CN110172736B - Chemical vapor deposition preparation method of large-size three-layer molybdenum sulfide single crystal - Google Patents

Chemical vapor deposition preparation method of large-size three-layer molybdenum sulfide single crystal Download PDF

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CN110172736B
CN110172736B CN201910491868.9A CN201910491868A CN110172736B CN 110172736 B CN110172736 B CN 110172736B CN 201910491868 A CN201910491868 A CN 201910491868A CN 110172736 B CN110172736 B CN 110172736B
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molybdenum
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soda
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CN110172736A (en
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李学飞
徐晓乐
吴燕庆
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Huazhong University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/46—Sulfur-, selenium- or tellurium-containing compounds

Abstract

The invention belongs to the field of two-dimensional material preparation, and discloses a chemical vapor deposition preparation method of a large-size three-layer molybdenum sulfide single crystal, which is characterized by comprising the following steps of: s1: respectively preparing clean and dry molybdenum foil and soda-lime glass, and respectively weighing sulfur powder and molybdenum trioxide as precursors; s2: placing a first carrier containing molybdenum foil, soda-lime glass and molybdenum trioxide and a second carrier containing sulfur powder in a CVD (chemical vapor deposition) deposition tube; s3: and carrying out chemical vapor deposition with temperature control in a dual-temperature area on the CVD deposition tube, thereby realizing deposition of three layers of molybdenum sulfide single crystals on the soda-lime glass. According to the invention, by improving the substrate material adopted by the key CVD process in the preparation method, the temperature setting of the double temperature zones and the like, compared with the prior art, the novel method for preparing the large-size three-layer molybdenum disulfide single crystal is provided, the longest length in the obtained three-layer molybdenum sulfide single crystal can reach 90 mu m, and the prepared three-layer molybdenum disulfide single crystal has good quality.

Description

Chemical vapor deposition preparation method of large-size three-layer molybdenum sulfide single crystal
Technical Field
The invention belongs to the field of two-dimensional material preparation, and particularly relates to a chemical vapor deposition preparation method of a large-size three-layer molybdenum sulfide single crystal.
Background
In recent years, two-dimensional materials such as graphene, transition metal sulfides, black phosphorus, and the like have attracted much attention due to their unique structures and outstanding properties. As one member of transition metal sulfide family, molybdenum disulfide has adjustable band gap of 1.2-1.9eV, and has wide application prospect in the aspects of logic devices, integrated circuits, photoelectrons and the like. The molybdenum disulfide is a layered material, each layer of molybdenum disulfide is combined by embedding a molybdenum atomic layer into an upper sulfur atomic layer and a lower sulfur atomic layer in a covalent bond mode, and the interlayer spacing is about
Figure BDA0002087303000000011
Compared with a single-layer molybdenum disulfide material formed by three atomic layers, the three-layer molybdenum disulfide material has higher carrier mobility and state density, so that the three-layer molybdenum disulfide-based deviceOften with higher electrical performance.
The preparation method of the molybdenum disulfide thin layer comprises a mechanical stripping method, a liquid phase stripping method, a gas phase growth method and the like. Mechanical stripping methods are time consuming, cannot be used for large-scale material preparation, and cannot control the number of layers, size, orientation, phase structure of the prepared material, which has high requirements for the individual experience of researchers. The molybdenum disulfide thin layer prepared by the liquid phase stripping method has poor quality and small size. The vapor phase growth method is a powerful means for preparing high-quality two-dimensional materials, wherein the chemical vapor deposition method is the method which is most widely used for preparing monolayer molybdenum disulfide so far, and can ensure that monolayer molybdenum disulfide with high quality and large area can be prepared on the premise of low cost, large scale and controllability. However, the existing three-layer molybdenum disulfide single crystal grown by chemical vapor deposition still has the problems of small size, poor quality and the like, and the maximum thickness of the molybdenum disulfide single crystal can only be 10 μ M (for example, refer to the documents: Zobel A, Boson A, Wilson P M, et al2Journal of Materials Chemistry C,2016,4(47): 11081-.
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, the present invention aims to provide a chemical vapor deposition method for preparing a large-size three-layer molybdenum sulfide single crystal, wherein a substrate material, a dual-temperature-zone temperature setting, and the like adopted in a key CVD process in the preparation method are improved.
In order to achieve the above object, according to the present invention, there is provided a method for preparing a large-sized triple-layer molybdenum sulfide single crystal by chemical vapor deposition, comprising the steps of:
s1: respectively preparing clean and dry molybdenum foil and soda-lime glass; then, respectively weighing sulfur powder and molybdenum trioxide as precursors, placing the sulfur powder in a second carrier boat, and placing the molybdenum trioxide in a first carrier boat, wherein the molybdenum trioxide is covered by a ceramic sheet; then, the molybdenum foil is placed in the first carrier, and the soda-lime glass is placed on the molybdenum foil;
s2: carrying out vacuum pumping treatment on a CVD deposition tube, wherein the temperature of the CVD deposition tube is provided by a heating furnace, and the heating furnace can freely move along the axial direction of the CVD deposition tube; the heating furnace at least comprises two temperature areas with independently controllable temperatures, the two temperature areas are respectively marked as a first temperature area and a second temperature area, and different areas of the CVD deposition tube correspond to the two temperature areas in advance; then, introducing inert gas into the CVD deposition tube to increase the pressure in the CVD deposition tube to normal pressure; then, the first boat obtained in the step S1 is transported to a position corresponding to the second temperature zone in the CVD deposition tube, the second boat is transported to a position corresponding to the first temperature zone in the CVD deposition tube, and the second boat is located upstream of the inert gas flow, the first boat is located downstream of the inert gas flow, and further, molybdenum trioxide in the first boat is located upstream of the inert gas flow, and soda-lime glass in the first boat is located downstream of the inert gas flow; then, vacuumizing the CVD deposition tube to ensure that the vacuum degree meets the requirement of background vacuum with the pressure intensity of less than 15 mTorr; then introducing inert gas into the CVD deposition tube again to restore the pressure in the CVD deposition tube to normal pressure;
s3: moving the heating furnace to a region corresponding to the downstream of the inert gas flow in the whole CVD deposition tube, and controlling the heating furnace to start heating under the condition of keeping the continuous introduction of the inert gas into the CVD deposition tube so as to enable the temperature of the first temperature region to reach a preset temperature value T1The temperature of the second temperature zone reaches a preset temperature value T2(ii) a Then, the heating furnace is moved to the area corresponding to the upstream of the inert gas flow in the whole CVD deposition tube, so that the second carrier boat is positioned in the first temperature area, the first carrier boat is positioned in the second temperature area, and the CVD chemical vapor deposition reaction is carried out(ii) a After the chemical vapor deposition treatment reaches the preset time t, cooling the CVD deposition tube, and depositing three layers of molybdenum sulfide single crystals on the soda-lime glass;
further, in the step S3: the T is1At a temperature of 200 ℃ to 230 ℃, the temperature T2At 800-; the continuous introduction of the inert gas is specifically to keep the flow rate of the inert gas at 40-60 sccm.
As a further preferred aspect of the present invention, in step S1: the mass of the sulfur powder is 1-1.4g, and the mass of the molybdenum trioxide is 3-6 mg;
the distance between the soda-lime glass and the molybdenum trioxide is 2-4 mm;
the size of the soda-lime glass and the size of the molybdenum foil both meet 2 × 2-4 × 4cm2The soda lime glass can be completely disposed on the molybdenum foil.
As a further preferred mode of the invention, in the step S3, the deposited molybdenum sulfide single crystal with three layers has the longest internal length of not less than 60 μm.
As a further preferred mode of the invention, in the step S3, the deposited molybdenum sulfide single crystal with three layers has the longest internal length of not less than 90 μm.
As a further preferred aspect of the present invention, in step S3: and cooling the CVD deposition tube, specifically, rapidly moving the heating furnace to a region corresponding to the downstream of the inert gas flow in the whole CVD deposition tube, and increasing the flow of the inert gas.
As a further preferred aspect of the present invention, in step S1:
the clean and dry molybdenum foil is obtained by sequentially ultrasonically cleaning the molybdenum foil with acetone, isopropanol and deionized water respectively and then blow-drying with nitrogen;
the clean and dry soda-lime glass is obtained by sequentially ultrasonically cleaning the soda-lime glass with acetone, isopropanol and deionized water respectively, blow-drying with nitrogen and then cleaning with plasma.
As a further optimization of the invention, the plasma cleaning treatment is specifically carried out for 2.5-3.5min in a plasma cleaner with the volume ratio of inert gas to oxygen gas being 5:1 to 4:1 and the radio frequency power being 9-11W.
In a further preferred embodiment of the present invention, in step S1, the first boat is a quartz boat, and the second boat is a corundum boat.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. simple operation and controllable growth. The conventional mechanical stripping method is too time-consuming to be used for large-scale material preparation, and cannot control the number of layers, size, orientation and phase structure of the prepared material, thus having high requirements on the personal experience of researchers. The chemical vapor deposition method can ensure that the molybdenum disulfide single crystal is prepared on the premise of low cost, large scale and controllability;
2. the sample size is large. The side length of the third layer of the prepared three-layer molybdenum disulfide single crystal can reach more than 60 mu m, even exceeds 90 mu m, and is far larger than the size of the three-layer molybdenum disulfide which is mechanically stripped. Molybdenum disulfide generally nucleates at impurities or defects on the surface of the substrate, while the liquid surface of soda-lime glass in a high-temperature molten state has fewer surface impurities and defects, and molybdenum disulfide is more prone to laterally grow at the nucleated molybdenum disulfide single crystal, so that the increase of the size of the single crystal is promoted; the liquid surface of the soda-lime glass in a high-temperature molten state has very low surface roughness, so that the transportation of a precursor is promoted, and the rate of chemical reaction is accelerated, thereby being more beneficial to the increase of the size of a single crystal; sodium element in the soda-lime glass is adsorbed on the growing edge of the molybdenum disulfide, so that the potential barrier of the molybdenum disulfide can be obviously reduced, and the growth rate of the molybdenum disulfide can be improved, thereby being more beneficial to the increase of the size of a single crystal;
3. the sample morphology is regular. The prepared three layers of molybdenum disulfide single crystals are regular triangles of a standard AAA stacking mode;
4. the sample is convenient to transfer. The deionized water transfer method suitable for the soda-lime glass substrate is simple to operate, does not need etching and consumes less time;
5. the quality of the sample is high. The soda-lime glass can eliminate self high-energy positions such as defects, kinks and the like in the high-temperature melting process, and ensures that three layers of high-quality molybdenum disulfide single crystals grow. Three layers of molybdenum disulfide single crystals grown on the soda-lime glass can be transferred by a green non-etching deionized water transfer method, so that the molybdenum disulfide single crystals are prevented from being damaged by etching agents such as hydrofluoric acid and the like.
The preparation method can be used for preparing three layers of molybdenum sulfide single crystals with the longest length inside not less than 60 mu m (the height can be ignored because the three layers of molybdenum disulfide still belong to two-dimensional materials, namely, the longest length inside the projection of the three layers of molybdenum sulfide single crystals on the plane of the surface is not less than 60 mu m). The invention can prepare the three-layer molybdenum sulfide single crystal with the longest internal length of 90 mu m by using soda-lime glass as a growth substrate and carrying out heat treatment for 8-10min by using a CVD deposition treatment process under the conditions that the temperature of a double-temperature region is respectively 200-230 ℃ (the treatment temperature corresponding to a sulfur source) and 800-830 ℃ (the treatment temperature corresponding to a molybdenum source and the soda-lime glass). The present invention preferably controls the distance between soda-lime glass and molybdenum trioxide to be 2-4mm, and uses 1-1.4g of sulfur powder and 3-6mg of molybdenum trioxide as precursors, and by preferably setting the mass of the sulfur source to be in an excessive state, the growth of molybdenum sulfide of three layers can be controlled by controlling only the mass of molybdenum trioxide. In addition, the soda-lime glass is preferably treated by adopting a specific cleaning process, so that the growing substrate of the soda-lime glass can be cleaner.
Drawings
FIG. 1 is a schematic diagram of an apparatus for CVD preparation of three layers of molybdenum disulfide single crystal in the present invention.
FIG. 2 is a schematic temperature profile of a three-layer molybdenum disulfide single crystal produced by CVD in accordance with example 1 of the present invention.
FIG. 3 is an optical micrograph of a triple-layered molybdenum disulfide single crystal of example 1 of the present invention.
FIG. 4 is a schematic diagram of the DI water transfer process for three layers of single crystals of molybdenum disulfide according to example 1 of the present invention.
Fig. 5(a) and 5(b) are Atomic Force Microscope (AFM) images of a three-layered molybdenum disulfide single crystal of example 1 in the present invention.
FIG. 6 is a Raman (Raman) spectrum of a triple layer single crystal of molybdenum disulfide of example 1 of the present invention.
FIG. 7 is a Photoluminescence (PL) spectrum of a triple layer molybdenum disulfide single crystal of example 1 of the present invention.
FIG. 8 is a schematic temperature profile of a three-layer single crystal of molybdenum disulfide produced by CVD in example 2 of the present invention.
FIG. 9 is an optical micrograph of a triple layer molybdenum disulfide single crystal of example 2 of the present invention.
FIG. 10 is a Raman (Raman) spectrum of a triple layer molybdenum disulfide single crystal of example 2 of the present invention.
FIG. 11 is a Photoluminescence (PL) spectrum of a triple layer molybdenum disulfide single crystal of example 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1: this example provides a Chemical Vapor Deposition (CVD) method for preparing a large-sized three-layer molybdenum disulfide single crystal, and a schematic diagram of the apparatus is shown in fig. 1, which includes the following steps:
1. cleaning a substrate: and ultrasonically cleaning the molybdenum foil and the soda-lime glass by acetone, isopropanol and deionized water respectively for 10min in sequence, and drying by using nitrogen. Then, the soda-lime glass substrate is put into a plasma cleaning machine for processing, the parameters of the plasma cleaning machine are set to be argon gas 40sccm, oxygen gas 10sccm, power is 11W, and time is 3.5min (the model of the plasma cleaning machine can be PLASMA CLEANER PDC-002-HP, and the model of the plasma flowmeter can be PLASMAFLO PDC-FMG-2);
2. weighing: and weighing the precursor by using a weighing balance. The sulfur powder, having a mass of 1.4g, was loaded into a corundum boat (of course, other boats resistant to the highest temperature of the subsequent treatment process and to sulfur vapor corrosion can be used as wellIn the subsequent treatment, the sulfur powder is large in amount and cannot be completely evaporated and exhausted, the residual sulfur is adhered to the carrying boat after being cooled and solidified, so that the carrying boat cannot be reused, the cheap corundum boat is preferably adopted, the mass of the molybdenum trioxide is 6mg, the molybdenum trioxide is supported by a 90nm silicon dioxide/silicon substrate and placed on the quartz boat (of course, besides the quartz boat, other carrying boats which can resist the highest temperature of the subsequent treatment process and can resist sulfur steam corrosion materials can also be adopted, the silicon substrate or the silicon dioxide substrate mainly has the effect of isolation, the molybdenum trioxide is prevented from being directly contacted with the carrying boat at the lower layer, the first carrying boat is prevented from being polluted, of course, other heat-resistant, explosion-proof and harmless inert substrates can also serve as isolation substrates), a ceramic wafer which can resist the highest temperature of the subsequent treatment process and resist sulfur steam corrosion is further laid on the quartz boat, and the ceramic wafer is placed on the quartz boat for preventing sulfur steam poisoning, and a4 × 4 cm-4 cm piece is placed on the quartz2The edge of the molybdenum foil is 4mm away from the molybdenum trioxide, and a soda-lime glass substrate is arranged right above the molybdenum foil; the molybdenum foil can prevent soda-lime glass in a high-temperature melting state from being adhered to the quartz boat on the lower layer during subsequent treatment;
3. breaking vacuum and lofting: starting a CVD equipment computer, operating a CVD control program, and setting argon gas introduced into the CVD equipment computer to increase the pressure in the tube to normal pressure within about 10 min. Opening the furnace cover, sending the quartz boat carrying the molybdenum trioxide into a second temperature zone by using a sample pushing rod, sending the corundum boat filled with the sulfur powder into the first temperature zone, and closing the furnace cover;
4. background vacuumizing: starting a vacuum pump and an angle valve, and determining that the background vacuum is well pumped when the pressure in the pipe is less than 15 mTorr;
5. breaking vacuum again: the reaction needs to be carried out under normal pressure, so that the reaction needs to be returned to the normal pressure;
6. setting reaction parameters: the reaction parameters which can be set by the program comprise the temperature of each temperature zone, the carrier gas flow and the growth time. The temperatures of the two temperature zones set by the experiment are respectively as follows: the temperature zone I (230 ℃) is controlled, and the temperature zone II (830 ℃) is controlled. The carrier gas flow is argon: 60 sccm. The growth time is 10 min;
7. setting a reaction flow: the CVD furnace was set to heat up at a rate of 25 deg.C/min to a specified temperature over a period of about 32 minutes. The tube furnace was then pulled rapidly from right to left and the reaction was carried out for 10 min. And then, rapidly pulling the furnace to the right side, completely opening the angle valve, and introducing a large-flow carrier gas (the flow is 900sccm), so as to realize the rapid cooling of the furnace body. FIG. 2 is a schematic diagram of temperature curves of various temperature zones in a tube furnace in the process of growing three layers of molybdenum disulfide single crystals by CVD;
8. breaking vacuum and sampling: after the vacuum is broken, the corundum boat and the quartz boat are pulled out by using a sample pushing rod, and the substrate is taken down by using tweezers and placed into the wafer box.
FIG. 3 is an optical microscope photograph of a molybdenum disulfide single crystal, which can be judged to have three layers according to color difference, and the side length of the third layer is 90 μm, and is a regular triangle of a standard AAA stacking mode, indicating that a large-sized three-layer molybdenum disulfide single crystal is successfully prepared.
In order to perform material characterization of the three layers of molybdenum disulfide single crystals, the three layers of molybdenum disulfide single crystals grown on soda lime glass need to be transferred to 300nm silica. Compared with the traditional hydrofluoric acid wet etching method (which is commonly used for etching substrates such as silicon dioxide and sapphire), the deionized water method transfer method is adopted in the embodiment, the method utilizes the hydrophilicity of the soda-lime glass, is simple to operate, does not need etching, consumes less time, and avoids the molybdenum disulfide self being damaged by hydrofluoric acid. The schematic diagram is shown in fig. 4, and the specific operation steps are as follows:
1. firstly, a molybdenum disulfide/soda-lime glass sample is coated with a layer of PMMA A4 glue in a spinning mode (the rotating speed is 500r/min, the time is 1min, and then the sample is dried by a hot plate (the temperature is 120 ℃, and the time is 5 min);
2. finding an ideal molybdenum disulfide area (namely an area where the grown molybdenum disulfide meets the use requirement) on PMMA/molybdenum disulfide/soda-lime glass under an optical microscope, and dividing the area by using a knife (generally in a shape of a Chinese character jing) so as to better allow water to permeate into the ideal area;
3. slowly immersing PMMA/molybdenum disulfide/soda-lime glass into a beaker filled with deionized water in an inclined manner, and separating a PMMA/molybdenum disulfide film in a region from the soda-lime glass and independently floating on the water surface after the region is divided to be permeated by water;
4. fishing out the PMMA/molybdenum disulfide film floating on the water surface by using 300nm silicon dioxide, and roughly blowing dry the water on the surface by using a nitrogen gun;
5. putting PMMA/molybdenum disulfide/silicon dioxide into a fume hood, air-drying for 2h to remove residual moisture, and then drying by a hot plate (the temperature is 100 ℃, and the time is 5min) to remove the residual moisture and enhance the adhesion between the molybdenum disulfide and the substrate;
6. and finally, soaking the PMMA/molybdenum disulfide/silicon dioxide in an acetone solution for at least 6 hours to fully dissolve the PMMA, then flushing the PMMA for 1min by using isopropanol, drying the PMMA by using a nitrogen gun, and taking the PMMA/molybdenum disulfide/silicon dioxide under a microscope to observe whether the transfer is successful.
Fig. 5(a) is an Atomic Force Microscope (AFM) image of three layers of molybdenum disulfide single crystals, in which the smooth surface morphology of the three layers of molybdenum disulfide single crystals can be observed, indicating that the surfaces of the three layers of molybdenum disulfide single crystals are very uniform. FIG. 5(b) is a graph showing AFM height measurement at the interface of each layer corresponding to FIG. 5(a), wherein the thickness of each layer in three layers of molybdenum disulfide single crystal is about 0.7nm, which is similar to the thickness of each molybdenum disulfide layer in the literature
Figure BDA0002087303000000091
The conclusion is not very different, thus indicating that three layers of molybdenum disulfide single crystals are successfully prepared.
FIG. 6 is a Raman spectrum of a single crystal of molybdenum disulfide in three layers, the peak E being characteristic of the single crystal1 2gAnd A1gAre respectively located at 383.7cm-1And 407.1cm-1At peak difference of 23.4cm-1This result is consistent with the results for the delaminated three layers of molybdenum disulfide, indicating that a three layer molybdenum disulfide single crystal was successfully produced.
Fig. 7 is a Photoluminescence (PL) spectrum of a three-layer molybdenum disulfide single crystal, an excitation peak of the three-layer molybdenum disulfide single crystal is located at 678nm, and according to the formula λ (nm) ═ 1240/eg (eV), a band gap is 1.83eV, and a small shoulder peak on the left side is energy band splitting caused by spin-orbit coupling of molybdenum disulfide.
Example 2:
this example provides a Chemical Vapor Deposition (CVD) method for preparing a large-sized three-layer molybdenum disulfide single crystal, and a schematic diagram of the apparatus is shown in fig. 1, which includes the following steps:
1. cleaning a substrate: and ultrasonically cleaning the molybdenum foil and the soda-lime glass by acetone, isopropanol and deionized water respectively for 10min in sequence, and drying by using nitrogen. Then, the soda-lime glass substrate is put into a plasma cleaning machine for treatment, the parameters of the plasma cleaning machine are set to be 50sccm of argon, 10sccm of oxygen and 9W of power, and the time is 2.5 min;
2. weighing precursor with weighing balance, weighing sulfur powder 1g in corundum boat, molybdenum trioxide 3mg in 90nm supported on silica/silicon substrate, placing on the quartz boat, and placing a 2 × 2cm quartz boat with a ceramic wafer thereon to prevent poisoning by sulfur vapor2The edge of the molybdenum foil is 2mm away from the molybdenum trioxide, and a soda-lime glass substrate is arranged right above the molybdenum foil;
3. breaking vacuum and lofting: starting a CVD equipment computer, operating a CVD control program, and setting argon gas introduced into the CVD equipment computer to increase the pressure in the tube to normal pressure within about 10 min. Opening the furnace cover, sending the quartz boat carrying the molybdenum trioxide into a second temperature zone by using a sample pushing rod, sending the corundum boat filled with the sulfur powder into the first temperature zone, and closing the furnace cover;
4. background vacuumizing: starting a vacuum pump and an angle valve, and determining that the background vacuum is well pumped when the pressure in the pipe is less than 15 mTorr;
5. breaking vacuum again: the reaction needs to be carried out under normal pressure, so that the reaction needs to be returned to the normal pressure;
6. setting reaction parameters: the reaction parameters which can be set by the program comprise the temperature of each temperature zone, the carrier gas flow and the growth time. The temperatures of the two temperature zones set by the experiment are respectively as follows: the temperature zone I (200 ℃) and the temperature zone II (800 ℃). The carrier gas flow is argon: 40 sccm. The growth time is 8 min;
7. setting a reaction flow: the CVD furnace was set to raise the temperature at a rate of 25 ℃/min to the specified temperature after about 31 minutes. The tube furnace was then pulled from the right to the left and the reaction was carried out for 10 min. And then the furnace is pulled to the right side, the angle valve is completely opened, and large-flow carrier gas (the flow is 900sccm) is introduced, so that the aim of quickly cooling the furnace body is fulfilled. FIG. 8 is a schematic diagram of temperature curves of various temperature zones in a tube furnace during CVD growth of three layers of molybdenum disulfide single crystals;
8. breaking vacuum and sampling: after the vacuum is broken, the corundum boat and the quartz boat are pulled out by using a sample pushing rod, and the substrate is taken down by using tweezers and placed into the wafer box.
FIG. 9 is an optical microscopic photograph of a molybdenum disulfide single crystal, which has three layers, and the side length of the third layer is 60 μm, which is a regular triangle of a standard AAA stacking mode, according to the color difference, indicating that a large-sized three-layer molybdenum disulfide single crystal is successfully prepared.
Similarly to example 1, to perform material characterization of three layers of molybdenum disulfide single crystals, three layers of molybdenum disulfide single crystals grown on soda lime glass were transferred onto 300nm silica using a deionized water transfer method.
FIG. 10 is a Raman spectrum of a single crystal of three layers of molybdenum disulfide having a characteristic peak E1 2gAnd A1gAre respectively positioned at 384.1cm-1And 407.7cm-1At peak difference of 23.6cm-1This result is consistent with the results for the delaminated three layers of molybdenum disulfide, indicating that a three layer molybdenum disulfide single crystal was successfully produced.
Fig. 11 is a Photoluminescence (PL) spectrum of a three-layer molybdenum disulfide single crystal, an excitation peak of the three-layer molybdenum disulfide single crystal is located at 675nm, a band gap is 1.84eV according to a formula λ (nm) ═ 1240/eg (eV), and a small shoulder peak on the left side is energy band splitting caused by spin-orbit coupling of molybdenum disulfide.
Comparative example:
in the comparative example, silica was used as a growth substrate instead of soda-lime glass, and the specific treatment process steps, parameter condition settings, and the like were all completely the same as those in example 1. The molybdenum sulfide is grown as a multilayer single crystal with extremely small size (5 μm).
In the above embodiment, argon gas is used as an example, and other inert gases may be used.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (7)

1. A chemical vapor deposition preparation method of a large-size three-layer molybdenum sulfide single crystal is characterized by comprising the following steps:
s1: respectively preparing clean and dry molybdenum foil and soda-lime glass; then, respectively weighing sulfur powder and molybdenum trioxide as precursors, placing the sulfur powder in a second carrier boat, and placing the molybdenum trioxide in a first carrier boat, wherein the molybdenum trioxide is covered by a ceramic sheet; then, the molybdenum foil is placed in the first carrier, and the soda-lime glass is placed on the molybdenum foil;
s2: carrying out vacuum pumping treatment on a CVD deposition tube, wherein the temperature of the CVD deposition tube is provided by a heating furnace, and the heating furnace can freely move along the axial direction of the CVD deposition tube; the heating furnace at least comprises two temperature areas with independently controllable temperatures, the two temperature areas are respectively marked as a first temperature area and a second temperature area, and different areas of the CVD deposition tube correspond to the two temperature areas in advance; then, introducing inert gas into the CVD deposition tube to increase the pressure in the CVD deposition tube to normal pressure; then, the first boat obtained in the step S1 is transported to a position corresponding to the second temperature zone in the CVD deposition tube, the second boat is transported to a position corresponding to the first temperature zone in the CVD deposition tube, and the second boat is located upstream of the inert gas flow, the first boat is located downstream of the inert gas flow, and further, molybdenum trioxide in the first boat is located upstream of the inert gas flow, and soda-lime glass in the first boat is located downstream of the inert gas flow; then, vacuumizing the CVD deposition tube to ensure that the vacuum degree meets the requirement of background vacuum with the pressure intensity of less than 15 mTorr; then introducing inert gas into the CVD deposition tube again to restore the pressure in the CVD deposition tube to normal pressure;
s3: moving the heating furnace to a region corresponding to the downstream of the inert gas flow in the whole CVD deposition tube, and controlling the heating furnace to start heating under the condition of keeping the continuous introduction of the inert gas into the CVD deposition tube so as to enable the temperature of the first temperature region to reach a preset temperature value T1The temperature of the second temperature zone reaches a preset temperature value T2(ii) a Then, moving the heating furnace to a region corresponding to the upstream of the inert gas flow in the whole CVD deposition tube, so that the second carrier boat is positioned in the first temperature region, and the first carrier boat is positioned in the second temperature region, and performing CVD chemical vapor deposition reaction; after the chemical vapor deposition treatment reaches the preset time t, cooling the CVD deposition tube, and depositing three layers of molybdenum sulfide single crystals on the soda-lime glass;
further, in the step S3: the T is1At a temperature of 200 ℃ to 230 ℃, the temperature T2At 800-; the continuous introduction of the inert gas is specifically to keep the flow rate of the inert gas at 40-60 sccm;
in step S1, the processing unit: the mass of the sulfur powder is 1-1.4g, and the mass of the molybdenum trioxide is 3-6 mg; the distance between the soda-lime glass and the molybdenum trioxide is 2-4 mm;
in the step S3, the deposited molybdenum sulfide single crystal with three layers has the longest internal length of not less than 60 μm.
2. The chemical vapor deposition method for producing a large-size trilayer molybdenum sulfide single crystal according to claim 1, wherein in step S1:
the size of the soda-lime glass and the size of the molybdenum foil both meet 2 × 2-4 × 4cm2The soda lime glass can be completely disposed on the molybdenum foil.
3. The chemical vapor deposition method for producing a large-sized trilayer molybdenum sulfide single crystal as claimed in claim 1, wherein in step S3, the deposited trilayer molybdenum sulfide single crystal has an inner longest length of not less than 90 μm.
4. The chemical vapor deposition method for producing a large-size trilayer molybdenum sulfide single crystal according to claim 1, wherein in step S3: and cooling the CVD deposition tube, specifically, rapidly moving the heating furnace to a region corresponding to the downstream of the inert gas flow in the whole CVD deposition tube, and increasing the flow of the inert gas.
5. The chemical vapor deposition method for producing a large-size trilayer molybdenum sulfide single crystal according to claim 1, wherein in step S1:
the clean and dry molybdenum foil is obtained by sequentially ultrasonically cleaning the molybdenum foil with acetone, isopropanol and deionized water respectively and then blow-drying with nitrogen;
the clean and dry soda-lime glass is obtained by sequentially ultrasonically cleaning the soda-lime glass with acetone, isopropanol and deionized water respectively, blow-drying with nitrogen and then cleaning with plasma.
6. The chemical vapor deposition process of preparing three-layer molybdenum sulfide single crystal of large size as claimed in claim 5, wherein the plasma cleaning treatment is carried out for 2.5-3.5min in a plasma cleaner with inert gas and oxygen gas in a volume ratio of 5:1 to 4:1 and with a radio frequency power of 9-11W.
7. The CVD method for producing a large-sized triple-layered molybdenum sulfide single crystal according to any of claims 1 to 6, wherein the first boat is a quartz boat and the second boat is a corundum boat in step S1.
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