Funded OA publications

The chemical energy released as heat during the exothermic reaction of reactive multilayer systems has shown potential applications in various technological areas, e.g., in joining applications. However, controlling the heat release rate and the propagation velocity of the reaction is required to enhance their performance in most of these applications. Herein, a method to control the propagation velocity and heat release rate of the system is presented. The sputtering of Al/Ni multilayers on substrates with periodic 2D surface structures promotes the formation of growth defects into the system. This modification in the morphology locally influences the reaction characteristics. Tailoring the number of 2D structures in the substrate enables the control of the velocity and maximum temperature of the propagation front. The morphology of the produced reactive multilayers is investigated before and after reaction using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. In addition, the enthalpy of the system is obtained through calorimetric analysis. The self-sustained and self-propagating reaction of the systems is monitored by a high-speed camera and a high-speed pyrometer, thus revealing the propagation velocity and the temperatures with time resolution in the microsecond regime.

The specific mechanical properties of fiber reinforced composite components are unmatched, considering their low weight. To optimize the lightweight potential of fiber reinforced composites, fiber volume contents have to be maximized and imperfections must be eliminated. However, during the production of fiber reinforced composite laminates via resin injection processes, the formation of microscopic voids is nearly inevitable. Even low amounts of imperfections can cause significant deteriorations in the mechanical properties of the material. To reduce the number of voids inside composite components, understanding the formation and transport of voids is essential. Numerous renowned models describe said formation of voids in dependence of local flow front conditions during the impregnation of textile preforms with thermoset resins. State of the art are models emphasizing the formation of meso-and microvoids in dependence of the modified capillary number. These models show plausible correlations when applied to unidirectional preforms or fabrics with constant permeability along the direction of flow. However, the formation of voids remains to be investigated at points of transitioning permeability, such as alterations in the setup of layers or abruptly changing cavity diameters. To expand the applicability of the existing models onto preforms with local changes in permeability, an experimental setup for gradually increasing cavity diameter and varying layer setup is introduced. A planar mold with three increasing levels of cavity height is used to induce changes in permeability. The rate of change in permeability is controlled by defining the slope between each level. In this study, injection pressure as well as flow front velocity were optically traced, and material data was measured. Resulting local void volume contents were quantified by calcination. It is demonstrated how alterations of diameter and layup take effect on the resulting local porosity. The observed impact on void formation is put in context to changes in tow permeability due to local differences in fiber volume content. By including the slope dependent rate of change in tow permeability into the existing model for calculation of void formation by GUEROULT ET AL., the accuracy of the model can be increased. Comparing the unaltered model to experimental results, the deviations between calculations and measurements were diminished when using the newly introduced factors. Although the error of prediction is being significantly reduced, calculations are still flawed since additional effects like overflow at level edges need to be considered. This discourse is meant to administer a starting point for considering rates of change in tow permeability into the commonly established use of shape factors of models of void formation.

2D metal phosphorous trichalcogenides (MPCh3) have attracted considerable attention in sustainable energy storage and conversion due to their distinct physical and chemical characteristics, such as adjustable energy bandgap, significant specific surface area, and abundant active sites. However, research on 2D MPCh3 primarily focuses on electrocatalysis, and understanding its energy conversion and storage mechanisms remains incomplete. This review comprehensively summarizes recent advancements in energy storage and conversion using 2D MPCh3-based materials of various structures. It begins with a discussion of the distinctive properties and preparation techniques of 2D MPCh3, followed by a focus on the rational design and development of these materials for diverse energy-related applications, including rechargeable batteries, supercapacitors, electrocatalysis, photocatalysis, and desalination. Finally, it outlines the key challenges and prospects for future research on 2D MPCh3 materials.

Materials with high RF performance are in increasing demand due to the needs of modern telecommunications. Glass and low-temperature co-fired ceramics (LTCCs) are both interesting candidates for the design of complex signal transmission systems. Glass can be processed in large panels, and has suitable structure dimensions for silicon processing, but its multilayer capability is limited. LTCC is a mature technology for complex multilayer assemblies, but the structure dimensions and conductor line resolution are restricted by the need to use screen printing technology. The approach presented here combines the advantages of both technological domains: a thin glass sheet is bonded with no additional material to a LTCC multilayer ceramic and sintered to form a tight joint. Metallization of the glass is created using printable pastes and electroplating. Two fabrication routes are compared: etching of printed thick film metal layers, and semi-additive structuring. The results of RF measurements show a low attenuation per unit length for both types of metallization, indicating that our approach is a promising one for the integration of heterogeneous systems of RF transmission modules.

Vibrational quanta of melamine and its tautomer are analyzed at the single-molecule level on Cu(100) with inelastic electron tunneling spectroscopy. The on-surface tautomerization gives rise to markedly different low-energy vibrational spectra of the isomers, as evidenced by a shift in mode energies and a variation in inelastic cross sections. Spatially resolved spectroscopy reveals the maximum signal strength on an orbital nodal plane, excluding resonant inelastic tunneling as the mechanism underlying the quantum excitations. Decreasing the probe-molecule separation down to the formation of a chemical bond between the melamine amino group and the Cu apex atom of the tip leads to a quenched vibrational spectrum with different excitation energies. Density functional and electron transport calculations reproduce the experimental findings and show that the shift in the quantum energies applies to internal molecular bending modes. The simulations moreover suggest that the bond formation represents an efficient manner of tautomerizing the molecule.