Universität Stuttgart
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Item Open Access Physics-informed transformers for electronic quantum states(2025) Sobral, João Augusto; Perle, Michael; Scheurer, Mathias S.Neural-network-based variational quantum states, particularly autoregressive models, are powerful tools for describing complex many-body wave functions. However, their performance depends on the computational basis chosen and they often lack physical interpretability. We propose a modified variational Monte-Carlo framework which leverages prior physical information to construct a complete computational many-body basis containing a reference state that serves as a rough approximation to the true ground state. A Transformer is used to parametrize and autoregressively sample corrections to this reference state, giving rise to a more interpretable and computationally efficient representation of the ground state. We demonstrate this approach in a fermionic model featuring a metal-insulator transition by employing Hartree-Fock and a strong-coupling limit to define physics-informed bases. We also show that the Transformer’s hidden representation captures the natural energetic order of the different basis states. This work paves the way for more efficient and interpretable neural quantum-state representations.Item Open Access Nanoscale mapping of magnetic auto-oscillations with a single spin sensor(2025) Hache, Toni; Anshu, Anshu; Shalomayeva, Tetyana; Richter, Gunther; Stöhr, Rainer; Kern, Klaus; Wrachtrup, Jörg; Singha, AparajitaSpin Hall nano-oscillators convert DC to magnetic auto-oscillations in the microwave regime. Current research on these devices is dedicated to creating next-generation energy-efficient hardware for communication technologies. Despite intensive research on magnetic auto-oscillations within the past decade, the nanoscale mapping of those dynamics remained a challenge. We image the distribution of free-running magnetic auto-oscillations by driving the electron spin resonance transition of a single spin quantum sensor, enabling fast acquisition (100 ms/pixel). With quantitative magnetometry, we experimentally demonstrate for the first time that the auto-oscillation spots are localized at magnetic field minima acting as local potential wells for confining spin-waves. By comparing the magnitudes of the magnetic stray field at these spots, we decipher the different frequencies of the auto-oscillation modes. The insights gained regarding the interaction between auto-oscillation modes and spin-wave potential wells enable advanced engineering of real devices.Item Open Access Direct electron beam patterning of electro-optically active PEDOT:PSS(2024) Doshi, Siddharth; Ludescher, Dominik; Karst, Julian; Floess, Moritz; Carlström, Johan; Li, Bohan; Mintz Hemed, Nofar; Duh, Yi-Shiou; Melosh, Nicholas A.; Hentschel, Mario; Brongersma, Mark; Giessen, HaraldThe optical and electronic tunability of the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has enabled emerging applications as diverse as bioelectronics, flexible electronics, and micro- and nano-photonics. High-resolution spatial patterning of PEDOT:PSS opens up opportunities for novel active devices in a range of fields. However, typical lithographic processes require tedious indirect patterning and dry etch processes, while solution-processing methods such as ink-jet printing have limited spatial resolution. Here, we report a method for direct write nano-patterning of commercially available PEDOT:PSS through electron-beam induced solubility modulation. The written structures are water stable and maintain the conductivity as well as electrochemical and optical properties of PEDOT:PSS, highlighting the broad utility of our method. We demonstrate the potential of our strategy by preparing prototypical nano-wire structures with feature sizes down to 250 nm, an order of magnitude finer than previously reported direct write methods, opening the possibility of writing chip-scale microelectronic and optical devices. We finally use the high-resolution writing capabilities to fabricate electrically-switchable optical diffraction gratings. We show active switching in this archetypal system with >95 % contrast at CMOS-compatible voltages of +2 V and -3 V, offering a route towards highly-miniaturized dynamic optoelectronic devices.Item Open Access Separation of short-chain fatty acids from primary sludge into a particle-fee permeate by coupling chamber filter-press and cross-flow microfiltration : optimization, semi-continuous operation, and evaluation(2025) Shylaja Prakash, Nikhil; Maurer, Peter; Horn, Harald; Saravia, Florencia; Hille-Reichel, AndreaShort-chain fatty acids (SCFAs) are valuable metabolic intermediates that are produced during dark fermentation of sludge, which, when capitalized on, can be used as chemical precursors for biotechnological applications. However, high concentrations of solids with SCFAs in hydrolyzed sludge can be highly detrimental to downstream recovery processes. This pilot-scale study addresses this limitation and explores the recovery of SCFAs from primary sludge into a particle-free permeate through a combination of chamber filter-press (material: polyester; mesh size: 100 µm) and cross-flow microfiltration (material: α-Al2O3; pore size: 0.2 µm; cross-flow velocity: 3 m∙s-1; pressure = 2.2 bars). Firstly, primary sludge underwent dark fermentation yielding a hydrolyzate with a significant concentration of SCFAs along with total solids (TS) concentration in the range of 20 to 30 g∙L-1. The hydrolyzate was conditioned with hydroxypropyl trimethyl ammonium starch (HPAS), and then dewatered using a filter press, reducing TS by at least 60%, resulting in a filtrate with a suspended solids concentration ranging from 100 to 1300 mg∙L-1. Despite the lower suspended solids concentration, the microfiltration membrane underwent severe fouling due to HPAS’s electrostatic interaction. Two methods were optimized for microfiltration: (1) increased backwashing frequency to sustain a permeate flux of 20 L∙m-2∙h-1 (LMH), and (2) surface charge modification to maintain the flux between 70 and 80 LMH. With backwashing, microfiltration can filter around 900 L∙meff-2 (without chemical cleaning), with the flux between 50 and 60 LMH under semi-continuous operation. Evaluating the particle-free permeate obtained from the treatment chain, around 4 gCSCFAs∙capita-1∙d-1 can be recovered from primary sludge with a purity of 0.85 to 0.97 CSCFAs∙DOC-1.Item Open Access Lateral torsional buckling of glulam beam-columns : axial compression and bending verification(2024) Töpler, Janusch; Kuhlmann, Ulrike; Schänzlin, JörgItem Open Access 3D microprinting of structures with lanthanide‐based fluorophores on optical fibers for multiplexed sensing(2025) Aslani, Valese; Baghapour, Shaghayegh; Warren‐Smith, Stephen C.; Zhang, Wenqi; Ebadati, Esmat; Plush, Sally E.; Herkommer, Alois; Toulouse, Andrea; Afshar V., ShahraamFemtosecond direct laser writing (fs‐DLW) has revolutionized the fabrication of micro‐optical elements, yet its potential in multiplexed sensing has remained constrained by material limitations and fluorescence crosstalk. Here, a novel platform that integrates lanthanide‐based fluorophores-specifically europium complexes-into commercial fs‐DLW resists (OrmoComp and IP‐Visio) to directly print nano/microstructures on the tips of optical fibers is reported. This strategy exploits the exceptional photostability, narrow emission lines, and long luminescence lifetimes to overcome spectral overlap and photobleaching commonly seen with organic fluorophores. By enabling spectral, temporal, and spatial multiplexing, this approach allows simultaneous detection of distinct biochemical and physical parameters. Five distinct structures are fabricated: two woodpile structures for temperature and redox sensing, a Fabry‐Pérot cavity for refractive index detection, and disc and annular geometries for spatially selective excitation. The results show that combining sub‐micron 3D microfabrication with lanthanide photophysics significantly enhances sensing fidelity, opening new avenues for compact, multi‐analyte fiber‐based diagnostics in biomedical applications.Item Open Access Bridging the gap : linking prototyping and technology readiness levels for integrative product development(2024) Rehberg, Laura; Brem, AlexanderShorter development cycles, increasing complexity due to the interaction of hardware and software and the simultaneous pressure to innovate and reduce costs lead to products being launched early that have not yet been sufficiently validated and tested. The prototyping phase is crucial to ensure maturity as a preliminary stage to series production. Although this validation is critical to ensure the maturity of the product or technology to avoid recalls, previous research has focused on exploring the phenomenon of prototyping in general. To fill this gap, we use the standardized framework of technology readiness levels and develop prototyping readiness levels that allow for a graded assessment of maturity. Our empirical study is based on the unique case of the Boeing 737 Max 8 and a research project to develop an automated prototyping hub. Our findings show how mismanagement of prototypes and inadequate technology readiness level (TRL) assessment can lead to serious safety issues. Based on these findings, we introduce prototyping readiness levels that complement the idea of TRLs to reduce and eliminate bottlenecks and errors in the early stages of the development process.Item Open Access A dual‐layered anode buffer layer structure for all solid‐state batteries(2024) Lu, Yushi; Chang, Hansen Michael; Birke, Kai PeterOver the past few decades, lithium‐ion batteries have garnered considerable attention, especially for their use in electric vehicles (EVs). In recent years, solid‐state batteries have become increasingly popular due to their excellent safety features and potential for high energy density. However, solid‐state batteries with lithium metal anodes present challenges in terms of electrochemical reactivity and cost. To address these challenges, alternative anode systems such as the “anode‐free” approach are being explored. In this study, we introduced a dual‐layered anode comprising a primary layer of physically vapor‐deposited zinc and a secondary layer of carbon black, focusing on investigating the influence of varying thicknesses of the lithiophilic zinc layer on cell cycling performance. Among the three different zinc thicknesses chosen for this purpose - categorized as thin (286 nm), medium (1.802 μm), and thick (6.519 μm) - the dual‐layered anode buffer layer was analyzed in a single‐layer full pouch cell. An in‐depth investigation into the lithium‐zinc alloying behavior was conducted through post‐mortem analysis. From the results, we found that the combination of the zinc layer with the carbon black layer improved cell cycling performance in terms of discharge capacity retention compared to a single layer of either zinc or carbon black. The cycling performance of this dual‐layered anode could be further enhanced by optimizing the zinc layer thickness, likely due to the irreversible alloying step of zinc and lithium. Among the various thicknesses evaluated, the thin zinc layer (286 nm) combined with the carbon black layer demonstrated the most promising cycling performance in all solid‐state batteries.Item Open Access Next-generation sustainable composites with flax fibre and biobased vitrimer epoxy polymer matrix(2025) Tran, Hoang Thanh Tuyen; Baur, Johannes; Radjef, Racim; Nikzad, Mostafa; Bjekovic, Robert; Carosella, Stefan; Middendorf, Peter; Fox, BronwynThis work presents the development of two vanillin-based vitrimer epoxy flax fibre-reinforced composites, with both the VER1-1-FFRC (a vitrimer-to-epoxy ratio of 1:1) and VER1-2-FFRC (a vitrimer-to-epoxy ratio of 1:2), via a vacuum-assisted resin infusion. The thermal and mechanical properties of the resulting vitrimer epoxy flax composites were characterised using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical four-point bending tests, alongside studies of solvent resistance and chemical recyclability. Both the VER1-1-FFRC (degradation temperature Tdeg of 377.0 °C) and VER1-2-FFRC (Tdeg of 395.9 °C) exhibited relatively high thermal stability, which is comparable to the reference ER-FFRC (Tdeg of 396.7 °C). The VER1-1-FFRC, VER1-2-FFRC, and ER-FFRC demonstrated glass transition temperatures Tg of 54.1 °C, 68.8 °C, and 83.4 °C, respectively. The low Tg of the vitrimer composite is due to the low crosslink density in the vitrimer epoxy resin. Particularly, the crosslinked density of the VER1-1-FFRC was measured to be 319.5 mol·m−3, which is lower than that obtained from the VER1-2-FFRC (434.7 mol·m-3) and ER-FFRC (442.9 mol·m-3). Furthermore, the mechanical properties of these composites are also affected by the low crosslink density. Indeed, the flexural strength of the VER1-1-FFRC was found to be 76.7 MPa, which was significantly lower than the VER1-2-FFRC (116.2 MPa) and the ER-FFRC (138.3 MPa). Despite their lower thermal and mechanical performance, these vitrimer composites offer promising recyclability and contribute to advancing sustainable composite materials.Item Open Access Surface charge density and induced currents by self-charging sliding drops(2024) Bista, Pravash; Ratschow, Aaron D.; Stetten, Amy Z.; Butt, Hans-Jürgen; Weber, Stefan A. L.Spontaneous charge separation in drops sliding over a hydrophobized insulator surface is a well-known phenomenon and lots of efforts have been made to utilize this effect for energy harvesting. For maximizing the efficiency of such devices, a comprehensive understanding of the dewetted surface charge would be required to quantitatively predict the electric current signals, in particular for drop sequences. Here, we use a method based on mirror charge detection to locally measure the surface charge density after drops move over a hydrophobic surface. For this purpose, we position a metal electrode beneath the hydrophobic substrate to measure the capacitive current induced by the moving drop. Furthermore, we investigate drop-induced charging on different dielectric surfaces together with the surface neutralization processes. The surface neutralizes over a characteristic time, which is influenced by the substrate and the surrounding environment. We present an analytical model that describes the slide electrification using measurable parameters such as the surface charge density and its neutralization time. Understanding the model parameters and refining them will enable a targeted optimization of the efficiency in solid–liquid charge separation.