Surface pre-treatment and its influence on electric functionality and the formability of screen printed steel sheet

Industrial development focuses on multifunctional components due to rising requirements regarding e.g. light weight and security. A beneficial possibility to extend the functionality of structural components produced by metal forming is the usage of screen printed metal blanks. During the printing process insulating and electric inks are applied. The examined printed layer structure consists of three insulating full area layers and one conductive layer in the form of strain gauges. The two applied inks are solvent-based and printed with a half-automatic machine. To improve the adhesion and electric functionality, the impact of different mechanical and physical surface pre-treatments on the electrical characteristics is investigated in tensile tests. In particular, abrasive peening, ball peening, grinding and polishing (mechanical) and in addition plasma and corona technology (physical) were utilised. Contrary to expectations, the surface pre-treatment does not affect the adhesion to the steel sheet. The cracking of the printed strain gauges takes place prior to the delamination of the coating. Explanatory models are elaborated. They are based on the measurements of roughness, surface energy, edge sharpness and the electrical resistance of printed conductive structures before, during and after forming.     

美国"精明增长"的策略、案例及在中国应用的思考

要将美国“精明增长”应用到中国就必须考虑中国特有的工业化、城市化背景。本文介绍了“精明增长”的有关策略及在美国较为成功的案例,提出在中国应用“精明增长”的一些思考。     

Direct structuring of C60 thin film transistors by photo-lithography under ambient conditions

Direct structuring techniques are an indispensable need for future low-cost applications of organic semiconductor materials in e.g. active matrix displays or integrated circuits. We demonstrate direct structuring of a small molecule organic semiconductor by a photo-lithography lift off process under ambient conditions. To show compatibility of this process, we fabricate organic thin film transistors (OTFT) containing the benchmark electron transporting semiconductor C60 as active material in a top-contact geometry. C60 as electron transporting semiconductor serves as good indicator for contamination and degradation caused by the structuring procedure. To disclose influences of structuring, we discuss the OTFT performance for different channel lengths from 100 μm down to 2.7 μm. In particular, we show that lithography processing gives rise to increased contact resistances. Apart from that, mobility of C60 as material parameter is only weakly affected which underlines the compatibility of the suggested structuring procedure. The potential of this structuring procedure for future integration of driving transistors in active matrix displays is demonstrated.     

Quantum paraelectricity in the self-consistent phonon approximation

Abstract

The dielectric susceptibility of potassium tantalate has been computed in the framework of an approach, earlier proposed by Vaks [V.G. Vaks. Vvedenie v mikroskopicheskuiu teoriju segnetoelektrikov. Moskva, Nauka 1973 (in Russian)]. This theory deals with a perturbation series for the temperature Green functions rather than with the mean field approach. The small parameter is the anharmonicity potential. The phonon spectrum, required for the computation, was taken from a recent study by Farhi et. al. [Europ. Phys. J. B (in print)]. Qualitative agreement has been obtained between theory and experiment.     

TEM investigations of biogenic magnetite extracted from the human hippocampus

Modification of chemical and magnetic extraction techniques has yielded biogenic magnetite/maghemite from human hippocampal tissue. Particles were identified using high resolution transmission electron microscopy, electron diffraction and elemental analysis. Though its presence has been inferred from magnetic analyses, this is the first direct observation of magnetic biominerals from the hippocampus.     

Reverse breakdown behavior in organic pin-diodes comprising C60 and pentacene: Experiment and theory

Charge carrier transport under reverse voltage conditions is of major relevance in devices like organic photo-detectors, organic solar cells (tandem cells), organic light emitting diodes (generation contacts), and organic Zener diodes. We present organic pin-diodes comprising molecular doped layers of pentacene and C60 with an adjustable and reversible reverse breakdown behavior. We discuss the electric field and temperature dependence of the breakdown mechanism and propose a coherent charge transport scenario to describe the experimental findings. Within this model a field assisted tunneling of charge carriers over a rather large distance from valence to conductance states (and vice versa) governs the breakdown behavior. This is in accordance to experimental observations where charge carriers can overcome a layer thickness of 110 nm in the breakdown regime.     

A method for determining buildings’ material composition prior to demolition

A prerequisite of the efficient recycling of demolition waste and its evaluation in terms of the material specific recycling rates is information on the composition of the building material stock (as the source of future demolition waste). A practical method is presented that characterizes the material composition of buildings prior to their demolition. The characterization method is based on the analysis of available construction documents and different approaches of on-site investigation. The method is tested in different buildings and the results from four case studies indicate that the documents are useful to quantify bulk materials (e.g. bricks, concrete, sand/gravel, iron/steel and timber). However, on-site investigations are necessary to locate and determine the trace materials such as metals (e.g. copper and aluminium), or different types of plastics. The overall material intensity of the investigated buildings ranges from 270 to 470?kg/m³ gross volume. With ongoing surveys about the composition of different buildings, the collected data will be used to establish a building-specific database about the amount of materials contained in Vienna's building stock.     

Zonal diffraction efficiencies and imaging of micro-Fresnel lenses

Abstract

The dependence of the zonal efficiency of a transmission Fresnel lens on the number of quantization levels and on the polarization of the light, without and with an antireflection (AR) overcoating is investigated. The height of the grooves with a blaze structure is locally optimized for maximum efficiency. A decreasing structure height over the zonal radius from the centre to the outer zones improves the efficiency because of a better-adapted blaze. An additional increase in the efficiency can be obtained by increasing the AR coating thickness over the zonal radius from the centre outwards. Furthermore, the point spread functions (PSFs) for several quantization levels are compared for both polarization cases. While the AR overcoating has nearly no effect on the shape of the x polarization PSF, the y polarization PSFs show differences between both AR coating and no coating and is reduced with an increasing number of levels. Finally, the comparison between the measured efficiency of coated silicon Fresnel lenses and a calculation lead to acceptable results. All calculations are performed with the integral equation system method with parametrization of the grating profile, an exact electromagnetic grating diffraction method for arbitrary profile shapes.