Defects contributing to hysteresis in few-layer and thin-film MoS2 memristive devices. - In: Materials, ISSN 1996-1944, Bd. 17 (2024), 6, 1350, S. 1-14
Molybdenum disulfide, a two-dimensional material extensively explored for potential applications in non-von Neumann computing technologies, has garnered significant attention owing to the observed hysteresis phenomena in MoS2 FETs. The dominant sources of hysteresis reported include charge trapping at the channel-dielectric interface and the adsorption/desorption of molecules. However, in MoS2 FETs with different channel thicknesses, the specific nature and density of defects contributing to hysteresis remain an intriguing aspect requiring further investigation. This study delves into memristive devices with back-gate modulated channel layers based on CVD-deposited flake-based and thin-film-based MoS2 FETs, with a few-layer (FL) and thin-film (TF) channel thickness. Analysis of current-voltage (I−V) and conductance-frequency (Gp/ω−f) measurements led to the conclusion that the elevated hysteresis observed in TF MoS2 devices, as opposed to FL devices, stems from a substantial contribution from intrinsic defects within the channel volume, surpassing that of interface defects. This study underscores the significance of considering both intrinsic defects within the bulk and the interface defects of the channel when analyzing hysteresis in MoS2 FETs, particularly in TF FETs. The selection between FL and TF MoS2 devices depends on the requirements for memristive applications, considering factors such as hysteresis tolerance and scaling capabilities.
https://doi.org/10.3390/ma17061350
The binding of the SARS-CoV-2 spike protein to platelet factor 4: a proposed mechanism for the generation of pathogenic antibodies. - In: Biomolecules, ISSN 2218-273X, Bd. 14 (2024), 3, 245, S. 1-14
Pathogenic platelet factor 4 (PF4) antibodies contributed to the abnormal coagulation profiles in COVID-19 and vaccinated patients. However, the mechanism of what triggers the body to produce these antibodies has not yet been clarified. Similar patterns and many comparable features between the COVID-19 virus and heparin-induced thrombocytopenia (HIT) have been reported. Previously, we identified a new mechanism of autoimmunity in HIT in which PF4-antibodies self-clustered PF4 and exposed binding epitopes for other pathogenic PF4/eparin antibodies. Here, we first proved that the SARS-CoV-2 spike protein (SP) also binds to PF4. The binding was evidenced by the increase in mass and optical intensity as observed through quartz crystal microbalance and immunosorbent assay, while the switching of the surface zeta potential caused by protein interactions and binding affinity of PF4-SP were evaluated by dynamic light scattering and isothermal spectral shift analysis. Based on our results, we proposed a mechanism for the generation of PF4 antibodies in COVID-19 patients. We further validated the changes in zeta potential and interaction affinity between PF4 and SP and found that their binding mechanism differs from ACE2-SP binding. Importantly, the PF4/SP complexes facilitate the binding of anti-PF4/Heparin antibodies. Our findings offer a fresh perspective on PF4 engagement with the SARS-CoV-2 SP, illuminating the role of PF4/SP complexes in severe thrombotic events.
https://doi.org/10.3390/biom14030245
Influence of metal surface structures on composite formation during polymer-metal-joining based on reactive Al/Ni multilayer foil. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, insges. 34 S.
Progressive developments in the field of lightweight construction and engineering demand continuous substitution of metals with suitable polymers. However, the combination of dissimilar materials results in a multitude of challenges based on different chemical and physical material properties. Reactive multilayer systems offer a promising joining method for flexible and low-distortion joining of dissimilar joining partners with an energy source introduced directly into the joining zone. Within this publication, hybrid lap joints between semi-crystalline polyamide 6 and surface-structured austenitic steel X5CrNi18-10 (EN 1.4301) were joined using reactive Al/Ni multilayer foils of the type Indium-NanoFoil®. Main objective is to examine possibilities of influencing crack initiation in the foil plane by variation of joining pressure and different metal surface structures with regard to geometry, density and orientation. Thus, the position of foil cracks is superimposed onto the metal structure and associated filling with molten plastic is improved. Consequently, characterisation of occurring crack positions as function of joining pressure and metal structure, analysis of the composite in terms of structural filling and joint strength as well as possible causes of crack initiation are evaluated.
https://doi.org/10.1002/adem.202302254
A novel method for preparation of Al-Ni reactive coatings by incorporation of Ni nanoparticles into an Al matrix fabricated by electrodeposition in AlCl3:1-ethyl-3-methylimidazolium chloride (1.5:1) ionic liquid containing Ni nanoparticles. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302217, S. 1-17
Al/Ni reactive coatings are fabricated via electrochemical deposition (ECD) at different applied voltages for reactive bonding application. AlCl3:1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) (1.5:1) ionic liquid electrolyte is used as source of Al, whereas Ni is in the bath and incorporated into final coatings as nanoparticles (NPs). Scanning electron microscopy and Auger electron spectroscopy reveal a homogeneous Ni particle dispersion, as well as a high amount of particle incorporation into the Al matrix. A maximum of 37 wt% (22 at%) of Ni is detected via atomic absorption spectroscopy in the Al/Ni coating deposited at −0.1 V from an electrolyte containing 20 g L−1 of Ni NPs. Previous literature show that for bonding application an ideal concentration is around 50 at% of Ni and 50 at% Al. However, this is achieved using high vacuum, time-consuming processes, and costly techniques like evaporation and magnetron sputtering. The ECD used in this work represents a more cost-efficient approach which is not reported up to date for the aforementioned application. The reactivity of the coatings is confirmed by Differential scanning calorimetry. Herein, an exothermic reaction is detected upon the mixing of Al and Ni occurring at high temperatures.
https://doi.org/10.1002/adem.202302217
Boosting the energy density of bowl-like MnO2carbon through lithium-intercalation in a high-voltage asymmetric supercapacitor with “water-in-salt” electrolyte. - In: Small, ISSN 1613-6829, Bd. 0 (2024), 0, 2310037, S. 1-11
Highly concentrated “‘water-in-salt”’ (WIS) electrolytes are promising for high-performance energy storage devices due to their wide electrochemical stability window. However, the energy storage mechanism of MnO2 in WIS electrolytes-based supercapacitors remains unclear. Herein, MnO2 nanoflowers are successfully grown on mesoporous bowl-like carbon (MBC) particles to generate MnO2/MBC composites, which not only increase electroactive sites and inhibit the pulverization of MnO2 particles during the fast charging/discharging processes, but also facilitate the electron transfer and ion diffusion within the whole electrode, resulting in significant enhancement of the electrochemical performance. An asymmetric supercapacitor, assembled with MnO2/MBC and activated carbon (AC) and using 21 m LiTFSI solution as the WIS electrolyte, delivers an ultrahigh energy density of 70.2 Wh kg−1 at 700 W kg−1, and still retains 24.8 Wh kg−1 when the power density is increased to 28 kW kg−1. The ex situ XRD, Raman, and XPS measurements reveal that a reversible reaction of MnO2 + xLi+ + xe−↔LixMnO2 takes place during charging and discharging. Therefore, the asymmetric MnO2/MBC//AC supercapacitor with LiTFSI electrolyte is actually a lithium-ion hybrid supercapacitor, which can greatly boost the energy density of the assembled device and expand the voltage window.
https://doi.org/10.1002/smll.202310037
Vector symbolic finite state machines in attractor neural networks. - In: Neural computation, ISSN 1530-888X, Bd. 36 (2024), 4, S. 549-595
Hopfield attractor networks are robust distributed models of human memory, but they lack a general mechanism for effecting state-dependent attractor transitions in response to input. We propose construction rules such that an attractor network may implement an arbitrary finite state machine (FSM), where states and stimuli are represented by high-dimensional random vectors and all state transitions are enacted by the attractor network’s dynamics. Numerical simulations show the capacity of the model, in terms of the maximum size of implementable FSM, to be linear in the size of the attractor network for dense bipolar state vectors and approximately quadratic for sparse binary state vectors. We show that the model is robust to imprecise and noisy weights, and so a prime candidate for implementation with high-density but unreliable devices. By endowing attractor networks with the ability to emulate arbitrary FSMs, we propose a plausible path by which FSMs could exist as a distributed computational primitive in biological neural networks.
https://doi.org/10.1162/neco_a_01638
Blooming and pruning: learning from mistakes with memristive synapses. - In: Scientific reports, ISSN 2045-2322, Bd. 14 (2024), 7802, S. 1-11
Blooming and pruning is one of the most important developmental mechanisms of the biological brain in the first years of life, enabling it to adapt its network structure to the demands of the environment. The mechanism is thought to be fundamental for the development of cognitive skills. Inspired by this, Chialvo and Bak proposed in 1999 a learning scheme that learns from mistakes by eliminating from the initial surplus of synaptic connections those that lead to an undesirable outcome. Here, this idea is implemented in a neuromorphic circuit scheme using CMOS integrated HfO2-based memristive devices. The implemented two-layer neural network learns in a self-organized manner without positive reinforcement and exploits the inherent variability of the memristive devices. This approach provides hardware, local, and energy-efficient learning. A combined experimental and simulation-based parameter study is presented to find the relevant system and device parameters leading to a compact and robust memristive neuromorphic circuit that can handle association tasks.
https://doi.org/10.1038/s41598-024-57660-4
Integration of multi-junction absorbers and catalysts for efficient solar-driven artificial leaf structures : a physical and materials science perspective. - In: Solar RRL, ISSN 2367-198X, Bd. 0 (2024), 0, S. 1-88
Artificial leaves could be the breakthrough technology to overcome the limitations of storage and mobility through the synthesis of chemical fuels from sunlight, which will be an essential component of a sustainable future energy system. However, the realization of efficient solar-driven artificial leaf structures requires integrated specialized materials such as semiconductor absorbers, catalysts, interfacial passivation, and contact layers. To date, no competitive system has emerged due to a lack of scientific understanding, knowledge-based design rules, and scalable engineering strategies. Here, we will discuss competitive artificial leaf devices for water splitting, focusing on multi-absorber structures to achieve solar-to-hydrogen conversion efficiencies exceeding 15%. A key challenge is integrating photovoltaic and electrochemical functionalities in a single device. Additionally, optimal electrocatalysts for intermittent operation at photocurrent densities of 10-20 mA cm^-2 must be immobilized on the absorbers with specifically designed interfacial passivation and contact layers, so-called buried junctions. This minimizes voltage and current losses and prevents corrosive side reactions. Key challenges include understanding elementary steps, identifying suitable materials, and developing synthesis and processing techniques for all integrated components. This is crucial for efficient, robust, and scalable devices. Here, we discuss and report on corresponding research efforts to produce green hydrogen with unassisted solar-driven (photo-)electrochemical devices. This article is protected by copyright. All rights reserved.
https://doi.org/10.1002/solr.202301047
Bipolar membrane Electrolyzer for CO2 electro-reduction to CO in organic electrolyte with NaClO produced as byproduct. - In: Electrochimica acta, ISSN 1873-3859, Bd. 483 (2024), 144056, S. 1-8
A novel electrolyzer has been proposed for CO2 reduction to CO, concurrently generating NaClO as a byproduct at the anode. The cell is divided into two compartments by a bipolar membrane, which plays a pivotal role in the dissociation of H2O into H^+ and OH^−. In the cathode compartment, CO2 is reduced to CO within a neutral organic solution. Simultaneously, in the anode compartment, Cl^− undergoes oxidation to form ClO^− within a basic aqueous solution. The electrolyzer remains stable during 10 h of electrolysis, and the current density reaches 76.35 mA cm^−2 at a potential of -2.4 V (vs SHE), with the Faradaic efficiency of CO formation stable at 93 %. By increasing the product values, CO2 electro-reduction technology can be promoted to industrial applications.
https://doi.org/10.1016/j.electacta.2024.144056
Towards fabrication of sub-micrometer cross-type aluminum Josephson junctions. - In: IEEE transactions on applied superconductivity, ISSN 1558-2515, Bd. 34 (2024), 3, 1101205, insges. 5 S.
The performance of superconducting electronic devices such as superconducting quantum bits (qubits) and superconducting quantum interference devices (SQUIDs) strongly relies on high-quality Josephson junctions (JJ) and their integration into surrounding circuit elements. Therefore, a corresponding fabrication technology should allow for the fabrication of all required elements including the JJs, inductances, capacitances and waveguides. For a long time, shadow evaporation technique was the state of the art for the implementation of sub-µm sized JJs based on aluminum for qubits of high coherence times. Although, the use of a single lithographic step represents a major advantage of this technique. However, shadowing effects limit sample size, device complexity, and thus scalability of the circuitry. To overcome these limitations and to meet the demands of next generation scalable quantum circuits, in this work we introduce our cross-type JJ aluminum technology, where JJs are defined by the overlap of two narrow perpendicular stripes. We discuss the technological challenges, with a focus on our newly developed dry etching process for patterning of the aluminum thin film. Compared to a lift-off based process, this advanced wafer-scale fabrication technology offers a high integration density and the required design flexibility. We will present first results on cross-type aluminum JJs.
https://doi.org/10.1109/TASC.2023.3343681