Preparation method of MoS2 film of EDTA-ethanolamine synergistic stable precursor

Abstract

The invention discloses a preparation method of a MoS2 film with an EDTA-ethanolamine synergistically stable precursor, which comprises the following steps: completely dissolving (NH4) 2MoS4 and EDTA in DMSO and ethanolamine to obtain a precursor solution; and obtaining a SiO2 substrate, uniformly coating the substrate with the precursor solution, drying the substrate to completely remove DMSO, and then carrying out a thermal decomposition reaction in an inert gas atmosphere until a MoS2 film is generated on the substrate. According to the preparation method, ammonium tetrathiomolybdate ((NH4) 2MoS4) is taken as a sulfur source and a molybdenum source, dimethyl sulfoxide (DMSO) is taken as a solvent, ethylenediamine tetraacetic acid (EDTA) is taken as a chelating agent, ethanolamine is taken as a cosolvent, EDTA is dissolved by ethanolamine, the stability of a solution system is remarkably enhanced based on the chelation of a large number of carboxyl groups, and the MoS2 film is prepared through high-temperature thermal decomposition of a precursor. And the film forming thickness is controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material preparation, and in particular to a method for preparing a MoS2 thin film using an EDTA-ethanolamine synergistically stabilized precursor. Background Art

[0002] Transition metal dichalcogenides have tunable band gaps, unique optical and electrical properties. As an important representative of TMDs, MoS2 is widely used in catalysis, energy storage, photovoltaics, biomedicine, gas sensing and other fields. Therefore, many researchers have carried out extensive research on the preparation of MoS2 thin films, such as mechanical exfoliation, chemical vapor deposition (CVD), hydrothermal and molybdenum precursor film sulfurization. Although some methods can also prepare large-area high-quality MoS2 films, salt-assisted CVD usually introduces impurities, and magnetron sputtering leads to high costs or poor film quality. In order to solve these problems, methods for preparing large-area, high-quality MoS2 films based on thermal decomposition of liquid precursors have developed rapidly.

[0003] To date, only a few solution systems have been used to prepare large-area MoS2 films. Among them, a simple and reproducible method for producing wafer-scale atomically thin MoS2 films has been achieved by adding ethylenediaminetetraacetic acid (EDTA) and (NH4)2MoS4 to dimethyl sulfoxide (DMSO). However, the solute in this solution system does not completely dissolve, which significantly affects the subsequent concentration control to achieve reproducible film thickness. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: how to provide a method for preparing MoS2 thin film by synergistically stabilizing the precursor with EDTA-ethanolamine, which helps to completely dissolve the solute, improve the stability of the precursor solution, and achieve controllable film thickness.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing a MoS2 thin film using an EDTA-ethanolamine synergistically stabilized precursor comprises the following steps: completely dissolving (NH4)2MoS4 and EDTA in DMSO and ethanolamine to obtain a precursor solution; obtaining a SiO2 substrate, uniformly coating the precursor solution on the substrate, drying the substrate to completely remove DMSO, and then performing a thermal decomposition reaction in an inert gas atmosphere until a MoS2 thin film is generated on the substrate.

[0007] As an optimization, the molar ratio of (NH4)2MoS4 to EDTA is 1:(0.5-2).

[0008] As an optimization, after (NH4)2MoS4 and EDTA were added to DMSO and ethanolamine, ultrasonic oscillation was used to dissolve (NH4)2MoS4 and EDTA.

[0009] As an optimization, the substrate is first placed in acetone, anhydrous ethanol and deionized water in turn for ultrasonic treatment, and then the substrate surface is blown clean with nitrogen. Finally, the substrate is placed in an ozone atmosphere for a period of time and then taken out before coating with the precursor solution.

[0010] As an optimization, the precursor solution is coated on the substrate by spin coating.

[0011] As an optimization, the substrate is rotated at a speed of 1000-2000 rpm, and the precursor solution is dripped on it so that the precursor solution completely covers the substrate surface. Then the substrate is rotated at a speed of 3000-6000 rpm to form a film of the precursor solution on the substrate surface.

[0012] As an optimization, after the MoS2 thin film is formed on the substrate, the substrate with the MoS2 thin film is annealed by transporting sulfur vapor using an inert gas as a carrier gas.

[0013] Compared with the existing technology, the present invention has the following beneficial effects: the present invention uses ammonium tetrathiomolybdate ((NH4)2MoS4) as a sulfur source and a molybdenum source, dimethyl sulfoxide (DMSO) as a solvent, ethylenediaminetetraacetic acid (EDTA) as a chelating agent, and ethanolamine as a co-solvent. Ethanolamine is used to dissolve EDTA, and the stability of the solution system is significantly enhanced based on the chelation effect of a large number of carboxyl groups. In this way, wafer-level MoS2 thin films are prepared by high-temperature thermal decomposition of the precursor, and the film thickness can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The SEM morphology of MoS2 film at 100k magnification is shown;

[0015] Figure 2 This is the EDS spectrum of Mo element in MoS2 film;

[0016] Figure 3 This is the EDS spectrum of the S element of MoS2 film;

[0017] Figure 4 This is a low-magnification TEM morphology characterization image of MoS2 film;

[0018] Figure 5 High-resolution HRTEM characterization image of MoS2 film in region I;

[0019] Figure 6 This is the enlarged image of the (100) crystal plane after DigitalMicrograph processing;

[0020] Figure 7 The (100) crystal plane lattice fringes after DigitalMicrograph processing;

[0021] Figure 8 is the statistical diagram of the lattice fringe spacing of the (100) crystal plane;

[0022] Figure 9 High-resolution HRTEM characterization of MoS2 film in region II;

[0023] Figure 10 This is an enlarged image of the (110) crystal plane after DigitalMicrograph processing;

[0024] Figure 11 The (110) crystal plane lattice fringes after DigitalMicrograph processing;

[0025] Figure 12 is the electron diffraction pattern of MoS2 thin film;

[0026] Figure 13 This is the Raman spectrum of MoS2 film;

[0027] Figure 14 This is the XPS overall spectrum of MoS2 film. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] In this specific embodiment, a method for preparing a MoS2 thin film using an EDTA-ethanolamine synergistically stabilized precursor is provided, wherein (NH4)2MoS4 and EDTA are completely dissolved in DMSO and ethanolamine to obtain a precursor solution; a SiO2 substrate is obtained, the precursor solution is evenly coated on the substrate, the precursor solution is dried to completely remove DMSO, and then a thermal decomposition reaction is carried out in an inert gas atmosphere until a MoS2 thin film is generated on the substrate.

[0030] In this specific embodiment, the molar ratio of (NH4)2MoS4 to EDTA is 1:(0.5-2).

[0031] In this specific embodiment, after (NH4)2MoS4 and EDTA are added to DMSO and ethanolamine, ultrasonic oscillation is used to dissolve (NH4)2MoS4 and EDTA.

[0032] In this specific embodiment, the substrate is first placed in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic treatment, then the substrate surface is cleaned with nitrogen, and finally the substrate is placed in an ozone atmosphere for a period of time and then taken out and coated with the precursor solution.

[0033] In this specific embodiment, the precursor solution is coated on the substrate by spin coating.

[0034] In this specific embodiment, the substrate rotates at a speed of 1000-2000 rpm, and the precursor solution is dripped thereon so that the precursor solution completely covers the substrate surface. Then the substrate is rotated at a speed of 3000-6000 rpm to form a film of the precursor solution on the substrate surface.

[0035] In this embodiment, after a MoS2 thin film is formed on a substrate, the substrate with the MoS2 thin film is annealed using sulfur vapor delivered by an inert gas as a carrier gas. The sulfur vapor can compensate for sulfur vacancy defects caused by the high temperature during the MoS2 production process, thereby improving the material quality.

[0036] In the specific implementation process, (NH4)2MoS4 and EDTA are mixed in a molar ratio of 1:1 and added to a mixed solution of DMSO and ethanolamine, and ultrasonic oscillation is performed until the solution is completely clarified without precipitation; a 4-inch wafer-level SiO2 / Si substrate with a SiO2 layer thickness of 300nm is taken, and ultrasonic treatment is performed with acetone, anhydrous ethanol and deionized water for 10 minutes respectively, and then the substrate is purged with nitrogen several times, and finally placed in an ozone cleaner for 15 minutes to enhance the hydrophilicity of the substrate surface; the cleaned substrate is placed on a glove box on a sizing machine, and the position of the substrate is adjusted at a low speed so that it is roughly located in the center of the sizing machine. This process requires multiple adjustments; after the substrate position is adjusted, it is purged several times; the precursor solution configured above (the precursor solution used here) is added dropwise The concentration is 200mM), and the precursor solution is spun at a low speed of 1000rpm for 9s to ensure that the precursor solution can completely cover the entire wafer-level substrate surface, and then spun at a high speed of 3000rpm for 30s to form a film; the spun-coated substrate is placed on a 150℃ heating table and heated for 15min to remove the DMSO organic solvent; the substrate is placed in a tube furnace, purged with argon gas multiple times to exclude oxygen, and then the temperature is raised from room temperature to 800℃ in 100sccm argon and maintained for 30min, and then slowly cooled; the prepared MoS2 thin film device is placed in a two-temperature zone tube furnace again for atmospheric pressure sulfurization, 0.2g of sulfur powder is placed in the first temperature zone and heated at 200℃, and the MoS2 thin film prepared by thermal decomposition is placed in the second temperature zone, heated at 800℃, and maintained at 100sccm argon.

[0037] The prepared MoS2 film was characterized by AFM. The entire area was 5μm×5μm in size, and the roughness was only within 10nm in the entire area, indicating that the MoS2 film prepared by this application has high quality. Figure 1 The MoS2 film was characterized by SEM morphology. The film showed tiny crystal particles at a magnification of 100k, so the film prepared in this application was of good quality. Figure 2 and Figure 3 Since the EDS peak positions of Mo and S are very close, only the uniform distribution of elements is observed there, and no element ratio analysis is performed. The successful preparation of large-area uniform MoS2 film is proved by element mapping.

[0038] MoS2 thin films were analyzed using transmission electron microscopy. Figure 4 Similarly, this application also conducted a low-magnification morphological exploration of the prepared MoS2 film. The white area is the small holes on the micro-grid copper mesh used in TEM. The left side of the figure is the area without material, and the right side is the MoS2 film. The film has no obvious defects. Under high-resolution HRTEM, the MoS2 film lattice was analyzed. Figure 5The red box position in the middle is transformed by Fourier transform and inverse Fourier transform in DigitalMicrograph software and the noise is eliminated, as shown in the figure. Figure 6 and Figure 7 , after such Figure 8 The statistical calculation of the lattice fringe spacing is 0.2707nm. Comparing the lattice spacing with the PDF card JCPDS NO.75-1539 (2H MoS2) in jade, it is found that it is roughly consistent with the lattice spacing of the (100) crystal plane, indicating that this is the (100) crystal plane of MoS2. Figure 9 The red box has a messy morphology at high resolution. It is preliminarily speculated that there is more than just a (100) face lattice. After Fourier transform and inverse Fourier transform in DigitalMicrograph software and noise elimination, the following is shown: Figure 10 and Figure 11 , we found other crystal planes at this location. After statistical analysis of the lattice fringes and comparison with the PDF card JCPDS NO.75-1539 in jade, we confirmed that there are not only (100) crystal planes but also (110) crystal planes with a lattice spacing of 0.158nm. Finally, as Figure 12 As shown, after distance measurement and analysis using DigitalMicrograph software, it was also concluded that there were mainly (100) crystal planes and (110) crystal planes, demonstrating that the MoS2 film prepared using the method of the present application has polycrystalline properties.

[0039] The Raman spectrum of MoS2 thin film was measured using an excitation wavelength of 532 nm. Figure 13 As shown, there are three main peaks in the figure, two of which are caused by the in-plane E 2g and out-of-plane A 1g Two characteristic modes, located at 382cm -1 and 406cm -1 , followed by the Raman characteristic peak of the Si-Si bond of the substrate, located at 520 cm -1 For single to four-layer MoS2 films, the E 2g The peak frequency is from 384.7cm -1 to 382.4cm -1 , E 2g The peak frequency is from 402.7cm -1 to 406.7cm -1 This is because the interlayer van der Waals forces in MoS2 suppress the atomic vibrations causing E 2g Blue shift, and A 1gThe red shift may be due to the stacking-induced structural changes in multilayer MoS2 or the changes in the atomic vibrations dominated by long-range Coulomb interlayer interactions, with the increase in interlayer van der Waals forces playing a secondary role. The MoS2 film prepared here was prepared by spin coating from a 100mM concentration precursor solution. From the Raman analysis, the film is a multilayer film. Then XPS was used to analyze the composition of the film. The total spectrum is as follows Figure 14 There are no other element peaks in the figure, only weak peaks originating from the Si and O signals of the substrate. Apart from that, there is only the characteristic peak of MoS2.

[0040] The following table 1 is a comparison of MoS2 thin film preparation methods:

[0041]

[0042] Table 1

[0043] In summary, this application proposes a method of using ethanolamine to dissolve EDTA to improve uniformity for the simple and controllable preparation of large-area high-quality MoS2 films. Finally, wafer-level MoS2 films are prepared by high-temperature thermal decomposition of the precursor film, providing new ideas for the preparation of high-quality two-dimensional films by low-cost liquid-phase precursor spin coating.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present invention that do not depart from the purpose and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a MoS2 thin film by synergistically stabilizing a precursor using EDTA and ethanolamine, characterized in that: Completely dissolve (NH4)2MoS4 and EDTA in DMSO and ethanolamine to obtain a precursor solution; obtain a SiO2 substrate, evenly coat the precursor solution on the substrate, dry it to completely remove DMSO, and then perform a thermal decomposition reaction in an inert gas atmosphere until a MoS2 film is generated on the substrate.

2. The method for preparing a MoS2 thin film by synergistically stabilizing a precursor using EDTA and ethanolamine according to claim 1, wherein: The molar ratio of (NH4)2MoS4 to EDTA is 1:(0.5~2).

3. The method for preparing a MoS2 thin film by synergistically stabilizing a precursor using EDTA and ethanolamine according to claim 1, wherein: After (NH4)2MoS4 and EDTA are added into DMSO and ethanolamine, ultrasonic oscillation is used to dissolve (NH4)2MoS4 and EDTA.

4. The method for preparing a MoS2 thin film by synergistically stabilizing a precursor using EDTA and ethanolamine according to claim 1, wherein: First, the substrate is placed in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic treatment, then the substrate surface is cleaned with nitrogen, and finally the substrate is placed in an ozone atmosphere for a period of time and then taken out, and then the precursor solution is coated.

5. The method for preparing a MoS2 thin film by synergistically stabilizing a precursor using EDTA and ethanolamine according to claim 1, wherein: The precursor solution is coated on the substrate by spin coating.

6. The method for preparing a MoS2 thin film using an EDTA-ethanolamine synergistically stabilized precursor according to claim 5, wherein: The substrate rotates at a speed of 1000~2000rpm, and the precursor solution is dripped on it so that the precursor solution completely covers the surface of the substrate. Then the substrate is rotated at a speed of 3000~6000rpm to form a film of the precursor solution on the surface of the substrate.

7. The method for preparing a MoS2 thin film using an EDTA-ethanolamine synergistically stabilized precursor according to claim 1, wherein: After the MoS2 thin film is formed on the substrate, the substrate with the MoS2 thin film is annealed by transporting sulfur vapor using an inert gas as a carrier gas.

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