CN112593205A - Method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water - Google Patents

Abstract

The invention discloses a method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water. The method comprises the steps of firstly carrying out oxygen plasma bombardment on a growth substrate, activating the surface of the substrate, spin-coating a PTAS organic dye to assist nucleation to obtain a spin-coated PTAS growth substrate, and simultaneously carrying out MoO₃/NH₄OH solution is spin-coated on a substrate and annealed at high temperature to obtain annealed MoO₃A source substrate, finally using a dual temperature zone tube furnace, placing sulfur powder at the upstream of the air flow, and annealing the MoO₃The source substrate and the growth substrate of the spin-coating PTAS are alternately placed at the downstream of the airflow to grow to obtain a large surfaceA layer of molybdenum disulfide is deposited. The method has the advantages of less consumption of solid growth source, good repeatability and high stability, and the prepared molybdenum disulfide has high purity and obviously increased crystal domain size, and is beneficial to subsequent material characterization, transfer and device construction.

Description

Method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water

Technical Field

The invention belongs to the field of preparation of single-layer transition metal chalcogenide materials, and relates to a method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water.

Background

The two-dimensional transition metal chalcogenide has a special energy band structure, has application prospects in various fields of electronics, optoelectronics, valley electronics and the like, and brings about wide attention in the fields of basic research and industrial application. With the rise and development of nanotechnology, chemical vapor deposition technology is widely used for preparing low-dimensional nanomaterials as a material science synthesis method.

The chemical vapor deposition technology mainly utilizes a gas-phase compound or a simple substance containing a film element to carry out chemical reaction on the surface of a substrate to generate a film, and is used for obtaining a large-area single-layer transition metal chalcogenide MX₂(MX₂: m is Mo or W; x ═ S, Se, Te, etc.) is one of the most effective methods, and the synthesized sample has the advantages of uniform thickness, good continuity, good crystal quality, etc. Molybdenum disulfide (MoS) produced at the earliest time₂) For example, the chemical vapor deposition method produces single-layer MoS₂The technical route of (2) can be divided into two paths: one is a "two-step process" in which elemental molybdenum or its oxide is first deposited on a substrate and then converted to MoS by sulfidation₂(ii) a The second is a 'one-step method', the gas molybdenum source and the sulfur source directly generate MoS on the substrate through chemical reaction₂. In 2014, Xi Ling et al system analyzed as F₁₆Precursors represented by CuPc, PTAS, PTCDA and CuPc are in MoS₂The chemical vapor deposition process assists in nucleation, but due to uneven spin coating of the precursor, the maximum value of the lateral dimension of the synthesized sample is about 50 μm, and the problems of uneven sample thickness, insufficiently clean sample surface and the like exist (Nano Lett.,2014,14: 464-. At present, chemical vapor deposition is usedMoS formation₂The technique of (1) is relatively mature, but the nucleation density is too high, and the sample size is small (single-layer MoS)₂Sample size stays on the order of a few to tens of microns). How to obtain a monolayer sample with larger size still adopts the chemical vapor deposition method to prepare MoS₂The research focus and the technical difficulty of (1).

Disclosure of Invention

Aiming at the problems, the invention provides a method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water.

MoS preparation by traditional chemical vapor deposition method₂Using MoO₃The powder and S powder are used as solid growth source, the reaction mechanism is that the reactant is placed in high temperature environment to form vapor precursor, and sulfur vapor is made to react with MoO by means of its strong reducibility₃Steam reaction to produce MoS₂And deposited onto a substrate. The film crystal grows outwards by taking the nucleus as a center, and a large-area two-dimensional film is gradually generated. However, due to the higher nucleation density, the single layer MoS produced by the chemical vapor deposition method₂The sample domain size is typically only on the order of a few to tens of microns. The key to improving the quality of the two-dimensional film sample is to improve the single crystal rate of the sample, which needs to further reduce the nucleation density and increase the size of the crystal domain in the process of growing the sample by chemical vapor deposition. However, it is very difficult to control the precursor vapor concentration to achieve the goal of reducing nucleation density, even if the reactant MoO is changed₃The amount of powder used also makes it difficult to precisely control the vapor concentration and nucleation density.

In order to solve the problems, the invention adopts the following technical scheme:

the method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water comprises the following steps:

step 1, cleaning a growth substrate: sequentially putting the growth substrate into acetone, absolute ethyl alcohol and water for ultrasonic cleaning to obtain a clean growth substrate;

step 2, growth substrate pretreatment: bombarding a clean growth substrate by using oxygen plasma, activating the surface of the substrate, spin-coating a PTAS organic dye to assist nucleation, and naturally drying to obtain the spin-coated PTAS growth substrate;

step 3, preparing a film precursor: adding MoO₃Dissolving the powder in ammonia water to obtain 10-50 mg/mL^-1Of MoO₃NH of (2)₄OH solution, spin-coating on the substrate;

and 4, annealing the film precursor: the MoO is spun on₃/NH₄Annealing the OH substrate at a high temperature of 200-350 ℃ to remove NH₄OH to obtain annealed MoO₃A source substrate;

and 5, growing the material: using inert gas Ar as carrier gas, using a double-temperature-zone tube furnace, placing sulfur powder at the upstream of gas flow (temperature zone I), and annealing MoO₃The source substrate and the growth substrate of the spin-coating PTAS are alternately placed at the downstream of the airflow (temperature zone II), the temperature zone I and the temperature zone II are respectively heated to 160 ℃ and 650-800 ℃ from the room temperature within 40-60 min, the temperature environment is kept for 5-10 min, then the temperature is naturally cooled to the room temperature, the whole growth process is carried out at normal pressure, and the large-area monolayer molybdenum disulfide is obtained.

In step 1, the substrate is a growth substrate conventionally used in the art, such as SiO₂Si substrate, strontium titanate (SrTiO)₃) Substrate, quartz plate, fluorine crystal mica, sapphire (Al)₂O₃) Substrates, wide bandgap semiconductor gallium nitride (GaN) substrates, gallium arsenide (GaAs) substrates, and the like.

In the step 1, the ultrasonic power is 28W, and the cleaning time is 5-10 min.

In step 2, the oxygen plasma treatment power is 716V/10mA/7.16W, and the treatment time is 20 s.

In step 2, the spin coating rate is 1500rpm (revolutions per minute), and the spin coating time is 30 s.

In step 2, the PTAS is a tetrapotassium salt of perylene-3, 4, 9, 10-tetracarboxylic acid, which is an aromatic compound and is available from 2D Semiconductors, usa. The concentration of the prepared aqueous solution is 20-50 mu M.

In the step 3, the spin-coating speed is 3000rpm, and the spin-coating time is 1 min.

Preferably, in step 3, said MoO₃/NH₄In OH solution, MoO₃In a concentration of15～25mg·mL^-1More preferably 20 mg/mL^-1。

In the step 4, the annealing time is 2-3 h.

Preferably, in the step 5, the growth temperature of the temperature zone II is 700-800 ℃, and more preferably 750 ℃.

Compared with the prior art, the invention has the following advantages:

1. the net content of molybdenum trioxide on a substrate per square centimeter is estimated to be about 1-10 micrograms, which is only 10 mass percent of the molybdenum trioxide solid source required by the traditional chemical vapor deposition method for growing a single layer of molybdenum disulfide^-2～10^-3The concentration of the precursor vapor is obviously reduced in the growth process, and the consumption of a solid growth source is greatly saved.

2. By utilizing the property that molybdenum trioxide is insoluble in water and easily soluble in ammonia water and strong alkali, the original solid powder precursor is replaced by the solution auxiliary film precursor, so that the supersaturation state of a vapor reactant can be reduced, the nucleation density is reduced, and the method is very important for growing large-size single crystal samples. In addition, the ammonia water is decomposed by heating, has extremely strong volatility, is easy to remove, and can not introduce defects or impurities for subsequent crystal synthesis to influence the crystal quality.

3. The chemical vapor deposition method adopts an open system and has the problems of low repeatability and stability. According to the invention, the concentration of the reactant can be accurately controlled by regulating and controlling the concentration of the solution, the reaction accuracy is improved, and the experimental repetition degree is improved. Based on the improved synthesis process, the crystal domain size of the molybdenum disulfide is obviously increased, and convenience is provided for subsequent material characterization, transfer and device construction.

Drawings

FIG. 1 is a schematic diagram of a film precursor pretreatment process for removing MoO₃Source substrate placed in single temperature zone tube furnace for high temperature annealing to volatilize NH₄And (4) an OH solvent.

FIG. 2 is a schematic diagram of the formal growth process using a dual temperature zone tube furnace with sulfur powder placed upstream of the gas flow (temperature zone I) and annealed MoO₃The source substrate and the growth substrate of the spin-coating PTAS are alternately arranged at the downstream of the air flow (temperature zone II) for sample growth。

FIG. 3 shows ammonia assisted chemical vapor deposition growth of single-layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 20 mg/mL^-1The growth temperature of the temperature zone II is 750 ℃, and the scale bar is as follows: 100 μm.

FIG. 4 shows ammonia assisted chemical vapor deposition growth of single-layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 10 mg/mL^-1And the growth temperature of the temperature zone II is 750 ℃.

FIG. 5 shows ammonia assisted chemical vapor deposition growth of single-layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 50 mg/mL^-1And the growth temperature of the temperature zone II is 750 ℃.

FIG. 6 shows ammonia assisted chemical vapor deposition growth of single-layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 20 mg/mL^-1And the growth temperature of the temperature zone II is 650 ℃.

FIG. 7 shows ammonia assisted chemical vapor deposition growth of single layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 20 mg/mL^-1And the growth temperature of the temperature zone II is 700 ℃.

FIG. 8 shows ammonia assisted chemical vapor deposition growth of single layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 20 mg/mL^-1And the growth temperature of the temperature zone II is 800 ℃.

FIG. 9 shows that no PTAS was introduced during growth, and MoO was used directly₃Powder source, MoS made without ammonia₂The optical image of (1).

FIG. 10 shows the introduction of PTAS during growth, using MoO directly₃Powder source, MoS made without ammonia₂The optical image of (1).

FIG. 11 shows ammonia assisted chemical vapor deposition growth of single layer MoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 5 mg/mL^-1And the growth temperature of the temperature zone II is 750 ℃.

FIG. 12 shows ammonia assisted CVD growth of a single layerMoS₂Optical image of, MoO₃/NH₄The concentration of the OH solution was 80 mg/mL^-1And the growth temperature of the temperature zone II is 750 ℃.

Detailed Description

The invention is further illustrated by the following figures and examples.

Example 1

Cleaning a growth substrate: growing a Substrate (SiO)₂the/Si substrate) is sequentially put into acetone, absolute ethyl alcohol and deionized water, and ultrasonic cleaning is respectively carried out for 5 min.

Preprocessing a growth substrate: the cleaned growth substrate is bombarded by oxygen plasma to activate SiO₂A surface. A50. mu.M aqueous solution of PTAS was prepared. And (3) spin-coating organic dye of the PTAS on a part of the substrate, and naturally airing to be used as a growth substrate.

③MoO₃Preparing a film precursor: 200mg of MoO₃The powder was dissolved in 10mL of aqueous ammonia (26%, Utility model) to obtain 20 mg. multidot.mL^-1Of MoO₃/NH₄OH solution is coated on the SiO film which has been cleaned, activated and the like on the other part₂On a Si substrate, the speed is 3000rpm, the duration is 1min, and the film is used as a film precursor.

④MoO₃Annealing the film precursor: as shown in FIG. 1, before formal growth, the thin film precursor is annealed at a high temperature of 300 ℃ for 2h, the carrier gas is Ar inert gas, the gas flow is 50sccm (standard milliliters per minute) to ensure NH₄The OH solvent evaporates. Annealed MoO₃The film surface is uniform, 25 is multiplied by 25 mu m²The roughness in the region was about 0.144nm with only a small amount of build-up at the edges.

⑤MoS₂And (3) growing a sample: using a two-zone tube furnace, as shown in FIG. 2, the sulfur powder was placed upstream of the gas flow (zone I), and the annealed MoO was removed₃The source substrate, the growth substrate of the spin-coated PTAS, were placed alternately downstream of the gas flow (temperature zone II). And (3) heating the temperature zone I and the temperature zone II to 160 ℃ and 750 ℃ within 40min, maintaining the temperature environment for 5min, and then naturally cooling to room temperature. The whole growth process is carried out under normal pressure, and the flow rate of Ar gas used is 15 sccm.

The comparison shows that: single-layer MoS synthesized by traditional chemical vapor deposition method₂The triangular side length is about 10-30 μm (as shown in FIG. 9 and FIG. 10), and the single-layer MoS can be grown by ammonia assisted chemical vapor deposition₂The triangle edge length extends to the order of hundreds of microns (as shown in figure 3), and the size of the crystal domain is obviously increased.

Example 2

This example is essentially the same as example 1, the only difference being MoO₃/NH₄The OH solution concentration was 10 mg/mL^-1. As shown in fig. 4, the lateral dimension of the sample is about 40 μm.

Example 3

This example is essentially the same as example 1, the only difference being MoO₃/NH₄ OH solution concentration 50 mg/mL^-1. As shown in FIG. 5, the lateral dimension of the sample is about 40 μm, and few layers are formed at the edges of the monolayer sample.

Example 4

This example is substantially the same as example 1 except that the growth temperature of the temperature zone II is set to 650 ℃ and 700 ℃. As shown in fig. 6 and 7, when the growth temperature of the temperature zone II is lower than the most preferable temperature (750 ℃), the sample tends to form a film, and when the temperature is lower (650 ℃, fig. 6), impurities are easily deposited on the surface of the sample; at higher temperatures (700 ℃, fig. 7), the samples formed uniform, clean films.

Example 5

This example is substantially the same as example 1 except that the growth temperature of the temperature zone II is set to 800 ℃. As shown in FIG. 8, when the temperature of temperature zone II growth is higher than the most preferable temperature (750 ℃), the sample tends to form discrete triangular MoS₂Single crystal, with lateral dimensions of about 40 μm.

Comparative example 1

In this comparative example, the PTAS precursor solution was not introduced, and MoO was a solid powder source₃Instead of MoO₃A source substrate. As shown in fig. 9, without PTAS and ammonia-assisted growth, the sample yield was low, the shape was irregular, and foreign materials and particles were deposited on the surface of the sample.

Comparative example 2

In this comparative example, a PTAS precursor was introducedBulk solution of MoO₃The powder serves as a molybdenum source. As shown in FIG. 10, the lateral dimension of the sample was only 10-30 μm without the ammonia-assisted growth.

Comparative example 3

This comparative example is essentially the same as example 1, except that 5 mg. multidot.mL was used^-1Of MoO₃/NH₄And (4) OH solution. When MoO, as shown in FIG. 11₃/NH₄When the concentration of the OH solution is too low, the sample yield is significantly reduced.

Comparative example 4

This comparative example is essentially the same as example 1, except that 80 mg. multidot.mL was used^-1Of MoO₃/NH₄And (4) OH solution. As shown in fig. 12, when MoO₃/NH₄When the concentration of the OH solution is too high, a large number of few-layer and multi-layer samples are generated at the edge and the junction of the single-layer sample.

Claims (10)

1. The method for preparing large-area single-layer molybdenum disulfide with assistance of ammonia water is characterized by comprising the following steps:

step 1, cleaning a growth substrate: sequentially putting the growth substrate into acetone, absolute ethyl alcohol and water for ultrasonic cleaning to obtain a clean growth substrate;

step 2, growth substrate pretreatment: bombarding a clean growth substrate by using oxygen plasma, activating the surface of the substrate, spin-coating a PTAS organic dye to assist nucleation, and naturally drying to obtain the spin-coated PTAS growth substrate;

step 3, preparing a film precursor: adding MoO₃Dissolving the powder in ammonia water to obtain 10-50 mg/mL^-1Of MoO₃NH of (2)₄OH solution, spin-coating on the substrate;

and 4, annealing the film precursor: the MoO is spun on₃/NH₄Annealing the OH substrate at a high temperature of 200-350 ℃ to remove NH₄OH to obtain annealed MoO₃A source substrate;

and 5, growing the material: using inert gas Ar as carrier gas, using a double-temperature-zone tube furnace, placing sulfur powder at the upstream of the gas flow, and annealing MoO₃Source substrate, spin-on growth substrate of PTASAnd (3) placing the temperature zone I and the temperature zone II at the downstream of the airflow within 40-60 min, respectively heating the temperature zone I and the temperature zone II to 160 ℃ and 650-800 ℃ from the room temperature, keeping the temperature environment for 5-10 min, then naturally cooling to the room temperature, and carrying out the whole growth process at normal pressure to obtain the large-area single-layer molybdenum disulfide.

2. The method of claim 1, wherein in step 1, the substrate is SiO₂a/Si substrate, a strontium titanate substrate, a quartz plate, fluorine crystal mica, a sapphire substrate, a wide-bandgap semiconductor gallium nitride substrate or a gallium arsenide substrate.

3. The method according to claim 1, wherein in step 1, the ultrasonic power is 28W, and the cleaning time is 5-10 min.

4. The method of claim 1, wherein in step 2, the oxygen plasma treatment power is 716V/10mA/7.16W, and the treatment time is 20 s.

5. The method of claim 1, wherein in step 2, the spin rate is 1500rpm and the spin time is 30 s.

6. The method according to claim 1, wherein in step 2, the PTAS is formulated in an aqueous solution at a concentration of 20 to 50 μ M.

7. The method of claim 1, wherein in step 3, the spin rate is 3000rpm and the spin time is 1 min.

8. The method of claim 1, wherein in step 3, said MoO is₃/NH₄In OH solution, MoO₃Has a concentration of 15 to 25 mg/mL^-1More preferably 20 mg/mL^-1。

9. The method according to claim 1, wherein in the step 4, the annealing time is 2-3 h.

10. The method according to claim 1, wherein in step 5, the growth temperature downstream of the gas stream is 700 to 800 ℃, more preferably 750 ℃.

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