Fraunhofer Institute for Microstructure of Materials and Systems

Abstract The surface topography of parts and components manufactured by direct energy deposition arc (DED-arc) based on additive manufacturing is crucial for fatigue behavior. In this study, DED-arc specimens made of AISI 316L are characterized according to their mechanical properties and surface topography (waviness). The specimen surface was digitized by 3D scanning. Fatigue tests were performed in as-printed condition and milled condition (flat surface). The crack initiation locations of each individual specimen were determined to correlate individual geometry and failure location. The specimens made of 316L showed a significant waviness of up to 1.4 mm. The fatigue tests were evaluated with different concepts: the nominal stress approach based on different definitions of the cross sections, as well as local approaches like the maximum stress (notch stress), critical distance, or stress gradient approach. The scatter in the S–N curves was significantly reduced by using all three local approaches, with the lowest scatter observed using the maximum stress approach. The fatigue life was assessed by linear elastic fracture mechanics (LEFM) using best practice input parameters based on the fatigue life assessment of welded joints. By LEFM, conservative fatigue life values could be reached according to the experiments, especially for low load levels. A combination of local approaches with LEFM leads to a very good agreement in the investigated case.

Polyaniline (PANI)-coated traditional Nepali paper composites were synthesized via an in situ chemical oxidative polymerization process. Fourier Transform Infra-red Spectroscopy (FTIR), X-ray Diffraction (XRD), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) confirmed the PANI-coating. Additionally, the synthesized PANI powder (emeraldine salt) exhibited good antibacterial activity against Bacillus subtilis and Escherichia coli (zone of inhibition, ZOI: 0.5 cm each) and antifungal activity against Candida albicans (ZOI: 0.4 cm). In contrast, PANI-coated NK exhibited lower antimicrobial activity compared to powdered PANI. It was more effective against E. coli (ZOI: 0.3 cm) than against B. subtilis (ZOI: 0.2 cm). The antifungal activity against C. albicans was the lowest, with a ZOI of 0.1 cm. These findings demonstrate the potential of the composites for sustainable packaging applications with modest antimicrobial properties. Optimizing the polymerization process and material formulation could enhance their efficacy for eco-friendly active packaging systems.

Abstract Our research focuses on verifying the design of efficient composite filtration mats using simulations based on XRM volumetric data. Three filter mats were prepared with different amounts of PET microfibers and electrospun PAN nanofibers, with and without a diblock copolymer. The structure of the PET-PAN mats was characterized by SEM and XRM. Three-dimensional XRM images were used in fluid flow simulations and the filtration properties were evaluated by standard methods. Incorporating 5-µm PET fibers with 1 wt% PAN nanofibers and a diblock copolymer doubled efficiency in single-pass filtration test at a small pressure drop. Raising PAN to 2 wt% increased efficiency to 72 % but also increased the pressure drop. Simulated permeabilities from XRM volumes follow the same order and lie within experimental uncertainties. Streamlines illustrate fluid flow paths within the simulated environment, showing locations where fiber bundles create straight-through pores. XRM simulations showed flow paths, confirmed permeability trends, and can guide the optimization of fiber dispersion. Discrepancies between XRM volumes and bulk tests show that microscale heterogeneity dominates resistance. Larger volumes are needed for accurate prediction. Streamline-guided rules can shorten development cycles by indicating where to adjust fiber orientation, nanofiber amounts and copolymer amounts.

• Performance of new dust mitigation strategy on PV Modules based on natural resuspension of dust. • Compares experimental results from the laboratory with outdoor tests. • Proof of the potential to reduce dust by 91%. • Describing dependencies on environmental conditions such as wind direction and wind speed. • Smart heating as a mitigation strategy leads to a negative energy balance of PV systems. Soiling impairs the energy yield of photovoltaic systems, particularly in arid and semi-arid regions. The primary scientific focus is therefore on the development of efficient cleaning technologies. Complementarily, this work considers a strategy for mitigating soiling through smart heating of photovoltaic modules. The findings suggest that the combination of heated photovoltaic modules with favorable wind conditions can lead to a reduction in dust accumulation. This reduction has the maximum potential to generate an estimated solar energy gain of up to 0.064 kWh/m 2 per day. However, a comprehensive evaluation of laboratory tests and outdoor experiments conducted in Morocco reveals an overall negative energy balance of −0.24 kWh/m 2 per day. The heating system consumed more energy than it mitigated soiling-losses. The study demonstrated that low wind speeds of less than 2.7 m/s and unfavorable north wind directions are unsuitable for generating significant resuspension effects despite heating. Consequently, the economic viability of this technology remains uncertain under real-world conditions. Furthermore, the study emphasizes the limitations of the proposed mitigation strategy and identifies the reasons for the overall negative energy yield.

Abstract Scanning Acoustic Microscopy (SAM) is a critical nondestructive technique for detecting buried defects in semiconductor devices [1]. However, interpreting the complex acoustic data requires expert knowledge, especially as microelectronic structures grow increasingly intricate. This study presents a novel, unsupervised approach for defect detection in SAM data using an autoencoder neural network trained exclusively on intact reference samples. The method exploits reconstruction error as an indicator of signal anomalies, identifying potential defects without prior knowledge of their characteristics or the need for defective training samples. The resulting similarity parameter facilitates intuitive visualization of outlier regions through overlay on high-resolution SAM images. This enhances defect detection sensitivity and operator support, making SAM more accessible for less experienced users and highly promising for automation in production environments. While the method effectively highlights signal deviations, it may also flag non-defect-related anomalies such as sample tilting. Nonetheless, it significantly advances automated and operator-independent semiconductor failure analysis by enabling reliable detection of structural anomalies through learned representations of intact signal patterns.

Supercrystalline nanocomposites (SCNCs) feature intriguing functionalities and exceptional mechanical properties, but they are usually confronted with challenges when it comes to processing them in larger bulk form. One way to tackle this problem is a hierarchical approach, for which spherical SCNCs, i.e. supraparticles (SPs), are promising candidates as building blocks. Understanding the mechanical behavior of SPs is thus a key step towards the development of robust, multifunctional and macroscopic SCNCs. Hereby, in situ compression tests are performed on SPs with varying sizes and levels of crosslinking of their organic ligands. A size-dependent deformation and fracture behavior emerges. Plasticity occurs in larger SPs, while small ones exhibit brittle fracture. Surface stress and compaction affect the elastic modulus. Fracture initiation sites shift from the center of SPs to their equatorial belts with the decrease of SPs’ size. The inverse scaling relationship between fracture strength and SPs’ sizes is rationalized via Griffith theory.

A glass with the molar composition 6.75 CaO – 6.75 Al 2 O 3 – 86.5 SiO 2 was prepared and subsequently crystallized at temperatures between 1100 and 1400 °C. As main crystal phase, cristobalite forms. The higher the temperature of heat treatment, the greater the amount of α-cristobalite. Lower temperatures favor the formation of the β-phase. The high temperature phase (β-cristobalite), which is known for its comparatively low coefficient of thermal expansion at high temperatures, is chemically stabilized by the incorporation of Ca 2+ and Al 3+ . However, microstructural insights and elemental analyses show that the mechanism of β-formation at room temperature is not a pure chemical stabilization. The maximum solubility of CaO and Al 2 O 3 within the cristobalite lattice was measured and is considerably lower than the composition of the base glass. A matrix, which is enriched in CaO and Al 2 O 3 , surrounds the crystals. Milling experiments, where the constraints from the matrix are removed, show that a pure chemical stabilization of β-cristobalite is not possible and is always supported by the (often undetected) surrounding matrix.

Two different solid solutions of CuI, namely, I and Mo x Cu 1– x I, have been deposited via reactive magnetron cosputtering to investigate the suppression of the zincblende γ‐CuI phase by the introduction of foreign atoms into the lattice. A comprehensive growth study is presented, in which sputtering in inert and reactive atmospheres (Ar + I 2 , Ar, N 2 + I 2 , N 2 ) is performed from metallic Cu, Sn, and Mo targets as well as from a CuI powder target. A strong influence of the iodine partial pressure during the deposition on the crystal quality of thin films is observed by X‐ray diffraction measurements. For optimized growth conditions, X‐ray amorphous thin films are achieved for solid solution Sn x Cu 1– x I and Mo x Cu 1– x I thin films deposited from the CuI powder target in an inert Ar atmosphere. However, a microstructural analysis of these thin films by transmission electron microscopy combined with energy‐dispersive X‐ray diffraction spectroscopy and selected area diffraction reveals a phase separation into Sn and O rich, (Mo and O rich, respectively) amorphous regions, and CuI crystallites. Oxygen concentrations between ≈10 at% and ≈70 at%, detected in the thin films, give reason to the assumption of an oxygen induced phase separation.

Epitaxial growth of phase-pure and high-quality spinel γ-Ga2O3-based semiconductor thin films has been a big challenge for fundamental research on metastable defective inverse spinel γ-Ga2O3 semiconductors in view of potential device application. We report experimental results on epitaxial growth, microstructural, and electrical transport properties of (001)-oriented nominal γ-(Ga0.8Ge0.2)2O3 alloy semiconductor single crystal thin films with a coherent interface on cubic spinel (001) MgAl2O4 substrates by pulsed laser deposition using a Ge-rich target. Pristine films are found to be composed of about 2 nm thick insulating Ge-rich surface layers and the high-quality epitaxial n-type semiconductor film layers consisting of partially subvalent Ge2+ and Ga1+ cations as well as major components of normal Ge4+ and Ga3+ cations. Epitaxial films exhibit a direct bandgap of about 5.2 ± 0.1 eV and a valence band maximum of about 3.3 ± 0.1 eV below the Fermi level at room temperature. We further report a demonstration of γ-(Ga0.8Ge0.2)2O3 thin film-based metal-semiconductor field-effect transistor (MESFET) with the PtOx/Pt Schottky gate contact realized upon the surface pretreatment by Ar/O2 plasma etching. The MESFET device exhibits a clear field-effect with drain current modulation of about 105 orders of magnitude. This work not only significantly advances the fundamental and application-oriented research on epitaxial spinel γ-Ga2O3-based semiconductor films for practical device application but also offers new insight into microstructural characteristics of ultrawide bandgap spinel oxide semiconductor epitaxial thin films.