CN114351112B - WSe 2 /WS 2 Vertical heterojunction nano material and preparation method thereof - Google Patents
WSe 2 /WS 2 Vertical heterojunction nano material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a WSe 2 /WS 2 A vertical heterojunction nano material and a preparation method thereof; the preparation method comprises the following steps: with WSe 2 Powder and WO 3 The powder is used as raw material, and WSe is grown on the surface of the substrate by first chemical vapor deposition 2 /WO 3 Nanosheets, then will contain WSe 2 /WO 3 Covering the substrate of the nano sheet in a container filled with NaCl powder, and leaving an opening in the container filled with NaCl powder, and in an environment containing S steam, in a WSe-containing environment 2 /WO 3 Carrying out secondary chemical vapor deposition on the substrate surface of the nanosheet, and controlling the temperature of the secondary chemical vapor deposition to be 530-570 ℃ to obtain WSe 2 /WS 2 A vertical heterojunction nanomaterial. The invention is achieved by WO 3 Method for obtaining WSe at lower temperature by nanosheet-assisted chemical vapor deposition 2 /WS 2 The vertical heterojunction nano material solves the problem of preparing WSe at high temperature in the prior art 2 /WS 2 When the heterojunction nano material is vertical, the problems of thermal decomposition and atom replacement of a bottom layer material are easily caused, and a new method idea is provided for preparing other high-quality two-dimensional heterojunctions.
Description
Technical Field
The invention relates to a WSe 2 /WS 2 A vertical heterojunction nano material and a preparation method thereof; belongs to the technical field of preparation of two-dimensional layered alloy material composite structures.
Background
Heterostructures, particularly Van der Waals heterostructures, have a wide application prospect in the field of optoelectronic devices due to their abundant interfacial properties, such as absence of dangling bonds, cleanliness, ultra-fast charge transfer, etc. At present, there are many researches on photoelectric devices based on two-dimensional heterostructure, including photoelectric detectors, light emitting devices, photovoltaic devices, etc. However, most of devices with excellent performance are made of materials prepared by a mechanical stripping method, and are limited in large-scale device application. From the practical application angle, the large-area and high-quality two-dimensional heterostructure capable of being controllably prepared on a large scale has important significance for the application of devices thereof.
At present, a plurality of work reports of controllable synthesis of two-dimensional heterostructures exist, but most of photoelectric devices have common performances. A key factor limiting its performance is material quality. This is mainly limited by the high temperature manufacturing process, and the materials in the middle sole are prone to thermal decomposition, atomic replacement, etc. To date, there has been some work to improve the quality of the materials produced by salt-assisted CVD from the standpoint of lowering the melting point of the metal oxide powder precursor, and thus the growth temperature, such as MoSe 2 /WSe 2 、WS 2 /MoS 2 . However, the metal oxide powder has low chemical reactivity, and thus the preparation process needs to be carried out at a relatively high temperature (above 700 ℃). There have also been some efforts to replace high melting point metal oxide powder precursors with low melting point salts (sodium molybdate, sodium tungstate, etc.) to obtain high quality MoSe 2 /NbSe 2 A heterostructure. However, this method is only suitable for growing chalcogenide-like heterostructures in one step, and limits the preparation of various heterostructures. Therefore, it is important to develop a universal CVD method which is not destructive to materials.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a WSe 2 /WS 2 A preparation method of the vertical heterojunction nano material; solves the problem of preparing WSe at high temperature in the prior art 2 /WS 2 When the heterojunction nano material is vertical, the bottom layer material is easy to generate the difficulties of thermal decomposition, atom replacement and the like.
It is a second object of the present invention to provide a high quality WSe prepared by the above preparation method 2 /WS 2 A vertical heterojunction nanomaterial.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a WSe 2 /WS 2 The preparation method of the vertical heterojunction nano material comprises the following steps:
with WSe 2 Powder and WO 3 The powder is used as raw material, and WSe is grown on the surface of the substrate by first chemical vapor deposition 2 /WO 3 Nanosheets, then will contain WSe 2 /WO 3 Covering the substrate of the nano-sheet in a container containing NaCl powder, leaving an opening in the container containing NaCl powder, and performing WSe (Wireless sensor element) in an environment containing S steam 2 /WO 3 Carrying out secondary chemical vapor deposition on the substrate surface of the nanosheet, and controlling the temperature of the secondary chemical vapor deposition to be 530-570 ℃ to obtain WSe 2 /WS 2 A vertical heterojunction nanomaterial.
The preparation method of the invention firstly generates the WSe 2 /WO 3 Nanosheet, and then in the environment of S steam, NaCl powder is used as a catalyst, so that WO 3 Reacts with S to finally generate WSe 2 /WS 2 Vertical heterojunction nano-materials, method of preparation of the invention, due to the WO formed 3 The nanosheet is lower in melting point and higher in chemical reaction activity, and can generate WSe at the temperature of below 600 ℃ under the promotion of NaCl powder serving as a catalyst 2 /WS 2 The vertical heterojunction nano material avoids the problems of thermal decomposition and atom replacement caused by high-temperature preparation.
In a preferred embodiment, the substrate is SiO 2 a/Si substrate. SiO used in the present invention 2 the/Si substrate is clean SiO 2 a/Si substrate.
Preferably, the temperature of the first chemical vapor deposition is 600-650 ℃, and the time of the first chemical vapor deposition is 2-5 min.
Within the time frame of the preferred embodiment, the WSe grown is allowed to grow 2 /WO 3 In the nanosheets, WSe 2 Nanosheets and WO 3 The nano-sheets are all single-layer, and the single-layerWO 3 The nano-sheet has higher reactivity, and is more beneficial to the reduction of the second chemical vapor deposition temperature.
In a preferred embodiment, the WSe 2 /WO 3 The growth process of the nanosheet is as follows: will contain WSe 2 Powder and WO 3 A container for the powder, the substrate being placed in a tube furnace having a gas inlet, a gas outlet and a central heating zone, in which WSe is contained 2 Powder and WO 3 The container of powder is placed in the central heating zone of the tube furnace and the substrate is placed in the downstream deposition zone of the tube furnace, said downstream deposition zone being close to the end of the gas outlet; then carrying out first vapor deposition on the surface of the substrate to grow and obtain WSe 2 /WO 3 Nanosheets.
Further preferably, the temperature of the central heating area is 980-1050 ℃.
In the invention, the temperature of the downstream deposition area is the temperature of the first chemical vapor deposition.
In a preferred scheme, the first chemical vapor deposition is carried out at normal pressure, argon is used as a carrier gas in the first chemical vapor deposition, and the flow rate of the argon is 50-80 sccm.
Preferably, the WSe will be included 2 /WO 3 Substrate of nanosheet, according to WSe 2 /WO 3 Covering a container filled with NaCl powder in a mode that the nano sheets face upwards, then placing the container in a central heating zone of a tubular furnace with a gas inlet, a gas outlet and the central heating zone, and placing the container containing S powder in an upstream zone, wherein the upstream zone is one end close to the gas inlet; then in a solution containing WSe 2 /WO 3 Carrying out second chemical vapor deposition on the substrate surface of the nanosheet to obtain WSe 2 /WS 2 A vertical heterojunction nanomaterial.
In the invention, the temperature of the second chemical vapor deposition is the temperature of the central heating zone of the tube furnace.
Further preferably, the temperature of the upstream zone is 100-200 ℃.
Preferably, the time of the second chemical vapor deposition is 5-10 min.
In a preferred embodiment, the pressure in the furnace during the second chemical vapor deposition is 1-10Torr, and most preferably 7 Torr.
The inventors have found that within the above-mentioned pressure range, WS can be made 2 Good nucleation and epitaxy, and is beneficial to WO 3 And NaCl evaporation, which is favorable for the reaction, and WS is unfavorable if the pressure is too low 2 Nucleation and epitaxy; too high pressure is detrimental to WO 3 And evaporation of NaCl, which is unfavorable for the reaction.
In a preferable scheme, the second chemical vapor deposition uses argon as a carrier gas, and the flow rate of the argon is 50-80 sccm.
The invention also provides WSe prepared by the preparation method 2 /WS 2 A vertical heterojunction nanomaterial.
In a preferred embodiment, the WSe 2 /WS 2 The vertical heterojunction nano material is in a vertically stacked layered structure, wherein the bottom layer is WSe 2 Layer, bottom layer stacked with WS 2 And (3) a layer.
In a preferred embodiment, the WSe 2 The layer is a monolayer and has a thickness of 0.9nm, WS 2 The layer was a single layer with a thickness of 0.9 nm.
Preferred embodiment, said WS 2 Layer stacked on WSe 2 Forming an overlap region behind the layers; the thickness of the overlapping area is 1.8 nm.
Preferably, WS is stacked on top 2 The area of the layer projected in the vertical direction is smaller than that of the bottom layer projected in the vertical direction.
WSe obtained by the invention 2 /WS 2 Compared with the heterostructure of a mechanical stripping stack, the vertical heterojunction nano material has strong interlayer coupling and small interlayer spacing. Under the irradiation of 488 nanometer laser, WSe 2 /WS 2 Significant interlayer exciton emission was observed for the vertical heterojunction nanomaterial region.
Principles and advantages
The preparation method of the present invention utilizes a two-step CVD process, the first process being WSe 2 And WO 3 The mixed powder is used as raw material, and the heating temperature of the raw material is strictly controlled so as to effectively control the raw materialEvaporation amount, carrier gas WSe 2 And WO 3 The vapor is sent to a deposition area, and when the temperature and the reactant concentration of the deposition area reach the most appropriate conditions, the WSe can be obtained 2 /WO 3 Nanosheets.
Second CVD Process, S powder and WO 3 The nano-sheet is used as a reaction raw material (the reaction zone is provided with WSe) 2 /WO 3 Si/SiO of nanosheet 2 Formed by spreading on a porcelain boat containing NaCl powder), due to Si/SiO 2 The sheet is laid on the NaCl powder and Si/SiO 2 WSe on a sheet 2 /WO 3 A certain gap is reserved between the nano-sheet and the NaCl powder, and WO with higher concentration exists in the gap 3 Steam, when S steam is first fed into the interspace by the carrier gas, with WO 3 Steam reaction to form WS 2 Nanosheet and deposition in WSe 2 Obtaining WSe on the nano-chip 2 /WS 2 Vertical heterojunction nanomaterials, simultaneous single layer WO 3 The nanosheet is more reactive and therefore can achieve WSe at a lower temperature 2 /WS 2 A vertical heterojunction nanomaterial.
The preparation method is simple and easy to operate, solves the technical problems that the bottom layer material of the vertical heterojunction nano material prepared by the two-step chemical vapor deposition method is easy to generate thermal decomposition, atom replacement and the like, and realizes high-quality WSe 2 /WS 2 And (3) preparing the vertical heterojunction nano material.
The preparation method can be popularized to the preparation of other transition metal chalcogenide heterostructures. The prepared sample has higher crystallization quality and has important significance for researching photoelectric integrated devices.
Drawings
FIG. 1 is a WSe prepared according to the present invention 2 /WS 2 A schematic diagram of a structure of a vertical heterojunction nano material and a schematic diagram of CVD growth.
FIG. 2 is the WSe prepared in example 1 2 /WS 2 Optical pictures of vertical heterojunction nanomaterials, where FIG. 2a is the WSe prepared in the first step 2 /WO 3 An optical picture of a vertical heterojunction nanomaterial; FIG. 2b shows a second stepObtained WSe 2 /WS 2 Optical pictures of vertical heterojunction nanomaterials.
FIG. 3 is the WSe prepared in example 1 2 /WS 2 TEM image of vertical heterojunction nanomaterial, wherein 3a is WSe prepared in example 1 2 /WS 2 A low-power transmission electron microscope photo of the vertical heterojunction nano material after being transferred to the copper mesh; FIG. 3b is the WSe prepared in example 1 2 /WS 2 Vertical heterojunction nano material and WSe 2 HRTEM picture of the interface region; FIG. 3c is the WSe prepared in example 1 2 /WS 2 An electron diffraction pattern of the vertical heterojunction nanomaterial stack region; FIG. 3d is the WSe prepared in example 1 2 /WS 2 Vertical heterojunction nanomaterial stacking region and WSe 2 Spectral characterization of the region.
FIG. 4 is the WSe prepared in example 1 2 /WO 3 And WSe 2 /WS 2 XPS spectra of vertical heterojunction nanomaterials.
FIG. 5 is the WSe prepared in example 2 2 /WS 2 Steady state photoluminescence spectra of vertical heterojunction nanomaterials. The black curve in the figure is in a single layer of WSe 2 Steady state photoluminescence spectra collected in regions corresponding to single layer WSe 2 The in-layer exciton emission of (a); the red curve is WSe 2 /WS 2 The photoluminescence spectrum, IE, collected by the heterostructure is an interlayer exciton emission peak, and an obvious interlayer exciton fluorescence emission peak indicates that effective charge transfer occurs between heterostructure layers, so that the interlayer excitons of each layer are converted into interlayer excitons. This efficient charge transfer results from strong interlayer coupling. Thus demonstrating strong interlayer coupling at the heterostructure.
Fig. 6 is an optical picture of a sample obtained in example, in which fig. 6a is an optical picture of comparative example 1, and fig. 6b is an optical picture of a sample obtained in example 2.
Detailed Description
The invention will now be further described with reference to the accompanying drawings in which:
example 1:
taking SiO 2 a/Si plate isCutting the substrate into size of 40mm × 300mm, ultrasonically washing in acetone solution for 20min, taking out, and oven drying at 60 deg.C. Taking a certain amount of WSe 2 And WO 3 The mixed powder is placed in a No. 1 porcelain boat and is placed in the center of a quartz tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (temperature of No. 2 porcelain boat: 640 ℃) in a heating furnace with the face facing upward. Ar inert gas with the flow rate of 80sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 1000 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 1000 ℃), and the temperature is kept for 3 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. Taking SiO above No. 2 porcelain boat 2 (ii)/Si wafer, FIG. 2a, optical microscope image shows the synthesized WSe 2 The layered nano sheet is triangular, the size of the layered nano sheet is about 50 mu m, and the thickness of the layered nano sheet is a single layer; WSe 2 WO of the above 3 The nano-sheet is circular, the size is about 10 mu m, and the thickness is a single layer.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, which is 25cm away from the center of the heating furnace, of the left side in the quartz tube. Placing appropriate amount of NaCl powder in No. 4 porcelain boat, and spreading two layers of WSe obtained in the first CVD process on the porcelain boat 2 /WO 3 Nanosheet of, SiO 2 The ceramic boat was placed face down in the heating center position in a heating furnace, then the internal pressure of the quartz tube was evacuated by a vacuum pump, Ar inert gas was introduced at a flow rate of 80sccm, and the pressure in the quartz tube was controlled to 7 Torr. The heating furnace is heated to 550 ℃ within 25 minutes (namely the heating temperature of the No. 4 porcelain boat is 550 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 5 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. Taking the obtained SiO 2 Longitudinal WSe on Si wafer 2 /WS 2 Vertical heterojunction nanomaterials, WSe, as shown in FIG. 2b 2 Upper WS 2 Is a single layer.
Example 2:
taking SiO 2 the/Si sheet is used as a substrate, cut into the size of 40mm multiplied by 300mm, ultrasonically washed in acetone solution for 20min, taken out and dried in an oven at 60 ℃. Taking a certain amount of WSe 2 And WO 3 Placing the mixed powder in a container 1And the porcelain boat is arranged in the center of the quartz tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (temperature of No. 2 porcelain boat: 640 ℃) in a heating furnace with the face facing upward. Ar inert gas with the flow rate of 70sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 980 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 980 ℃), and the temperature is kept for 5 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, which is 25cm away from the center of the heating furnace, of the left side in the quartz tube. Placing appropriate amount of NaCl powder in No. 4 porcelain boat, and spreading two layers of WSe obtained in the first CVD process on the porcelain boat 2 /WO 3 Nanosheet of, SiO 2 The ceramic boat was placed face down in the heating center position in a heating furnace, then the internal pressure of the quartz tube was evacuated by a vacuum pump, Ar inert gas was introduced at a flow rate of 80sccm, and the pressure in the quartz tube was controlled to 7 Torr. The heating furnace is heated to 550 ℃ within 25 minutes (namely the heating temperature of the No. 4 porcelain boat is 550 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 10 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. Taking the obtained SiO 2 Longitudinal WSe on Si wafer 2 /WS 2 Vertical heterojunction nanomaterial, stacked layer WS as shown in FIG. 6b 2 The coverage area of (2) becomes large, WSe 2 Upper WS 2 Is a single layer.
Comparative example 1:
taking SiO 2 the/Si sheet is used as a substrate, cut into the size of 40mm multiplied by 300mm, ultrasonically washed in acetone solution for 20min, taken out and dried in an oven at 60 ℃. Taking a certain amount of WSe 2 And WO 3 The mixed powder is placed in a No. 1 porcelain boat and is placed in the center of a quartz tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (650 ℃ for porcelain boat No. 2) in the heating furnace with the face facing upward. Ar inert gas with the flow rate of 50sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 1050 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 1050 ℃), and the temperature is kept for 2 minutes. After the reaction is finished, naturally cooling the heating furnace toAnd (4) room temperature.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, which is 25cm away from the center of the heating furnace, of the left side in the quartz tube. An empty porcelain boat 4 is placed in the heating center of the heating furnace, and two layers of WSe obtained in the first CVD process are laid on the porcelain boat 2 /WO 3 Nanosheet of, SiO 2 Face down, then the pressure in the quartz tube was evacuated by vacuum pump, Ar inert gas was introduced at a flow rate of 80sccm, and the pressure in the quartz tube was controlled to 7 Torr. The heating furnace is heated to 550 ℃ within 25 minutes (namely the heating temperature of the No. 4 porcelain boat is 550 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 10 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. Taking the obtained SiO 2 Samples on/Si wafers As shown in FIG. 6a, monolayer WSe 2 Without depositing WS thereon 2 Nanosheets.
Comparative example 2:
taking SiO 2 the/Si sheet is used as a substrate, cut into the size of 40mm multiplied by 300mm, ultrasonically washed in acetone solution for 20min, taken out and dried in an oven at 60 ℃. Taking a certain amount of WSe 2 And WO 3 The mixed powder is placed in a No. 1 porcelain boat and is placed in the center of a quartz tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (645 ℃ for porcelain boat No. 2) in a heating furnace with the face facing upward. Ar inert gas with the flow rate of 60sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 1020 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 1020 ℃), and the temperature is kept for 3 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, which is 25cm away from the center of the heating furnace, of the left side in the quartz tube. Placing appropriate amount of NaCl powder in No. 4 porcelain boat, and spreading two layers of WSe obtained in the first CVD process on the porcelain boat 2 /WO 3 Nanosheet of, SiO 2 The ceramic boat is placed at the heating center position in a heating furnace with the surface facing downwards, then the internal pressure of the quartz tube is forcibly pumped to vacuum by a vacuum pump, Ar inert gas with the flow rate of 80sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The furnace is put in 25 minutesThe temperature is increased to 550 ℃ (namely the heating temperature of the No. 4 porcelain boat is 550 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 5 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. The resulting SiO 2 No deposition of WS on the/Si wafer 2 Nanosheets.
Comparative example 3:
taking SiO 2 the/Si sheet is used as a substrate, cut into the size of 40mm multiplied by 300mm, ultrasonically washed in acetone solution for 20min, taken out and dried in an oven at 60 ℃. Taking a certain amount of WSe 2 And WO 3 The mixed powder is placed in a No. 1 porcelain boat and is placed in the center of a quartz tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (temperature of No. 2 porcelain boat: 640 ℃) in a heating furnace with the face facing upward. Ar inert gas with the flow rate of 70sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 980 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 980 ℃), and the temperature is kept for 5 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, with the distance of 25cm from the center of the heating furnace, of the left side in the quartz tube. Placing appropriate amount of NaCl powder in No. 4 ceramic boat, on which two layers of WSe obtained in the first CVD process are laid 2 /WO 3 Nanosheet of, SiO 2 The ceramic boat was placed face down in the heating center position in a heating furnace, then the internal pressure of the quartz tube was evacuated by a vacuum pump, Ar inert gas was introduced at a flow rate of 80sccm, and the pressure in the quartz tube was controlled to 7 Torr. The heating furnace is heated to 600 ℃ within 26 minutes (namely the heating temperature of the No. 4 porcelain boat is 600 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 10 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. The resulting SiO 2 WSe on/Si wafer 2 Decomposition of the nanosheet without WS 2 And (4) depositing the nano-sheets.
Comparative example 4:
taking SiO 2 the/Si sheet is used as a substrate, cut into the size of 40mm multiplied by 300mm, ultrasonically washed in acetone solution for 20min, taken out and dried in an oven at 60 ℃. Taking a certain amount of WSe 2 Placing the powder in No. 1 porcelain boat and quartzThe center of the tube. No. 2 porcelain boat is paved with 1 piece of SiO 2 Si wafer, SiO 2 The porcelain boat was placed in a low temperature position (temperature of No. 2 porcelain boat: 640 ℃) in a heating furnace with the face facing upward. Ar inert gas with the flow rate of 80sccm is introduced, and the pressure in the quartz tube is controlled to be normal pressure. The heating furnace is heated to 1020 ℃ within 15 minutes (namely the heating temperature of the No. 1 porcelain boat is 1020 ℃), and the temperature is kept for 3 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature.
In the second CVD process, a certain amount of S powder is placed in a No. 3 porcelain boat and is placed in the position, which is 25cm away from the center of the heating furnace, of the left side in the quartz tube. Appropriate amount of NaCl and WO 3 Placing the mixed powder in No. 4 porcelain boat, and spreading WSe obtained in the first CVD process on the porcelain boat 2 Nanosheets, SiO 2 The ceramic boat was placed face down in the heating center position in a heating furnace, then the internal pressure of the quartz tube was evacuated by a vacuum pump, Ar inert gas was introduced at a flow rate of 80sccm, and the pressure in the quartz tube was controlled to 7 Torr. The heating furnace is heated to 550 ℃ within 24 minutes (namely the heating temperature of the No. 4 porcelain boat is 550 ℃), the heating temperature of the No. 3 porcelain boat is 200 ℃, and the temperature is kept for 10 minutes. And after the reaction is finished, naturally cooling the heating furnace to room temperature. The resulting SiO 2 WSe obtained by the first process of the Si wafer 2 Nanosheets, not having WS 2 And (4) depositing the nano-sheets.
Claims (6)
1. WSe 2 /WS 2 The preparation method of the vertical heterojunction nano material is characterized by comprising the following steps: the method comprises the following steps: with WSe 2 Powder and WO 3 The powder is used as raw material, and WSe is grown on the surface of the substrate by first chemical vapor deposition 2 /WO 3 The temperature of the first chemical vapor deposition is 600-650 ℃, the time of the first chemical vapor deposition is 2-5min, the first chemical vapor deposition is carried out under normal pressure, argon is used as carrier gas in the first chemical vapor deposition, the flow rate of the argon is 50-80 sccm, and then the WSe-containing component is added 2 /WO 3 Covering the substrate of the nano sheet in a container filled with NaCl powder, and leaving an opening in the container filled with NaCl powder, and in an environment containing S steam, in a WSe-containing environment 2 /WO 3 Carrying out second chemical vapor deposition on the surface of the substrate of the nanosheet, controlling the temperature of the second chemical vapor deposition to be 530-570 ℃, controlling the time of the second chemical vapor deposition to be 5-10min, and controlling the pressure in the furnace to be 1-10Torr during the second chemical vapor deposition; the second chemical vapor deposition takes argon as carrier gas, and the flow rate of the argon is 50-80 sccm; namely to obtain WSe 2 /WS 2 A vertical heterojunction nanomaterial.
2. A WSe according to claim 1 2 /WS 2 The preparation method of the vertical heterojunction nano material is characterized by comprising the following steps: the WSe 2 /WO 3 The growth process of the nanosheet is as follows: will contain WSe 2 Powder and WO 3 A container for the powder, the substrate being placed in a tube furnace having a gas inlet, a gas outlet and a central heating zone, in which WSe is contained 2 Powder and WO 3 The container of powder is placed in the central heating zone of the tube furnace and the substrate is placed in the downstream deposition zone of the tube furnace, said downstream deposition zone being close to one end of the gas outlet; then carrying out first vapor deposition on the surface of the substrate to grow and obtain WSe 2 /WO 3 Nanosheets; the temperature of the central heating area is 980-1050 ℃.
3. A WSe according to claim 1 2 /WS 2 The preparation method of the vertical heterojunction nano material is characterized by comprising the following steps: will contain WSe 2 /WO 3 Substrate of nanosheet, according to WSe 2 /WO 3 Covering a container filled with NaCl powder in a mode that the nanosheets face upwards, then placing the container in a central heating area of a tube furnace with a gas inlet, a gas outlet and the central heating area, and placing the container containing S powder in an upstream area, wherein the upstream area is one end close to the gas inlet; then in a solution containing WSe 2 /WO 3 Carrying out second chemical vapor deposition on the substrate surface of the nanosheet to obtain WSe 2 /WS 2 A vertical heterojunction nanomaterial; the temperature of the upstream zone is 100-200 ℃.
4. The article of any one of claims 1-3Preparation method of prepared WSe 2 /WS 2 A vertical heterojunction nanomaterial.
5. WSe prepared by the preparation method according to any one of claims 1 to 3 2 /WS 2 The vertical heterojunction nano material is characterized in that: the WSe 2 /WS 2 The vertical heterojunction nano material is in a vertically stacked layered structure, wherein the bottom layer is WSe 2 Layer, bottom layer stacked with WS 2 And (3) a layer.
6. WSe prepared by the preparation method according to any one of claims 1 to 3 2 /WS 2 The vertical heterojunction nano material is characterized in that: the WSe 2 The layer is a monolayer and has a thickness of 0.9nm, WS 2 The layer is a single layer with a thickness of 0.9 nm;
the WS 2 Layer stacked on WSe 2 Forming an overlap region behind the layers; the thickness of the overlapping region is 1.8 nm;
said stacked WS on top layer 2 The area of the layer projected in the vertical direction is smaller than that of the bottom layer projected in the vertical direction.
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