Modification of doping front migration in electrochemical devices and application to organic electronics

We demonstrate several methods of modifying the doping front migration process in multilayer structures, enabling control of migration velocity and switching between different migration mechanisms. Sharp jumps in migration velocity may be induced using a delamination effect. The influence of migration layer thickness and composition is examined. Migration velocity may also be influenced by exposing the system to a defined relative humidity or by varying the concentration of a hygroscopic salt in the migration layer. The migration mechanisms can be explained in terms of diffusion, capillary transport, and delamination. By tailoring the migration process a variety of polymer electronic structures such as pseudo transistors (enhancement and depletion type) and electrical switches (ON–OFF and OFF–ON) may be fabricated. Further examinations about the doping front width are given and the phenomenon of a double front is described.     

Strain Rate Dependence of the Hardness of Glass and Meyer's Law

Depth-sensing Vickers hardness test on glass for various loading regimes were analyzed by applying a flow law for material deformation behavior used by Han and Tomozawa, who investigated the creep behavior of glassy materials during indentation experiments. Load, indentation depth, and time were measured simultaneously at deformation rates covering 6 orders of magnitude. In all cases, the results yielded the well-known Meyer hardness law, by which the parameters of flow law are unequivocally determined using experimentally estimated Meyer parameters. Experiments conducted with various dependencies on commercial sheet glass all gave material parameters in good agreement. Differences originating from different loading regimes must be resolved in future works.     

Reducing shadowing losses with femtosecond‐laser‐written deflective optical elements in the bulk of EVA encapsulation

A new approach on decreasing the optical shadowing of the solar cell grid fingers is presented. The approach relies on a local change of the optical properties in the bulk of the photovoltaic module encapsulation material ethylene vinyl acetate (EVA). In particular, scattering and diffractive optical elements are locally generated within the volume of cross‐linked EVA encapsulation material by applying a femtosecond‐laser‐writing process. When these optical elements are located above the metal grid fingers, the optical shadowing of these grid fingers can be decreased. In an experimental proof of concept, the optical performance of this approach is demonstrated. The best results obtained so far indicate a decrease in optical shadowing by 17%. The material characteristics of the volume optics were investigated by applying confocal Raman microscopic characterisation, which indicates that the EVA material partially degraded upon the impact of the laser beam and is partly carbonised. Supplementary optical simulations show that the light deflection is caused by diffraction. However, parasitic absorption substantially deteriorates the optical performance of the deflective volume optics. Copyright © 2014 John Wiley & Sons, Ltd.     

Non-local regularization for FE simulation of damage in ductile materials

The paper presents an application of the non-local regularization to the finite element modelling of ductile damage and tearing. In order to model the damage growth in ductile materials of structural components, integral limiters have been introduced. These integral limiters, which are spatial averaging operators, can prevent the problem of mesh-sensitivity of the finite element computations. Hence, it was important to establish the characteristic length l_c for spatial averaging operators of the non-local regularization. More formally, the in-plane distance l_c and the out-of-plane FE dimension have been specified, characterizing the volume over which averaging of stress and strain was carried out to ensure that the continuum theory can represent the physical process of damage.

In order to check the reliability and transferability of the method, FE simulations of various testing examples have been carried out, namely ductile fracture in notched tensile specimens, ductile crack growth in C(T) specimens and application to the pipe-bending test.     

Definitions and engineering classifications of tropical lowland peats

Peat classification methods for engineering purposes and the main factors and aspects of these classification systems are discussed. Among the factors that enter into the classification of tropical lowland peats are the organic content and degree or level of humification (on the von Post scale). The organic content as a percentage of the total content determines whether an organic soil is classified as a slightly organic soil (3–20 % organic content), an organic soil (20–75 % organic content), or a peat (more than 75 % organic content). The ASTM standard method of classifying peat is outlined in the Standard Classification of Peat Samples by Laboratory Testing (ASTM D 4427), which includes the use of the ASTM D 5715 (fiber content by field testing for degree of humification) field test method. The von Post humification test (von Post classification system) involves squeezing the peat and the material that is extruded between the fingers, examining the material, and classifying the soil as belonging to one of ten (H1–H10) humification or decomposition categories. Peats are then further subdivided into fibric or fibrous peats (humification range of H1–H3), hemic or moderately decomposed peats (H4–H6), or sapric or amorphous peats (H7–H10). The classification of organic soil or peat for engineering purposes mainly involves using the ignition test (ASTM D 2974) to determine the organic content or determining the percentage of organic content lost on ignition.     

Efficacy of Nerve-Derived Hydrogels to Promote Axon Regeneration Is Influenced by the Method of Tissue Decellularization

Injuries to large peripheral nerves are often associated with tissue defects and require reconstruction using autologous nerve grafts, which have limited availability and result in donor site morbidity. Peripheral nerve-derived hydrogels could potentially supplement or even replace these grafts. In this study, three decellularization protocols based on the ionic detergents sodium dodecyl sulfate (P1) and sodium deoxycholate (P2), or the organic solvent tri-n-butyl phosphate (P3), were used to prepare hydrogels. All protocols resulted in significantly decreased amounts of genomic DNA, but the P2 hydrogel showed the best preservation of extracellular matrix proteins, cytokines, and chemokines, and reduced levels of sulfated glycosaminoglycans. In vitro P1 and P2 hydrogels supported Schwann cell viability, secretion of VEGF, and neurite outgrowth. Surgical repair of a 10 mm-long rat sciatic nerve gap was performed by implantation of tubular polycaprolactone conduits filled with hydrogels followed by analyses using diffusion tensor imaging and immunostaining for neuronal and glial markers. The results demonstrated that the P2 hydrogel considerably increased the number of axons and the distance of regeneration into the distal nerve stump. In summary, the method used to decellularize nerve tissue affects the efficacy of the resulting hydrogels to support regeneration after nerve injury.     

Tailoring defect structure and optical absorption of porous anodic aluminum oxide membranes

Defects influence the optical and electronic properties of nanostructured materials that may be relevant for applications. In self-organized anodic aluminum oxide (AAO) templates we have investigated the effect of annealing, doping and nanoscale metal deposition. Optical absorption spectroscopy has been used as a sensitive probe for the defect density in AAO templates. The electronic spectra are found to be dominated by bands which originate from oxygen-deficient color centers (F⁺, F and F₂). In annealing studies, the integrated absorption of the bands changes non-monotonically with annealing temperature and annealing time. This demonstrates that the concentration of defects can be optimized to tailor the optical properties of the AAO. Metallic Au wires are deposited in the template to establish a plasmonic template or array. The investigations provide an interesting insight into the interplay of reactivity and diffusivity on nanoscales.