Domain Growth Process Research Articles

Spectral energy transfers in domain growth problems.

In the domain growth process, small structures gradually vanish, leaving behind larger ones. We investigate spectral energy transfers in two standard models for domain growth: (a) the Cahn-Hilliard (CH) equationwith conserved dynamics and (b) the time-dependent Ginzburg-Landau (TDGL) equationwith nonconserved dynamics. The nonlinear terms in these equationsdissipate fluctuations and facilitate energy transfers among Fourier modes. In the TDGL equation, only the ϕ(k=0,t) mode survives, and the order parameter ϕ(r,t) approaches a uniform state with ϕ=+1 or -1. On the other hand, there is no dynamics of the ϕ(k=0,t) mode in the CH equationdue to the conservation law, highlighting the different dynamics of these equations.

Coexistence and Interplay of Two Ferroelectric Mechanisms in Zn1-xMgxO.

Ferroelectric materials promise exceptional attributes including low power dissipation, fast operational speeds, enhanced endurance, and superior retention to revolutionize information technology. However, the practical application of ferroelectric-semiconductor memory devices has been significantly challenged by the incompatibility of traditional perovskite oxide ferroelectrics with metal-oxide-semiconductor technology. Recent discoveries of ferroelectricity in binary oxides such as Zn1-xMgxO and Hf1-xZrxO have been a focal point of research in ferroelectric information technology. This work investigates the ferroelectric properties of Zn1-xMgxO utilizing automated band excitation piezoresponse force microscopy. This findings reveal the coexistence of two ferroelectric subsystems within Zn1-xMgxO. A "fringing-ridge mechanism" of polarization switching is proposed that is characterized by initial lateral expansion of nucleation without significant propagation in depth, contradicting the conventional domain growth process observed in ferroelectrics. This unique polarization dynamics in Zn1-xMgxO suggests a new understanding of ferroelectric behavior, contributing to both the fundamental science of ferroelectrics and their application in information technology.

Spiral packing and chiral selectivity in model membranes probed by phase-resolved sum-frequency generation microscopy

Since the lipid raft model was developed at the end of the last century, it became clear that the specific molecular arrangements of phospholipid assemblies within a membrane have profound implications in a vast range of physiological functions. Studies of such condensed lipid islands in model systems using fluorescence and Brewster angle microscopies have shown a wide range of sizes and morphologies, with suggestions of substantial in-plane molecular anisotropy and mesoscopic structural chirality. Whilst these variations can significantly alter many membrane properties including its fluidity, permeability and molecular recognition, the details of the in-plane molecular orientations underlying these traits remain largely unknown. Here, we use phase-resolved sum-frequency generation microscopy on model membranes of mixed chirality phospholipid monolayers to fully determine the three-dimensional molecular structure of the constituent micron-scale condensed domains. We find that the domains possess curved molecular directionality with spiralling mesoscopic packing, where both the molecular and spiral turning directions depend on the lipid chirality, but form structures clearly deviating from mirror symmetry for different enantiomeric mixtures. This demonstrates strong enantioselectivity in the domain growth process and indicates fundamental thermodynamic differences between homo- and heterochiral membranes, which may be relevant in the evolution of homochirality in all living organisms.

Domain Growth in Polycrystalline Graphene.

Graphene is a two-dimensional carbon allotrope which exhibits exceptional properties, making it highly suitable for a wide range of applications. Practical graphene fabrication often yields a polycrystalline structure with many inherent defects, which significantly influence its performance. In this study, we utilize a Monte Carlo approach based on the optimized Wooten, Winer and Weaire (WWW) algorithm to simulate the crystalline domain coarsening process of polycrystalline graphene. Our sample configurations show excellent agreement with experimental data. We conduct statistical analyses of the bond and angle distribution, temporal evolution of the defect distribution, and spatial correlation of the lattice orientation that follows a stretched exponential distribution. Furthermore, we thoroughly investigate the diffusion behavior of defects and find that the changes in domain size follow a power-law distribution. We briefly discuss the possible connections of these results to (and differences from) domain growth processes in other statistical models, such as the Ising dynamics. We also examine the impact of buckling of polycrystalline graphene on the crystallization rate under substrate effects. Our findings may offer valuable guidance and insights for both theoretical investigations and experimental advancements.

Magnetic-field-controlled growth of magnetoelastic phase domains in FeRh

Magnetic phase transition materials are relevant building blocks for developing green technologies such as magnetocaloric devices for solid-state refrigeration. Their integration into applications requires a good understanding and controllability of their properties at the micro- and nanoscale. Here, we present an optical microscopy study of the phase domains in FeRh across its antiferromagnetic–ferromagnetic phase transition. By tracking the phase-dependent optical reflectivity, we establish that phase domains have typical sizes of a few microns for relatively thick epitaxial films (200 nm), thus enabling visualization of domain nucleation, growth, and percolation processes in great detail. Phase domain growth preferentially occurs along the principal crystallographic axes of FeRh, which is a consequence of the elastic adaptation to both the substrate-induced stress and laterally heterogeneous strain distributions arising from the different unit cell volumes of the two coexisting phases. Furthermore, we demonstrate a magnetic-field-controlled directional growth of phase domains during both heating and cooling, which is predominantly linked to the local effect of magnetic dipolar fields created by the alignment of magnetic moments in the emerging (disappearing) FM phase fraction during heating (cooling). These findings highlight the importance of the magnetoelastic character of phase domains for enabling the local control of micro- and nanoscale phase separation patterns using magnetic fields or elastic stresses.

General theory on the growth kinetics of topological domain structure in hexagonal manganites

Although the dynamics of domain growth has been a long-standing topic in ferroic systems, its science complexity and important guidance to practical applications cannot be overemphasized. Highly anisotropic systems with only domain-wall-type defects and roughly isotropic systems with only vortex-type defects have been extensively studied as two ideal and extreme examples in terms of domain growth dynamics. The domain growth processes in these two types of systems are believed to follow two different scaling laws. The driving forces behind are domain wall motion and vortex–antivortex annihilation, respectively. However, no realistic ferroic systems have ever been found to exhibit a domain growth process that strictly follows these scaling laws. Fortunately, we now have a realistic ferroic system, i.e., the ferroelectric hexagonal manganite family in which the aforementioned two types of defects coexist. This system supports a fascinating topological vortex–antivortex domain structure and is a unique platform for probing a generalized theory on the domain growth dynamics that covers the two extremes. In this work, we investigate this vortex–antivortex domain structure and its growth dynamics within the framework of the Landau theory using phase-field simulations. It is revealed that morphology of this domain structure can be controlled by a correlation length Lc that is different from the conventional correlation length. More importantly, this domain structure can be seen as an intermediate state between the two extremes in terms of domain growth dynamics. When Lc is very small, the domain growth process in this domain structure is driven by domain wall motion and follows the well-known Allen–Cahn scaling law. As Lc increases, vortex–antivortex annihilation will dominate the domain growth process and the scaling law will need a logarithmical correction. The present work provides a comprehensive understanding of the domain growth behavior in such a realistic ferroic system of much attention and represents a substantial extension of domain growth dynamics toward complicated multi-defect systems.

Uncovering the path to low-field colossal magnetoresistance: A microscopic view of field driven percolative insulator-to-metal transition in manganites

For perovskite manganites, their colossal magnetoresistance (CMR) requires a large field, which limits their potential applications. In order to uncover the path to achieve low-field CMR, it is crucial to understand the microscopic process of the field driven insulator-to-metal transition (IMT) in manganites. This is particularly true considering the fact that the IMT is of a percolative type, in which the interplay between nucleation and growth of the electronic phase separation domains under magnetic field is not well investigated. In this work, we investigate the magnetic field driven percolative IMT in a model system of La1−x−yPrxCayMnO3 in real space via magnetic force microscopy (MFM). Our experimental observations show unambiguously three stages of the IMT phase transition where domain nucleation and domain growth exhibit distinctly different features in the global initial magnetization measurements. Moreover, MFM reveals that domain growth requires a much lower field than domain nucleation, which provides critical information on how to achieve low-field CMR. It is believed that the exchange field provided by ferromagnetic metallic domains at the boundary with antiferromagnetic insulating domains plays a critical role in assisting the domain growth process. Optimizing such internal exchange fields in manganites is a potential route to achieve CMR without the need of a large external field.

Film Formation Kinetics of Polymer Donor and Nonfullerene Acceptor Active Layers During Printing Out of 1,2,4‐Trimethylbenzene in Ambient Conditions

Slot‐die coating is a promising upscaling fabrication method to promote commercialization in the field of organic solar cells. Herein, the nonfullerene active layer blend of a conjugated polymer PffBT4T‐2OD and a small molecule acceptor EH‐IDTBR, which is printed out of the nonhalogenated solvent 1,2,4‐trimethylbenzene, is studied. The film formation kinetics of the active layer PffBT4T‐2OD:EH‐IDTBR is probed in terms of the temporal evolutions in morphology as well as molecular conformation and aggregation as revealed by in situ grazing‐incidence small angle X‐ray scattering and UV–vis spectroscopy during the film printing process. A five‐regime mesoscale domain growth process is observed in the active layer from the liquid state to the final dry state. The solvent evaporation‐induced domain growth is accompanied with molecular stacking in a distinct J‐type aggregation of the acceptor and a slight H‐type aggregation of the donor molecules. The printed active layers exhibit an edge‐on dominated PffBT4T‐2OD and a face‐on dominated EH‐IDTBR crystallite structure. Compared to the neat PffBT4T‐2OD and EH‐IDTBR films, in the active layer, the crystallite structure deviates slightly in lattice spacing.

Direct visualization of percolating metal-insulator transition in V2O3 using scanning microwave impedance microscopy

Using the extensively studied V2O3 as a prototype system, we investigate the role of percolation in metal-insulator transition (MIT). We apply scanning microwave impedance microscopy to directly determine the metallic phase fraction p and relate it to the macroscopic conductance G, which shows a sudden jump when p reaches the percolation threshold. Interestingly, the conductance G exhibits a hysteretic behavior against suggesting two different percolating processes upon cooling and warming. Based on our image analysis and model simulation, we ascribe such hysteretic behavior to different domain nucleation and growth processes between cooling and warming, which is likely caused by the decoupled structural and electronic transitions in V2O3 during MIT. Our work provides a microscopic view of how the interplay of structural and electronic degrees of freedom affects MIT in strongly correlated systems.

Frequency dependence of antiferroelectricferroelectric phase transition of PLZST ceramic

AbstractAntiferroelectric (AFE) ceramics are promising for applications in high‐power density capacitors, transducers, etc. The forward switching field and backward switching field are critical performance indicators for AFE ceramics, and the coupling between the structure transition and domain orientation makes them different from the coercive field of ferroelectric (FE). Moreover, in practical applications, AFE ceramics are often required to operate at varying frequencies. However, systematic studies regarding the frequency dependence of and are insufficient. In this work, (PLZST) AFE ceramic was fabricated, and two empirical formulas (, ) were proposed to predict the frequency dependence of and . The formulas are based on the electric field–induced phase transition characteristics of AFE and the Kolmogorov–Avrami–Ishibashi domain nucleation‐switching model. Furthermore, the dynamic hysteresis loops of PLZST at various frequencies (1–1000 Hz) and temperatures (–) were investigated. The results show that the electric field–induced phase transition of AFE ceramic is dominated by the coupling between the structural transition and domain orientation. The domain orientation hinders the structure transition, leading to an increase in and a decrease in as the frequency of applied electric field increases. Meanwhile, the domain growth process is affected by the structure of AFE, and the value of (domain growth dimensionality) increases with the stability of the AFE structure. For comparison, (PLBZST) relaxor FE ceramic was fabricated. Due to the high mobility of the microdomain, the dynamic hysteresis loop of PLBZST ceramic exhibits excellent frequency stability. The charge–discharge experiment with an ultrahigh equivalent frequency (100 kHz) was performed to investigate the frequency stability of energy release of PLZST and PLBZST. The results may provide guidance for research pertaining to ceramic capacitors with high‐power density and high‐frequency stability.

Numerical simulation of domain wall motion in a surface discharge over a ferroelectric

The article presents a simplified numerical simulation of a vacuum ferroelectric cathode operating in a low-current mode (without surface plasma formation). The field emission from the cathode was simulated for the range of applied electric field magnitudes. The polarization domain growth process during the charging of ferroelectric surface was simulated using Landau-Ginzburg-Devonshire model. Interaction of the electrons with a depolarization field of a domain wall led to an attraction of the electrons to the polarization domain boundaries. A close to the linear dependence of the equilibrium domain wall position from the applied electric field was found with the total emitted charge proportional to the domain size.

Electrically Induced Alignment of Semiconductor Nanosheets in Niobate-Clay Binary Nanosheet Colloids toward Significantly Enhanced Photocatalysis.

Aqueous binary colloids of niobate and clay nanosheets, prepared by the exfoliation of their mother layered crystals, are unique colloidal systems characterized by the separation of niobate and clay nanosheet phases, where niobate nanosheets form liquid crystalline domains with the size of several tens of micrometers among isotropically dispersed clay nanosheets. The binary colloids show unusual photocatalytic reactions because of the spatial separation of photocatalytically active niobate and photochemically inert clay nanosheets. The present study shows structural conversion of the binary colloids with an external electric field, resulting in the onsite alignment of colloidal nanosheets to improve the photocatalytic performance of the system. The colloidal structure is reshaped by the growth of liquid crystalline domains of photocatalytic niobate nanosheets and by their electric alignment. Niobate nanosheets are assembled by the domain growth process and then aligned by AC voltage, although clay nanosheets do not respond to the electric field. Photocatalytic decomposition of the cationic rhodamine 6G dye, which is selectively adsorbed on clay nanosheets, is examined for the niobate-clay binary nanosheet colloids with or without domain growth and electric field. The fastest decomposition is observed for the electrically aligned colloid without the domain growth, whereas the sample with the domain growth and without the electric alignment shows the slowest decomposition. The results demonstrate the improvement of the photocatalytic performance by changing the colloidal structure, even though the sample composition is the same.

Domain growth dynamics in (K, Na)NbO 3 ferroelectric thin films

(K,Na)NbO3 (KNN) based lead-free materials have gained great progress and drawn much attention recently, due to their attractive piezoelectric performance and the demand for environmental protection. As is known, domain motion is essential for piezoelectric output; however, there is limited understanding on this topic for KNN. In the present study, the domain growth process of the KNN thin film is studied by piezoresponse force microscopy (PFM). The domain size shows a linear dependence on the pulse voltage and a complex dependence, unlike the commonly accepted logarithmic relationship, on the pulse duration. Meanwhile, a power decay relationship between the domain wall velocity and the domain size is observed. The extremely low dynamical exponent proves that our sample is influenced by extremely strong pinning effects caused by defects, resulting in the uncommon pulse duration dependence of domain size.

Nonequilibrium dynamics of the three-dimensional Edwards-Anderson spin-glass model with Gaussian couplings: strong heterogeneities and the backbone picture

We numerically study the three-dimensional Edwards-Anderson model with Gaussian couplings, focusing on the heterogeneities arising in its nonequilibrium dynamics. Results are analyzed in terms of the backbone picture, which links strong dynamical heterogeneities to spatial heterogeneities emerging from the correlation of local rigidity of the bond network. Different two-times quantities as the flipping time distribution and the correlation and response functions, are evaluated over the full system and over high- and low-rigidity regions. We find that the nonequilibrium dynamics of the model is highly correlated to spatial heterogeneities. Also, we observe a similar physical behavior to that previously found in the Edwards-Anderson model with a bimodal (discrete) bond distribution. Namely, the backbone behaves as the main structure that supports the spin-glass phase, within which a sort of domain-growth process develops, while the complement remains in a paramagnetic phase, even below the critical temperature.

Domain switching kinetics in vinylidene fluoride/tetrafluoroethylene copolymer thin films

The local domain switching of vinylidene fluoride/tetrafluoroethylene copolymer thin films with different higher order structures was investigated by piezoresponse force microscopy. It was found that one-dimensionally grown domains were formed on highly crystallized needle-like crystals after local voltage pulse application. This is because each needle-like crystal consisted of parallel-stacked lamellae with chain folding along its major axis. In addition, it showed two-step domain growth processes, namely, inter lamella domain growth and the growth between lamellae. On the other hand, circular domains were formed on polycrystalline plate-like crystals and as-coated films.

Polarization switching characteristics of vinylidene fluoride/tefrafluoroethylene copolymer thin films

The polarization switching characteristics of vinylidene fluoride/tetrafluoroethylene (VDF/TeFE) copolymer thin film obtained from a melt-crystallization process were investigated over a wide electric field range from 80 to 180 MV/m. It was found that full polarization reversal occurred in 210-, 270-, and 320-nm-thick films; such reversal is independent of film thickness. The analysis of the switching kinetics based on the Avrami equation indicated a one- or two-dimensional domain growth process. The switching time obeyed the exponential law as evidence of the linear relationship between log τs and 1/E, which is consistent with the results for the vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer. The switching time for VDF/TeFE was shorter than that for VDF/TrFE. For instance, switching times at 120 MV/m were 1.8 and 3.3 µs for VDF/TeFE and VDF/TrFE, respectively. It was revealed that the polarization switching of the VDF/TeFE can be achieved in a shorter time than that of the VDF/TrFE.

Domain Dynamics in Nonequilibrium Random-Field Ising Models

We employ Monte Carlo simulations in order to study dynamics of the magnetization and domain growth processes in the random-field Ising models with uniform and Gaussian random field distributions of varying strengths. Domain sizes are determined directly using the Hoshen-Kopelman algorithm. For either case, both the magnetization and the largest domain growth dynamics are found to follow the power law with generally different exponents, which exponentially decay with the random field strength. Moreover, for relatively small random fields the relaxation is confirmed to comply with different regimes at early and later times. No significant differences were found between the results for the uniform and Gaussian distributions, in accordance with the universality assumption.

Kinetics of phase transitions in quark matter

We study the kinetics of chiral transitions in quark matter using a phenomenological framework (Ginzburg-Landau model). We focus on the effect of inertial terms on the coarsening dynamics subsequent to a quench from the massless quark phase to the massive quark phase. The domain growth process shows a crossover from a fast inertial regime (with ) to a diffusive Cahn-Allen regime (with ).

Crystallization time scales for polydisperse hard-sphere fluids

We study the evolution of crystallization in dense mono- and polydisperse hard sphere fluids, initially quenched to an amorphous configuration. We use as signatures of crystallization both the decay of the reduced pressure Z and the increase in the local and global orientational order parameters Q[over ¯](6). For a given realization of the crystallization process these parameters show sudden changes, both large and small, separated by long periods of quiescence. However, averaging over a large number of realizations, a well-defined scenario for their evolution appears. We find an initial fast relaxation to a disordered state, followed by a period of slow variation, associated to the presence of nucleation events, followed by a fast change, composed of the growth of a few crystals with different orientations, and a final and slow coarsening in a domain-growth process. No clear scaling for this whole process was found. We also find that the transition to an stable glassy fluid is quite sharp as the polydispersity is increased, showing a probable first-order phase transition behavior. A well-defined boundary between crystallizing and permanently amorphous fluids should exist, at least for a region in packing fractions. We looked for segregation at large values of polydispersity, but no effects of this type were found.

Microscopic spin-distortion model for switchable molecular solids: Spatiotemporal study of the deformation field and local stress at the thermal spin transition

We design a microscopic model for switchable molecular solids (e.g., spin crossover), based on the elastic properties of a discrete lattice made of switchable sites, denoted high spin (HS) or low spin (LS). The elastic interactions and equilibrium distances between sites are written as explicit functions of their HS or LS states. The model was solved by Monte Carlo technique, alternatively running on the electronic and position variables. In the present work we investigate the thermal transition in the case of a square two-dimensionsal lattice, including short-range interactions up to the second neighbors in order to maintain the stability of the lattice. The input values of the elastic parameters are selected so as to lead to realistic values of the bulk modulus and Debye temperature. We show that the elastic interactions act as effective Ising interactions, leading to the expected transition and phase diagram, in terms of transition temperature vs elastic interaction parameter. We study the domain growth of the LS or HS species at different temperatures along the thermal loop and obtain features consistent with the experimental data. We also follow the mechanical properties of the system by calculating the displacement field and the internal stresses produced by the domain growth process. The resulting maps evidence the leading role of the HS/LS interface and the crucial effect of the edges of the lattice, thus paving the way to a real understanding of the shape effects in spin transition nanocrystals.