Domain Switching Research Articles

Promotion of Probabilistic Bit Generation in Mott Devices by Embedded Metal Nanoparticles.

Considerable attention has been drawn to the use of volatile two-terminal devices relying on the Mott transition for the stochastic generation of probabilistic bits (p-bits) in emerging probabilistic computing. To improve randomness and endurance of bit streams provided by these devices, delicate control of the transient evolution of switchable domains is required to enhance stochastic p-bit generation. Herein, it is demonstrated that the randomness of p-bit streams generated via the consecutive pulse inputs of pump-probe protocols can be increased by the deliberate incorporation of metal nanoparticles (NPs), which influence the transient dynamics of the nanoscale metallic phase in VO2 Mott switches. Among the vertically stacked Pt-NP-containing VO2 threshold switches, those with higher Pt NP density show a considerably wider range of p-bit operation (e.g., up to ≈300% increase in ΔVprobe upon going from (Pt NP/VO2)0 to (Pt NP/VO2)11) and can therefore be operated under the conditions of high speed (400 kbit s-1), low power consumption (14 nJ per bit), and high stability (>105200 bits) for p-bit generation. Thus, the study presents a novel strategy that exploits nanoscale phase control to maximize the generation of nondeterministic information sources for energy-efficient probabilistic computing hardware.

A phase-field model for study of ferroelastic deformation behavior in yttria stabilized zirconia

A modified phase-field model coupled with linear elasticity is formulated to study the effect of ferroelastic domain switching on the deformation behavior of tetragonal-prime yttria-stabilized zirconia. Simulations are performed under uniaxial tension and compression using realistic domain microstructures. This work provides new insights into the mechanism of ferroelastic deformation by studying the evolution of domains under different loading directions and strain rates. The model predicts realistic stress-strain curves consisting of stress-plateaus with accurate domain switching behavior without setting a switching criterion based on a critical stress for nucleation of new domains. The results reveal that the origin of coercive stress lies in the balance between the energy absorbed by the domain switching process and the externally applied energy. Loading in different directions but parallel to the spontaneous strain results in different levels of coercive stress as domain switching absorbs different amounts of energy. For the same reason when the strain-rate increases, the coercive stress also increases. This work establishes the relation between the coercive stress and microstructural changes during ferroelastic domain switching.

Spin‐Orbit Torque Switching of Magnetization in Ultra‐Thick Ferromagnetic Layers

AbstractCurrent‐induced magnetization switching via spin‐orbit torque (SOT) holds great potential for applications in high‐speed and energy‐efficient magnetic memory and logic devices. In the extensively studied heavy metal/ferromagnet (HM/FM) SOT heterostructures, the thickness of the FM layer is typically restricted to a few nanometers or less due to the rapid spin dephasing, making it challenging to implement thermally stable memory cells with high density. In this study, it is demonstrated that this thickness constraint can be significantly alleviated by utilizing an oxide ferromagnet La0.67Sr0.33MnO3 (LSMO). Through electrical transport and magnetic optical measurements, it is found that the SOT can switch the magnetization in Pt/LSMO heterostructures even at an LSMO thickness of 35 nm, which is one order of magnitude larger than that for metallic FMs, such as CoFeB. Furthermore, based on the FM thickness dependence of the switching current and the domain switching type revealed by magnetic optical Kerr effect imaging (MOKE), a possible picture is proposed to describe the SOT switching in Pt/LSMO, which highlights the critical role of the domain wall propagation in the vertical direction. The work provides valuable insights into the behavior of SOT switching in ultra‐thick FM films, offering new possibilities for their practical applications.

Domain Switching Characteristics in Ga-Doped HfO2 Ferroelectric Thin Films with Low Coercive Field.

The gallium-doped hafnium oxide (Ga-HfO2) films with different Ga doping concentrations were prepared by adjusting the HfO2/Ga2O3 atomic layer deposition cycle ratio for high-speed and low-voltage operation in HfO2-based ferroelectric memory. The Ga-HfO2 ferroelectric films reveal a finely modulated coercive field (Ec) from 1.1 (HfO2/Ga2O3 = 32:1) to an exceptionally low 0.6 MV/cm (HfO2/Ga2O3 = 11:1). This modulation arises from the competition between domain nucleation and propagation speed during polarization switching, influenced by the intrinsic domain density and phase dispersion in the film with specific Ga doping concentrations. Higher Ec samples exhibit a nucleation-dominant switching mechanism, while lower Ec samples undergo a transition from a nucleation-dominant to a propagation-dominant reversal mechanism as the electric field increases. This work introduces Ga as a viable dopant for low Ec and offers insights into material design strategies for HfO2-based ferroelectric memory applications.

Organic-Inorganic Hybrid Perovskite Ferroelectric Nanosheets Synthesized by a Room-Temperature Antisolvent Method.

Over the past years, the application potential of ferroelectric nanomaterials with unique physical properties for modern electronics is highlighted to a large extent. However, it is relatively challenging to fabricate inorganic ferroelectric nanomaterials, which is a process depending on a vacuum atmosphere at high temperatures. As significant complements to inorganic ferroelectric nanomaterials, the nanomaterials of molecular ferroelectrics are rarely reported. Here a low-cost room-temperature antisolvent method is used to synthesize free-standing 2D organic-inorganic hybrid perovskite (OIHP) ferroelectric nanosheets (NSs), that is, (CHA)2PbBr4 NSs (CHA = cyclohexylammonium), with an average lateral size of 357.59nm and a thickness ranging from 10 to 70nm. This method shows high repeatability and produces NSs with excellent crystallinity. Moreover, ferroelectric domains in single NSs can be clearly visualized and manipulated using piezoresponse force microscopy (PFM). The domain switching and PFM-switching spectroscopy indicate the robust in-plane ferroelectricity of the NSs. This work not only introduces a feasible, low-cost, and scalable method for preparing molecular ferroelectric NSs but also promotes the research on molecular ferroelectric nanomaterials.

Membrane protein guided and ATP-gated dual module DNA nanodevice for amplified fluorescence labeling of cancer cells

The occurrence and progression of tumors are accompanied by changes in both the microenvironment and cancer cells. Therefore, the detection of extracellular alert molecule accumulation, as well as the identification of abnormal cancer biomarkers both contribute to the accurate localization of individual cancer cells. Here, we have designed a cancer cell fluorescence labeling nanodevice with a membrane protein targeting domain and extracellular ATP-fueled amplification switch. The AND logic-based nanodevice light-up the cancer cell membrane only in the coexistence of target membrane proteins and abnormal ATP concentration. We demonstrated the ability of the nanodevice to selectively label target cells in a cell mixture supplemented with ATP at concentrations within the range in the tumor microenvironment (1–5×10−4 M). Additionally, the modular design of DNA nanodevices enables broad application to different cancer cells by replacing them with corresponding membrane protein aptamers. Our fluorescence labeling nanodevice with signal amplification shows promise in serving as an imaging tool for visualizing the impact of ATP regulation on cancer evolution.

Ultrahigh strain and superior temperature stability in lead-free ceramics via synergetic texture technique and phase structure engineering

Lead-free piezoelectric ceramics with large strain response and good temperature stability are highly required for actuator applications. However, the search for lead-free ceramics with both enhanced strain and reduced thermal-dependent behavior is a great challenge. In this work, by employing templated grain growth technique and elaborately modulate the phase structure, large unipolar strain of 0.30 %, low strain hysteresis Hs ∼ 12 %, along with small strain variation 11.8 % between 20 and 100 °C are achieved in (001)C-oriented (Ba0.95Ca0.05)(Sn0.04Ti0.96)O3 ceramics, being the optimal level of BaTiO3 family. It is revealed the ceramics exhibit a coexistence of orthorhombic and tetragonal phases. The inherent piezoelectric anisotropy of orthorhombic phase, the reversible a→c domain switch, along with the refined non-180° domain structures contribute to the remarkable electrostrain characteristic. This study proposed a promising strategy to develop high performance piezoelectric materials for actuator applications.

Significant Enhancement of Electrocaloric Effect in Ferroelectric Polycrystalline Ceramics Through Grain Boundary Barrier Engineering

AbstractA key challenge currently for the new ferroelectric refrigeration with high efficiency and environmental friendliness lies in the urgent demand for ferroelectric materials with huge electrocaloric effects (ECE). Ferroelectric polycrystalline ceramics with high ECE stand out as one of the most promising candidates for electrocaloric cooling applications. However, the grain boundary network, as a barrier for the cross‐transmission of charged carriers, widely exists in electrocaloric polycrystalline ceramics and is often neglected in favor of focusing more on composition regulation and structural design. Herein, a grain boundary barrier engineering is proposed that regulates the Schottky barrier at the grain boundary network in the Ba0.8Zr0.2TiO3 ceramics by a maneuverable annealing process and clarifies its critical role in enhancing the ECE of polycrystalline ceramics. As a result, a substantial enhancement of the EC performance (from 0.68 to 1.63 K at 50 °C and 80 kV cm−1, ≈2.4 times) has been achieved in the annealed Ba0.8Zr0.2TiO3 ceramics with a lower Schottky barrier. The microstructural and electrical characterization reveals that the lower Schottky barrier in the grain boundary network facilitates the domain switching and electronic transition, hence resulting in enhanced polarization response and EC performance.

Phosphorylation in the Ser/Arg-rich region of the nucleocapsid of SARS-CoV-2 regulates phase separation by inhibiting self-association of a distant helix

The nucleocapsid protein (N) of SARS-CoV-2 is essential for virus replication, genome packaging, evading host immunity, and virus maturation. N is a multidomain protein composed of an independently folded monomeric N-terminal domain that is the primary site for RNA binding, and a dimeric C-terminal domain that is essential for efficient phase separation and condensate formation with RNA. The domains are separated by a disordered Ser/Arg-rich region preceding a self-associating Leu-rich helix. Phosphorylation in the Ser/Arg region in infected cells decreases the viscosity of N:RNA condensates promoting viral replication and host immune evasion. The molecular level effect of phosphorylation, however, is missing from our current understanding. Using NMR spectroscopy and analytical ultracentrifugation we show that phosphorylation destabilizes the self-associating Leu-rich helix 30 amino acids distant from the phosphorylation site. NMR and gel shift assays demonstrate that RNA binding by the linker is dampened by phosphorylation, whereas RNA binding to the full-length protein is not significantly affected presumably due to retained strong interactions with the primary RNA binding domain. Introducing a switchable self-associating domain to replace the Leu-rich helix confirms the importance of linker self-association to droplet formation and suggests that phosphorylation not only increases solubility of the positively charged elongated Ser/Arg region as observed in other RNA binding proteins but can also inhibit self-association of the Leu-rich helix. These data highlight the effect of phosphorylation both at local sites and at a distant self-associating hydrophobic helix in regulating liquid-liquid phase separation of the entire protein.

Effect of Pr3+ doping on relaxation behavior and strain response of PHT-based piezoelectric ceramics

Heterovalent ion doping has influenced the further development of piezoelectric applications. Pr3+ doping in relaxor ferroelectrics is rarely focused on piezoelectric performance enhancement. 0.51 Pb(Ni1/3Nb2/3)O3-0.49 Pb(Hf0.3Ti0.7)O3 (PNN-49PHT) ceramics with Pr3+ doping ceramics were designed and fabricated by a two-step precursor method. Excellent dielectric diffusion coefficient (γ) of 1.96 was achieved at the low Pr3+ doping concentration of 0.2 %. Increased relaxation enhanced the nanoscale domains formation, resulting in a giant strain response (d*33) of 1400 pm/V at 10 kV/cm, and a total strain (Stol) of 0.27 % at 20 kV/cm. Structural refinement unveiled that the high piezoelectricity originated from the mainly substitution of Pr3+ for Pb2+ at the A-site, inducing lattice distortion and phase transitions. Local domain switching and long-range ordered destruction were investigated by piezoresponse force microscopy (PFM) and Scanning Electron Microscopy (SEM). These findings contribute to the advancement of piezoelectric devices and provide valuable insights for the design and optimization of high-performance piezoelectric ceramics.

Domain wall dynamics in stress annealed microwires

In this work we investigate the effect of stress-annealing on the magnetic properties and domain wall dynamics of CoFeNi-based microwires with nearly-zero magnetostriction. Among the annealing parameters whose influence we studied are time and temperature, as well as the magnitude of the stresses applied during annealing. We demonstrate that heat treatment and stress application have the opposite effects on the switching field and domain wall mobility. Therefore, their combination can be used to tune the parameters of the domain wall dynamics over the wide range. We found that stress annealing can increase the domain wall mobility by up to 3 times comparing to annealing without any stress. The maximum domain wall mobility achieved for the studied microwire is 95 m2/sA.

Enhanced electric field-induced strain performance in 0–3 composite ceramics by strain and polarization coupling

Inferior electric field-induced strain and large hysteresis in the high-temperature (1-x)BiFeO3-xBaTiO3-based piezoceramics under low driving electric field, which restricts their practical applications, are dramatically technical bottlenecks. Herein, we successfully prepare the 0–3 type composite piezoceramics with super strain properties under a small electric field. Electric field-induced strain and normalized strain coefficient in the 0–3 composite piezoceramics have been severally increased by 161% and 215% than those of non-composite piezoceramics, and the hysteresis and remnant strain in the 0–3 composite piezoceramics have been decreased by 230% and 165% compared with non-composite piezoceramics. Superior electric field-induced strain properties originate from strain and polarization couple, promoting domain switching at low driving electric field, and the novel strategy will accelerate the development and practical applications of lead-free piezoelectric ceramics.

Novel strategies for low-voltage NAND flash memory with negative capacitance effect

Here, we present a novel approach to employing a negative capacitance (NC) phenomenon in the blocking oxide of charge trap flash (CTF) memory. To achieve this, we developed an inversible mono-domain like ferroelectric (IMFE) film through high-pressure post-deposition annealing in a forming gas at 200 atm (FG-HPPDA). The FG-HPPDA process enables to form a uniform alignment of domains and facilitates invertible domain switching behavior in ferroelectrics, generating an internal field by the flexo-electric effect as well as interface-pinned polarization by chemical reaction. Subsequently, to stabilize the NC effect, we fabricated the IMFE/Al2O3 heterostructure, which exhibits an outstanding capacitance-boosting feature. Finally, we successfully demonstrate unprecedented CTF memory with the NC effect in a blocking oxide. Our unique CTF device shows the improved performance (maximum incremental-step-pulse-programming (ISPP) slope ∼1.05) and a large MW (>8 V), attributed to the capacitance boosting by NC phenomenon.

Large electrocaloric effect near room temperature induced by domain switching in ferroelectric nanocomposites

The solid-state refrigeration technique based on the electrocaloric effect (ECE) of ferroelectric materials has been regarded as a promising alternative to vapor compression systems due to its advantages of high efficiency and easy miniaturization. However, the small adiabatic temperature change (ATC) and narrow operating temperature range of ferroelectric materials are key obstacles for their practical applications of ECE refrigeration. To improve the ECE performance of ferroelectric polymer poly(vinylidene fluoride) [P(VDF-TrFE)], PbZr1−xTixO3 (PZT) nanoparticles with larger polarization is herein introduced to form ferroelectric nanocomposites. The phase-field simulation is employed to investigate the dynamic hysteresis loops and corresponding domain evolution of the ferroelectric nanocomposites. The temperature-dependent ATC values are calculated using the indirect method based on the Maxwell relation. The appearance of the double hysteresis loop is observed in P(VDF-TrFE) nanocomposite filled with PbZr0.1Ti0.9O3 nanoparticles [P(VDF-TrFE)–PZT0.9], which is mainly caused by a microscopic domain transition from single domain to polar vortex. Compared to the P(VDF-TrFE), enhanced ATC values associated with the domain transition are unveiled in P(VDF-TrFE)–PZT0.9, and the temperature range of excellent ECE is also effectively broadened. In addition, as the component x of filled PZT nanoparticles increases to cross the morphotropic phase boundary (MPB), the maximum ATC value shows a significant increase. The results presented in this work not only explain the mechanism of domain transition induced excellent ECE in the P(VDF-TrFE)–PZT nanocomposite, but also stimulate future studies on enhancing ECE of P(VDF-TrFE) by introducing ferroelectric nanofillers.

Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane.

The engineering of ferroic orders, which involves the evolution of atomic structure and local ferroic configuration in the development of next-generation electronic devices. Until now, diverse polarization structures and topological domains are obtained in ferroelectric thin films or heterostructures, and the polarization switching and subsequent domain nucleation are found to be more conducive to building energy-efficient and multifunctional polarization structures. In this work, a continuous and periodic strain in a flexible freestanding BaTiO3 membrane to achieve a zigzag morphology is introduced. The polar head/tail boundaries and vortex/anti-vortex domains are constructed by a compressive strain as low as ≈0.5%, which is extremely lower than that used in epitaxial rigid ferroelectrics. Overall, this study c efficient polarization structures, which is of both theoretical value and practical significance for the development of next-generation flexible multifunctional devices.

Domain reorientation due to smectic layer instability in high tilt angle-based surface stabilized ferroelectric liquid crystal cell

High tilt angle (45°) ferroelectric liquid crystal (FLC) in surface stabilized geometry, having no chiral smectic A (SmA∗) phase, has been studied for the reorientation of the smectic layers near the transition temperature (Tc). The electro-optical studies have shown the stripe domain formation in which the liquid crystal molecules are aligned along the rubbing direction, but the smectic layers are tilted away from the rubbing direction at room temperature. In such high tilt angle FLCs, the molecular alignment and smectic layer formation start from bottom and top rubbed grooves at Tc. The domain formation of the FLC takes place in the middle of the top and bottom surfaces due to the frustration of the dipolar interaction. The smectic layer switching is observed by optical microscopy and confirmed by the dielectric spectroscopy method near Tc of SmC∗ and chiral nematic phases. Domain switching has shown a larger switching angle than the molecular tilt angle within the smectic layer. These studies are expected to be significant for understanding the smectic layer structure and the domain switching process, which may pave the way for large optical switching devices.

A remarkable genetic shift in a transmitted/founder virus broadens antibody responses against HIV-1

A productive HIV-1 infection in humans is often established by transmission and propagation of a single transmitted/founder (T/F) virus, which then evolves into a complex mixture of variants during the lifetime of infection. An effective HIV-1 vaccine should elicit broad immune responses in order to block the entry of diverse T/F viruses. Currently, no such vaccine exists. An in-depth study of escape variants emerging under host immune pressure during very early stages of infection might provide insights into such a HIV-1 vaccine design. Here, in a rare longitudinal study involving HIV-1 infected individuals just days after infection in the absence of antiretroviral therapy, we discovered a remarkable genetic shift that resulted in near complete disappearance of the original T/F virus and appearance of a variant with H173Y mutation in the variable V2 domain of the HIV-1 envelope protein. This coincided with the disappearance of the first wave of strictly H173-specific antibodies and emergence of a second wave of Y173-specific antibodies with increased breadth. Structural analyses indicated conformational dynamism of the envelope protein which likely allowed selection of escape variants with a conformational switch in the V2 domain from an α-helix (H173) to a β-strand (Y173) and induction of broadly reactive antibody responses. This differential breadth due to a single mutational change was also recapitulated in a mouse model. Rationally designed combinatorial libraries containing 54 conformational variants of V2 domain around position 173 further demonstrated increased breadth of antibody responses elicited to diverse HIV-1 envelope proteins. These results offer new insights into designing broadly effective HIV-1 vaccines.

A remarkable genetic shift in a transmitted/founder virus broadens antibody responses against HIV-1.

A productive HIV-1 infection in humans is often established by transmission and propagation of a single transmitted/founder (T/F) virus, which then evolves into a complex mixture of variants during the lifetime of infection. An effective HIV-1 vaccine should elicit broad immune responses in order to block the entry of diverse T/F viruses. Currently, no such vaccine exists. An in-depth study of escape variants emerging under host immune pressure during very early stages of infection might provide insights into such a HIV-1 vaccine design. Here, in a rare longitudinal study involving HIV-1 infected individuals just days after infection in the absence of antiretroviral therapy, we discovered a remarkable genetic shift that resulted in near complete disappearance of the original T/F virus and appearance of a variant with H173Y mutation in the variable V2 domain of the HIV-1 envelope protein. This coincided with the disappearance of the first wave of strictly H173-specific antibodies and emergence of a second wave of Y173-specific antibodies with increased breadth. Structural analyses indicated conformational dynamism of the envelope protein which likely allowed selection of escape variants with a conformational switch in the V2 domain from an α-helix (H173) to a β-strand (Y173) and induction of broadly reactive antibody responses. This differential breadth due to a single mutational change was also recapitulated in a mouse model. Rationally designed combinatorial libraries containing 54 conformational variants of V2 domain around position 173 further demonstrated increased breadth of antibody responses elicited to diverse HIV-1 envelope proteins. These results offer new insights into designing broadly effective HIV-1 vaccines.

Polarization fatigue mechanism of laminated hafnium zirconium oxide ferroelectric thin films

Laminated HfO2-based ferroelectric thin films (FE-HfO2) have offered unexpected opportunities to implement the high-density ferroelectric memory and on chip piezoelectric or pyroelectric devices. But the polarization fatigue performance is poor and the underlying mechanism is unknown. In this work, we comprehensively investigate the polarization fatigue behaviors of Hf0.5Zr0.5O2(HZO)/Al2O3/HZO laminated thin films. Several possible mechanisms for the fatigue performances are discussed in detail. On basis of the analysis of micro-structures and domain switching dynamics before and after fatigue, we confirm that domain wall pinning phenomenon exists in the fatigued laminated HZO, without field-induced phase transition as well as thickness and chemical properties changes of interfacial layers. Moreover, we discover by a pulse measurement method that domain wall pinning induced by the increase of Al2O3/HZO interface trap charge is responsible for the fatigue performances of the laminated films. This work will provide useful guidance for designing high-reliability laminated FE-HfO2, and contribute to understand the physical mechanisms of FE-HfO2.

Simultaneously enhanced of energy storage and energy harvesting performances of [(Bi0.5Na0.5)TiO3–BaTiO3] ceramics by addition of SrTiO3

As is well known, relaxor dielectrics are characterized by high energy storage efficiency (η), while high recoverable energy storage density (Wrec) can be achieved by anti-ferroelectric ceramics. Herein, our approach is to find relaxor- anti-ferroelectric coexistence phases of (Bi0.5Na0.5)TiO3- BaTiO3 ceramics for achieving high performance in energy storage and energy harvesting as well. Therefore, [(0.9-x) ( Bi0.5Na0.5)TiO3-xSrTiO3-0.1BaTiO3] (abbreviation (0.9-x) NBT-0.1BT-xST) (0.0 ≤ x ≤ 0.4) were synthesized via the solid-state reaction route in air. The tolerance factor (τ) increased from 0.9901 to 0.9998 when ST-content increased from 0.0 to 0.4, indicating an increase in crystal lattice symmetry. The FT-IR de-convolution vibration modes shown in the TiO6 octahedra exhibit two peaks at ∼550 and 650 cm−1, which indicate present coexistence phases of the crystal structure. Ferroelectric to relaxor phase crossover has been detected by the addition of ST with the present anti-ferroelectric phase in particular dopant ST = 0.2. The increasing into the diffused phase transition (γ) is signified by enhancement of the relaxor degree of NBT-BT at high content of ST. The rapidly suppressed remnant polarization (Pr) at high content of ST is due to substitute iso-valence (Sr2+) by tri-valence (Bi3+) and mono-valence (Na1+). Ultrahigh Wrec = 1.13 J/ cm3 with excellent η = 92.62% were obtained at ST = 0.3 at low electric field (E = 110 kV cm−1). A remarkable response of the strain with a high converse piezoelectric coefficient ( d33* = 390.47 pm V−1) at ST = 0.2 was obtained due to decreasing the non-revisable 180° domain switching. Based on the obtained results, the addition of ST to NBT-BT ceramics can provide a head start in the implementation of ceramic capacitors for potential effective into energy harvesting and energy storage applications.