Filament Formation Research Articles

Multilevel Resistive Switching Dynamics by Controlling Phase and Self-Assembled Nanochannels in HfO2.

A resistive switching device with precise control over the formation of conductive filaments (CF) holds immense potential for high-density memory arrays and atomic-scale in-memory computing architectures. While ion migration and electrochemical switching mechanisms are well understood, controlling the evolution of CF remains challenging for practical resistive random-access memory (RRAM) deployment. This study introduces a systematic approach to modulate oxygen vacancies (OV) in HfO2 films of Ag/HfO2/Pt-based RRAM devices by controlling the substrate temperature. At 300°C, the HfO2 film exhibits a dominant monoclinic phase with maximum OV concentration, which plays a key role in achieving optimal multilevel resistive switching behavior. Self-assembled nanochannels in the HfO2 films guide CF evolution, and the diffusion of Ag at inside these films suggests a synergistic interplay between OV and Ag⁺ ion migration for reseting the voltage-controlled resistive states. This approach addresses the endurance/retention trade-off with an impressive Ron/Roff ratio of ≈8000while demonstrating growth temperature-driven OV modulation as a tool for multi-bit data storage. These findings provide a blueprint for developing high-performance oxide-based RRAM devices and offer valuable insights into multilevel resistive switching mechanisms, paving the way for future low-power, high-density memory technologies.

Cryo-EM Structure of AAA + ATPase Thorase Reveals Novel Helical Filament Formation.

The AAA+ (ATPases associated with a variety of cellular activities) ATPase, Thorase, also known as ATAD1, plays multiple roles in synaptic plasticity, mitochondrial quality control and mTOR signaling through disassembling protein complexes like AMPAR and mTORC1 in an ATP-dependent manner. The Oligomerization of Thorase is crucial for its disassembly and remodeling functions. We show that wild-type Thorase forms long helical filaments in vitro, dependent on ATP binding but not hydrolysis. We report the Cryogenic Electron Microscopy (cryo-EM) structure of the Thorase filament at a resolution of 4 Å, revealing the dimeric arrangement of the basic repeating unit that is formed through a distinct interface compared to the hexameric MSP1/ATAD1E193Q assembly. Structure-guided mutagenesis confirms the role of critical amino acid residues required for filament formation, oligomerization and disassembly of mTORC1 protein complex. Together, our data reveals a novel filament structure of Thorase and provides critical information that elucidates the mechanism underlying Thorase filament formation and Thorase-mediated disassembly of the mTORC1 complex.

Effect of Al2O3 on the operation of SiNX-based MIS RRAMs

The role of a 3 nm Al2O3 layer on top of stoichiometric LPCVD SiNx MIS RRAM cells is investigated by using various electrical characterization techniques. The conductive filament formation is explained, and a compact model is used to fit the current–voltage curves and find its evolution during each operation cycle. The conduction in SiNx is also studied.

Targeting Protein Misfolding and Aggregation as a Therapeutic Perspective in Neurodegenerative Disorders.

The abnormal deposition and intercellular propagation of disease-specific protein play a central role in the pathogenesis of many neurodegenerative disorders. Recent studies share the common observation that the formation of protein oligomers and subsequent pathological filaments is an essential step for the disease. Synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA) are neurodegenerative diseases characterized by the aggregation of the α-synucleinprotein in neurons and/or in oligodendrocytes (glial cytoplasmic inclusions), neuronal loss, and astrogliosis. A similar mechanism of protein Tau-dependent neurodegeneration is a major feature of tauopathies, represented by Alzheimer's disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PD). The specific inhibition of the protein misfolding and their interneuronal spreading represents a promising therapeutic strategy against both disease pathology and progression. The most recent research focuses on finding potential applications targeting the pathological forms of proteins responsible for neurodegeneration. This review highlights the mechanisms relevant to protein-dependent neurodegeneration based on the most common disorders and describes current therapeutic approaches targeting protein misfolding and aggregation.

Streaming Instabilities in Accreting Protoplanetary Disks: A Parameter Study

The streaming instability (SI) is currently the leading candidate for triggering planetesimal formation in protoplanetary disks. Recently, a novel variation, the “azimuthal-drift” streaming instability (AdSI), was discovered in disks exhibiting laminar gas accretion. Unlike the classical SI, the AdSI does not require pressure gradients and can concentrate dust even at low abundances. We extend previous simulations of the AdSI to explore the impact of dust abundance, accretion-flow strength, pressure gradients, and grain size. For a dimensionless accretion-flow strength α M = 0.1 and particle Stokes number St = 0.1, we find the AdSI produces dust filaments for initial dust-to-gas ratios as low as ϵ = 0.01. For ϵ ≳ 1, maximum dust-to-gas ratios of order 100 are attained, which can be expected to undergo gravitational collapse. Furthermore, even in systems dominated by the classical SI, an accretion flow drives filament formation, without which the disk remains in a state of small-scale turbulence. Our results suggest that an underlying accretion flow facilitates dust concentration and may thus promote planetesimal formation.

Investigation of resistive switching behavior driven by active and passive electrodes in MoO2–MoS2 core shell nanowire memristors

Memristive devices based on layered materials have the potential to enable low power electronics with ultra-fast operations toward the development of next generation memory and computing technologies. Memristor performance and switching behavior crucially depend on the switching matrix and on the type of electrodes used. In this work, we investigate the effect of different electrodes in 1D MoO2–MoS2 core shell nanowire memristors by highlighting their role in achieving distinct switching behavior. Analog and digital resistive switching are realized with carbon based passive (multi-layer graphene and multiwall carbon nanotube) and 3D active metal (silver and nickel) electrodes, respectively. Temperature dependent electrical transport studies of the conducting filament down to cryogenic temperatures reveal its semiconducting and metallic nature for passive and active top electrodes, respectively. These investigations shed light on the physics of the filament formation and provide a knob to design and develop the memristors with specific switching characteristics for desired end uses.

SN 1054 as a Pulsar-Driven Supernova: Implications for the Crab Pulsar and Remnant Evolution

Abstract One of the most studied objects in astronomy, the Crab Nebula, is the remnant of the historical supernova SN 1054. Historical observations of the supernova imply a typical supernova luminosity, but contemporary observations of the remnant imply a low explosion energy and low ejecta kinetic energy. These observations are incompatible with a standard 56Ni-powered supernova, hinting at an an alternate power source such as circumstellar interaction or a central engine. We examine SN 1054 using a pulsar-driven supernova model, similar to those used for superluminous supernovae. The model can reproduce the luminosity and velocity of SN 1054 for an initial spin period of ∼ 14 ms and an initial dipole magnetic field of 1014 − 15 G. We discuss the implications of these results, including the evolution of the Crab pulsar, the evolution of the remnant structure, formation of filaments, and limits on freely expanding ejecta. We discuss how our model could be tested further through potential light echo photometry and spectroscopy, as well as the modern analogues of SN 1054.

Integration of CeO2-Based Memristor with Vertically Aligned Nanocomposite Thin Film: Enabling Selective Conductive Filament Formation for High-Performance Electronic Synapses.

The CeO2-based memristor has attracted significant attention due to its intrinsic resistive switching (RS) properties, large on/off ratio, and great plasticity, making it a promising candidate for artificial synapses. However, significant challenges such as high power consumption and poor device reliability hinder its broad application in neuromorphic microchips. To tackle these issues, in this work, we design a novel bilayer (BL) memristor by integrating a CeO2-based memristor with a Co-CeO2 vertically aligned nanocomposite (VAN) layer and compare it with the single layer (SL) memristor. Preliminary electrical testing reveals that the BL memristor offers a reduced set/reset voltage (∼67% lower), a higher on/off ratio (∼5 × 102), enhanced device reliability, and improved device-to-device variation compared to the SL memristor. Insight from COMSOL simulation, coupled with microstructural analysis, provides a comprehensive elucidation on how the VAN layer facilitates the selective conductive filament (CF) formation. Subsequently, the plasticity of the BL memristor is evaluated through long-term potentiation/depression (LTP/LTD), paired-pulse facilitation (PPF), and spike-time-dependent plasticity (STDP). The spiking neural network (SNN) built upon the BL memristor achieves remarkable accuracy (∼94%) after only 12 iterations, underscoring its potential for high-performance neural networks.

Post-Translational Modifications Control Phase Transitions of Tau.

The self-assembly of Tau into filaments, which mirror the structures observed in Alzheimer's disease (AD) brains, raises questions about the role of AD-specific post-translational modifications (PTMs) in the formation of paired helical filaments (PHFs). To investigate this, we developed a synthetic approach to produce Tau(291-391) featuring N-acetyllysine, phosphoserine, phosphotyrosine, and N-glycosylation at positions commonly modified in post-mortem AD brains. Using various electron and optical microscopy techniques, we discovered that these modifications generally hinder the in vitro assembly of Tau into PHFs. Interestingly, while acetylation's effect on Tau assembly displayed variability, either promoting or inhibiting phase transitions in cofactor-free aggregation, heparin-induced aggregation, and RNA-mediated liquid-liquid phase separation (LLPS), phosphorylation uniformly mitigated these processes. Our observations suggest that PTMs, particularly those situated outside the rigid core, are pivotal in the nucleation of PHFs. Moreover, with heparin-induced aggregation leading to the formation of heterogeneous aggregates, most AD-specific PTMs appeared to decelerate aggregation. The impact of acetylation on RNA-induced LLPS was notably site-dependent, whereas phosphorylation consistently reduced LLPS across all proteoforms examined. These insights underscore the complex interplay between site-specific PTMs and environmental factors in modulating Tau aggregation kinetics, highlighting the role of PTMs located outside the ordered filament core in driving the self-assembly.

Conductive Islands Assisted Resistive Switching in Biomimetic Artificial Synapse for Associative Learning and Image Recognition

AbstractSolution‐processed memristor devices hold significant potential for advancing synaptic applications, offering scalable, cost‐effective, and efficient solutions for next‐generation neuromorphic systems. These devices replicate the behavior of biological synapses with their gradual and continuous changes in resistance, making them promising for neuromorphic computing and artificial neural networks. However, understanding the temporal characteristics and cumulative effect of successive pulses on the devices is essential for emulating the dynamics of biological synapses. This study proposes a hybrid materials‐based conductive islands‐assisted resistive switching (CIARS) in a solution‐processed active layer consisting of thermally exfoliated graphitic carbon nitride (g‐C3N4 abbreviated as CN) nanosheets embedded with silver nanoparticles (Ag NPs). The fabricated devices demonstrate repeatable and bipolar memory features with a lower operating voltage (≤0.5 V), emulating the frequency and amplitude‐dependent synaptic plasticities. The threshold switching occurs due to the formation of conduction filaments (CFs) of silver ion (Ag+), whereas the analog behavior results from the voltage pulse‐dependent modulation of Schottky barrier height combined with metallic CFs formation. The experimental findings demonstrate the efficacy of the CIARS mechanism within the material platform, highlighting its potential for applications in associative learning, Morse code detection, and image recognition.

Memristor Array Based on Wafer-Scale 2D HfS2 for Dual-Mode Physically Unclonable Functions.

Conventional Si-based physically unclonable functions (PUFs) take advantage of the unique variations in the fabrication processes. However, these PUFs are hindered by limited entropy sources and susceptibility to noise interference. Here we present a memristive device based on wafer-scale (2-in.) two-dimensional (2D) hafnium disulfide (HfS2) grown by molecular beam epitaxy (MBE). The polycrystalline HfS2 thin film can offer enhanced entropy sources for PUF applications, such as lattice defects, which can facilitate the random formation of conductive filaments and result in significant device-to-device (D2D) variations. Our proposed PUF design seamlessly integrates two distinct operating modes within a single circuit module. First, a reconfigurable and highly secure mode 1, and second, an ultrareliable mode 2, both with near-ideal Entropy (∼1.0), normalized Hamming distance (∼0.5) and correlation coefficient (∼0.0). Additionally, a predictive Fourier regression model further confirms the unpredictable nature of our dual-mode PUF, with an average prediction accuracy of ∼50%.

Stable Millivolt Range Resistive Switching in Percolating Molybdenum Nanoparticle Networks.

To overcome the limitations of the conventional Von Neumann architecture, inspiration from the mammalian brain has led to the development of nanoscale neuromorphic networks. In the present research, molybdenum nanoparticles (NPs), which were produced by means of gas phase condensation based on magnetron sputtering, are shown to be the constituents of electrically percolating networks that exhibit stable, complex, neuron-like spiking behavior at low potentials in the millivolt range, satisfying well the requirement of low energy consumption. Characterization of the NPs using both scanning electron microscopy and scanning transmission electron microscopy revealed not only pristine shape, size, and density control of Mo NPs but also a preliminary proof of the working mechanism behind the spiking behavior due to filament formations. Furthermore, electrostatics COMSOL Multiphysics simulations of the morphology of the NPs provided evidence that the stable switching is due to the as-deposited stellate Mo NPs creating high electric field strengths, while keeping them separated, not seen before in other percolating networks based on spherical NPs. Hence, our results show the working mechanism behind switching in percolating Mo NP networks and show that they are very promising for realistic neuromorphic systems.

Macroscopic creep behavior of spheroids derived from mesenchymal stem cells under compression

Spheroid culture, where cells are aggregated three-dimensionally, is expected to have applications as a model that better recapitulates invivo environment beyond two-dimensional environments. When human mesenchymal stem cells are subjected to spheroid culture in the presence of osteogenesis supplements, the gene expression of osteocyte differentiation marker is greatly increased within a short period compared to two-dimensional culture. However, how such alterations may be reflected to mechanical properties of the spheroid remains unknown. In this study, using a uniaxial compression system, we evaluated the macroscopic mechanical properties of human mesenchymal stem cell-derived spheroids including viscoelastic behavior. The Young's modulus of spheroids cultured for 2 days was about 18 kPa, whereas that of individual cells is around 1–10 kPa. We also found that creep behavior of the spheroid was greater in 50% strain compression beyond 10 or 30% strain, indicating that they are viscoelastic materials. Upon release from compression, the spheroids tended to revert to their original shape through elastic deformation. However, spheroids in which actin filament formation was inhibited exhibited a remarkably greater plastic deformation, suggesting that the actin filaments play a crucial role in the elastic behavior of spheroids. By understanding the mechanical properties and behavior of spheroids, it provides a framework for predicting and manipulating the development of tissues and organs in the field of morphogenesis.

Cationic lipid transfection induces nuclear actin filaments.

Cationic lipids are widely used for gene delivery. Here, we report the transient formation of nuclear actin filaments in mammalian cells transfected with commercially available transfection reagents regardless of the proteins transfected. Readily detectable with phalloidin, nuclear actin ranges from short filaments to a fully developed network. Nuclear actin filaments persist for hours, peak 20 h after transfection, and may be involved in DNA damage repair.

Laser modulation of the FePS3 memristors.

Ternary two-dimensional (2D) material-based memristors have garnered significant attention in the fields of machine learning, neuromorphic computing due to their low power consumption, rapid learning, and synaptic-like behavior. Although such memristors often exhibit high ON/OFF ratios and exceptional pulse response characteristics, they have also to face some challenges concerning reusability and switching cycles, which arise from the filament instability issues.. Here we propose a modulation strategy to improve performance of 2D-material memristors with synaptic and flexible features. By laser-modulating few-layer FePS3, we induced the formation of conductive filaments, realized a major improvement in performance of the FePS3 memristors, achieving an on/off ratio of nearly 104, low power consumption at approximately 10-7 W of single switching operation, and maintaining stability even after over 500 cycles. The performance promotion has been ascribed to enhancement of conductive filament induced by laser-modulation. Furthermore, we have identified the effectiveness of our laser modulation under strain by building the high-performance flexible FePS3 memristor. Meanwhile, we discovered a novel strain-dominant erasure method for the flexible memristors. Our work confirms that laser modulation is a viable method for enhancing the performance of 2D material-based memristive devices.&#xD.

Rad52 sorts and stacks Rad51 at the DNA junction to promote homologous recombination.

Homologous recombination (HR) repairs double-stranded DNA breaks (DSBs). The DSBs are resected to yield single-stranded DNA (ssDNA) that are coated by Replication Protein A (RPA). Rad51 is a recombinase and catalyzes strand invasion and the search for homology. However, it binds to ssDNA with lower affinity than RPA. Thus, mediator proteins such as Rad52/BRCA2 are required to promote Rad51 binding to RPA-coated ssDNA, but the underlying mechanisms remain poorly understood. Saccharomyces cerevisiae Rad52 interacts with Rad51 through two distinct binding modes. We here uncover that the Rad51-binding site in the disordered C-terminus of Rad52 (mode-1) sorts polydisperse Rad51 into discrete monomers. The second Rad51 binding site resides in the ordered N-terminal ring of Rad52 (mode-2), but this interaction occurs at only one position on the ring. In single molecule confocal fluorescence microscopy combined with optical tweezer analysis, we directly visualize filament formation using fluorescent-Rad51. Rad52 catalyzes Rad51 loading onto RPA-coated ssDNA, with a distinct preference for junctions, but no filament growth is observed. Deletion of the C-terminus of Rad52 results in loss of Rad51 sorting and abrogates Rad51 binding to RPA-coated DNA. While BRCA2 and Rad52 are structurally unrelated, many of these functional features are conserved. We describe a concerted Sort & Stack mechanism for mediator proteins in promoting HR.

A semiconducting supramolecular Co(II)-metallogel based resistive random access memory (RRAM) design with good endurance capabilities.

A highly efficient approach for synthesizing a supramolecular metallogel of Co(II) ions, denoted as CoA-TA, has been established under room temperature and atmospheric pressure conditions. This method employs the metal-coordinating organic ligand benzene-1,3,5-tricarboxylic acid as a low molecular weight gelator (LMWG) in DMF solvent. A comprehensive analysis of the mechanical properties of the resulting supramolecular Co(II)-metallogel was conducted through rheological investigation, considering angular frequency and thixotropic study. The hierarchical rocky network structure of the supramolecular Co(II)-metallogel was unveiled using field emission scanning electron microscopy (FESEM). Transmission electron microscopic (TEM) analysis showed rod-shaped structures via low-magnification high angle annular dark field (HAADF) bright field scanning transmission electron microscopic (STEM) imaging, while energy dispersive X-ray (EDX) elemental mapping confirmed its primary chemical constituents. The formation mechanism of the metallogel was examined via fourier transform infrared spectroscopy (FTIR) spectroscopy. The nature of the synthesized CoA-TA metallogel was affirmed through powder X-ray diffraction (PXRD) analysis. Furthermore, this study involved fabrication of Schottky diode structures in a metal-semiconductor-metal geometry based on cobalt(II) metallogel (CoA-TA), enabling observation of charge transport behavior. Remarkably, a resistive random access memory (RRAM) device utilizing cobalt(II) metallohydrogel (CoA-TA) demonstrated bipolar resistive switching at room temperature and under ambient conditions. The switching mechanism was investigated, revealing the formation and rupture of conductive filaments between metal electrodes that govern the resistive switching behavior. This RRAM device exhibited an impressive ON/OFF ratio (~ 414) and exceptional endurance over 5000 switching cycles. These structures offer great potential for diverse applications such as non-volatile memory design, neuromorphic computing, flexible electronics and optoelectronics. Their advantages lie in their fabrication process, reliable resistive switching behavior and overall performance stability.

Bio‐Realistic Synaptic‐Replicated “V” Type Oxygen Vacancy Memristor

AbstractThe development of an artificial synaptic device is essential for the construction of a brain‐like neuromorphic computing architecture. In this study, the goal is to create a multi‐layer HfOx memristor with a “V” type oxygen vacancy (Vo) distribution to mimic the function of calcium ions (Ca2+) during synaptic information transmission. By adjusting voltage and compliance current (Icc), the HfOx memristor can open or close different levels of volt‐controlled Ca2+ channels, thus enabling the replication of synaptic structure, neurotransmitter release/acceptor, and information transmission. A mathematical model is adopted to describe the behavior of volt‐controlled Ca2+ channels, which demonstrates that the device exhibits consistent characteristics with biological synapses. The device forms an “hourglass” conductive filament (CF) within its middle functional layer, allowing for precise control over filament formation and positioning. This results in ultra‐low power consumption for erasing (581 fJ), fast erasing speed (10 ns), and a low resistance difference coefficient of only 1.8%. Furthermore, the device successfully simulates the physical dynamics of Ca2+ during short‐term potentiation (STP) and long‐term potentiation (LTP) in biological synapses while replicating various guided synaptic behaviors. This study provides a straightforward method for memristors to realize bio‐realistic artificial neuromorphic applications.

Hydrophobic Domain Modulation of Chemical Responsiveness in a Bolaamphiphile-Based Supramolecular Monomer.

Self-immolative chemistries that respond in an irreversible manner to external stimuli are highly attractive to permanently degrade filamentous supramolecular biomaterials. Within the monomer, a balance needs to be struck between its capacity to be supramolecularly polymerized and degraded at an appropriate rate for a given application. Herein, we unravel the structure-property-function relationships of a library of squaramide-based bolaamphiphiles bearing a central disulfide-based self-immolative spacer to construct supramolecular polymers responsive to chemical stimuli in aqueous solutions. We examine the impact of changing the alkyl domain length (2 to 12 methylene units) on the formation of supramolecular filaments and their rate of degradation in response to a biological antioxidant, glutathione. A minimum of an octyl spacer is required to robustly form supramolecular polymers that can be irreversibly degraded through a cyclization-elimination reaction of the self-immolative spacer triggered by thiol-disulfide exchange. Further increasing the peripheral alkyl chain length to a decyl spacer increases the ordered packing of the amphiphiles, hindering their chemical degradation. This study provides a framework to design chemically responsive filamentous supramolecular polymers based on bolaamphiphiles that can be irreversibly degraded in aqueous solutions for their eventual application as biomedical materials.

Improving the Nonvolatile Memory Characteristics of Sol-Gel-Processed Y2O3 RRAM Devices Using Mono-Ethanolamine Additives.

In this study, Y2O3-based resistive random-access memory (RRAM) devices with a mono-ethanolamine (MEA) stabilizer fabricated using the sol-gel process on indium tin oxide/glass substrates were investigated. The effects of MEA content on the structural, optical, chemical, and electrical characteristics were determined. As the MEA content increased, film thickness and crystallite size decreased. In particular, the increase in MEA content slightly decreased the oxygen vacancy concentration. The decreased film thickness decreased the physical distance for conductive filament formation, generating a strong electric field. However, owing to the lowest oxygen vacancy concentration, a large electrical field is required. To ensure data reliability, the endurance cycles across several devices were measured and presented statistically. Additionally, endurance performance improved with the increase in MEA content. Reduced oxygen vacancy concentration can successfully suppress the excess formation of the Ag conductive filament. This simplifies the transition from the high- to the low-resistance state and vice versa, thereby improving the endurance cycles of the RRAM devices.