Magnetic introduction method of two-dimensional material and magnetic structure

Abstract

The embodiment of the invention provides a magnetic introduction method of a two-dimensional material. The magnetic introduction method comprises the following steps: preparing a substrate with a step structure; and preparing a two-dimensional material layer on the substrate to introduce magnetism into the two-dimensional material layer at the step structure region of the substrate. According to the magnetism introduction method of the two-dimensional material provided by the embodiment of the invention, the two-dimensional material layer is formed on the step-type substrate, so that the two-dimensional material layer covering the step generates strain, uniform magnetism in the step direction is generated, intrinsic element composition of the material can be kept, and the preparation process is simple and easy to implement. The embodiment of the invention further provides a magnetic structure.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of magnetic materials, and more specifically, to a method for introducing magnetism into two-dimensional materials and a magnetic structure. Background Art

[0002] Due to their unique atomic structures and elemental compositions, atomically thin two-dimensional materials exhibit excellent electronic and optical properties, showing good application prospects in fields such as optoelectronic detection and spintronics. However, two-dimensional materials that do not contain magnetic atoms, such as graphene and some transition metal chalcogenides, generally do not have intrinsic magnetism, thus limiting their applications in spintronic devices.

[0003] Therefore, how to introduce magnetism into non-magnetic two-dimensional materials is an urgent problem to be solved in the fields of spintronics and materials science. Existing methods for introducing magnetism, such as element doping and structural phase transition, usually affect the elemental composition and crystal phase structure of the materials, thus bringing uncontrollable adverse effects to two-dimensional materials. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the embodiments of the present application provide a method for introducing magnetism into two-dimensional materials and a magnetic structure. By forming a two-dimensional material layer on a stepped substrate, strain is generated in the two-dimensional material layer covering the steps, thereby generating uniform magnetism along the step direction, which can maintain the intrinsic elemental composition of the material, the preparation process is simple, and it is easy to implement.

[0005] In a first aspect, the embodiments of the present application provide a method for introducing magnetism into two-dimensional materials, including the following steps:

[0006] Preparing a substrate having a stepped structure; and

[0007] Preparing a two-dimensional material layer on the substrate to introduce magnetism into the two-dimensional material layer located in the stepped structure region of the substrate.

[0008] Further, the substrate is a bilayer graphene substrate, and preparing the substrate having a stepped structure includes:

[0009] Performing high-temperature annealing on silicon carbide to form the bilayer graphene substrate, and the bilayer graphene substrate has a stepped structure.

[0010] Further, the aspect ratio of the stepped structure of the bilayer graphene substrate is greater than 0.24.

[0011] Further, the two-dimensional material layer is a monolayer niobium diselenide, and forming the two-dimensional material on the substrate includes:

[0012] A monolayer of niobium diselenide is formed on the bilayer graphene substrate by molecular beam epitaxy, and the monolayer of niobium diselenide has local magnetism distributed along the direction of the step structure of the bilayer graphene substrate.

[0013] Further, the high-temperature annealing of the silicon carbide to form the bilayer graphene substrate includes:

[0014] The silicon carbide is subjected to high-temperature annealing at an annealing temperature of 1250 degrees Celsius for an annealing duration of 60 minutes to form the bilayer graphene substrate.

[0015] Further, the formation of the monolayer of niobium diselenide on the bilayer graphene substrate by molecular beam epitaxy includes:

[0016] Selenium atoms and niobium atoms with a beam ratio greater than 10:1 are used to form the monolayer of niobium diselenide on the bilayer graphene substrate by molecular beam epitaxy.

[0017] In a second aspect, an embodiment of the present application provides a magnetic structure, including a substrate and a two-dimensional material layer. The two-dimensional material layer is formed above the substrate. The substrate has a step structure, and the two-dimensional material layer has magnetism in the step structure region of the substrate.

[0018] Further, the substrate is a bilayer graphene substrate, and the step structure is formed on the bilayer graphene substrate.

[0019] Further, the aspect ratio of the step structure of the bilayer graphene substrate is greater than 0.24.

[0020] Further, the two-dimensional material layer is a monolayer of niobium diselenide, and the monolayer of niobium diselenide has local magnetism distributed along the direction of the step structure of the bilayer graphene substrate.

[0021] The embodiments of the present application bring the following beneficial effects:

[0022] In the method for introducing magnetism into a two-dimensional material provided by the embodiments of the present application, first, a substrate with a step structure is prepared, and then a two-dimensional material layer is prepared on the substrate to introduce magnetism into the two-dimensional material layer located in the step structure region of the substrate. In the method for introducing magnetism into a two-dimensional material provided by the embodiments of the present application, by forming a two-dimensional material layer on a stepped substrate, strain is generated in the two-dimensional material layer covering the steps, thereby generating uniform magnetism along the step direction. At the same time, the intrinsic elemental composition of the material can be maintained, the preparation process is simple, and it is easy to implement. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0024] Figure 1 Schematic flowchart of the method for introducing magnetism into two-dimensional materials provided by an embodiment of the present application;

[0025] Figure 2 Schematic structural diagram of the substrate made by the method for introducing magnetism into two-dimensional materials provided by an embodiment of the present application;

[0026] Figure 3 Scanning tunneling microscope image of the bilayer graphene substrate with a stepped structure used in the method for introducing magnetism into two-dimensional materials provided by an embodiment of the present application;

[0027] Figure 4 Schematic process diagram of growing monolayer niobium diselenide on a bilayer graphene substrate by molecular beam epitaxy technology used in the method for introducing magnetism into two-dimensional materials provided by an embodiment of the present application;

[0028] Figure 5 Scanning tunneling microscope image of the strain region of the niobium diselenide layer formed above the stepped structure of the bilayer graphene substrate involved in the method for introducing magnetism into two-dimensional materials provided by an embodiment of the present application;

[0029] Figure 6 For Figure 5 Differential conductance spectrum of the strain region collected along the dotted arrow in

[0030] The realization of the purpose of the present application, functional features and advantages will be further described in conjunction with the embodiments and with reference to the drawings. Detailed implementation manners

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0032] In the description and claims of this application and the above-mentioned drawings, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise stated, the meaning of "a plurality" is two or more. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] Figure 1 is a flowchart of a method for introducing magnetism into a two-dimensional material according to an embodiment of this application. As Figure 1 shown, the method for introducing magnetism into a two-dimensional material according to an embodiment of this application includes the following steps:

[0034] S101: Prepare a substrate with a stepped structure; and

[0035] Specifically, the substrate material needs to be a van der Waals material, and the interaction between the substrate and the target material is a van der Waals force, so as to reduce the influence of the substrate on the electronic properties of the target material. The size of the stepped structure needs to meet the stress range that the target material can withstand to avoid fracture of the target material.

[0036] S102: Prepare a two-dimensional material layer on the substrate to introduce magnetism into the two-dimensional material layer located in the stepped structure area of the substrate.

[0037] The two-dimensional material layer is also a van der Waals material, and the interaction between the two-dimensional material layer and the substrate is a van der Waals force, so as to reduce the influence of the substrate on the electronic properties of the target material. The lattice strain is generated in the area of the two-dimensional material layer above the stepped structure of the substrate. This strain affects the interatomic bond length and charge distribution, and can make the strain area generate a uniform non-zero magnetic moment, and at the same time, the lattice structure of the strain area does not undergo a phase change.

[0038] In the method for introducing magnetism into a two-dimensional material provided by an embodiment of this application, first, a substrate with a stepped structure is prepared, and then a two-dimensional material layer is prepared on the substrate to introduce magnetism into the two-dimensional material layer located in the stepped structure area of the substrate. The method for introducing magnetism into a two-dimensional material provided by an embodiment of this application makes the two-dimensional material layer covering the steps generate strain by forming a two-dimensional material layer on a stepped substrate, so as to generate uniform magnetism along the step direction, and at the same time, it can maintain the elemental composition of the material. The preparation process is simple and easy to implement.

[0039] Further, referring to Figures 2 to 4 , the substrate is a bilayer graphene substrate, and the preparation of the substrate with a stepped structure includes:

[0040] The silicon carbide is subjected to high-temperature annealing to form the bilayer graphene substrate, and the bilayer graphene substrate has a stepped structure.

[0041] Specifically, as Figure 2 shown, the silicon carbide is subjected to high-temperature annealing treatment to prepare a substrate with steps. In a vacuum environment, the silicon carbide crystal is subjected to high-temperature annealing treatment to prepare a substrate covered with bilayer graphene on the surface. Due to the slight angular deviation during the cutting process, a periodic stepped structure will naturally form on the surface. During the high-temperature annealing process, silicon atoms preferentially sublime from the surface, and at the same time, the carbon atoms on the surface are rearranged to form graphene. The growth rate of graphene at the steps is different, further enhancing the visibility of the steps and forming a regular stepped distribution. As Figure 3 shown, after the treated silicon carbide is cooled, scanning tunneling microscopy characterization is performed, and it can be seen that the surface is already covered with bilayer graphene, and there are steps between adjacent planes.

[0042] Furthermore, the aspect ratio of the stepped structure of the bilayer graphene substrate is greater than 0.24.

[0043] Referring to Figure 5 , Figure 5 is a scanning tunneling microscopy image of the strained region of the niobium diselenide layer formed above the stepped structure of the bilayer graphene substrate involved in the method for introducing magnetism into the two-dimensional material provided in the embodiment of the present application. In Figure 5 , the upper figure is the topography of niobium diselenide in the stepped region, and the lower figure is the corresponding height map. 0.78 nm and 3.00 nm in the height map represent the height and width of the niobium diselenide layer in the stepped structure region, respectively. Among them, the larger the ratio of the height to the width of the niobium diselenide layer in the stepped structure region, the greater the strain degree here. When the aspect ratio is greater than 0.24, the strained region exhibits magnetism. Therefore, in the method for introducing magnetism into the two-dimensional material provided in the embodiment of the present application, by forming a two-dimensional material layer on the stepped substrate, the two-dimensional material layer covering the steps generates strain, thereby generating uniform magnetism along the step direction. At the same time, without introducing heteroatoms, the intrinsic elemental composition of the material can be maintained, the preparation process is simple, and it is easy to implement.

[0044] Referring to Figure 6 , Figure 6 is the differential conductance spectrum of the strained region collected along the Figure 5 dashed arrow in Figure 6 . The splitting phenomenon of the density of states peak in the conductance spectrum of Figure 5 indicates, combined with the prediction of theoretical calculation, that the niobium diselenide in this strained region has a local magnetic moment. The conductance spectra continuously collected along the direction of the stepped structure (

[0045] Figure 5 dashed arrow marked) show that the local magnetic moment of the niobium diselenide in the strained region is uniformly distributed along the direction of the stepped structure.

[0045] Further, referring again to Figure 4 , the two-dimensional material layer is a single-layer niobium diselenide, and forming the two-dimensional material on the substrate includes:

[0046] Forming a single-layer niobium diselenide on the bilayer graphene substrate by molecular beam epitaxy technology, and the single-layer niobium diselenide has local magnetism distributed along the direction of the step structure of the bilayer graphene substrate.

[0047] Specifically, molecular beam epitaxy technology is a technology for epitaxial growth of single crystal films under ultra-high vacuum conditions. Similar to vacuum evaporation coating, the components and pre-doped atoms (molecules) that make up the crystal are sprayed onto the substrate from the injection furnace at a certain thermal motion speed and in a certain proportion for crystal epitaxial growth. After the bilayer graphene substrate is prepared, a single-layer niobium diselenide is formed on the bilayer graphene substrate by molecular beam epitaxy technology, and the single-layer niobium diselenide has local magnetism distributed along the step direction of the bilayer graphene substrate, which is also convenient for subsequent regulation of the local magnetism of the two-dimensional material.

[0048] Further, the high-temperature annealing of silicon carbide to form the bilayer graphene substrate includes:

[0049] Performing high-temperature annealing on the silicon carbide at an annealing temperature of 1250 degrees Celsius and an annealing duration of 60 minutes to form the bilayer graphene substrate.

[0050] As described above, high-temperature annealing treatment is performed on silicon carbide, for example, the annealing temperature is 1250 degrees Celsius and the annealing duration is 60 minutes, so as to prepare a substrate with steps. In a vacuum environment, high-temperature annealing treatment is performed on the silicon carbide crystal to prepare a substrate covered with bilayer graphene on the surface. Due to the slight angular deviation during the cutting process, a periodic step structure will naturally form on the surface. During the high-temperature annealing process, silicon atoms are preferentially sublimated from the surface, and at the same time, the carbon atoms on the surface are rearranged to form graphene. The growth rate of graphene at the steps is different, which further enhances the visibility of the steps and forms a regular step distribution. After the treated silicon carbide is cooled down, scanning tunneling microscopy characterization shows that the surface is already covered with bilayer graphene and there are steps between adjacent planes.

[0051] It should be noted that graphene wrinkles can also be prepared by high-temperature annealing of silicon carbide followed by rapid cooling to provide a substrate with height fluctuations, so as to prepare a target sample thereon, and the required strain effect can also be achieved to introduce the required magnetism.

[0052] Further, forming a single-layer niobium diselenide on the bilayer graphene substrate by molecular beam epitaxy technology includes:

[0053] Selenium atoms and niobium atoms with a beam current ratio greater than 10:1 are used to form the monolayer niobium diselenide on the bilayer graphene substrate through molecular beam epitaxy technology.

[0054] Specifically, in a vacuum environment, first, high-temperature annealing of silicon carbide is carried out. For example, the annealing temperature is 1250 °C and the duration is about 60 min to prepare a bilayer graphene substrate. Then, through molecular beam epitaxy technology, monolayer niobium diselenide is prepared on the graphene surface. The beam current ratio of high-purity selenium atoms and niobium atoms is greater than 10:1 to provide a selenium-rich environment and reduce the generation of domain boundaries and vacancy defects during the preparation process, obtaining high-quality monolayer niobium diselenide. Since the silicon carbide substrate covered with graphene has steps, strain is generated in the niobium diselenide above the steps. When the strain is large enough, it can induce local magnetism distributed along the step direction.

[0055] In addition, as an alternative solution, after preparing a stepped substrate or a wrinkled substrate, nanoislands of the target sample can be grown thereon, and then through scanning tunneling microscope tip manipulation technology, the nanoislands are pushed from the flat area to above the steps or wrinkles, so that the nanoislands cover the step or wrinkled area at any angle to achieve the required strain effect and introduce the required magnetism.

[0056] Refer again to Figure 4 , an embodiment of the present application provides a magnetic structure, including a substrate and a two-dimensional material layer. The two-dimensional material layer is formed above the substrate. The substrate has a stepped structure, and the two-dimensional material layer has magnetism in the stepped structure area of the substrate.

[0057] Specifically, lattice strain is generated in the area of the two-dimensional material layer above the stepped structure of the substrate. This strain affects the interatomic bond length and charge distribution, and can make the strained area generate a uniform non-zero magnetic moment, and at the same time, the lattice structure of the strained area does not undergo a phase change. The magnetic structure provided by the embodiment of the present application forms a two-dimensional material layer on a stepped substrate, so that the two-dimensional material layer covering the steps generates strain, thereby generating uniform magnetism along the step direction, and at the same time, the intrinsic element composition of the material can be maintained. The preparation process is simple and easy to implement.

[0058] Further, in some embodiments of the present application, the substrate is a bilayer graphene substrate, and the stepped structure is formed on the bilayer graphene substrate.

[0059] As described above, high-temperature annealing treatment is performed on silicon carbide to prepare a substrate with steps. In a vacuum environment, high-temperature annealing treatment is performed on a silicon carbide crystal to prepare a substrate covered with a bilayer graphene on the surface. Due to a slight angular deviation during the cutting process, a periodic step structure will naturally form on the surface. During the high-temperature annealing process, silicon atoms preferentially sublime from the surface, and at the same time, carbon atoms on the surface are rearranged to form graphene. The growth rate of graphene at the steps is different, which further enhances the visibility of the steps and forms a regular step distribution. As Figure 3 shown, after cooling the treated silicon carbide, scanning tunneling microscopy characterization is performed, and it can be seen that the surface is already covered with bilayer graphene, and there are steps between adjacent planes.

[0060] Furthermore, in some embodiments of the present application, the aspect ratio of the step structure of the bilayer graphene substrate is greater than 0.24.

[0061] Specifically, the larger the ratio of the height to the width of the niobium diselenide layer in the step structure region of the substrate, the greater the strain degree here. When the aspect ratio is greater than 0.24, the strained region exhibits magnetism. Therefore, the magnetic structure provided by the embodiments of the present application forms a two-dimensional material layer on a stepped substrate, causing the two-dimensional material layer covering the steps to generate strain, thereby generating uniform magnetism along the step direction. At the same time, without introducing heteroelements, it can maintain the elemental composition of the material, the preparation process is simple, and it is easy to implement.

[0062] Furthermore, in some embodiments of the present application, the two-dimensional material layer is a single layer of niobium diselenide, and the single layer of niobium diselenide has local magnetism distributed along the direction of the step structure of the bilayer graphene substrate.

[0063] Specifically, in the magnetic structure provided by the embodiments of the present application, first, a substrate with uniform steps on the surface is prepared, and then the target two-dimensional material (such as NbSe 2 , NbS 2 etc.) is prepared on the surface of the substrate. The target material generates lattice distortion with the substrate morphology as a template, and the lattice generates tensile strain in the direction perpendicular to the steps, thereby inducing magnetism uniformly distributed along the strained region, thus realizing the introduction of magnetism of the two-dimensional material, and thus realizing the spontaneous magnetization of the strained region. The target sample can have magnetism after being strained, and the magnetization range shows a one-dimensional distribution along the step direction, and the unstrained region still maintains the original electronic and crystal structure of the target sample.

[0064] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structural transformation made under the application concept of the present application, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present application.

Claims

1. A method for magnetic introduction of two-dimensional materials, characterized in that: The following steps are involved: preparing a substrate having a step structure; and A two-dimensional material layer is prepared on the substrate to introduce magnetism into the two-dimensional material layer at a step structure region of the substrate.

2. The method according to claim 1, characterized in that The substrate is a double-layer graphene substrate, and the step of preparing the substrate with a step structure comprises: The silicon carbide is subjected to high temperature annealing to form the double-layer graphene substrate, wherein the double-layer graphene substrate has a step structure.

3. The method according to claim 2, characterized in that The height-to-width ratio of the step structure of the double-layer graphene substrate is greater than 0.

24.

4. The method according to any one of claims 1 to 3, characterized in that: The two-dimensional material layer is a single layer of niobium diselenide, and the two-dimensional material is formed on a substrate, comprising: A single layer of niobium diselenide is formed on the double-layer graphene substrate by molecular beam epitaxy technology, and the single layer of niobium diselenide has local magnetism distributed along the direction of the step structure of the double-layer graphene substrate.

5. The method according to claim 2, characterized in that: The step of annealing silicon carbide at high temperature to form the double-layer graphene substrate comprises: The silicon carbide is subjected to high temperature annealing at a temperature of 1250 degrees Celsius for 60 minutes to form the double-layer graphene substrate.

6. The method according to claim 4, characterized in that The method of forming a single layer of niobium diselenide on the double-layer graphene substrate by molecular beam epitaxy technology comprises: The single-layer niobium diselenide is formed on the double-layer graphene substrate by molecular beam epitaxy technology using selenium atoms and niobium atoms with a beam ratio greater than 10:

1.

7. A magnetic structure, characterized in that: The invention comprises a substrate and a two-dimensional material layer, wherein the two-dimensional material layer is formed on the substrate, the substrate has a step structure, and the two-dimensional material layer has magnetism in a step structure region of the substrate.

8. The magnetic structure according to claim 7, characterized in that: The substrate is a double-layer graphene substrate, and the step structure is formed on the double-layer graphene substrate.

9. The magnetic structure according to claim 8, characterized in that: The height-to-width ratio of the step structure of the double-layer graphene substrate is greater than 0.

24.

10. The magnetic structure according to claim 8, characterized in that: The two-dimensional material layer is a single-layer niobium diselenide, and the single-layer niobium diselenide has local magnetism distributed along the direction of the step structure of the double-layer graphene substrate.

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