Publikationen

Semiconducting materials show high potential for solar energy harvesting due to their suitable bandgaps, which allow the efficient utilization of light energy larger than their bandgaps. However, the photon energy smaller than their bandgap is almost unused, which significantly limits their efficient applications. Herein, plasmonic Pd/SnS2 microcubes with abundant Pd nanoparticles attached to the SnS2 nanosheets are fabricated by an in situ photoreduction method. The as-prepared Pd/SnS2 microcubes extend the light-harvesting ability of SnS2 beyond its cutoff wavelength, which is attributed to the localized surface plasmon resonance (LSPR) effect of the Pd nanoparticles and the 3D structure of the SnS2 microcubes. Pd nanoparticles can also enhance the light absorption of TiO2 nanoparticles and NiPS3 nanosheets beyond their cutoff wavelengths, revealing the universality for promoting absorption above the cutoff wavelength of the semiconductors. When the plasmonic Pd/SnS2 microcubes are integrated into a hydrophilic sponge acting as the solar evaporator, a solar-to-vapor efficiency of up to 89.2% can be achieved under one sun. The high solar-to-vapor conversion efficiency and the broad applicability of extending the light absorption far beyond the cutoff wavelength of the semiconductor comprise the potential of innovative plasmonic nanoparticle/semiconductor composites for solar desalination.

This study investigates the effects of sputtering and electron beam evaporation (e-beam) on the microstructure and reactive properties of Al/Ni reactive multilayers (RMLs). The intermixing zone, a critical factor influencing reaction kinetics, is characterized using high-resolution transmission electron microscopy and found to be consistently 3 nm for both fabrication methods. Differential scanning calorimetry reveals that e-beam samples, with thicker Al layers, exhibit slightly higher total molar enthalpy and maintain high reaction temperatures despite reduced reaction velocities in comparison to sputtered samples. X-ray diffraction confirms the formation of both Al3Ni2 and AlNi phases in the e-beam samples. These findings indicate that while thicker bilayer structures reduce reaction velocity, they keep thermal output and mitigate the impact of intermixing zones, leading to similar total molar enthalpy. This analysis underscores the significance of deposition technique and bilayer thickness in optimizing the performance of Al/Ni RML, offering the possibility to establish different phase formations in thicker RML. It advances the control over the reactive properties of RMLs in their applications, for example, reactive bonding.

Al/Ni reactive multilayer systems (RMS) with a bilayer thickness of Λ = 50 nm and total thickness th = 5 μm on a SiO2 substrate exhibit a self-propagating reaction after ignition. A common method to initiate the self-propagating reaction is by electric spark ignition. Herein, RMS are ignited by a mechanical impact using various materials with indeterminate geometries to investigate the basic mechanisms. SiO2, glass, PMMA, and resin-bonded SiC particles are used as impacting material with different geometrical impact areas. The used materials are placed on top of the RMS and a mechanical impulse is applied. The ignition behavior of the RMS is subsequently evaluated and classified. Additionally, the impacted RMS are examined by microscopy to reveal the damage pattern. By correlating particle size ⟨Dparticle⟩ and spacing ⟨dhole⟩ of the penetrating materials, an ignition threshold can be established. Moreover, the results demonstrate that the energy input threshold can be reduced through a strategic distribution of particles within the impacting and penetrating geometry. This provides valuable insights into the mechanical ignition fundamental and supports future applications of mechanical ignition of RMS.

Reactive multilayers comprising alternating nanoscale layers of Al and Ni exhibit potential across various applications, including localized heating for welding and joining. Control over reaction properties is pivotal for emerging applications, such as chemical time delays or neutralization of biological or chemical weapons. In this research, insights are offered into the intricate interplay between substrate thickness, surface roughness, and the behavior of Al/Ni reactive multilayers, opening avenues for tailored applications in various domains. To observe this interplay, silica with various thicknesses from 0.4 to 1.6 μm is deposited on polished single-crystalline Si and rough poly-Si base substrates. Additionally, to analyze the impact of varying silica thickness along the sample length on reaction behavior, silica in steplike shape is fabricated. Subsequently, Al/Ni multilayers with 5 μm total thickness and 20 or 50 nm bilayer periodicities are deposited. Reaction velocity and temperature are monitored with a high-speed camera and pyrometer. In the results, it is indicated that silica thickness significantly affects self-propagation in multilayers. The reaction is not self-sustained for silica layers ≤ 0.4 μm, depending on bilayer periodicity and substrate roughness. The velocity increases or decreases based on the direction of reaction propagation, whether it moves upward or downward, in relation to the thickness of silica.

Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: β-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from −50 to −200 V, the wear mechanisms change as follows: oxidative &flech; fatigue and oxidative &flech; adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.