Stacking Order Research Articles

Unveiling the stacking-dependent electronic properties of the 2D ultrathin rare-earth metalloxenes family LnX2 (Ln = Eu, Gd, Dy; X = Ge, Si)

It is discovered that in 2D rare-earth metalloxenes the capping layer enables the modification of the stacking order within metalloxene film and induces changes in the electronic band-structure and magnetic ground-state.

Effect of annealing on the molecular ordering and crystal structure of iron phthalocyanine thin films on Si (111) surface

The Effect of annealing on molecular ordering in Iron Phthalocyanine (FePc) thin films deposited on Si (111) substrate surface was investigated using lab source (Cu Kα) based x-ray diffraction, synchrotron based 2-dimensional grazing incidence x-ray diffraction, polarization dependent x-ray absorption spectroscopy and hard x-ray photoelectron spectroscopy. Room temperature deposition of FePc on Si substrate resulted in amorphous thin films with randomly oriented FePc molecules. However, annealing of these amorphous films at 200°C led to crystallization with highly ordered FePc molecules having monoclinic crystal lattice structure. The ordered FePc molecules followed edge-on stacking on Si substrate surface with an azimuthally averaged tilt angle of 75±5° between molecular plane and substrate surface. Also, the b-c plane of the unit cell was lying almost parallel to the substrate surface. The edge-on stacking ordering of FePc molecules in annealed thin films led to higher charge conduction as compared to as-deposited films.

Stacking Order Engineering of Two-Dimensional Materials and Device Applications.

Stacking orders in 2D van der Waals (vdW) materials dictate the relative sliding (lateral displacement) and twisting (rotation) between atomically thin layers. By altering the stacking order, many new ferroic, strongly correlated and topological orderings emerge with exotic electrical, optical and magnetic properties. Thanks to the weak vdW interlayer bonding, such highly flexible and energy-efficient stacking order engineering has transformed the design of quantum properties in 2D vdW materials, unleashing the potential for miniaturized high-performance device applications in electronics, spintronics, photonics, and surface chemistry. This Review provides a comprehensive overview of stacking order engineering in 2D vdW materials and their device applications, ranging from the typical fabrication and characterization methods to the novel physical properties and the emergent slidetronics and twistronics device prototyping. The main emphasis is on the critical role of stacking orders affecting the interlayer charge transfer, orbital coupling and flat band formation for the design of innovative materials with on-demand quantum properties and surface potentials. By demonstrating a correlation between the stacking configurations and device functionality, we highlight their implications for next-generation electronic, photonic and chemical energy conversion devices. We conclude with our perspective of this exciting field including challenges and opportunities for future stacking order engineering research.

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T' Transition Metal Dichalcogenide Nanosheets.

The past few decades have witnessed a notable increase in transition metal dichalcogenide (TMD) related research not only because of the large family of TMD candidates but also because of the various polytypes that arise from the monolayer configuration and layer stacking order. The peculiar physicochemical properties of TMD nanosheets enable an enormous range of applications from fundamental science to industrial technologies based on the preparation of high-quality TMDs. For polymorphic TMDs, the 1T/1T' phase is particularly intriguing because of the enriched density of states, and thus facilitates fruitful chemistry. Herein, we comprehensively discuss the most recent strategies for direct synthesis of phase-pure 1T/1T' TMD nanosheets such as mechanical exfoliation, chemical vapor deposition, wet chemical synthesis, atomic layer deposition, and more. We also review frequently adopted methods for phase engineering in TMD nanosheets ranging from chemical doping and alloying, to charge injection, and irradiation with optical or charged particle beams. Prior to the synthesis methods, we discuss the configuration of TMDs as well as the characterization tools mostly used in experiments. Finally, we discuss the current challenges and opportunities as well as emphasize the promising fields for the future development.

Error-Aware, Layer-Resolved Characterisation of Lithium-Ion Batteries Based on Ultrasonic Resonance and Parametric Analysis

With the prevalence of electrification in transportation and grid storage sectors, lithium-ion batteries (LIBs) are becoming one of the most fundamental energy storage elements and undergoing a profound trend of performance upscaling. The upscaled batteries demand next-level characterisation methodologies, and particularly appealing is the capability to resolve inner structural and morphological information physically, so as to identify the internal state and evolutions precisely and cost-effectively. In recent years, ultrasonic measurements have been proven as promising candidates for probing and inspecting LIBs. However, such approaches can only measure peripheral geometric features at a cell-level resolution and their characterisation performances tend to be subject to empirical configurations and sensitive to measurement conditions. To address these issues, this work reports an ultrasonic resonance-based method, featuring reliable characterisation performance, to realise layer-level robust inversion of the layered structure within LIBs. Firstly, a generalised theoretical model is introduced to capture the interaction characteristics between the ultrasound and the multilayer structure inside LIBs. By incorporating the captured characteristics into the analytic-signal procedure, a systematical framework is established to retrieve the stacking order, individual thickness, and local geometry information in a layer-resolved manner1, 2. Then, the relationship between the measurement parameters and the characterisation performance is analytically investigated. By considering both the temporal and spatial metrics, the performance evaluation indices are determined, with the critical measurement parameters recognised according to their physical significance. After that, the impacts of measurement parameters on the characterisation performance of LIBs are thoroughly studied by carrying out parametric analysis on the response signal simulated by the ultrasonic resonance model. Guided by such a relationship, an optimal strategy for parameter selection is developed to ascertain reliable characterisation, with its level of errors being predictable. Finally, experimental studies are carried out on different batteries with the ground truth obtained by the micro X-ray computed tomography, and the effectiveness and reliability of the proposed characterisation method are carefully validated. The proposed method demonstrates reliable performance in characterising layered structure within LIBs and could pave the way for developing performance-informed monitoring and prediction algorithms for state of health and state of safety estimations of LIBs. References M. Huang, N. Kirkaldy, Y. Zhao, Y. Patel, F. Cegla, and B. Lan, Journal of Energy Storage, 50 104585 (2022).R. A. Smith, L. J. Nelson, M. J. Mienczakowski, and P. D. Wilcox, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 65 (2), 231-243 (2018).

Experimental and numerical evaluation of mechanical performances of hybrid Palmyra-Palm-Leaf-Stalk/Glass fiber reinforced polyester composites

In the present work, four layered Palmyra-Palm-Leaf-Stalk (PPLSF)/Glass hybrid composites laminates with six distinct stacking orders were made by following hand lay-up method. Different experiments were carried out to determine the tensile, flexural, impact and hardness of the laminates as per ASTM standard. The results reveal that the addition of glass fiber to PPLSF significantly enhanced the mechanical performance of the laminates. On successive replacement of PPLSF by glass fiber, an enhancement of properties such as 291.39% for tensile strength, 72.08% for flexural strength, 75.82% for impact strength, and 78.44% for micro-hardness was observed. Again, it is also noticed that the stacking order plays an important role in influencing the properties while comparing experimental finding of laminates with equal weight percentages PPLSF and glass fiber. Further to perform Finite Element Analysis (FEA), a 3D CAD model of tensile and flexural specimen was created in space-claim modeler of ANSYS R19.0 and subsequently imported to generate numerical predicted values. While comparing the numerical and experimental results, there was very good agreement among the results was found. Scanning Electron Microscope (SEM) was used for fractography analysis of the tested samples to examine the different mode of failures.

Stacking-Controlled Growth of rBN Crystalline Films with High Nonlinear Optical Conversion Efficiency up to 1.

Nonlinear optical crystals lie at the core of ultrafast laser science and quantum communication technology. The emergence of 2Dmaterials provides a revolutionary potential for nonlinear optical crystals due to their exceptionally high nonlinear coefficients. However, uncontrolled stacking orders generally induce the destructive nonlinear response due to the optical phase deviation in different 2D layers. Therefore, conversion efficiency of 2D nonlinear crystals is typically limited to less than 0.01% (far below the practical criterion of >1%). Here, crystalline films of rhombohedral boron nitride (rBN) with parallel stacked layers are controllably synthesized. This success is realized by the utilization of vicinal FeNi (111) single crystal, where both the unidirectional arrangement of BN grains into a single-crystal monolayer and the continuous precipitation of (B,N) source for thick layers are guaranteed. The preserved in-plane inversion asymmetry in rBN films keeps the in-phase second-harmonic generation field in every layer and leads to a record-high conversion efficiency of 1% in the whole family of 2D materials within the coherence thickness of only 1.6µm. The work provides a route for designing ultrathin nonlinear optical crystals from 2D materials, and will promote the on-demand fabrication of integrated photonic and compact quantum optical devices.

Controlling spin polarization of gapless states in defected trilayer graphene with a gate voltage

Trilayer graphene exhibits valley-protected gapless states when the stacking order changes from ABC to CBA and a gate voltage is applied to outer layers. Some of these states survive strong distortions of the trilayer. For example, they persist when the outer layers are partially devoid yielding a system of two trilayers of different stacking order connected by a strip of a single graphene layer. Here we investigate how these states respond to another perturbation, i.e., the presence of magnetic defects, which we model as π-vacancies. We show that the gap states hybridize with the defect states and strongly spin-split. More importantly, it is demonstrated that by changing the gate voltage value one can change the spin density of the gap states and the corresponding currents at the Fermi level.

Polytypic transformation behavior from 4H-SiC to 3C-SiC during high-speed scratching of single crystalline silicon carbide

The phase transformation behavior and associated mechanism of 4H-SiC induced by dynamic processing at room temperature conditions can be investigated with high-speed scratching tests. A dedicated high-speed scratching setup is developed to achieve the speed range over 10 m/s to 30 m/s while microscopic detection is performed to study the microstructural alteration of 4H–SiC. Raman spectra analyses indicate that the polytypic transformation from 4H to 3C occurs during high-speed scratching of single crystalline silicon carbide. Transmission electron microscopy demonstrates a shift in the stacking order of the atomic layers to face-centered cubic at the subsurface of the scratched groove, which reveals the formation mechanism of 3C-SiC. Furthermore, the 4H to 3C polytypic transformation exhibits a sensitive scratching speed correlation. The research can enhance the fundamental understanding of the mechanisms of damage formation during manufacturing of 4H-SiC components and provide g guidance for high-quality processing of 4H-SiC crystals.

Controlling the 2D Magnetism of CrBr3 by van der Waals Stacking Engineering.

The manipulation of two-dimensional (2D) magnetic order is of significant importance to facilitate future 2D magnets for low-power and high-speed spintronic devices. van der Waals stacking engineering makes promises for controllable magnetism via interlayer magnetic coupling. However, directly examining the stacking order changes accompanying magnetic order transitions at the atomic scale and preparing device-ready 2D magnets with controllable magnetic orders remain elusive. Here, we demonstrate the effective control of interlayer stacking in exfoliated CrBr3 via thermally assisted strain engineering. The stable interlayer ferromagnetic (FM), antiferromagnetic (AFM), and FM-AFM coexistent ground states confirmed by the magnetic circular dichroism measurements are realized. Combined with the first-principles calculations, the atomically resolved imaging technique reveals the correlation between magnetic order and interlayer stacking order in CrBr3 flakes unambiguously. A tunable exchange bias effect is obtained in the mixed phase of FM and AFM states. This work will introduce new magnetic properties by controlling the stacking order and sequence of 2D magnets, providing ample opportunities for their application in spintronic devices.

Layer number and stacking order dependent thermal transport in molybdenum disulfide with sulfur vacancies

Layer number and stacking order dependent thermal transport in molybdenum disulfide with sulfur vacancies

LVI and CAI Analysis of Woven Carbon Fiber Reinforced Composite Laminates with Different Stacking Sequence

The study investigates LVI testing on woven carbon fiber-reinforced composite laminates at three different energy levels and assesses the specimens for their compressive strengths. X-ray CT scans are used to study the damaged envelopes, which allows better insights into the damage progression and failure mechanisms of the composite. The study investigates how post-impact damage propagation is influenced by alterations in impact energy and stacking orientation. The findings demonstrated that several variables, such as the characteristics of the constituent materials, the stacking order, laminate thickness, and ply orientations, had an impact on the CAI strength of the composite laminate. These findings highlight the importance of considering multiple factors when designing composite materials that can withstand impact loading and maintain their structural integrity. Even in specimens showing barely perceptible surface damage, a considerable drop in compressive strength is seen after the LVI testing. When specimens are struck with 25 J of energy, the compressive strength reduction reached a maximum value of 15.68%. In CAI testing, it is typical for sub-laminates to buckle near the impact-induced damage zone, resulting in failure. The magnitude of impact damage area can significantly affect the CAI strength, as the damaged area may create a stress concentration that can lead to buckling or other types of failure. Therefore, it is important to consider the impact energy and damage size when evaluating the CAI strength of composite materials.

Ballistic performance of spaced multi-ply soft fabrics: Experimental and numerical investigation

It has been reported that the ply gap influences the ballistic resistance of spaced multi-ply fabric systems, but its working mechanism was not well-understood. This paper reports the experimental and numerical approaches and results of an investigation on the mechanisms that enable the improved ballistic performance of spaced multi-ply systems. Penetration tests were performed over a range of impact velocities ranging from 200 m/s to 400 m/s. The results confirmed that the ply gap is beneficial to the energy absorption capability of the systems. This is because the front plies tend to absorb more energy when they are not immediately constrained by the rear plies. During a ballistic event, the gap relieves the reflection of the compressive pulse, prolonging the projectile engagement time with the front plies; on the other hand, the rear plies become increasingly less active in dissipating energy as the gap increases. When the gap is sufficiently widened to avoid any interference between the plies before the failure of the front ply, the responses of the whole system no longer vary. It was also found that the ballistic performance of the spaced systems is influenced by ply thickness, impact velocity, and the stacking order of the ply gap.

Influence of hydrothermal conditions on the mechanical properties of hybrid composite pipes

Composite materials are becoming widespread in many sectors today, especially in the defence and space industry. Composite materials can be exposed to significant temperature changes and various environmental conditions depending on their usage areas. Therefore, composite materials with high resistance to high temperatures and harsh environmental conditions are being studied today. In this study, four types of 6-layer composite pipes with glass/glass/glass, basalt/basalt/basalt, glass/basalt/glass and basalt/glass/basalt stacking sequences were fabricated with filament wound method. In order to simulate the behavior of composite materials under environmental conditions, specimens were subjected to hydrothermal aging in pure water at 70°C for three different periods of 500, 1000 and 1500 hours. During the aging process, the mass changes of the pipes were measured regularly, and the water absorption behavior was determined with reference to ASTM D5229 standard. Hardness tests were carried out with Rockwell hardness tester based on ASTM D785 standard. As a result of the study, it was determined that the mechanical performance of hybrid specimens was higher than that of non-hybrid specimens. It was observed that the hydrothermal aging process caused a loss of mechanical strength in all specimens. It was concluded that the hybrid composite specimen with basalt/glass/basalt stacking order had the highest resistance to hydrothermal aging.

Controlled light energy and perfect absorption in twisted bilayer graphene.

We theoretically study the components of the dynamical optical conductivity tensor and associated finite-frequency dielectric response of bilayer graphene (BLG), where one graphene layer can slide in-plane or commensurably twist on top of the other. Our results reveal that even slight deviations from the conventional AA, AB, or AC stacking orders yield a finite transverse conductivity. Upon calculating the optical conductivity of the BLG at any arbitrary interlayer displacement, Δ, and chemical potential, µ, it is utilized for a layered device with an epsilon-near-zero (ENZ) insert and metallic back plate. We find that both Δ and µ can effectively control the polarization, energy flow direction, and absorptivity of linearly polarized incident light. By appropriately tailoring Δ and µ, near-perfect absorption and tunable dissipation can be accessible through particular angles of incidence and a broad range of ENZ layer thicknesses. Our findings can be applied to the design of programmable optoelectronics devices.

High-permittivity Solvents Increase MXene Stability and Stacking Order Enabling Ultraefficient Terahertz Shielding.

2Dtransition metal carbides and nitrides (MXenes) suggest an uncommonly broad combination of important functionalities amongst 2D materials. Nevertheless, MXene suffers from facile oxidation and colloidal instability upon conventional water-based processing, thus limiting applicability. By experiments and theory, It is suggested that for stability and dispersibility, it is critical to select uncommonly high permittivity solvents such as N-methylformamide (NMF) and formamide (FA) (εr =171, 109), unlike the classical solvents characterized by high dipole moment and polarity index. They also allow high MXene stacking order within thin films on carbon nanotube (CNT) substrates, showing very high Terahertz (THz) shielding effectiveness (SE) of 40-60dB at 0.3-1.6 THz in spite of the film thinness <2µm. The stacking order and mesoscopic porosity turn relevant for THz-shielding as characterized by small-angle X-ray scattering (SAXS). The mechanistic understanding of stability and structural order allows guidance for generic MXene applications, in particular in telecommunication, and more generally processing of 2D materials.

Effects of kaolinite and halloysite as raw material on solid-state reaction to form kalsilite

This study investigated the effects of the stacking order, morphology, and calcination of kaolinite and halloysite specimens, 1:1 type layered aluminosilicates (Al2Si2O5(OH)4), as raw materials for the solid-state reaction to form kalsilite (KAlSiO4). Thus, this study mainly investigated the solid-state reaction of potassium carbonate (K2CO3) with kaolinite or halloysite specimens at 1000 °C after wet grinding of the reactants. Compared with pristine kaolinite, amorphous KAlSiO4 was generated using disorderly stacked kaolinite by the expansion of its layers as the raw material. Such an amorphous KAlSiO4 was also obtained when halloysite having a tubular morphology with a disputed stacking order was used as the raw material. In addition, the resultant amorphous KAlSiO4 was composed of smaller particles than the KAlSiO4 prepared using kaolinite. When metakaolinite and metahalloysite (i.e., amorphous and dehydroxylated layered aluminosilicates (Al2O3・2SiO2)) were used as raw materials, crystalline kalsilite specimens were obtained. Therefore, the results demonstrated that the crystallinity and particle shape of KAlSiO4 were controlled by the specific types of kaolinite and halloysite as raw materials. Importantly, the stacking order, particle size, morphology, and impurities of kaolinite or halloysite typically vary depending on their geographical origin. Consequently, this study lays the groundwork for the development of cost-effective and environmentally friendly methods for preparing ceramic materials.

Identifying Detrital and Diagenetic Minerals in Paleosols of the Illinois Basin

Phyllosilicates are hypothesized to be primarily of pedogenic origin in shallowly buried paleosols (≤3 km depth), regardless of the age of the paleosol. To test this hypothesis, this work evaluates the possible presence of detrital and diagenetic phyllosilicates in middle and upper Pennsylvanian paleosols, collected from three drill cores along a north–south transect in the Illinois Basin. The abundances of 2M1 muscovite, quartz, and K-feldspar are greater in a morphologically immature Protosol from the southernmost core; 1Md illite and interstratified illite-smectite with R1 and R0 stacking orders are more abundant in the more mature Vertisols of the central and northern cores. K-Ar age values of multiple clay-size fractions from each paleosol averaged ~260 Ma in the northern core, 270 Ma in the central core, and 295 Ma in the southern core. While considering the complex tectonic and thermal history of the Illinois Basin, detrital minerals are more abundant in immature paleosols that experienced relatively greater maximum burial depths and thus greater sediment supply whereas illitization in more mature paleosols was probably initiated primarily during protracted burial diagenesis. As the present study found evidence for diagenetic and detrital minerals in clay-size fractions of shallowly buried, deep-time paleosols, caution is advised when using paleosol minerals for ancient climate and environment reconstructions.

The Electronic Structure and Stability of Ti2SnC/Ag Interface Studied by First‐Principles Calculations

AbstractIn this paper, the electronic properties, the adhesive energy, and the interface energy of the MAX phase Ti2SnC(0001)/Ag(111) interface are systematically investigated using first principles based on density functional theory. Four different terminations of Ti2SnC(0001) are considered, and 16 different Ti2SnC(0001)/Ag(111) interface configurations are obtained by varying the stacking positions of the atoms. After calculating the electronic structure, adhesion work, and interface energy of these interface model interfaces with the same terminal but different atomic positions, it is found that the interface of the same terminal has a very limited effect on the interface bonding of the interface model by changing the stacking order of the interface atomic layer. By comparing the adhesion work and interface energy of 16 interface models, it is found that the HCP2 configuration of C‐Ti2SnC(0001)/Ag(111)interface structure has the highest adhesion work and the lowest interface energy. The larger the adhesion work is, the stronger the bonding between the interface atoms is. Meanwhile, the smaller the interface energy (positive value) is, the more stable the interface is. By calculating the electronic structure of the interface, the accuracy of the above results is further verified after analyzing the partial density of states (PDOS) and charge density difference of the interface.

Spontaneous broken-symmetry insulator and metals in tetralayer rhombohedral graphene.

Interactions among charge carriers in graphene can lead to the spontaneous breaking of multiple degeneracies. When increasing the number of graphene layers following rhombohedral stacking, the dominant role of Coulomb interactions becomes pronounced due to the significant reduction in kinetic energy. In this study, we employ phonon-polariton-assisted near-field infrared imaging to determine the stacking orders of tetralayer graphene devices. Through quantum transport measurements, we observe a range of spontaneous broken-symmetry states and their transitions, which can be finely tuned by carrier density n and electric displacement field D. Specifically, we observe a layer-antiferromagnetic insulator at n = D = 0 with a gap of approximately 15 meV. Increasing D allows for a continuous phase transition from a layer-antiferromagnetic insulator to a layer-polarized insulator. By simultaneously tuning n and D, we observe isospin-polarized metals, including spin-valley-polarized and spin-polarized metals. These transitions are associated with changes in the Fermi surface topology and are consistent with the Stoner criteria. Our findings highlight the efficient fabrication of specially stacked multilayer graphene devices and demonstrate that crystalline multilayer graphene is an ideal platform for investigating a wide range of broken symmetries driven by Coulomb interactions.