Antiphase Domain Research Articles

Engineering antiphase domain boundaries boosted tunable ferromagnetic insulation

Interface-engineered superlattices composed of perovskite PrCoO3 and brownmillerite CaCoO2.5 ([(PCO)n/(CCO)n]m) were designed and fabricated on (001) SrTiO3 substrates with integrated antiphase domain boundaries (APBs) for investigating ferromagnetic insulating phenomenon. The APBs were formed at the surface-step-terrace edges, and the densities of APBs can be regulated by the periods of the superlattices. In these superlattices, ferromagnetic insulating properties were found to be significantly modulated by the APBs. The room-temperature resistivity of the n = 1 superlattice increases by more than three orders of magnitude than that of the n = 5 superlattice and more than five orders of magnitude than that of the Pr0.5Ca0.5CoO3-δ alloy films. The insulation behavior is primarily derived from the charge carriers scattering at the APBs, which block the charge carriers transferring along the in-plane direction. These results could propel the advancement of multifunctional material genetics and provide a strategic approach for the development of artificial materials with tunable properties.

Exploring the atomic-scale dynamics of Fe3O4(001) at catalytically relevant temperatures using FastSTM

Surfaces and interfaces of functional nanoscale materials are typically highly dynamic when employed at elevated temperatures. Both, lateral surface and vertical bulk exchange diffusion processes set in, which can be relevant for applications such as heterogeneous catalysis. Time-resolved scanning tunneling microscopy (STM) is being pushed to ever faster measurement modes to follow such dynamic phenomena in situ. Here, we present FastSTM movies monitoring a range of atomic-scale dynamics of a prototypical reducible oxide catalyst support, Fe3O4(001), at elevated temperatures. Antiphase domain boundaries between two domains of the reconstructed surface exhibit local mobility from around 350 K, while Fe-rich point defects, in a stable equilibrium with the bulk, appear to diffuse in a peculiar zigzag pattern above 500 K. Finally, exploiting the diffusivity of Fe interstitials, we follow the propagation of step edges in the topmost atomic layer of the Fe3O4(001) surface in an oxygen atmosphere.

Al-Si Order and Chemical Composition Model across Scapolite Solid Solutions with Evidence from Rietveld Structure Refinements

Scapolite forms solid solutions between the end members marialite, Na4[Al3Si9O24]Cl = Me0, and meionite, Ca4[Al6Si6O24]CO3 = Me100. Al-Si order and chemical composition models are proposed for the scapolite solid solutions. These models predict the chemical composition, Al-Si order, and average <T–O> distances between Me0–Me100. These models are based on the observed order of clusters and on two solid solutions that meet at Me75 coupled with predicted chemical compositions and <T–O> distances. The [Na4·Cl]3+ and [NaCa3·CO3]5+ clusters are ordered between Me0–Me75, whereas the clusters [NaCa3·CO3]5+ and [Ca4·CO3]6+ are disordered from Me75–Me100. To confirm the structural model, the crystal structure of 27 scapolite samples between Me6–Me93 has been obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. The structure was refined in space group P42/n for all the samples. The <T–O> distances indicate that the T1 (=Si), T2 (=Al), and T3 (=Si) sites are completely ordered at Me37.5, where the 1:1 ratio of [Na4·Cl]3+:[NaCa3·CO3]5+ clusters are ordered and gives rise to antiphase domain boundaries (APBs) based on Cl-CO3 order instead of Al-Si order. The presence of APBs based on Cl-CO3 order and cluster order indicate that neither space group P42/n nor I4/m are correct for the structure of scapolite, but the lower symmetry space group P42/n is a good approximation for modeling the average structure of scapolite. The complete Al-Si order at Me37.5 changes in a regular and predictable manner toward the end members: Me0, Me75, and Me100. The observed unit cell and several structural parameters show a discontinuity at Me75, where the series is divided into two. There is no structural evidence to support any phase transition in the scapolite series. The T1 site contains only Si from Me0–Me37.5; from Me37.5–Me100, Al atoms enter the T1 site and the <T1–O> distance increases linearly to Me100.

In situ X-ray diffraction evidence of field-induced transitions in a PbHfO3 single crystal

Antiferroelectric (AFE) materials are interesting due to recent discoveries of new prospective applications, although the mechanisms of the phase transitions that are at the heart of these applications remain incompletely understood. This work is devoted to the study of a single crystal of a model AFE, lead hafnate, by X-ray diffraction with in situ application of an electric field to trigger the transition to a polar phase. Two consecutive experiments were carried out on a 35 µm thick plate with [110] surface normal orientation over a field range from 0 to 330 kV cm−1 and back. A sharp drop in the intensity of R- and Σ-type reflections around 225 kV cm−1 was registered, with almost complete disappearance after 250 kV cm−1. This is compatible with a field-induced phase transition from the AFE to the R3m polar phase, which was suggested earlier on the basis of non-diffraction characterizations. X-ray diffraction reveals that the AFE domains with displacements parallel to the field direction react much more smoothly to the field, gradually reducing the AFE order at very small fields instead of holding it almost constant up to the critical field value, which is naturally expected. This expectation is fulfilled for domains with other orientations, but only for the first switching cycle; in the second switching cycle the AFE order already shows a notable decrease at subcritical fields. It is suggested that these observations could be linked with the antiphase domain wall population being affected by the field, which is consistent with the observation of diffuse rods between the Γ and Σ points. Another remarkable observation is the much smoother recovery of the AFE phase compared with its sharp disappearance at the critical field.

Simulation of microtextural evolution in omphacite: Ordering transformation kinetics as unexplored archives of slab eclogitization

Earth's subduction zone processes and surface environments are intricately governed by mass transfer phenomena at plate convergent boundaries. The determination of their rates and timings from high-pressure metamorphic rocks (e.g., eclogite), or remnants of ancient convergent boundaries, remains an ongoing challenge. Here, we proposed the potential and versatility of ordering transformation kinetics of omphacite, an essential mineral found in eclogite, as a dynamic recorder of the metamorphic history. Through macroscopic phase-field simulation, we explored the growth of antiphase domains (APDs) in metastable disordered omphacite, discussing the feasibility of constraining metamorphic reaction kinetics based on the size and morphology of omphacite APDs in eclogitized oceanic crust. Our simulation corroborated that omphacite nucleating later during the prograde metamorphism can exhibit an incompletely ordered state with sparsely distributed ordered domains, which suggests their usefulness in estimating the recrystallization timing of the omphacite. Additionally, we confirmed that the APD formation dynamics are significantly influenced by the initial cation configuration of the disordered matrix. This implies the APD morphology in natural omphacite under slab-surface conditions may reflect their precipitation kinetics. These findings provide valuable insights into the microtextural evolution of omphacite due to its ordering transformation, thereby enhancing our ability to interpret morphological features.

The Atomic Atmosphere at the Antiphase Domain Boundary in Ni3Al: A Phase‐Field Study

The atomic atmosphere and formation mechanism of the antiphase domain boundary (APB) may depend on the environmental variables of the phase transformation for the L12‐structural Ni3Al phase, which is the first important precipitate phase for Ni‐based superalloys. Herein, a discrete phase field method is used to reproduce the complete formation process of an APB without preset restrictions. Numerical calculations are performed to classify the atomic atmosphere, and its formation mechanism is revealed by calculating and analyzing the functional properties of the driving force. The formation process shows that four types of antiphase domains survive to form the APB. The numerical calculation results demonstrate that the atomic atmosphere has the same temperature dependence for hypostoichiometric, stoichiometric, and hyperstoichiometric systems. However, Al plays two opposite roles in influencing the atomic atmosphere according to the changes in the alloy system. The positive and negative values of the driving force determine whether the atomic atmosphere is segregated or depleted, and the magnitude of the absolute value determines the atomic atmosphere level. This atomic‐scale study of nanoscale ordered domain boundaries can provide theoretical information for further understanding of these and similar interfaces in ordered precipitation‐strengthened phases.

Структурные домены аустенита нестехиометрических сплавов Гейслера на основе Ni-Mn-In

The relationship between antiphase boundaries (APBs), antiphase domains (APDs) and the functional properties of alloys of the Ni-Mn-In system has been studied. The density of APBs was controlled using various thermal treatments. The fine domain structure was observed by transmission electron microscopy (TEM), high-angle dark-field scanning transmission electron microscopy (HAADF-STEM), and electron backscatter diffraction (EBSD). The results obtained are discussed in the context of the possibility of modeling and designing materials with specified characteristics and properties.

Resolving the long-standing discrepancy in Fe3Al ordering mobilities: A synergistic experimental and phase-field study

This study addressed the long-standing challenge of determining the growth kinetic of Antiphase Domains (APDs) with D03-ordered structure in Fe3Al by the combination of phase-field (PF) simulations and transmission electron microscopy (TEM) observation. The “shape coefficient” which correlates the growth rate of APD with 3-dimensional intricate shape and the shrinking rate of 2-dimensional circular antiphase boundaries (APBs) in thin film was assessed through a comparative analysis of PF simulations involving the shrinking of 2D circular APBs and the growth of 3D APDs emerged from a disordered state. Simultaneously, the increase rate in APD size in bulk samples after heat treatment was measured using TEM. By incorporating the calculated shape coefficient and experimental data on APD growth rates, we successfully derived accurate values of mobility for forming D03 type ordered structure. The ordering mobilities evaluated by this approach align more closely with those obtained through traditional X-ray powder diffraction of order-order relaxation rather than those obtained through in-situ TEM observation. This finding lays the foundation for optimizing heat treatment conditions to regulate APD structure and enhance the superelasticity of Fe3Al primarily due to the interaction between dislocation and APBs. This methodology can be extended to estimate the ordering mobility of other intermetallic.

Time-resolved surface reaction kinetics in the pressure gap.

We extend the use of our recently developed Near-Ambient Pressure Velocity Map Imaging (NAP-VMI) technique to study the kinetics and dynamics of catalytic reactions in the pressure gap. As an example, we show that NAP-VMI combined with molecular beam surface scattering allows the direct measurement of time- and velocity-resolved kinetics of the scattering and oxidation of CO on the Pd(110) surface with oxygen pressures at the surface up to 1 × 10-5 mbar, where different metastable surface structures form. Our results show that the c(2 × 4) oxide structure formed at low O2 pressure is highly active for CO oxidation. The velocity distribution of the CO2 products shows the presence of two reaction channels, which we attribute to reactions starting from two distinct but rapidly interconverting CO binding sites. The effective CO oxidation reaction activation energy is Er = (1.0 ± 0.13) eV. The CO2 production is suppressed at higher O2 pressure due to the number of antiphase domain boundaries increasing, and the missing row sites are filled by O-atoms at O2 pressures approaching 1 × 10-6 mbar. Filling of these sites by O-atoms reduces the CO surface lifetime, meaning the surface oxide is inactive for CO oxidation. We briefly outline further developments planned for the NAP-VMI and its application to other types of experiments.

Development of “GaSb-on-silicon” metamorphic substrates for optoelectronic device growth

The epitaxial development and characterization of metamorphic “GaSb-on-silicon” buffers as substrates for antimonide devices is presented. The approach involves the growth of a spontaneously and fully relaxed GaSb metamorphic buffer in a primary epitaxial reactor, and use of the resulting “GaSb-on-silicon” wafer to grow subsequent layers in a secondary epitaxial reactor. The buffer growth involves four steps—silicon substrate preparation for oxide removal, nucleation of AlSb on silicon, growth of the GaSb buffer, and finally capping of the buffer to prevent oxidation. This approach on miscut silicon substrates leads to a buffer with negligible antiphase domain density. The growth of this buffer is based on inducing interfacial misfit dislocations between an AlSb nucleation layer and the underlying silicon substrate, which results in a fully relaxed GaSb buffer. A 1 μm thick GaSb layer buffer grown on silicon has ∼9.2 × 107dislocations/cm2. The complete lack of strain in the epitaxial structure allows subsequent growths to be accurately lattice matched, thus making the approach ideal for use as a substrate. We characterize the GaSb-on-silicon wafer using high-resolution x-ray diffraction and transmission electron microscopy. The concept’s feasibility is demonstrated by growing interband cascade light emitting devices on the GaSb-on-silicon wafer. The performance of the resulting LEDs on silicon approaches that of counterparts grown lattice matched on GaSb.

The Correlation between the Microstructure and the Characteristic Luminescence in the High Crystalline α-Ga2O3 Grown on the Thin-Wall Single Crystal Al2O3

A high-quality alpha-Ga2O3 thin film was grown on an Al2O3 single-crystal thin-wall channel structure. Alpha-Ga2O3 crystals are grown with a 3-fold symmetry template provided by the Al2O3 surface, which forms domain boundaries from the small rotation of the mosaic structure. The anti-phase domain (APD) was confirmed by convergent-beam electron diffraction (CBED), and it is believed to be developed at the stage of nucleation based on the unstable, or uneven Al-O bonding on the Al2O3 surface. The in-phase domain and the APD boundaries exhibit bright contrast in ADF, which originates from a local strain of crystallographic rotation and not from the local elemental fluctuations of gallium. As confirmed by CL measurement in TEM, the bandgap energy of alpha-Ga2O3 is inferred to be 5.56 eV with a near band edge transition of ~ 223 nm. Even though the heights and positions of peaks vary slightly from area to area, 4 distinct luminescence peaks and a long tail of wavelength are commonly observed throughout the crystal. 2-dimensional mapping with the specific wavelength window reveals a clear difference between the inside domain, in-phase domain boundary, and APD boundary. A luminescence peak of distinct 350 nm was observed at the APD boundary. Misorientation between domains was found, which leads to an in-plane mismatch in crystallographic lattices at the boundary when the two misoriented domains grow and the growth front merges. The imperfect lattice structure at the boundary is believed to create strain and intermediate states.

The Microstructures, Mechanical Properties, and Deformation Mechanism of B2-Hardened NbTiAlZr-Based Refractory High-Entropy Alloys.

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm3) have excellent compressive-specific yield strength (σYS/ρ) at 1023 K (~131 MPa·cm3/g) and 1123 K (~104.2 MPa·cm3/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](101_) and [111](112_) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K.

Pancake-like antiphase domains in perfect nitrogen-expanded austenite by TEM characterization

Elongated superstructure diffraction spots were observed in perfect nitrogen-expanded austenite without stress or plastic strain, which was prepared by plasma-based low-energy nitrogen-ion implanting Fe-Cr-Ni austenitic alloy foils at low temperature of 380 °C. The Fe4N-like ordered nitrogen-expanded austenite (γ′N) antiphase domains formed in the disordered nitrogen-expanded austenite (γ N) matrix. Only the high Cr-content alloys presented elongated diffraction spots. The reconstruction of the diffraction spots strength distribution shows an elongated egg-shape in reciprocal space. This elongation corresponded to a pancake-like antiphase domains distribution in matrix, which was confirmed in dark field images as a lamellar structural feature. The Cr-N short-range ordering (SRO) and anisotropic elastic module rather than the constrained strain in the γ N phase layer determine the formation of γ′N antiphase domains.

High-temperature structural and mechanical stability of refractory high-entropy alloy Nb40Ti25Al15V10Ta5Hf3W2

Refractory high-entropy alloys (RHEAs) with superior mechanical properties have been considered as a potential next-generation candidate for high-temperature structural materials. However, the structural stability of RHEAs at high temperatures is still noncommittal so far. Especially, the Al containing RHEAs with coherent BCC/B2 microstructure usually form intermetallic phases following short/long term aging at elevated temperatures, which deteriorate the mechanical performance. In this work, we systematically determine the microstructural evolution, including intergranular precipitates, BCC/B2 morphology, and corresponding mechanical properties changes of the Nb40Ti25Al15V10Ta5Hf3W2 RHEA from 923 K to 1123 K. The density of antiphase domain boundaries (APBs) in the RHEA after aging at 923 K is significantly higher than at 1023 K and 1123 K. Only a low volume fraction of tetragonal (Nb, Hf)2Al phase precipitates along grain boundaries after aging at 1123 K. However, the microhardness and yield strengths of the RHEA after aging at 923 K - 1123 K are close to those of the as-cast RHEA, which proves that the APBs and low-density (Nb, Hf)2Al precipitates have a negligible effect on the mechanical performance of the RHEA. Therefore, the Nb40Ti25Al15V10Ta5Hf3W2 RHEA exhibits superior structural stability from 923 K to 1123 K, which also imparts the mechanical stability. This work guides towards tailoring the composition and microstructure of RHEAs for even better high-temperature mechanical performance.

A Multitechnique Study of C2H4 Adsorption on Fe3O4(001).

The adsorption/desorption of ethene (C2H4), also commonly known as ethylene, on Fe3O4(001) was studied under ultrahigh vacuum conditions using temperature-programmed desorption (TPD), scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT)-based computations. To interpret the TPD data, we have employed a new analysis method based on equilibrium thermodynamics. C2H4 adsorbs intact at all coverages and interacts most strongly with surface defects such as antiphase domain boundaries and Fe adatoms. On the regular surface, C2H4 binds atop surface Fe sites up to a coverage of 2 molecules per (√2 × √2)R45° unit cell, with every second Fe occupied. A desorption energy of 0.36 eV is determined by analysis of the TPD spectra at this coverage, which is approximately 0.1-0.2 eV lower than the value calculated by DFT + U with van der Waals corrections. Additional molecules are accommodated in between the Fe rows. These are stabilized by attractive interactions with the molecules adsorbed at Fe sites. The total capacity of the surface for C2H4 adsorption is found to be close to 4 molecules per (√2 × √2)R45° unit cell.

Enhanced coercivity and emergent spin-cluster-glass state in 2D ferromagnetic material, Fe[formula omitted]GeTe[formula omitted

Two-dimensional (2D) van der Waals (vdW) magnetic materials with high coercivity and high TC are desired for spintronics and memory storage applications. Fe3GeTe2 (F3GT) is one such 2D vdW ferromagnet with a reasonably high TC, but with a very low coercive field, HC (≲100 Oe). Here we present a phase-engineered sample of F3GT with enhanced coercivity (7–10 times), without compromising its fundamental magnetic properties (TC≃ 210 K). The parent F3GT phase is infused with a small percentage of randomly embedded clusters of a coplanar FeTe (FT) phase, which serves as both mosaic pinning centers between grains of F3GT above its antiferromagnetic transition temperature (TC1∼ 70 K) and also as anti-phase domains below TC1. As a result, the grain boundary disorder and metastable nature are greatly augmented, leading to highly enhanced coercivity, cluster spin glass, and meta-magnetic behavior. The enhanced coercivity (≃1 kOe) makes F3GT-2 much more useful for memory storage applications.

8.1 μ m-emitting InP-based quantum cascade laser grown on Si by metalorganic chemical vapor deposition

This study presents the growth and characterization of an 8.1 μm-emitting, InGaAs/AlInAs/InP-based quantum cascade laser (QCL) formed on an InP-on-Si composite template by metalorganic chemical vapor deposition (MOCVD). First, for the composite-template formation, a GaAs buffer layer was grown by solid-source molecular-beam epitaxy on a commercial (001) GaP/Si substrate, thus forming a GaAs/GaP/Si template. Next, an InP metamorphic buffer layer (MBL) structure was grown atop the GaAs/GaP/Si template by MOCVD, followed by the MOCVD growth of the full QCL structure. The top-surface morphology of the GaAs/GaP/Si template before and after the InP MBL growth was assessed via atomic force microscopy, over a 100 μm2 area, and no antiphase domains were found. The average threading dislocation density (TDD) for the GaAs/GaP/Si template was found to be ∼1 × 109 cm−2, with a slightly lower defect density of ∼7.9 × 108 cm−2 after the InP MBL growth. The lasing performance of the QCL structure grown on Si was compared to that of its counterpart grown on InP native substrate and found to be quite similar. That is, the threshold-current density of the QCL on Si, for deep-etched ridge-guide devices with uncoated facets, is somewhat lower than that for its counterpart on native InP substrate, 1.50 vs 1.92 kA/cm2, while the maximum output power per facet is 1.64 vs 1.47 W. These results further demonstrate the resilience of QCLs to relatively high residual TDD values.

3C-SiC Island Growth on 4H-Sic Terraces: Statistical Evidence for the Orientation Selection Rule

3C-SiC islands were grown on atomically flat (111) 4H-SiC terraces and characterized by micro-Raman and FTIR. The islands initially have a triangular shape as defined by three {100} planes and over time evolve into hexagonal shaped islands. The triangular shape reveals the domain orientation of the island and is easily observed with an optical microscope. Examining 347 3C-SiC islands on 17 4H-SiC terraces we found that islands grown on the same terrace have the same domain orientation with 99.6% probability. The orientation of 3C-SiC islands grown on adjacent terraces was found to be close to random. This work confirms an orientation selection rule with high probability, suggesting that 3C-SiC can be grown without anti-phase domains or DPBs when grown on a single atomically flat 4H-SiC terrace, even when there are multiple nucleation sites.

Synthetic first-principles studies from phase equilibria to microstructural formation in the Fe-Pt L10 phase

Electronic-structure calculations, the cluster-variation method of statistical mechanics, and the phase-field method were combined in attempted first-principles calculations of phase equilibria and microstructural evolution associated with the disorder-$\mathrm{L}{1}_{0}$ transition of the Fe-Pt system. The calculated disorder-$\mathrm{L}{1}_{0}$ transition temperature was within $\ensuremath{\sim}10$ K difference from the experimental value, and the locus of spinodal ordering temperature is placed in the phase diagram. The calculated microstructure demonstrates preferential growth of the ordered domain along the 100> direction and, in the later period, an anisotropic morphology of an antiphase domain structure develops. We offered an interpretation from the atomistic point of view for this morphology. We therefore achieved consistent first-principles multiscale calculations of phase equilibria and microstructural evolution, bridging microscopic to mesoscopic scales without any adjusting parameters.

Epitaxial Growth of III‐Vs on On‐Axis Si: Breaking the Symmetry for Antiphase Domains Control and Burying

AbstractThis work reports on the precise control of III‐V semiconductors’ antiphase domain formation and evolution during the epitaxial growth on an “on‐axis” Si (001) substrate with a very low but controlled miscut. Especially, it is shown how, starting from a Si surface having a regular array of terraces, the crystal polarity of thin GaAs epilayers grown by molecular‐beam epitaxy is defined through the Si surface topology, leading to a quasi‐periodic 1D pattern of antiphase domains in the GaAs layer. Furthermore, this work demonstrates how this configuration breaks the symmetry between the two different III‐V phases, without any step‐flow‐induced asymmetry. Following this strategy, an early burying of antiphase domains is demonstrated in GaAs epitaxially grown on a low‐miscut Si substrate. This study generalizes previous models describing antiphase domain formation and evolution and establishes the important growth parameters for the development of high crystal quality III‐V semiconductor devices monolithically integrated on low‐miscut silicon substrates.