A universal method for achieving polar order in two-dimensional silicon oxides

Abstract

This invention provides a universal method for achieving polarization order in two-dimensional silicon oxide compounds. The universal method includes the following steps: S1: Constructing a two-dimensional silicon oxide compound and optimizing its structure; S2: Inserting insertion atoms into the structure optimized in step S1 and optimizing the structure; S3: Calculating the phonon vibration spectrum of the structure optimized in step S2 and performing imaginary frequency vibration vector analysis, analyzing the polarization distortion structure, and then optimizing the structure; S4: Calculating the phonon vibration spectrum based on the structure optimized in step S3 to identify a stable structure; S5: Performing symmetry analysis on the stable structure from step S4 to confirm a new structure with ferroelectric / antiferroelectric polarization order. This universal method achieves ferroelectric polarization in two-dimensional silicon oxide compounds, which is beneficial for promoting the development of silicon-based nanoelectronic devices and ferroelectric memory electronic devices.

Description

Technical Field

[0001] This invention relates to the field of low-dimensional silicon-based electronic devices and ferroelectric devices, and in particular to a universal method for achieving polarization order in two-dimensional silicon oxides. Background Technology

[0002] Ferroelectric materials possess reversible polarization states that can be controlled by an external field, making them highly valuable for applications in sensors, optoelectronic devices, and memory. However, bulk ferroelectric materials (such as the most common perovskite materials) often lose their polarization when their thickness is reduced to a certain level due to the depolarization field, which is detrimental to the development of modern high-density nanodevices. In recent years, two-dimensional ferroelectric materials have gradually developed and have been theoretically confirmed to possess non-zero polarization magnitudes; however, experimentally verified two-dimensional ferroelectric materials are limited to only two or three types, significantly restricting the development of related fields.

[0003] Silicon oxide (the oxide of silicon) is one of the most common forms of silicon found in nature. Silicon oxide possesses relatively stable chemical properties, does not readily react with water or oxygen, and exhibits good fire resistance and insulation properties. Silicon oxide has various applications, including but not limited to glass, optical fibers, and dielectric insulation. As a high-dielectric-constant material, silicon oxides play a crucial role in silicon-based electronic devices. In recent years, with the development of growth techniques, two-dimensional silicon oxides have been successfully prepared and characterized. They can not only be grown on semiconductor surfaces, enabling large-scale fabrication using semiconductor processes, but also self-supporting two-dimensional silicon oxides can be generated through exfoliation, allowing them to form heterojunctions with other two-dimensional materials to fabricate nanoscale multifunctional devices. These advancements have laid a foundation for nanoscale silicon-based devices.

[0004] Although two-dimensional silicon oxides possess various structures, none exhibit intrinsic polarization properties. If ferroelectric / antiferroelectric polarization ordering can be achieved in two-dimensional silicon oxides, it will be possible to design multifunctional devices based on single-phase, two-dimensional silicon oxides, such as ferroelectric silicon-based optoelectronic devices and ferroelectric silicon-based memory devices.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a universal method for achieving polarization order in two-dimensional silicon oxide compounds, which can achieve ferroelectric polarization in two-dimensional silicon oxide compounds.

[0007] This invention provides a universal method for achieving polarization order in two-dimensional silicon oxide compounds, comprising the following steps:

[0008] S1: Construct two-dimensional silicon oxide compounds and optimize their structure;

[0009] S2: Insert the insertion atoms into the structure optimized in step S1 and perform structural optimization;

[0010] S3: Calculate the phonon vibration spectrum of the optimized structure in step S2 and perform imaginary frequency vibration vector analysis. After analyzing the polarization distortion structure, perform structural optimization.

[0011] S4: Calculate the phonon vibration spectrum based on the optimized structure in step S3, and find the stable structure;

[0012] S5: Perform symmetric analysis on the stable structure of step S4 to confirm the new structure with ferroelectric / antiferroelectric polarization order.

[0013] In this invention, atoms with small radii that are easily inserted are selected as insertion atoms based on the size of the pores in the two-dimensional silicon oxide compound. The radius of the insertion atom is smaller than the size of the pores in the two-dimensional silicon oxide compound; for example, it can be a lithium atom. Furthermore, the insertion position of the insertion atom can be determined based on the size and number of pores in the two-dimensional silicon oxide compound. For example, insertion can be performed at highly symmetric large pore positions, and the number of insertions can be consistent with the number of pores. In experiments, the insertion of metallic lithium can be carried out using conventional methods, such as lithium-ion solid-state modulation (therefore, it is feasible). Inserting lithium atoms into the optimized two-dimensional silicon oxide compound forms a hybrid coupling between lithium s electrons and two-dimensional silicon oxide compound p electrons, achieving ferroelectric / antiferroelectric polarization order by inducing a phonon soft film.

[0014] In this invention, the two-dimensional silicon oxide compound can be a common two-dimensional silicon oxide compound with a large porous structure. It can be either a two-dimensional self-supporting structure or a substrate-supported structure, and the two types of structures do not need to be exactly the same. Specifically, the two-dimensional silicon oxide compound can be at least one of a self-supporting two-dimensional silicon oxide compound and a substrate-supported two-dimensional silicon oxide compound. The silicon to oxygen ratio in the two-dimensional silicon oxide compound often satisfies 1:2 or close to 1:2, for example, it can be 1:(2-2.5) to achieve sp... 2 to sp 3 The hybridization of the structure allows for the realization of relatively large pore structures in the two-dimensional limit.

[0015] In this invention, the self-supporting two-dimensional silicon oxide compound is a self-supporting two-dimensional hexagonal Si4O8; the substrate-supporting two-dimensional silicon oxide compound is a SiC-supported two-dimensional Si2O5.

[0016] Furthermore, for self-supporting two-dimensional silicon oxides: the lattice constant of the structure optimized in step S1 is: The lattice constant of the optimized structure after step S2 is: For substrate-supported two-dimensional silicon oxides: the optimized structure maintains the lattice constant of the substrate.

[0017] In this invention, the method for constructing a self-supporting two-dimensional silicon oxide compound may include:

[0018] a) Construct two-dimensional honeycomb-cage-mesh silicon-oxygen structure and oxygen atom honeycomb structure respectively;

[0019] b) Connect the upper and lower two-dimensional honeycomb-cage-silicon-oxygen structures through an oxygen atom honeycomb structure.

[0020] At this point, the upper and lower layers of the self-supporting two-dimensional silicon oxide compound are two-dimensional honeycomb-cage-mesh silicon oxide structures, with the upper and lower layers sharing the middle oxygen atom honeycomb structure.

[0021] In this invention, the method for constructing a substrate-supported two-dimensional silicon oxide compound may include:

[0022] a) Construct two-dimensional honeycomb-cage-mesh silicon-oxygen structures and oxygen atom honeycomb structures respectively, and connect the two-dimensional honeycomb-cage-mesh silicon-oxygen structures through the oxygen atom honeycomb structures;

[0023] b) Cut the silicon carbide, use hydrogen atoms to saturate the bottom broken bonds to expose the surface of the top silicon atoms, and reconstruct the surface of the silicon atoms.

[0024] c) Perform lattice matching and connection on the structures from steps a) and b).

[0025] Furthermore, the reconstruction of the silicon atomic surface includes: a 30° rotation and root 3 reconstruction of the silicon atomic surface.

[0026] In step S5, the symmetry analysis requires analyzing the polarity of the corresponding point group and the possibility of polarization phase reversal, while the polarization phase energy must be lower than that of the parent structure.

[0027] In this invention, the VASP software package is used, and first-principles calculations are performed using PAW-PBE. Due to the presence of oxygen atoms, the cutoff energy for the plane wave is taken as 550 eV. The convergence criterion for the calculation is: energy 1 × 10⁻⁶. -6 eV and force Since silicon oxides have a two-dimensional structure, the calculations employed a slab model and utilized... The vacuum layer is used. For the unit cell structure, a 7×7×1k-point grid is used for calculation. The phonon vibration spectrum is calculated using the finite displacement method and phonopy software. It should be noted that the method of this invention is not limited to these software programs; it is sufficient to ensure the correct optimization and characterization of the structure and the accuracy of the vibration spectrum.

[0028] The implementation of this invention has at least the following advantages:

[0029] 1. This invention achieves hybrid coupling between the s orbitals of small atoms such as lithium atoms and the p orbitals of silicon oxide by inserting small atoms into two-dimensional silicon oxide compounds, thereby realizing the distortion shift of lithium atoms and thus realizing a new ordered phase, namely ferroelectric / antiferroelectric polarized order, and achieving a stable polarized ordered structure.

[0030] 2. This invention designs a universal method for achieving polarization order in non-polar two-dimensional silicon oxide semiconductors. This method can easily introduce polarization into non-polar silicon oxides, which is beneficial for combining silicon-based electronics and ferroelectric electronics to design more efficient multifunctional silicon-based nanoelectronic devices, and promotes the development of applications based on silicon-based nanoelectronic devices and ferroelectric memory electronics. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of a self-supporting two-dimensional silicon oxide compound;

[0033] Figure 2 A schematic diagram of the structure of a self-supporting two-dimensional silicon oxide compound after lithium atoms are inserted into highly symmetric holes;

[0034] Figure 3 Phonon vibrational spectrum of a self-supporting two-dimensional silicon oxide compound after lithium atoms are inserted into highly symmetric holes;

[0035] Figure 4 The stable distorted structure and phonon vibration spectrum of a self-supporting two-dimensional silicon oxide compound after lithium atom insertion are shown; where (a) is the ferroelectric (FE) phase and (b) is the antiferroelectric (AFE) phase.

[0036] Figure 5 The phase transition energy barrier for a self-supporting two-dimensional silicon oxide stable polarization structure;

[0037] Figure 6 A schematic diagram of a two-dimensional silicon oxide structure supported by silicon carbide;

[0038] Figure 7 A schematic diagram of a highly symmetric structure of a silicon carbide-supported two-dimensional silicon oxide compound after lithium atoms are inserted into highly symmetric holes.

[0039] Figure 8 A schematic diagram of the stable ferroelectric distortion structure corresponding to a two-dimensional silicon oxide compound supported by silicon carbide after lithium atom insertion.

[0040] Figure 9 This serves as a ferroelectric transition energy barrier to support the stable polarization structure of two-dimensional silicon oxide compounds in silicon carbide. Detailed Implementation

[0041] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0042] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0043] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0044] This invention uses a common self-supporting two-dimensional silicon oxide compound and another silicon oxide compound supported by a silicon carbide substrate as examples, and utilizes the insertion of lithium atoms to achieve ferroelectric / antiferroelectric polarization order. The technical solution mainly includes: utilizing the large pores of the two-dimensional silicon oxide compound, inserting metallic lithium atoms into it to achieve polarization order throughout the material. Specifically, using two-dimensional self-supporting hexagonal Si4O8 and two-dimensional Si2O5 on the SiC(0001) surface as model materials, and common metallic lithium as the inserting atom, it is inserted into the highly symmetric pores of the silicon oxide compound. Utilizing the sp orbital hybridization of lithium and silicon oxide, the highly symmetric lithium atoms are shifted, thereby forming polarization order.

[0045] The specific steps are as follows:

[0046] 1) Construct a self-supporting two-dimensional silicon oxide structure and optimize its structure; the obtained self-supporting hexagonal Si4O8 lattice constant Specifically, the upper and lower layers of the structure are honeycomb-cage-mesh silicon-oxygen layers, sharing a middle honeycomb structure oxygen atom layer;

[0047] 2) Construct a SiC(0001) surface and then construct a two-dimensional Si2O5 on it. Specifically, expose the Si atomic planes on the SiC(0001) surface and reconstruct them by rotating them by 30° to form a root 3×root 3 surface, which is then connected to the O atoms on the lower surface of the two-dimensional Si2O5 to form a hexagonal porous structure.

[0048] 3) Select the two optimized structures from steps 1)-2) and analyze their highly symmetric pore locations; since this structure has a hexagonal honeycomb structure, the two-dimensional central pore is the largest, making it most suitable for small atom insertion;

[0049] 4) Select lithium atoms to be inserted into the two structures optimized in steps 1)-2), with the number of insertions matching the number of holes, and place them at the center of the holes to form a highly symmetrical insertion structure;

[0050] 5) Based on the insertion structure in steps 1)-4), calculate the phonon vibration spectrum and analyze the vibration spectrum;

[0051] 6) Based on the vibration spectrum analysis results of step 5), select all unstable vibration spectra for analysis and determine the stable structure; specifically, by analyzing the vibration modes of all negative vibration frequencies, identify possible distorted structures and optimize the structure.

[0052] 7) Based on all the optimized structures in step 6), determine the stable new structure and compare it with the high symmetry structure to determine the energy level and potential barrier, and finally determine the ferroelectric / antiferroelectric polarized ordered phase; specifically, analyze the point group polarity of the new structure, determine its polarization axis and the feasibility of reversal, and calculate the energy difference between phases.

[0053] Example 1

[0054] This embodiment achieves polarization ordering in a self-supporting two-dimensional silicon oxide compound, and the steps are as follows:

[0055] 1) Construct a two-dimensional honeycomb-cage-mesh silicon-oxygen structure, and simultaneously construct an oxygen atom honeycomb structure. Connect the two layers of two-dimensional honeycomb-cage-mesh silicon-oxygen structures by sharing the oxygen atom honeycomb structure to form a self-supporting two-dimensional hexagonal Si4O8 with a silicon-oxygen atom ratio of 4:8.

[0056] Subsequently, the structure of the self-supporting two-dimensional hexagonal Si4O8 was optimized, and the lattice constant was fitted: the optimized energy was calculated by taking different lattice constants a=b, and the optimal lattice constant was obtained by fitting. (A vacuum layer is applied in the vertical direction) ).

[0057] 2) In the self-supporting two-dimensional hexagonal Si4O8 optimized in step 1), a smaller and commonly used insertion atom is selected for insertion; in this embodiment, the most common metallic lithium is selected as the insertion atom, which not only meets the requirements of small atomic size, but also has s electrons, which are expected to hybridize with the p electrons of silicon oxide compounds.

[0058] 3) Lithium atoms were placed in the highly symmetric pores of the self-supporting two-dimensional hexagonal Si4O8 optimized in step 1). The insertion was performed according to the number of pores, and the number of insertions was consistent with the number of pores. The entire structure was then fully optimized to obtain a new lattice constant.

[0059] 4) Perform phonon vibration spectrum calculation on the optimized structure in step 3) to find imaginary frequency vibration modes (i.e., vibration frequencies less than zero), analyze possible polarization distortion structures, further optimize these structures, and perform phonon vibration spectrum calculation to find stable new structures (i.e., with almost no negative vibration frequencies).

[0060] 5) Perform symmetry analysis on the new structure stabilized in step 4) to confirm whether it has a polar (polarization) axis and can be flipped, that is, confirm that its energy is lower than that of the highly symmetric parent structure and that the reversal barrier is appropriate, thus confirming that the new structure has polarization order.

[0061] In this embodiment, Figure 1 The structure of a self-supporting two-dimensional silicon-oxygen compound is shown, which has a large central void that is also the center of structural symmetry. Due to the large lattice constant of silicon-oxygen structures, there is... Small atom insertion is entirely possible, so a lithium atom is placed at the center of the hole, such as... Figure 2 As shown. The overall structure with a centrally inserted lithium atom has a large virtual vibration frequency, i.e., the frequency is negative, such as... Figure 3 As shown. The vibration modes of the highly symmetric points M(0.5, 0, 0), Γ(0, 0, 0), and K(1 / 3, 1 / 3, 0) are analyzed, and the corresponding distorted structures are optimized. Only the first two can maintain a stable structure, and their corresponding vibration modes no longer have imaginary frequencies, as shown. Figure 4 As shown. In the new structure corresponding to Γ, all lithium atoms are oriented in the same direction. Based on symmetry analysis, the shifted axis has polarity and can be flipped; therefore, this new structure is called a ferroelectric (FE) phase, as shown. Figure 4 As shown in (a), in the new structure corresponding to M, adjacent lithium atoms face opposite directions. Based on symmetry analysis, the axis of each row of atoms after movement still retains polarity and can be flipped. Therefore, this new structure is called an antiferroelectric (AFE) phase, as shown in (a). Figure 4 As shown in (b). Simultaneously, energy calculations confirm that the energies of the two polarized ordered structures are lower than those of the high-symmetry structure, and the transition barrier matches the experimentally achievable value, as shown in (b). Figure 5 As shown.

[0062] Example 2

[0063] This embodiment achieves polarization ordering in silicon carbide-supported two-dimensional silicon oxide compounds, and the steps are as follows:

[0064] 1) Construct a two-dimensional honeycomb-cage-mesh silicon-oxygen structure, and simultaneously construct an oxygen atom honeycomb structure. Connect one layer of the two-dimensional honeycomb-cage-mesh silicon-oxygen structure with the oxygen atom honeycomb structure to form a silicon-oxygen atom ratio of 2:5.

[0065] 2) The (0001) face of the H phase silicon carbide is cut. Since the surface needs to be simulated, 12 atomic layers will be used, and hydrogen atoms will be used to saturate the broken bonds of the bottom layer to simulate the surface of the top exposed silicon atoms. The silicon atom surface will then be reconstructed by a 30° rotation and root 3.

[0066] 3) Perform lattice matching on the structures of steps 1) and 2), i.e., make the silicon-oxygen lattice constant consistent with the root 3 surface, and connect the two structures, i.e. connect the honeycomb oxygen atom layer with the surface silicon atoms; perform structural optimization on the entire structure without changing the lattice constant, and keep the 4 substrate atom layers and the hydrogen atoms used for saturation unchanged during optimization.

[0067] 4) Lithium atoms are placed in the highly symmetric pores of the SiC-supported two-dimensional Si2O5 optimized in step 3). The insertion is performed according to the number of pores, and the number of insertions is consistent with the number of pores. The entire structure is then fully optimized.

[0068] 5) The optimized structure from step 4) is used to shift lithium atoms to form a ferroelectric configuration similar to that in Example 1, and the structure is fully optimized to confirm its stability.

[0069] 6) Perform symmetry analysis on the new structure stabilized in step 5) to confirm whether it has a polarization axis and whether the energy valley is flipped, and then confirm that its energy is lower than that of the high symmetry structure; confirm the transition energy barrier and whether it is in the energy valley, i.e., the stable position, thereby confirming that the new structure has polarization order.

[0070] In this embodiment, Figure 6 The diagram illustrates a silicon carbide-supported two-dimensional silicon oxide structure. This structure also exhibits a large central void, the center of which is the center of symmetry within the structure's plane. Due to the large lattice constant of silicon carbide, ... The pores in the silicon oxide compound above allow for the insertion of small atoms; therefore, placing a lithium atom at the center of the pore is possible. Figure 7 As shown. Taking into account the self-supporting condition, ferroelectric structures are obtained by shifting lithium atoms, as shown. Figure 8As shown. Simultaneously, energy calculations confirm that the energy of the polarized ordered structure is lower than that of the original central insertion structure, and the ferroelectricity is in a valley state. The transition barrier matches the experimentally achievable value, as shown. Figure 9 As shown.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A universal method for achieving polarization order in two-dimensional silicon oxide compounds, characterized in that, Includes the following steps: S1: Construct two-dimensional silicon oxide compounds and optimize their structure; S2: Insert the inserted atom into the structure optimized in step S1 and perform structural optimization. The radius of the inserted atom is smaller than the pore size of the two-dimensional silicon oxide compound. S3: Calculate the phonon vibration spectrum of the optimized structure in step S2 and perform imaginary frequency vibration vector analysis. After analyzing the polarization distortion structure, perform structural optimization. S4: Calculate the phonon vibration spectrum based on the optimized structure in step S3, and find the stable structure; S5: Perform symmetric analysis on the stable structure of step S4 to confirm the new structure with ferroelectric / antiferroelectric polarization order.

2. The universal method according to claim 1, characterized in that, The inserted atom is a lithium atom.

3. The universal method according to claim 2, characterized in that, Lithium atoms are inserted into optimized two-dimensional silicon oxide compounds to form hybrid coupling between lithium s electrons and two-dimensional silicon oxide compound p electrons, thereby achieving ferroelectric / antiferroelectric polarization order by inducing phonon soft films.

4. The universal method according to claim 1, characterized in that, The two-dimensional silicon oxide compound is at least one of a self-supporting two-dimensional silicon oxide compound and a substrate-supported two-dimensional silicon oxide compound.

5. The universal method according to claim 4, characterized in that, In two-dimensional silicon oxide compounds, the ratio of silicon to oxygen is 1:(2-2.5) to achieve sp. 2 to sp 3 Hybridization.

6. The universal method according to claim 4, characterized in that, The self-supporting two-dimensional silicon oxide compound is a self-supporting two-dimensional hexagonal Si4O8; the substrate-supporting two-dimensional silicon oxide compound is a SiC-supported two-dimensional Si2O5.

7. The universal method according to claim 6, characterized in that, For self-supporting two-dimensional silicon oxides: the lattice constant of the structure optimized in step S1 is: The lattice constant of the optimized structure after step S2 is: For substrate-supported two-dimensional silicon oxides: the optimized structure maintains the lattice constant of the substrate.

8. The universal method according to claim 4, characterized in that, Methods for constructing self-supporting two-dimensional silicon oxide compounds include: a) Construct two-dimensional honeycomb-cage-mesh silicon-oxygen structure and oxygen atom honeycomb structure respectively; b) Connect the upper and lower two-dimensional honeycomb-cage-silicon-oxygen structures through an oxygen atom honeycomb structure.

9. The universal method according to claim 4, characterized in that, Methods for constructing substrate-supported two-dimensional silicon oxide compounds include: a) Construct two-dimensional honeycomb-cage-mesh silicon-oxygen structures and oxygen atom honeycomb structures respectively, and connect the two-dimensional honeycomb-cage-mesh silicon-oxygen structures through the oxygen atom honeycomb structures; b) Cut the silicon carbide, use hydrogen atoms to saturate the bottom broken bonds to expose the surface of the top silicon atoms, and reconstruct the surface of the silicon atoms. c) Perform lattice matching and connection on the structures from steps a) and b).

10. The universal method according to claim 9, characterized in that, Reconstructing the silicon atomic surface includes: performing a 30° rotation and root 3 reconstruction on the silicon atomic surface.

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