We experimentally demonstrate the enhancement of the spontaneous emission rate of GaAs quantum wells embedded in rolled-up metamaterials. We fabricate microtubes whose walls consist of alternating Ag and (In)(Al)GaAs layers with incorporated active GaAs quantum-well structures. By variation of the layer thickness ratio of the Ag and (In)(Al)GaAs layers we control the effective permittivity tensor of the metamaterial according to an effective medium approach. Thereby, we can design samples with elliptic or hyperbolic dispersion. Time-resolved low temperature photoluminescence spectroscopy supported by finite-difference time-domain simulations reveal a decrease of the quantum well's spontaneous emission lifetime in our metamaterials as a signature of the crossover from elliptic to hyperbolic dispersion.

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Reciprocal space engineering allows tailoring the scattering response of media with a low refractive‐index contrast. Here it is shown that a quasiperiodic leveled‐wave structure with well‐defined reciprocal space and random real space distribution can be engineered to open a complete photonic bandgap (CPBG) for any refractive‐index contrast. For these structures, an analytical estimation is derived, which predicts that there is an optimal number of Bragg peaks for any refractive‐index contrast. A finite 2D or 3D CPBG is expected at this optimal number even for an arbitrarily small refractive‐index contrast. Results of numerical simulations of dipole emission in 2D and 3D structures support the estimations. In 3D simulations, an emission suppression of almost 10 dB is demonstrated with a refractive index down to 1.38. The 3D structures are realized by additive manufacturing on millimeter scale for a material with a refractive index of n ≈ 1.59. Measurements confirm a strong suppression of microwave transmission in the expected frequency range.

In dieser Studie wird die Entwicklung verschiedener thermisch gespritzter Beschichtungen für den Einsatz im Armaturenbau diskutiert. Basierend auf etablierten Verschleißschutzschichten der Armaturenindustrie wurden verschiedene Festschmierstoffe in diese Beschichtungen integriert, um das Verschleiß-und Reibungsverhalten bei anwendungsnahen Belastungen für Armaturen zu verbessern. Für die Anwendungen wurden Verschleißschutzschichten auf Basis von WC/CoCr und Cr 3 C 2 /NiCr entwickelt. Als Festschmierstoffe wurden nickelumhülltes Graphit und hexagonales Bornitrid untersucht. Die Verfahrensvarianten Hochgeschwindigkeitsflammspritzen mit Sauerstoff (HVOF) und das neuartige Ultrahochgeschwindigkeitsflammspritzen (UH-VOF) wurden untersucht. Die Ergebnisse zeigen, dass durch eine passende Beschichtungszusammensetzung eine Reduktion des Verschleißes von 53 % und der Reibung von 31 % unter anwendungsnahen Belastungen möglich ist.Schlüsselwörter: Armaturenbau / Festschmierstoffe / Reibung / Verschleiß / Korrosion / Thermisches Spritzen This study discusses the development of various thermally sprayed coatings for the use in the valve industry. Based on established coating systems for wear protection, different solid lubricants were integrated into these coatings in order to optimize the wear and friction behavior at application oriented loads. Wear protection coatings based on WC/CoCr and Cr 3 C 2 /NiCr were applied. As solid lubricants, nickel-encapsulated graphite and hexagonal boron nitride were investigated. The thermal spraying processes high velocity oxygen fuel flame spraying (HVOF) and the novel ultra high velocity flame spraying (UHVOF) were investigated. The results show that through an appropriate coating composition a wear reduction of 53 % and a friction reduction of 31 % are possible.

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