Alexander Welle

This study investigates the embrittlement of TiAl after high‐temperature air exposure. The loss of room‐temperature tensile ductility persists even when tested under liquid nitrogen (−196 °C), with brittle fracture occurring at higher stress levels than typical room‐temperature fracture. Existing embrittlement mechanisms in TiAl literature fail to explain this phenomenon under liquid nitrogen. Using secondary ion mass spectrometry (SIMS), surface chemistry analysis of binary TiAl alloys exposed at 700 °C for 4 h in an artificial air‐like environment (containing heavy water, ¹⁵ N ₂ , and ¹⁸ O ₂ ) revealed dissociation of water vapor at the TiAl surface and absorption of deuterium into the material. This marks the first report of water vapor dissociation and deuterium (or hydrogen under natural conditions) ingress into heated TiAl specimens. A localized enrichment of hydrogen and deuterium was observed beneath the surface. Given that traditional embrittlement mechanisms do not account for the increased fracture stress under liquid nitrogen, it is proposed that hydrogen absorption during exposure and its near‐surface enrichment contribute to embrittlement under these conditions.

As the perovskite solar cell (PSC) industry moves toward large‐scale manufacturing, production processes must enable high‐throughput fabrication and simple process integration. The hybrid two‐step deposition route has emerged as a promising method for achieving conformal coatings on micron‐scale textures, a critical feature for perovskite/silicon tandem photovoltaics. In this work, we present a fully sequential route, wherein the inorganic materials CsCl and PbI ₂ are deposited separately, allowing for facile industrial implementation as compared to the commonly codeposited inorganic scaffold. Microstructural analysis reveals a change in preferred crystal orientation of the PbI ₂ platelets with codeposition resulting in horizontal growth, whereas sequential deposition promotes vertical growth with a secondary tilted orientation. Elemental mapping of the final perovskite absorber shows homogeneous distribution of Cs, formamidinium, and I, while Pb and Cl largely retain their initial scaffold positions. PSCs fabricated via sequential deposition of the inorganic scaffold demonstrate improved process repeatability and reach an efficiency of 20.3%, ranking among the highest reported efficiencies for wide‐bandgap hybrid two‐step processed PSCs. These findings underscore the potential of fully sequential hybrid deposition as a viable route toward industrial PSC production.

A custom‐built laser‐induced forward transfer (LIFT) setup was developed to fabricate multimaterial organic light emitting diode (OLED) stacks under ambient laboratory conditions without the use of a cleanroom or encapsulation. The process enables precise control of layer thickness through parameter tuning as confirmed by vertical scanning interferometry (VSI), yielding smooth and homogeneous layers with surface roughness values down to . The process achieves tunable thicknesses between 19 nm and 45 nm, while the lateral resolution is limited to about . A three‐layer OLED stack (total thickness ) was printed and structurally characterized using focused ion beam scanning electron microscopy (FIB‐SEM) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), revealing distinct, well‐defined layer boundaries. First functional tests demonstrated electroluminescence at with an operational lifetime of at least . Despite the lack of encapsulation, the OLEDs remained stable under ambient conditions with a shelf life of up to days. These results confirm the potential of LIFT as a scalable and precise tool for the additive manufacturing of flexible thin‐film devices such as OLEDs, solar cells and fuel cells.

For practical superconducting quantum processors, orders of magnitude improvement in coherence is required, motivating efforts to optimize hardware design and explore new materials. Among the latter, the coherence of superconducting transmon qubits has been shown to improve by forming the qubit capacitor pads from α-tantalum, avoiding the metastable β-phase that forms when depositing tantalum at room temperature, and has been previously identified to be a source of microwave losses. In this work, we show lumped element resonators containing β-phase tantalum in the form of inclusions near the metal–substrate interface with internal quality factors (Qi) up to 5.0 ± 2.5×106 in the single photon regime. They perform at least as good as resonators with no sign of the β-phase in x-ray diffraction and thermal quasi-particle loss. Our results indicate that small concentrations of β-phase can be beneficial, enhancing critical magnetic fields and potentially, for improving coherence in tantalum-based superconducting circuits.

In this paper, we investigate the mineral interface doping (MID) process of silicon substrates, using various minerals to explore the role of the metal ions involved. Specifically, we use metal ions with +1, +2, and +3 charge states to determine whether the observed effects are unique to individual metals or if they reflect broader trends within charge groups. Silicon wafers are coated with different minerals and doped by rapid thermal annealing (RTA). The process is subsequently analyzed as a function of temperature using time-of-flight secondary ion mass spectrometry (ToF-SIMS), infrared spectroscopy (IR), and electrochemical impedance spectroscopy (EIS). To unravel the underlying atomistic mechanisms, we perform density functional theory (DFT) simulations, obtaining the kinetic activation energies of the corresponding doping processes and their dependence on metal valence. Our findings reveal that the required doping temperature decreases with the charge density of metal ions; however, there is a required minimum temperature to achieve the diffusion of phosphorus into the silicon bulk. During the MID process, metal silicates are first formed at the interface, while the atomic phosphorus constituents diffuse into the silicon substrate. Finally, the metal silicates are removed post-doping using non-toxic acids, thus making the process broadly applicable.

The application of an artificial LiBFEP‐SEI on thin 48 µm Lithium‐Metal‐Anodes (LiBFEP = Li[O₂P(OCH₂CF₃)₂]; SEI = solid electrolyte interphase) induces improved plating/stripping of lithium at the interphase with an almost doubling of the lifetime for Li–Li symmetrical cells. Four lithium‐fluoroalkylphosphates other than LiBFEP are tested, but all perform inferior to the control. Lithium‐metal full cells with various NMC‐cathodes and LP57 standard electrolyte are employed to confirm the superior performance of the LiBFEP artificial SEI (LP57 = 1 m Li[PF₆] in ethylene carbonate/ethyl methyl carbonate 3:7 wt%). A tripling of the cell lifetime is observed using realistic cell‐cycle parameters. The stabilization of the modified anodes is evidenced by SEM‐EDX, ToF‐SIMS, PEIS measurements and led to an improved anode structure. The performance of the artificial SEI is further improved with the introduction of a novel low‐concentration and low‐polarity electrolyte (0.2 m lithium perfluoroalkoxyaluminate (Li[Al(OR^F)₄]; R^F = C(CF₃)₃) in 1,2‐difluorobenzene). Cycling is sustained over 350 cycles with realistic conditions at a current density of 1 mA cm⁻² and 48 µm thin Lithium‐Metal‐Anodes. This work provides a comprehensive understanding of how the artificial LiBFEP‐SEI influences the performance of Lithium‐Metal‐Battery full cells, confirming the simplicity/effectiveness of the immersion process for the LiBFEP‐coating.