Domain Rotation Research Articles

Heteroepitaxial Growth of NiO Thin Films on (‐201) β‐Ga2O3 by Mist Chemical Vapor Deposition

The growth of NiO epitaxial thin films on (‐201) β‐Ga2O3 by mist chemical vapor deposition (CVD) and the effects of carrier gas selection (N2 and O2) and substrate preannealing treatment on the structural and morphological properties on the grown thin films are explored. X‐ray diffraction analysis reveals successful epitaxial growth with the orientation relationship (111) NiO [0‐11] || (‐201) β‐Ga2O3 [010]. As a carrier gas, O2 results in single‐domain NiO films while N2 leads to the formation of rotational domains. Atomic force microscopy and field‐emission scanning electron microscopy confirm the lateral growth of NiO films, thus highlighting the importance of substrate preannealing at 1200 °C in oxygen atmosphere to obtain flat, high‐quality films. The results demonstrate that the method of mist CVD combined with appropriate substrate preparation and carrier gas selection is effective for the growth of high‐quality NiO/β‐Ga2O3 heterostructures. This achievement opens new possibilities for the development of wide‐bandgap p–n heterojunctions, potentially advancing the field of high‐power oxide‐based electronic devices.

A high-power piezoelectric ceramic with great electrical properties and temperature stability

Lead-based Pb(Zr, Ti)O3 ceramics have been widely used in high-power piezoelectric applications, but its stable operation at high temperature is still a grand challenge. In this work, the third element Pb(Mn1/3Sb2/3)O3 (PMS) was incorporated into Pb(Zr0.48Ti0.52)O3 (PZT) to design the xPb(Mn1/3Sb2/3)O3-(1-x)Pb(Zr0.48Ti0.52)O3 (PMS-PZT) ternary ceramics through the phase diagram. The ceramics with morphotropic phase boundary (MPB) structure and uniform grain size were fabricated successfully. The dielectric, ferroelectric and piezoelectric properties of the ceramics were probed respectively. Excellent piezoelectric properties (Qm=1595, kp=0.61, d33=318pC/N, tanδ=0.60 %, Tc=300℃) were obtained in 0.075PMS-0.925PZT ceramic, which can be attributed to its MPB structure and the pinning effect of defect dipoles on domain rotation. Moreover, the T-phase dominated 0.075PMS-0.925PZT ceramic obtains great temperature stability with a low variation of resonant frequency below 2.2 % and no variation of non-resonant frequency in the temperature range from 25°C to 175°C. These results make the ceramic as a good candidate for piezoelectric frequency applications that require constant performance within a wide temperature range.

Molecular mechanism of β-arrestin-2 pre-activation by phosphatidylinositol 4,5-bisphosphate

Phosphorylated residues of G protein-coupled receptors bind to the N-domain of arrestin, resulting in the release of its C-terminus. This induces further allosteric conformational changes, such as polar core disruption, alteration of interdomain loops, and domain rotation, which transform arrestins into the receptor-activated state. It is widely accepted that arrestin activation occurs by conformational changes propagated from the N- to the C-domain. However, recent studies have revealed that binding of phosphatidylinositol 4,5-bisphosphate (PIP2) to the C-domain transforms arrestins into a pre-active state. Here, we aimed to elucidate the mechanisms underlying PIP2-induced arrestin pre-activation. We compare the conformational changes of β-arrestin-2 upon binding of PIP2 or phosphorylated C-tail peptide of vasopressin receptor type 2 using hydrogen/deuterium exchange mass spectrometry (HDX-MS). Introducing point mutations on the potential routes of the allosteric conformational changes and analyzing these mutant constructs with HDX-MS reveals that PIP2-binding at the C-domain affects the back loop, which destabilizes the gate loop and βXX to transform β-arrestin-2 into the pre-active state.

Rotation and Self-Assembly Driving NLRP3 Activation.

As a critical sensor protein, NLRP3 detects cellular perturbation caused by diverse exogenous and endogenous stimuli. NLRP3 activation requires domain rotation within the NEK7-bound NLRP3 monomer and assembly. However, a detailed molecular mechanism for NLRP3 assembly and activation remains elusive, particularly in terms of dynamics and energetics. In this work, all-atom molecular dynamics (MD) simulations are executed to describe large-amplitude closed-to-open conformational transitions along the rotational pathway. From the MD trajectories, the computed potential of mean force (PMF) shows that NLRP3 activation through monomeric domain rotation is an uphill process, during which the active conformation of the NLRP3-NEK7 monomer cannot be stabilized. Further binding free-energy calculations for two neighboring NLRP3-NEK7 subunits in a disc assembly with the C10 symmetry reveal that the protein self-assembly starts approximately at the 86.5° position on the rotary pathway, along which the NLRP3 activation becomes a downhill process to the active state at 90.5°. The active NLRP3-NEK7 monomeric conformation in the disc assembly is stabilized because of the interactions between the neighboring subunits, involving mainly FISNA loop 1 in one subunit and a "crocodile-clip" structure formed by the NBD helix-loop-strand motif (residues 351-373) and the WHD β-hairpin loop (residues 501-521) in the other. Our simulations also demonstrate that NEK7 plays an important role in the NLRP3 cage dissociation in the centrosome, which is consistent with biological experiments. The computational results provide kinetic, energetic, and structural insights into the molecular mechanisms of the activation of NLRP3 and the NEK7-driven dissociation of inactive NLRP3 cages. The activation mechanism of NLRP3 proposed in this work is significantly different from those of previous structural studies.

MHz cut-off frequency and permeability mechanism of iron-based soft magnetic composites

Abstract The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments. Here, a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported. The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring, the distribution of particles, and the particle size. The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect. An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data. This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.

Mapping the antiparallel aligned domain rotation by microwave excitation

Mapping the antiparallel aligned domain rotation by microwave excitation

Magnetic Barkhausen Noise: Aspects of Generation and Modeling

The Magnetic Barkhausen noise (MBN) techniquemeasures discrete changes in magnetization, known as“Barkhausen jumps”, whi ch can be seen as steps i n the hysteresis curve. When a ferro-magnetic material issubjected to an external varying magnetic field, themagnetization of the material wil l change in a non-linearway. These changes in magnetization are described by thehysteresis curve and are the result of modifications of domain structure of the material. Changes in magnetizationare caused by domain wall creation, domain wallannihilation, domain wall motion and rotation. In order toimprove the interpretation of Barkhausen noise, models areneeded which describe the dependence of magnetization on material properties.

Improving interfacial magnetoelastic effect and complex permeability of FeSiAl alloy powders for broadband decimeter-wave absorption via Cr doping

This study showcases the interfacial magnetoelastic effect observed in flaky FeSiAl alloy powder absorbents, aimed at enhancing permeability in the decimeter-wave band for better absorption performance through Cr doping via wet ball-milling and subsequent annealing processes. The wet ball milling process facilitates the formation of a lamellar structure by inducing slip along shear stress in DO3 and α-Fe nanocrystals. During annealing, the introduced Cr element partially impedes the transition from the α-Fe phase to the DO3 phase, thereby amplifying the difference in magnetostrictive coefficients between these phases. Consequently, the flaky FeSiAlCr powders exhibit notably increased initial permeability and resonance frequency, particularly around 3 GHz, owing to domain rotation in the DO3 phase. In comparison to previously reported counterparts, the composite derived from these powders demonstrates a significant enhancement in the real part of effective permeability by approximately 66 %, alongside a 17 % reduction in density. Consequently, this composite exhibits a lowered reflection loss of below −5 dB within the frequency range of 0.7–3 GHz, reaching a minimum of −11 dB at 1.57 GHz, specifically with a thickness of 1.6 mm. These findings present an effective strategy for enhancing the magnetic permeability of alloy powders. The resultant microwave absorbing materials hold promising applications in stealth technology and wireless communication electronics.

Sn-doped β-Ga2O3 thin films grown on off-axis sapphire substrates by LPCVD using Ga-Sn alloy solid source

Adopting low pressure chemical vapor deposition (LPCVD), Sn-doped β-Ga2O3 thin films were heteroepitaxially grown on c-plane sapphire substrates with off-axis angles towards 〈11–20〉 direction. The influences of off-axis angle on crystal structures, electrical properties, surface morphology, and chemical compositions were thoroughly investigated. As a result, the crystallinity of the β-Ga2O3 films is improved with increasing off-axis angles because in-plane rotational domains are effectively suppressed, demonstrating a full width at half maximum (FWHM) down to 0.64°. Correspondingly, the Hall carrier mobility is promoted from 4.7 to 17.9 cm2/V·s at carrier concentration of 9 × 1017 cm−3, which is believed highly competitive among reported Sn-doped β-Ga2O3 films by LPCVD. These results demonstrate an alternative pathway to heteroepitaxially grow high electrical quality n-doped β-Ga2O3 films for the advancement of Ga2O3 materials and devices.

Arg40 is critical for stability and activity of Adenylosuccinate lyase; a purine salvage enzyme from Leishmania donovani

Purine salvage enzymes have been of significant interest in anti-Leishmanial drug development due to the parasite's critical dependence on this pathway for the supply of nucleotides in the absence of a de novo purine synthesis pathway. Adenylosuccinate lyase (ADSL) one of the key enzymes in this pathway is a homo-tetramer, where the active site is formed by residues from three distinct subunits. Analysis of the subunit interfaces of LdADSL, revealed a conserved Arg40 forming critical inter-subunit interactions and also involved in substrate binding. We hypothesized that mutating this residue can affect both the structural stability and activity of the enzyme. In our study, we used biochemical, biophysical, and computational simulation approaches to understand the structural and functional role of Arg40 in LdADSL. We have replaced Arg40 with an Ala and Glu using site directed mutagenesis. The mutant enzymes were similar to wild-type enzyme in secondary structure and subunit association. Thermal shift assays indicated that the mutations affected the protein stability. Both mutants showed decreased specific activities in both forward and reverse directions with significantly weakened affinities towards succinyl-adenosine monophosphate (SAMP). The mutations resulted in changes in C3 loop conformation and D3 domain rotation. Consequently, the orientation of the active site amino acid residues changed resulting in compromised activity and stability. Studies so far have majorly focused on the ADSL active site for designing drugs against it. Our work indicates that an alternative inhibitory mechanism for the enzyme can be designed by targeting the inter-subunit interface.

Texture and phase transition hysteresis in epitaxially integrated VO2 films on TiN/Si(100)

Vanadium oxide (VO2), which exhibits a metal-to-insulator (MIT) transition at 68∘C, has been of immense technological interest for many applications such as sensor, electro-optic, and memory devices. In this work, we demonstrate the epitaxial integration of VO2 onto Si(100) via a TiN buffer layer, which is compatible with complementary metal–oxide–semiconductor (CMOS) technology. Our study revealed that the growth of epitaxial VO2 on TiN was mediated by a thin layer of epitaxial TiO2. The orientation relationship between various layers was established to be (011)V O2M∥ (110)TiO2∥ (100)TiN∥ (100)Si and [100]V O2M∥ [001]TiO2∥ [011]TiN∥ [011]Si. Through pole figures, reciprocal space maps (RSM), and transmission electron microscopy (TEM), we confirmed the presence of tilted rotational domains. We quantified the degree of misorientation in various VO2 films by introducing a relevant parameter, η, determined by analyzing the (011) pole figures. We found a correlation indicating that the thermal hysteresis of the phase transition, determined from in-situ temperature-dependent XRD, decreases with the degree of misorientation. This decrease in misorientation suggests the presence of more geometrically compatible grain boundaries, leading to a decrease in thermal hysteresis.

Structure of an open KATP channel reveals tandem PIP2 binding sites mediating the Kir6.2 and SUR1 regulatory interface

ATP-sensitive potassium (KATP) channels, composed of four pore-lining Kir6.2 subunits and four regulatory sulfonylurea receptor 1 (SUR1) subunits, control insulin secretion in pancreatic β-cells. KATP channel opening is stimulated by PIP2 and inhibited by ATP. Mutations that increase channel opening by PIP2 reduce ATP inhibition and cause neonatal diabetes. Although considerable evidence has implicated a role for PIP2 in KATP channel function, previously solved open-channel structures have lacked bound PIP2, and mechanisms by which PIP2 regulates KATP channels remain unresolved. Here, we report the cryoEM structure of a KATP channel harboring the neonatal diabetes mutation Kir6.2-Q52R, in the open conformation, bound to amphipathic molecules consistent with natural C18:0/C20:4 long-chain PI(4,5)P2 at two adjacent binding sites between SUR1 and Kir6.2. The canonical PIP2 binding site is conserved among PIP2-gated Kir channels. The non-canonical PIP2 binding site forms at the interface of Kir6.2 and SUR1. Functional studies demonstrate both binding sites determine channel activity. Kir6.2 pore opening is associated with a twist of the Kir6.2 cytoplasmic domain and a rotation of the N-terminal transmembrane domain of SUR1, which widens the inhibitory ATP binding pocket to disfavor ATP binding. The open conformation is particularly stabilized by the Kir6.2-Q52R residue through cation-π bonding with SUR1-W51. Together, these results uncover the cooperation between SUR1 and Kir6.2 in PIP2 binding and gating, explain the antagonistic regulation of KATP channels by PIP2 and ATP, and provide a putative mechanism by which Kir6.2-Q52R stabilizes an open channel to cause neonatal diabetes.

Recent Developments in (K, Na)NbO3-Based Lead-Free Piezoceramics.

(K0.5Na0.5)NbO3 (KNN)-based ceramics have been extensively investigated as replacements for Pb(Zr, Ti)O3-based ceramics. KNN-based ceramics exhibit an orthorhombic structure at room temperature and a rhombohedral-orthorhombic (R-O) phase transition temperature (TR-O), orthorhombic-tetragonal (O-T) phase transition temperature (TO-T), and Curie temperature of -110, 190, and 420 °C, respectively. Forming KNN-based ceramics with a multistructure that can assist in domain rotation is one technique for enhancing their piezoelectric properties. This review investigates and introduces KNN-based ceramics with various multistructures. A reactive-templated grain growth method that aligns the grains of piezoceramics in a specific orientation is another approach for improving the piezoelectric properties of KNN-modified ceramics. The piezoelectric properties of the [001]-textured KNN-based ceramics are improved because their microstructures are similar to those of the [001]-oriented single crystals. The improvement in the piezoelectric properties after [001] texturing is largely influenced by the crystal structure of the textured ceramics. In this review, [001]-textured KNN-based ceramics with different crystal structures are investigated and systematically summarized.

Extracting Micro-Doppler Features from Multi-Rotor Unmanned Aerial Vehicles Using Time-Frequency Rotation Domain Concentration

This study addresses the growing concern over the impact of small unmanned aerial vehicles (UAVs), particularly rotor UAVs, on air traffic order and public safety. We propose a novel method for micro-Doppler feature extraction in multi-rotor UAVs within the time-frequency transform domain. Utilizing competitive learning particle swarm optimization (CLPSO), our approach divides population dynamics into three subgroups, each employing unique optimization mechanisms to enhance local search capabilities. This method overcomes limitations in traditional Particle Swarm Optimization (PSO) algorithms, specifically in achieving global optimal solutions. Our simulation and experimental results demonstrate the method’s efficiency and accuracy in extracting micro-Doppler features of rotary-wing UAVs. This advancement not only facilitates UAV detection and identification but also significantly contributes to the fields of UAV monitoring and airspace security.

Atomic-scale investigation of γ-Ga2O3 deposited on MgAl2O4 and its relationship with β-Ga2O3

Nominally phase-pure γ-Ga2O3 was deposited on (100) MgAl2O4 within a narrow temperature window centered at ∼470 °C using metal-organic chemical vapor deposition. The film deposited at 440 °C exhibited either poor crystallization or an amorphous structure; the film grown at 500 °C contained both β-Ga2O3 and γ-Ga2O3. A nominally phase-pure β-Ga2O3 film was obtained at 530 °C. Atomic-resolution scanning transmission electron microscopy (STEM) investigations of the γ-Ga2O3 film grown at 470 °C revealed a high density of antiphase boundaries. A planar defect model developed for γ-Al2O3 was extended to explain the stacking sequences of the Ga sublattice observed in the STEM images of γ-Ga2O3. The presence of the 180° rotational domains and 90° rotational domains of β-Ga2O3 inclusions within the γ-Ga2O3 matrix is discussed within the context of a comprehensive investigation of the epitaxial relationship between those two phases in the as-grown film at 470 °C and the same film annealed at 600 °C. The results led to the hypotheses that (i) incorporation of certain dopants, including Si, Ge, Sn, Mg, Al, and Sc, into β-Ga2O3 locally stabilizes the “γ-phase” and (ii) the site preference(s) for these dopants promotes the formation of “γ-phase” and/or γ-Ga2O3 solid solutions. However, in the absence of such dopants, pure γ-Ga2O3 remains the least stable Ga2O3 polymorph, as indicated by its very narrow growth window, lower growth temperatures relative to other Ga2O3 polymorphs, and the largest calculated difference in Helmholtz free energy per formula unit between γ-Ga2O3 and β-Ga2O3 than all other polymorphs.

A DNA rotary nanodevice operated by enzyme-initiated strand resetting.

DNA nanostructures that respond to external stimuli have found applications in several areas such as biosensing, drug delivery and molecular computation. The use of different types of stimuli in a single operation provides another layer of control for the reconfiguration of nucleic acid nanostructures. This work demonstrates the use of a ribonuclease to "unset" a nucleic acid nanodevice based on the paranemic crossover (PX) DNA and specific DNA inputs to "reset" the structure into a juxtaposed DNA (JX2) configuration, resulting in a 180° rotation of the helical domains. Such operations would be useful in translational applications where DNA nanostructures can be designed to reconfigure on the basis of more than one stimulus.

Tunable sequential pathways through spatial partitioning and frustration tuning in soft metamaterials.

Elastic instabilities have been leveraged in soft metamaterials to attain novel functionalities such as mechanical memory and sequential pathways. Pathways have been realized in complex media or within a collection of hysteretic elements. However, much less has been explored in frustrated and partitioned soft metamaterials. In this work, we introduce spatial partitioning as a method to localize deformation in sub-regions of a large and soft metamaterial. The partitioning is achieved through the strategic arrangement of soft inclusions in a soft lattice, which form distinct regions behaving as mechanical units. We examine two partitions: an equally spaced layer partition with mechanical units connected in series, and a cross partition, represented by interconnected series of mechanical units in parallel. Sequential pathways are obtained by frustrating the partitioned metamaterial post-manufacture and are characterized by tracking the polarization change in each partition region. Through a combination of experiments and simulations, we demonstrate that partitioning enables tuning the pathway from longitudinal with weak interactions to a pathway exhibiting strong interactions rising from geometric incompatibility and central domain rotation. We show that tuning the level of uniform lateral pre-strain provides a wide range of tunability from disabling to modifying the sequential pathway. We also show that imposing a nonuniform confinement and altering the tilting of one or two of the domain edges enables to program the pathway, access a larger set of states, and tune the level of interaction between the regions.

An improved stress-dependent magnetostriction model of silicon steel based on simplified multi-scale and Jiles–Atherton theory

Due to the magnetic domain movement and energy change under magnetic field and stress applied, the macroscopic magnetic properties and magnetostriction properties of non-oriented (NO) silicon steel are influenced. To present this effect of the magnetic domains’ motion mechanism, a stress-dependent magnetostriction must be modeled. This paper proposes an improved stress-dependent magnetostriction model (I-SDM model) for NO silicon steel based on a simplified multi-scale model. Firstly, the stress-dependent expression of the anhysteretic magnetization, obtained by assuming a six-domain structure and considering the volume fraction of magnetic domain energy, is introduced into the inverse Jiles–Atherton (JA) model. In this way, the stress-dependent hysteresis model is constructed. Then, coupling with the improved quadratic domain rotation model that considers pinning effects, the I-SDM model for NO silicon steel is built. Finally, with the parameters obtained from experimental results, the proposed model under varying stresses is simulated and compared with other models. It shows that the proposed model has the highest simulated accuracy for both λ-H loop and λ-B loop with stress applied.

Exceptional stress-director coupling at the crack tip of a liquid crystal elastomer

A liquid crystal elastomer (LCE) is a special elastomer containing rod-like liquid crystals, which align in a certain direction, called the director. The director of a LCE can rotate under stress, resulting in large spontaneous strain and soft elastic behavior. This study unravels how the strong stress-director coupling in a monodomain LCE induces unique crack-tip fields and fracture behavior. Through stretching edge-cracked LCEs with various initial directors, we characterize the displacement and director fields theoretically and experimentally. The results reveal that the directors undergo significant and inhomogeneous rotation at the crack tips, leading to very different stress/strain distributions from traditional elastomers. Particularly, when the initial director is tilted to the loading direction, the stress/strain distributions are asymmetrical about the crack plane. Notably, we discover a domain wall forms along a certain polar angle at the crack tip, with opposite director rotation, and thereby shear strain, on the two sides of the domain wall. Moreover, LCEs with a tilted initial director to the loading exhibit much smaller crack openings and energy release rates than those of neo-Hookean materials, while LCEs with a parallel director exhibit higher values. We attribute these findings to a combined effect of bulk softening at the remote region and the formation of domains of opposite director rotation near the crack tip. This study provides an understanding of how the stress-director coupling of LCEs triggers their unique crack-tip fields, and insights into strategies to enhance the fracture properties of LCEs for future applications.

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.