WO2017166028A1 - Tungsten sulfide film and preparation method therefor - Google Patents

Abstract

A method for preparing a large-area tungsten sulfide film, comprising the following steps: plating an atomically thin W layer on a silicon substrate; plating an atomically thin S layer on the W layer; and plating another atomically thin W layer on the S layer, so as to obtain a monolayer WS₂ film with a W-S-W layered structure.

Description

 Tungsten sulfide film and preparation method thereof Technical field

The invention belongs to the technical field of inorganic nano film materials, in particular to a tungsten sulfide film and a preparation method thereof.

Background technique

The tungsten sulfide (WS ₂ ) film is similar in structure and properties to the molybdenum sulfide film, and the tungsten sulfide film also has a controllable band gap. The band gap WS _{2 has} a band gap of 1.3 eV, and its electronic transition mode indirect transition; when the thickness is a single layer, the band gap of WS ₂ can reach 2.1 eV, and its electronic transition mode is converted into a direct transition. Therefore, the unique structure and excellent physical properties of the WS ₂ film and the adjustable band gap make it a two-dimensional nanomaterial with very important application prospects in the field of electronic devices, especially in the fields of electricity, optics and semiconductors. Due to its special optical and electrical properties, tungsten disulfide films have been widely used in optoelectronics and are widely used in the manufacture of field effect transistors, sensors, light-emitting diodes, bulk capacitor memories and lithium battery electrodes. At the same time, due to their special crystal structure, they are also widely used in the fields of catalysis and friction reduction. Although WS ₂ film has great application potential, the single-layer WS ₂ film is grown in the prior art, and its product surface is small in size, relatively dense, and has a large sulfur vacancy, resulting in a film having better performance. difference.

technical problem

In order to solve the above technical problems, the present invention provides a method for preparing a tungsten sulfide film, which aims to obtain a better method for preparing a large-area high-quality WS ₂ film, and to make up for the deficiencies of the WS ₂ film in the process preparation method.

Technical solution

The present invention is achieved by a method for preparing a tungsten sulfide film, comprising the steps of:

Step 1: plating a layer of W with a thickness of one atom on the silicon substrate;

Step 2: plating an S layer having a thickness of one atom on the W layer;

Step 3: plating another layer of W layer having a thickness of one atom on the S layer to obtain a WS ₂ film;

The WS ₂ film is a single layer film of a WSW layered structure.

Further, the material of the silicon substrate is SiO ₂ .

Further, the silicon substrate is cleaned before use, and the cleaning process is: sequentially performing ultrasonic soaking of acetone, deionized water cleaning, cleaning of hydrogen peroxide and concentrated sulfuric acid, and deionized water cleaning on the silicon substrate.

Further, the mass ratio of acetone used in the ultrasonic soaking of the acetone to the silicon substrate is 20:1.

Further, the ultrasonic soaking frequency of the acetone is 28 kHz, the power is 150 W, and the cleaning time is 10 to 25 min.

Further, the cleaning process of the hydrogen peroxide and concentrated sulfuric acid mixture is: the silicon substrate is placed in the mixed solution for 2h-3h.

Further, the mixture of the hydrogen peroxide and the concentrated sulfuric acid is prepared by adding a 30% aqueous solution of hydrogen peroxide to 98% concentrated sulfuric acid, stirring, and completely cooling the solution to obtain a mixed solution; the volume ratio of the aqueous hydrogen peroxide solution to the concentrated sulfuric acid solution is 1 :3.

Further, the techniques used in the first step and the third step to plate a layer of W atoms include one of an ALD technique (atomic layer deposition technique), a pulsed laser deposition technique, and a magnetron sputtering technique.

Further, the method used in the second step is a CVD method (chemical vapor deposition method).

The present invention also provides a tungsten sulfide film which is produced by the above-described preparation method.

Further, the film is a one-piece continuous type having an area of 1-3 square centimeters.

Beneficial effect

Compared with the prior art, the present invention has the beneficial effects that the present invention first coats a silicon atom layer on a silicon substrate by using an ALD technique, and then uses a CVD method to grow a layer of S atoms on the W atom layer, and then A layer of W atoms was plated using ALD technology to grow a single layer WS ₂ film of WSW layered structure. By the method of the invention, large-area preparation of the WS ₂ film can be achieved; and the prepared WS ₂ film has good compactness and less sulfur vacancies, which makes the quality thereof significantly improved, thereby greatly improving the electrical properties of the WS ₂ film.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of the ALD basic reaction cycle in the present invention.

2 is a schematic view showing the process flow of the technical solution of the present invention.

Figure 3 is a test result of an optical microscope and a Raman spectrometer; wherein Fig. 3 (a) Raman test results, and Fig. 3 (b) are PL test results.

Embodiments of the invention

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Chemical vapor deposition (CVD): refers to a process in which a vapor containing a gaseous reactant or a liquid reactant constituting a thin film element and other gases required for the reaction are introduced into a reaction chamber to chemically react on the surface of the substrate to form a thin film.

Atomic Layer Deposition (ALD): A method in which materials can be plated on the surface of a substrate layer by layer in the form of a monoatomic film. The basic process of atomic layer deposition technology is to alternately pass the gas phase precursor pulse into the reaction chamber, and a surface chemisorption reaction occurs on the deposition substrate to form a thin film. Atomic layer deposition is similar to ordinary chemical deposition.

Pulsed Laser Deposition (PLD): A means of bombarding an object with a laser and then depositing the bombarded material onto a different substrate to obtain a precipitate or film.

Magnetron sputtering technology: electrons collide with argon atoms during the acceleration of flying into the substrate under the action of an electric field, ionizing a large amount of argon ions and electrons, and electrons fly toward the substrate. The argon ions accelerate the bombardment of the target under the action of the electric field, and sputter a large number of target atoms, and a neutral target atom (or molecule) is deposited on the substrate to form a film.

According to the technical solution of the present invention, a tungsten sulfide film is prepared, and the process is as follows:

First, a SiO ₂ silicon substrate was prepared, and it was washed with acetone, deionized water, a mixture of hydrogen peroxide and concentrated sulfuric acid. Specifically, the mixture of hydrogen peroxide and concentrated sulfuric acid is prepared by adding a 30% aqueous solution of hydrogen peroxide to 98% concentrated sulfuric acid, stirring, and completely cooling the solution to obtain a mixed solution; the volume ratio of the aqueous hydrogen peroxide solution to the concentrated sulfuric acid solution is 1: 3.

The SiO ₂ silicon substrate was sequentially subjected to acetone ultrasonic soaking, deionized water washing, hydrogen peroxide mixed with concentrated sulfuric acid, and deionized water washing. Specifically, ultrasonic cleaning with acetone for 20 min, wherein the mass ratio of acetone used to the silicon substrate is 20:1; the frequency of acetone soaking is 28 kHz, the power is 150 W; then it is washed with deionized water; Soak the mixture of hydrogen peroxide and concentrated sulfuric acid for 2h-3h, then rinse with deionized water.

Preparation of tungsten sulfide film, the specific operation process is as follows:

Step one, using a ALD technique to plate a layer of W atoms on the silicon substrate:

This process is performed using ALD technology, which is not a continuous process but consists of a series of semi-reactions. Figure 1 is a schematic diagram of the ALD basic reaction cycle. Each unit cycle is usually divided into four steps: First, a precursor A vapor pulse is introduced into the reaction chamber, and a chemisorption reaction occurs on the exposed substrate surface; then a purge gas is introduced. (usually an inert gas such as high-purity nitrogen or argon), bringing the unadsorbed precursor A vapor and reaction by-products out of the reaction chamber; then passing the precursor B vapor pulse to surface chemistry with the surface-adsorbed A The reaction is finally passed again to remove the excess B vapor and reaction by-products out of the reaction chamber. Theoretically, a single atomic layer is deposited on the surface of the substrate for each cycle. L in Figure 1 is a precursor ligand. Specifically, in combination with FIG. 1, A vapor and B vapor are reaction gases in the ALD growth process, and corresponding to the growth of the tungsten atomic layer A vapor in the process is WF ₆ , B vapor Si ₂ H ₆ .

For the growth of the tungsten atomic layer in this process, the reaction is extremely stable based on the Si-F bond, resulting in a typical exothermic reaction. The complete chemical reaction is WF ₆ +Si ₂ H ₆ → W+SiF ₃ H+2H ₂ . The molar reaction of this chemical process is 焓H=-181 kcal/mol. The tungsten hexafluoride and disilane react to obtain a very smooth and pure tungsten film. The growth rate at a low temperature is approximately 1 molecule per cycle (0.25 nm per cycle), and the film thickness is proportional to the number of cycles. It shows that a complete surface reaction between the two precursors confirms the occurrence of two saturated self-limiting half-reactions, ie

W-SiHF* ₂ +WF ₆ (g) → W-WF* ₅ +SiHF ₃ (g)

W-WF* ₅ + Si ₂ H ₆ (g) → WW-SiHF* ₂ + 2H ₂ (g) + SiHF ₃ .

The total reaction is: WF ₆ (g) + Si ₂ H ₆ (g) → W + SiHF ₃ + 2H ₂ (g).

The W film in the work of the present invention is a BENEQ TFS model manufactured by Finnish Beneq. Prepared by 200-124 atomic depositor, the process flow is as follows:

(1) Turn on N2, the power pressure is set to 0.5Mpa, and the load pressure is set to 0.14Mpa;

(2) Open the power control box;

(3) Open the mechanical pump;

(4) Open the control software;

(5) The set temperature is 60 ° C;

(6) When the temperature of the reaction chamber reaches about 60 °C, click the vent button to inflate the chamber, then open the cover and insert the silicon wafer, and close it;

(7) Continue to vacuum until the pressure in the chamber is stable;

(8) Setting the reaction temperature: 300 ° C;

(9) Set the precursor gas pressure:

WF ₆ (g): 6.5×10-8pa

Si ₂ H ₆ (g): 2.2×10-9pa

(10) Setting the reaction formula: growing a W film of 0.25 nm;

(11) At the end of the reaction, take out the sample and turn off the device.

Step two, plating a layer of S atom on the layer of W atoms:

The process is carried out by using the CVD method. The experimental conditions of the process of the present invention are: sulfur powder (0.1g) as a sulfur source, high purity argon gas as a carrier gas (flow rate is 15sccm), temperature of 300 ° C, and heat preservation for 2 min. A WS ₂ film was prepared on a silica sheet having a W atomic layer deposited thereon.

Step three, plating another layer of W atoms on the S atom layer to obtain a WS ₂ film:

This process is also carried out using ALD technology, and the specific operation process and principle are the same as those in step one.

A schematic diagram of a specific film growth process is shown in FIG. By the method of the present invention, may be implemented WS ₂ Preparation of large-area films; WS ₂ film prepared as a single layer film WSW layered structure, good compactness, low sulfur vacancy, WS ₂ only improve the quality of the film, while reducing WS ₂ film material defect, thereby greatly improving the electrical properties of WS ₂ films.

The product obtained under the process conditions proposed by the present invention is a WS ₂ film. Raman spectroscopy (Raman) and PL (photoluminescence) techniques are important methods for studying tungsten sulfide thin films. We will use laser Raman spectroscopy to characterize two Raman-active vibrational peaks in Raman spectra. The vibration modes of E ¹ _2g and A _1g respectively belonging to tungsten disulfide, and their corresponding Raman shifts are 355.6 cm ^-1 and 418.3 cm ^{-1 , respectively} . According to the experimental results of the literature, the Raman frequency shift of the E ¹ _2g vibration mode of the single-layer WS ₂ is 356 cm ^-1 , and the Raman shift of the A _1g vibration mode is 417.5 cm ^-1 person with the increase of the number of layers, E ¹ _2g vibration slows (redshift occurs, frequency shift becomes smaller) and A _1g vibration increases (blue shift occurs, frequency shift increases), E ¹ _2g and A _1g vibration mode Raman frequency shift of tungsten disulfide bulk material They are 355.5 cm ^-1 and 420.5 cm ^{-1 respectively} . In comparison with the positions of the different layers of tungsten disulfide E ¹ _2g and A _1g vibration mode characteristic peaks provided by the literature, the Raman spectrum of the sample measured is consistent with the single layer WS ₂ map.

At the same time, we also use laser Raman spectroscopy to perform fluorescence scanning (PL mapping) on the sample film. The shape and thickness of the film are characterized according to the different light-emitting properties of the crystal film. When the thickness is a single layer, the band gap of WS ₂ can reach 2.1eV. The experiment proves that the present invention is prepared as a single layer of WS ₂ . Figure 3 below shows the results of optical microscopy and Raman spectroscopy, in which Figure 3 (a) Raman test results; Figure 3 (b) shows PL (photoluminescence) test results.

It can be seen from the Raman spectrum and the PL spectrum that the product obtained by the process conditions proposed by the present invention is indeed a WS ₂ single layer film and the quality is very good. In addition, the present invention can be practiced in addition to ALD growing the W atomic layer, including a series of other methods, such as pulsed laser deposition techniques and magnetron sputtering techniques to grow the W atomic layer.

As can be seen from the measurement, the WS ₂ film prepared by the present invention is a continuous one-piece film having an area of 1-3 square centimeters. The present invention enables the preparation of large-area WS ₂ film; film quality and WS ₂ produced significantly increased, but also greatly improves the electrical properties of WS ₂ films.

In the field of application of tungsten sulfide thin films, when the two-dimensional transition metal dichalcogenide changes from a bulk to a single layer, the band gap of the electron also changes from a direct band gap to a direct band gap, and its optical properties occur simultaneously. Corresponding changes can produce a series of changes in optical properties such as photoluminescence, electroluminescence, and photovoltaic effects. The photosensitivity of two-dimensional transition metal disulfides is several times higher than that of graphene. At the same time, due to the band gap problem, the electron mobility is smaller than that of graphene, and the response is not so fast, so it can be used to produce high performance. Optical sensors, photodetectors and other devices. It has been reported that flexible LED devices made of a single-layer MoS ₂ film have emerged and have good optical properties, so WS ₂ films are also widely used. In addition, graphene-like transition metal disulfides have certain characteristics in many aspects such as mechanics, optics, electricity, electrochemistry, etc. The layer-like structure of graphene-like crystals has a larger specific surface area, and the unit area is externally irritating. The acceptance is more. As a semiconductor material, the switching response of WS ₂ graphene transition metal disulfide device is obvious, and the high electron mobility brought by its own layer structure makes it respond quickly; the surface activity of the material is high, which is convenient for it. The surface is modified to enhance sensitivity and detection range. This series of advantages makes the WS ₂ sensor a sensitive, responsive, and versatile sensor with excellent application prospects. The technical solution provided by the invention provides another broad prospect for the application of the WS ₂ film.

The technical solution of the present invention will be further described below in conjunction with specific embodiments.

Example 1

A SiO ₂ silicon substrate was prepared, and it was washed with acetone, deionized water, a mixture of hydrogen peroxide and concentrated sulfuric acid. Specifically, the mixture of hydrogen peroxide and concentrated sulfuric acid is prepared by adding a 30% aqueous solution of hydrogen peroxide to 98% concentrated sulfuric acid, stirring, and completely cooling the solution to obtain a mixed solution; the volume ratio of the aqueous hydrogen peroxide solution to the concentrated sulfuric acid solution is 1: 3.

The SiO ₂ silicon substrate was sequentially subjected to acetone ultrasonic soaking, deionized water washing, hydrogen peroxide mixed with concentrated sulfuric acid, and deionized water washing. Specifically, ultrasonic cleaning with acetone for 20 min, wherein the mass ratio of acetone used to the silicon substrate is 20:1; the frequency of acetone soaking is 28 kHz, the power is 150 W; then it is washed with deionized water; Soak the mixture of hydrogen peroxide and concentrated sulfuric acid for 3 hours, then rinse with deionized water.

Preparation of tungsten sulfide film, the specific operation process is as follows:

Step one, using a ALD technique to deposit a layer of W atoms on the silicon substrate;

Step two, plating a layer of S atom on the layer of W atoms:

A WS ₂ film was prepared on a silica sheet having a W atomic layer deposited by using 0.1 g of sulfur powder as a sulfur source, high purity argon as a carrier gas (flow rate of 15 sccm), a temperature of 300 ° C, and holding for 2 min.

In step three, another layer of W atoms is plated on the S atom layer to obtain a WS ₂ film.

It can be seen from the measurement that the WS ₂ film prepared in this example is a continuous one-piece film having an area of 2 square centimeters.

Example 2

A SiO ₂ silicon substrate was prepared, and it was washed with acetone, deionized water, a mixture of hydrogen peroxide and concentrated sulfuric acid. Specifically, the mixture of hydrogen peroxide and concentrated sulfuric acid is prepared by adding a 30% aqueous solution of hydrogen peroxide to 98% concentrated sulfuric acid, stirring, and completely cooling the solution to obtain a mixed solution; the volume ratio of the aqueous hydrogen peroxide solution to the concentrated sulfuric acid solution is 1: 3.

The SiO ₂ silicon substrate was sequentially subjected to acetone ultrasonic soaking, deionized water washing, hydrogen peroxide mixed with concentrated sulfuric acid, and deionized water washing. Specifically, ultrasonic cleaning with acetone for 15 min, wherein the mass ratio of acetone used to the silicon substrate is 20:1; the frequency of acetone soaking is 28 kHz, the power is 150 W; then it is washed with deionized water; Soak the mixture of hydrogen peroxide and concentrated sulfuric acid for 3 hours, then rinse with deionized water.

Preparation of tungsten sulfide film, the specific operation process is as follows:

Step one, using a ALD technique to deposit a layer of W atoms on the silicon substrate;

Step two, plating a layer of S atom on the layer of W atoms:

A WS ₂ film was prepared on a silica sheet having a W atomic layer deposited by using 0.1 g of sulfur powder as a sulfur source, high purity argon as a carrier gas (flow rate of 15 sccm), a temperature of 300 ° C, and holding for 2 min.

In step three, another layer of W atoms is plated on the S atom layer to obtain a WS ₂ film.

It can be seen from the measurement that the WS ₂ film prepared in this example is a continuous one-piece film having an area of 1 cm 2 .

The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. Within the scope.

Claims (10)

1.  A method for preparing a tungsten sulfide film, comprising the steps of:

   Step 1: plating a layer of W with a thickness of one atom on the silicon substrate;

   Step 2: plating an S layer having a thickness of one atom on the W layer;

   Step 3: plating another layer of W layer having a thickness of one atom on the S layer to obtain a WS ₂ film;

   The WS ₂ film is a single layer film of a WSW layered structure.
2. The method according to claim 1, wherein the material of the silicon substrate is SiO ₂ .
3. The preparation method according to claim 1, wherein the silicon substrate is cleaned before use, and the cleaning process is: sequentially performing ultrasonic soaking on a silicon substrate, deionized water cleaning, hydrogen peroxide and concentration. Sulfuric acid mixture cleaning and deionized water cleaning.
4. The preparation method according to claim 3, wherein a mass ratio of the acetone used in the ultrasonic soaking of the acetone to the silicon substrate is 20:1; the frequency of the ultrasonic soaking of the acetone is 28 kHz, and the power is 150 W; The cleaning time is 10 to 25 minutes.
5. The preparation method according to claim 3, wherein the cleaning process of the hydrogen peroxide and concentrated sulfuric acid mixture is performed by immersing the silicon substrate in the mixed solution for 2-3 hours.
6. The preparation method according to claim 3, wherein the mixture of the hydrogen peroxide and the concentrated sulfuric acid is prepared by adding a 30% aqueous solution of hydrogen peroxide to 98% concentrated sulfuric acid, stirring, and completely cooling the solution to obtain a mixed solution; The volume ratio of the aqueous solution of hydrogen peroxide to the concentrated sulfuric acid solution is 1:3.
7. The method according to claim 1, wherein the technique for plating the W layer in the first step and the third step comprises one of an ALD technique, a pulsed laser deposition technique, and a magnetron sputtering technique.
8. The method according to claim 1, wherein the method used in the second step is a CVD method.
9. A tungsten sulfide film produced by the production method according to any one of claims 1 to 8.
10. The tungsten sulfide film according to claim 9, wherein said film is a one-piece continuous type having an area of from 1 to 3 square centimeters.