A class of two-dimensional transition metal selenides and their preparation methods

Abstract

This invention relates to the field of two-dimensional selenide technology, specifically to a class of two-dimensional transition metal selenides and their preparation method. The method first mixes transition metal oxophosphate powder and selenium-containing salt powder in a certain molar ratio and places them in a tube furnace. Then, the mixed salt reacts at high temperature to generate two-dimensional transition metal selenides. The two-dimensional transition metal selenides are then heated and deposited on a growth substrate to obtain single-layer / multi-layer two-dimensional transition metal selenides. The method for preparing single-layer / multi-layer two-dimensional transition metal selenides of this invention has the characteristics of low energy consumption, simple operation, economy and strong universality.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional selenide technology, specifically to a class of two-dimensional transition metal selenides and their preparation methods. Background Technology

[0002] In recent years, two-dimensional transition metal selenides (2D TMSe) have shown great potential in catalysis, gas sensing, energy storage and conversion, and electronic / optoelectronic device applications. Chemical vapor deposition (CVD) is one of the most promising techniques suitable for large-scale synthesis of 2D TMSe. Currently, various CVD methods have been developed for growing 2D TMSe, such as conventional CVD (using selenium (Se) powder to selenize transition metal oxides at high temperatures), halide-assisted CVD, and molten salt-assisted CVD. However, these methods have many drawbacks: conventional CVD involves complex synthesis procedures and yields poor sample quality; in halide-assisted CVD, uneven evaporation of the transition metal precursor can lead to difficulty in controlling sample thickness and generate many byproducts; the main problem with molten salt-assisted CVD is the difficulty in controlling sample thickness and size due to uneven selenium evaporation. All these defects are detrimental to the synthesis of high-quality 2D TMSe. Therefore, developing a novel CVD technology that is easy to operate, time-saving, labor-saving, economical, and widely applicable for the synthesis of 2D TMSe is very important for promoting its research and application. Summary of the Invention

[0003] The purpose of this invention is to solve the problem of how to develop a novel CVD technology that is easy to operate, time-saving, labor-saving, economical, and widely applicable for the preparation of 2D TMSe, and to provide a class of two-dimensional transition metal selenides and their preparation methods.

[0004] To achieve the above objectives, this invention discloses a method for preparing a class of two-dimensional transition metal selenides, comprising the following steps:

[0005] S1, after mixing the transition metal oxoate and the selenium-containing salt, put them into an open container, place the growth substrate on top of the container, and then place the container in a tube furnace;

[0006] S2, a mixture of hydrogen and inert gas is introduced into a tube furnace, and the mixed salt powder obtained in step S1 is heated. When the growth temperature is reached, the reaction is maintained at this temperature to grow 2D TMSe.

[0007] In step S1, the transition metal oxophosphate is K2MoO4, the selenium-containing salt is Na2Se, and the growth temperature in step S2 is 760℃.

[0008] In step S1, the transition metal oxophosphate is Na2WO4·2H2O, and the selenium-containing salt is Na2Se. In step S2, the growth temperature is 800℃.

[0009] In step S1, the transition metal oxoate is NaReO4, the selenium-containing salt is Na2Se, and the growth temperature in step S2 is 700℃.

[0010] In step S1, the molar ratio of transition metal oxophosphates and selenium-containing salts is 1:9.

[0011] In step S1, the open container is a quartz boat or a ceramic boat.

[0012] In step S1, the growth substrate is aluminum oxide or a silicon wafer with a silicon oxide layer on its surface.

[0013] In step S2, the inert gas is nitrogen or argon.

[0014] The heating rate in step S2 is 20°C / minute.

[0015] The present invention also discloses a class of two-dimensional transition metal selenides prepared by the above preparation method.

[0016] Compared with existing technologies, the advantages of this invention are as follows: the method for preparing single-layer / multi-layer 2D TMSe has the characteristics of highly controllable layer number, low energy consumption, simple operation, economy, and strong universality. By replacing the selenium powder used in traditional CVD methods with selenium-containing salts, the problem of difficult-to-control selenium evaporation can be effectively solved. By mixing transition metal oxometalate powder and selenium-containing salt powder in a molar ratio and grinding them evenly, the distribution of selenium precursor in the raw materials is more uniform, thereby obtaining high-quality, uniform 2D TMSe in subsequent growth. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the tubular furnace structure used in this invention;

[0018] Figure 2 This is a characterization of the monolayer MoSe2 in Embodiment 1 of the present invention. Figure 2 a is an optical microscope image of a monolayer MoSe2 sample from the example. Figure 2 b is the Raman spectrum of the monolayer MoSe2 sample in the example. Figure 2 c is the photoluminescence spectrum of monolayer MoSe2 in the example sample;

[0019] Figure 3This is a characterization of the monolayer WSe2 in Embodiment 3 of the present invention. Figure 3 a is an optical microscope image of a single layer of WSe2 in the example sample. Figure 3 b is the Raman spectrum of monolayer WSe2 in the example sample. Figure 3 c is the photoluminescence spectrum of monolayer WSe2 in the example sample;

[0020] Figure 4 This is a characterization of the few-layer ReSe2 in Embodiment 5 of the present invention. Figure 4 a is an optical microscope image of the few-layer ReSe2 sample from the example. Figure 4 b is the Raman spectrum of the few-layer ReSe2 sample in the example. Figure 4 c is the photoluminescence spectrum of the few-layer ReSe2 sample in the example;

[0021] Figure 5 Characterization of the selenides obtained at different temperatures in Examples 1-6 of this invention. Figure 5 a and Figure 5 b are optical microscope images of MoSe2 grown at 760℃ and 860℃, respectively. Figure 5 c and Figure 5 Image d shows optical microscope images of WSe2 grown at 760℃ and 800℃, respectively. Figure 5 e and Figure 5 f are optical microscope images of ReSe2 grown at 700℃ and 800℃, respectively.

[0022] The numbers in the image represent:

[0023] 1-Heater; 2-Open container; 3-Growth substrate; 4-Growth furnace cavity. Detailed Implementation

[0024] The above and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0025] The present invention provides a method for preparing monolayer / multilayer 2D TMSe using mixed salt precursors, which mainly includes two steps: the first step is to mix transition metal oxophosphate powder and selenium-containing salt powder in a certain molar ratio, and the second step is to synthesize monolayer / few-layer 2D TMSe using CVD technology.

[0026] Transition metal oxoate powder and selenium-containing salt powder are mixed in a certain molar ratio. Specifically, a certain amount of selenium-containing salt powder is weighed, and the mass of transition metal oxoate powder to be weighed is calculated according to the molar ratio. After weighing, the powder is poured into a mortar and mixed with the selenium-containing salt powder. The mixture is then ground with a pestle to ensure that the two are fully and evenly mixed.

[0027] The synthesis steps of 2D TMSe include the following:

[0028] S11: After mixing the transition metal oxoate powder and the selenium-containing salt powder in a certain molar ratio, put them into an open container, place the growth substrate on top of the container, and then place the container in a tube furnace.

[0029] S12: A mixture of hydrogen and inert gas (nitrogen, argon, etc.) is passed through a tube furnace at a certain flow rate and the mixture is heated; when the growth temperature is reached, the temperature is maintained for a certain time to grow 2DTMSe on the growth substrate.

[0030] Figure 1 This is a schematic diagram of the tube furnace structure used in the above steps. In the diagram, 1 is the heater, 2 is the open container, 3 is the growth substrate placed above the open container, and 4 is the furnace cavity of the growth furnace.

[0031] In the above-described 2D TMSe synthesis steps, the transition metal oxoate powder can be a sodium salt containing the target transition metal element, a potassium salt containing the target transition metal element, or other salts containing the target transition metal element; the selenium-containing salt can be a selenium-containing sodium salt, a selenium-containing potassium salt, or other salts containing sulfur. By selecting suitable transition metal oxoates and selenium-containing salts, this invention can prepare most types of 2D TMSe.

[0032] Example 1

[0033] A 2 mg Na₂Se / K₂MoO₄ mixed salt with a molar ratio of 9:1 was placed in a quartz boat, and the SiO₂ / Si growth substrate was placed directly above the mixture. The quartz boat was placed in a tube furnace, and the mixture was heated to 760 °C at a heating rate of 20 °C / min and held at that temperature for 10 minutes. After the reaction was completed, the system was allowed to cool naturally to room temperature, and the gas supply was turned off to complete the growth of MoSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 cubic centimeters per minute (SCCM), of which the nitrogen flow rate was 300 SCCM and the hydrogen flow rate was 2 SCCM.

[0034] Example 2

[0035] 2 mg of a Na₂Se / K₂MoO₄ mixed salt with a molar ratio of 9:1 was placed in a quartz boat, and the growth substrate SiO₂ / Si was placed directly above the mixture. The quartz boat was placed in a tube furnace, and the mixture was heated to 860°C at a heating rate of 20°C / min and held at that temperature for 10 minutes. After the reaction was completed, the system was allowed to cool naturally to room temperature, and the gas supply was turned off to complete the growth of MoSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 SCCM, with nitrogen at a flow rate of 300 SCCM and hydrogen at a flow rate of 2 SCCM.

[0036] Example 3

[0037] 4 mg of a Na₂Se / Na₂WO₄·2H₂O mixed salt with a molar ratio of 9:1 was placed in a quartz boat, and the growth substrate SiO₂ / Si was placed directly above the mixture. The quartz boat was placed in a tube furnace, and the mixture was heated to 760°C at a heating rate of 20°C / min and held at that temperature for 10 minutes. After the reaction was completed, the system was allowed to cool naturally to room temperature and the gas supply was turned off to complete the growth of WSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 SCCM, with nitrogen at a flow rate of 300 SCCM and hydrogen at a flow rate of 2 SCCM.

[0038] Example 4

[0039] 3 mg of a Na₂Se / Na₂WO₄·2H₂O mixed salt with a molar ratio of 9:1 was placed in a quartz boat, and the growth substrate SiO₂ / Si was placed directly above the mixture. The quartz boat was placed in a tube furnace, and the mixture was heated to 800°C at a heating rate of 20°C / min and held at that temperature for 10 minutes. After the reaction was completed, the system was allowed to cool naturally to room temperature and the gas supply was turned off to complete the growth of WSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 SCCM, with nitrogen at a flow rate of 300 SCCM and hydrogen at a flow rate of 2 SCCM.

[0040] Example 5

[0041] A quartz boat was filled with 4 mg of a Na₂Se / NaReO₄ mixed salt at a molar ratio of 9:1, and a SiO₂ / Si growth substrate was placed directly above the mixture. The quartz boat was then placed in a tube furnace, and the mixture was heated to 700°C at a heating rate of 20°C / min and held at that temperature for 10 minutes. After the reaction was complete, the system was allowed to cool naturally to room temperature, and the gas supply was shut off to complete the growth of ReSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 SCCM, with nitrogen at 300 SCCM and hydrogen at 2 SCCM.

[0042] Example 6

[0043] A quartz boat was filled with 4 mg of a Na₂Se / NaReO₄ mixed salt at a molar ratio of 9:1, and the SiO₂ / Si growth substrate was placed directly above the mixture. The quartz boat was placed in a tube furnace, and the mixture was heated to 800°C at a heating rate of 20°C / min and held at that temperature for 10 minutes. After the reaction was complete, the system was allowed to cool naturally to room temperature, and the gas supply was shut off to complete the growth of ReSe₂. Throughout the heating, holding, and cooling processes, the flow rate of the nitrogen / hydrogen mixed gas was maintained at 302 SCCM, with nitrogen at 300 SCCM and hydrogen at 2 SCCM.

[0044] Figure 2 This is a characterization of the monolayer MoSe2 sample from Example 1 of the present invention. Figure 2 Image a is an optical microscope image of a monolayer MoSe2 sample from the example, showing a typical triangular morphology of the grown sample. Figure 2 b and 2c are the Raman spectrum and photoluminescence spectrum of monolayer MoSe2, respectively.

[0045] Figure 3 This is a characterization of the monolayer WSe2 sample from Example 3 of the present invention. Among them, Figure 3 Image a is an optical microscope image of a monolayer WSe2 sample from the example, showing a typical triangular morphology of the grown sample. Figure 3 b and 3c are the Raman spectrum and photoluminescence spectrum of monolayer WSe2, respectively.

[0046] Figure 4 This is a characterization of the ReSe2 sample from Example 5 of the present invention. Figure 4 Image a is an optical microscope image of the ReSe2 sample from the example, showing a typical morphology of the grown sample. Figure 4 b and 4c are the Raman spectrum and photoluminescence spectrum of ReSe2, respectively.

[0047] Figure 5 These are optical microscope images of selenides obtained at different temperatures in Examples 1-6 of the present invention. Figure 5 a and Figure 5 b are optical microscope images of MoSe2 grown at 760℃ and 860℃, respectively. Figure 5 c and Figure 5 Image d shows optical microscope images of WSe2 grown at 760℃ and 800℃, respectively. Figure 5 e and Figure 5 Images f are optical microscope images of ReSe2 grown at 700℃ and 800℃, respectively. As can be seen from the figures, sample quality is closely related to growth temperature, indicating that this technique allows for the control of sample quality by adjusting the growth temperature.

[0048] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing a class of two-dimensional transition metal selenides, characterized in that, Includes the following steps: S1, after mixing the transition metal oxoate and the selenium-containing salt, put them into an open container, place the growth substrate on top of the container, and then place the container in a tube furnace; S2, a mixture of hydrogen and inert gas is introduced into a tube furnace, and the mixed salt powder obtained in step S1 is heated. When the growth temperature is reached, the temperature is maintained to grow a two-dimensional transition metal selenide. In step S1, the transition metal oxoate is K2MoO4, the selenium-containing salt is Na2Se, and the growth temperature in step S2 is 760 ℃. Alternatively, in step S1, the transition metal oxoate is Na2WO4·2H2O, the selenium-containing salt is Na2Se, and the growth temperature in step S2 is 800 ℃; Alternatively, the transition metal oxoate in step S1 may be NaReO4, the selenium-containing salt may be Na2Se, and the growth temperature in step S2 may be 700 ℃.

2. The method for preparing a type of two-dimensional transition metal selenide as described in claim 1, characterized in that, In step S1, the molar ratio of transition metal oxophosphates and selenium-containing salts is 1:

9.

3. The method for preparing a type of two-dimensional transition metal selenide as described in claim 1, characterized in that, In step S1, the open container is a quartz boat or a ceramic boat.

4. The method for preparing a type of two-dimensional transition metal selenide as described in claim 1, characterized in that, In step S1, the growth substrate is aluminum oxide or a silicon wafer with a silicon oxide layer on its surface.

5. The method for preparing a type of two-dimensional transition metal selenide as described in claim 1, characterized in that, In step S2, the inert gas is argon.

6. The method for preparing a type of two-dimensional transition metal selenide as described in claim 1, characterized in that, The heating rate in step S2 is 20 °C / min.

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