Two-dimensional layered material with sliding ferroelectricity and polarization intensity regulation and control method thereof

Abstract

The invention discloses a two-dimensional layered material with sliding ferroelectricity and a polarization intensity regulation and control method thereof, and belongs to the field of two-dimensional semiconductor materials. The material comprises two layers of single-layer materials with P6m < 2 > point group symmetry, and the two layers of single-layer materials are combined in a BA or AB sliding stacking configuration; the sliding stack generates ferroelectric polarization perpendicular to the plane, and a built-in electric field caused by charge transfer exists between the two layers of single-layer materials. The polarization intensity of the sliding ferroelectric phase can be obviously enhanced by regulating and controlling the interlayer spacing; ferroelectric flipping energy barrier calculation shows that the switching potential barrier between an AB phase and a BA phase is only 11.5 meV, and the material has a good reversible flipping characteristic. According to the method, a complete design model from a non-polar single layer to a sliding ferroelectric double layer is established through calculation according to a first principle, a physical mechanism taking the interlayer spacing as a key regulation and control parameter is disclosed, and a new theoretical scheme is provided for design of a high-performance and adjustable two-dimensional ferroelectric device.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional semiconductor materials, specifically relating to two-dimensional layered materials with sliding ferroelectricity and methods for controlling their polarization intensity. Background Technology

[0002] Two-dimensional sliding ferroelectric materials, as an emerging state of matter, have attracted widespread attention in recent years because they can generate and switch polarization through interlayer translation rather than traditional lattice distortion. This mechanism overcomes the size effect and depolarization field bottlenecks faced by traditional ferroelectrics (such as BaTiO3 and PbTiO3) when thinned to the nanoscale, providing a highly promising material platform for developing atomically thin non-volatile electronic devices.

[0003] In recent years, the two-dimensional sliding ferroelectric mechanism based on interlayer slip has provided a breakthrough approach for realizing ferroelectricity at the atomic scale. This mechanism does not rely on the lattice distortion of traditional ferroelectric materials, but induces and flips out-of-plane polarization by controlling the relative slip between the layers of two-dimensional materials, thus theoretically avoiding the size effect limitation of ferroelectricity. However, systematic methods and clear guidance on how to effectively control the intensity of ferroelectric polarization are still lacking.

[0004] In the core area of ​​control methods, current research faces significant bottlenecks: although parameters such as interlayer spacing, torsion angle, and interfacial charge have been preliminarily identified as potential control mechanisms, the microscopic mechanisms by which these factors quantitatively affect interlayer coupling and charge transfer, thereby determining the specific value of polarization intensity, remain unclear. Achieving large-scale, continuous tunability of polarization intensity is difficult. Currently, there is a lack of both a unified theoretical model describing the polarization behavior of different material systems and reliable criteria to guide experimental design and achieve target polarization intensity. Therefore, developing a set of quantitative control theories and computational methods from microscopic mechanisms to macroscopic performance has become a key challenge in promoting the practical application of two-dimensional sliding ferroelectric materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies in two-dimensional sliding ferroelectric materials, such as the lack of systematic design models, unclear control mechanisms, and insufficient performance prediction methods, this invention provides a material design model, control calculation method, and property prediction system for simulating, optimizing, and verifying two-dimensional sliding ferroelectricity. Taking a single-layer CrSe2 with P6m2 point group symmetry as an example, this invention constructs and verifies a bilayer ferroelectric model based on slip stacking, thereby revealing the physical mechanism of interlayer spacing as a key control parameter, and forming a general analysis method and performance prediction framework that can be extended to similar symmetry material systems.

[0006] The objective of this invention can be achieved through the following technical solutions: A two-dimensional layered material with sliding ferroelectricity comprises two monolayers with P6m2 point group symmetry, the two monolayers being combined in a BA or AB sliding stack configuration; the sliding stack generates ferroelectric polarization perpendicular to the plane, and there is an internal electric field between the two monolayers caused by charge transfer.

[0007] Furthermore, the monolayer material with P6m2 point group symmetry is CrSe2; Furthermore, the slip stacking includes: the upper layer slipping relative to the lower layer along a high-symmetry direction of the hexagonal lattice; The AB sliding stacking method is as follows: the Se atoms in the upper layer are aligned with the Cr atoms in the lower layer in the vertical direction; The BA sliding stacking method is as follows: the Cr atoms in the upper layer are aligned with the Se atoms in the lower layer in the vertical direction; Furthermore, the switching barrier of the ferropolarization is 11.5 meV.

[0008] Furthermore, the interlayer spacing between the two monolayer materials is adjustable to control the intensity of ferroelectric polarization.

[0009] The above-mentioned method for adjusting the ferroelectric polarization intensity of a two-dimensional layered material with sliding ferroelectricity includes: applying external stress to adjust the interlayer spacing between the two single-layer materials.

[0010] Furthermore, the ferropolar polarization intensity is negatively correlated with the interlayer spacing.

[0011] Furthermore, the ferroelectric polarization intensity can be adjusted within a range of 0.4 to 1.16 pC / m.

[0012] Furthermore, the external stress is a compressive stress perpendicular to the material plane, used to reduce the interlayer spacing.

[0013] The above-mentioned two-dimensional layered materials with sliding ferroelectricity are applied in the fabrication of non-volatile electronic devices. This invention also provides an application of the described method in the simulation and design of non-volatile electronic devices, including polarization multistate simulation based on the model, prediction of low-power switching behavior, and simulation optimization of device performance. The beneficial effects of this invention are: 1. This invention discovers and verifies a significant negative correlation between ferroelectric polarization intensity and interlayer spacing in this two-dimensional layered material; specifically, reducing the interlayer spacing leads to a significant increase in ferroelectric polarization intensity. When the interlayer spacing is adjusted from its initial value, the polarization intensity can be increased to approximately 1.16 pC / m, showing a significant relative increase.

[0014] 2. In the two-dimensional layered material of the present invention, the switching between the AB phase and the BA phase (i.e., two ferroelectric states with opposite polarization directions) can be achieved by in-plane slip, and its ferroelectric reversal energy barrier is about 11.5 meV, indicating that the ferroelectric state has good reversible reversal characteristics at room temperature.

[0015] 3. This invention establishes a complete design model from nonpolar monolayer to slip ferroelectric bilayer through first-principles calculations, and reveals the physical mechanism of interlayer spacing as a key control parameter, providing a new theoretical solution for the design of high-performance, controllable two-dimensional ferroelectric devices and nonvolatile electronic devices.

[0016] 4. This invention provides a novel method for realizing sliding ferroelectrics based on two-dimensional van der Waals materials. This method eliminates the dependence of traditional perovskite ferroelectrics on specific three-dimensional crystal structures, and can create and manipulate ferroelectricity at the atomic scale by using simple interlayer stacking slip, greatly expanding the candidate system of ferroelectric materials and demonstrating high compatibility with existing two-dimensional material device processes.

[0017] 5. The two-dimensional sliding ferroelectric material of this invention is an ideal candidate material for the fabrication of next-generation high-performance non-volatile electronic devices. Its tunable polarization intensity can be used to design multi-state memory devices, and its extremely low switching energy barrier is conducive to achieving ultra-low power consumption and high-speed read and write operations. It has important application prospects in high-density memory, neuromorphic computing, reconfigurable logic circuits and other fields. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 Structure and band structure of H-CrSe2, a single-layer P6m2 symmetric material; Figure 2 Molecular dynamics and phonon spectra of the monolayer material H-CrSe2; Figure 3 The charge density distribution diagram of the stacked ferroelectric phases AB and BA, and the variation function of the plane-average differential charge density along the vertical direction; Figure 4 Schematic diagram of the projected band structure and structural model of the upper and lower layers of the BA stacked system; Figure 5 This is a graph showing the flipping path, polarization value, and interlayer spacing control data of ferroelectric materials. Figure 6 This is a diagram showing the energy-polarization phase evolution of ferroelectric materials. Figure 7 This is a diagram showing the average electrostatic potential distribution in a two-layer AB / AA / BA stacked plane. Figure 8 This is a schematic diagram of the transition from a centrosymmetric PE phase to an FE phase (±P state) with opposite out-of-plane polarization via interlayer sliding. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 First, the structure of the two-dimensional semiconductor material was optimized using the first-principles calculation software VASP (Vienna Ab Initio Simulation Package). During the optimization process, the generalized gradient approximation (GGA-PBE) was used to describe the exchange-correlation functional, and DFT-D3 van der Waals correction was added to accurately describe the interlayer interactions. The plane wave cutoff energy was set to 500 eV, and the Brillouin zone was sampled using a 9×9×1 Monkhorst-Pack grid centered at the Γ point. The structural optimization results show that, as Figure 1 As shown in (a), the monolayer material H-CrSe2 has a hexagonal lattice with lattice constants a = b = 3.19 Å, belonging to the P6m2 point group symmetry, and its horizontal mirror plane and spatial inversion symmetry are intact. Further calculations of the electronic band structure of the monolayer material are performed, as shown in (a). Figure 1 As shown in (b) above. The results indicate that the material is a direct bandgap semiconductor with a bandgap value of approximately 0.81 eV. No flat band or magnetic instability characteristics were observed near the Fermi level, confirming it as a non-magnetic semiconductor material, such as... Figure 2 As shown in (a), molecular dynamics simulations revealed that the total energy fluctuated only slightly around the equilibrium value, with no structural collapse or atomic reconstruction observed. These results demonstrate the excellent stability of the material.

[0022] like Figure 2 As shown in (b), the dynamic properties of the material are analyzed using phonon spectroscopy. All phonon frequencies are positive throughout the Brillouin zone, with no imaginary frequencies. This proves that the structure is at a local energy minimum and is dynamically stable, thus ruling out the possibility of spontaneous distortion due to lattice instability. This provides an ideal building block material for the subsequent construction of a sliding ferroelectric bilayer structure.

[0023] Example 2 In this embodiment, a two-dimensional layered material (CrSe2) with P6m2 point group symmetry, as the basic unit, is constructed using the single-layer material (CrSe2) from Example 1, and its slip ferroelectric properties are systematically studied. 1. Construction and symmetry analysis of stacked configurations: Using the optimized monolayer material (CrSe2) as the basic unit, such as Figure 8 As shown, three double-layer stacked configurations are constructed: 1) AA stacking In the AA stacked configuration, the atoms of the upper and lower layers are strictly aligned, fully preserving the P6m2 space group symmetry of a single-layer H-CrSe2. The horizontal mirror planes inherent in this symmetry give the structure centrosymmetry, preventing spontaneous polarization perpendicular to the plane and resulting in a nonpolar paraelectric ground state. Specifically, the two layers are perfectly aligned, serving as a nonpolar reference structure; after optimization, its planar average electrostatic potential is symmetrically distributed along the vertical direction, as shown below. Figure 7 The planar average electrostatic potential distribution diagram of (b)AA in the figure is shown, which verifies its central symmetry (P6m2) and lack of net dipole moment.

[0024] 2) Stacking of AB and BA In AB and BA stacking configurations, the upper layer undergoes relative slippage with respect to the lower layer along a high-symmetry lattice direction: in AB stacking, the upper Se atoms are perpendicularly aligned with the lower Cr atoms, while in BA stacking, the upper Cr atoms are perpendicularly aligned with the lower Se atoms. These two configurations are energy degenerate but have opposite polarization directions. This slippage disrupts the system's horizontal mirror plane and spatial inversion symmetry. This symmetry breaking leads to a redistribution of interlayer charge, causing electrons to transfer from one layer to another, thus forming a net electric dipole moment in the vertical direction and achieving stable out-of-plane ferroelectric polarization. Figure 7 (a) and (c) in the figure show the electrostatic potential distribution under the two stacks of AB and BA, respectively. The potentials of the two stacks are related by opposite gradient directions, which verifies that the AB and BA stacks correspond to two ferroelectric states with opposite polarization directions.

[0025] Specifically, AB stacking involves shifting the upper layer relative to the lower layer along the crystallographic direction [1 / 3, 2 / 3, 0] by approximately 1 / 3 of the lattice constant. For example... Figure 3 As shown in (a), this slip operation completely destroys the horizontal mirror and spatial inversion symmetry of a single layer. The BA stack is constructed as a mirror operation of the AB stack, as follows: Figure 3 As shown in (b), its structure is mirror-symmetric to AB.

[0026] 2. Origin of ferroelectricity and polarization calculation: Ferropolarization originates from interlayer charge transfer caused by symmetry breaking due to slip. Figure 3 The differential charge density (Δρ) distribution of the AB and BA stacks is clearly shown. in, The total charge density of the two-layer coupled system. and These are the charge densities of the upper and lower layers, respectively, while maintaining the atomic positions unchanged.

[0027] The asymmetrical vertical distribution of the yellow (electron accumulation) and cyan (electron depletion) regions visually demonstrates the net charge transfer from one layer to another. To quantify the polarization intensity, the Berry phase method is used for calculation. Out-of-plane polarization intensity P Z The calculation formula is: Where p is the dipole moment value extracted from OUTCAR (electrons × Å), V is the volume of the unit cell (ų), and c is the component of the third lattice vector in the z-direction.

[0028] 3. Electronic structure and built-in electric field: Figure 4 The projected band structure of BA stacks is shown; Figure 4 In the diagram, (a) represents the projected band structure of the top layer, with color depth indicating the intensity of the contribution; (b) represents the projected band structure of the bottom layer, with color depth indicating the intensity of the contribution. (c) represents the bilayer sliding ferroelectric structure model, with the red rectangle representing the top layer and the purple rectangle representing the bottom layer. The bilayer structure has an upward built-in electric field; it can be observed that the valence band top (VBM) is mainly contributed by the bottom layer electronic states (color depth represents the degree of contribution), while the conduction band bottom (CBM) is mainly contributed by the top layer. This spatial separation of interlayer electronic states is direct evidence for the generation of a vertically oriented built-in electric field.

[0029] 4. Calculation of Ferroelectric Flip Path and Energy Barrier Ferroelectric inversion is achieved through in-plane slip. Based on the AA (energy maxima) and AB / BA (energy minima) structures, a continuous slip path (defined by slip distances dx and dy) is constructed. Figure 5 This demonstrates the total energy change and out-of-plane polarization evolution along this path. Figure 5 In the diagram, (a) represents the transition path during the polarization conversion of the CrSe2 bilayer; (b) represents the evolution of the vertical polarization intensity; and (c) represents the effect of the interlayer spacing on the polarization value. It can be observed that the polarization value continuously varies between -0.40 pC / m (BA) and +0.40 pC / m (AB), forming a typical double-potential-well characteristic.

[0030] Figure 6The energy-polarization two-dimensional profile plot provides a more complete view of the energy distribution across the entire two-dimensional slip surface. It can be seen that the two energy troughs (FE1: AB, FE2: BA) correspond to two ferroelectric states. The minimum energy path connecting them (the white dashed line in the figure) is the ferroelectric flip path. The flip energy barrier is defined as the difference between the saddle point energy on this path and the ferroelectric steady-state energy (AB / BA). Figure 5 As shown, the calculated energy barrier height is approximately 11.5 meV, indicating that this ferroelectric state possesses good reversible switching characteristics.

[0031] 5. Key regulation of polarization intensity: interlayer spacing effect This invention reveals for the first time in this material system that the interlayer spacing *d* is a key external parameter for controlling the ferroelectric polarization intensity *P*. The interlayer spacing was simulated by applying out-of-plane stress, and the polarization values ​​under different *d* values ​​were calculated.

[0032] like Figure 5 As shown in (c), the results indicate a significant negative correlation between polarization intensity P and interlayer spacing d. Specifically, reducing the interlayer spacing significantly enhances interlayer orbital coupling and charge transfer efficiency. The polarization intensity can be increased dramatically from 0.40 pC / m to 1.16 pC / m. This finding not only reveals a strong coupling mechanism but also provides a clear scheme for achieving large-scale, continuous control of polarization intensity through stress engineering.

[0033] Through the calculations and graphical analysis of the above system, this embodiment fully demonstrates the entire process of designing a bilayer material with significant and tunable slip ferroelectricity from a nonpolar monolayer, and deeply explains its physical origin, flipping characteristics and key control mechanisms.

[0034] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A two-dimensional layered material exhibiting sliding ferroelectricity, characterized in that, It comprises two monolayer materials with P6m2 point group symmetry, the two monolayer materials being combined in a BA or AB slip stack configuration; the slip stack generates ferroelectric polarization perpendicular to the plane, and there is an internal electric field between the two monolayer materials caused by charge transfer.

2. The two-dimensional layered material with sliding ferroelectricity according to claim 1, characterized in that, The single-layer material with P6m2 point group symmetry is CrSe2.

3. The two-dimensional layered material with sliding ferroelectricity according to claim 2, characterized in that, The slip stacking includes: the upper layer slipping relative to the lower layer along the high symmetry direction of the hexagonal lattice; The AB sliding stacking method is as follows: the Se atoms in the upper layer are aligned with the Cr atoms in the lower layer in the vertical direction; The BA sliding stacking method is such that the Cr atoms in the upper layer are aligned with the Se atoms in the lower layer in the vertical direction.

4. The two-dimensional layered material with sliding ferroelectricity according to claim 1, characterized in that, The switching barrier of the ferropolarization is 11.5 meV.

5. The two-dimensional layered material with sliding ferroelectricity according to claim 1, characterized in that, The interlayer spacing between the two monolayer materials is adjustable to control the intensity of ferroelectric polarization.

6. The method for adjusting the ferroelectric polarization intensity of a two-dimensional layered material with sliding ferroelectricity as described in any one of claims 1-5, characterized in that, include: External stress is applied to adjust the interlayer spacing between the two single-layer materials.

7. The method for adjusting the ferroelectric polarization intensity of a two-dimensional layered material with sliding ferroelectricity according to claim 6, characterized in that, The ferropolar polarization intensity is negatively correlated with the interlayer spacing.

8. The method for adjusting the ferroelectric polarization intensity of a two-dimensional layered material with sliding ferroelectricity according to claim 6, characterized in that, The adjustment range of the ferroelectric polarization intensity is 0.4 ~ 1.16 pC / m.

9. The method for adjusting the ferroelectric polarization intensity of a two-dimensional layered material with sliding ferroelectricity according to claim 6, characterized in that, The external stress is a compressive stress perpendicular to the material plane, used to reduce the interlayer spacing.

10. The use of the two-dimensional layered material with sliding ferroelectricity as described in any one of claims 1-5 in the fabrication of non-volatile electronic devices.

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