In-situ nitriding of Fe₂VAl during laser surface remelting to manipulate microstructure and crystalline defects

Tailoring the physical properties of complex materials for targeted applications requires optimizing the microstructure and crystalline defects that influence electrical and thermal transport and mechanical properties. Laser surface remelting can be used to modify the subsurface microstructure of bulk materials and hence manipulate their properties locally. Here, we introduce an approach to perform remelting in a reactive nitrogen atmosphere to form nitrides and induce segregation of nitrogen to structural defects. These defects arise from the fast solidification of the full-Heusler Fe2VAl compound that is a promising thermoelectric material. Advanced scanning electron microscopy, including electron channeling contrast imaging and three-dimensional electron backscatter diffraction, is complemented by atom probe tomography to study the distribution of crystalline defects and their local chemical composition. We reveal a high density of dislocations, which are stable due to their character as geometrically necessary dislocations. At these dislocations and low-angle grain boundaries, we observe segregation of nitrogen and vanadium, which can be enhanced by repeated remelting in nitrogen atmosphere. We propose that this approach can be generalized to other additive manufacturing processes to promote local segregation and precipitation states, thereby manipulating physical properties

Machine-learning-enhanced time-of-flight mass spectrometry analysis

Mass spectrometry is a widespread approach used to work out what the constituents of a material are. Atoms and molecules are removed from the material and collected, and subsequently, a critical step is to infer their correct identities based on patterns formed in their mass-to-charge ratios and relative isotopic abundances. However, this identification step still mainly relies on individual users' expertise, making its standardization challenging, and hindering efficient data processing. Here, we introduce an approach that leverages modern machine learning technique to identify peak patterns in time-of-flight mass spectra within microseconds, outperforming human users without loss of accuracy. Our approach is cross-validated on mass spectra generated from different time-of-flight mass spectrometry (ToF-MS) techniques, offering the ToF-MS community an open-source, intelligent mass spectra analysis

Chemical segregation and precipitation at anti-phase boundaries in thermoelectric Heusler-Fe₂VAl

International audienceFe2VAl exhibits promising properties for thermoelectric applications. Here, we investigated the microstructure of melt spun Fe2VAl using electron microscopy, atom probe tomography and field ion microscopy. We observe platelet-shaped VCxNy precipitates in the vicinity of antiphase boundaries (APB) oriented along the {010}-plane. The mean distance between these precipitates is (140 ± 40) nm. This distance is shorter than the mean free phonon path at room temperature in Fe2VAl, thus, these VCxNy precipitates, combined with the APB may efficiently lower the thermal conductivity of the alloy

Bifacial Color-Tunable Electroluminescent Devices

Alternate current electroluminescent (ACEL) devices provide a range of interesting properties, such as facile large-area processability, mechanical flexibility, and outstanding resilience, when compared with other large-area light-emitting technologies. To widen the scope of possible applications for ACEL devices, color tunability and white light emission are desirable. Here, we introduce a novel three-terminal device architecture based on two monolithically stacked ACEL devices (e.g., orange and blue) that allows for color tunability via independent operation of the subdevices. The tandem devices comprise semitransparent bottom and top electrodes based on networks of silver nanowires, which endow the tandem ACEL device with bifacial Janus-type emission. We provide a detailed analysis of the sources of optical losses in single and tandem ACEL devices. Our novel device concept enables novel facets of applications for ACEL in signage and lighting. © 2021 The Authors. Published by American Chemical Society

Perovskite–organic tandem solar cells with indium oxide interconnect

Multijunction solar cells can overcome the fundamental efficiency limits of single junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures. Combinations with silicon and copper indium gallium selenide CIGS , as well as all perovskite tandem cells, have been reported. Meanwhile, narrow gap non fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells. Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite organic tandems show subpar efficiencies and are limited by the low open circuit voltage Voc of wide gap perovskite cells and losses introduced by the interconnect between the subcells. Here we demonstrate perovskite organic tandem cells with an efficiency of 24.0 per cent certified 23.1 per cent and a high Voc of 2.15 amp; 8201;volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high Voc and fill factor. The organic subcells provide a high external quantum efficiency in the near infrared and, in contrast to paradigmatic concerns about limited photostability of non fullerene cells, show an outstanding operational stability if excitons are predominantly generated on the non fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin approximately 1.5 amp; 8201;nanometres metal like indium oxide layer with unprecedented low optical electrical losses. This work sets a milestone for perovskite organic tandems, which outperform the best p i n perovskite single junctions and are on a par with perovskite CIGS and all perovskite multijunction