Hybrid Platforms of Silicon Nanowires and Carbon Nanotubes in an Ionic Liquid Bucky Gel

Silicon nanowires (NWs) are appealing building blocks for low-cost novel concept devices with improved performances. In this research paper, we realized a hybrid platform combining an array of vertically oriented Si NWs with different types of bucky gels, obtained from carbon nanotubes (CNT) dispersed into an ionic liquid (IL) matrix. Three types of CNT bucky gels were obtained from imidazolium-based ionic liquids (BMIM-I, BIMI-BF₄, and BMIM-Tf₂N) and semiconductive CNTs, whose structural and optical responses to the hybrid platforms were analyzed and compared. We investigated the electrical response of the IL-CNT/NW hybrid junctions in dark and under illumination for each platform and its correlation to the ionic liquid characteristics and charge mobility. The reported results confirm the attractiveness of such IL-CNT/NW hybrid platforms as novel light-responsive materials for photovoltaic applications. In particular, our best performing cell reported a short-circuit current density of 5.6 mA/cm² and an open-circuit voltage of 0.53 V.     

Carbonyl derivatives of phthalocyaninatoiron(II), especially those containing group VI axial donor atoms. Crystal and molecular structure of carbonyl(N,N-dimethylformamide)phthalocyaninatoiron(II) and mössbauer studies of some of the products

The carbonyl adduct of phthalocyaninatoiron(II), FePc, with N,N-dimethylformamide (DMF) as axial ligand, FePc(CO)DMF, was prepared by the reaction of iron carbonyls, Fe(CO)₅ or Fe₂(CO)₉, with o-phthaalonitrile in DMF as solvent. Several carbonyl adducts of FePc of general formula FePc (CO)L are reported, with L being a ligand with oxygen, sulphur and nitrogen donor atoms (L = tetrahydrofuran, H₂O, CH₃OH, dimethylsulphoxide, tetrahydrothiophene, ammonia, n-propylamine, diethylamine, triethylamine). The crystal and molecular structure of FePc(CO)DMF·DMF was investigaed by X-ray diffraction methods. The compound has a monoclinic unit cell and space group P2₁/n, a 9.86(1), b 17.35(3), c 19.79(4) », β 87.9(2)°, Z = 4, U 3383 »³, D₃ 1.458 g cm^?3. The iron atom is hexacoordinated to the four inner nitrogen atoms of the macrocyle, to carbon monoxide (Fe—C distance 1.72(2) ») and to DMF (Fe—O distance 2.07(1) »). The extra DMF occupies lattice sites. All of the compounds reported in this paper are substantially diamagnetic. Mössbauer spectra show typical isomer shift parameters for the bis-adducts and for the carbonyl adduct, substantially independent of the nature of the axial ligand. The quadrupole splitting parameter of the carbonyl adducts is strongly affected by the nature of the axial ligand.     

Large-deflection and post-buckling behavior of slender beam-columns with non-linear end-restraints

The large-deflection analysis and post-buckling behavior of laterally braced or unbraced slender beam-columns of symmetrical cross section subjected to end loads (forces and moments) with both ends partially restrained against rotation, including the effects of out-of-plumbness, are developed in a classical manner. The classical theory of the “Elastica” and the corresponding elliptical functions utilized herein are those presented previously by Aristizabal-Ochoa [1]. The proposed method can be used in the large-deflection analysis and post-buckling behavior of elastic slender beam-columns with rigid, semi-rigid, and simple flexural connections at both ends including linear and non-linear inelastic connections like those that suffer from flexural degradation (such as flexural cracking and elasto-plastic connections) or flexural stiffening. Only bending strains are considered in the proposed analysis. Results from the proposed method are theoretically exact from small to very large curvatures and transverse and longitudinal displacements for laterally braced or unbraced slender beam-columns under bending caused by end loads. The large-deflection analysis and post-buckling behavior of slender beam-columns with both supports partially restrained against rotation and with sway inhibited or uninhibited are complex problems requiring the simultaneous solution of two coupled non-linear equations with elliptical integrals whose unknowns are the limits of the integrals. The validity of the proposed method and equations are verified against solutions available in the technical literature. Three comprehensive examples are included that show the effects of linear and non-linear connections at both ends on the large-deflection analysis and post-buckling behavior of slender beam-columns.     

Stability and second-order non-linear analysis of 2D multi-column systems with semirigid connections: Effects of initial imperfections

An analytical method and closed-form equations that evaluate the elastic stability and second-order response of 2D multi-column systems with initial geometric imperfections (i.e., columns with initial curvature or out-of-straightness and out-of-plumbness in the plane of bending) and semirigid connections subjected to eccentric axial loads and to a lateral load at the top floor level are derived in a classical manner. The proposed method is based on the Euler–Bernoulli theory and limited to 2D multi-column systems with sidesway uninhibited or partially inhibited subjected to gravity loads. The combined effects of initial imperfections and semirigid connections in the plane of bending are condensed into the proposed equations, which can also be used to evaluate the induced elastic bending moments and second-order deflections along each column member of a multi-column system as the lateral and axial loads are applied. The effects of torsion, shear and axial deformations along each column and out-of-plane deformations are not included. Three examples are presented in detail that demonstrate the effectiveness of the proposed method and the corresponding closed form equations showing the importance of initial imperfections, semirigid connections and lateral bracing on the stability and second-order behavior of multi-column systems.     

Effects of the Water Quantity on the Solventless TEOS Hydrolysis Under Ultrasound Stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxysilane(TEOS)-water mixtures was studied at 40°C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ratio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrolysed quantity was found to be approximately independent of the water/TEOS molar ratio, even for r < 4. Polycondensation reaction takes place mainly for low water/TEOS molar ratio in order to supply water to allow almost complete hydrolysis. The overall process of dissolution and hydrolysis has reasonably been described by a previous modelling. The dissolution process of water in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction instead of the initial water quantity present in the mixture.     

Hydrogenation of acetylene–ethylene mixtures on Pd catalysts: study of the surface mechanism by computational approaches. Metal dispersion and catalytic activity

The hydrogenation mechanism of acetylene–ethylene mixtures on Pd catalysts under different experimental conditions was studied by employing a time-dependent Monte Carlo approach set to use a fixed series of event probabilities. The dependence of the catalyst activity and selectivity on the sizes of the metal particles was simulated at microscopic level and the results, also refined by fitting procedures, suggested proper explanations for the apparent nonuniformity of the related experimental findings. The use of the steric hindrance parameter of the surface species and the available surface energy on the metallic catalyst sites was decisive for reproducing the experimental results. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000