Twin Domains Research Articles

Dynamic Unbalance Identification in Steady-State Rotating Machinery: A Hybrid Methodology Integrating Physical and Data-Driven Techniques

Rotating machinery plays a strategic role in key industrial sectors, making its analysis a subject of great interest for both academia and industry. Effective maintenance planning for this equipment is essential for asset management and for meeting current industrial requirements. To address this demand, this work presents a novel unbalance identification approach based on a digital representation of a rotating machine's dynamic behavior in relation to the development of specific faults. A hybrid methodology is proposed, integrating Finite Element Modeling, a Kalman Filter for parameter estimation, and Referenced Moving Window Principal Component Analysis. This Principal Component Analysis extension enhances vibration pattern recognition, enabling accurate fault quantification directly from slight changes in the system's steady-state behavior. The methodology uniquely eliminates the need for phase angle measurements, facilitating continuous monitoring of unbalance progression in steady-state conditions. Two case studies demonstrate the methodology's potential: one utilizing synthetic data from a Floating Production Storage and Offloading centrifugal compressor unit, and the other based on real data from a hydroelectric turbine-generator. These studies illustrate the integration of computational modeling, data-driven analysis, and monitored vibration data, achieving robust and accurate unbalance identification. This approach provides valuable insights into current capabilities and opens promising pathways for future applications, particularly in the digital twin domain for rotating machinery.

{101¯4} twin boundary in calcite: Structure and physical properties

Calcite, a CaCO3 polymorph, is one of the most significant materials in nature. In addition to its fundamental role in the global carbon cycle, it fills an unparalleled range of applications, both as a natural biomineral and more directly engineered materials. One of the most notable characteristics of calcite is its tendency to form twins, the boundaries of which are expected to determine key attributes of the host mineral at mesoscopic scales. Using a classical molecular dynamics simulation performed with a thermodynamically consistent rigid-ion force field, we show that the walls between the two twin domains aligned along the hexagonal (101¯4) plane of calcite have some unexpected properties: (1) rather than monoatomic planes, these twin walls are composed of two layers with fundamentally different distortions, (2) atomic shifts within the twin walls create strong polarity while the bulk remains centrosymmetric, and (3) the temperature evolution of the structural order parameter is mostly, but not completely, related to the tilt and rotation of CO32− molecules. Molecular dynamics simulations using thermodynamically accurate interatomic potentials demonstrate that the temperature evolution of twin walls is different from that of the bulk material. We show that kinks in twin walls have a low energy and generate high structural disorder near the kink position. Our methods are applicable to other molecular systems and emphasize the dominance of twin walls in materials. Published by the American Physical Society 2024

Twin-free thermal laser epitaxy of Si on sapphire

The heteroepitaxial growth of silicon (Si) is essential for modern electronics. Our study investigates the potential of thermal laser epitaxy (TLE) for Si epitaxy. A systematic study on the evaporation behavior of Si during TLE identifies and addresses the causes of notable flux rate fluctuations, resulting in a Si flux with ±0.3% stability over time. We also demonstrate heteroepitaxy of Si on c-plane sapphire substrates via TLE. High-temperature substrate preparation combined with deposition at a substrate temperature of 1000 °C produced high-quality epitaxial Si (111) films without twin domains.

Defect Structure and Luminescence of κ‐Ga2O3 Micro‐Monocrystals

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

Transcribing RNA polymerases: Dynamics of twin supercoiled domains

Gene transcription by an RNA polymerase (RNAP) enzyme requires that double-stranded DNA be locally and transiently opened, which results in an increase of DNA supercoiling downstream of the RNAP and a decrease of supercoiling upstream of it. When the DNA is initially torsionally relaxed and the RNAP experiences sufficiently large rotational drag, these variations lead to positively supercoiled plectonemes ahead of the RNAPs and negatively supercoiled ones behind it, a feature known as “twin supercoiled domain” (TSD). This work aims at deciphering into some more detail the torsional dynamics of circular DNA molecules being transcribed by RNAP enzymes. To this end, we performed Brownian dynamics simulations with a specially designed coarse-grained model. Depending on the superhelical density of the DNA molecule and the ratio of RNAP’s twist injection rate and rotational relaxation speed, simulations reveal a rich panel of behaviors, which sometimes differ markedly from the crude TSD picture. In particular, for sufficiently slow rotational relaxation speed, positively supercoiled plectonemes never form ahead of an RNAP that transcribes a DNA molecule with physiological negative supercoiling. Rather, negatively supercoiled plectonemes form almost periodically at the upstream side of the RNAP and grow up to a certain length before detaching from the RNAP and destabilizing rapidly. The extent to which topological barriers hinder the dynamics of TSDs is also discussed.

Digital Twins Verification and Validation Approach through the Quintuple Helix Conceptual Framework

The concept of digital twins has been in the field for a long time, constantly challenging the specification, modeling, design, implementation, and exploitation of complex cyber–physical systems. Despite the various foundations, standards, and platforms in systems engineering, there are ongoing challenges with verification and validation methodology. This study aims to establish a generic framework that addresses the various aspects of digital twinning. The multifaceted nature of the problem requires raising the abstraction level in both the real (actual) and virtual domains, effective dissemination of information resources, and a design inspired by verification and validation. The proposed framework combines the quintuple helix model with the problem and operational domains of a real (actual) twin, the solution and implementation domains of a virtual twin, and the execution domain as the bridge that links them. Verification and validation dimensions follow the meta object facility abstraction layers (instance, model, meta-model, and meta-meta-model) mapping over five helices. Embedding the complexity reduction mechanisms in the proposed framework builds a suite for extendible and verifiable digital twinning in simulation and real-time scenarios. The application of main conceptual framework mechanisms in a real-world example study aids the verification of this research’s intentions. The validation is a matter of further research endeavors.

Solute Segregation and Pinning Effect on Lateral Twin Boundary in Magnesium

Deformation twinning creates a three-dimensional twin domain via the migration of forward, normal and lateral twin boundaries (TBs) with respect to twin shear direction, normal to twin plane and twin lateral direction. Solute segregation and pinning effect on the forward and normal TBs have been experimentally observed and demonstrated via atomistic simulations. Here, we conducted a comprehensive study of solute segregation and the pinning effect on the lateral TBs in Mg. First-principles density functional theory calculations were used to obtain the segregation and formation energies of 19 alloying elements in coherent regions of lateral TBs. Alloying elements with greater difference in atomic radius from Mg generally show more negative segregation energy. Moreover, alloying elements with good solubility are selected to demonstrate the pinning effect on a coherent interface. Ge, Ga, Y, Gd, La and Ca show negative segregation energy and solubility energy, indicating that these elements can form stable segregation and have a strong pinning effect at the lateral boundary. Molecular dynamics simulations revealed that solutes in coherent regions are more effective in pinning lateral TBs than those in misfit regions. The results provide insight into the selection of solute atoms for tailoring twinning behavior.

Enhancing the mechanical and electrochemical corrosion properties of Cu composites via manipulation of intragranular graphene quantum dots cluster

Intragranular distribution of reinforcements is highly valued for simultaneously improving strength and corrosion resistance in metal composites. Here, we manipulated zero-dimensional graphene quantum dots (GQDs) clusters into Cu grain interiors via a “nanodispersion-in-grains” strategy. The uniformly dispersed GQDs clusters activate multiple hardening mechanisms resulted in superior mechanical strengthening efficiency (Seff = 228). Furthermore, GQDs clusters contribute to induce the twin domains in composites via forming high stress field, which would elevate the grain boundary stability and in turn restrained the corrosion process. Compared with pure Cu, 0.2 GQDs/Cu composite has a lower corrosion current density (1.50 × 10−5 A cm−2), reducing the corrosion rate by 31.2%. Our work has provided a feasible route to broaden the Cu composites application as reliable structural components.

Reaction-controlled shape evolution and insights into the growth mechanism of CsPbBr3 nanocrystals

The correlation between structural transformation and optical characteristics of cesium lead bromide (CsPbBr3) nanocrystals (NCs) suggests insights into their growth mechanism and optical performance. Systematic control of reaction parameters led to the successful fabrication of on-demand shape-morphing CsPbBr3 NCs. Transmission electron microscopy observations showed that the shape transformation from nanocubes to microcrystals could be accelerated by increasing the precursor:ligand molar ratio and reaction time. Further evidence for orthorhombic CsPbBr3 NCs was obtained from their selected-area electron diffraction pattern, which exhibits a twin domain induced by the presence of large NCs. Likewise, we observed a substantial decrease in photoluminescence (PL) intensity of CsPbBr3 due to surface decomposition or surface ligand loss resulting from increased size. In addition, fusion of smaller particles having other dimensionality induced the increase in the PL full-width at half maximum. In particular, existence of larger bulk material caused a reduction in the peak intensity in the absorption spectra and a trend of decreasing tendency in intensity of the absorption bands related to bromoplumbate species provided direct evidence of fully converted Cs-oleate.

The Role of Interfacial Interactions and Oxygen Vacancies in Tuning Magnetic Anisotropy in LaCrO3/LaMnO3 Heterostructures

AbstractThe interplay of lattice, electronic, and spin degrees of freedom at epitaxial complex oxide interfaces provides a route to tune their magnetic ground states. Unraveling the competing contributions is critical for tuning their functional properties. The relationship between magnetic ordering and magnetic anisotropy and the lattice symmetry, oxygen content, and film thickness in compressively strained LaMnO3 (LMO)/LaCrO3 (LCO) superlattices is investigated. Mn–O–Cr antiferromagnetic superexchange interactions across the heterointerface result in a net ferrimagnetic magnetic structure. Bulk magnetometry measurements reveal isotropic in‐plane magnetism for as‐grown oxygen‐deficient thin samples due to equal fractions of orthorhombic a+a‐c‐, and a‐a+c‐ twin domains. As the superlattice thickness is increased, in‐plane magnetic anisotropy emerges as the fraction of the a+a‐c‐ domain increases. On annealing in oxygen, the suppression of oxygen vacancies results in a contraction of the lattice volume, and an orthorhombic to rhombohedral transition leads to isotropic magnetism independent of the film thickness. The complex interactions are investigated using high‐resolution synchrotron diffraction and X‐ray absorption spectroscopy. These results highlight the role of the evolution of structural domains with film thickness, interfacial spin interactions, and oxygen‐vacancy‐induced structural phase transitions in tuning the magnetic properties of complex oxide heterostructures.

Lattice match between coexisting cubic and tetragonal phases in PMN-PT at the phase transition

(1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) perovskite-like solid solutions are recognized for their outstanding electromechanical properties, which are of technological importance. However, some significant aspects of the crystal structures and domain assemblages in this system and the role of these characteristics in defining the functional performance of PMN-PT remain uncertain. Here, we used synchrotron x-ray diffraction to investigate the phase transition linking the paraelectric (cubic) and ferroelectric (tetragonal) phases in a single crystal of 0.65PMN-0.35PT. We analyzed the evolution of reciprocal-space maps across this transition. These maps were collected using small temperature step (1 K) and a high reciprocal-space resolution to reveal changes in the splitting of Bragg peaks caused by the formation of ferroelastic domains in the low-symmetry phase. Our results uncovered a two-phase state, cubic plus tetragonal phases, which exists over a narrow temperature range of only ≈4 K and exhibits a thermal hysteresis of ≈1.8 K. Remarkably, within this state, the lattice parameter of the cubic phase, aC, matches the orientational average of the lattice parameters for the tetragonal polymorph, 23aT+13cT. We discuss the implications of this matching, highlighting the possibility of it being realized by the formation of an assemblage of tetragonal twin domains separated from the cubic phase by a strain-free {110} boundary, as in the “adaptive phase” but without domain miniaturization.

High-resolution spectroscopy of LaAlO3-Pr3+ pseudo-cubic perovskite single crystals: Crystal-field parameters, hyperfine and deformation splittings

We report high-resolution measurements and analysis of the optical transmission and emission spectra of a concentration series of La(1-x)PrxAlO3 (x = 10−3, 9 ⋅ 10−3, and 2 ⋅ 10−2) single crystals in a wide frequency range ((2-27) ⋅ 103 cm−1) at temperatures 5–300 K, below the structural phase transition from the cubic Pm3‾m to the rhombohedral R3‾c phase. Pr3+ ions substitute for La3+ ions at sites with point symmetry D3. All recorded spectral lines are assigned to specific initial and final crystal-field (CF) energy levels, the scheme of CF levels is constructed and described by an appropriate set of CF parameters. The structural phase transition is accompanied by shear strains and the formation of ferroelastic twin domains of four types compressed along one of the four C3 axes in the parent cubic crystal lattice. Specific features of the measured spectra, namely, anomalous broadening of spectral lines and doublet structure of some lines corresponding to transitions between CF singlets and doublets, are considered as a result of interaction of 4f electrons with the field of random shear deformations competing at the boundaries of twin domains. Modeling of the observed line shapes was performed taking into account both hyperfine interactions and random lattice strains, as well as the effect of temperature. The width (6.6 ± 0.7)⋅10− 4 of the introduced two-dimensional distribution function of random strains was found from a comparison of simulated and measured profiles of the split spectral lines. The results of this work can be applied for quantitative assessment of crystal quality.

Ilmenite phase transformations in suevite from the Ries impact structure (Germany) record evolution in pressure, temperature, and oxygen fugacity conditions

Abstract Aggregates of ilmenite with varying amounts of rutile, ferropseudobrookite, and pseudorutile in suevites from the Ries impact structure have been analyzed by light microscopy, analytical scanning electron microscopy, electron microprobe analysis, and Raman spectroscopy to constrain their formation conditions. The tens to hundreds of micrometer aggregates comprise isometric ilmenite grains up to 15 µm in diameter that form a foam structure (i.e., smoothly curved grain boundaries and 120° angles at triple junctions). Grains with foam structure show no internal misorientations, indicating a post-impact formation. In contrast, ilmenite grains with internal misorientation occurring in the core of the aggregates are interpreted as shocked remnant ilmenite originating from the target gneisses. They can contain twin lamellae that share a common {1120} plane with the host, and the c-axis is oriented at an angle of 109° to that of the host. Similarly, the new grains with foam structure display up to three orientation domains, sharing one common {1120} plane for each pair of domains and c-axes at angles of 109° and 99°, respectively. This systematic orientation relationship likely reflects a cubic supersymmetry resulting from the transformation of the initial ilmenite upon shock (>16 GPa) to a transient perovskite-type high-pressure phase (liuite), subsequent retrograde transformation to the polymorph wangdaodeite, and then back-transformation to ilmenite. Whereas, the new grains with foam structure formed from complete transformation, the twin domains in the shocked ilmenite are interpreted to represent only partial transformation. Ferropseudobrookite occurs mostly near the rim of the aggregates. An intergrowth of ferropseudobrookite, ilmenite, and rutile, as well as magnetite or rarely armalcolite occurs at contact with the (devitrified) matrix. The presence of ferropseudobrookite indicates high temperature (>1140 °C) and reducing conditions. The surrounding matrix provided Mg2+ to form the ferropseudobrookite-armalcolite solid solution. Rutile can occur within the aggregates and/or along the ilmenite boundaries; it is interpreted to have formed together with iron during the decomposition of ilmenite at lower temperatures (850–1050 °C). We suggest magnetite in the rims formed by electrochemical gradients driven by the presence of a reducing agent, where Fe2+ within ilmenite diffused toward the rim. Subsequent cooling under oxidizing conditions led to the formation of magnetite from the iron-enriched rim as well as pseudorutile around ilmenite grains. Our study demonstrates that the specific crystallographic relationships of ilmenite grains with foam structure indicate a back-transformation from high (shock) pressures >16 GPa; moreover, the presence of associated Fe-Ti-oxides helps indicate local temperature and oxygen fugacity conditions.

Monoclinic Pleysteinite and Hochleitnerite from the Hagendorf-Süd Pegmatite: Synchrotron Microfocus Diffraction Studies on Twinned Members of Paulkerrite-Group Minerals

Abstract Single-crystal X-ray diffraction data sets for pleysteinite, [(H2O)K]Mn2Al3(PO4)4F2(H2O)10·4H2O, and hochleitnerite, [(H2O)K]Mn2(Ti2Fe)(PO4)4O2(H2O)10·4H2O, collected using a synchrotron microfocus beam, gave monoclinic unit cells, in contrast to previously reported orthorhombic cells obtained using laboratory-based sealed-tube diffractometer data. The differences are attributed to twinning in crystals of the two minerals. As the laboratory diffractometer beam diameter of the sealed-tube SXRD is larger than the crystals that were analyzed, the diffraction results were averaged over the different twin domains, whereas those obtained with the synchrotron microfocus beam gave diffraction data wholly or predominantly from a single domain. Data from the synchrotron datasets give a = 10.440(5) Å, b = 20.588(5) Å, c = 12.234(2) Å, β = 90.38(1)° for pleysteinite and a = 10.547(2) Å, b = 20.577(4) Å, c = 12.373(2) Å, β = 90.09(3)° for hochleitnerite. The crystal structures for both minerals were refined in P21/c, giving Robs = 0.059, 0.058 for 5951, 6718 reflections with I > 3σ(I), respectively. The ideal formulae for the two minerals in this setting conform to the general formula A1A2M12M22M3(PO4)4X2(H2O)10·4H2O, with K and H2O ordered at separate A sites, whereas K and H2O were disordered over a single A site in the orthorhombic models (space group Pbca). Crystal-chemical aspects of the paulkerrite-group minerals, pleysteinite, hochleitnerite, paulkerrite, rewitzerite, and macraeite, are compared and discussed.

Electronic Properties of W’ Twin Walls in Ferroelastic BiVO4

AbstractTopological defects in ferroic materials can exhibit intrinsic properties that differ from the bulk. Here， structural and electronic variations of non‐prominent (W’) ferroelastic twin domain walls are investigated in BiVO4, a widely investigated photocatalytic material. Using aberration‐corrected scanning transmission electron microscopy (STEM), a kink configuration of the sharp ferroelastic twin wall with an altered electronic structure is revealed. Nanoscale conductivity measurements by conductive atomic force microscopy (c‐AFM) show higher conductivity at twin walls compared to non‐conductive bulk domains. Electronic structure investigation by electron energy loss spectroscopy (EELS) shows a higher density of oxygen vacancies and possible polaron accumulation at the wall. These findings reveal the electronic properties of BiVO4 domain walls, which are interesting for nanoscale‐engineered catalytic concepts of BiVO4 and materials design for photochemistry‐relevant applications.

Effect of carbon coating on surface structure in annealing process of high-dose implanted/annealed SiC

The effect of carbon coating on a surface structure of a high-dose implanted/annealed silicon carbide (SiC) during annealing was examined using scanning probe microscopy (SPM), deep-ultraviolet (DUV) Raman spectroscopy, and transmission electron microscopy (TEM). In SPM, the surfaces of 500- and 30 °C-implanted/annealed SiC samples without coating exhibited a periodic-step structure and granular structure, respectively. The difference between these surfaces is attributed to the absence or presence of residual implantation damage. In contrast, surface flatness was maintained in the 500 °C-implanted/annealed SiC sample with carbon coating. However, the surface of the coated 30 °C-implanted/annealed SiC sample exhibited a geometric structure with a lattice pattern parallel to the ⟨112¯0⟩ axes. The DUV Raman spectra and TEM images indicated that the implanted layer of this sample metamorphosed into a mixture of 3C-SiC twin domains and amorphous-SiC regions. During the cooling process after annealing, the 3C-SiC region was more raised than the amorphous-SiC region owing to the difference in the thermal expansion coefficients, thus resulting in the generation of a geometric surface structure. In the metamorphosed implanted layer, the carbon coating does not completely prevent surface roughening.

Synthesis and crystal structure of (NH4)[Ni3(HAsO4)(AsO4)(OH)2

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate di-hydroxide, was synthesized under hydro-thermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexa-gonal (001) 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octa-hedra and [AsO3.5(OH)0.5] tetra-hedra as the building units. The hydrogen atom of the OH group shows occupational disorder and was refined with a site occupation factor of 1/2, indicating the equal presence of [HAsO4]2- and [AsO4]3- groups. Strong asymmetric hydrogen bonds between symmetry-related (O,OH) groups of the arsenate units [O⋯O = 2.588 (18) Å] as well as hydrogen bonds accepted by these (O,OH) groups from OH groups bonded to the NiII atoms [O⋯O = 2.848 (12) Å] link adjacent layers. Additional consolidation of the packing is achieved through N-H⋯O hydrogen bonds from the ammonium ion, which is sandwiched between adjacent layers [N⋯O = 2.930 (7) Å] although the H atoms could not be located in the present study. The presence of the pseudo-hexa-gonal 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers may be the reason for the systematic threefold twinning of (NH4)[Ni3(HAsO4)(AsO4)(OH)2] crystals. Significant overlaps of the reflections of the respective twin domains complicated the structure solution and refinement.

Electronic structure along Sm[formula omitted]Co[formula omitted]Ge[formula omitted] twin boundaries

Ln2Co3Ge5 (Ln = lanthanide) intermetallics possess intriguing electronic and magnetic properties. The compound Sm2Co3Ge5 exhibits antiferromagnetic ordering coupled with a magnetic moment that exceeds the theoretical moment of trivalent Sm suggesting a magnetic contribution from Co. Twinning is observed in Sn flux-grown monoclinic Sm2Co3Ge5 along (100) planes. While the influence of twin boundaries on superconducting oxides and 2D-materials is well-studied, its effects on bulk lanthanide-based intermetallics are rarely explored. Using monochromated electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (TEM), we investigate the impact of twin domains on the local strain and electronic structure of Sm2Co3Ge5. The boundaries between twinned domains primarily exhibit shear strain and have a constant oxidation state, but fine structure emerges in the Co L2,3 edges at twin boundaries, indicative of 3d-electron hybridization and occupation of states not present in bulk grain spectra. These findings provide insights into tuning the bulk properties of lanthanide-transition metal systems with complex magnetism.

Human-Robot handover task intention recognition framework by fusing human digital twin and deep domain adaptation

Industry 5.0 is conceived to achieve the expected high level of smart manufacturing and the more proactive and adaptive human-robot collaboration (HRC). In particular, human-robot handover tasks (HRHTs) are a notably crucial aspect of HRC, and resolving how to motivate robots to comprehend human handover intentions constitutes an exigent issue that demands resolution. To address these problems, A framework that integrates hierarchical human digital twin (HHDT) and deep domain adaptation is proposed, where HHDT model is built to digitise the human physical and physiological state and enhance the robot's perception of humans, a feature extractor-based on bidirectional long-short-term memory and spatio-temporal graph convolution network (BiLSTM-ST-GCN) is devised to extract latent spatio-temporal features of HRHTs intentions. Additionally, the framework incorporates a deep domain adaptation layer (DDAL) that facilitates knowledge transfer of HRHTs intentions by accounting for the distribution differences between the source and target operator objects. Extensive experiments demonstrate the superior performance of the proposed framework for HRHTs intention recognition and extraction of domain invariant features.

Molecular Beam Epitaxy of β-(InxGa1-x)2O3 on β-Ga2O3 (010): Compositional Control, Layer Quality, Anisotropic Strain Relaxation, and Prospects for Two-Dimensional Electron Gas Confinement.

In this work, we investigate the growth of monoclinic β-(InxGa1-x)2O3 alloys on top of (010) β-Ga2O3 substrates via plasma-assisted molecular beam epitaxy. In particular, using different in situ (reflection high-energy electron diffraction) and ex situ (atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, and transmission electron microscopy) characterization techniques, we discuss (i) the growth parameters that allow for In incorporation and (ii) the obtainable structural quality of the deposited layers as a function of the alloy composition. In particular, we give experimental evidence of the possibility of coherently growing (010) β-(InxGa1-x)2O3 layers on β-Ga2O3 with good structural quality for x up to ≈ 0.1. Moreover, we show that the monoclinic structure of the underlying (010) β-Ga2O3 substrate can be preserved in the β-(InxGa1-x)2O3 layers for wider concentrations of In (x ≤ 0.19). Nonetheless, the formation of a large amount of structural defects, like unexpected () oriented twin domains and partial segregation of In is suggested for x > 0.1. Strain relaxes anisotropically, maintaining an elastically strained unit cell along the a* direction vs plastic relaxation along the c* direction. This study provides important guidelines for the low-end side tunability of the energy bandgap of β-Ga2O3-based alloys and provides an estimate of its potential in increasing the confined carrier concentration of two-dimensional electron gases in β-(InxGa1-x)2O3/(AlyGa1-y)2O3 heterostructures.