A VS 2x Se 2(1-x) Two-dimensional alloy materials and their controllable work function preparation methods and applications

Abstract

This invention belongs to the field of two-dimensional materials technology, specifically relating to a VS 2x Se 2(1‑x) A method for preparing two-dimensional alloy materials with controllable work function involves placing VCl3, Se powder, and S powder in a weight ratio of 1–3:9–11:1 in the high-temperature, medium-temperature, and low-temperature zones of a vapor deposition tube, respectively. Heating in each zone causes the raw materials to volatilize and chemically deposit on the substrate surface under the transport of a carrier gas. During this process, the alloy composition of the chemically deposited product is controlled by adjusting the temperature in the low-temperature zone, thereby controlling the work function of the product and obtaining VCl3 alloys with different work functions. 2x Se 2(1‑x) Alloy two-dimensional materials; where, 0

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material preparation, specifically relating to the CVD preparation of alloy two-dimensional materials. Technical Background

[0002] Transition metal chalcogenides (TMDs), with their unique structure, physical, electrical, and optical properties, have brought breakthroughs to the study of fundamental physical phenomena and created entirely new devices, attracting widespread attention. 1-3 Precise control of the spatial distribution of chemical composition and electronic structure in two-dimensional TMDs and their heterostructures is of great significance for exploring their potential applications. In particular, chemical vapor deposition (CVD) has enabled the systematic and continuous control of the electronic and optical properties of two-dimensional alloy TMDs through compositional modulation. For example, continuous control of the bandgap through alloy composition modulation. 4-5 Phase transition 6-7 Electronic properties 5 wait.

[0003] Two-dimensional semiconductor TMDs (s-TMDs) have shown great potential as channel materials in next-generation electronic devices. 8-10 However, non-ideal metal / semiconductor contacts severely affect the electrical properties of two-dimensional s-TMDs. These include unavoidable chemical disorder, lattice defects, and interface contamination during photolithography and deposition, leading to Fermi level pinning (FLP) at the contact interface and resulting in high contact resistance. 11 Recent studies have shown that metal / semiconductor van der Waals (vdW) contacts can avoid severe interfacial damage during metal deposition, thereby creating an FLP-free interface. 12-13 Therefore, the Schottky potential defense height (φ) SB It is highly adjustable, determined by the work function of the metal and semiconductor, and can be used to manufacture high-performance transistors with ohmic contacts or near-ideal rectifiers with Schottky contacts. 14-15 Two-dimensional metallic TMDs (m-TMDs, such as NbX2, VX2, and TaX2, where X = S, Se, and Te) exhibit excellent electrical conductivity. 16-18 In situ growth of two-dimensional m-TMD vdW contact field-effect transistors exhibits better device performance and yield. 19-20 However, current research largely focuses on characterizing near-ideal vdW interfaces, with limited experimental studies on the work function of two-dimensional m-TMDs, remaining largely theoretical. Furthermore, synthesized vdW heterostructures are limited to specific two-dimensional metals with fixed work functions. Continuous and broader work function engineering is crucial for constructing high-performance or multifunctional two-dimensional nanodevices, but it remains a challenge.

[0004] References

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[0025] To fill VS 2x Se 2(1-x) There is a gap in the technology for preparing two-dimensional alloy materials. The primary objective of this invention is to provide a VS material with controllable work function. 2x Se 2(1-x) The CVD preparation method for two-dimensional alloy materials aims to achieve flexible control of the work function of the product.

[0026] This invention also includes VS prepared by the aforementioned method. 2x Se 2(1-x) Two-dimensional alloy materials and their applications.

[0027] This invention also provides a VS 2x Se 2(1-x) Alloy two-dimensional materials / MX2 semiconductor two-dimensional material heterojunctions and their preparation and application.

[0028] VS 2x Se 2(1-x) Two-dimensional alloy materials remain a gap in the industry. To address this gap in materials and their preparation, this invention attempts to synthesize them using CVD methods. However, early research revealed that CVD synthesis is significantly less efficient than traditional methods.2x Se 2(1-x) In the process of preparing VS alloy two-dimensional materials, single-phase heterophases often exist, and it is difficult to obtain VS with high crystallinity and phase purity. 2x Se 2(1-x) Composite phase, moreover, there is also VS 2x Se 2(1-x) The problem that the alloy components of alloy two-dimensional materials are difficult to be continuously and linearly regulated. To solve this problem, the present invention provides the following solutions:

[0029] A method for controllably preparing the work function of VS 2x Se 2(1-x) Alloy two-dimensional materials, in which VCl3, Se powder and S powder with a weight ratio of 1-3:9-11:1 are respectively arranged in the high-temperature zone, medium-temperature zone and low-temperature zone of the vapor deposition tube, and each temperature zone is heated to volatilize each raw material and chemically deposit on the surface of the substrate under the carrier gas; during this period, the alloy components of the chemical deposition product are regulated by regulating the temperature of the low-temperature zone, so as to regulate the work function of the product, and VS alloy two-dimensional materials with different work functions are prepared; 2x Se 2(1-x) Alloy two-dimensional materials;

[0030] Among them, 0 < x < 1; the regulation range of the temperature in the low-temperature zone is 170-215 °C;

[0031] The temperature of the high-temperature zone is 400-500 °C, the temperature of the medium-temperature zone is 300-400 °C, the temperature of the chemical deposition stage is 570-620 °C, and the carrier gas is a hydrogen-containing atmosphere.

[0032] Aiming at the problems faced in the CVD preparation of VS 2x Se 2(1-x) Alloy two-dimensional materials, which are prone to form single-phase heterophases, and the continuous linear regulation of the alloy components of VS alloy two-dimensional materials is difficult. The present invention innovatively reacts and deposits the VCl3, Se powder and S powder with the above weight ratio in the chamber, and innovatively regulates the alloy components by the temperature of the low-temperature zone where the sulfur powder is located, so that VS alloy two-dimensional materials can be synthesized with unexpectedly high crystallinity and phase purity. 2x Se 2(1-x) In addition, the continuous linear regulation of the alloy components of the product and the control of the alloy work function can be realized. 2x Se 2(1-x) Alloy two-dimensional materials, in addition, the continuous linear regulation of the alloy components of the product and the control of the alloy work function can be realized.

[0033] The research of the present invention finds that the raw materials of VCl3, Se powder and S powder are used as precursor raw materials, and based on the combined control of the proportions of the three, it is beneficial to the synthesis of the VS 2x Se 2(1-x) Alloy two-dimensional materials, and based on the temperature regulation means in the low-temperature zone, the linear interval and linear relationship of the regulation of the alloy components of the product are synergistically improved.

[0034] Preferred raw materials: VCl3, Se powder, and S powder with a purity greater than 99%;

[0035] Preferably, the ratio of VCl3, Se powder, and S powder is 1.5–2.5:9.5–10.5:1, and more preferably 2:10:1.

[0036] In this invention, the temperature of the high-temperature zone refers to the temperature range where VCl3 is located, which can be understood as the volatilization temperature of VCl3. Preferably, the temperature of the high-temperature zone is 470–490°C;

[0037] The temperature in the intermediate temperature zone refers to the temperature range where the selenium powder is located, which can be understood as the volatilization temperature of Se. Preferably, the temperature in the intermediate temperature zone is 370–390°C.

[0038] In this invention, the temperature of the low-temperature zone refers to the temperature at which the sulfur powder is located, which can be understood as the volatilization temperature of sulfur (S). This invention has discovered that, unlike the method of controlling product x based on material ratios, this invention, under a fixed precursor raw material ratio, can unexpectedly achieve synergy through the joint control of the temperature in the low-temperature zone. This improves the continuous control effect of the product alloy composition, enhances the linear range and linear relationship of the control, and achieves more sensitive and precise control of alloy composition and work function.

[0039] Preferably, the temperature range for the low-temperature zone is 175–210°C. This invention has found that, under the aforementioned preparation process, continuous linear control of the alloy phase composition can be achieved at the specified temperature.

[0040] In this invention, the hydrogen-containing atmosphere is a mixture of hydrogen and protective gas.

[0041] In this invention, the protective gas is, for example, at least one of nitrogen or an inert gas (such as the commonly used Ar).

[0042] In this invention, during the chemical deposition stage, the flow rate of the protective gas is 60-100 sccm, and the flow rate of the hydrogen gas is 1-4 sccm; preferably, the flow rate of the protective gas is 70-90 sccm, and the flow rate of the hydrogen gas is 2-3 sccm.

[0043] Preferably, the temperature for chemical deposition is 580–600°C, and more preferably 585–595°C.

[0044] In this invention, the chemical deposition time is preferably 3 to 20 minutes, more preferably 5 to 15 minutes, and further preferably 9 to 12 minutes.

[0045] The present invention also provides a VS prepared by the above preparation method. 2x Se 2(1-x)Two-dimensional alloy materials.

[0046] This invention also provides a VS 2x Se 2(1-x) The alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction is the VS described in this invention. 2x Se 2(1-x) A heterojunction material formed by an alloy two-dimensional material and an MX2 semiconductor two-dimensional material, wherein the absolute value of the difference in the work functions of the two materials is less than or equal to 100 meV;

[0047] Preferably, M is at least one of W and Mo;

[0048] Preferably, X is at least one of Se and S.

[0049] The present invention also provides the aforementioned VS 2x Se 2(1-x) A method for preparing a heterojunction of alloy two-dimensional material / MX2 semiconductor two-dimensional material involves first depositing MX2 semiconductor two-dimensional material on a substrate, and then, based on the work function characteristics of MX2 semiconductor two-dimensional material, using the work function controllable preparation method described in this invention, depositing a VS junction on the surface of MX2 semiconductor two-dimensional material with a work function matching that of the MX2 semiconductor two-dimensional material. 2x Se 2(1-x) The VS alloy two-dimensional material was prepared to obtain the aforementioned VS 2x Se 2(1-x) Alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction.

[0050] In this invention, based on the work function controllable preparation method described above, synthesis conditions such as the temperature in the low-temperature region and VS can be constructed. 2x Se 2(1-x) The linear relationship curve of the work function of the alloy two-dimensional material is obtained, and based on the work function characteristics of the MX2 semiconductor two-dimensional material, the VS value that matches its work function (the absolute value of the work function difference is less than or equal to 100 meV) is determined. 2x Se 2(1-x) The synthesis conditions of the alloy two-dimensional material (mainly referring to the temperature in the low-temperature region) are then used to deposit VS on the MX2 semiconductor two-dimensional material. 2x Se 2(1-x) This invention provides a novel approach to fabricating heterojunctions based on work function matching, enabling the precise and non-blind preparation of two-dimensional alloy materials while maintaining excellent performance.

[0051] The present invention also provides the aforementioned VS 2x Se 2(1-x) Applications of alloy two-dimensional materials / MX2 semiconductor two-dimensional material heterojunctions in the fabrication of electronic devices;

[0052] Preferably, it is used to fabricate field-effect transistor devices;

[0053] Preferably, the fabrication steps of the field-effect transistor device are as follows:

[0054] Electron beam lithography in VS 2x Se 2(1-x) A field-effect transistor was fabricated by exposing and marking a sample on a two-dimensional alloy material, followed by depositing metal on the sample using electron beam evaporation.

[0055] Preferably, the metals deposited by electron beam evaporation are In and Au.

[0056] The present invention also provides a field-effect transistor device comprising the VS described herein. 2x Se 2(1-x) Two-dimensional alloy material; preferably, comprising the aforementioned VS 2x Se 2(1-x) Alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction.

[0057] Beneficial effects

[0058] 1. Based on the aforementioned CVD synthesis and control method, this invention can successfully prepare the aforementioned VS 2x Se 2(1-x) This invention relates to two-dimensional alloy materials, enabling continuous and linear control of the alloy composition of the products. Through Kelvin probe force microscopy, this invention discovered that VS... 2x Se 2(1-x) The work function of two-dimensional alloy materials also changes monotonically with changes in composition. This enables continuous control of the work function of metals by adjusting the composition of two-dimensional alloy materials.

[0059] 2. This invention benefits from the VS described in this invention. 2x Se 2(1-x) The excellent controllability of the work function of alloy two-dimensional materials allows for the purposeful control of VS based on the characteristics of the work function of semiconductor two-dimensional materials. 2x Se 2(1-x) The work function of the alloy two-dimensional material is used to match the work functions of the two materials, thereby enabling the purposeful preparation of high-performance metal-semiconductor heterostructure materials. Attached Figure Description

[0060] Figure 1 To prepare VS 2x Se 2(1-x) An atmospheric pressure chemical vapor deposition apparatus for alloy two-dimensional materials and WSe2 substrates;

[0061] Figure 2 Examples 1-1 show VS grown on different substrates. 2x Se2(1-x) Schematic diagram of optical properties of two-dimensional alloy materials, where the left image represents T. S The image shows the deposition products on a mica substrate at 175℃. The right image is T. S This image shows the deposition product on a SiO2 / Si substrate at 175℃.

[0062] Figure 3 Different components VS prepared in Example 1-1 2x Se 2(1-x) TEM characterization images of two-dimensional materials;

[0063] Figure 4 VS for different alloy compositions in Examples 1-1 2x Se 2(1-x) XRD and XPS characterization images of two-dimensional materials;

[0064] Figure 5 The graphs show the relationship between the vapor pressure of the S source and the composition of the S alloy as a function of the S source temperature in Examples 1-1.

[0065] Figure 6 The graph shows the relationship between the proportion of raw materials and the composition of S alloy in Comparative Example 1-1.

[0066] Figure 7 The base temperature T in Examples 1-2 Sub Schematic diagram illustrating the impact on growth;

[0067] Figure 8 The selenium source temperature T in Examples 1-3 Se Schematic diagram illustrating the impact on growth;

[0068] Figure 9 VS of different components grown on HOPG in Examples 1-4 2x Se 2(1-x) Optical schematic diagram of two-dimensional materials;

[0069] Figure 10 VS for different S components on HOPG substrates in Examples 1-4 2x Se 2(1-x) Statistical graph showing the changing trends of surface potential difference and work function in two-dimensional materials;

[0070] Figure 11 VS in Example 2-1 2x Se 2(1-x) / WSe2vdWHs optical schematic diagram;

[0071] Figure 12 For different S components VS in Example 2-1 2x Se 2(1-x)Surface potential difference variation trend of / WSe2vdWHs two-dimensional material ( Figure 12 a) and band structure diagram ( Figure 12 b);

[0072] Figure 13 VS in Example 2-1 2x Se 2(1-x) The output characteristic curve and transfer characteristic curve of the / WSe2(x=0.00)vdWHs field-effect transistor.

[0073] Figure 14 The WSe2 field-effect transistors (a, b) and VS with In / Au contacts in Example 2-1 and Comparative Example 2-1 are shown. 2x Se 2(1-x) Output and transfer characteristic curves of the / WSe2(x=0.56)vdWHs field-effect transistor (c, d).

[0074] Figure 15 For different S components VS in Example 2-2 2x Se 2(1-x) The surface potential difference trend and band structure of / MoS2 vdWHs are shown in the figure.

[0075] Figure 16 VS in Example 2-2 2x Se 2(1-x) The output characteristic curve and transfer characteristic curve of the / MoS2(x=1.00)vdWHs field-effect transistor.

[0076] Figure 17 VS in Example 2-2 2x Se 2(1-x) / MoS2(x=0.00), VS 2x Se 2(1-x) The output characteristic curve and transfer characteristic curve of the / WSe2(x=0.52)vdWHs field-effect transistor. Detailed implementation method:

[0077] The present invention will be further illustrated by the following implementation examples, but the content of the present invention is not limited to the following content.

[0078] A VS 2x Se 2(1-x) This invention discloses a method for preparing two-dimensional alloy materials. A three-temperature zone tube furnace is used as the reaction apparatus. S powder, Se powder, and VCl3 are placed in the desired temperature zones for volatilization. The volatilized raw materials are then chemically deposited onto the substrate surface under a carrier gas and at a temperature of 570–620°C to obtain VS. 2x Se 2(1-x) Two-dimensional alloy materials.

[0079] In a preferred embodiment of the present invention, the volatilization temperature of VCl3 is 400-500℃; and the volatilization temperature of Se powder is 300-400℃.

[0080] As a preferred embodiment, the carrier gas is a mixture of an inert protective gas and hydrogen, wherein the flow rate of the inert protective gas is 60-100 sccm and the flow rate of the hydrogen is preferably 1-4 sccm.

[0081] In this invention, as a preferred embodiment, the weight ratio of VCl3, Se powder and S powder is 1-3:9-11:1, preferably 2:10:1.

[0082] In this invention, the prepared VS can be controlled by adjusting the volatilization temperature of S under a given raw material ratio. 2x Se 2(1-x) The two-dimensional alloy material x and its work function allow for continuous and near-linear control of the alloy composition x within the range of 0 to 1. Compared to raw material quality control, this method achieves more precise and stable control, improving the linear relationship and range of the control. In this invention, Kelvin probe force microscopy revealed that VS... 2x Se 2(1-x) The work function of two-dimensional alloy materials also changes monotonically with changes in composition. This enables continuous control of the work function of metals by adjusting the composition of two-dimensional alloy materials.

[0083] In this invention, it can also be based on the aforementioned VS 2x Se 2(1-x) Work function modulation synthesis of two-dimensional alloy materials enables precise fabrication of work function-matched heterojunctions. For example, an MX2 two-dimensional material is pre-formed, and VS is deposited on its surface. 2x Se 2(1-x) In the process of forming heterojunctions from two-dimensional alloy materials, the work function of MX2 two-dimensional materials can be utilized to select a VS that is compatible with its work function. 2x Se 2(1-x) The synthesis conditions of two-dimensional alloy materials are determined to precisely prepare heterojunctions with suitable work functions, thereby improving the performance of heterojunctions.

[0084] In one embodiment of the present invention, M in the MX2 two-dimensional material is a transition metal element, more preferably W or Mo. X is a chalcogenide element, more preferably S or Se. Preferably, the MX2 two-dimensional material has an atomically flat surface and a regular shape. Preferably, the size of the two-dimensional material is greater than 50 μm, more preferably greater than 100 μm.

[0085] In this invention, the MX2 two-dimensional material can be prepared based on known methods. For example, in the following case, the synthesis conditions of the MX2 two-dimensional material are:

[0086] In this case, the preparation steps for WSe2 are as follows: 100 mg of WSe2 powder is weighed and placed in a quartz boat, which is then placed in the center of the tubular furnace temperature zone. The SiO2 / Si substrate is placed in the downstream transition temperature zone. The reaction chamber is purged with 1000 sccm of high-purity argon for 10 min to remove residual oxygen and moisture. Then, with argon at 80 sccm, the temperature of the central temperature zone is raised to 1160°C using a reverse gas flow (gas flowing from the substrate to the raw material). The gas flow is then switched, and the temperature is maintained at a forward gas flow for 5 min. Natural cooling yields the WSe2 substrate. The preparation steps for MoS2 are as follows: 5 mg of MoO3 powder (Alfa, 99%) is evenly spread in a quartz boat in the central zone (720°C) of the furnace. A SiO2 / Si substrate is placed face down on the MoO3 powder as a growth substrate. Sulfur powder (Macklin, 99.9%) is placed in the variable temperature zone (approximately 220°C). Then, the entire reactor was purged with high-purity argon at 1000 sccm for 10 minutes to maintain a completely inert reaction atmosphere. The argon flow rate was adjusted to 60 sccm, and the temperature was raised to 720°C. After reaching the target temperature, growth was maintained for 4 minutes, followed by natural cooling to obtain the MoS2 substrate. It should be noted that the substrate and preparation methods described are merely examples of technical solutions and do not constitute a necessary technical limitation of the method of this invention.

[0087] In this invention, the deposition process can be implemented using existing equipment, as long as the temperature control method described above is met.

[0088] In this invention, the materials described herein can be used to prepare different devices using known methods.

[0089] 1. VS 2x Se 2(1-x) Preparation and characterization of alloy nanosheets

[0090] Example 1-1

[0091] VS 2x Se 2(1-x) Experimental apparatus for two-dimensional alloy materials, such as Figure 1 As shown in Figure a, the ingredients were prepared according to a weight ratio of VCl3, Se powder, and S powder of 2:10:1, and the S powder was placed in Zone I for volatilization at 175-210℃. S Se powder is placed in Zone II at a volatilization temperature of 380°C (T). Se VCl3 is placed in the transition temperature zone between temperature zones II and III, and volatilizes at 480℃ (T). VCl3The substrate (mica or SiO2 / Si substrate) is placed downstream of VCl3 (Zone III). The volatilized precursor materials are deposited at a temperature of 590℃ (T). substrate The reaction was carried out under an argon / hydrogen mixed carrier gas for 10 min, and the VS material was grown on the substrate surface. 2x Se 2(1-x) Two-dimensional alloy material. The carrier gas in the reaction process includes an inert protective gas and hydrogen, wherein the flow rate of the inert protective gas is 80 sccm; and the flow rate of the hydrogen is preferably 2.5 sccm.

[0092] Silvery-white VS will appear on mica or SiO2 / Si substrates. 2x Se 2(1-x) Single crystal formation, preparation of VS 2x Se 2(1-x) Two-dimensional material optical images, such as Figure 2 As shown.

[0093] Figure 2 a is T S VS on a mica substrate at 175℃ 2x Se 2(1-x) Two-dimensional material, gray as mica base, silver-white and nearly transparent as VS 2x Se 2(1-x) Single-crystal nanosheets with a thickness of 4–30 nm, a lateral dimension of 3–6 μm, and a scale bar of 5 μm. Figure 2 b is T S VS on a SiO2 / Si substrate at 175℃ 2x Se 2(1-x) Two-dimensional material; light purple represents the SiO2 / Si substrate; the silver-white six-nanosheet marked 1 is a VS material grown parallel to the substrate. 2x Se 2(1-x) Single-crystal nanosheets, with a thickness of 100–200 nm, a lateral dimension of 10–15 μm, and a scale bar of 20 μm, are marked as VS nanosheets grown perpendicular to the substrate. 2x Se 2(1-x) Single-crystal nanosheets.

[0094] Regulation of T S Single-crystal nanosheets with different alloy phases were prepared at different temperatures, for example, when T S At 175℃, VS was prepared with x = 0.12 ± 0.009. 2x Se 2(1-x) Single-crystal nanosheets. When T S At 180℃, VS was prepared with x = 0.21 ± 0.017. 2x Se 2(1-x) Single-crystal nanosheets. When T SAt 190℃, VS with x = 0.41 ± 0.045 was obtained. 2x Se 2(1-x) Single-crystal nanosheets. When Ts is 200℃, VS nanosheets with x = 0.63 ± 0.046 were prepared. 2x Se 2(1-x) Single-crystal nanosheets. When T S At 210℃, VS with x = 0.84 ± 0.025 was obtained. 2x Se 2(1-x) Single-crystal nanosheets.

[0095] Figure 3 Different components VS prepared in Example 1-1 2x Se 2(1-x) TEM characterization images of the two-dimensional material show that the prepared material has good crystallinity and compositional homogeneity. Furthermore, the interplanar spacing tends to decrease with increasing S alloy content (Note: x = 0.42 is T). S The product is at 190℃, and x = 0.63 is the temperature at T. S (A product of 200℃).

[0096] Figure 4 VS for different alloy compositions in Examples 1-1 2x Se 2(1-x) XRD and XPS characterization images of the two-dimensional material; it can be seen that the position and intensity of the XRD and XPS peaks change regularly with the change of alloy composition, proving that the VS2 peaks on the entire SiO2 / Si substrate... 2x Se 2(1-x) Uniform alloying of two-dimensional materials.

[0097] Figure 5 The graphs show the relationship between the vapor pressure of the sulfur source and the composition of the sulfur alloy as a function of the sulfur source temperature. Keeping other growth conditions constant, the vapor pressure of sulfur powder was varied from 175 to 210 °C to obtain the vapor pressure of sulfur (S) under different temperature gradients. 2x Se 2(1-x) Alloy nanosheets. Five samples were grown at sulfur source temperatures of 175℃, 180℃, 190℃, 200℃, and 210℃, respectively. The alloy content was analyzed using scanning electron microscopy and energy dispersive spectroscopy. The average statistical data was used to obtain the alloy composition x at different sulfur source temperatures. Figure 3 As can be seen from the red curve, the vapor pressure of sulfur increases in a quasi-linear manner with increasing source temperature. Figure 3 The blue curve shows that the S component exhibits a good linear trend with the S source temperature, consistent with the trends of vapor pressure and temperature changes.

[0098] Comparative Example 1-1

[0099] Compared to Example 1-1, the only difference is that the raw material ratio of S powder and Se powder precursors is used to control the alloy composition. Everything else is the same as in Example 1-1.

[0100] During the adjustment of growth parameters, we found that, in addition to the controllable adjustment of the sulfur source temperature, VS 2x Se 2(1-x) Besides the elemental content of the alloy nanosheets, the sulfur-selenium ratio also significantly affects the alloy content. To eliminate interference from other conditions, we first ensured that the evaporation temperatures of temperature zone I (sulfur source), temperature zone II (selenium source), and temperature zone III (vanadium trichloride and substrate), as well as the substrate deposition temperature, remained unchanged from those in Example 1-1. For example, we maintained the temperature at T... s =200℃, T se =380℃, T VCl3 =480℃ and T substrate =590℃ remained constant. Argon / hydrogen flow rates were 80 / 2.5 sccm, respectively. Growth time was 10 min. Then, with the selenium powder mass fixed at 400 mg, the sulfur source precursor ratio S / (S+Se) was adjusted by changing the sulfur powder mass to 0.0278, 0.2, 0.4, 0.6, and 0.8, respectively. The prepared VS 2x Se 2(1-x) The content of alloy nanosheets was determined using scanning electron microscopy and energy dispersive spectroscopy. Analysis of the data ultimately yielded the relationship between sulfur content and the sulfur-selenium raw material ratio.

[0101] like Figure 6 As shown, when S / (S+Se) = 0.0278, the sulfur content is approximately x = 0.03. As the mass ratio of sulfur precursor S / (S+Se) gradually increases, the sulfur content x also gradually increases. When S / (S+Se) = 0.4, the sulfur content x = 0.88. When S / (S+Se) > 0.4, the increasing trend of sulfur content slows down, and then gradually approaches saturation until the sulfur content x = 1. By comparing Comparative Example 1-1 with Example 1-1, it can be seen that the example has a wider range of component adjustment and a more linear relationship.

[0102] Examples 1-2

[0103] Compared with Example 1-1, the only difference is that the control T Sub The temperatures were 620℃, 600℃, and 580℃, respectively. Other conditions were the same as in Example 1-1 (e.g., Ts was 200℃).

[0104] like Figure 7 As shown in ac (scale bar 20 μm), while keeping other growth conditions constant, by increasing the substrate temperature T Sub The VS was prepared by gradually decreasing the temperature from 620℃ to 580℃. 2x Se 2(1-x)The lateral dimensions and thickness of the alloy nanosheets gradually decrease, increasing the T... Sub By controlling the temperature at 580–590℃, better continuous linear preparation of the work function can be achieved.

[0105] Examples 1-3

[0106] Compared with Example 1-1, the only difference is T Se The temperatures were 280℃ and 400℃, respectively. Other conditions were the same as in Example 1-1 (e.g., Ts was 200℃).

[0107] like Figure 8 As shown in a, when T Se At a temperature of 280℃, the Se precursor in the cavity is insufficient to provide a sufficient Se atmosphere to react chemically with VCl3, therefore a large amount of unreacted VCl3 will be generated on the substrate. Figure 8 (as shown in red circle 1). But, when T Se When the temperature rises to 400℃, an excess of Se atmosphere will lead to the formation of thicker nanosheets. Figure 8 (as shown in b). T Se By controlling the temperature between 370 and 390°C, better continuous linear preparation of the work function can be achieved.

[0108] Examples 1-4

[0109] Compared with the preparation method of Example 1-1, the only difference is that HOPG is used as the growth substrate, replacing the mica or SiO2 / Si substrate in Example 1-1. Otherwise, it is the same as Example 1-1.

[0110] By controlling the temperature Ts, single-crystal nanosheets with different alloy phases were prepared. For example, when Ts was 175℃, VS nanosheets with x = 0.12 ± 0.009 were prepared. 2x Se 2(1-x) Single-crystal nanosheets. When Ts is 180℃, VS nanosheets with x = 0.21 ± 0.017 were prepared. 2x Se 2(1-x) Single-crystal nanosheets. When Ts is 190℃, VS nanosheets with x = 0.41 ± 0.045 were prepared. 2x Se 2(1-x) Single-crystal nanosheets. When Ts is 200℃, VS nanosheets with x = 0.63 ± 0.046 were prepared. 2x Se 2(1-x) Single-crystal nanosheets. When Ts is 210℃, VS nanosheets with x = 0.84 ± 0.025 were prepared. 2x Se 2(1-x) Single-crystal nanosheets.

[0111] Figure 9 VS for different components grown on HOPG 2x Se2(1-x) Optical schematic diagram of two-dimensional materials. Gray represents the HOPG substrate, and the materials with darker contrast and distinct triangular or hexagonal outlines on the substrate are VS materials. 2x Se 2(1-x) Two-dimensional material. Thickness 30–100 nm, lateral dimension 10–40 μm. Scale bar 20 μm.

[0112] Figure 10 VS for different S components on HOPG substrate 2x Se 2(1-x) Statistical graph showing the changing trends of surface potential difference and work function in two-dimensional materials. Figure 10 Illustrations show different S components VS 2x Se 2(1-x) The KPFM morphology image from / HOPG shows nanosheets as black contrast, indicating VS 2x Se 2(1-x) The potential of is less than the potential of HOPG. From Figure 9 The line graph shows that the surface potential and work function gradually decrease with increasing S alloy composition. As the S composition increases from x = 0.00 to x = 1.00, the surface potential gradually decreases from 187.58 ± 8.21 mV (x = 0.00) to 36.89 ± 10.00 mV (x = 1.00); calculated using the formula, the work function decreases from 4.79 ± 0.008 eV (x = 0.00) to 4.62 ± 0.010 eV (x = 1.00).

[0113] 2. VS 2x Se 2(1-x) Fabrication of heterojunctions and their field-effect transistors

[0114] Example 2-1

[0115] Compared with Example 1-1, the only difference is that SiO2 / Si with WSe2 grown on it is used as the growth substrate, replacing the mica substrate in Example 1-1. Otherwise, it is the same as Example 1-1.

[0116] Regulation of T S Single-crystal nanosheets with different alloy phases were prepared on WSe2 substrates at various temperatures. The experimental groups were as follows:

[0117] Group A: x = 0, no S source was added when the heterojunction was formed;

[0118] Group B: When T S At 180℃, VS with x = 0.23 was prepared. 2x Se 2(1-x) / WSe2 heterojunction.

[0119] Group C: When T SAt 195℃, VS with x = 0.56 was prepared. 2x Se 2(1-x) / WSe2 heterojunction;

[0120] Group D: When T S At 205℃, VS with x = 0.78 was prepared. 2x Se 2(1-x) / WSe2 heterojunction;

[0121] Group E: When T S At 215℃, VS with x = 0.92 was prepared. 2x Se 2(1-x) / WSe2 heterojunction.

[0122] Figure 11 VS on WSe2 substrate 2x Se 2(1-x) Two-dimensional material (Ts = 180℃), SiO2 / Si substrate is light purple, WSe2 is pink, VS 2x Se 2(1-x) It is silvery-white, with a scale bar of 20 μm. The morphology of the products under other Ts conditions is similar.

[0123] Figure 12 VS for different S components on WSe2 substrate 2x Se 2(1-x) Surface potential difference variation trend of two-dimensional materials (Figure) Figure 12 a) and band structure diagram ( Figure 12 b). Figure 12 An illustration shows the different S components VS 2x Se 2(1-x) KPFM morphology of / WSe2. It can be seen that as the S component gradually increases, VS... 2x Se 2(1-x) The potential difference of / WSe2 gradually increased from 114.10±7.18mV (x=0.00) to 252.15±6.05mV (x=0.92), which means that as the S composition increases, the Schottky barrier of the contact becomes larger, resulting in poorer device performance. Figure 12 The band diagram (b) shows the corresponding band bending and Schottky barrier changes.

[0124] VS 2x Se 2(1-x) The fabrication method of / WSe2 vdWHs field-effect transistors, using a two-step CVD method to fabricate VS... 2x Se 2(1-x) / WSe2 vdWHs (material obtained in Example 2-1). The alloy composition was controlled by adjusting the sulfur source temperature. Two-dimensional materials prepared from groups A and C were used to prepare the following:

[0125] VS 2x Se 2(1-x) / WSe2(x=0.00)vdWHs

[0126] VS 2x Se 2(1-x) / WSe2(x=0.56)vdWHs

[0127] From Example 2-1 Figure 12 VS 2x Se 2(1-x) The potential difference of / WSe2 KPFM can be obtained from VS. 2x Se 2(1-x) The potential difference (i.e., the work function difference) of / WSe2(x=0.00)vdWHs is approximately 115mV VS 2x Se 2(1-x) The potential difference of / WSe2(x=0.56)vdWHs is around 210mV, and the difference in work function is much higher than that of VS. 2x Se 2(1-x) / WSe2(x=0.00)vdWHs(115mV).

[0128] Electron beam exposure is used to expose the desired electrodes on the metal material, followed by electron beam evaporation to deposit 10 / 70 nm In / Au. Excess metal is then removed to obtain VS. 2x Se 2(1-x) / WSe2 vdWHs field-effect transistor.

[0129] Figure 13 For VS 2x Se 2(1-x) The output curve (a) and transfer curve (b) of the / WSe2(x=0.56)vdWHs field-effect transistor.

[0130] Comparative Example 2-1

[0131] The fabrication method of the WSe2 field-effect transistor differs from that in Example 2-1 in that a secondary growth of VS on WSe2 is not performed. 2x Se 2(1-x) Two-dimensional material, in which deposited metal In / Au is in direct contact with WSe2.

[0132] Figure 14 WSe2 field-effect transistors with In / Au contacts (a, b) and VS 2x Se 2(1-x) Output and transfer characteristic curves of the / WSe2(x=0.56)vdWHs field-effect transistor (c, d).

[0133] Example 2-2

[0134] Compared with Example 2-1, the only difference is that SiO2 / Si, which is a semiconductor material with a lower work function MoS2, is used as the growth substrate instead of the WSe2 substrate in Example 2-1. Otherwise, the material preparation method is the same as in Example 2-1.

[0135] Regulation of T S At different temperatures, single-crystal nanosheets of different alloy phases were prepared on a MoS2 substrate. For example, the experimental groups were:

[0136] Group A: x = 0, no S source was added when the heterojunction was formed;

[0137] Group B: When T S At 185℃, VS with x = 0.32 was prepared. 2x Se 2(1-x) / WSe2 heterojunction.

[0138] Group C: When T S At 195℃, VS with x = 0.52 was prepared. 2x Se 2(1-x) / WSe2 heterojunction;

[0139] Group D: When T S At 210℃, VS with x = 0.81 was obtained. 2x Se 2(1-x) / WSe2 heterojunction;

[0140] Group E: x = 1, no Se source was added when forming the heterojunction.

[0141] Depend on Figure 15 Result: VS 2x Se 2(1-x) The potential difference of / MoS2(x=0.00)vdWHs is -71.5mV, at which point VS 2x Se 2(1-x) The work function of (x=0.00) is greater than that of MoS2, and the contact is a Schottky contact with an electron blocking layer; VS 2x Se 2(1-x) The potential difference of / MoS2(x=0.52)vdWHs is approximately -18.5mV, at which point VS 2x Se 2(1-x) The work function of (x=0.52) is approximately equal to that of MoS2, and the contact is an ohmic contact with almost no electron blocking layer; VS 2x Se 2(1-x) The potential difference of / MoS2(x=1.00)vdWHs is 59.3mV, at which point VS 2x Se 2(1-x) The work function of (x=0.52) is less than that of MoS2, and the contact is an ohmic contact with an electron antiblocking layer.

[0142] Figure 15 VS for different S components on MoS2 substrate 2x Se 2(1-x) Surface potential difference variation trend and band structure variation of two-dimensional materials.

[0143] Figure 16 For VS 2x Se 2(1-x) The output characteristic curve and transfer characteristic curve of the / MoS2(x=1.00)vdWHs field-effect transistor.

[0144] Figure 17 For VS 2x Se 2(1-x) / MoS2(x=0),VS 2x Se 2(1-x) The output characteristic curve and transfer characteristic curve of the / WSe2(x=0.52)vdWHs field-effect transistor.

[0145] As can be seen from all the embodiments and comparative examples, for p-type WSe2 field-effect transistors, the performance of transistors using van der Waals contact electrodes is greatly improved compared to conventional vapor-deposited electrodes (Comparative Example 2-1). Furthermore, by adjusting VS... 2x Se 2(1-x) Alloy composition ranges from x = 0.52 to x = 0.00, VS 2x Se 2(1-x) The work function difference of / WSe2vdWHs decreased from approximately 210 meV to 115 meV, resulting in a heterojunction with a more matched work function. This further improved device performance, achieving a current density of -44.87 μA / μm and an on / off ratio of approximately 10. 7 The device mobility is approximately 91 cm⁻¹. 2 V -1 S -1 .

[0146] To further verify the crucial role of the adjustable work function between two-dimensional metal / semiconductor vdWHs in contact engineering, we selected MoS2, an n-type semiconductor material with a smaller work function, as the channel material. By adjusting the work function of the two-dimensional metal / semiconductor vdWHs... 2x Se 2(1-x) The alloy composition changes from x = 0.00 to x = 0.52 and then to x = 1.00, VS 2x Se 2(1-x) The work function difference of / MoS2 increases from approximately -71.5 meV to -10 meV and then to 59.3 meV, indicating that charge transfer between heterojunctions originates from the Schottky contact (x = 0.00, W) where an electron blocking layer exists at the Schottky barrier. m >W sFrom the point where there is almost no Schottky barrier, to the Ohmic contact (x = 0.52, W) m =W s Then it transforms into an ohmic contact with no Schottky barrier, forming an anti-electron blocking layer (x = 1.00, W). m <W s The electrical performance has been improved step by step.

[0147] In summary, this invention has found that, through the innovative regulation of Ts, VS can be continuously regulated. 2x Se 2(1-x) The work function, through its adjustable properties, allows for precise selection of a more suitable VS based on the characteristics of the work function of a two-dimensional basis. 2x Se 2(1-x) Deposition parameters are used to purposefully synthesize high-performance heterojunction materials.

[0148] Electricity transmission research and VS 2x Se 2(1-x) Alloy, VS 2x Se 2(1-x) / WSe2 and VS 2x Se 2(1-x) The KPFM characteristics of / MoS2vdWHs show a good match, which strongly confirms the key role of work function matching in tuning the performance of 2D semiconductor field-effect transistors. The tunable work function of two-dimensional metals and band alignment in two-dimensional metal / semiconductor heterostructures can provide new avenues for the flexible design and optimization of two-dimensional metal / semiconductor vdW heterostructures, and will lead to new applications.

Claims

1. A VS 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: VCl3, Se powder, and S powder, in a weight ratio of 1~3:9~11:1, were respectively placed in the high-temperature, medium-temperature, and low-temperature zones of the vapor deposition tube. Heating in each zone caused the raw materials to volatilize and chemically deposit on the substrate surface under the transport of a carrier gas. During this process, the alloy composition of the chemically deposited product was controlled by adjusting the temperature in the low-temperature zone, thereby controlling the work function of the product and obtaining VCl3 with different work functions. 2x Se 2(1-x) Alloy two-dimensional materials; Among them, 0 < x < 1; the temperature control range in the low-temperature zone is 170~215°C; The temperature in the high-temperature zone is 400~500°C, the temperature in the medium-temperature zone is 300~400°C, the temperature in the chemical deposition stage is 570~620°C, and the carrier gas is a hydrogen-containing atmosphere.

2. The VS as described in claim 1 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: The purity of the raw materials of VCl3, Se powder, and S powder is greater than 99%.

3. The VS as described in claim 1 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: The raw material ratio of VCl3, Se powder, and S powder is 1.5~2.5:9.5~10.5:

1.

4. The VS as described in claim 1 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: The temperature in the high-temperature zone is 470~490°C; The temperature in the medium-temperature zone is 370~390°C.

5. The VS as described in claim 1 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: The hydrogen-containing atmosphere mentioned above is a mixture of hydrogen and a protective gas.

6. The VS as described in claim 5 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: In the chemical deposition stage, the flow rate of the protective gas is 60~100 sccm, and the flow rate of hydrogen is 1~4 sccm.

7. The VS as described in claim 6 2x Se 2(1-x) A method for preparing two-dimensional alloy materials with controllable work function, characterized in that: The flow rate of the protective gas is 70~90 sccm; the flow rate of hydrogen is 2~3 sccm; the chemical deposition time is 3~20 min.

8. A VS product prepared by the method according to any one of claims 1 to 7 2x Se 2(1-x) Two-dimensional alloy materials.

9. A VS 2x Se 2(1-x) Alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction, characterized in that, The VS as described in claim 8 2x Se 2(1-x) A heterojunction material formed by an alloy two-dimensional material and an MX2 semiconductor two-dimensional material, wherein the absolute value of the difference in the work functions of the two materials is less than or equal to 100 meV; The M mentioned above is at least one of W and Mo; The X mentioned above is at least one of Se and S.

10. A VS as described in claim 9 2x Se 2(1-x) A method for preparing a heterojunction of alloy two-dimensional material / MX2 semiconductor two-dimensional material, characterized in that, A two-dimensional MX2 semiconductor material is pre-deposited on a substrate. Then, based on the work function characteristics of the MX2 semiconductor material, a VS material matching its work function is deposited on the surface of the MX2 semiconductor material using the method described in any one of claims 1 to 4. 2x Se 2(1-x) The VS alloy two-dimensional material was prepared to obtain the aforementioned VS 2x Se 2(1-x) Alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction.

11. A VS as described in claim 10 2x Se 2(1-x) The application of alloy two-dimensional materials / MX2 semiconductor two-dimensional material heterojunctions is characterized by, It is used for the preparation of electronic devices.

12. The VS as described in claim 11 2x Se 2(1-x) The application of alloy two-dimensional materials / MX2 semiconductor two-dimensional material heterojunctions is characterized by, It is used to prepare field effect transistor devices.

13. The VS as described in claim 12 2x Se 2(1-x) The application of alloy two-dimensional materials / MX2 semiconductor two-dimensional material heterojunctions is characterized by, The preparation steps of the field effect transistor device are as follows: Electron beam lithography in VS 2x Se 2(1-x) A field-effect transistor was fabricated by exposing and marking a sample on a two-dimensional alloy material, followed by depositing metal on the sample using electron beam evaporation. The metals deposited by electron beam evaporation are In and Au.

14. A field-effect transistor device, characterized in that, VS prepared by any one of claims 1 to 7 2x Se 2(1-x) Two-dimensional alloy materials.

15. The field-effect transistor device as claimed in claim 14, characterized in that, Includes the VS as described in claim 9 2x Se 2(1-x) Alloy two-dimensional material / MX2 semiconductor two-dimensional material heterojunction.

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