Charged Domain Research Articles

Adiabatic leaky integrate and fire neurons with refractory period for ultra low energy neuromorphic computing

In recent years, the in-memory-computing in charge domain has gained significant interest as a promising solution to further enhance the energy efficiency of neuromorphic hardware. In this work, we explore the synergy between the brain-inspired computation and the adiabatic paradigm by presenting an adiabatic Leaky Integrate-and-Fire neuron in 180 nm CMOS technology, that is able to emulate the most important primitives for a valuable neuromorphic computation, such as the accumulation of the incoming input spikes, an exponential leakage of the membrane potential and a tunable refractory period. Differently from previous contributions in the literature, our design can exploit both the charging and recovery phases of the adiabatic operation to ensure a seamless and continuous computation, all the while exchanging energy with the power supply with an efficiency higher than 90% over a wide range of resonance frequencies, and even surpassing 99% for the lowest frequencies. Our simulations unveil a minimum energy per synaptic operation of 470 fJ at a 500 kHz resonance frequency, which yields a 9x energy saving with respect to a non-adiabatic operation.

Design and implementation of a charge-sharing in-memory-computing macro with sparse feature for quantized neural network

With the rapid development of artificial intelligence technology, in-memory computing has become a research hotspot. In this article, we propose an in-memory computing (IMC) architecture that achieves high energy efficiency and performance. Our work is based on the working mechanism of charge sharing, enabling configurable multi-bit Multiply-Accumulate operations. This work employs a unique bit-cell structure to implement sparse strategies at the bit-level in IMC arrays and compensates for errors caused by non-ideal effects, thus achieving better energy efficiency and performance. A hardware-aware quantification method and a hardware simulation model based on Pytorch have been proposed to evaluate the hardware mapping and compare with other charge domain IMC works. The MNIST and CIFAR-10 datasets have been used to validate algorithm models and chip performance, achieving accuracy rates of 97.6% and 90.5%respectively. The IMC chip was fabricated with a 180 nm CMOS process. The measurement shows that the chip achieves an energy efficiency of 41.8 TOPS/W.

Effect of framework and complementarity determining region H1 charge on the human VH-B1a domain expression, folding, stability, and solubility

Many difficulties related to using antibodies in diagnostic and therapeutic applications can sometimes be circumvented by using smaller, less complex single domain antibodies based on variable heavy chain (VH) domain constructs such as camelid VHH domains. However, VH domains have their own limitations, including an increased tendency to aggregate. VH domains often contain hydrophobic residues within their complementarity-determining regions (CDRs) that facilitate binding to target antigens but can also mediate VH domain aggregation, which is a concern for therapeutic applications since this can trigger immune responses. In this study, we engineered the human VH-1Ba domain to improve its stability and solubility by introducing charged amino acids in the VH domain framework region and CDRH1. We followed two strategies to improve the stability and solubility of VH domains. First, we introduced positive and negatively charged amino acids in the framework region of an autonomous human VH domain (VH–B1a) and observed the effect of framework net charge on VH domain refolding, stability, and solubility. Introducing positive charge into the VH-B1a framework increased its thermostability but slightly lowered its refolding ability and solubility. We were not able to obtain correctly folded negatively charged (-VH) VH domains. Second, we introduced a series of positive and negatively charged amino acids in the CDRH1 loop of near-neutral (VH–B1a) and positively charged (+VH) VH domains, and observed their effect on expression, refolding, stability, and solubility. For both the VH-B1a and +VH domains, we observed a decrease in melting temperature (Tm) and room temperature solubility as more negative or positive charged amino acids were added to the CDRH1. The VH-B1a domain had higher room temperature solubility for negative and slightly positive CDRH1 net charges. The + VH domain had higher Tms for all CDRH1 net charges and was better able to tolerate the adverse effects of adding positive charge to CDRH1. We observed a similar response in refolding and solubility of VH-B1a and +VH in response to changes in CDRH1 net charge after temperature-induced denaturation for negative and neutral CDRH1s. We observed a positional effect with a single Lys (31K) and double Lys (31, 32 KK) substitutions in CDRH1, which promoted VH-B1a aggregation and was partially overcome by the +VH domain. In summary, this study provides information for designing VH domains with improved biophysical properties and a +VH domain that will be useful for applications where positive surface charge and CDRH1 are desirable.

Structural Properties of [N1888][TFSI] Ionic Liquid: A Small Angle Neutron Scattering and Polarizable Molecular Dynamics Study.

In this study, we investigate the quaternary ammonium-based ionic liquid (QAIL), methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N1888][TFSI], utilizing small angle neutron scattering (SANS) measurements and polarizable molecular dynamics (MD) simulations to characterize the short- and long-range liquid structure. Scattering structure factors show signatures of three length scales in reciprocal space indicative of alternating polarity (k ∼ 0.44 Å-1), charge (k ∼ 0.75 Å-1), and neighboring or adjacent (k ∼ 1.46 Å-1) domains. Excellent agreement between simulation and experimental scattering structure factors validates various simulation analyses that provide detailed atomistic characterization of the different length scale correlations. The first solvation shell structure is illustrated by obtaining radial, angular, dihedral, and combined distribution functions, where two dominant spatial motifs, N+···N- and N+···O-, compete for optimal packing around the polar head of the [N1888]+ cation. Intermediate and long-range structures are governed by the balance between local electroneutrality and octyl chain networking, respectively. By computing the charge-correlation structure factor, SZZ, and the spatial extent of the octyl chain network using graph theory, the bulk-phase structure of [N1888][TFSI] is characterized in terms of electrostatic screening and apolar domain formation length scales.

Ferroelectric Domain Modulation with Tip-Poling Engineering in BiFeO3 Films.

BiFeO3 (BFO) films with ferroelectricity are the most promising candidates regarding the next generation of storage devices and sensors. The comprehensive understanding of ferroelectric switchable properties is challenging and critical to robust domain wall nanoelectronics. Herein, the domain dynamic was explored in detail under external bias conditions using scanning probe microscopy, which is meaningful for the understanding of domain dynamics and the foundation of ferroelectric devices. The results show that domain reversal occurred under external electric fields with sufficient energy excitation, combined with the existence of a charged domain wall. These findings extend the domain dynamic and current paths in ferroelectric films and shed light on the potential applications for ferroelectric devices.

Single-crystal ferroelectric LiNbO3 thin film-based synaptic devices enabled with tunable domain wall current for neuromorphic computing

Neuromorphic devices can emulate the human brain to process information, which receives lots of attention in the field of artificial intelligence. Synaptic devices based on ferroelectric thin films feature low-power consumption, multifunctionality, and scalability. Among them, ferroelectric charged domain wall (CDW) devices have attracted intensive interest for the implementation of memristive devices due to their ultrahigh integration ability inherited from the nanoscale domain wall thickness. In particular, the preparation of wafer-scale single-crystalline ferroelectric thin films via ion-sliced heterogeneous wafer bonding lays a good foundation for large-scale integration of ferroelectric devices with functional circuits. However, the biomimic synaptic characteristics and the systematic demonstration of synaptic devices are largely unexplored for this material system. Here, we demonstrate a model synaptic device based on a single-crystal ferroelectric LiNbO3 thin film, which provides the desired characteristics for neuromorphic computing. The conductance modulation demonstrates good linearity for efficient neuromorphic computing applications. Simulations using the Modified National Institute of Standards and Technology handwritten recognition dataset prove that LiNbO3-based synaptic devices can operate with an online learning accuracy of 95.1%. The injection and annihilation of the CDW are proposed as the basis of the conductivity modulation by combining with the piezoresponse force microscopy and conductive atomic force microscopy mapping measurements. With the mature fabrication process of the ultrathin high-quality ferroelectric thin films, LiNbO3-based synaptic devices have an extensive application prospect for future neuromorphic computing systems.

ProtonationDriven Polarization Retention Failure in Nano-Columnar Lead-Free Ferroelectric Thin Films.

Understanding microscopic mechanisms of polarization retention characteristics in ferroelectric thin films is of great significance for exploring unusual physical phenomena inaccessible in the bulk counterparts and for realizing thin-film-based functional electronic devices. Perovskite (K,Na)NbO3 is an excellent class of lead-free ferroelectric oxides attracting tremendous interest thanks to its potential applications to nonvolatile memory and eco-friendly energy harvester/storage. Nonetheless, in-depth investigation of ferroelectric properties of (K,Na)NbO3 films and the following developments of nano-devices are limited due to challenging thin-film fabrication associated with nonstoichiometry by volatile K and Na atoms. Herein, ferroelectric (K,Na)NbO3 films of which the atomic-level geometrical structures strongly depend on thickness-dependent strain relaxation are epitaxially grown. Nanopillar crystal structures are identified in fully relaxed (K,Na)NbO3 films to the bulk states representing a continuous reduction of switchable polarization under air environments, that is, polarization retention failures. Protonation by water dissociation is responsible for the humidity-induced retention loss in nano-columnar (K,Na)NbO3 films. The protonation-driven polarization retention failure originates from domain wall pinning by the accumulation of mobile hydrogen ions at charged domain walls for effective screening of polarization-bound charges. Conceptually, the results will be utilized for rational design to advanced energy materials such as photo-catalysts enabling ferroelectric tuning of water splitting.

Rotating AdS3× S3 and dyonic strings from 3-dimensions

We make a general Killing spinor analysis of a particular D = 3, N = 4 gauged supergravity that comes from a consistent S3 reduction of D = 6, N = (1, 0) supergravity coupled to a single chiral tensor multiplet. We then focus on its supersymmetric solutions with a null Killing vector and find three new ones. Two of these, namely the null warped AdS3 (also known as the Schrödinger spacetime) and the charged domain wall solutions, admit non-trivial gauge fields which give rise to rotating solutions in 6-dimensions. The uplift of the first one produces an interesting AdS3 × S3 background with a non-trivial rotation in the U(1) fiber direction of the S3 which retains the Schrödinger scale invariance that the seed solution has. The second one leads to the well-known rotating dyonic string solution. Finally, the uplift of the third one, which is a domain wall solution with no gauge fields, results in a distribution of dyonic strings.

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Sequence diversity in the monooxygenases involved in oxime production in plant defense and signaling: a conservative revision in the nomenclature of the highly complex CYP79 family.

Cytochrome P450 monooxygenases of the CYP79 family catalyze conversion of specific amino acids into oximes feeding into a variety of metabolic plant pathways. Here we present an extensive phylogenetic tree of the CYP79 family built on carefully curated sequences collected across the entire plant kingdom. Based on a monophyletic origin of the P450s, a set of evolutionarily distinct branches was identified. Founded on the functionally characterized CYP79 sequences, sequence features of the individual substrate recognition sites (SRSs) were analyzed. Co-evolving amino acid residues were identified using co-evolutionary sequence analysis. SRS4 possesses a specific sequence pattern when tyrosine is a substrate. Except for the CYP79Cs and CYP79Fs, substrate preferences toward specific amino acids could not be assigned to specific subfamilies. The highly diversified CYP79 tree, reflecting recurrent independent evolution of CYP79s, may relate to the different roles of oximes in different plant species. The sequence differences across individual CYP79 subfamilies may facilitate the in vivo orchestration of channeled metabolic pathways based on altered surface charge domains of the CYP79 protein. Alternatively, they may serve to optimize dynamic interactions with oxime metabolizing enzymes to enable optimal ecological interactions. The outlined detailed curation of the CYP79 sequences used for building the phylogenetic tree made it appropriate to make a conservative phylogenetic tree-based revision of the naming of the sequences within this highly complex cytochrome P450 family. The same approach may be used in other complex P450 subfamilies. The detailed phylogeny of the CYP79 family will enable further exploration of the evolution of function in these enzymes.

Nanoscale Topography Dictates Residue Hydropathy in Proteins.

Proteins exhibit diverse structures, including pockets, cavities, channels, and bumps, which are crucial in determining their functions. This diversity in topography also introduces significant chemical heterogeneity, with polar and charged domains often juxtaposed with nonpolar domains in proximity. Consequently, accurately assessing the hydropathy of amino acid residues within the intricate nanoscale topology of proteins is essential. This study presents quantitative hydropathy data for 277,877 amino acid residues, computed using the Protocol for Assigning a Residue's Character on a Hydropathy (PARCH) scale. Leveraging this data set comprising 1000 structurally diverse proteins sourced from the Protein Data Bank, we examined residues situated in various nanoscale environments and analyzed hydropathy in relation to protein topography. Our findings indicate that the hydropathy of a residue is intricately linked to both its individual characteristics and the geometric features of its neighboring residues in response to water. Changes in the number and chemical identity of the neighbors, as well as the nanoscale topography surrounding a residue, are mirrored in its hydropathy profile. Our calculations reveal the intricate interplay of hydrophilic, hydroneutral, and hydrophobic residues distributed across the surface and core of proteins. Notably, we observe that protein surfaces can be ten times more hydrophilic than their cores.

Magnetoelectric Phase Control at Domain‐Wall‐Like Epitaxial Oxide Multilayers

AbstractFerroelectric domain walls are nanoscale objects that can be created, positioned, and erased on demand. They often embody functional properties that are distinct from the surrounding bulk material. Enhanced conductivity, for instance, is observed at charged ferroelectric domain walls. Regrettably, domain walls of this type are scarce because of the energetically unfavorable electrostatics. This hinders the current technological development of domain‐wall nanoelectronics. Here this constraint is overcome by creating robust domain‐wall‐like objects in epitaxial oxide heterostructures. Charged head‐to‐head (HH) and tail‐to‐tail (TT) junctions are designed with two ferroelectric layers (BaTiO3 and BiFeO3) that have opposing out‐of‐plane polarization. To test domain‐wall‐like functionalities, an ultrathin ferromagnetic La0.7Sr0.3MnO3 layer is inserted into the junctions. The interfacial electron or hole accumulation at the interfaces, set by the HH and TT polarization configurations, respectively, controls the LSMO conductivity and magnetization. Thus it is proposed that trilayers reminiscent of artificial domain walls provide magnetoelectric functionality and may constitute an important building block in the design of oxide‐based electronic devices.

Supersymmetry on the honeycomb lattice: Resonating charge stripes, superfrustration, and domain walls

Supersymmetry on the honeycomb lattice: Resonating charge stripes, superfrustration, and domain walls

Intrinsically Stable Charged Domain Walls in Molecular Ferroelectric Thin Films

AbstractCharged domain walls in ferroelectrics hold great promise for applications in ferroelectric random‐access memory (FeRAM), with advantages such as low energy consumption, high density, and non‐destructive operation. Due to the mechanical compatibility condition, the neutral domain walls are dominant in traditional ferroelectric thin films. Herein, using phase‐field simulations, the formation of intrinsically stable charged domain walls (CDWs) in the molecular ferroelectric films is demonstrated, which can be mainly attributed to the small mechanical stiffness. The switching kinetics are further investigated for the CDWs, showing a lower switching barrier as compared to the neutral counterparts. Moreover, it is indicated that increasing the compressive misfit strain can lead to prolonged switching time, with a significantly increased switching energy barrier. These findings pave the way for the potential applications of metal‐free organic ferroelectric materials in FeRAM devices.

Atomic-Scale Scanning of Domain Network in the Ferroelectric HfO2 Thin Film.

Ferroelectric HfO2-based thin films have attracted much interest in the utilization of ferroelectricity at the nanoscale for next-generation electronic devices. However, the structural origin and stabilization mechanism of the ferroelectric phase are not understood because the film is typically nanocrystalline with active yet stochastic ferroelectric domains. Here, electron microscopy is used to map the in-plane domain network structures of epitaxially grown ferroelectric Y:HfO2 films in atomic resolution. The ferroelectricity is confirmed in free-standing Y:HfO2 films, allowing for investigating the structural origin for their ferroelectricity by 4D-STEM, high-resolution STEM, and iDPC-STEM. At the grain boundaries of <111>-oriented Pca21 orthorhombic grains, a high-symmetry mixed-(R3m, Pnm21) phase is induced, exhibiting enhanced polarization due to in-plane compressive strain. Nanoscale Pca21 orthorhombic grains and their grain boundaries with mixed-(R3m, Pnm21) phases of higher symmetry cooperatively determine the ferroelectricity of the Y:HfO2 film. It is also found that such ferroelectric domain networks emerge when the film thickness is beyond a finite value. Furthermore, in-plane mapping of oxygen positions overlaid on ferroelectric domains discloses that polarization is suppressed at vertical domain walls, while it is active when domains are aligned horizontally with subangstrom domain walls. In addition, randomly distributed 180° charged domain walls are confined by spacer layers.

Intrinsic Conductance of Ferroelectric Charged Domain Walls

Intrinsic Conductance of Ferroelectric Charged Domain Walls

Antipolar 2D Metallicity with Tunable Valence Wx+ (5 ≤ x ≤ 5.6) in the Layered Monophosphate Tungsten Bronzes [Ba(PO4)2]WmO3m-3.

The newly discovered series of layered monophosphate tungsten bronzes (L-MPTB) [Ba(PO4)2]WmO3m-3 consist of m-layer-thick slabs of WO6 octahedra separated by barium-phosphate spacers. They display a 2D metallic behavior confined in the central part of the perovskite slabs. Here, we report the missing m = 2 member of this series, containing the rather uncommon W5+ oxidation state. We have analyzed its structure-property relationships in relation to the other members of the L-MPTB family. In particular, we have determined its crystal structure by means of single-crystal X-ray and electron diffraction and investigated its physical properties from resistivity, Seebeck-coefficient and heat-capacity measurements combined with first-principles calculations. All the L-MPTB compounds show metallic behavior down to 1.8 K without any clear charge-density-wave (CDW) order. The m = 2 member, however, displays an increased influence of the spacer that translates into anisotropic negative thermal expansion, reversed thermopower and reversed crystal-field splitting of the tungsten t2g orbitals. Our analysis of the full [Ba(PO4)2]WmO3m-3 series reveals a systematic and significant W off-centering in their octahedral coordination. We identify the resulting anti-polar character of these W displacements as the crucial aspect behind the 2D metallicity of these systems: It leads to the presence of bound charges whose screening determines the distribution of mobile charges, tending to accumulate at the center of the [WmO3-m] block. We argue that this mechanism is analogous to enhanced conductivity observed for charged domain walls in ferroelectrics, thus providing a general design rule to promote 2D metallicity in layered systems.

A negatively charged cluster in the disordered acidic domain of GPIHBP1 provides selectivity in the interaction with lipoprotein lipase

GPIHBP1 is a membrane protein of endothelial cells that transports lipoprotein lipase (LPL), the key enzyme in plasma triglyceride metabolism, from the interstitial space to its site of action on the capillary lumen. An intrinsically disordered highly negatively charged N-terminal domain of GPIHBP1 contributes to the interaction with LPL. In this work, we investigated whether the plethora of heparin-binding proteins with positively charged regions found in human plasma affect this interaction. We also wanted to know whether the role of the N-terminal domain is purely non-specific and supportive for the interaction between LPL and full-length GPIHBP1, or whether it participates in the specific recognition mechanism. Using surface plasmon resonance, affinity chromatography, and FRET, we were unable to identify any plasma component, besides LPL, that bound the N-terminus with detectable affinity or affected its interaction with LPL. By examining different synthetic peptides, we show that the high affinity of the LPL/N-terminal domain interaction is ensured by at least ten negatively charged residues, among which at least six must sequentially arranged. We conclude that the association of LPL with the N-terminal domain of GPIHBP1 is highly specific and human plasma does not contain components that significantly affect this complex.

Multi-step switchable superdomain architecture with enhanced photoelectrical performance in epitaxial ferroelectrics

Ferroic domains and relevant topological defects, such as domain walls and vortices, have gained significant attention as functional units for potential advancements in nanoelectronics. Pb(ZrxTi1-x)O3 (PZT) is a tetragonal ferroelectric material at room-temperature, exhibiting remarkable piezoelectricity and intricate domain structures. In this work, we explore the ferroelectric properties, photoelectric reactions, and efficient manipulation pathways of the unconventional superstructures in epitaxial (101)-oriented PZT thin films. Employing piezoresponse force microscopy (PFM) and conductive atomic force microscopy (cAFM), we unveil the three-dimensional polarization configurations of the superdomain structures inherently featuring conductive charged domain walls. Our findings reveal an increase in photoactivity at the head-side charged domain walls, attributed to the band-bending mechanism. Additionally, we discover the enhanced photoelectrochemical (PEC) performance in the superdomain structures compared to the (101)-oriented PZT films with conventional c/a domains. Furthermore, time-dependent pulse voltages are utilized to dynamically assess local currents and realize direct conductivity modulation by manipulating distinct polarization states. The elucidation of the photoelectrical mechanism and delineation of diverse pathways for intermediate state control underscore the potential of ferroelectric superdomains in constructing functional photoelectronic nanodevices.

Cooperative β-sheet coassembly controls intermolecular orientation of amphiphilic peptide-polydiacetylene conjugates

In this work, we elucidated the structural organization of stimuli-responsive peptide-polydiacetylene (PDA) conjugates that can self-assemble as 1D nanostructures under neutral aqueous conditions. The amino acid sequences bear positively or negatively charged domains at the periphery of the peptide segments to promote solubility in water while also driving assembly of the individual and combined components into β-sheets. The photopolymerization of PDA, as well as the sensitivity of the resulting optical properties of the polymeric material to external stimuli, highly depends on the structural organization of the assembly of amphiphilic peptide-diacetylene units into 1D-nanostructures. Solid-state NMR measurements on 13C-labeled and 15N-labeled samples show that positively charged and negatively charged peptide amphiphiles are each capable of self-assembly, but self-assembly favors antiparallel β-sheet structure. When positively and negatively charged peptide amphiphiles interact in stoichiometric solutions, cooperative coassembly dominates over self-assembly, resulting in the desired parallel β-sheet structure with a concomitant increase in structural order. These results reveal that rational placement of oppositely charged residues can control β-strand organization in a peptide amphiphile coassembly, which would have implications on the adaptive properties of stimuli-responsive biomaterials such as the peptide-PDAs studied here.