Methods for preparing two-dimensional TMDs alloys from non-metallic chalcogenides

Abstract

This invention provides a method for preparing two-dimensional TMDs alloys using non-metallic chalcogenides. It is a modified CVD method in which a non-metallic chalcogenide containing two chalcogen elements replaces the elemental chalcogenides as the non-metallic growth source. The ratio of the two chalcogen elements in the TMDs alloy can be changed by adjusting the weight ratio of the non-metallic growth source to the metallic growth source. Adding 40 mg of WO3 and 55, 38, 26, and 15 mg of SeS2 respectively yielded WS... 0.96 Se 0.04 WS 0.65 Se 0.35 WS 0.5 Se 0.5 WS 0.27 Se 0.73 Four types of TMD alloy single crystals can be fabricated. Large-size single crystals and large-area thin films of two-dimensional TMD alloys with tunable chemical composition and uniform layer number can be prepared. This provides more options for optoelectronic devices with specific spectral responses, field-effect transistors, and flexible electronic devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of two-dimensional material preparation, and particularly relates to a method for preparing a transition metal dichalcogenide (TMDs) alloy with adjustable chemical composition by using a nonmetallic chalcogen compound containing two chalcogen elements as a growth source. BACKGROUND

[0002] Transition metal dichalcogenides (TMDs) are a kind of layered sandwich structure materials, and the band gap structure is related to the layer number. Single-layer two-dimensional TMDs are widely used in optoelectronic devices because of the direct band gap structure and the band gap in the visible light range. However, the band gap of common single-layer two-dimensional TMDs is very single, which has great limitations in wide-range light emission regulation. Researchers have found that alloys can be formed by replacing chalcogen atoms or transition metal atoms in two-dimensional TMDs. This replacement of atoms can not only maintain the original lattice structure, but also realize the regulation of band gap and carrier transport type by regulating the proportion of different element atoms, so as to realize the regulation of optoelectronic properties. Therefore, the chemical composition regulation of two-dimensional TMDs alloy can greatly improve the flexibility of optoelectronic device design.

[0003] At present, many two-dimensional TMDs alloys have been successfully prepared, but the two-dimensional TMDs alloys prepared based on traditional chalcogen elements as nonmetallic sources are not continuous and comprehensive in chemical composition regulation, and the size is not large enough and the layer number is not uniform enough. Therefore, we use a chalcogen compound containing two chalcogen elements as a nonmetallic source for growth. The lower energy barrier and fixed stoichiometric ratio make us more flexible in the chemical composition regulation of two-dimensional TMDs alloy. By regulating the content of nonmetallic chalcogen compound, the proportion of different elements in two-dimensional TMDs alloy can be adjusted, thereby realizing the preparation of two-dimensional TMDs alloy single crystals and thin films with continuous adjustable chemical composition and uniform layer number. In addition, by changing the type and growth temperature of the nonmetallic chalcogen compound, two-dimensional TMDs alloy single crystals and thin films of different types and thicknesses can be prepared.

[0004] The preparation of two-dimensional TMDs alloy with continuous adjustable chemical composition and uniform layer number is the premise of realizing the regulation of its light emission band gap and wide application. The proposal of the present application has certain reference significance for the preparation, composition regulation, physical property research and application of two-dimensional TMDs alloy. SUMMARY

[0005] The application adopts a non-metallic chalcogenide containing two chalcogen elements as a growth source to prepare a large-size single crystal and a large-area film of two-dimensional TMDs alloy with adjustable chemical composition and uniform layer number, aims to solve the problems of uncontrollable chemical composition, small size and non-uniform layer number of two-dimensional TMDs alloy in current research, and lays a foundation for realizing the regulation of wide-range light-emitting devices and the application thereof.

[0006] The method for preparing a two-dimensional TMDs alloy single crystal and a film with adjustable chemical composition and uniform layer number by using a non-metallic chalcogenide containing two chalcogen elements as a growth source comprises the following specific steps:

[0007] The method for preparing a two-dimensional TMDs alloy by using a non-metallic chalcogenide as a growth source adopts a CVD method, and the non-metallic growth source is a non-metallic chalcogenide containing two chalcogen elements;

[0008] The ratio of the relative content (stoichiometric ratio) of the two chalcogen elements in the TMDs alloy is changed by adjusting the weight ratio of the addition amount of the non-metallic growth source to the addition amount of the metal growth source;

[0009] The non-metallic chalcogenide includes SeS2, SeTe and / or TeS2;

[0010] The growth temperature is 700-1000 DEG C, and hydrogen and inert gas are introduced during the growth process;

[0011] The non-metallic chalcogenide is SeS2, SeTe and / or TeS2, the metal reaction source is WO3 or MoO3, and the substrate is gold or a non-metallic substrate (silicon wafer, sapphire, mica, quartz, etc.);

[0012] The use temperature of the non-metallic chalcogenide, including SeS2, SeTe and / or TeS2, is 100-300 DEG C;

[0013] The use amount of the metal growth source ranges from 1 to 200 mg, and the use amount of the non-metallic growth source ranges from 1 to 100 mg;

[0014] In the prepared two-dimensional TMDs alloy, the stoichiometric ratio of the two chalcogen elements ranges from 0 to 1;

[0015] The prepared two-dimensional TMDs alloy has uniform layer number, and the layer number is 1-10 layers.

[0016] The application provides a method for preparing two-dimensional TMDs alloy by using non-metallic chalcogen compounds, which is a modified CVD method, and the non-metallic chalcogen compound containing two chalcogen elements is used as a non-metallic growth source instead of the elemental chalcogen element; the ratio of the relative content (stoichiometric ratio) of the two chalcogen elements in the TMDs alloy can be changed by adjusting the weight ratio of the non-metallic growth source and the metal growth source; WO3 is added by 40 mg, and SeS2 is added by 55 mg, 38 mg, 26 mg and 15 mg respectively, and four kinds of WS 0.96 Se 0.04 , WS 0.65 Se 0.35 , WS 0.5 Se 0.5 , WS 0.27 Se 0.73 TMDs alloy monocrystals are obtained. The application can prepare two-dimensional TMDs alloy monocrystals with adjustable chemical composition and uniform layers, and large-size monocrystals and large-area films.

[0017] The application has the following advantages and beneficial effects:

[0018] 1) The non-metallic growth source of the application contains two chalcogen elements, and compared with the common elemental chalcogen growth source, the relatively low energy diffusion barrier and the fixed stoichiometric ratio make the growth rate of the two-dimensional TMDs alloy faster, and the chemical composition of the TMDs alloy can be more easily adjusted.

[0019] 2) The two-dimensional TMDs alloy monocrystals and films prepared by using the non-metallic growth source containing two chalcogen elements have the characteristics of large size, high quality and uniform layers, which provides more choices for the two-dimensional TMDs alloy with high quality and uniform layers in the aspects of photoelectron devices with specific spectral response, field effect transistors and flexible electronic devices, and also provides a reference for the preparation of other kinds of two-dimensional materials and alloys.

[0020] 3) The non-metallic growth source of the application is the chalcogen compound containing two chalcogen elements, which can perform chemical reaction under normal pressure chemical vapor deposition, so that the sample preparation has the advantages of convenient operation, easy composition adjustment and easy large-area preparation. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The experimental device for preparing the TMDs alloy monocrystals and films with adjustable chemical composition and uniform layers by using the non-metallic growth source containing two chalcogen elements (SeS2) and the metal growth source of metal oxide comprises: 1, a gas inlet; 2, a non-metallic growth source; 3, a metal growth source; 4, a growth substrate; 5, a gas outlet; and 6, a heating furnace.

[0022] Figure 2 Uniform monolayer WS2 grown on gold foil surface 2x Se 2(1-x) Optical image of alloy single crystal with about 0.92 atomic percent S;

[0023] Figure 3 Monolayer WS2 2x Se 2(1-x) Atomic force microscope image of alloy single crystal;

[0024] Figure 4 Four different chemical compositions of uniform monolayer WS2 2x Se 2(1-x) Photoluminescence (PL) spectrum of alloy single crystal;

[0025] Figure 5 Large area continuous WS2 completely covering gold foil 2x Se 2(1-x) Photograph of alloy thin film and uniform monolayer WS2 on gold foil surface 2x Se 2(1-x) Optical image of alloy thin film;

[0026] Figure 6 Double layer WS2 2x Se 2(1-x) Atomic force microscope image of alloy single crystal;

[0027] Figure 7 Four layer WS2 2x Se 2(1-x) Atomic force microscope image of alloy single crystal;

[0028] Figure 8 Uniform monolayer WS2 grown on sapphire substrate surface 2x Se 2(1-x) Optical image of alloy single crystal;

[0029] Figure 9 Uniform monolayer MoS2 grown on gold foil surface 2x Se 2(1-x) Optical image of alloy single crystal and its photoluminescence (PL) spectrum with about 0.89 atomic percent S. DETAILED DESCRIPTION

[0030] Example 1 Method of preparing two-dimensional TMDs alloy from non-metallic chalcogenides

[0031] As Figure 1As shown, a non-metallic sulfide compound (SeS2) containing two chalcogen elements is used as a non-metallic growth source, WO3 is used as a metal growth source, and a large-size single-layer WS 2x Se 2(1-x) alloy monocrystal is prepared on a metal substrate. Here, the chemical composition of the alloy is variable and adjustable, and the chemical formula is WS 2x Se 2(1-x) x is the atomic percentage of the non-metallic element S in the total two non-metallic elements, so the adjustable alloy composition specifically refers to the change of the value of x.

[0032] A horizontal reaction furnace is provided with a gas inlet 1 and a gas outlet 5 at both ends, respectively, and the non-metallic growth source and the metal growth source are located at 2 and 3, respectively. A gold foil is placed in the high-temperature zone of the horizontal reaction furnace, and the heating zone position is as shown at 6. 40 mg of tungsten trioxide powder (WO3, purity 99.999 %) is placed in the central high-temperature zone of the horizontal reaction furnace (furnace tube diameter 25 mm, reaction zone length 5 cm), and a gold foil (10 mm x 10 mm x 100 microns, purity 99.99 wt%) is placed horizontally 2 cm behind the tungsten trioxide powder. 47 mg of selenium disulfide powder (SeS2, purity 97 %) is placed at a position of about 150 ℃ in the horizontal reaction furnace, and the hollow air in the furnace tube is first purged with argon for 5 minutes, and then the reaction furnace is heated to 800 ℃ in an argon atmosphere (argon flow rate is 100 ml / min, the temperature is first raised to 750 ℃ at a rate of 25 ℃ / min, and then raised to 800 ℃ at a rate of 15 ℃ / min), and when the furnace temperature rises to 800 ℃, a mixed gas of hydrogen and argon is introduced (gas flow rate is hydrogen 4 ml / min and argon 100 ml / min), at this time the evaporated precursor carried by the mixed gas will nucleate and grow on the surface of the gold foil, and the growth time is 1.5 minutes. After the growth is completed, the sample is directly pushed out of the high-temperature zone so that the sample is rapidly cooled at room temperature, and finally a large-size, high-quality WS 2x Se 2(1-x) alloy monocrystal is obtained on the surface of the gold foil.

[0033] The morphology and photoluminescence (PL) peak of the sample are characterized by optical microscopy and Raman spectrometer, as shown in Figure 2 (a), the morphology of the prepared WS 2x Se 2(1-x) alloy monocrystal is an independent triangle, and the maximum size can reach 730 µm. This independent triangular morphology is WS 2x Se 2(1-x) alloy monocrystal. Figure 2 (b) is the photoluminescence spectrum of the WS 2x Se 2(1-x) alloy monocrystal, and the luminescence peak is at 638 nm.

[0034] To further determine the WS 2x Se 2(1-x) The chemical composition of the alloy single crystal, i.e. the atomic percentage of two non-metallic elements in the alloy, the optical band gap obtained from the luminescence peak position wherein is the Planck constant, is the speed of light, is the wavelength corresponding to the photoluminescence peak) is approximately taken as the actual band gap of the alloy, the proportion of S element in the alloy can be fitted according to the band gap from the following empirical formula:

[0035]

[0036] wherein is the band gap of WS2, the specific value is 1.968 eV, is the band gap of WSe2, the specific value is 1.632 eV, b is the band bending constant, the specific value is 0.2, and x is the proportion of sulfur element in the two non-metallic elements in the alloy. The value of x is about 0.92, i.e. the proportion of sulfur element is 0.92, and the proportion of selenium element is 0.08, so the obtained large-size alloy single crystal is WS 1.84 Se 0.16 ;

[0037] The thickness of the WS 1.84 Se 0.16 alloy single crystal is 0.92 nm, which confirms that the obtained large-size WS 1.84 Se 0.16 alloy single crystal is monolayer, as shown in Figure 3 .

[0038] Example 2 Composition control

[0039] As shown in Figure 1 , a large-size monolayer WS 2x Se 2(1-x) alloy single crystal with adjustable chemical composition and uniform layer number is prepared on a metal substrate by using a non-metallic chalcogenide compound (SeS2) containing two chalcogen elements as a non-metallic growth source and WO3 as a metal growth source. Here, by changing the content of the non-metallic chalcogenide compound (SeS2), i.e. changing the proportion of sulfur element in the two non-metallic elements in the reaction precursor, large-size monolayer WS 2x Se 2(1-x) alloy single crystals with different chemical compositions are obtained, and the specific implementation is as follows:

[0040] ​The horizontal reaction furnace is respectively provided with a gas inlet 1 and a gas outlet 5 at two ends, a nonmetal growth source and a metal growth source are respectively located at 2 and 3, a gold foil is placed in a high-temperature area of the horizontal reaction furnace, and a heating area position is like 6. 40 mg of tungsten trioxide powder (WO3, purity is 99.999 %) is placed in a central high-temperature area of the horizontal reaction furnace (furnace tube diameter is 25 mm, and a reaction area length is 5 cm), the gold foil (10 mm x 10 mm x 100 microns, purity is 99.99 wt %) is horizontally placed at a position 2 cm behind the tungsten trioxide powder, and the selenium disulfide powder (SeS2, purity is 97 %) is placed at a position at about 150 DEG C of the horizontal reaction furnace. The content of the selenium disulfide powder is changed to be 55 mg, 38 mg, 26 mg and 15 mg in turn each time of growth. After 5 minutes of argon gas is passed to exhaust air in the furnace tube, the reaction furnace is heated to 800 DEG C in an argon atmosphere (argon flow is 100 ml / min, the temperature is first raised to 750 DEG C at a speed of 25 DEG C / min, and then raised to 800 DEG C at a speed of 15 DEG C / min), when the furnace temperature rises to 800 DEG C, a mixed gas of hydrogen and argon (hydrogen flow is 4 ml / min, and argon flow is 100 ml / min) is introduced. At this time, the mixed gas carries the evaporated precursor to nucleate and grow on the surface of the gold foil, and the growth time is 1.5 min. After the growth is completed, the sample is directly pushed out of the high-temperature area to rapidly cool the sample at room temperature, and finally four single-layer WS 2x Se 2(1-x) alloy monocrystals with different chemical compositions are prepared.

[0041] The metal reaction source is: under the condition that the tungsten trioxide powder (WO3, purity is 99.999 %) is 40 mg, the nonmetal reaction source selenium disulfide powder is added to be 55 mg, 38 mg, 26 mg and 15 mg respectively, and four single-layer WS 2x Se 2(1-x) alloy monocrystals are obtained. 2x Se 2(1-x) The PL characterization is performed on the four single-layer WS Figure 4 Se 2x alloy monocrystals with different chemical compositions, and the photoluminescence spectrum obtained is as shown in 2(1-x) The values of x are calculated to be 0.96, 0.65, 0.5 and 0.27 respectively, that is, the four alloys with different compositions obtained are: a large-size single-layer WS 1.92 Se 0.08 alloy monocrystal with a sulfur element ratio of 0.96 and a selenium element ratio of 0.04; a large-size single-layer WS 1.30 Se 0.70 alloy monocrystal with a sulfur element ratio of 0.65 and a selenium element ratio of 0.35; a large-size single-layer WS 1.0Se 1.0 alloy single crystal; the proportion of sulfur element is 0.27, and the proportion of selenium element is 0.73 0.54 Se 1.46 alloy single crystal. This shows that we can realize the WS 2x Se 2(1-x) alloy chemical composition regulation.

[0042] Example 3 Continuous and complete large-area WS 2x Se 2(1-x) alloy thin film

[0043] As Figure 1 shown, a non-metallic chalcogen compound (SeS2) containing two chalcogen elements is used as a non-metallic growth source, WO3 is used as a metal growth source, and a large-area WS 2x Se 2(1-x) alloy thin film is prepared on a metal substrate. Here, by prolonging the growth time, the size of the independent WS 2x Se 2(1-x) alloy single crystal continues to increase, and finally the adjacent independent triangular-shaped single crystals are spliced with each other to obtain a continuous and complete large-area WS 2x Se 2(1-x) alloy thin film, and the specific size depends on the size of the growth substrate.

[0044] The horizontal reaction furnace is provided with a gas inlet 1 and a gas outlet 5 at two ends, respectively, the non-metallic growth source and the metallic growth source are located at 2 and 3, respectively, the gold foil is placed in the high-temperature zone of the horizontal reaction furnace, and the heating zone position is as shown at 6. 30 milligrams of tungsten trioxide powder (WO3, purity 99.999 %) is placed in the central high-temperature zone of the horizontal reaction furnace (furnace tube diameter 25 millimeters, reaction zone length 5 centimeters), and the gold foil (10 millimeters x 20 millimeters x 100 micrometers, purity 99.99 wt %) is placed horizontally at a position 2 centimeters behind the tungsten trioxide powder; 50 milligrams of selenium disulfide powder (SeS2, purity 97 %) is placed at a position at about 150 ℃ of the horizontal reaction furnace, first purging the air in the hollow tube with argon for 5 minutes, and then heating the reaction furnace to 800 ℃ in an argon atmosphere (argon flow rate 100 milliliters / minute, the temperature is first raised to 750 ℃ at a rate of 25 ℃ / minute, and then raised to 800 ℃ at a rate of 15 ℃ / minute), when the furnace temperature rises to 800 ℃, a mixed gas of hydrogen and argon (gas flow rates are hydrogen 4 milliliters / minute and argon 100 milliliters / minute) is introduced, at this time, the evaporated precursors carried by the mixed gas will nucleate and grow on the surface of the gold foil, and the growth time is 2 minutes; after the growth is completed, the sample is directly pushed out of the high-temperature zone so that the sample is rapidly cooled at room temperature, and finally a uniform and continuous large-area WS2x Se 2(1-x) alloy thin film, here the area of the film is 2 As Figure 5 shown in (a); under optical microscope, large-area WS 2x Se 2(1-x) alloy thin film is uniform and consistent, as Figure 5 shown in (b).

[0045] Example 4 Double-layer WS 2x Se 2(1-x) alloy single crystal

[0046] As Figure 1 shown in (a), a double-layer WS 2x Se 2(1-x) alloy single crystal with adjustable chemical composition and uniform layer number is prepared on a metal substrate by using a nonmetallic chalcogenide (SeS2) containing two chalcogen elements as a nonmetallic growth source and WO3 as a metallic growth source. Here, the thermodynamic reaction barrier is reduced by increasing the growth temperature, making the growth of the double layer easy, and ultimately obtaining a double-layer WS 2x Se 2(1-x) alloy single crystal.

[0047] The horizontal reaction furnace is provided with a gas inlet 1 and a gas outlet 5 at both ends, respectively, and the nonmetallic growth source and the metallic growth source are located at 2 and 3, respectively. The gold foil is placed in the high-temperature zone of the horizontal reaction furnace, and the heating zone position is as shown in 6. 40 milligrams of tungsten trioxide powder (WO3, purity 99.999%) is placed in the central high-temperature zone of the horizontal reaction furnace (furnace tube diameter 25 mm, reaction zone length 5 cm), and the gold foil (10 mm x 10 mm x 100 microns, purity 99.99 wt%) is placed horizontally at a position 2 cm behind the tungsten trioxide powder. 31 milligrams of selenium disulfide powder (SeS2, purity 97%) is placed at a position at about 150 ℃ of the horizontal reaction furnace. First, the furnace tube is purged of air for 5 minutes, and then the reaction furnace is heated to 900 ℃ in an argon atmosphere (argon flow rate 100 ml / min, temperature rising speed first 25 ℃ / min to 750 ℃, then 15 ℃ / min to 900 ℃). When the furnace temperature rises to 900 ℃, a mixed gas of hydrogen and argon is introduced (hydrogen flow rate 4 ml / min, argon flow rate 100 ml / min). At this time, the evaporated precursors carried by the mixed gas will nucleate and grow on the surface of the gold foil, and the growth time is 1.5 minutes. After the growth is completed, the sample is directly pushed out of the high-temperature zone so that the sample is rapidly cooled at room temperature, and ultimately a double-layer WS 2x Se 2(1-x) alloy single crystal is obtained on the surface of the gold foil.

[0048] The sample thickness obtained by atomic force microscopy characterization is 1.73 nm, and the thickness of each layer is theoretically 0.7 nm~1 nm, so the obtained WS 2x Se 2(1-x) alloy single crystal is a double layer, such as Figure 6 as shown.

[0049] Example 5 Four-layer WS 2x Se 2(1-x) alloy single crystal

[0050] As shown in Figure 1 , a non-metallic sulfide compound (SeS2) containing two chalcogen elements is used as a non-metallic growth source, WO3 is used as a metal growth source, and a four-layer WS 2x Se 2(1-x) alloy single crystal with adjustable chemical composition and uniform layer number is prepared on a metal substrate. Here, by increasing the growth temperature, the thermodynamic reaction barrier is reduced, making the growth of four layers easy, and ultimately obtaining a four-layer WS 2x Se 2(1-x) alloy single crystal with uniform layer number.

[0051] The horizontal reaction furnace is provided with a gas inlet 1 and a gas outlet 5 at both ends, and the non-metallic growth source and the metallic growth source are located at 2 and 3 respectively. The gold foil is placed in the high temperature zone of the horizontal reaction furnace, and the heating zone position is as shown in 6. 60 milligrams of tungsten trioxide powder (WO3, purity 99.999%) is placed in the central high temperature area of the horizontal reaction furnace (furnace tube diameter 25 mm, reaction zone length 5 cm), and the gold foil (10 mm x 10 mm x 100 microns, purity 99.99 wt%) is placed horizontally 2 cm behind the tungsten trioxide powder. 10 milligrams of selenium disulfide powder (SeS2, purity 97%) is placed at a position of about 150 ℃ in the horizontal reaction furnace. First, the furnace tube is purged of air for 5 minutes, then the reaction furnace is heated to 920 ℃ in an argon atmosphere (argon flow rate is 100 milliliters / minute, the temperature is first raised to 750 ℃ at a rate of 25 ℃ / minute, and then raised to 920 ℃ at a rate of 15 ℃ / minute), and when the furnace temperature rises to 920 ℃, a mixed gas of hydrogen and argon is introduced (gas flow rate is hydrogen 4 milliliters / minute, argon 100 milliliters / minute). At this time, the evaporated precursor carried by the mixed gas will nucleate and grow on the surface of the gold foil, and the growth time is 1.5 minutes. After the growth is completed, the sample is directly pushed out of the high temperature zone to rapidly cool the sample at room temperature, and ultimately a four-layer WS 2x Se 2(1-x) alloy single crystal with uniform layer number is obtained on the surface of the gold foil.

[0052] The thickness of the sample obtained by atomic force microscopy characterization is 3.5 nm, and the thickness of each layer is theoretically 0.7 nm~1 nm, so the obtained WS2x Se 2(1-x) Alloy single crystal is four layers, such as Figure 7

[0053] Example 6 WS2Se Alloy Single Crystal on Sapphire Substrate 2x Se 2(1-x) Growth of Alloy Single Crystal

[0054] As shown in Figure 1 , a non-metallic chalcogenide (SeS2) containing two chalcogen elements is used as a non-metallic growth source, and WO3 is used as a metal growth source to prepare a single-layer WS2Se alloy single crystal with adjustable chemical composition and uniform layer number on a sapphire substrate. 2x Se 2(1-x) Alloy single crystal. Sapphire, as a non-metallic growth substrate, does not have the catalytic activity possessed by metal substrates, which makes it very difficult to grow alloys on sapphire using traditional elemental sulfur (S) and elemental selenium (Se) as non-metallic growth sources. However, the sulfur monomer (S) and selenium monomer (Se) obtained by thermal decomposition of the non-metallic chalcogen compound (SeS2) have relatively low energy diffusion barriers and formation energies, which makes it easier for them to diffuse on the surface of sapphire and form WS2Se alloy single crystals than the sulfur dimer (S2) and selenium dimer (Se2) obtained by thermal decomposition of elemental sulfur (S) and elemental selenium (Se). 2x Se 2(1-x) Alloy single crystal, thereby realizing the growth of WS2Se alloy single crystal on sapphire substrate. 2x Se 2(1-x) Growth of Alloy Single Crystal. Due to the lack of catalytic ability of the substrate, the sample size on the sapphire substrate is smaller than that on the metal substrate.

[0055] ​The horizontal reaction furnace is provided with a gas inlet 1 and a gas outlet 5 at two ends respectively, and the nonmetal growth source and the metal growth source are located at 2 and 3 respectively. The sapphire substrate is placed in the high-temperature zone of the horizontal reaction furnace, and the heating zone position is as shown at 6. 50 mg of tungsten trioxide powder (WO3, purity 99.999 %) is placed in the central high-temperature zone of the horizontal reaction furnace (furnace tube diameter 25 mm, reaction zone length 5 cm), and a sapphire substrate (10 mm x 10 mm x 500 microns, double-side polished) is horizontally placed at a position 2 cm behind the tungsten trioxide powder. 70 mg of selenium disulfide powder (SeS2, purity 97 %) is placed at a position at about 150 °C of the horizontal reaction furnace. After the hollow air in the furnace tube is exhausted by passing argon for 5 minutes, the reaction furnace is heated to 900 °C in an argon atmosphere (argon flow rate 100 ml / min, the temperature is first raised to 750 °C at a rate of 25 °C / min, and then raised to 900 °C at a rate of 15 °C / min). When the furnace temperature rises to 900 °C, a mixed gas of hydrogen and argon is introduced (hydrogen flow rate 4 ml / min, argon flow rate 100 ml / min). At this time, the vaporized precursors carried by the mixed gas will nucleate and grow on the surface of the sapphire substrate, and the growth time is 10 minutes. After the growth is completed, the sample is directly pushed out of the high-temperature zone so that the sample is rapidly cooled at room temperature, and finally a high-quality uniform layer of WS 2x Se 2(1-x) alloy single crystal is obtained on the sapphire substrate.

[0056] The morphology of the WS 2x Se 2(1-x) alloy single crystal obtained on the sapphire substrate under an optical microscope is as shown in Figure 8 , which exhibits a triangular morphology.

[0057] Example 7 Preparation of a large-size single-layer MoS 2x Se 2(1-x) alloy single crystal on a metal substrate

[0058] As shown in Figure 1 , a large-size single-layer MoS 2x Se 2(1-x) alloy single crystal is prepared on a metal substrate by using a nonmetal chalcogenide (SeS2) containing two kinds of chalcogen elements as a nonmetal growth source and MoO3 as a metal growth source. Here, the chemical composition of the alloy is variable and adjustable, and the chemical formula is MoS 2x Se 2(1-x) , wherein x is the atomic percentage of the nonmetal element S in the total two nonmetal elements.

[0059] The horizontal reactor has a gas inlet 1 and a gas outlet 5 at both ends. The non-metal growth source and the metal growth source are located at 2 and 3 respectively. The gold foil is placed in the high-temperature zone of the horizontal reactor, and the heating zone is located as shown at 6. 20 mg of molybdenum trioxide powder (MoO3, purity 99.999%) was placed in the central high-temperature zone of a horizontal reactor (furnace tube diameter 25 mm, reaction zone length 5 cm). Gold foil (10 mm × 10 mm × 100 μm, purity 99.99 wt%) was placed horizontally 3 cm behind the molybdenum trioxide powder. 35 mg of selenium disulfide powder (SeS2, purity 97%) was placed at approximately 150 °C in the horizontal reactor. Argon gas was first passed through the furnace tubes for 5 minutes to purge the air. Then, the reactor was heated to 750 °C in an argon atmosphere (argon flow rate 100 mL / min, heating rate initially 25 °C / min to 650 °C, then 15 °C / min to 750 °C). The reactor temperature was maintained at 750 °C. A mixture of hydrogen and argon gas (flow rates of 4 mL / min for hydrogen and 100 mL / min for argon) was introduced at ℃. The evaporated precursors carried by the gas mixture nucleated and grew on the gold foil surface for 1.5 minutes. After growth, the sample was directly removed from the high-temperature zone and rapidly cooled to room temperature, ultimately yielding a high-quality monolayer of MoS2 on the gold foil surface. 2x Se 2(1-x) Alloy single crystal.

[0060] The morphology and photoluminescence (PL) peak positions of the samples were characterized using optical microscopy and Raman spectroscopy. Figure 9 As shown in (a), the MoS₂ we prepared 2x Se 2(1-x) Alloy single crystals are independent triangles. Figure 9 (b) is the measured photoluminescence spectrum line, with an emission peak at 705 nm and a shoulder peak at 642 nm;

[0061] To further determine MoS 2x Se 2(1-x) The chemical composition of an alloy single crystal, i.e., the atomic percentage of the two non-metallic elements in the alloy, is used to determine the optical band gap obtained from the emission peak position. ( ,in It is Planck's constant. It's the speed of light. The wavelength corresponding to the photoluminescence peak is approximated as the actual band gap of the alloy. The proportion of sulfur in the alloy can be obtained by fitting the band gap using the following empirical formula:

[0062]

[0063] in The specific band gap value of MoS2 is 1.856 eV. is the band gap of MoSe2, the specific value of b is 0.05, and x is the proportion of sulfur in the two non-metallic elements in the alloy. The value of x is about 0.89, that is, the proportion of sulfur is 0.89, and the proportion of selenium is 0.11. Therefore, the obtained alloy single crystal is MoS 0.89 Se 0.11 .

Claims

1. A method for preparing two-dimensional TMDs alloy from non-metallic chalcogenides using CVD method, characterized in that: The nonmetal growth source is a nonmetal chalcogenide containing two chalcogen elements; The nonmetal chalcogenide containing two chalcogen elements is SeS2; The metal growth source is WO3 or MoO3; The substrate is a metal or nonmetal substrate, and the nonmetal substrate includes a silicon wafer, sapphire, mica or quartz; The proportion of the two chalcogen elements in the TMDs alloy is changed by adjusting the weight ratio of the nonmetal growth source to the metal growth source.

2. The method for preparing two-dimensional TMDs alloys from non-metallic chalcogenides according to claim 1, characterized in that: The growth temperature is 700-1000 ℃, and hydrogen and inert gas are introduced during the growth process.

3. The method of claim 1 or 2, wherein: The metal growth source is 1-200 mg, the nonmetal growth source is 1-100 mg, and the weight ratio of the metal growth source to the nonmetal growth source is 0.1-10.

4. The method for preparing two-dimensional TMDs alloys from non-metallic chalcogenides according to claim 3, characterized in that: The prepared two-dimensional TMDs alloy layer is uniform, and the number of layers is 1-10.

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