Reaction kinetics of organo-clay hybrid films: In-situ IRRAS, FIM and AFM studies

In this paper we report the reaction kinetics of nanodimensional clay saponite and hectorite with an amphiphilic cation octadecyl rhodamine B (RhB) in hybrid Langmuir monolayer at the air-aqueous clay dispersion interface. The surface pressure-molecular area (π-A) isotherms were strongly influenced by the presence of clay and the lift-off area of the cationic amphiphile shifted to progressively larger area. In-situ fluorescence imaging microscopic (FIM) studies showed the formation of micro-order domains in the organo-clay hybrid monolayer films at the air-clay dispersion interface. In-situ infrared reflection-absorption spectroscopy (IRRAS) was used to demonstrate the reaction kinetics. The time taken to complete the reaction kinetics for RhB-hectorite hybrid films is larger than for RhB-saponite hybrid films. Atomic force microscopic images of hybrid Langmuir-Blodgett films gave compelling visual evidence of the incorporation of clay platelets into the hybrid films, whose density increased with the progress of reaction kinetics.     

CdTe and PbTe nanostructures on the oxidized pentagonal surface of an icosahedral AlPdMn quasicrystal

By means of congruent evaporation, we have deposited CdTe and PbTe onto the oxidized fivefold-symmetry surface of an icosahedral AlPdMn quasicrystal. This procedure results in the formation of nanocrystals in both cases. While the azimuthal orientations of the crystallites are random, the polar orientations are well defined. The crystalline CdTe and PbTe domains expose their (1 1 1) and (0 0 1) faces, respectively, which are aligned parallel to the pentagonal surface of the quasicrystal. The nanometric size of the domains is not a result of the lattice mismatch between the growing film and the substrate as usually observed in molecular-beam epitaxy, but of the limited size of the oxide domains of the substrate surface.     

Fabrication of Ru(bpy)3-titanate nanotube nanocomposite and its application as sensitive solid-state electrochemiluminescence sensor material

A novel and facile method for effective immobilization of Ru(bpy)₃²⁺ within titanate nanotubes (TiNTs) and its application as a sensitive solid-state electrochemiluminescence (ECL) sensor material was studied. The process involved the formation of Ru(bpy)₃²⁺-titanate nanotube nanocomposite (Ru-TiNTs) via electrostatic interactions by mixing TiNTs and Ru(bpy)₃(ClO₄)₂ in aqueous medium. Then Ru-TiNTs were attached to the surface of a Pt electrode to form an ECL sensor. Characterization of Ru(bpy)₃²⁺-titanate nanotube nanocomposite was accomplished by transmission electron microscopy, X-ray photoelectron spectrum, and field emission scanning electron microscope. The electrochemistry and ECL behavior of Ru(bpy)₃²⁺ immobilized on TiNTs were studied with tripropylamine as a coreactant. As-prepared Ru-TiNTs exhibited very good stability and Ru(bpy)₃²⁺ species contained showed excellent ECL behavior. Therefore, the as-prepared Ru(bpy)₃²⁺-titanate nanotube nanocomposite exhibited great promise as new luminescent materials for solid-state ECL detection.     

Surface resistance measurements at the metal/electrolyte interface of Ag(100) and Ag(111) thin film electrodes

The conductivity of thin film metal electrodes with a thickness of the order of the mean free path of the conduction electrons (50 nm at 300 K) is sensitive to several processes on the metal surface (e.g. adsorption and desorption of ions). We developed epitaxially grown Ag(100)/MgO(100) and Ag(111)/TiO₂(110) electrodes of 20 nm thickness. The change in the surface resistance of Ag(100) thin film electrodes during adsorption of the halide ions Cl⁻, Br⁻ and I⁻ shows the different strengths of specific adsorption. We investigated the phase transition of thiocyanate (SCN⁻) on Ag(100) electrodes by combining the surface resistance method with voltammetric, capacitance and ex-situ XPS measurements. The influence of adsorbed uracil on the resistance of Ag(100) films was demonstrated. The surface resistance is very sensitive to small concentrations of metal cations (e.g. Tl⁺). The surface resistance of Ag(100) and Ag(111) thin film electrodes shows the typical difference in the stripping potential of Tl⁺ of about 100 mV.     

Numerical simulation of the horizontal Bridgman growth. Part III: Calculation of the interface

We study the transient motion of the solidification front during the growth of semiconductor crystals in the horizontal Bridgman geometry. The calculation is based on a two-dimensional flow. We use finite elements which deform with the motion of the interface. The energy equation is coupled with the isothermal constraint of the interface in an implicit transient algorithm. Several examples show the oscillatory motion of the interface caused by the periodic flow of the melt, and they reveal the importance of the growth rate on the shape of the interface.     

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

We report the details of the construction and calibration of a sensitive surface rheometer, inspired by an instrument described in the literature, adapted to the study of photosensitive polymeric materials. By high resolution video tracking of the motion of a floating magnetized needle we are able to measure the viscoelastic complex shear modulus G of a Langmuir monolayer with an accuracy of 5*10^− 6 N/m. This instrument is then employed for the rheological characterization of a Langmuir monolayer of a photosensitive azobenzene polymer, which can be brought out of equilibrium by a suitable photoperturbation. The shear modulus is measured as a function of temperature, illumination power and wavelength. The reversible rheological changes induced in the film by photo-perturbation are monitored during time, observing a transition from a predominantly elastic (G mainly real) to a viscoelastic regime (real and imaginary parts of G comparable). These results are confirmed by a comparison with independent measurements performed using other rheological techniques. Finally a discussion is made, taking into account the results of a recent X-ray photon correlation spectroscopy (XPCS) experiment on the same polymer in equilibrium and out of equilibrium.     

A mesoscopic model of the intermixing during nanoenergetic materials processing

A general mesoscopic model for the simulation of thin-film vapor deposition applied to energetic materials, specifically bimetallic multilayers, is presented. We describe the setup of this mesoscopic simulator developed in the frame of a multiscale study by implementing ab initio data into a set of differential equations. We present numerical results relative to the formation of barrier layers as a result of interdiffusion between successive bimetallic AlNi multilayers. The key role of the vacancies species created during deposition is highlighted.     

The influence of the growth temperature and interruption time on the crystal quality of InGaAs/GaAs QW structures grown by MBE and MOCVD methods

The impact of two technological parameters, i.e., the growth temperature and the interface growth interruption, on the crystal quality of strained InGaAs/GaAs quantum well (QW) structures was studied. The investigated heterostructures were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapour deposition (MOCVD) under As-rich conditions. Photoluminescence (PL), reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) were adopted for the evaluation of specified interfaces smoothness and the quality of layers. Comparison between both epitaxial techniques allowed us to find, that the growth temperature plays more significant role in the case of structures grown by MBE technique, whereas the quality of MOCVD grown structures is more sensitive to the growth interruption. Optimum values of the investigated parameters of QW crystallization were obtained for both growth techniques.     

Localized plastic strain in polycrystalline materials with hole and notches

Analyzed numerically are the localized strain of polycrystalline materials subjected to quasi-static loading. The objective is to study the peculiarities associated with the deformation process close to the stress concentrators such as holes, notches and interfaces of internal structure. Analytical results show that geometry and/or heterogeneous internal structure of material together with the action of maximum shear result in the development of a system of plastically deformed shear bands. Shears and rotations in the regions of strain localization are found to be higher than in other parts of the specimen while rotations are more sensitive to localization.     

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films

The injection of pure spin current into the non-magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (≈20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni₈₀Fe₂₀) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin-mixing conductance of ≈1.02×10¹⁸ m⁻², a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy-pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.