In-situ encapsulated two-dimensional material and preparation method thereof

Abstract

The present invention provides an in-situ encapsulated two-dimensional material and a preparation method thereof, the method comprising the following steps: (1) using a mechanical cleavage method to cleave a first two-dimensional material on a substrate to form a first two-dimensional material layer; and (2) using a chemical vapor deposition method to in-situ grow a second two-dimensional material between the first two-dimensional material layer and the substrate to form a second two-dimensional material layer. In the in-situ encapsulated two-dimensional material prepared by the present invention, the second material grows between the first material layer and the substrate. Since the first material layer covers the second material from the beginning of the growth of the second material, it constitutes an in-situ encapsulation layer of the second material. The first material layer can block oxygen and water in the air, thereby protecting the second material. Therefore, when the second material is an air-unstable material, the preparation method of the present invention is particularly useful.

Description

Technical Field

[0001] The invention relates to an in-situ packaged two-dimensional material and a preparation method thereof. Background Art

[0002] Two-dimensional materials refer to crystalline materials composed of a single atomic layer or several atomic layers. In 2004, the Geim research group at the University of Manchester in the UK used tape to mechanically cleave bulk graphite to produce single-atomic-layer graphene, pioneering the research field of two-dimensional materials. Since then, the categories of two-dimensional materials have gradually become richer. In addition to graphene, two-dimensional materials also include hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs). These two-dimensional materials contain rich low-dimensional physical properties and show great application potential in the fields of electronics, energy, and biomedicine.

[0003] At present, there are usually two technical solutions for the preparation of two-dimensional materials: cleavage (such as mechanical dissociation and liquid phase dissociation) and growth (such as molecular beam epitaxy and chemical vapor deposition). Cleavage is the separation of two-dimensional materials from existing bulk materials; growth is the synthesis of two-dimensional materials from precursor materials. Overall, the growth technology solution has significant advantages such as low cost, high yield and good crystal quality, and is the premise and basis for the practical application of two-dimensional materials. In the existing growth technology solution, two-dimensional materials often need to be taken out of the inert growth environment after growth is completed and subsequently processed and developed in the air. However, some two-dimensional materials are unstable in the air (such as TMD-niobium diselenide with superconductivity). This type of air-unstable two-dimensional material gradually deteriorates under the action of oxygen and water in the air, and its intrinsic properties and application value are lost. Therefore, it is very necessary to develop a growth technology solution specifically suitable for air-unstable two-dimensional materials. Summary of the invention

[0004] Therefore, the purpose of the present invention is to solve the problem of air instability of certain two-dimensional materials produced by existing growth methods, and to propose an in-situ encapsulated two-dimensional material and a preparation method thereof to avoid direct exposure of unstable two-dimensional materials to air.

[0005] The present invention provides a method for preparing an in-situ packaged two-dimensional material, the method comprising the following steps:

[0006] (1) using a mechanical cleavage method to cleave a first two-dimensional material (or referred to as "first material") on a substrate to form a first two-dimensional material layer (or referred to as "first material layer"); and

[0007] (2) A second two-dimensional material (or referred to as "second material") is in-situ grown between the first two-dimensional material layer and the substrate using chemical vapor deposition to form a second two-dimensional material layer (or referred to as "second material layer").

[0008] The first two-dimensional material may be any air-stable two-dimensional material, for example, graphene or hexagonal boron nitride.

[0009] In the in-situ encapsulated two-dimensional material prepared by the present invention, the second material grows between the first material layer and the substrate. Since the first material layer covers the second material from the beginning of the growth of the second material, it constitutes an in-situ encapsulation layer of the second material. The first material layer can block oxygen and water in the air, thereby protecting the second material. Therefore, when the second material is an air-unstable material, the preparation method of the present invention is particularly useful.

[0010] According to the preparation method provided by the present invention, there is no particular restriction on the selection of the substrate, as long as it is a material that is stable at high temperature (for example, stable at 1000° C.), for example, it can be a silicon substrate, a silicon dioxide substrate, a SiO2 / Si substrate, a sapphire substrate, etc. Preferably, in order to reduce costs, a silicon wafer can be selected as the substrate. The surface of the silicon wafer can be optionally covered with a silicon dioxide layer, for example, a commercial SiO2 / Si substrate can be selected as the substrate.

[0011] According to the preparation method provided by the present invention, the mechanical cleavage method described in step (1) is a method commonly used in the art for preparing two-dimensional nanomaterials. The thickness of the first material layer obtained in step (1) can be 0.3 to 100 nanometers. Furthermore, step (1) can also include pre-cleaning the silicon wafer substrate using oxygen plasma to increase the yield of the mechanical cleavage method.

[0012] According to the preparation method provided by the present invention, the second material can be generated by a gas phase reaction between a first precursor material and a second precursor material. In this case, the step (2) comprises: placing the substrate with the first material layer cleaved in step (1) at a position 0.1 to 2 mm above the first precursor material with the first material layer facing downward, and placing it in the downstream temperature zone of the tube furnace; placing the second precursor material in the upstream temperature zone of the tube furnace.

[0013] The first precursor material may be one or more of a simple substance, an oxide and a chloride of a transition metal element, for example, a simple substance of niobium, niobium pentoxide or niobium pentachloride.

[0014] The second precursor material may be one or more simple substances of Group VI elements, for example, simple substance selenium.

[0015] Preferably, the temperature of the downstream temperature zone of the tube furnace is 700-900° C., the temperature of the upstream temperature zone is 100-300° C., and the growth time can be 0.5-5 minutes.

[0016] Preferably, the carrier gas in the chemical vapor deposition process is argon or a mixture of argon and argon. When a mixture of argon and argon is used, the flow ratio of hydrogen to argon can be 1:(5-20) (V:V).

[0017] In a specific embodiment of the present invention, the first two-dimensional material is graphene, the substrate is a silicon wafer with 280-300nm SiO2 covered on the surface, the second two-dimensional material is niobium diselenide, and the preparation method comprises:

[0018] (1) Using mechanical cleavage to cleave graphene onto a silicon wafer;

[0019] (2) placing a mixed powder of niobium pentoxide, niobium element and sodium chloride in a first quartz boat (or ceramic boat), placing a silicon wafer with cleaved graphene upside down on the first quartz boat, and placing the first quartz boat in the downstream temperature zone of the tubular furnace; placing a second quartz boat filled with selenium powder and / or selenium block in the upstream temperature zone of the tubular furnace; introducing a mixed gas of hydrogen and argon into the quartz tube of the tubular furnace, controlling the temperature of the downstream temperature zone to 780-860°C and the temperature of the upstream temperature zone to 220-260°C, and keeping the temperature constant for 0.5-5 minutes.

[0020] Furthermore, in step (2), the mass ratio of niobium pentoxide, niobium element and sodium chloride is (1-4):(1-4):1. Most preferably, the mass ratio of niobium pentoxide, niobium element and sodium chloride is 2:2:1. Preferably, the preparation method further comprises placing niobium pentoxide powder, niobium element powder and sodium chloride particles in an agate mortar and grinding them with an agate pestle for 5-120 minutes.

[0021] Furthermore, the undercut in step (2) makes the distance between the silicon wafer with cleaved graphene and the mixed powder be 0.5 to 2 mm.

[0022] On the other hand, the present invention also provides an in-situ encapsulated two-dimensional material prepared by the above method, which includes a first two-dimensional material layer cleaved on a substrate and a second two-dimensional material layer in-situ grown between the first two-dimensional material layer and the substrate.

[0023] The in-situ packaged two-dimensional material of the present invention can be applied to basic research on two-dimensional superconductivity and the construction of two-dimensional superconducting electronic devices.

[0024] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0025] In the in-situ encapsulated two-dimensional material prepared by the present invention, the second material grows between the first material layer and the substrate. Since the first material layer covers the second material from the beginning of the growth of the second material, it constitutes an in-situ encapsulation layer of the second material. The first material layer can block oxygen and water in the air, thereby protecting the second material. Therefore, when the second material is an air-unstable material, the preparation method of the present invention is particularly useful. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, wherein:

[0027] Figure 1 This is an optical microscope photograph of the in-situ encapsulated two-dimensional material prepared in Example 1 of the present invention;

[0028] Figure 2 The cross-sectional chemical element distribution photos of the in-situ encapsulated two-dimensional material prepared in Example 1 of the present invention (the left photo is a cross-sectional niobium element distribution photo, and the right photo is a cross-sectional carbon element distribution photo);

[0029] Figure 3 This is the Raman spectrum of the in-situ encapsulated two-dimensional material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0031] Example 1

[0032] Preparation of the in-situ encapsulated two-dimensional material of the present invention

[0033] (1) selecting a silicon wafer substrate with a surface covered with 285 nanometers of silicon dioxide, pre-cleaning the silicon wafer substrate using oxygen plasma, and cleaving graphene on the silicon wafer substrate using a mechanical cleavage method;

[0034] (2) Using chemical vapor deposition to grow niobium diselenide between graphene and silicon wafer substrate:

[0035] (2-1) Using a balance, 2 g of niobium pentoxide powder, 2 g of niobium elemental powder, and 1 g of sodium chloride particles were weighed into an agate mortar and ground using an agate pestle for 30 minutes;

[0036] (2-2) Take two clean quartz boats, use a balance to weigh 2 mg of the ground mixed powder into the first quartz boat, and use a balance to weigh excess selenium powder (200 mg) into the second quartz boat;

[0037] (2-3) placing the silicon wafer substrate with cleaved graphene upside down on the mixed powder in the first quartz boat, with the distance between the silicon wafer substrate and the mixed powder being 1 mm;

[0038] (2-4) placing the first quartz boat in the center of the downstream temperature zone of the tube furnace, placing the second quartz boat in the center of the upstream temperature zone of the tube furnace, and then replacing the air in the quartz tube of the tube furnace with argon gas;

[0039] (2-5) introducing hydrogen gas at a flow rate of 15 standard ml / min and argon gas at a flow rate of 135 standard ml / min into the quartz tube of the tubular furnace;

[0040] (2-6) Heating to make the temperature in the center of the downstream temperature zone 835°C and the temperature in the center of the upstream temperature zone 240°C; constant temperature growth, making the downstream temperature zone and the upstream temperature zone maintain a constant temperature for 0.5 minutes; when the downstream temperature zone of the tubular furnace drops to room temperature, taking out the silicon wafer substrate with cleaved graphene, to obtain the in-situ encapsulated two-dimensional material of the present invention.

[0041] Performance Characterization

[0042] (1) The prepared in-situ encapsulated two-dimensional material was observed using an optical microscope. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the morphology of niobium diselenide is triangular, with a size of 2 to 3 microns and uniform contrast.

[0043] (2) Using scanning transmission electron microscopy and electron energy loss spectrometry, the cross-sectional chemical element analysis of the prepared in-situ encapsulated two-dimensional material was performed. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the niobium element is distributed below the carbon element in the cross section, so the niobium diselenide grows between the graphene and the silicon wafer substrate. In addition, the distribution width of the niobium element in the cross section is only about 1 nanometer, so the niobium diselenide is an ultra-thin layer of two-dimensional material.

[0044] (3) Raman spectrometer was used to perform Raman spectroscopy test on the prepared in-situ encapsulated two-dimensional material in air. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the ultra-thin layer of niobium diselenide exhibits two characteristic Raman peaks of the material, so it has the expected crystal structure and good crystallinity. In addition, the characteristic Raman peaks of ultra-thin layer of niobium diselenide can be obtained using conventional test parameters in air, indicating that graphene as an in-situ encapsulation layer blocks oxygen and water in the air, and plays a protective role for ultra-thin layer of niobium diselenide during the Raman spectrum test.

[0045] Figure 1-3The reference numerals in the figures indicate: 1-silicon wafer substrate, 2-graphene, 3-niobium diselenide, 4-one of the characteristic Raman peaks of niobium diselenide, 5-the second characteristic Raman peak of niobium diselenide.

[0046] This embodiment is only a preferred embodiment of the present invention and is only used to explain the present invention, not to limit the present invention. Modifications, substitutions, changes, etc. made by those skilled in the art without departing from the spirit of the present invention should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ encapsulated two-dimensional material, the method comprising the following steps: (1) Using mechanical cleavage to cleave graphene onto a silicon dioxide substrate; (2) placing a mixed powder of niobium pentoxide, niobium element and sodium chloride in a first quartz boat, placing a silicon dioxide substrate with cleaved graphene upside down on the first quartz boat, and placing the first quartz boat in the downstream temperature zone of a tube furnace; placing a second quartz boat filled with selenium powder and / or selenium blocks in the upstream temperature zone of the tube furnace; introducing a mixture of hydrogen and argon into the quartz tube of the tube furnace, controlling the temperature of the downstream temperature zone to 780-860°C and the temperature of the upstream temperature zone to 220-260°C, maintaining the temperature constant for 0.5-5 minutes, and in-situ growing niobium diselenide between the graphene and the silicon dioxide substrate by chemical vapor deposition to obtain an in-situ encapsulated niobium diselenide two-dimensional material. The silicon dioxide substrate is a silicon wafer with a surface covered with 280-300 nanometers of silicon dioxide, and the thickness of the graphene obtained in step (1) is 0.3-100 nanometers. Wherein, the step (2) comprises: placing the silicon dioxide substrate with cleaved graphene obtained in step (1) at a distance of 0.1-2 mm above the mixed powder with the graphene facing downward, and the flow ratio of hydrogen gas to argon gas is 1:(5-20).

2. An in-situ encapsulated two-dimensional material prepared by the preparation method according to claim 1, comprising graphene cleaved on a silicon dioxide substrate and a niobium diselenide two-dimensional material in-situ grown between the graphene and the silicon dioxide substrate.

Images