Domain Width Research Articles

Heteroepitaxy of Dirac semimetal Cd3As2 by metal-organic chemical-vapor deposition

We present progress on the synthesis of semimetal Cd3As2 by metal–organic chemical-vapor deposition (MOCVD). Specifically, we have optimized the growth conditions needed to obtain technologically useful growth rates and acceptable thin-film microstructures, with our studies evaluating the effects of varying the temperature, pressure, and carrier-gas type for MOCVD of Cd3As2 when performed using dimethylcadmium and tertiarybutylarsine precursors. In the course of the optimization studies, exploratory Cd3As2 growths are attempted on GaSb substrates, strain-relaxed InAs buffer layers grown on GaSb substrates, and InAs substrates. Notably, only the InAs-terminated substrate surfaces yield desirable results. Extensive microstructural studies of Cd3As2 thin films on InAs are performed by using multiple advanced imaging microscopies and x-ray diffraction modalities. The studied films are 5–75 nm in thickness and consist of oriented, coalesced polycrystals with lateral domain widths of 30–80 nm. The most optimized films are smooth and specular, exhibiting a surface roughness as low as 1.0 nm rms. Under cross-sectional imaging, the Cd3As2-InAs heterointerface appears smooth and abrupt at a lower film thickness, ~30 nm, but becomes quite irregular as the average thickness increases to ~55 nm. The films are strain-relaxed with a residual biaxial tensile strain (εxx = +0.0010) that opposes the initially compressive lattice-mismatch strain of Cd3As2 coherent on InAs (εxx = −0.042). Importantly, phase-identification studies find a thin-film crystal structure consistent with the P42/nbc space group, placing MOCVD-grown Cd3As2 among the Dirac semimetals of substantial interest for topological quantum materials studies.

Electric-Field Control of Propagating Spin Waves by Ferroelectric Domain-Wall Motion in a Multiferroic Heterostructure.

Magnetoelectric coupling in multiferroic heterostructures offers a promising platform for electric-field control of magnonic devices based on low-power spin-wave transport. Here, electric-field manipulation of the amplitude and phase of propagating spin waves in a ferromagnetic Fe film on top of a ferroelectric BaTiO3 substrate is demonstrated experimentally. Electric-field effects in this composite material system are mediated by strain coupling between alternating ferroelectric stripe domains with in-plane and perpendicular polarization and fully correlated magnetic anisotropy domains with differing spin-wave transport properties. The propagation of spin waves across the strain-induced magnetic anisotropy domains of the Fe film is directly imaged and it is shown how reversible electric-field-driven motion of ferroelectric domain walls and pinned anisotropy boundaries turns the spin-wave signal on and off. Furthermore, linear electric-field tuning of the spin-wave phase by altering the width of strain-coupled stripe domains is demonstrated. The results provide a new route toward energy-efficient reconfigurablemagnonics.

Programming piston displacements for constant flow rate piston pumps with trigonometric transition functions

Abstract. An analytical method for programming piston displacements for constant flow rate piston pumps is presented. A total of two trigonometric transition functions are introduced to express the piston velocities during the transition processes, which can guarantee both constant flow rates and the continuity of piston accelerations. A kind of displacement function of pistons, for two-piston pumps, and two other kinds, for three-piston pumps, are presented, and the physical meaning of their parameters is also discussed. The results show that, with the given transition functions, cam profiles can be designed analytically with parameterized forms, and the maximum accelerations of the pistons are determined by the width of the transition domain and the rotational velocities of the cams, which will affect contact forces between cams and followers.

Submicron periodical poling in Z-cut lithium niobate thin films

The creation of the stripe domain structures with submicron periods by local switching using a biased tip of a scanning probe microscope was studied on Z-cut of lithium niobate on insulator (LNOI). The width of isolated stripe domains and duty cycle of periodically poled lithium niobate (PPLN) were controlled by varying the voltage applied. Three types of the domain width dependences on the period were distinguished: widening, constriction, and merging. The stability of PPLN in LNOI was confirmed. Domain structures could be removed locally by a biased tip. The obtained knowledge can be used for development of the nanodomain engineering.

Effect of Ho addition on AC soft magnetic property, microstructure and magnetic domain of FeCoNi(CuAl)0.8Hox (x = 0–0.07) high-entropy alloys

The FeCoNi(CuAl)0.8 high-entropy alloy (HEA) consists of both face-centered cubic (FCC) phase and body-centered cubic (BCC) phase which allows for a fine tuning of the magnetic properties by controlling the concentration, morphology, and distribution of each phase. In this work, we report the effect of Ho addition on the microstructure, magnetic domains, and alternating current (AC) magnetic properties. FeCoNi(CuAl)0.8Ho0.05 (x = 0.05) HEA exhibits the optimum AC magnetic property with the minimum AC coercivity, hysteresis loss, eddy current loss and total loss among samples studied at both 50 Hz and 950 Hz. Ho addition increases the volume fraction of BCC phase. SEM-EDX results show that Cu and Ho elements are aggregated together at boundaries in Ho-containing alloys. Magnetic domain structure shows that stripe domains are observed in FCC phase and BCC phase with different domain width. Finely spaced domain in BCC phase leads to low eddy current loss. No domain pattern at boundaries is observed indicating that boundaries can hinder motion of domain resulting in an increase of the energy loss. Our findings provide a valid approach toward optimizing the desired physical properties of HEA magnets by adding a small fraction of rare earth element.

Forward domain growth on the non-polar cut of lithium niobate crystal during irradiation by focused ion beam

We have studied the domain forward growth (growth in polar direction) on the non-polar cut of lithium niobate crystal as a result of focused ion beam irradiation. The nonlinear dose dependencies of the length and width of the wedge-like domains were observed. The domain growth was considered in terms of the kinetic approach. The spatial distribution of a polar component of the electric field produced by the injected charge was calculated using the point charge model. The proposed approach allowed estimating the amount of the effective charge at the irradiated surface about 1% of the irradiation dose.

Characteristics of Avalanche Charge Domain in High-Power GaAs Devices

The formation of avalanche charge domain in high-power GaAs device has been studied numerically. According to the numerical simulation results of the distribution of electric field in the bulk of the device, the variation rules of peak electric field within the domain and the domain width with the bias electric field, the carrier concentration, and the device length are obtained, respectively, and by the comparison of the variation rules with and without considering carrier impact ionization, the effect of the carrier impact ionization on the peak electric field and the domain width have been obtained. It shows that 1) the peak electric field is mainly determined by the bias electric field, the carrier concentration and the device length, and the domain width is mainly determined by the carrier concentration and the device length; 2) the carrier impact ionization and avalanche multiplication have a significant effect on the peak electric field and domain width; and 3) the value of the peak electric field and domain width are closely related to the position of domain in the direction of domain motion. Based on the variation of peak electric field and domain width, the formation of avalanche charge domain is discussed. Our results can deepen the understanding of breakover mechanism of GaAs devices and contribute to the optimization of GaAs devices performance.

Chiral magnetic domain walls under transverse fields: A semi-analytical model

An analytical model for the domain wall structure in ultrathin films with perpendicular easy axis and interfacial Dzyaloshinskii-Moriya interaction, submitted to an arbitrary in-plane magnetic field, is presented. Its solution is simplified to the numerical minimization of an analytic function of just one variable. The model predictions are compared to numerical micromagnetic simulations, using parameters of existing samples, revealing a very good agreement. Remaining differences are analyzed, and partly corrected. Differences with the predictions of the simplest model, usually found in the literature, in which only the domain wall moment’s in-plane orientation can vary, are exemplified. The model allows accurate computations, as a function of in-plane field module and orientation, of the domain wall tension and width, quantities controlling the creep motion of domain walls in such films.

Finite‐gain event‐triggered interval observers design for continuous‐time linear systems

AbstractThis work introduces a new approach based on an event‐triggered mechanism (ETM) to design finite‐gain interval observers for linear continuous‐time systems in the presence of unknown‐but‐bounded uncertainties with a priori known bounds on state disturbances and measurement noises. In this setting, aperiodic measurements sampling is controlled in a way to reduce online communication between the sensors and the estimation algorithm. The proposed ETM relies on a dynamic condition that depends on the width of the feasible domain of the system's uncertainties and the width of the estimated state enclosures. Moreover, the proposed approach guarantees the existence of a positive lower bound on the interevent times, which avoids the Zeno phenomenon. On the other hand, although the sensors data are used in an irregular sampling way, the ‐stability performance of the estimation error is satisfied. Finally, simulation results are given to illustrate the effectiveness of the proposed method.

Surface microstructural design to improve mechanical and giant magneto-impedance properties of melt-extracted CoFe-based amorphous wires

The influence of surface microstructural regulation mechanisms on the mechanical and giant magneto-impedance (GMI) properties of as-cast melt-extracted CoFe-based wires has been systematically researched based on morphology, phase distribution and domain structure parameters. A series of statistical models were applied to analyze the mechanical properties and followed by mapping the curve of cumulative failure rate for wire application. It was found that the average and highest fracture strengths, average tensile strain increased with Cu substitution and reached peaks of ~3725 MPa, ~4250 MPa and ~2.7%, respectively. Verified structure-simulation experiments revealed that surface Rayleigh waves effectively split the main crack and the diffusely distributed nanocrystalline in surface area acted as a pinning point to impede the crack growth, enhancing the mechanical properties. The GMI ratio displayed similar variations and attained a maximum value of 700 ± 5% as well as the resistance and reactance ratios improved to ~687% and ~2206%, respectively. The enhanced relative dielectric permeability μs resulting from the increased domain wall energy density and the decreased surface domain width. The unique synchronous enhancement of CoFe-based wires satisfies the demand for emerging magnetoelectric sensor applications, e.g. flexible and wearable sensors, equipment self-monitoring sensors, and array robotic skin sensors under harsh working environments.

Large-eddy simulation of pollutant dispersion in generic urban street canyons: Guidelines for domain size

Pollutant dispersion in urban street canyons has been widely investigated by large-eddy simulation (LES). Many LES studies focused on generic street canyons under a wind direction perpendicular to the street axis. Accurate LES simulations require a sufficiently large domain size to minimize the effects of the artificial boundary conditions at the domain faces on the results. As opposed to RANS simulations, there is a lack of guidelines for an appropriate domain size for LES simulations of wind flow and pollutant dispersion in street canyons. The present study systematically investigates the effect of the domain width, domain height and upstream and downstream domain lengths on the wind flow and pollutant dispersion within a generic 2.5D street canyon with spanwise periodic boundary conditions. Following a validation study, 16 LES simulations are performed for different domain sizes. The results show that the minimum requirement for the domain width is 2.5H, where H is the roof height of the street canyon. For the domain height, upstream domain length and downstream domain length, 7.5H, 5H and 10H are recommended, respectively. These guidelines should help to reduce the computational costs of this type of simulation without significantly compromising the accuracy.

Guidelines for the computational domain size on an urban-scale VAWT

Focusing on the H-type vertical axis wind turbines (VAWTs) widely used in urban, the SST k - ω turbulence model was selected to establish a two-dimensional Computational Fluid Dynamics (CFD) model, the moment coefficient (Cm), and power coefficient (Cp) was taken as the evaluation indicators. The CFD model was used in different domain sizes. The simulation results under the sizes were used to investigate the effect of the computational domain size on the numerical simulation results of the aerodynamic performance of the VAWT. Furthermore, a distance from the turbine center to the domain inlet and outlet of 10D (D: diameter of the turbine) each, a domain width of 10D and a diameter of the rotating core of 1.5D are found to be safe choices to minimize the effects of blockage and uncertainty in the boundary conditions on the results. It provides a reference for the selection of the domain size when CFD simulation is implemented in a vertical axis turbine to get its prediction of the performance in the future accurately.

Formation of submicron stripe domain ensembles during polarization reversal in Rb doped KTP crystal covered by dielectric layer

The formation of self-organized quasi-regular domain structure in Rb:KTP crystals covered by photoresist layer was studied. The instability of domain wall shape resulting in formation of domain streamers on the wall was revealed. The streamers structure appeared on Z+ polar surface and grew in polar direction. The minimal obtained structure period was 1 µm and the structure length reached 50 μm. The width of the stripe domains between the neighboring streamers went down to 100 nm and the resulting aspect ratio was 500. The obtained effect is very promising for the submicron periodical poling in the crystals of KTP family.

Radial Domains in DyPr–FeCo–B Microwires

In DyPr–FeCo–B microwires with easy magnetization axis directed along the microwire axis, domains with radial magnetization are detected using magneto-optical indicator films. The width of radial domains decreases as the field increases to 30 mT and increases with the microwire diameter in the range of 60–105 μm. In wires of smaller diameter, the critical field of radial domain formation is lower. The effect of the periodic relief produced by scribing on the magnetization distribution perpendicular to the microwire is detected.

Distributed sliding mode control for time-varying formation tracking of multi-UAV system with a dynamic leader

Time-varying formation tracking control problems for the multi-UAV system are investigated in this paper, where a leader with dynamic input is considered. Based on the sliding mode control theory, continuous-time and discrete-time distributed formation tracking protocols are proposed by utilizing the neighboring relative information. Using Lyapunov stability approach, sufficient conditions for the multi-UAV system to achieve the desired formation tracking are given and the width of quasi-sliding mode domain for the discrete-time protocol is expressed. Algorithms to construct the designed continuous-time and discrete-time protocols for multi-UAV systems are provided. Based on the Gazebo simulator, a formation tracking virtual experiment platform for multi-UAV systems is constructed. Virtual experiments with multiple UAVs are performed to demonstrate the effectiveness of the continuous and discrete formation tracking protocols.

Preoperative botulinum toxin A injection in complex abdominal wall reconstruction– a propensity-scored matched study

IntroductionFascial closure during complex abdominal wall reconstruction (AWR) improves recurrence and wound infection rates. To facilitate fascial closure in massive ventral hernias preoperative Botulinum Toxin A (BTA) injection can be used. Methods2:1 propensity-scored matching of patients undergoing AWR with and without BTA was performed based on BMI, defect width, and loss of domain using CT-volumetric analysis. Results145 patients without BTA and 75 with BTA were comparable on hernia size (240vs251cm2, p = 0.589) and hernia volume (1405vs1672cm3, p = 0.243). Patients with BTA had higher wound class (CDC≥3 37%vs13%, p < 0.001). Patients with BTA had a higher fascial closure rate (92%vs81%, p = 0.036), received more components separation (61%vs47%, p = 0.042), lower wound infection rate (12%vs26%,p = 0.019) and comparable recurrence rates (9%vs12%, p = 0.589). Recurrences occurred more often without complete fascial closure compared to patients with (33%vs7%, p < 0.001). ConclusionIn patients with massive ventral hernias and severe loss of domain, preoperative BTA-injection improves fascial closure rates during AWR.

Microstructure and electrical properties of CuO-doped K0.5Na0.5NbO3-based single crystals with low dielectric loss

CuO-doped K0.5Na0.5NbO3 (KNN)-based lead-free piezoelectric single crystals were realized by using a seed-free solid-state crystal growth (SFSSCG) method. The effect of the CuO addition on the single-crystal growth, microstructure and electrical properties of the systems was studied systemically. The addition of CuO is beneficial for the growth of the KNN-based crystals and decreases the width of ferroelectric domains of the crystals. In particular, the CuO doping significantly reduces the dielectric loss of the crystals. The lowest dielectric loss tanδ of 1% was achieved for the CuO-doped crystals with high piezoelectric constant and Curie temperature. The study on the leakage behavior of the crystals shows that the main electrical conduction mechanism is the space-charge-limited-current (SCLC). A coexisting crystalline structure with orthorhombic and tetragonal phases forms in the (1 − x)[KNN-LiBiO3]-xCuO crystals at x = 0.007–0.009. The growth kinetics and mechanism of the crystals were also investigated.

Investigation of the Domain Structure of Co-based Microwires by Magneto-Optical Indicator Films Method

The investigation of domain structure of Co-based microwires with negative magnetostriction was provided by magnetooptical method of indicator films. The thickness of the domain layer and the width of the surface domains were determined. It has been suggested that in thin microwires (with the diameter of about several tens of microns) with negative magnetostriction, the Neel-type of domain walls between the domains of the surface layer are observed. A number of assumptions about the regularities of the surface domain structure formation of microwires with negative magnetostriction have been put forward.

Micromagnetic modelling of stripe domains in thin films with a columnar microstructure

A micromagnetic model of thin films with columnar microstructure in the form of a matrix with reduced magnetic properties and embedded columns with high aspect ratio is presented. Such microstructure is typical for some films based on rare-earth and 3d transition metal alloys, in particular for La-Co films, that were chosen as an object for our modelling. Described structural features promote an effective perpendicular magnetic anisotropy that for thick enough films leads to formation of the stripe domain pattern. Our work addresses to the problem of finding equilibrium characteristics of stripe domains for the case of infinite columnar films. Herein it is shown how width of stripe domains, remanent magnetization and energies depend on number of replicas of periodic boundary conditions and the size of modelling volume. Equilibrium values of listed quantities can be found by extrapolating obtained dependencies.

Recent advances in graphene nanoribbons for biosensing and biomedicine.

In recent years, a new type of quasi-one-dimensional graphene-based material, graphene nanoribbons (GNRs), has attracted increasing attention. The limited domain width and rich edge configurations of GNRs endow them with unique properties and wide applications in comparison to two-dimensional graphene. This review article mainly focuses on the electrical, chemical and other properties of GNRs, and further introduces the typical preparation methods of GNRs, including top-down and bottom-up strategies. Then, their biosensing and biomedical applications are highlighted in detail, such as biosensors, photothermal therapy, drug delivery, etc. Finally, the challenges and future prospects in the synthesis and application of functionalized GNRs are discussed. It is expected that GNRs will have significant practical use in biomedical applications in the future.