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    Paradigm change in hydrogel sensor manufacturing: From recipe-driven to specification-driven process optimization
    (Göttingen : Copernicus Publ., 2016) Windisch, M.; Eichhorn, K.-J.; Lienig, J.; Gerlach, G.; Schulze, L.
    The volume production of industrial hydrogel sensors lacks a quality-assuring manufacturing technique for thin polymer films with reproducible properties. Overcoming this problem requires a paradigm change from the current recipe-driven manufacturing process to a specification-driven one. This requires techniques to measure quality-determining hydrogel film properties as well as tools and methods for the control and optimization of the manufacturing process. In this paper we present an approach that comprehensively addresses these issues. The influence of process parameters on the hydrogel film properties and the resulting sensor characteristics have been assessed by means of batch manufacturing tests and the application of several measurement techniques. Based on these investigations, we present novel methods and a tool for the optimization of the cross-linking process step, with the latter being crucial for the sensor sensitivity. Our approach is applicable to various sensor designs with different hydrogels. It has been successfully tested with a sensor solution for surface technology based on PVA/PAA hydrogel as sensing layer and a piezoelectric thickness shear resonator as transducer. Finally, unresolved issues regarding the measurement of hydrogel film parameters are outlined for future research.
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    Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity
    (Melville, NY : AIP Publishing LLC, 2021) Chardonnet, Valentin; Hennes, Marcel; Jarrier, Romain; Delaunay, Renaud; Jaouen, Nicolas; Kuhlmann, Marion; Ekanayake, Nagitha; Léveillé, Cyril; von Korff Schmising, Clemens; Schick, Daniel; Yao, Kelvin; Liu, Xuan; Chiuzbăian, Gheorghe S.; Lüning, Jan; Vodungbo, Boris; Jal, Emmanuelle
    During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm (≃310 eV), we were able to probe close to the Fe L3 edge (706.8 eV) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.