, Sweden: Results of Radioactive Tracer Migration Studies in a Single Fracture

Three radially converging in situ migration experiments over a distance of 5 m were performed in a single fracture at a depth of 400 m in the Äspö Hard Rock Laboratory. Injection and breakthrough curves were obtained for uranine,H³HO (HTO), ²²Na⁺, ⁴²K⁺, ⁴⁷Ca²⁺, ⁵⁸Co(II), ⁸²Br^–, ⁸⁵Sr²⁺, ⁸⁶Rb⁺, ^99mTc (no breakthrough), ¹³¹I^–, ^131,133Ba²⁺ and ^134,137Cs⁺. The in situ experiments lasted for nearly 1.5 years, with single experimental times up to 10,000 hours. The tracer concentrations span over seven orders of magnitude between injection and sampling under practically undisturbed chemical conditions. Dynamic ranges in the breakthrough curves of up to four orders of magnitude were obtained. Thus, the use of radioactive (especially -emitting) tracers showed to be a most useful tool for in situ tracer experiments. The relative retardation sequence obtained in the field experiment was Na < Ca Sr < K < Ba Rb < Co Cs, which was the same as the relative sequence of the sorption coefficients obtained in the laboratory experiments using crushed rock material. Thus, no scale effect was indicated in the relative retardation sequence between laboratory and field experiments. High recoveries, >90%, were obtained for uranine, HTO, Br, I, Na and Sr and lower recoveries for Ba, Rb, Cs and Co. However, there were indications that there would have been higher recoveries of these elements if it had been possible to continue monitoring over longer experimental times. The low recoveries of Cs and Co indicate either slowly reversible or non-reversible sorption behavior. The laboratory diffusion experiments showed lower diffusivities and porosities and somewhat lower sorptivity of all studied tracers in the site-specific rock samples, dominated by mylonite, than in the diorite host rock. Matrix diffusion and associated sorption within the rock matrix is indicated in the in situ experiments, although this can not be verified without modeling that involves such processes.     

Analytical approach in torsional multi-mass discrete-continuous systems with variable inertia

In the paper the systems torsionally deformed consisting of an arbitrary number of elastic elements connected by rigid bodies using the perturbation approach are investigated. The first rigid body represents a motor working with a constant speed, and the last one has a mass moment of inertia depending on the angular displacement. The problem is nonlinear and it is linearized after appropriate transformations. Exemplary numerical results for angular displacements for a two-mass and a three-mass systems are presented.     

Catalytic and kinetic study of the liquid-phase hydrogenation of various organic substrates over a polymer-anchored Pd(II) catalyst

A polymer-anchored Pd(II) complex has been prepared and characterized using scanning electron microscopy, elemental analysis, atomic absorption spectroscopy and FTIR. The catalyst shows excellent catalytic activity in the liquid-phase hydrogenation of substituted nitrobenzenes at normal pressure of hydrogen gas at 25 °C in DMF medium. We have also studied the liquid-phase hydrogenation of other organic substrates such as alkenes, alkynes, aromatic aldehydes, etc. The influences of various parameters such as amount of catalyst, concentration of substrate, temperature and solvent have been studied. The catalyst can be used five times without much loss in activity.     

Polymer‐anchored Ru(II) complex as an efficient catalyst for the synthesis of primary amides from nitriles and of secondary amides from alcohols and amines

A polymer‐anchored ruthenium(II) catalyst was synthesized and characterized. Its catalytic activity was evaluated for the preparation of primary amides from aqueous hydration of nitriles in neutral condition. A range of nitriles were successfully converted to their corresponding amides in good to excellent yields. The catalyst was also effective in the preparation of secondary amides from the coupling of alcohols and amines. The catalyst can be facilely recovered and reused six times without a significant decrease in its activity. Copyright © 2014 John Wiley & Sons, Ltd.