A method for adjusting wide spectrum detection of transition metal chalcogenide by using vacancy defects

Abstract

A method for adjusting the wide spectrum detection of transition metal chalcogenides by using vacancy defects belongs to the field of two-dimensional materials. In the method, transition metal oxides are used as metal sources, two different chalcogen elements are used as sulfur sources, and a single-layer ternary transition metal chalcogen compound with uniform element distribution is grown by using a chemical vapor deposition method. By using the difference in the stability of the chemical bonds between alloy elements, the unstable chemical bonds are broken by hydrogen-assisted annealing, and the generated chalcogen element vacancy defects are uniformly distributed in the ternary transition metal chalcogen compound. The chalcogen element vacancy defects introduce defect energy levels between the conduction band and the valence band of the transition metal chalcogen compound, generate new photoluminescence peaks, and widen the spectrum detection range. The experimental method is simple in process, good in repeatability, can accurately control the type, distribution and number of defects, and is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of two-dimensional materials, and relates to a method for adjusting wide-spectrum detection of transition metal chalcogenide compounds by using vacancy defects. TECHNICAL BACKGROUND

[0002] Two-dimensional transition metal chalcogenide (TMDs) has a wide range of applications in the fields of electricity and photoelectricity due to its atomic layer thickness, adjustable band gap, high carrier mobility and other characteristics. In order to further regulate and widen the spectral response range of TMDs materials, methods such as stress application, alloying, interlayer coupling and defect engineering have been developed to adjust the energy band. However, the band gap of TMDs materials can be adjusted to a certain extent through the methods of stress and alloying, but the adjustment range is limited due to the inherent band gap of the material. Although the band gap of TMDs materials can be adjusted in a wide range through the method of interlayer coupling, it faces the problem of low light response, which is mainly caused by the fact that the electrons in the conduction band and the holes in the valence band are not in the same position in the K space when two different TMDs materials are stacked together. Defect engineering is a more effective method to adjust the energy band, which introduces a defect level between the conduction band and the valence band of the material, thereby adjusting the band gap. At present, there are articles that introduce the method of pulsed laser deposition to prepare MoS 1.89 materials, and the detection wavelength can reach 2.7 microns. By proton beam irradiation on MoS2, WS2, MoSe2, WSe2 and other materials, a sub-bandgap photoluminescence peak can be introduced below the neutral exciton peak by 100-200 meV. In addition, the band gap of WSe2 can be changed from 1.6 eV to 1.3 eV through annealing. The methods of pulsed laser deposition or proton / ion beam irradiation face the problems of time-consuming and high cost; the methods of plasma irradiation and heating are difficult to control the type and number of defects. SUMMARY

[0003] In view of the above problems, the application provides a method for adjusting the band gap of the material by using alloying and defects. First, a ternary transition metal chalcogenide with uniform distribution of elements is synthesized by chemical vapor deposition to adjust the band gap of the material to a certain extent; second, by using the difference in the stability of the chemical bonds between alloying elements, the unstable chemical bonds are broken by hydrogen-assisted annealing to prepare a ternary transition metal chalcogenide with uniform distribution of chalcogen vacancy defects. Defect levels are introduced between the conduction band and the valence band of the ternary transition metal chalcogenide, thereby adjusting the band gap.

[0004] To solve the above problems, the technical scheme adopted by the application is as follows:

[0005] The application discloses a method for adjusting wide-spectrum detection of a transition metal chalcogenide compound by defect engineering, and is characterized in that: a salt is added to a transition metal oxide as a promoter, a growth temperature is controlled at 750-850 DEG C, a large-area ternary transition metal chalcogenide compound (composed of two chalcogen elements and metal elements Mo or / and W) is prepared, and the ternary transition metal chalcogenide compound is annealed by a hydrogen-assisted annealing method, so that the ternary transition metal chalcogenide compound with a certain defect concentration is prepared.

[0006] Specifically, the method comprises the following steps:

[0007] (1) cleaning the surface of a growth substrate;

[0008] (2) preparing the salt, grinding the salt with large particles into powder by using a mortar, and weighing a certain mass of the salt; weighing a certain mass of transition metal source powder as a metal source;

[0009] (3) weighing a certain mass of two chalcogen element powders, pouring the two chalcogen element powders into a centrifugal tube according to a certain proportion, and stirring uniformly, and weighing a certain mass of the chalcogen element mixed powder as a sulfur source;

[0010] (4) transferring the weighed transition metal source powder and the salt powder to a corundum boat, mixing, placing the growth substrate above the transition metal source, and polishing the surface downward for growing the ternary alloy, and then pushing the corundum boat to the center temperature zone position of the tube furnace by using a furnace hook; pouring the weighed chalcogen element mixed powder into a glass boat, and placing the glass boat in a low-temperature zone upstream of the carrier gas flow at a certain distance from the center position of the tube furnace; the carrier gas enters from one end of the tube furnace and is discharged from the other end;

[0011] (5) in the chemical vapor deposition reaction process, inert gas is used as the carrier gas, and the temperature at the center of the tube furnace is set according to time periods as follows: the temperature is divided into three stages, the first stage is a tube furnace exhaust stage of passing in the carrier gas, the second stage is a ternary alloy growth stage, the ternary alloy is grown by passing in the carrier gas according to a certain temperature rising rate, then reaching a certain temperature T2 and being kept at the temperature T2 for a period of time, and the hydrogen gas is passed in when the temperature rises to T1 until the growth is completed; the third stage is a natural cooling stage;

[0012] (6) annealing the sample, taking out the sample for Raman and PL characterization, placing the sample with the growth surface upward in a clean corundum boat after the characterization is completed, and placing the corundum boat in a clean quartz tube.

[0013] (7) sequentially washing the quartz tube by passing in inert gas and hydrogen gas, heating the furnace, keeping for a period of time, and naturally cooling.

[0014] Preferably, the cleaning in step (1) is ultrasonic cleaning with acetone, alcohol and deionized water in sequence, the ultrasonic time is 5-15 min, and the power is set to 40-100 W.

[0015] Preferably, the salt in step (2) includes sodium chloride, potassium iodide, etc.

[0016] Preferably, the transition metal source in step (2) includes one or more of MoO3 and WO3.

[0017] Preferably, the two chalcogen elements in step (3) are S powder and Te powder, or Se powder and Te powder; and the mass ratio of the S powder and Te powder, or Se powder and Te powder is preferably 3:100-8:100.

[0018] Preferably, the growth substrate in step (4) includes a silicon / silicon dioxide substrate, sapphire, mica, etc., and the silicon / silicon dioxide substrate is preferred.

[0019] Preferably, the mass ratio of the transition metal source powder, the salt powder and the two chalcogen elements in step (4) is (1-10):(0.5-4):(200-400), and the corresponding masses are preferably 1-10 mg, 0.5-4 mg and 200-400 mg, respectively.

[0020] Preferably, the distance of the glass boat from the center of the furnace in step (4) is 13.5-16 cm, and the temperature is maintained at 250-600 ℃.

[0021] Preferably, the carrier gas in step (5) is an inert gas, and Ar gas or N2 gas is preferred; the flow rate of the inert gas in the first stage is 200-400 sccm, and the gas flushing time is 10-30 min.

[0022] Preferably, the flow rate of the carrier gas in the second stage in step (5) is 45-60 sccm.

[0023] Preferably, the hydrogen gas in step (5) is introduced when the furnace temperature T1 reaches 600 ℃; and the flow rate of the hydrogen gas in the second stage in step (5) is preferably 5-10 sccm, and more preferably 5 sccm.

[0024] Preferably, the second stage T2 growth temperature in step (5) is 750-850 ℃, and more preferably 750 ℃.

[0025] Preferably, the second stage growth time in step (5), i.e., the holding time at the T2 temperature, is 3-15 min, and more preferably 3-5 min.

[0026] Preferably, in step (7), the annealing temperature is 200-350 DEG C, the annealing time is 10-60 min, the argon flow is 40-60 sccm, and the hydrogen flow is 5-15 sccm.

[0027] The advantages of the present application are as follows:

[0028] The present application adopts the atmospheric pressure chemical vapor deposition method to grow and prepare defects of ternary transition metal chalcogenide compounds.

[0029] The present application adopts the chemical vapor deposition method to prepare monolayer ternary transition metal chalcogenide compounds, wherein the elements are uniformly distributed in the ternary transition metal chalcogenide compounds.

[0030] The present application utilizes the difference in chemical bond stability among the elements in the ternary transition metal chalcogenide compounds, and breaks the chemical bonds with poor stability through hydrogen-assisted annealing, thereby preparing ternary transition metal chalcogenide compounds with uniform distribution of chalcogen vacancy defects.

[0031] Since the Se atoms or S atoms and part of the Te atoms are retained, the framework structure of the ternary transition metal chalcogenide compounds is maintained, and the stability of the alloy structure is ensured.

[0032] Firstly, the band gap of the ternary transition metal chalcogenide compound is adjusted by the alloy method, which reduces the band gap to a certain extent; secondly, the defect energy level is introduced into the ternary transition metal chalcogenide compound by the defect introduction method in step (7), and a new PL peak appears, which enables the wide spectrum detection (relative to the spectrum without entering the defect).

[0033] The present method is simple, reproducible, and can accurately control the type, distribution and number of defects, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The chemical vapor deposition growth of WSe 2(1-x) Te 2x The experimental device of the alloy;

[0035] Figure 2 The Raman and PL spectra of WSe2 in Example 1;

[0036] Figure 3 The optical microscope and atomic force microscope images of WSe 1.7 Te 0.3 in Example 2;

[0037] Figure 4 The optical microscope and atomic force microscope images of WSe 1.7 Te 0.3Raman and PL spectra of the alloy;

[0038] Figure 5 WSe2 after annealing in Example 2 1.7 Te 0.3 Raman and PL spectra of the alloy;

[0039] Figure 6 WSe2 after annealing in Example 3 1.7 Te 0.3 Raman and PL spectra of the alloy;

[0040] Figure 7 WSe2 after annealing in Example 3 1.7 Te 0.3 Response of the alloy to light of different wavelengths DETAILED DESCRIPTION

[0041] The application will be further described below in conjunction with the accompanying drawings and examples, but is not limited to the application.

[0042] Example 1:

[0043] A 400-μm-thick SiO2 / Si (wherein the SiO2 is 285 nm) was used as a growth substrate, a 4-inch silicon wafer was cut into a 1-cm*1-cm square, and acetone, alcohol, and deionized water were used for ultrasonic cleaning for 15 min, with the power set to 100 W; 8 mg of WO3 powder and 1 mg of NaCl powder were weighed into a corundum boat, the Si / SiO2 substrate was placed obliquely above the WO3 and NaCl powders, and pushed to the center position of the tube furnace; 300 mg of Se powder was weighed into a small quartz boat, and the quartz boat was placed in the upstream area of the tube furnace, at a distance of 14 cm from the center temperature zone of the tube furnace. WSe2 2(1-x) Te 2x The experimental device for growing the alloy is shown in Figure 1 .

[0044] Gas washing was performed with 200 sccm of argon, and the gas washing time was set to 15-20 min; after gas washing, the flow rate of argon was adjusted to 45 sccm for the growth of WSe2 alloy, the furnace was heated at a rate of 50 ℃ / min to 750 ℃, and was kept at this temperature for 3 min. When the furnace temperature was raised to 600 ℃, 5 sccm of hydrogen was introduced. After the growth was completed, when the furnace temperature was cooled to 600 ℃, the hydrogen was turned off, the furnace was opened, and natural cooling to room temperature was performed. The Raman and PL spectra of the obtained WSe2 are shown in Figure 2 . It can be seen from the figure that the PL peak of WSe2 is located at 765 nm.

[0045] Example 2:

[0046] A 400μm thick SiO2 / Si (where SiO2 is 285nm) substrate was used as the growth substrate. A 4-inch silicon wafer was cut into 1cm*1cm squares and ultrasonicated for 15 minutes each with acetone, alcohol, and deionized water, with the power set at 100W. 8mg of WO3 powder and 1mg of NaCl powder were weighed and poured into an alumina boat. The Si / SiO2 substrate was tilted and placed on top of the WO3 and NaCl powders and pushed to the center of the tube furnace. 300mg of a mixture of Se powder and Te powder (mass ratio of 5:100) was weighed and placed in a quartz boat. The quartz boat was placed in the upstream area of ​​the tube furnace, 14cm away from the center temperature zone of the tube furnace.

[0047] Purging was performed using argon gas at a flow rate of 200 sccm for 15-20 minutes; after purging, the argon gas flow rate was adjusted to 45 sccm for WSe purification. 2(1-x) Te 2x For alloy growth, the furnace was heated to 750°C at a rate of 50°C / min and held at this temperature for 3 minutes. When the furnace temperature reached 600°C, hydrogen gas was introduced at a flow rate of 5 sccm. After growth, the furnace temperature was allowed to drop to 600°C, the hydrogen gas was turned off, the furnace was opened, and the furnace was allowed to cool naturally to room temperature. The resulting WSe... 1.7 Te 0.3 Optical microscopy, AFM, Raman, and PL spectra of the alloy are shown below. Figure 3 and Figure 4 AFM characterization of the grown WSe 1.7 Te 0.3 The alloy thickness is 0.76 nm, indicating that it is monolayer. Raman characterization shows that WSe has grown. 1.7 Te 0.3 Alloy, and WSe 1.7 Te 0.3 The PL peak of the alloy is located at 800 nm, which is shifted 25 nm to the right compared to the PL peak of WSe2. This is mainly due to the incorporation of Te, which makes WSe2 more volatile. 1.7 Te 0.3 The band gap of the alloy decreases.

[0048] The grown sample was placed in a new corundum boat and a new quartz tube, with the corundum boat positioned in the center of the furnace. The quartz tube was purged with argon gas at 200 sccm for 15-20 minutes to remove air. After purging, the argon flow rate was adjusted to 45 sccm; hydrogen gas was then introduced at 5 sccm. The furnace was started, and the heating rate was set to 30℃ / min, reaching 250℃, and annealed at this temperature for 30 minutes. After annealing, the hydrogen gas was turned off, the furnace was opened, and the sample was allowed to cool naturally to room temperature. The annealed WSe... 1.7 Te 0.3The Raman and PL spectra of the alloy are shown in Figure 5 ; the unannealed WSe 1.7 Te 0.3 The alloy only has a PL peak at 800 nm Figure 4 , while the WSe 1.7 Te 0.3 alloy has PL peaks at 800 nm and 876 nm, which is mainly due to the fact that the annealing process breaks the unstable W-Te bond, introduces a defect energy level between the conduction band and the valence band of the alloy, and causes the appearance of a new 876 nm peak.

[0049] Example 3:

[0050] A 400-μm-thick SiO2 / Si (with SiO2 being 285 nm) was used as a growth substrate, a 4-inch silicon wafer was cut into a 1 cm*1 cm square, and acetone, alcohol, and deionized water were used for ultrasonic cleaning for 15 min, with the power being set to 100 W; 8 mg of WO3 powder and 1 mg of NaCl powder were poured into a corundum boat, the Si / SiO2 substrate was placed obliquely above the WO3 and NaCl powder, and was pushed to the center of the tube furnace; 300 mg of a mixed powder of Te powder and Se powder (mass ratio of 5:100) was placed in a small quartz boat, and the small quartz boat was placed in the upstream area of the tube furnace, at a distance of 14 cm from the center temperature zone of the tube furnace;

[0051] 200 sccm of argon was used for gas washing, and the gas washing time was set to 15-20 min; after the gas washing was completed, the flow rate of argon was adjusted to 45 sccm for the growth of WSe 2(1-x) Te 2x alloy, the furnace was heated to 750℃ at a heating rate of 50℃ / min, and was kept at this temperature for 3 min. When the furnace temperature was raised to 600℃, 5 sccm of hydrogen was introduced. After the growth was completed, when the furnace temperature was cooled to 600℃, the hydrogen was turned off, the furnace was opened, and the natural cooling to room temperature was performed.

[0052] The grown sample was placed in a new corundum boat, and the corundum boat was placed in the center of the furnace. Similarly, 200 sccm of argon was used for gas washing for 15-20 min, and the air in the quartz tube was removed. After the gas washing was completed, the flow rate of argon was adjusted to 45 sccm; 5 sccm of hydrogen was introduced. The furnace was started, the heating rate of the furnace was set to 30℃ / min, and the furnace was heated to 280℃, and was annealed at this temperature for 30 min. After the annealing was completed, the hydrogen was turned off, the furnace was opened, and the natural cooling to room temperature was performed. The Raman and PL spectra of the annealed WSe 1.7 Te 0.3 alloy are shown in Figure 6 . Figure 6WSe annealed in the middle 1.7 Te 0.3 A new PL peak of 910 nm appears, Figure 5 WSe annealed in the middle 1.7 Te 0.3 A PL peak of 876 nm appears, Figure 6 The wavelength of the newly appearing PL peak is larger than Figure 5 The wavelength of the newly appearing PL peak is larger, which is mainly due to the increase of the annealing temperature, and more Te vacancy defects are introduced. Figure 7 WSe 1.7 Te 0.3 The light response of the alloy annealed at 280 DEG C to different wavelengths, since it can have light response to 1000 nm light, it can perform wide spectrum detection.

[0053] The application grows ternary transition metal chalcogenide with uniform distribution of elements by chemical vapor deposition, the ternary transition metal chalcogenide is composed of two chalcogen elements and metal elements Mo or / and W, the difference in stability of chemical bonds between elements is utilized, then hydrogen assisted annealing is used to make the chemical bonds with poor stability break, produce ternary transition metal chalcogenide with uniform distribution of chalcogen element vacancy defects, introduce defect energy level between the conduction band and the valence band of the ternary transition metal chalcogenide alloy, a new PL peak appears, and it can perform relatively wider spectrum detection.

Claims

1. A method for preparing transition metal chalcogenide capable of wide spectrum detection by defect engineering, characterized in that, The ternary transition metal chalcogenide with uniform distribution of elements is grown by chemical vapor deposition, the ternary transition metal chalcogenide is composed of two chalcogen elements and metal elements Mo or / and W, the chemical bond stability difference between elements is utilized, the chemical bond with poor stability is broken by hydrogen assisted annealing, the ternary transition metal chalcogenide with uniform distribution of chalcogen element vacancy defects is generated, the defect energy level is introduced between the conduction band and the valence band of the ternary transition metal chalcogenide alloy, a new PL peak appears, and relatively wider spectrum detection can be performed; Specifically, the method comprises the following steps: (1) cleaning the surface of a growth substrate; (2) preparing a salt, grinding the salt with large particles into powder with a mortar, and weighing a certain amount of the salt; weighing a certain amount of transition metal source powder as a metal source; (3) weighing a certain amount of two kinds of chalcogen element powders, pouring them into a centrifuge tube according to a certain proportion, and stirring uniformly, and weighing a certain amount of chalcogen element mixed powder as a sulfur source; (4) transferring the weighed transition metal source powder and salt powder to a corundum boat, mixing, placing the growth substrate above the transition metal source with the polished surface downward for growing the ternary alloy, and then pushing the corundum boat to the center temperature zone position of the tube furnace with a furnace hook; pouring the weighed chalcogen element mixed powder into a glass boat, placing the glass boat in the low temperature zone upstream of the carrier gas flow at a certain distance from the center position of the tube furnace; the carrier gas enters from one end of the tube furnace and is discharged from the other end; (5) during the chemical vapor deposition reaction process, inert gas is used as the carrier gas, and the temperature at the center of the tube furnace is set as follows according to time periods: the temperature is divided into three stages, the first stage is a tube furnace exhaust stage by passing in the carrier gas, the second stage is a ternary alloy growth stage, which is heated at a certain heating rate under the condition of passing in the carrier gas, then reaches a certain temperature T2 and is kept at this temperature for a period of time, and hydrogen is passed in when the temperature reaches T1 until the growth is completed; the third stage is a natural cooling stage; (6) annealing of the sample; removing the sample for Raman and PL characterization, placing the sample with the grown surface upward in a clean corundum boat after the characterization is completed, and then placing the corundum boat in a clean quartz tube, sequentially washing the quartz tube with inert gas and hydrogen, heating the furnace, keeping the temperature for a period of time, and then naturally cooling.

2. The method of claim 1, wherein, The cleaning in step (1) is ultrasonic cleaning with acetone, alcohol and deionized water in sequence, the ultrasonic time is 5-15 min, and the power is set to 40-100 W.

3. The method of claim 1, wherein, The salt in step (2) includes sodium chloride and potassium iodide; the transition metal source in step (2) includes one or more of MoO3 and WO3; and the two kinds of chalcogen elements in step (3) are S powder and Te powder, or Se powder and Te powder.

4. The method of claim 3, wherein, The mass ratio of the S powder and the Te powder is 3:100-8:100, or the mass ratio of the Se powder and the Te powder is 3:100-8:

100.

5. The method of claim 1, wherein, The growth substrate in step (4) includes silicon / silicon dioxide substrate, sapphire, mica; the mass ratio of transition metal source powder, salt powder and two chalcogen elements in step (4) is (1-10):(0.5-4):(200-400); the distance between the glass boat in step (4) and the center of the furnace is 13.5-16 cm, and the temperature is maintained at 250-600℃.

6. The method of claim 1, wherein, The carrier gas in step (5) is inert gas or N2; the flow rate of the inert gas in the first stage is 200-400sccm, and the gas washing time is 10-30min; The flow rate of the carrier gas in the second stage in step (5) is 45-60sccm; The hydrogen gas in step (5) is introduced when the furnace temperature T1 reaches 600℃; the flow rate of the hydrogen gas in the second stage in step (5) is 5-10sccm; The second stage T2 growth temperature in step (5) is 750-850℃; The second stage growth time in step (5) is the holding time at T2 temperature, which is 3-15min.

7. The method of claim 1, wherein, The carrier gas in step (5) is Ar; the second stage growth time in step (5) is the holding time at T2 temperature, which is 3-5min.

8. The method of claim 1, wherein, The annealing temperature in step (6) is 200-350℃, the annealing holding time is 10-60min; the flow rate of the introduced argon gas is 40-60sccm, and the flow rate of the introduced hydrogen gas is 5-15sccm.

9. A defect transition metal chalcogenide prepared according to the method of any one of claims 1-8.

10. Use of a defect transition metal chalcogenide prepared according to the method of any one of claims 1-6 for a wider spectral detection than a relatively non-defect transition metal chalcogenide.

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