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Item type:Publication, Access status: without files , Shaping the electric field: overcoming geometric inhomogeneities in the electrochemical fabrication of mesoporous materialsIntegrating porous systems such as mesoporous silicon (pSi) into reliable macroscopic devices for sensing, photonics and energy storage requires stringent control over their structural homogeneity. While radial variations in layer thickness and porosity are frequently attributed to edge sealing effects or pinned gas, the macroscopic impact of the electrochemical cell’s internal geometry is largely overlooked. Using pSi as a model system, we demonstrate that the insulating cell body acts as a significant field-shaping component. Combining 2D axisymmetric finite element simulations of the current distribution with spatially resolved near-infrared (NIR) spectrometry, we investigate distortions caused by standard cell features. We reveal that the internal container widening step, commonly used to accommodate counter electrodes, strongly compresses the electric field and generates localized, ring-shaped zones of accelerated etching. Optimizing this step height reduced the radial thickness deviation of a pSi layer 6-fold to just 2%. Furthermore, predictive simulations demonstrate that internal obstacles, such as stirring rods, can be deliberately positioned to either prevent unwanted current shadows or actively manipulate the current distribution for precise three-dimensional structuring. Ultimately, mindful hardware design that prioritizes spatial current distribution is a critical and efficient strategy to maximize the yield of highly homogeneous porous media, directly enhancing their scalability and performance in functional nanomaterial applications.Publicationtype: Journal Article12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Directional dark field for nanoscale full-field transmission X-ray microscopyDark-field X-ray imaging visualizes structural inhomogeneities through small-angle scattering, but existing directional methods are confined to the micrometer scale. While recent advances have extended dark-field capabilities to nanoscale transmission X-ray microscopy, directional scattering retrieval - critical for characterizing anisotropic nanostructures - has remained inaccessible for imaging resolutions in the sub-micrometer scale. Here, we demonstrate the first directional dark-field setup for nanoimaging, achieving orientation mapping of scattering features below the spatial resolution limit. Our method is experimentally simple to implement with existing transmission X-ray microscopy setups. We validate its performance by successfully resolving sub-resolution test structure orientations, cross-correlating orientational changes within hierarchical nanoporous materials, and mapping the directional arrangement of hydroxyapatite nanocrystals 30 - 70 nm within human tooth enamel. By utilizing shadow regions in the optical configuration, we further extend the detectable scattering vector range, demonstrating a pathway toward size-selective dark-field imaging. This advancement enables the quantitative structural characterization of anisotropic nanomaterials, which are critical to biomineralization, advanced materials, and nanotechnology applications.Publicationtype: Journal Article45 48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Additive manufacturing of hierarchically porous silicon and silica glass(Deutsche Gesellschaft für Materialkunde e.V. (DGM), 2026-03-24); ; ; ; Publicationtype: Conference Presentation105 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Directional dark field for nanoscale full-field transmission X-ray microscopy(2025-06-20); ; 37 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A Mott-Schottky analysis of mesoporous silicon in aqueous electrolyte solution by electrochemical impedance spectroscopyNanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. In recent years, it has been shown that filling the pores with aqueous electrolytes, in addition opens a particularly wide field for modifying and achieving active control of these functionalities, e.g., for electrochemo-mechanical actuation and tunable photonics, or for the design of on-chip supercapacitors. However, a mechanistic understanding of these new features has been hampered by the lack of a detailed characterization of the electrochemical behavior of mesoporous silicon in aqueous electrolytes. Here, the capacitive, potential-controlled charging of the electrical double layer in a mesoporous silicon electrode (pore diameter 7nm) imbibed with perchloric acid solution is studied by electrochemical impedance spectroscopy. Thorough measurements with detailed explanations of the observed phenomena lead to a comprehensive understanding of the capacitive properties of porous silicon. An analysis based on the Mott-Schottky equation enables the determination of essential parameters such as the flatband potential, the carrier concentration and the width of the space charge region. A comparison with bulk silicon shows that the flatband potential in particular is significantly altered by the introduction of nanopores, as it shifts from 1.4±0.1V to 1.9±0.2V.Publicationtype: Journal Article91 64