Preparation method of two-dimensional transition metal oxide film with controllable thickness

Abstract

The application discloses a preparation method of a two-dimensional transition metal oxide (TMOs) film with controllable thickness. The method comprises the following steps: mixing a transition metal oxide precursor for two-dimensional TMOs growth and an alkali metal salt, placing the mixed powder in a corundum boat under a substrate, and then heating the mixed powder to make the mixed powder react and melt; and controlling a cooling rate to obtain the two-dimensional TMOs film with controllable thickness on the substrate. The method is simple and convenient in operation, good in repeatability, and wide in applicability, can realize preparation of a large-area two-dimensional TMOs film, and has important significance for application and subsequent research of the two-dimensional TMOs. In addition, the prepared TMOs film is good in crystallinity and large in lateral size, thereby laying a foundation for subsequent device preparation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of integrated circuit manufacturing, and particularly relates to a preparation method of a two-dimensional transition metal oxide (TMO) film with controllable thickness. BACKGROUND

[0002] Semiconductor technology is the cornerstone of modern social development. In recent years, the development of semiconductor technology almost follows Moore's law, but as the number of transistors on a chip develops to a certain number, whether Moore's law can be continued faces great challenges. Since 2004, graphene has been discovered for the first time, opening the door for people to explore two-dimensional materials. Two-dimensional materials can be divided into two categories: layered two-dimensional materials and two-dimensional non-layered materials. Non-layered materials are formed by chemical bonding in three-dimensional directions and generate unsaturated dangling bonds on the surface, thereby inducing high activity and high energy surfaces, which enable them to have high-efficiency catalytic ability and energy storage performance. In addition, two-dimensional non-layered materials have the properties and characteristics of block structure and two-dimensional structure, thereby showing rich and unique physical phenomena.

[0003] Two-dimensional non-layered materials include metals, transition metal oxides (TMOs), organic-inorganic perovskites, etc. Among them, TMOs have attracted widespread attention due to their high chemical stability, low cost, high refractive index, and non-toxicity. Most TMOs have strong interlayer ionic bonds and no obvious delamination structure in their 3D interiors. However, due to the limitation of block structure, in practical applications, three-dimensional transition metal oxides (3D-TMOs) usually only have the outermost atoms and active sites on the block surface that can play a role, while other atoms and active sites are covered due to the blocking of peripheral atoms and chemical bonds, which is a great waste for the utilization and full play of the performance of the material. If the traditional 3D-TMOs are made into ultra-thin 2D structures, these problems can be solved to some extent, and the obtained 2D non-layered TMO materials exhibit diverse and adjustable optical, electrical, magnetic, and catalytic properties, which have very broad prospects in the future large-scale application of 2D materials.

[0004] The simplest method for preparing traditional two-dimensional materials is mechanical exfoliation, but this method is not suitable for non-layered materials because there is no obvious natural delamination in the crystal. The current methods for preparing non-layered two-dimensional materials include surface oxidation, self-assembly, template-assisted synthesis, and solvothermal method. However, there are some inevitable drawbacks in the above methods, such as low yield, sensitivity to experimental conditions, poor repeatability, etc. Although chemical vapor deposition (CVD) has been proved to be a method for controllable and high-yield preparation of two-dimensional materials, the size of the product obtained by using CVD to prepare two-dimensional transition metal oxides is usually small. For example, the size of MoO2 prepared by CVD is mostly less than 20 μm, which limits its research and large-scale application. Therefore, it is necessary to provide a new, convenient, and less polluting method for preparing large-area two-dimensional TMOs with controllable thickness. SUMMARY

[0005] In view of the shortcomings of the prior art, the purpose of the present application is to provide a method for preparing two-dimensional TMOs thin films with controllable thickness by using alkali metal molten salt, which solves the problems of complex preparation process, difficulty in preparing large-area TMOs thin films with controllable thickness, and limitation of research and large-scale application of two-dimensional TMOs in the prior art.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for preparing two-dimensional transition metal oxide thin films with controllable thickness, comprising the following steps:

[0008] 1) Clean the substrate and place it in the heating area of the tube furnace;

[0009] 2) Mix the transition metal oxide precursor powder and the alkali metal salt powder uniformly, and then place them in the corundum boat below the substrate, with the side of the substrate for deposition facing the mixed powder;

[0010] 3) Heat the tube furnace to a constant temperature under the condition of continuous inert gas flow, so that the transition metal oxide precursor and the alkali metal salt react to form a molten intermediate;

[0011] 4) Cool at a certain rate to make the two-dimensional transition metal oxide precipitate from the molten intermediate and deposit on the substrate to obtain the two-dimensional transition metal oxide thin film.

[0012] Further, the substrate in step 1) can be selected from any one of silicon dioxide / silicon, mica, sapphire, strontium carbonate, gallium nitride, titanium oxide, hafnium oxide, vanadium oxide, silicon nitride, silicon carbide, aluminum oxide, and metal sheets (such as gold, copper, nickel, platinum, etc.). That is, in the actual preparation process, according to the different two-dimensional TMOs to be prepared, a suitable substrate can be selected from the above materials for the growth of two-dimensional materials, which can be selected by lattice mismatch, surface flatness, and catalytic performance.

[0013] Further, when the substrate is silicon dioxide / silicon, strontium carbonate, gallium nitride, titanium oxide, hafnium oxide, vanadium oxide, silicon nitride, silicon carbide, or aluminum oxide, the cleaning method is to place the substrate in a cleaned glass container, first ultrasonic cleaning with acetone, then ultrasonic cleaning with ethanol, then ultrasonic cleaning with deionized water, and finally drying with nitrogen.

[0014] When the substrate is a metal sheet, the cleaning method is to cut and polish the metal sheet first, then rinse with deionized water, then dry with high-purity nitrogen, and then place it in a cleaned glass container for storage.

[0015] When the substrate is mica, the cleaning method is to cut the mica to expose a clean surface, and then place it in a cleaned glass container for storage.

[0016] When the substrate is sapphire, the cleaning method is to rinse with acetone or ethanol, then rinse with isopropyl alcohol, and then dry with high-purity nitrogen.

[0017] Further, the mass ratio of the transition metal oxide precursor powder and the alkali metal salt powder used in step 2) is 0.1-10.

[0018] Further, the transition metal oxide precursor used includes any one of M0O2, M0O3, WO2, V2O5, and MnO2. The corresponding two-dimensional transition metal oxide thin film formed is a M0O2 thin film, a M0O3 thin film, a WO2 thin film, a V2O5 thin film, or a MnO2 thin film.

[0019] Further, the alkali metal salt used includes any one of K2M0O4, Na2M0O4, K2M0O7, Na2M0O7, K2M0 10 3O 10 , NaCl, KI, NaI, KBr, and NaBr. That is, different alkali metal salts can be selected according to the different two-dimensional TMOs to be prepared, based on the different solubility of different two-dimensional TMOs in different alkali metal salts.

[0020] Further, the vertical distance between the substrate and the corundum boat below in step 2) is 1 cm.

[0021] Further, the flow rate of the inert gas in step 3) is 20-300 sccm.

[0022] Further, the constant temperature in step 3) is 550-1450℃, i.e. exceeding the melting point of the alkali metal salt used, such as potassium molybdate, sodium molybdate, etc. That is, in the actual preparation process, the corresponding temperature can be selected in the range of 550-1450℃ according to the different two-dimensional TMOs to be prepared and the different alkali metal salts.

[0023] Further, the cooling rate in step 4) is 2-60℃ / min. That is, different cooling rates can be selected in the range of 2-60℃ / min according to the thickness of the two-dimensional TMOs to be prepared, the faster the cooling rate, the thinner the thickness, and the slower the cooling rate, the thicker the thickness.

[0024] Further, the thickness of the obtained two-dimensional transition metal oxide film can be controlled between 0.1-300 nm.

[0025] Further, the size of the obtained two-dimensional transition metal oxide film is micron or wafer level. That is, in the actual preparation process, the size of the two-dimensional TMOs film prepared can vary between micron and wafer level according to different application scenarios.

[0026] The significant advantages of the present application are:

[0027] (1) The present application provides a method for preparing a two-dimensional TMOs film with controllable thickness. The reaction is based on CVD, using a mixture of alkali metal salt and transition metal oxide precursor powder. After heating, the two react to form an intermediate containing alkali metal elements. Continue to heat to exceed the melting point of the intermediate, and the intermediate is in a molten state. At this time, the two-dimensional TMOs film is precipitated from the intermediate by cooling at a constant rate. The present application is simple to operate, and the intermediate and residues generated by the reaction can be removed by deionized water cleaning method without introducing impurities that are difficult to remove.

[0028] (2) Compared with the two-dimensional TMOs film generated by directly heating the precursor, the crystal quality prepared by the molten salt method is better, and the thickness control of the two-dimensional TMOs film can be realized by controlling the cooling rate.

[0029] (3) The present application is convenient to operate, simple in process, small in pollution, and can provide a large-area two-dimensional TMOs film with controllable thickness. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Scanning electron microscope image of the MoO2 film prepared in Example 1.

[0031] Figure 2 Transmission electron microscope image of the MoO2 thin film prepared for Example 1.

[0032] Figure 3 Selected area electron diffraction image of the MoO2 thin film prepared for Example 1.

[0033] Figure 4 Optical microscope image of the MoO2 thin film prepared for Example 1.

[0034] Figure 5 Atomic force microscope image of the MoO2 thin film prepared for Example 1.

[0035] Figure 6 Optical microscope image of the MoO2 thin film prepared for Example 2. DETAILED DESCRIPTION

[0036] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor should fall within the protection scope of the present application.

[0037] Example 1

[0038] 1) Put the silicon dioxide / silicon substrate into a cleaned glass container, and then sequentially perform ultrasonic cleaning with acetone, ethanol and deionized water, and finally dry with nitrogen;

[0039] 2) Weigh 20 mg of MoO3 powder and 5 mg of K2Mo3O 10 powder, mix them and then place them in a corundum boat;

[0040] 3) Place the corundum boat in the heating area of the CVD tube, and fix the cleaned silicon dioxide / silicon substrate 1 cm above the corundum boat, so that the deposition side of the substrate faces the mixed powder in the corundum boat;

[0041] 4) Clean the heating area with nitrogen, and then continuously introduce 30 sccm of nitrogen;

[0042] 5) Start heating, and after reaching 850 ℃, keep the temperature for 30 minutes, so that the MoO3 powder and the K2Mo3O 10 powder react and are in a molten state;

[0043] 6) cooling at a rate of 5 °C / min to precipitate MoO2 from the melt to obtain MoO2 thin film on the silica / silicon substrate.

[0044] Figure 1 The figure is a scanning electron microscope image of the obtained MoO2 thin film. As can be seen from the figure, the obtained MoO2 thin film presents a two-dimensional rhombus morphology with a size of 130 μm.

[0045] Figure 2 The figure is a transmission electron microscope image of the obtained MoO2 thin film. As can be seen from the figure, there are lattice fringes in two directions, with lattice spacings of 0.28 and 0.24 nm, corresponding to the (102) and (020) crystal planes in the MoO2 monoclinic system (PDF #78-1069).

[0046] Figure 3 The figure is a selected area electron diffraction image of the obtained MoO2 thin film. The results show that the measured crystal planes are (102) and (020), which correspond to the transmission electron microscope results.

[0047] Figure 4 The figure is an optical microscope image of the obtained MoO2 thin film. As shown in the figure, when the cooling rate is 5 °C / min, the obtained MoO2 thin film presents a purple red color under the optical microscope, and its thickness is thin, and the substrate surface morphology can be clearly seen through the MoO2.

[0048] Figure 5 The figure is an atomic force microscope image of the obtained MoO2 thin film. As shown in the figure, the thickness of the obtained two-dimensional MoO2 thin film is 10.5 nm.

[0049] Example 2

[0050] 1) Put the silica / silicon substrate into a cleaned glass container, first ultrasonic cleaning with acetone, then ultrasonic cleaning with ethanol, then ultrasonic cleaning with deionized water, and finally dry with nitrogen;

[0051] 2) weigh 20 mg of MoO3 powder and 5 mg of K2Mo3O 10 powder, mix and place in a corundum boat;

[0052] 3) Place the corundum boat in the heating area of the CVD tube, and fix the cleaned silica / silicon above the corundum boat 1 cm away, so that the side of the substrate for deposition faces the mixed powder in the corundum boat;

[0053] 4) Purge the heating area with nitrogen, then continuously purify with 30 sccm of nitrogen;

[0054] 5) Start heating to 850°C and keep for 30 minutes to make MoO3 powder and K2Mo3O 10 react and be in a molten state;

[0055] 6) Cool down at a rate of 2°C / min to make MoO2 precipitate from the melt and thus obtain a MoO2 film on the silica / silicon substrate.

[0056] Figure 6 The optical microscope image of the obtained MoO2 film is shown in the figure. As shown, when the cooling rate is 2°C / min, the obtained MoO2 appears dark yellow and the film thickness is too thick to see the substrate surface morphology through the MoO2.

[0057] The above examples are only illustrative of the principles of the present application and its efficacy, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for preparing a two-dimensional transition metal oxide film with controllable thickness, characterized in that, The method comprises the following steps: 1) cleaning the substrate and placing it in the heating area of a tube furnace; 2) placing the transition metal oxide precursor powder and alkali metal salt powder mixed uniformly in a corundum boat under the substrate, and placing the substrate with the deposition side facing the mixed powder; 3) heating the tube furnace to a constant temperature under the condition of continuously passing inert gas, and making the mixed powder react and melt; 4) cooling at a certain rate to deposit the two-dimensional transition metal oxide film on the substrate; The mass ratio of the transition metal oxide precursor powder and the alkali metal salt powder used in step 2) is 0.1-10; wherein the transition metal oxide precursor used is MoO3, and the alkali metal salt used is K2Mo3O 10 ; The cooling rate in step 4) is 2-5 ℃ / min.

2. The method of claim 1, wherein the two-dimensional transition metal oxide film is prepared by a method comprising: The substrate in step 1) is selected from any one of silica / silicon, mica, sapphire, strontium carbonate, gallium nitride, titanium oxide, hafnium oxide, vanadium oxide, silicon nitride, silicon carbide, aluminum oxide, and metal sheet.

3. The method for preparing a two-dimensional transition metal oxide thin film according to claim 1, characterized by, The vertical distance between the substrate and the corundum boat below it in step 2) is 1 cm.

4. The method of claim 1, wherein the two-dimensional transition metal oxide film is prepared by a method comprising: The flow rate of the inert gas in step 3) is 20-300 sccm; the constant temperature is 550-1450 ℃.

5. The method of claim 1, wherein the two-dimensional transition metal oxide film is prepared by a method comprising: The thickness of the obtained two-dimensional transition metal oxide film is 0.1-300 nm.

6. The method of claim 1, wherein: The size of the obtained two-dimensional transition metal oxide film is micron or wafer level.

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