Hetero-halogen-polarized two-dimensional rare earth oxyhalide material and preparation method

Abstract

The application discloses a kind of two-dimensional rare earth oxyhalogen materials of heterogeneous halogen polarization and preparation method, by introducing heterogeneous halogen ion in rare earth oxyhalide lattice, using heterogeneous halogen induced lattice shrinkage and symmetry breaking distortion synergistic enhancement ion polarization, while using the electronegativity difference of heterogeneous halogen enhances electronic polarization, both improve dielectric constant, also maintain the long-range order and stability of crystal structure.The thickness of nanosheet prepared by the method can be precisely controlled, and excellent atomic-level surface flatness and crystalline quality are exhibited.In addition, the dielectric properties and insulation withstand voltage of the material are synergistically enhanced, effectively breaking the inverse correlation constraint between dielectric constant and breakdown field strength in traditional dielectric materials.The application breaks through the bottleneck of insufficient polarization intensity of traditional rare earth oxyhalide, and the method is suitable for light, medium and heavy three types of rare earth elements and various halogen combination systems, and has good universality.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional materials and microelectronics technology, and more specifically, relates to a heterogeneous halogen-polarized two-dimensional rare earth oxyhalogen material and its preparation method. Background Technology

[0002] As Moore's Law approaches its physical limits, two-dimensional semiconductor materials (such as MoS2 and WS2) are considered among the most promising channel materials in the post-Moore era due to their atomic-level thickness and excellent electrical properties. However, the actual performance of two-dimensional semiconductor devices largely depends on the performance of the gate dielectric material integrated with them. An ideal gate dielectric material needs to simultaneously possess a high dielectric constant (κ) to enhance gate coupling, an atomically smooth surface to form a high-quality interface, a wide bandgap to suppress leakage current, and a high breakdown field strength to ensure device reliability.

[0003] Currently, conventional gate dielectric materials such as Al2O3 (dielectric constant κ≈8.5), H f Although O2 (dielectric constant κ≈26) has been extensively studied, its non-layered structure leads to dangling bonds and charge traps with two-dimensional semiconductor channels, severely limiting device performance. Hexagonal boron nitride (h-BN, κ≈5), while possessing an atomically smooth van der Waals surface, has an excessively low dielectric constant, failing to meet the requirements of high-performance devices. To address these issues, researchers have attempted to modify dielectric materials through elemental doping. For example, patent CN102148238A discloses a composite dielectric material doped with rare earth metal oxides and its manufacturing method. This method embeds rare earth metal oxide nanoparticles into a silica glass substrate to form a glass composite through a sol-gel method. This method solves the technical problems of grain boundary effect and high leakage current caused by the polycrystalline structure of traditional high dielectric constant oxide materials. Patent document CN102054858A discloses an amorphous ternary high-κ gate dielectric material and its preparation method. This method forms an amorphous thin film by doping gadolinium oxide in hafnium oxide. The prepared gate dielectric film has a high dielectric constant and a very small leakage current density, effectively solving the problems of low crystallization temperature, severe oxygen diffusion, and low dielectric constant of hafnium oxide gate dielectric materials. Patent document CN119662253A discloses a rare earth-doped bismuth halide material and its preparation method. This method uses bismuth nitrate and erbium nitrate as raw materials to prepare rare earth-doped bismuth halide material through a hydrothermal method, solving the technical problem of optimizing the performance of luminescent materials.

[0004] In recent years, two-dimensional rare-earth oxyhalides have attracted attention due to their theoretically high dielectric constant and natural van der Waals layered structure. Theoretical predictions indicate that the κ value of LaOCl can reach 55.8. However, the dielectric constant of experimentally synthesized LnOX materials is far lower than the theoretical value (κ values ​​are all below 20), exhibiting a significant problem of insufficient polarization intensity. This "polarization bottleneck" stems from the inherent limitations of ionic and electronic polarization in two-dimensional rare-earth oxyhalides. Ionic polarization is limited by the degree of ion displacement in the crystal lattice, while electronic polarization is limited by the deformation capability of the electron cloud. Both are already close to their intrinsic limits in pure-phase rare-earth oxyhalides, making it difficult to further overcome through conventional pure-phase synthesis or morphology control methods. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides heterogeneous halogen-polarized two-dimensional rare-earth oxyhalide materials and their preparation method. By introducing heterogeneous halide ions into the rare-earth oxyhalide lattice, the ionic polarization is synergistically enhanced by the lattice contraction and symmetry breaking distortion induced by the heterogeneous halogens. Simultaneously, the electronegativity difference of the heterogeneous halogens enhances electronic polarization, thereby improving the dielectric constant while maintaining the long-range order and stability of the crystal structure. The thickness of the nanosheets prepared by this method can be precisely controlled, exhibiting excellent atomic-level surface smoothness and crystal quality. Furthermore, the dielectric properties and dielectric withstand voltage of the material are synergistically enhanced, effectively breaking the inverse correlation constraint between the dielectric constant and breakdown field strength in traditional dielectric materials. This invention overcomes the bottleneck of insufficient polarization intensity in traditional rare-earth oxyhalides, and the method is applicable to light, medium, and heavy rare-earth elements and various halogen combinations, demonstrating good versatility.

[0006] To achieve the above objectives, according to one aspect of the present invention, a heterogeneous halogen-polarized two-dimensional rare-earth oxyhalide material is provided, the material having the chemical formula LnOX. 1-m Y m Where m = 0.09~0.12, Ln is one of the rare earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, X is one of Cl, Br, and I, and Y is one of F, Cl, Br, and I, and X and Y are different.

[0007] Preferably, the dielectric constant κ of the material is greater than 20.

[0008] Preferably, the material has a two-dimensional layered crystal structure with a space group of P4 / nmm and a thickness of 0.8 nm to 35 nm.

[0009] According to a second aspect of the present invention, a method for preparing a heterogeneously halogenated two-dimensional rare-earth oxyhalide material is provided, comprising the following steps: The main rare earth halide precursor, the heterogeneous rare earth halide precursor, and the mixed molten salt are mixed evenly to obtain a precursor mixture. The precursor mixture was calcined at high temperature. After calcination, it was immediately removed and rapidly cooled at room temperature. After cooling, the residual molten salt was washed off and dried to finally obtain the heterogeneous halogen-polarized two-dimensional rare earth oxyhalogenated material.

[0010] Preferably, the main rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, and LnI3, and the heterojunction rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, LnI3, and LnF3. The main rare earth halide precursor and the heterojunction rare earth halide precursor contain the same rare earth elements but different halogen elements.

[0011] Preferably, the mixed molten salt is one of the following: a mixed molten salt of KCl and LiCl, a mixed molten salt of KBr and LiBr, or a mixed molten salt of KI and LiI, and the halogen element of the mixed molten salt is consistent with the halogen element contained in the main rare earth halide precursor.

[0012] Preferably, the molar ratio of KCl to LiCl, KBr to LiBr, or KI to LiI is 1.76:3 to 2:3.

[0013] Preferably, the total mass ratio of the main rare earth halide precursor, the heterojunction rare earth halide precursor and the mixed molten salt is 1:30 to 1:60.

[0014] Preferably, the mass ratio of the main rare earth halide precursor to the heterojunction rare earth halide precursor is 2:1 to 4:1.

[0015] Preferably, the high-temperature calcination temperature is 800 ℃~1000 ℃, and the calcination time is 5 minutes~10 minutes.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1. This invention constructs a novel two-dimensional dielectric material system with polarization enhancement effect by introducing heterogeneous halide ions into a two-dimensional rare-earth oxyhalide lattice. This two-dimensional dielectric material retains the natural van der Waals layered structure and atomically smooth surface of rare-earth oxyhalides, while enhancing ionic polarization through the synergistic enhancement of lattice contraction induced by heterogeneous halides and the breaking of local symmetry. At the same time, it enhances electronic polarization by utilizing the electronegativity difference between heterogeneous halides. Thus, it achieves synergistic optimization between the intrinsic structure and polarization capability of the material, effectively breaking through the bottleneck of insufficient polarization intensity of traditional rare-earth oxyhalide materials, and significantly improving the dielectric properties of the material.

[0017] 2. This invention establishes a simple, rapid, and universally applicable method for preparing two-dimensional rare-earth oxyhalide nanosheets using a molten salt-assisted synthesis method. This method achieves uniform doping of heterogeneous halide ions into the rare-earth oxyhalide lattice in a molten salt environment, and combines high-temperature calcination with rapid cooling to precisely control the thickness and morphology of the nanosheets. The prepared nanosheets exhibit a root-mean-square surface roughness as low as 0.21 nm, and their thickness can be precisely controlled within the range of 0.8 nm to 35 nm. Furthermore, this method is applicable to light, medium, and heavy rare-earth elements and various halogen combinations, and can obtain two-dimensional nanosheets with uniform morphology, regular structure, and pure phase in various material systems, demonstrating excellent synthetic universality and process stability.

[0018] 3. The heterogeneous halogen-polarized two-dimensional rare-earth oxide halide nanosheets prepared in this invention possess high dielectric constant, ultra-low equivalent oxide layer thickness, and high breakdown field strength, among which the monolayer LaOCl... 0.91 F 0.09 The nanosheets exhibit a dielectric constant of 79.5 at 1 MHz, an equivalent oxide layer thickness as low as 0.086 nm, and a breakdown field strength of 15.28 MV·cm. -1 This study achieves synergistic optimization of high dielectric constant and high breakdown field strength, breaking the inverse correlation constraint between the two in traditional dielectric materials. Furthermore, the material exhibits excellent frequency stability with no significant dielectric dispersion over a wide frequency range (100 kHz to 1 MHz), providing a stable and scalable material and process foundation for the application of high-performance two-dimensional nanoelectronic device gate dielectric materials. Attached Figure Description

[0019] Figure 1 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 AFM images of nanosheets; Figure 2 PrOBr prepared in Example 2 of this invention 0.88 Cl 0.12 AFM images of nanosheets; Figure 3 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 XRD patterns of nanosheets; Figure 4 NdOBr prepared in Example 3 of this invention 0.9 F 0.1 XRD patterns of nanosheets; Figure 5 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 EDS spectra of nanosheets; Figure 6 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Raman spectra of nanosheets; Figure 7 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 STEM image of nanosheets; Figure 8 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Comparison curves of dielectric constant versus thickness between nanosheets and LaOCl nanosheets prepared in Comparative Example 1; Figure 9 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Comparison curves of EOT versus thickness between nanosheets and LaOCl nanosheets prepared in Comparative Example 1; Figure 10 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 The dielectric constant versus frequency curve of nanosheets; Figure 11 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Schematic diagram of the breakdown field strength of nanosheets. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] This invention provides a heterogeneous halogen-polarized two-dimensional rare-earth oxyhalogen material and its preparation method, wherein the chemical formula of the material is LnOX. 1-m Y m Where m = 0.09~0.12, Ln is one of the rare earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, X is one of Cl, Br, and I, and Y is one of F, Cl, Br, and I, and X and Y are different. The dielectric constant κ of the material is greater than 20. The material has a two-dimensional layered crystal structure with space group P4 / nmm and a thickness of 0.8 nm to 35 nm.

[0022] The preparation method of the heterogeneous halogen-polarized two-dimensional rare earth oxyhalide material includes the following steps: mixing the main rare earth halide precursor, the heterogeneous rare earth halide precursor, and the mixed molten salt uniformly to obtain a precursor mixture; the main rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, and LnI3, and the heterogeneous rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, LnI3, and LnF3; the main rare earth halide precursor and the heterogeneous rare earth halide precursor contain the same rare earth elements but different halogen elements. The mixed molten salt is one of the following: a mixed molten salt of KCl and LiCl, a mixed molten salt of KBr and LiBr, or a mixed molten salt of KI and LiI, and the halogen element of the mixed molten salt is consistent with the halogen element contained in the main rare earth halide precursor; the molar ratio of KCl to LiCl, KBr to LiBr, or KI to LiI is 1.76:3 to 2:3; the total mass ratio of the main rare earth halide precursor, the heterojunction rare earth halide precursor, and the mixed molten salt is 1:30 to 1:60; the mass ratio of the main rare earth halide precursor to the heterojunction rare earth halide precursor is 2:1 to 4:1.

[0023] The precursor mixture was calcined at 800 ℃~1000 ℃ for 5 minutes to 10 minutes. After calcination, it was immediately removed and rapidly cooled at room temperature. After cooling, the residual molten salt was washed off and dried to finally obtain the heterogeneous halogen polarized two-dimensional rare earth oxyhalide material.

[0024] The design principle of this invention is as follows: This invention enhances the polarization intensity of materials by introducing heterogeneous halide ions into rare earth oxyhalide lattices, thereby synergistically improving the polarization intensity from both ionic and electronic polarization levels.

[0025] Regarding ionic polarization, the introduction of heterohalogen ions leads to lattice contraction and symmetry breaking distortion. For example, F... - For example, the bond length of the La-F bond (3.125 Å) is significantly shorter than that of the La-Cl bond (3.209 Å), and this bond length contraction makes Ln 3+ Ions deviate from their centrosymmetric positions, generating intrinsic dipole moments. Under the influence of an applied electric field, these dipole moments undergo angular deflection, significantly enhancing the net polarization intensity.

[0026] Regarding electronic polarization, heterogeneous halide ions (such as F) - The strong electron-withdrawing properties of Ln make 3+ The electron cloud becomes polarized, increasing the displacement between the atomic nucleus and the electron charge center. Under an applied electric field, these dipole moments are reoriented, further enhancing the overall polarization intensity.

[0027] The molten salt-assisted synthesis method used in this invention provides a uniform liquid-phase reaction environment through a molten halide medium, which allows rare earth halide precursors and hetero halogen precursors to be fully mixed and reacted at the atomic scale, thereby achieving uniform doping of hetero halogens in the rare earth oxyhalide lattice. At the same time, the thickness and morphology of the nanosheets are effectively controlled by the confinement effect of the molten salt medium on crystal growth.

[0028] The present invention will be described in detail below with reference to specific embodiments.

[0029] Example 1 LaOCl 0.91 F 0.09 Preparation of nanosheets KCl and LiCl were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. LaCl3·6H2O and LaF3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0030] The precursor mixture was calcined at 1000 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity LaOCl. 0.91 F 0.09 Nanosheets.

[0031] Example 2 PrOBr 0.88 Cl 0.12 Preparation of nanosheets KBr and LiBr were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. PrBr3·6H2O and PrCl3·6H2O were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0032] The precursor mixture was calcined at 800 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity PrOBr. 0.88 Cl 0.12 Nanosheets.

[0033] Example 3 NdOBr 0.9 F 0.1 Preparation of nanosheets KBr and LiBr were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. NdBr3·xH2O and NdF3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0034] The precursor mixture was calcined at 1000 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity NdOBr. 0.9 F 0.1 Nanosheets.

[0035] Example 4 GdOCl 0.9 F 0.1 Preparation of nanosheets KCl and LiCl were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. GdCl3·6H2O and GdF3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:30 and ground evenly to obtain a precursor mixture.

[0036] The precursor mixture was calcined at 1000 °C for 8 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity GdOCl. 0.9 F 0.1 Nanosheets.

[0037] Example 5 SmOBr 0.9 Cl 0.1 Preparation of nanosheets KBr and LiBr were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. SmBr3·6H2O and SmCl3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0038] The precursor mixture was calcined at 900 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity SmOBr. 0.9 Cl 0.1 Nanosheets.

[0039] Example 6 DyOI 0.9 F 0.1 Preparation of nanosheets KI and LiI were mixed evenly at a molar ratio of 1.76:3 to serve as a molten salt medium. DyI3 and DyF3 were mixed at a mass ratio of 3:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:58 and ground evenly to obtain a precursor mixture.

[0040] The precursor mixture was calcined at 1000 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity DyOI. 0.9 F 0.1 Nanosheets.

[0041] Example 7 ErOCl 0.9 F 0.1 Preparation of nanosheets KCl and LiCl were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. ErCl3·6H2O and ErF3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:40 and ground evenly to obtain a precursor mixture.

[0042] The precursor mixture was calcined at 1000 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity ErOCl. 0.9 F 0.1 Nanosheets.

[0043] Example 8 YbOBr 0.9 F 0.1 Preparation of nanosheets KBr and LiBr were mixed evenly at a molar ratio of 2:3 to serve as a molten salt medium. YbBr3·xH2O and YbF3 were mixed at a mass ratio of 2:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0044] The precursor mixture was calcined at 1000 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity YbOBr.0.9 F 0.1 Nanosheets.

[0045] Example 9 LuOI 0.9 Cl 0.1 Preparation of nanosheets KI and LiI were mixed evenly at a molar ratio of 1.76:3 to serve as a molten salt medium. LuI3 and LuCl3·6H2O were mixed at a mass ratio of 4:1 to serve as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0046] The precursor mixture was calcined at 800 °C for 10 minutes. Immediately after calcination, the reaction mixture was removed and rapidly cooled to room temperature. After the sample temperature dropped to room temperature, residual molten salt was washed off, and the sample was filtered and dried. The washed sample was then dried at 60 °C for 4 hours to obtain high-purity LuOI. 0.9 Cl 0.1 Nanosheets.

[0047] Example 10 CeOCl 0.91 F 0.09 Preparation of nanosheets The preparation process of the nanosheets in this embodiment is basically the same as that in Example 1, except that the precursors are CeCl3·6H2O and CeF3.

[0048] Example 11 EuOCl 0.91 F 0.09 Preparation of nanosheets The preparation process of the nanosheets in this embodiment is basically the same as that in Example 1, except that the precursors are EuCl3·6H2O and EuF3.

[0049] Example 12 TbOBr 0.88 Cl 0.12 Preparation of nanosheets The preparation process of the nanosheets in this embodiment is basically the same as that in Example 2, except that the precursors are TbBr3·6H2O and TbCl3.

[0050] Example 13 HoOBr 0.88 Cl 0.12 Preparation of nanosheets The preparation process of the nanosheets in this embodiment is basically the same as that in Example 2, except that the precursors are HoBr3·6H2O and HoCl3.

[0051] Example 14 LuOBr 0.9 F 0.1 Preparation of nanosheets The preparation process of the nanosheets in this embodiment is basically the same as that in Example 3, except that the precursors are LuBr3·6H2O and LuF3.

[0052] Comparative Example 1 Preparation of LaOCl nanosheets KCl and LiCl were mixed evenly at a molar ratio of 2:3 to form a molten salt medium, and LaCl3·6H2O was used as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0053] The precursor mixture was calcined at 800 °C for 10 minutes. After calcination, the reaction mixture was immediately removed and rapidly cooled at room temperature. After the sample temperature dropped to room temperature, the residual molten salt was washed off and filtered. The sample was then dried and dried at 60 °C for 4 hours to obtain high-purity LaOCl nanosheets.

[0054] Comparative Example 2 Preparation of LaOBr nanosheets KBr and LiBr were mixed evenly at a molar ratio of 2:3 to form a molten salt medium, and LaBr3·6H2O was used as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0055] The precursor mixture was calcined at 800 °C for 10 minutes. After calcination, the reaction mixture was immediately removed and rapidly cooled at room temperature. After the sample temperature dropped to room temperature, the residual molten salt was washed off and filtered. The sample was then dried and dried at 60 °C for 4 hours to obtain high-purity LaOBr nanosheets.

[0056] Comparative Example 3 Preparation of LaOI nanosheets KI and LiI were mixed evenly at a molar ratio of 1.76:3 to form a molten salt medium, and LaI3 was used as a precursor. The precursor and the molten salt medium were mixed at a mass ratio of 1:60 and ground evenly to obtain a precursor mixture.

[0057] The precursor mixture was calcined at 800 °C for 10 minutes. After calcination, the reaction mixture was immediately removed and rapidly cooled at room temperature. After the sample temperature dropped to room temperature, the residual molten salt was washed off and filtered. The sample was then dried and dried at 60 °C for 4 hours to obtain high-purity LaOI nanosheets.

[0058] It should be noted that no comparative example of LaOF was included in this comparative example because LaOF crystals have a non-layered structure and its space group is P63 / mmc, which is different from the P4 / nmm space group of the two-dimensional layered rare earth oxide halides of this invention. This material does not have a van der Waals layered structure and its crystal morphology is three-dimensional bulk particles rather than two-dimensional nanosheets. Therefore, it is impossible to prepare two-dimensional nanosheets.

[0059] The two-dimensional rare-earth oxyhalide nanosheets prepared in the above embodiments and comparative examples were characterized by atomic force microscopy (AFM). The root mean square (RMS) roughness values ​​were obtained by statistically analyzing the height data of each point within the scanning area of ​​the nanosheet surface. Furthermore, to determine the dielectric constant of each nanosheet, the heterogeneous halogen-polarized rare-earth oxyhalide nanosheets prepared in the above embodiments were assembled into a metal-insulator-metal (MIM) capacitor structure. The fabrication process of the capacitor device involved first transferring the nanosheets onto a silicon wafer already coated with a bottom electrode, then patterning them using maskless photolithography, and finally magnetron sputtering Au (50 nm) and Cr (30 nm) coatings as the top electrode. The thickness and surface RMS of each nanosheet were measured using atomic force microscopy (AFM) with a scanning range of 1 μm × 1 μm. The dielectric constant was measured using an impedance analyzer at a frequency of 1 MHz after the nanosheets were assembled into a MIM capacitor structure. The test results are shown in Table 1 below.

[0060] Table 1. Morphology parameters and dielectric constants of nanosheets in each embodiment and comparative example. As shown in Table 1, the heterogeneous halogen-polarized two-dimensional rare-earth oxide halide nanosheets prepared in each embodiment all possess smooth surface morphology, with RMS roughness ranging from 0.21 to 0.37 nm, and exhibit high dielectric constants at different thicknesses. Among them, the LaOCl nanosheet in Example 1, with a thickness of 0.8 nm, is particularly noteworthy. 0.91 F 0.09The nanosheets exhibit a dielectric constant of 79.5 at 1 MHz, while the pure-phase LaOCl nanosheets with a thickness of 0.8 nm in Comparative Example 1 have a dielectric constant of only 16.4 under the same conditions, with the former being approximately 4.8 times higher than the latter. Examples 2-9 further verify the universality of this effect in other rare earth elements and various halogen combinations, with dielectric constants ranging from 34.3 to 48, all significantly higher than the pure-phase materials of Comparative Examples 1-3 (κ = 14.7-16.4). The LaOCl, LaOBr, and LaOI nanosheets prepared in Comparative Examples 1-3 all have dielectric constants below 17, indicating that the dielectric constants of two-dimensional rare earth oxyhalides without heterohalogen polarization are generally low, making it difficult to meet the requirements of high-κ gate dielectric materials. The above results demonstrate that the present invention can significantly improve the dielectric constant of materials by introducing heterohalogens into rare earth oxyhalides, and this technical solution is applicable to different rare earth elements and different halogen combinations.

[0061] The nanosheets prepared in Examples 1-3 above were subjected to morphology, thickness, and phase characterization tests, and the results are shown in the figure. Figure 1 , Figure 2 , Figure 3 and Figure 4 ; Figure 1 and Figure 2 The images show the atomic force microscopy (AFM) morphology and thickness characterization of the nanosheets prepared in Examples 1 and 2, respectively. It can be clearly observed that the LaOCl nanosheets prepared in Example 1... 0.91 F 0.09 The nanosheets exhibit a typical ultrathin two-dimensional sheet structure, with a sample thickness of only 0.8 nm, corresponding to a complete monolayer rare-earth oxide halide lattice structure. Simultaneously, the root-mean-square surface roughness is as low as 0.21 nm, possessing atomically flat surface characteristics and extremely low defect density, providing a high-quality interface foundation for device fabrication. The PrOBr prepared in Example 2... 0.88 Cl 0.12 The nanosheets also maintained a regular two-dimensional sheet morphology, without obvious agglomeration or stacking defects, confirming that this doping preparation process is applicable to praseodymium oxybromide systems and can stably synthesize ultrathin two-dimensional nanomaterials with excellent morphology. A comparison of AFM results from two different matrices and different doping ion systems fully demonstrates that this synthesis method is universally applicable to various rare earth oxyhalide systems, and can prepare two-dimensional nanosheets with uniform morphology, smooth surface, and regular structure.

[0062] Figure 3 and Figure 4 The images show the X-ray diffraction (XRD) phase characterization patterns of the nanosheets prepared in Examples 1 and 3, respectively. It can be seen that the LaOCl nanosheets in Example 1... 0.91 F 0.09All diffraction peaks of the sample closely matched the standard card for pure-phase LaOCl, which corresponds to a tetragonal P4 / nmm space group crystal structure. This close matching indicates that heterogeneous halogen doping did not alter the parent crystal structure of the material, maintaining its complete layered configuration. Furthermore, the absence of characteristic diffraction peaks for impurities such as LaF demonstrates that F was successfully incorporated into the LaOCl lattice via isomorphic substitution without inducing impurity phase precipitation, thus successfully obtaining a pure-phase doped material. The NdOBr prepared in Example 3... 0.9 F 0.1 The XRD patterns of the samples also showed no impurity peaks, and all characteristic diffraction peaks were attributed to the NdOBr parent phase crystal structure. The samples maintained a complete substrate lattice configuration after doping, demonstrating excellent crystal structure stability. The combined XRD results from multiple sets indicate that the halide ion doping strategy employed in this experiment can achieve precise and controllable isomorphic doping in various rare-earth oxyhalide systems, effectively avoiding impurity phase formation and ensuring the phase purity of samples with different doping compositions and matrix systems. This provides a reliable structural basis for achieving superior electrical properties.

[0063] To further clarify the regulatory mechanism of heterogeneous halogen doping on the microstructure and dielectric properties of two-dimensional rare-earth oxychlorides, the LaOCl prepared in Example 1 was analyzed. 0.91 F 0.09 The nanosheets underwent further testing for fine structure and electrical properties, and the relevant characterization results are as follows: Figures 5 to 11 As shown.

[0064] Figure 5 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Energy-dispersive X-ray spectroscopy (EDS) characterization of the nanosheets shows that La, O, Cl, and F are uniformly distributed within the nanosheet region, with no obvious elemental agglomeration, segregation, or local deficiencies, indicating good elemental uniformity. This demonstrates that fluorine ions have been successfully and uniformly doped into the LaOCl matrix lattice without the formation of fluoride impurity phase agglomerations.

[0065] Figure 6 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 Raman spectroscopy of the nanosheets shows that, compared to undoped pure LaOCl, the characteristic Raman vibration peaks of the LaOClF sample exhibit a significant blue shift, with intact peak shapes and no additional impurity peaks, indicating high spectral purity. This suggests that fluorine ion doping effectively modulates the bond length and bonding strength of the LaOCl lattice chemical bonds, significantly improving lattice rigidity. The parent phase structure of the crystal remains unchanged after doping, demonstrating excellent structural stability.

[0066] Figure 7 LaOCl prepared in Example 1 of this invention0.91 F 0.09 Scanning transmission electron microscopy (STEM) images of the nanosheets show that the prepared doped nanosheets have clear, regular, and continuous lattice fringes, with no obvious lattice defects or dislocations, indicating excellent crystal quality. Compared to LaOCl, the interplanar spacing of the (200) sample shrank from 2.102 Å to 2.039 Å, with a lattice shrinkage rate of 3.0%. This indicates that isomorphic substitution by small-radius fluoride ions can effectively induce moderate lattice shrinkage, achieving precise control over the microcrystalline structure of LaOCl.

[0067] Figure 8 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 The comparison curves of the dielectric constant versus thickness of the nanosheets and the LaOCl nanosheets prepared in Comparative Example 1 show that the dielectric properties of the materials exhibit a significant thickness-dependent characteristic. At a testing frequency of 1 MHz, the dielectric constant of the 0.8 nm thick monolayer LaOClF nanosheets reaches 36.4, which is much higher than that of undoped pure-phase LaOCl. Furthermore, as the nanosheet thickness increases to 32 nm, the dielectric constant can be further improved to 79.5. This indicates that reasonable control of the nanosheet thickness can synergistically optimize the polarization ability of fluorine-doped modified materials and significantly improve the dielectric properties of the system.

[0068] Figure 9 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 The comparison curves of the equivalent oxide layer thickness (EOT) versus thickness for the LaOCl nanosheets prepared in Comparative Example 1 and the LaOCl nanosheets in Comparative Example 1 show that LaOCl... 0.91 F 0.09 The equivalent oxide layer thickness of the nanosheets exhibits excellent controllability as the physical thickness changes, with the equivalent oxide layer thickness of single-layer nanosheets as low as 0.086 nm, far lower than that of traditional dielectric materials. This indicates that the two-dimensional nanomaterials prepared in this invention possess extremely strong charge coupling capabilities, effectively overcoming the ultrathin thickness limitations of traditional gate dielectrics, and demonstrating excellent application advantages in advanced ultrathin gate dielectric devices.

[0069] Figure 10 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 The dielectric constant versus frequency curves of the nanosheets show that the material exhibits excellent dielectric stability over a wide frequency range. At a low frequency of 100 kHz, the peak dielectric constant reaches 79.3, and even at a high frequency of 1 MHz, it maintains a stable high dielectric value of 36.4 without significant dielectric dispersion or performance degradation. This indicates that LaOClF material has stable high-frequency dielectric properties and is suitable for the operating requirements of high-frequency microelectronic devices.

[0070] Figure 11 LaOCl prepared in Example 1 of this invention 0.91 F 0.09 The schematic diagram of the breakdown field strength of the nanosheets shows that the breakdown field strength of this doped nanosheet material is stably distributed in the range of 12–16 MV·cm, where LaOCl... 0.91 F 0.09 The nanosheets exhibit an optimal breakdown field strength of 15.28 MV·cm, with extremely low leakage current in the low electric field range and no obvious soft breakdown behavior, demonstrating excellent insulation properties. This indicates that the two-dimensional nanomaterials prepared in this invention possess both high dielectric constant and excellent insulation and withstand voltage characteristics, resulting in outstanding overall electrical performance and suitability for high-performance gate dielectrics and energy storage devices.

[0071] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hetero-halide polarized two-dimensional rare earth oxyhalide material, characterized in that, The material has a chemical formula of LnOX 1-m Y m wherein m=0.09~0.12, Ln is one of rare earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, X is one of Cl, Br, I, Y is one of F, Cl, Br, I, and X and Y are different.

2. The heterogeneous halogen-polarized two-dimensional rare-earth oxygen-halogen material according to claim 1, characterized in that, The dielectric constant of the material is κ>20.

3. The heterogeneous halogen-polarized two-dimensional rare-earth oxygen-halogen material according to claim 1, characterized in that, The material has a two-dimensional layered crystal structure with a space group of P4 / nmm and a thickness of 0.8 nm to 35 nm.

4. A method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen-halogen material according to any one of claims 1-3, characterized in that, Includes the following steps: The main rare earth halide precursor, the heterogeneous rare earth halide precursor, and the mixed molten salt are mixed evenly to obtain a precursor mixture. The precursor mixture was calcined at high temperature. After calcination, it was immediately removed and rapidly cooled at room temperature. After cooling, the residual molten salt was washed off and dried to finally obtain the heterogeneous halogen-polarized two-dimensional rare earth oxyhalogenated material.

5. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen halide material according to claim 4, characterized in that, The main rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, and LnI3, and the heterojunction rare earth halide precursor is one of LnCl3·6H2O, LnBr3·6H2O, LnI3, and LnF3. The main rare earth halide precursor and the heterojunction rare earth halide precursor contain the same rare earth elements but different halogen elements.

6. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen-halogen material according to claim 4, characterized in that, The mixed molten salt is one of the following: a mixed molten salt of KCl and LiCl, a mixed molten salt of KBr and LiBr, or a mixed molten salt of KI and LiI, and the halogen element of the mixed molten salt is consistent with the halogen element contained in the main rare earth halide precursor.

7. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen halide material according to claim 6, characterized in that, The molar ratios of KCl to LiCl, KBr to LiBr, or KI to LiI are all 1.76:3 to 2:

3.

8. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen halide material according to claim 4, characterized in that, The total mass ratio of the main rare earth halide precursor, the heterojunction rare earth halide precursor, and the mixed molten salt is 1:30 to 1:

60.

9. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen halide material according to claim 8, characterized in that, The mass ratio of the main rare earth halide precursor to the heterojunction rare earth halide precursor is 2:1 to 4:

1.

10. The method for preparing a heterogeneous halogen-polarized two-dimensional rare-earth oxygen halide material according to claim 4, characterized in that, The high-temperature calcination temperature is 800 ℃~1000 ℃, and the calcination time is 5 minutes~10 minutes.

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