Method for the preparation of two-dimensional lateral heterojunctions on the basis of selective reactions on transition metal chalcogenide matrices

Abstract

The application discloses a method for preparing a two-dimensional lateral heterojunction on the basis of selective reaction on a transition metal chalcogenide substrate, and belongs to the technical field of nanometer material preparation. The specific steps are as follows: a transition metal chalcogenide film is irradiated by laser direct writing, the transition metal chalcogenide film material is oxidized, and an oxidation area and a non-oxidation area constitute a non-oxidation area-oxidation area heterojunction; then, the sample is globally heated by a gas phase deposition method, the oxidation area is rich in defects and has reactivity, the reaction process is selectively caused to occur in the oxidation area, a third phase area is formed, the non-oxidation area remains unchanged, and a non-oxidation area-third phase area two-dimensional lateral heterojunction is obtained. The oxidation material obtained by laser irradiation is rich in defects and has high activity and selectivity, so that in the gas phase deposition process, the growth reaction is selectively caused to occur in the oxidation area, the non-oxidation area which is not irradiated by laser remains unchanged, and a TMD-TMD' two-dimensional lateral heterojunction is formed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial preparation, and particularly relates to a method for preparing a two-dimensional lateral heterojunction on a transition metal chalcogenide base based on a selective reaction. BACKGROUND

[0002] Transition metal dichalcogenides (TMDs) have attracted much attention due to their unique mechanical, optical and electrical properties. Two-dimensional (2D) TMD heterostructures are essential components in emerging 2D electronic devices. In recent years, these heterostructures have been realized by a variety of methods, including van der Waals stacking, epitaxial growth and laser-assisted growth. However, these methods cannot guarantee the ability to design patterns while not introducing pollution in the synthesis process. In addition, the existing laser-assisted in-situ growth method is very low in efficiency because each point needs a certain time to crystallize under laser irradiation, and is not suitable for large-scale growth. Therefore, in order to truly realize large-scale integrated circuits based on 2D materials, it is urgent to develop an efficient scalable method for manufacturing 2D heterostructure arrays, whether vertical heterojunctions or planar heterojunctions. SUMMARY

[0003] In order to solve the above problems, the application provides a method for preparing a two-dimensional lateral heterojunction on a transition metal chalcogenide base based on a selective reaction, which specifically comprises the following steps:

[0004] 1) irradiating a transition metal chalcogenide film by laser direct writing, and oxidizing the transition metal chalcogenide film material, so as to form a non-oxidation zone-oxidation zone heterojunction composed of an oxidation zone and a non-oxidation zone; the thickness of the oxidation zone is 0.5-10 nm; and the transition metal chalcogenide film is prepared on a base;

[0005] 2) globally heating the sample obtained in step 1) by a vapor deposition method, and since the oxidation zone is rich in oxygen vacancy defects and has reactivity, a reaction process selectively occurs in the oxidation zone, a third phase zone is formed, the non-oxidation zone remains unchanged, and a non-oxidation zone-third phase zone two-dimensional lateral heterojunction is obtained, wherein the non-oxidation zone-third phase zone two-dimensional lateral heterojunction has different patterns, including a curved line pattern, a straight line pattern and an array pattern.

[0006] The reaction process in step 2) includes a selenization reaction, a tellurization reaction or a sulfidation reaction.

[0007] The material of the transition metal chalcogenide film in step 1) includes MoS2, MoSe2, MoTe2, WS2, WSe2 or NbS2.

[0008] Further, the material of the oxidation zone is MoO x , WO xor NbO x ;

[0009] Further, the third phase region material generated by the corresponding selenization reaction is MoSe2, WSe2 or NbSe2, the third phase region material generated by the tellurization reaction is MoTe2, WTe2 or NbTe2, and the third phase region material generated by the sulfuration reaction is MoS2, WS2 or NbS2.

[0010] The thickness of the transition metal chalcogenide film is 0.5-10 nm;

[0011] Further, the thickness of the transition metal chalcogenide film is 0.5-5 nm or 0.7-10 nm;

[0012] Further, the thickness of the transition metal chalcogenide film is 0.5-1 nm.

[0013] The method for preparing the transition metal chalcogenide film on the substrate comprises the following steps:

[0014] a1) sequentially placing the substrate into deionized water, acetone and isopropanol for ultrasonic cleaning, and then blowing dry with nitrogen; placing it in a double-end opening quartz boat with transition metal oxide, and placing it in the reaction cavity of a tube furnace;

[0015] b1) placing a quartz boat containing chalcogen single element on the upstream of the gas flow of the substrate;

[0016] c1) after washing with argon in the tube furnace, passing 5 sccm of argon, and after the gas flow is stable, heating the chalcogen single element and the transition metal oxide respectively to obtain a monolayer transition metal chalcogenide film grown on the substrate.

[0017] The chalcogen single element is sulfur powder, tellurium powder or sulfur powder;

[0018] Further, when the chalcogen single element is sulfur powder and the transition metal oxide is molybdenum trioxide, the sulfur powder and the molybdenum trioxide are heated to a temperature of 130-140℃ and 645-655℃ respectively, and the temperature is kept constant for 5-10 minutes.

[0019] The substrate in step a1) is a SiO2-Si substrate.

[0020] The laser direct writing process comprises the following specific steps:

[0021] The required pattern is connected with the laser direct writing device by software,

[0022] The laser power is set to 1-1000 kW / mm 2 ;

[0023] Further, the laser power is 11-1000 kW / mm2 or 1~500kW / mm 2 ;

[0024] Further, the laser power is 1~11kW / mm 2 .

[0025] The laser scanning speed is 1um / s~100m / s.

[0026] Further, the laser scanning speed is 1um / s~50m / s.

[0027] Further, the laser scanning speed is 1um / s~1m / s.

[0028] The wavelength of the laser is 365-780nm.

[0029] Step 1) by controlling the laser to oxidize the desired pattern area on the transition metal chalcogenide film, the transition metal chalcogenide film material TMD is oxidized to form an ultra-thin TMO oxidation area with high reaction activity, that is, a patterned TMD-TMO heterojunction is formed.

[0030] The selenium reaction, tellurium reaction or sulfur reaction is specifically as follows: the sample obtained in step 1) is placed in a growth cavity, selenium powder, tellurium powder or sulfur powder is used as a precursor, a vapor deposition method is adopted, growth conditions are set, and the selenium reaction, tellurium reaction or sulfur reaction is performed.

[0031] Further, the selenium powder is used as a precursor, a vapor deposition method is adopted, the furnace temperature is controlled to be 700 DEG C, the temperature of the precursor selenium powder is 340 DEG C, and the growth atmosphere with a volume ratio of 10% H2 and 90% Ar is grown for 10 min.

[0032] The TMO oxidation area obtained by laser irradiation in step 2) has a defect morphology and extremely high reaction activity, so that the subsequent seleniumization, tellurization or sulfurization reaction has very high selectivity, and during the reaction process, only the TMO oxidation area reacts to form a TMD' third phase area, and the non-oxidized TMD area not irradiated by the laser remains unchanged during the seleniumization process.

[0033] The method of the application synthesizes a TMD-TMD' lateral heterostructure by a two-step method of completely oxidizing the specified area of the TMDs material by laser and then selectively seleniumizing in-situ. The completely oxidized area is quickly defined by directly performing a high-intensity laser direct writing operation on the TMD material, and then the atomic-level thick and high-reactivity oxidation product is used as a precursor to be seleniumized, tellurized or sulfurized by heating the whole through a tube furnace.

[0034] In this process, only the high reactivity TMO region is reduced or synthesized into the third phase TMD' material, while the original TMD region can remain unchanged during the growth process, and finally a TMD-TMD' heterojunction is formed. Unlike the ordinary CVD growth method, since the growth precursor here is the patterned TMO region, which has an atomic level thickness and is often rich in oxygen vacancy defects and has high reactivity, the reduction reaction can occur at a growth temperature of 50-200 DEG C lower than the conventional method. At this time, the original TMD region (the region not oxidized in advance) is not irradiated by laser, and itself does not contain defect structure, and the reactivity is low, so the conditions required for chemical vapor deposition reaction are more stringent, and the required reaction temperature is higher, and can remain intact without reaching the reaction temperature of the conventional synthesis method with powder oxide as the precursor. Therefore, this reaction process has high selectivity, and the reaction only occurs in the TMO region. Therefore, the laser oxidation process is the determining step for controlling the shape, position and size of the heterojunction, unlike the conventional growth method which relies on the nucleation and growth of the material itself.

[0035] A two-dimensional lateral heterojunction material prepared on the basis of selective reaction on a transition metal chalcogenide substrate.

[0036] A method for preparing a two-dimensional lateral heterojunction on the basis of selective reaction on a transition metal chalcogenide substrate for the application of preparing a field effect transistor.

[0037] Further, 4wt% of polymethyl methacrylate material PMMA is spin-coated on the surface of the MoS2-MoSe2 heterostructure sample, and the sample surface is exposed to light by an electron beam exposure system NPGS to make a source and drain pattern. Then, 20nm Ti and 50nm Au are evaporated on the sample surface by electron beam evaporation to make a transistor device based on the MoS2-MoSe2 heterostructure.

[0038] Unlike the conventional chemical vapor deposition (CVD) growth method which can only grow at the edge or surface active site, the TMO region prepared by laser irradiation in this method has high reactivity, and complex patterns and patterns with curvature, including circles, ellipses, or the required patterns of smiley faces and trees, can be designed, which cannot be realized by traditional CVD growth method. Laser is equivalent to a brush, and TMD material is equivalent to a drawing board. Controlling the path of the laser can define the required pattern, whether it is a triangle, a quadrilateral, a polygon, a circle, or other irregular patterns or arrays.

[0039] The beneficial effects of the present application are:

[0040] 1. The present application separates the patterning process and the heterojunction growth process, synthesizes TMD-TMD' heterojunction arrays with artificially designed complex patterns in a two-step method, effectively prepares heterojunction arrays with irregular patterns, and effectively improves the synthesis efficiency of the heterojunction array.

[0041] 2. The ultra-thin oxidation zone material obtained by laser irradiation is rich in defects and has extremely high reactivity and selectivity, so that in the subsequent vapor deposition process, the growth reaction only selectively occurs in the oxidation zone, and the non-oxidation zone not irradiated by the laser remains unchanged, forming a TMD-TMD' two-dimensional lateral heterojunction.

[0042] 3. The method separates the pattern forming step and the chemical vapor deposition reaction step, and the heterojunction boundary shape, size and position can be controlled by laser, realizing array preparation. The whole process becomes more efficient and time-saving, making mass production promising, and the method is simple and controllable, paving the way for rapid large-scale integration of devices based on 2D heterostructures.

[0043] 4. The method overcomes the defects of traditional growth methods relying on nucleation growth of the material itself, and the process of obtaining high-reactivity oxidation zone material by laser oxidation gives the subsequent selenization, tellurization or sulfuration reaction extremely high selectivity, which is a key step to control the shape, position and size of the heterojunction. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The flow chart of the heterojunction synthesis of the present application and the corresponding micrograph;

[0045] Figure 2 Raman spectrum characterization of MoS2-MoSe2 heterojunction synthesized in Example 1 of the present application;

[0046] Figure 3 Raman scan map characterization (straight line) of MoS2-MoSe2 heterojunction synthesized in Example 1 of the present application;

[0047] Figure 4 Raman scan map characterization (curve) of MoS2-MoSe2 heterojunction synthesized in Example 1 of the present application;

[0048] Figures 5a-5e Comparison chart of Auger characterization of S, Mo, O, Se and Si elements before and after treatment in the synthesis process in Example 1 of the present application;

[0049] Figure 6a Schematic diagram of a transistor device based on MoS2-MoSe2 heterostructure synthesized in Example 4 of the present application;

[0050] Figure 6bThe heterojunction device in Example 4 of the present application exhibits p-type as a transistor.

[0051] Figure 7 MoS2-MoO x Microscopic image of a heterojunction letter pattern;

[0052] Figure 8 MoS2-MoO x Microscopic image of a heterojunction smiley face pattern;

[0053] Figure 9 MoS2-MoO x Microscopic image of a heterojunction tree pattern;

[0054] Figure 10 MoS2-MoO x Microscopic image of a heterojunction array pattern array. DETAILED DESCRIPTION

[0055] The present application will be further described in conjunction with the accompanying drawings and specific examples:

[0056] Example 1

[0057] Preparation of a transition metal chalcogenide thin film on a substrate:

[0058] a1) A SiO2-Si substrate was used as a base, with the thickness of the silicon oxide being 300 nm, and the base was sequentially subjected to ultrasonic cleaning in deionized water, acetone and isopropanol, and then dried with nitrogen; it was placed in a double-end opening quartz boat that had been placed in MoO3, and was placed in a tube furnace reaction cavity;

[0059] b1) A quartz boat containing sulfur powder was placed on the upstream airflow of the base;

[0060] c1) After purging the tube furnace with argon, 5 sccm of argon was introduced, and after the airflow was stabilized, the sulfur powder and MoO3 were heated to temperatures of 130-140°C and 645-655°C, respectively, and were kept at constant temperature for 5-10 minutes, to obtain a monolayer MoS2 thin film grown on the base, with a film thickness of 0.7 nm.

[0061] Example 2

[0062] Appendix Figure 1 a-1c shows a schematic diagram of the heterojunction preparation process, which is synthesized and prepared according to the process shown in the figure.

[0063] The specific steps for preparing the MoS2-MoSe2 heterojunction are as follows:

[0064] 1) Laser direct writing process:

[0065] The desired pattern was connected to the laser direct writing equipment using software. Using a TANGO translation stage and control software, the monolayer MoS2 thin film grown on the substrate of Example 1 was placed at the starting point of the scanned image. A 532nm wavelength laser was used along the specified path of the desired pattern at a speed of 20.4kW / mm². 2 Irradiation scanning was performed on the surface of a monolayer MoS2 film at a power of 10 μm / s, resulting in ultrathin, highly reactive, and patterned MoO2 films. x Oxidized regions, total oxidized regions (TMO), and non-oxidized regions (TMD) co-form MoS2-MoO with the desired pattern on the matrix. x Samples with heterostructures (TMD-TMO heterojunction).

[0066] This step controls the laser to oxidize the desired patterned region on the transition metal chalcogenide thin film, oxidizing the TMD material to form an ultrathin TMO region with high reactivity, that is, forming a patterned TMD-TMO heterojunction.

[0067] 2) Using chemical vapor deposition, the sample obtained in step 1) is placed in the growth chamber of the chemical vapor deposition system. Selenium powder is used as the precursor. The furnace temperature is controlled at 700℃ and the precursor temperature is controlled at 340℃. The selenization reaction is carried out in a growth atmosphere with a volume ratio of 10% H2 and 90% Ar for 10 min.

[0068] Step 2) The reaction exhibits excellent selectivity, only reacting with highly reactive MoO. x The oxidized region (TMO) is reduced to MoSe2 (TMD'), while the non-oxidized region (TMD) of MoS2 remains unchanged, ultimately forming a MoS2-MoSe2 heterojunction (TMD-TMD' transverse heterostructure).

[0069] In step 2), although the sample prepared in Example 2 is placed in the growth chamber, the growth reaction process only reduces or synthesizes the highly reactive TMO region into the third phase TMD' material, while the unreacted TMD region remains unchanged during the growth process, eventually forming a TMD-TMD' heterojunction.

[0070] Figure 1 d- Figure 1 f is the corresponding Figure 1 a- Figure 1 c. During the synthesis process, the non-oxidized region contains MoS2, and the oxidized region contains MoO2. x Microscopic images of MoSe2 in the third phase region taken with an Olympus microscope.

[0071] The triangular MoS2-MoO x Raman spectra of the heterojunction (i.e. TMD-TMO heterojunction) are shown in Figure 2 From the spectra, it can be seen that the oxidized region MoO x After selenization growth, the third phase region MoSe2 is generated, while the non-oxidized region MoS2 remains intact, proving the synthesis of MoS2-MoSe2 heterojunction (i.e. TMD-TMD' heterojunction).

[0072] MoS2-MoO x Raman scanning images of the heterojunction are shown in Figure 3 and Figure 4 . Figure 3 It is shown that the pattern heterostructure formed by straight lines can be prepared by the method, Figure 4 It is shown that the pattern heterostructure formed by curves can be prepared by the method, and the smaller the gray scale of the region in the figure, the stronger the corresponding Raman peak, that is, the more the material corresponding to the Raman peak in this region. It is proved that the method has the characteristic of flexible patterning.

[0073] MoS2-MoO x Auger characterization of the heterojunction formation process is shown in Figures 5a-5e From the element distribution, it can be seen that the oxidized region MoO x After selenization growth, the third phase region MoSe2 is generated, while the original MoS2 non-oxidized region does not undergo selenization, proving the synthesis of MoS2-MoSe2 heterojunction, which is consistent with the results of the Raman scanning images, further proving that the method has good selectivity.

[0074] Example 3

[0075] Unlike the ordinary CVD growth method which can only grow at the edge or surface active sites, since the growth precursor here is a laser-patterned TMO region, this region has only atomic thickness and has high reactivity due to its defect-richness, so the reduction reaction can occur at a growth temperature of about 50-200°C lower than the conventional method. At this time, the TMD region (non-oxidized region) can remain intact because it does not reach the reaction temperature of the conventional synthesis method using powder oxides as precursors. Therefore, this reaction process has high selectivity, and the reaction only occurs in the TMO region.

[0076] The present application overcomes the complex patterns and patterns with curvature that cannot be realized by the conventional CVD growth method, Figure 7 , Figure 8 , Figure 9 andFigure 10 Different patterns of heterostructure materials prepared by the method are shown, including letters, smiley faces, trees, array and other patterns. In the method, the laser is equivalent to a brush, and the TMD material is equivalent to a drawing board. The path of the laser is controlled to define the required pattern, whether it is a triangle, a quadrilateral, a polygon, a circle, or other irregular shapes or arrays.

[0077] Example 4

[0078] The method of the present application is used to prepare a field effect transistor, and the specific steps are as follows:

[0079] A 4wt% polymethacrylate liquid material PMMA is spin-coated on the surface of the MoS2-MoSe2 heterostructure sample, and the surface of the sample is exposed to light using an electron beam exposure system (NPGS) to make source and drain patterns. Then 20nm Ti and 50nm Au are evaporated on the surface of the sample by electron beam evaporation to make a transistor device based on the MoS2-MoSe2 heterostructure, as shown in Figure 6a .

[0080] The electrical property measurements are performed on a Casecade Microtech MPS150 probe station and an Agilent B1500 semiconductor parameter analyzer. Figure 6b The heterojunction device of this example is shown to exhibit p-type as a transistor.

[0081] Example 7

[0082] Other heterojunction structure materials and related parameters of the preparation process are listed in Table 1.

[0083] Table 1 Composition and preparation parameters of heterojunction materials of Examples 5-15

[0084]

[0085]

[0086] Of course, the present application can have various embodiments, and those skilled in the art can make various corresponding changes and modifications based on the disclosure of the present application without departing from the spirit and essence of the present application.

[0087] Those skilled in the art can make various corresponding changes and modifications based on the disclosure of the present application, and these corresponding changes and modifications shall all fall within the protection scope of the claims of the present application.

Claims

1. A method for producing a two-dimensional lateral heterojunction on a transition metal chalcogenide matrix based on selective reaction, characterized in that, Specifically comprising the following steps: 1) irradiating the transition metal chalcogenide film with laser direct writing, the transition metal chalcogenide film material is oxidized, and the oxidation zone and the non-oxidation zone form a non-oxidation zone-oxidation zone heterojunction; the transition metal chalcogenide film is prepared on a substrate; 2) placing the sample obtained in step 1) into a growth cavity, using selenium powder, tellurium powder or sulfur powder as a precursor, and using vapor deposition method to carry out a selenization reaction, a tellurization reaction or a sulfurization reaction; since the oxidation zone is rich in oxygen vacancy defects and has reactivity, the selenization reaction, the tellurization reaction or the sulfurization reaction selectively occurs in the oxidation zone, forming a third phase zone, and the non-oxidation zone remains unchanged, obtaining a non-oxidation zone-third phase zone two-dimensional lateral heterojunction.

2. The method for preparing two-dimensional lateral heterojunctions on a transition metal chalcogenide matrix based on selective reaction according to claim 1, characterized in that, The material of the transition metal chalcogenide film in step 1) includes MoS2, MoSe2, MoTe2, WS2, WSe2 or NbS2.

3. The method for fabricating two-dimensional lateral heterojunctions on transition metal chalcogenide hosts by selective reaction according to claim 1, characterized in that, The thickness of the transition metal chalcogenide film is 0.5-10 nm.

4. The method for preparing two-dimensional lateral heterojunctions on a transition metal chalcogenide matrix based on selective reaction according to claim 1, characterized in that, The method for preparing the transition metal chalcogenide film on the substrate comprises the following steps: a1) sequentially placing the substrate into deionized water, acetone and isopropanol for ultrasonic cleaning, and blowing dry with nitrogen; placing the substrate into a double-end opening quartz boat containing transition metal oxide, and placing the quartz boat into a tube furnace reaction cavity; b1) placing a quartz boat containing chalcogen elemental substance on the heating zone upstream of the gas flow of the substrate; c1) after washing with argon in the tube furnace, passing 5 sccm of argon, and after the gas flow is stable, heating the chalcogen elemental substance and the transition metal oxide respectively to obtain a monolayer transition metal chalcogenide film grown on the substrate.

5. The method for preparing two-dimensional lateral heterojunctions on a transition metal chalcogenide matrix based on selective reaction according to claim 4, characterized in that, The chalcogen elemental substance is selenium powder, tellurium powder or sulfur powder.

6. The method for fabricating two-dimensional lateral heterojunctions on a transition metal chalcogenide matrix based on selective reaction according to claim 1, characterized in that, The laser direct writing process step is: using the required pattern with the laser direct writing device, placing the transition metal chalcogenide film at the starting point of the scanning pattern, and irradiating and scanning the film surface according to the specified path of the required pattern; the laser power is 1-1000 kW / mm 2 , the laser scanning speed is 1 μm / s-100 m / s, and the laser wavelength is 365-780 nm.

7. A two-dimensional lateral heterojunction material prepared on the basis of selective reaction on the transition metal chalcogenide substrate according to claim 1.

8. Application of the method for preparing a two-dimensional lateral heterojunction on the basis of selective reaction on the transition metal chalcogenide substrate according to claim 1 to the preparation of a field effect transistor.

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