Degradation of zinc oxide thin films in aqueous environment: Part I – Bare Films

As their optical, electrical, and electrochemical properties can be modified, zinc oxide thin films are employed as optically transparent conductors in the production of many different microdevices. Although microdevices are generally encapsulated for protection from aggressive environment, the zinc oxide thin films can still degrade with a resultant decrease in device performance. The investigation of the mechanism of degradation for these films is, therefore, of significant interest in prolonging the lifetime of many electronic devices. In this paper, the behaviour of bare zinc oxide thin films produced by magnetron‐sputtering (MS‐ZnO) and exposed to aqueous aerated 3.5% NaCl at 25°C was investigated. Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS) and DC measurements were employed to study the degradation mechanisms of two sputtered‐ZnO films having different microstructures. The experimental tests were primarily focused on defining the relationship between microstructure and the degradation rate of the ZnO thin films. Due to the development of moisture induced microfractures in the ZnO films, a two stage mechanism was suggested. Two different equivalent electrical circuits are, thus, proposed to interpret the EIS data at different stages in the degradation. The parameters of the equivalent network were related to degradation development, the change of degradation mechanism and the extent of microfracture in the film.     

Modelisticinterpretation of the impedance response of a polymer electrolyte fuel cell

In this work, several aspects related to the limiting polarization behavior of polymer electrolyte fuel cells were studied using ac impedance spectroscopy. The results were analyzed taking into account the different types of potential losses caused by the interfacial reaction kinetics, the conductance of the electrolyte in the catalyst layer, the oxygen diffusion in the gas phase, in the thin film and in the distributed agglomerate regions of the gas diffusion electrodes and the balance of water in the membrane. The main conclusion is that the water transport in the membrane plays an important role in establishing the limiting polarization behavior of polymer electrolyte fuel cells, corresponding to the only limiting factor when pure oxygen is employed as the cathodic reagent. When the oxygen source is air, the diffusion of oxygen in the gas phase becomes a limiting factor, but for pressurized systems the diffusion of water can also be observed, especially for thick membranes.     

Localization of glycosylation sites in the golgi apparatus using immunolabeling and cytochemistry

This review summarizes data on the distribution of certain glycosylation steps in the Golgi apparatus as revealed by immunolabeling and lectin techniques. The methodical basis for such investigations was provided by the introduction of the colloidal gold marker system for immunolabeling and the development of new means of tissue processing such as the low-temperature embedding technique using Lowicryl K4M. The application of these techniques together with highly specific antibodies has provided much of the basis for our current understanding of the Golgi apparatus in functional terms. Thus, in many cell types, three Golgi apparatus compartments can be distinguished, whereas in others no such functional subdivision is evident. Investigations on sialyltransferase distribution have also provided direct evidence that GERL is structurally and functionally part of the Golgi apparatus.     

Surface characterization of flax,hemp and cellulose fibers; Surface properties and the water uptake behavior

The surface characteristics of several natural fibers—flax, hemp and cellulose—were investigated using scanning electron microscopy, BET-surface area and zeta (ζ-) potential measurements. ζ-Potential measurements using the streaming potential method were performed in order to study the water uptake behavior as well as the surface properties of several natural fibers. The influence of different flax-fiber separation methods and several modifications, like industrial purification, and such a treatment followed by alkaline purification as well as polypropylene grafting on the fiber surface morphology, surface area and time- and pH-depending ζ-potentials were studied. The time-dependence of the ζ-potential, measured in 1 mM KCl solution, offeres and alternative possibility to estimate the water uptake behavior for nearly all investigated natural fibers. The water uptake data derived from the ζ-potential measurements (ζ = f(t)) were compared with data from conventional water adsorption studies for some chosen examples.