Two-dimensional metal oxide based on van der waals surface reconfiguration engineering epitaxial growth and preparation method thereof

Abstract

The application provides a two-dimensional metal oxide based on van der Waals surface reconstruction engineering directional epitaxial growth and a preparation method thereof, and the application reconstructs a fluorophlogopite substrate surface to serve as a van der Waals epitaxial substrate for chemical vapor deposition growth of a two-dimensional metal oxide single crystal thin film. Metal oxide particles interact with the reconstructed fluorophlogopite surface (exposed oxygen atom plane) to form an energy minimized structure. Under strict single orientation conditions, four kinds of two-dimensional metal oxides are successfully prepared to form a centimeter scale single crystal thin film. These results demonstrate the potential of the synthesis strategy and open up a new exploration direction for the application of two-dimensional metal oxides in quantum physics and spin electronic devices.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional nanomaterial preparation, specifically to a two-dimensional metal oxide and its preparation method based on directional epitaxial growth using van der Waals surface reconstruction engineering. Background Technology

[0002] Epitaxial growth of high-quality single-crystal semiconductor thin films (e.g., GaN, AlGaN, GaAs) is a crucial technology for advanced electronics, energy science research, and industrial applications. Over the past decade, two-dimensional van der Waals layered materials have shown immense potential in electronics, catalysis, and energy applications, creating a demand not only for synthesizing atomically thin two-dimensional single-crystal films but also for extending this size reduction requirement from layered to non-layered materials. The primary motivation for reducing material thickness to two dimensions is due to their unique physical properties, such as two-dimensional electron gas, the quantum Hall effect, and charge density waves, which are results of carriers and photons being confined by dimensionality. Furthermore, unprecedented tunability has been achieved for ultrathin two-dimensional geometries, as the entire material essentially becomes a surface affected by external perturbations, such as interfacial polar coupling or interactions with another two-dimensional layer (e.g., lattice orientation distortion). However, synthesizing ultrathin two-dimensional single-crystal films remains a significant challenge for most non-layered materials due to their stable bulk structures. For example, metal oxides (MOs), as one of the most widely used materials in electronics and optoelectronics, include semiconductors (such as In₂O₃ and ZnO), dielectric materials (such as HfO₂ and Al₂O₃), ferroelectric materials (such as BaTiO₃), ferromagnetic materials (such as Fe₃O₄ and NiFe₂O₄), and ferromagnetic semiconductors. Although there have been reports on two-dimensional metal oxide nanosheets, the successful synthesis of single-crystal metal oxide thin films remains limited to date, with the main difficulty being controlling the orientation of the metal oxides during the initial nucleation stage.

[0003] Recent research reports indicate that controlling the surface energy of the interface between the nucleation layer and the substrate through surface reconstruction of single-crystal substrates is an effective method for achieving ordered epitaxial growth of two-dimensional van der Waals materials. For example, through annealing, the surfaces of single-crystal copper, nickel, and sapphire can be reconstructed to form specific atomic steps. Guided by the edges of these steps, the growth of unidirectional hBN and TMD domains was successfully achieved, ultimately merging into a single-crystal monolayer film. However, these non-van der Waals substrates are unsuitable for the epitaxial growth of two-dimensional non-layered materials because chemical bonds easily form at the interface due to dangling bonds on both sides. Non-van der Waals epitaxial growth is strictly limited by the requirements of similar lattice symmetry and constants between the film and the substrate, which not only makes it difficult to obtain ultrathin, high-quality two-dimensional films but also complicates the release of the epitaxial layer from the growth substrate. In contrast, van der Waals substrates with self-passivated atomically flat surfaces are more suitable for the epitaxial growth of two-dimensional non-layered materials. For example, mica is a commercially available large-size single-crystal van der Waals substrate with low cost and high-temperature tolerance, making it widely used in the epitaxial growth of non-layered materials, especially compared to graphene / graphite, hBN, or TMD materials. However, to date, there is still no effective method to precisely control the epitaxial orientation of MO particles. Therefore, there is an urgent need to develop a general and reliable strategy to achieve unidirectional epitaxial growth of two-dimensional MO nanosheets and ultimately obtain single-crystal two-dimensional MO thin films. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a two-dimensional metal oxide based on van der Waals surface reconstruction engineering directional epitaxial growth and its preparation method.

[0005] The technical solution adopted in this invention is as follows: The first aspect of this invention provides a method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering-directed epitaxial growth, comprising the following steps: S1. Place the fluorophlogopite substrate in an annealing apparatus and anneal it in an air atmosphere to obtain an annealed van der Waals material substrate. The annealing temperature is 300-400℃ and the annealing time is 40-60 min. S2. Take MX2 powder as a precursor, place the annealed fluorophlogopite substrate on the precursor and heat it, and at the same time introduce water vapor into the annealing equipment. Use the water vapor to deposit a two-dimensional metal oxide film on the surface of the annealed fluorophlogopite substrate. Wherein, M is at least one of Co, Fe, Mn, and Ni, and X is I.

[0006] Preferably, the heating temperature in step S2 is 480-750℃ and the heating time is 20-40 min.

[0007] Preferably, M is Co, and the heating temperature in step S2 is 490-530℃.

[0008] Preferably, M is Fe, and the heating temperature in step S2 is 480-550℃.

[0009] Preferably, M is Mn, and the heating temperature in step S2 is 500-650℃.

[0010] Preferably, M is Ni, and the heating temperature in step S2 is 600-750℃.

[0011] The second aspect of the present invention provides a two-dimensional metal oxide based on van der Waals surface reconstruction engineering directional epitaxial growth, which is prepared by the preparation method described above.

[0012] The beneficial effects of this invention are as follows: This invention reconstructs the surface of a fluorophlogopite substrate, making it a van der Waals epitaxial substrate for the chemical vapor deposition growth of two-dimensional metal oxide single-crystal thin films. The metal oxide particles interact with the reconstructed fluorophlogopite surface (exposed oxygen atom planes) to form a structure with minimized energy. Under strictly single-orientation conditions, four types of two-dimensional metal oxides were successfully prepared, forming centimeter-scale single-crystal thin films. These results demonstrate the potential of this synthesis strategy and open up new avenues for exploration in the application of two-dimensional metal oxides in quantum physics and spintronic devices. Attached Figure Description

[0013] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0014] Figure 1 A schematic diagram illustrating the preparation steps and directional epitaxial growth of a two-dimensional metal oxide based on van der Waals surface reconstruction engineering, provided for this invention. Figure 2 The images show the low-energy ion scattering and X-ray photoelectron spectra of mica after annealing in this embodiment of the invention. Figure 3 The microstructure diagrams and DFT theoretical calculations of the products obtained in Comparative Example 1 and Example 1 are shown. Figure 4 These are photographs showing the morphology of the two-dimensional CoO crystal materials with the same orientation prepared in Examples 1-3 of this invention as single-crystal thin films. Figure 5These are photographs showing the morphology of the two-dimensional Fe3O4 crystal materials with the same orientation prepared in Examples 4-6 of this invention, as well as their transformation into single-crystal thin films. Figure 6 These are photographs showing the morphology of the two-dimensional MnO crystal materials with the same orientation prepared in Examples 7-9 of this invention, as well as their transformation into single-crystal thin films. Figure 7 These are photographs showing the morphology of the two-dimensional NiO crystal materials with the same orientation prepared in Examples 10-13 of this invention, as well as their transformation into single-crystal thin films. Figure 8 The following are thickness measurement diagrams of single-crystal thin films prepared according to embodiments of the present invention: a is the two-dimensional CoO single-crystal thin film prepared in embodiment 3 of the present invention, b is the two-dimensional Fe3O4 single-crystal thin film prepared in embodiment 6, c is the two-dimensional MnO single-crystal thin film prepared in embodiment 7, and d is the thickness measurement diagram of the two-dimensional NiO single-crystal thin film prepared in embodiment 12. Figure 9 The following are phase characterization diagrams of the crystal materials prepared in the embodiments of the present invention: a is the phase characterization diagram of the two-dimensional CoO crystal material prepared in Example 2 of the present invention; b is the phase characterization diagram of the two-dimensional Fe3O4 crystal material prepared in Example 5; c is the phase characterization diagram of the two-dimensional MnO crystal material prepared in Example 8; and d is the phase characterization diagram of the two-dimensional NiO crystal material prepared in Example 11. Figure 10 These are photographs showing the morphology of two-dimensional MOs nanosheets prepared using unannealed mica as a substrate in Comparative Examples 1-3 of this invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0016] Example 1 This embodiment provides a two-dimensional metal oxide prepared by directional epitaxial growth based on van der Waals surface reconstruction engineering, and the preparation method includes the following steps: S1. Using a muffle furnace as the annealing device, the fluorophlogopite substrate is placed in a ceramic plate and then placed in the muffle furnace for annealing in an air atmosphere. The annealing temperature is set to 300-400 ℃, specifically 350 ℃ in this embodiment, and the annealing time is set to 30 min. After naturally cooling to room temperature, it is taken out.

[0017] S2. A horizontal tube furnace was used as the deposition equipment, with a tube length of 80 cm, a central temperature zone of 10 cm, and a temperature set at 490 °C at a heating rate of 25 °C / min. CoI2 powder was used as the reaction source, which was uniformly placed in a quartz boat. An annealed fluorophlogopite substrate was then placed upside down on top of the reaction source. Before the reaction, a pre-vacuum was applied, followed by 200 sccm of Ar to atmospheric pressure, and the gas was purged for at least 10 min to remove residual gases. During this process, the Ar rate was 50 sccm. Once the target temperature was reached, the quartz boat containing the precursor was pushed into the center of the furnace using an external rod. Simultaneously, a constant amount of water vapor was introduced into the furnace through a bubbler connected to a separate gas line. The reaction time was 30 min. After the reaction, the carrier gas remained unchanged, and the product was cooled to room temperature with the furnace. The product was collected on a mica substrate to obtain two-dimensional CoO nanosheets with the same orientation.

[0018] Example 2 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and Embodiment 1 is that in step S2, the temperature is set to 500℃, and two-dimensional CoO nanosheets with the same orientation are finally obtained.

[0019] Example 3 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and Embodiment 1 is that in step S2, the temperature is set to 530℃, and a centimeter-scale CoO single crystal thin film is finally obtained.

[0020] Example 4 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and Embodiment 1 is that in step S2, the temperature is set to 480℃, FeI2 powder is used as the reaction source, and Fe3O4 nanosheets with the same orientation are finally obtained.

[0021] Example 5 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 4 is that in step S2, the temperature is set to 510℃, and two-dimensional Fe3O4 nanosheets with the same orientation are finally obtained.

[0022] Example 6 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 4 is that in step S2, the temperature is set to 550℃, and a centimeter-scale Fe3O4 single crystal thin film is finally obtained.

[0023] Example 7 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 1 is that in step S2, the temperature is set to 520℃, MnI2 powder is used as the reaction source, and MnO nanosheets with the same orientation are finally obtained.

[0024] Example 8 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 7 is that in step S2, the temperature is set to 550℃, and MnO nanosheets with the same orientation are finally obtained.

[0025] Example 9 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 7 is that in step S2, the temperature is set to 600℃, and a centimeter-scale MnO single crystal thin film is finally obtained.

[0026] Example 10 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 1 is that in step S2, the temperature is set to 620℃, NiI2 powder is used as the reaction source, and NiO nanosheets with the same orientation are finally obtained.

[0027] Example 11 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 9 is that in step S2, the temperature is set to 660℃, and NiO nanosheets with the same orientation are finally obtained.

[0028] Example 12 This embodiment provides a two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering. The difference between this embodiment and embodiment 9 is that in step S2, the temperature is set to 700℃, and a meter-scale NiO single crystal thin film is finally obtained.

[0029] Comparative Example 1 A horizontal tube furnace was used as the deposition equipment, with a tube length of 80 cm, a central temperature zone of 10 cm, and a temperature set at 500 °C at a heating rate of 25 °C / min. CoI₂ powder was used as the reaction source, uniformly placed in a quartz boat. A fresh fluorophlogopite substrate was then placed upside down on top of the reaction source. Before the reaction, a pre-vacuum was applied, followed by 200 sccm of Ar to atmospheric pressure, followed by purging for at least 10 min to remove residual gases. During this process, the Ar rate was 50 sccm. Once the target temperature was reached, an external rod was used to push the quartz boat containing the precursor into the center of the furnace. Simultaneously, a constant amount of water vapor was introduced into the furnace through a bubbler connected to a separate gas line. The reaction time was 30 min. After the reaction, the carrier gas remained constant, and the product was cooled to room temperature with the furnace. The product was collected on a mica substrate to obtain two oriented two-dimensional CoO nanosheets.

[0030] Comparative Example 2 A horizontal tube furnace was used as the deposition equipment, with a tube length of 80 cm, a central temperature zone of 10 cm, and a temperature set at 510 °C at a heating rate of 25 °C / min. FeI2 powder was used as the reaction source, uniformly placed in a quartz boat. A fresh fluorophlogopite substrate was then placed upside down on top of the reaction source. Before the reaction, a pre-vacuum was applied, followed by 200 sccm of Ar to atmospheric pressure, followed by purging for at least 10 min to remove residual gases. During this process, the Ar rate was 50 sccm. Once the target temperature was reached, an external rod was used to push the quartz boat containing the precursor into the center of the furnace. Simultaneously, a constant amount of water vapor was introduced into the furnace through a bubbler connected to a separate gas line. The reaction time was 30 min. After the reaction, the carrier gas remained constant, and the product was cooled to room temperature with the furnace. The product was collected on a mica substrate to obtain two oriented two-dimensional Fe3O4 nanosheets.

[0031] Comparative Example 3 A horizontal tube furnace was used as the deposition equipment, with a tube length of 80 cm, a central temperature zone of 10 cm, and a temperature set at 660 °C at a heating rate of 25 °C / min. NiI₂ powder was used as the reaction source, uniformly placed in a quartz boat. A fresh fluorophlogopite substrate was then placed upside down on top of the reaction source. Before the reaction, a pre-vacuum was applied, followed by 200 sccm of Ar to atmospheric pressure, followed by purging for at least 10 min to remove residual gases. During this process, the Ar rate was 50 sccm. Once the target temperature was reached, an external rod was used to push the quartz boat containing the precursor into the center of the furnace. Simultaneously, a constant amount of water vapor was introduced into the furnace through a bubbler connected to a separate gas line. The reaction time was 30 min. After the reaction, the carrier gas remained constant, and the product was cooled to room temperature with the furnace. The product was collected on a mica substrate to obtain two oriented two-dimensional NiO nanosheets.

[0032] Test Result Analysis Figure 1 This invention provides a schematic diagram of the preparation steps and directional epitaxial growth of a two-dimensional metal oxide based on van der Waals surface reconstruction engineering. Figure 2 The low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) of mica after annealing in this embodiment of the invention verify the effectiveness of the annealing process in removing potassium ions from the mica surface. Annealing causes the mica substrate surface to reconstruct. Figure 3 The diagram shows the microstructure of the products obtained in Comparative Example 1 and Example 1, along with DFT theoretical calculations.

[0033] The morphology of the two-dimensional metal oxide crystal materials prepared in Examples 1-12 was characterized using an optical microscope, and the results are as follows: Figures 4-7 As shown. Figure 4 These are photographs showing the morphology of the two-dimensional CoO crystal materials with the same orientation prepared in Examples 1-3 of this invention as single-crystal thin films. Figure 5 These are photographs showing the morphology of the two-dimensional Fe3O4 crystal materials with the same orientation prepared in Examples 4-6 of this invention, as well as their transformation into single-crystal thin films. Figure 6 These are photographs showing the morphology of the two-dimensional MnO crystal materials with the same orientation prepared in Examples 7-9 of this invention, as well as their transformation into single-crystal thin films. Figure 7 These are photographs showing the morphology of the same-oriented two-dimensional NiO crystal material to single-crystal thin films prepared in Examples 10-13 of this invention. Figures 4-7 As can be seen, as the growth temperature increases, the material progresses from well-oriented domains to extended domains, eventually forming a continuous thin film.

[0034] The thickness of the two-dimensional metal oxide single-crystal thin films prepared in Examples 3, 6, 9, and 12 was measured by scanning the sample surface using an atomic force microscope. The thickness of the CoO single-crystal thin film prepared in Example 3 was measured to be approximately 7.4 nm. The measurement results are as follows: Figure 8 As shown in Figure a; the thickness of the Fe3O4 single crystal thin film prepared in Example 6 is approximately 8.8 nm, and the measurement results are as follows. Figure 8 As shown in b; the thickness of the MnO single crystal film prepared in Example 9 is approximately 7.8 nm, and the measurement results are as follows. Figure 8 As shown in c; the thickness of the NiO single crystal film prepared in Example 12 is approximately 8.5 nm, and the measurement results are as follows. Figure 8 As shown in d.

[0035] The two-dimensional metal oxide crystal materials prepared in Examples 2, 5, 8, and 11 were characterized by transmission electron microscopy, and the results are as follows: Figure 9 As shown in a-9d, high-quality MOs with excellent crystallinity were synthesized.

[0036] The two-dimensional MOs crystal material prepared in Comparative Example 1 was analyzed using an optical microscope, and the results are as follows: Figure 10 As shown, if unannealed mica is used as a substrate to prepare two-dimensional MOs, their orientations are two, and there is no tendency for them to connect into a film. Considering the entire preparation process, since mica is a layered silicate composed of aluminosilicate and K... + Layers alternate, in K + Layers readily split. On freshly cut mica surfaces, the exposed potassium atom planes exhibit six-fold rotational symmetry. The formation energy of growing MOs with triple rotational symmetry on mica surfaces with six-fold rotational symmetry may exhibit multiple minima, with two orientations being more common.

[0037] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering-directed epitaxial growth, characterized in that, Includes the following steps: S1. Place the fluorophlogopite substrate in an annealing apparatus and anneal it in an air atmosphere to obtain an annealed van der Waals material substrate. The annealing temperature is 300-400℃ and the annealing time is 40-60 min. S2. Take MX2 powder as a precursor, place the annealed fluorophlogopite substrate on the precursor and heat it, and at the same time introduce water vapor into the annealing equipment. Use the water vapor to deposit a two-dimensional metal oxide film on the surface of the annealed fluorophlogopite substrate. Wherein, M is at least one of Co, Fe, Mn, and Ni, and X is I.

2. The method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering through directional epitaxial growth according to claim 1, characterized in that: The heating temperature in step S2 is 480-750℃, and the heating time is 20-40 minutes.

3. The method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering through directional epitaxial growth according to claim 1, characterized in that: M represents Co, and the heating temperature in step S2 is 490-530℃.

4. The method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering-directed epitaxial growth according to claim 1, characterized in that: M is Fe, and the heating temperature in step S2 is 480-550℃.

5. The method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering-directed epitaxial growth according to claim 1, characterized in that: M is Mn, and the heating temperature in step S2 is 500-650℃.

6. The method for preparing two-dimensional metal oxides based on van der Waals surface reconstruction engineering-directed epitaxial growth according to claim 1, characterized in that: M is Ni, and the heating temperature in step S2 is 600-750℃.

7. A two-dimensional metal oxide grown by directional epitaxial growth based on van der Waals surface reconstruction engineering, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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