Method for controllably adjusting growth of 2H-WS2 to 1T-WS2

Abstract

The invention discloses a method for controllable and adjustable growth of 2H-WS2 to 1T-WS2, and belongs to the technical field of two-dimensional material preparation. Comprising the following steps: dispersing 2H-phase WS2 in a solvent to obtain a 2H-WS2 solution; the 2H-WS2 solution is dropped onto a SiN substrate chip, drying is carried out, and a plurality of independent 2H-WS2 nanosheet crystals are obtained; and simultaneously carrying out high-temperature treatment and electron beam irradiation on any two 2H-WS2 nanosheet crystals, and observing the phase transformation process through a transmission electron microscope to obtain the 1T-WS2 nanosheet. Controllable phase transformation from 2H phase to 1T phase WS2 is realized by utilizing the synergistic effect of high-temperature treatment and electron beam irradiation. The method not only can accurately regulate and control the phase transformation process, but also can generate large-area 1T-phase WS2 nanosheets, and has important application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material preparation, and particularly relates to a method for controllably adjusting the growth of 2H-WS2 to 1T-WS2. Background Technique

[0002] Transition Metal Dichalcogenides (TMDs) are a class of two-dimensional layered materials composed of transition metals (such as Mo, W, Re, etc.) and chalcogen elements (S, Se, Te) with a chemical stoichiometry of MX2 type. These materials form a hexagonal lattice within the layer through covalent bonds formed by metal atoms and chalcogen elements, while the layers are stacked through weak van der Waals forces. This unique structure endows them with excellent mechanical flexibility and exfoliation characteristics. Since the rise of graphene research, TMDs have rapidly become a research hotspot in the field of two-dimensional materials due to their tunable bandgap (0.1 - 2.5 eV), high carrier mobility (~200 cm 2 V -1 s -1 ), and significant optoelectronic response characteristics.

[0003] Among many TMDs, tungsten disulfide (WS2) has attracted much attention due to its special electronic structure and photophysical properties. Its crystal structure has different phases such as 1T (octahedral coordination, metallic), 2H (trigonal prismatic coordination, semiconducting), and 3R (rhombohedral stacking). Among them, the 2H phase WS2 is the most stable thermodynamically, showing a layer-dependent bandgap of 1.3 - 2.1 eV. Its monolayer structure can produce a strong photoluminescence effect at room temperature, with a luminescence efficiency of over 10%. This property makes it have important application potential in the field of optoelectronic devices: for example, a field-effect transistor (FET) based on WS2 has achieved a switching ratio of up to 10 8 , and the responsivity of a photodetector constructed with its heterostructure with graphene can reach 10 3 A / W magnitude. However, the semiconducting properties of the 2H phase limit its application in scenarios that require high conductivity such as electrocatalysis.

[0004] To address this limitation, researchers have found that the 2H phase can be transformed into the 1T phase through chemical intercalation, strain engineering, or plasma treatment. The metallicity of the 1T phase WS2 (the conductivity is increased by 3 - 4 orders of magnitude) and the exposed octahedral coordination structure significantly increase the density of active sites (such as edge sulfur vacancies and bridging S2 2- sites), making it show excellent performance in the electrocatalytic hydrogen evolution reaction (HER). Experiments show that the initial overpotential of 1T-WS2 in a 0.5 M H2SO4 electrolyte can be as low as 50 mV, and the Tafel slope is only 40 - 60 mV dec -1, its performance is superior to traditional platinum-based catalysts. In addition, its interlayer spacing (~0.62 nm) is conducive to proton transport, and the high electronegativity of surface sulfur atoms can effectively reduce the hydrogen adsorption free energy (ΔGH≈0.08 eV), further enhancing the catalytic kinetics.

[0005] However, the thermodynamic stability of 1T-phase TMDs is relatively low, and natural 1T-phase is difficult to obtain. Traditional synthesis methods of 1T-phase WS2 mostly use alkali metal or ammonium ions as intercalating agents, but these methods not only have harsh conditions and complex processes, but may also produce toxic by-products, limiting their large-scale applications. Therefore, developing an efficient, simple and environmentally friendly method for preparing 1T-phase WS2 has become a key topic in this field. Summary of the Invention

[0006] In view of the above technical problems, the present invention proposes a method for controllably adjusting the growth of 2H-WS2 to 1T-WS2. This method uses high temperature and electron beam assisted method to cause phase transformation of 2H-phase WS2 nanosheets, so as to achieve the purpose of generating 1T-phase WS2.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the objects of the present invention is to provide a method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, including the following steps: dispersing 2H-phase WS2 in a solvent to obtain a 2H-WS2 solution; dropping the 2H-WS2 solution onto a SiN substrate chip and drying to obtain a plurality of independent 2H-WS2 nanosheet crystals; simultaneously performing high temperature treatment and electron beam irradiation on any two of the 2H-WS2 nanosheet crystals, and observing the phase transformation process through a transmission electron microscope to obtain 1T-WS2 nanosheets.

[0009] High temperature treatment provides activation energy for the 2H→1T phase transformation, overcoming the phase transformation energy barrier (about 0.2-0.3 eV). At high temperature, the vibration amplitude of W atoms increases, and the S atomic layer slips (from trigonal prism coordination → octahedral coordination); electron beam irradiation generates S vacancies and breaks W-S bonds, reducing the phase transformation activation energy, and promoting interlayer slip and structural reorganization through electron-phonon coupling. The structure of 2H-phase WS2 is trigonal prism coordination and has semiconductor characteristics; while 1T-phase WS2 is octahedral coordination and exhibits metallic characteristics. The driving force for phase transformation lies in the change of electronic structure. When external conditions (such as electron beam irradiation or high temperature treatment) are introduced, the electron distribution of WS2 will be changed, resulting in the transformation of its semiconductor 2H-phase to metallic 1T-phase. In the present invention, high temperature treatment and electron beam irradiation act together to provide energy for phase transformation. High temperature makes the chemical bonds between atoms in WS2 easier to break, and electron beam irradiation further induces the change of electronic structure, thus promoting phase transformation.

[0010] Further, the solvent is ethanol.

[0011] The polarity of ethanol (dielectric constant ~24.3) matches the surface hydrophobicity of WS2. Through hydrogen bonding, monolayer / few-layer exfoliation (thickness <5 nm) can be achieved, avoiding aggregation, so that 2H-phase WS2 is uniformly dispersed to form a stable solution, which is convenient for subsequent operations. Moreover, its low boiling point (78 °C) can ensure that the nanosheets are evenly spread on the SiN substrate during the drying process, reducing the coffee ring effect.

[0012] The SiN substrate used in the present invention has good chemical stability and compatibility with transmission electron microscopy (TEM), which is convenient for subsequent observation and analysis. When the 2H-WS2 solution is dropped onto the SiN substrate chip, multiple independent 2H-phase WS2 nanosheet crystals will be formed, which is convenient for subsequent high-temperature treatment and electron beam irradiation operations.

[0013] Further, the conditions for the phase transition process are: the orientation angle between two 2H-WS2 nanosheet crystals >10°, and there needs to be contact between any two of the 2H-WS2 nanosheet crystals, that is, the two nanosheet crystals cannot be separated independently.

[0014] When two 2H-WS2 nanosheets are stacked with a large misorientation angle, lattice mismatch stress is formed at the interface, inducing local octahedral coordination reconstruction. At the same time, the thermal gradient generated by electron beam irradiation and the stress act synergistically to trigger the phase transition preferentially at the interface. When the orientation angle between two 2H-phase WS2 nanosheet crystals is greater than 10°, the symmetry of its crystal structure is broken, and it is more likely to undergo a phase transition under the action of an external field, which not only increases the probability of the phase transition but also improves the generation efficiency of 1T-phase WS2.

[0015] Further, the step further includes: the generated 1T-WS2 nanosheets continue to contact with the surrounding 2H-WS2 nanosheet crystals, and large-area 1T-WS2 nanosheets are generated under the combined action of high-temperature treatment and electron beam irradiation. At this time, the conditions for the phase transition process to generate large-area 1T-WS2 nanosheets are: the orientation angle between the 1T-WS2 nanosheets and the 2H-WS2 nanosheet crystals is any value.

[0016] The generated 1T-WS2 nanosheets act as'seeds'. By contacting with the surrounding 2H-WS2 nanosheet crystals, under the synergistic action of high-temperature treatment and electron beam irradiation, cascade phase transitions are triggered, and finally large-area 1T-WS2 nanosheets are formed, with its high conductivity (σ ~ 10 4(S / m) promotes the transfer of the electron beam energy to the surrounding 2H phase, forming a cascade phase transition chain. At this time, the charge redistribution at the 1T / 2H interface (work function difference ~ 0.5 eV) further reduces the phase transition barrier. When the 1T-phase WS2 nanosheets are in crystal contact with the surrounding 2H-phase WS2 nanosheets, due to the interaction and energy transfer at the phase interface, phase transition can be further induced, thus realizing the expansion from the local 1T phase to the large-area 1T-phase WS2 nanosheets, and improving the uniformity and consistency of the material.

[0017] Further, the specific operation steps of the high-temperature treatment include: heating to 800 - 1000 °C at a heating rate of 5 - 15 °C / s, and holding at this temperature for 2 - 3 min.

[0018] Rapid heating can inhibit the oxidation of WS2 (critical oxidation temperature < 600 °C) and the volatilization of S element (temperature at which the sulfur vapor pressure increases significantly > 800 °C); high temperature can provide sufficient thermal energy to rearrange the atomic structure of 2H-phase WS2, thereby reducing the energy barrier of phase transition, and high temperature can promote the transformation of 2H-phase WS2 to 1T-phase. At the same time, the control of the high-temperature treatment time can avoid excessive thermal decomposition or other side reactions; the holding time is to balance the phase transition kinetics (nucleation time of 1T phase ~ 10 - 100 s) and grain growth (grain boundary migration rate ~ 1 nm / s).

[0019] Further, the parameters of the electron beam irradiation are: the electron beam energy is 1 - 5 A / cm 2 and the irradiation time is 2 - 3 min.

[0020] Electron beam irradiation can introduce high-energy electrons, further change the electronic structure of WS2, and accelerate the phase transition process. The penetration depth of the 1 - 5 A / cm 2 electron beam defined in the present invention can cover multiple layers of WS2, and at the same time, the electron energy loss is sufficient to break the W - S bond; acting synergistically with the high-temperature treatment, it can improve the efficiency and conversion rate of phase transition. At the same time, controlling the irradiation energy and time can avoid damaging the structure of the nanosheets, and achieve the purpose of completely transforming the 2H phase into the 1T phase.

[0021] The second object of the present invention is to provide a 1T-WS2 nanosheet film prepared by the above method.

[0022] The third object of the present invention is to provide an application of the 1T-WS2 nanosheet film in the preparation of electronic devices.

[0023] The fourth object of the present invention is to provide an application of the 1T-WS2 nanosheet film in the electrolysis of water to produce hydrogen reaction.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The present invention utilizes the synergistic effect of high-temperature treatment and electron beam irradiation to achieve a controllable phase transition from the 2H phase to the 1T phase of WS2. This method can not only precisely regulate the phase transition process but also generate large-area 1T-phase WS2 nanosheets, showing important application prospects.

[0026] The present invention can form two-dimensional 1T-phase WS2 nanosheets with relatively large sizes through the way of contact diffusion, and is expected to be used as electronic devices to meet the application requirements in the fields of electronic devices and the like.

[0027] The method of the present invention does not need to use intercalating agents or toxic solvents, and realizes the phase transition through physical external field regulation, having the advantages of environmental friendliness and process simplification.

[0028] By controlling the heating temperature and the orientation difference of the nanosheets, the phase transition process can be effectively regulated to achieve the controllable synthesis of 1T-phase WS2 nanosheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0030] Figure 1 is a schematic diagram of the phase transition of the present invention;

[0031] Figure 2 is a comparison diagram of WS2 nanosheets before and after the reaction in Example 1, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b is the 1T-WS2 nanosheet after the reaction;

[0032] Figure 3 is a comparison diagram of WS2 nanosheets before and after the reaction in Example 2, where a are adjacent 1T-WS2 nanosheet and 2H-WS2 nanosheet crystals before the reaction, and b is the large-area 1T-WS2 nanosheet after the reaction;

[0033] Figure 4 is a comparison diagram of WS2 nanosheets before and after the reaction in Example 3. The left figure is adjacent 1T-WS2 nanosheet and 2H-WS2 nanosheet crystals before the reaction, and the right figure is the large-area 1T-WS2 nanosheet after the reaction;

[0034] Figure 5 is a comparison diagram of WS2 nanosheets before and after the reaction in Example 4, where a are adjacent 1T-WS2 nanosheet and 2H-WS2 nanosheet crystals before the reaction, and b is the large-area 1T-WS2 nanosheet after the reaction;

[0035] Figure 6Comparison diagram of WS2 nanosheets before and after the reaction of Comparative Example 1, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b are 2H-WS2 nanosheets after the reaction;

[0036] Figure 7 Comparison diagram of WS2 nanosheets before and after the reaction of Comparative Example 2, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b are 2H-WS2 nanosheets after the reaction;

[0037] Figure 8 Comparison diagram of WS2 nanosheets before and after the reaction of Comparative Example 3, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b are 2H-WS2 nanosheets after the reaction;

[0038] Figure 9 High-resolution image of 1T-phase WS2 nanosheets prepared in Example 3. Detailed implementation mode

[0039] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0040] It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0042] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation modes of the present invention specification, which are obvious to those skilled in the art. Other implementation modes obtained from the present invention specification are also obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0043] As used herein, terms such as "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0044] The operation steps of the method of the present invention are as follows: After processing the raw materials and the substrate material, the whole is placed in a transmission electron microscope. At this time, the whole sample is subjected to high-temperature treatment. At the same time, electron beam irradiation is only carried out on two crystals that are in contact and have an orientation angle > 10° between them. When the phase change is completely occurred between the two, continue to perform electron beam irradiation on the phase-changed nanosheets and the third crystal (at this time, there is only a requirement for contact between the phase-changed nanosheets and the crystal that has not undergone phase transformation, and there is no angle requirement), and so on until the target size requirement is reached. It should be noted that the high-temperature treatment continues, and the crystal that is only under high-temperature treatment without being subjected to electron beam irradiation will not completely undergo phase transformation and will produce impurity phases.

[0045] The embodiment of the present invention provides a method for controllably adjusting the growth from 2H-WS2 to 1T-WS2, including the following steps:

[0046] 1) Raw material preparation: Disperse 2H-phase WS2 in ethanol (95%) to form a uniform 2H-WS2 solution;

[0047] 2) Substrate treatment: Drop the 2H-WS2 solution onto the SiN substrate chip, dry it to obtain a plurality of independent 2H-WS2 nanosheet crystals; Mount the chip on the sample rod and insert it into the transmission electron microscope;

[0048] 3) High-temperature treatment: Use software to control the chip, heat the above SiN substrate chip to 800 - 1000 °C, and maintain this temperature for a period of time to make the 2H-phase WS2 nanosheet crystals come into contact and fuse under high-temperature conditions;

[0049] 4) Electron beam irradiation assistance: During the high-temperature treatment process, perform electron beam irradiation on the 2H-phase WS2 nanosheet crystals to enhance the atomic rearrangement and phase transformation process to obtain 1T-WS2 nanosheets.

[0050] In some feasible embodiments, the condition for the phase change to generate 1T-WS2 nanosheets in step 4) is that the orientation angle between two 2H-WS2 nanosheet crystals > 10°. Under the combined action of high-temperature treatment and electron beam irradiation, when two 2H-phase WS2 nanosheet crystals with a large orientation difference (> 10°) come into contact, the atoms in the contact area rearrange and phase-transform into 1T-phase WS2. For example, the angles of the two crystals can be selected as 11°, 12° or 13°.

[0051] In some feasible embodiments, the specific operation steps of the high-temperature treatment include: heating to 800-1000 °C at a heating rate of 5-15 °C / s and holding at this temperature for 2-3 min.

[0052] In some feasible embodiments, the parameters of the electron beam irradiation are: the electron beam energy is 1-5 A / cm 2 , and the irradiation time is 2-3 min.

[0053] The embodiment of the present invention also provides a method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, including the following steps:

[0054] 1) Raw material preparation: Dispersing 2H-phase WS2 in ethanol (95%) to form a uniform 2H-WS2 solution;

[0055] 2) Substrate treatment: Dropping the 2H-WS2 solution onto a SiN substrate chip, drying to obtain a plurality of independent 2H-WS2 nanosheet crystals; mounting the chip on a sample rod and inserting it into a transmission electron microscope;

[0056] 3) High-temperature treatment: Using software to control the chip, heating the above SiN substrate chip to 800-1000 °C and maintaining this temperature for a period of time to cause the 2H-phase WS2 nanosheet crystals to come into contact and fuse under high-temperature conditions;

[0057] 4) Electron beam irradiation assistance: During the high-temperature treatment, irradiating the 2H-phase WS2 nanosheet crystals with an electron beam to enhance the atomic rearrangement and phase change process. Obtaining 1T-WS2 nanosheets;

[0058] 5) Diffusion growth: Continuing to contact the generated 1T-WS2 nanosheets with the surrounding 2H-WS2 nanosheet crystals, and undergoing a phase change under the combined action of high-temperature treatment and electron beam irradiation to generate large-area 1T-WS2 nanosheets.

[0059] In some feasible embodiments, the condition for the phase change in step 5) to generate large-area 1T-WS2 nanosheets is: the orientation angle between the 1T-WS2 nanosheets and the 2H-WS2 nanosheet crystals is any value, that is, there is no angular limitation. After the generated 1T-WS2 nanosheets come into contact with the surrounding 2H-WS2 nanosheet crystals, through the way of contact diffusion, the 2H-WS2 nanosheet crystals are further transformed into 1T-phase WS2, and finally large-area 1T-WS2 nanosheets are formed.

[0060] In some feasible embodiments, the specific operation steps of the high-temperature treatment in step 4) and step 5) are as follows: heating at a heating rate of 5-15 °C / s to 800-1000 °C, and holding at this temperature for 2-3 min. Exemplarily, in the following embodiments of the present invention, the heating rate of the high-temperature treatment can be selected as 5 °C / s, the temperature can be selected as 800 °C or 1000 °C, and the holding time can be selected as 3 min.

[0061] In some feasible embodiments, the parameters of the electron beam irradiation in step 4) and step 5) are: the electron beam energy is 1-5 A / cm 2 , and the irradiation time is 2-3 min. The general setting range of the conventional electron beam energy is 0.03-5 A / cm 2 . As a typical but non-limiting example, in the following embodiments of the present invention, the electron beam energy is 3.35 A / cm 2 is taken as an example for effect verification. The irradiation time can be selected as 3 min.

[0062] Both of the above two methods can be used to prepare the 1T-WS2 nanosheet film.

[0063] The 1T-WS2 nanosheet film can be applied in the preparation of electronic devices.

[0064] The 1T-WS2 nanosheet film can be applied in the electrolytic water hydrogen production reaction.

[0065] In the present invention, the "room temperature" refers to 20-30 °C unless otherwise specified.

[0066] The 2H-phase WS2 used in the embodiments of the present invention was purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd., and the rest of the raw materials were obtained by purchasing on the market.

[0067] The technical solutions of the present invention are further described below through examples.

[0068] Figure 1 It is a phase transition schematic diagram of the present invention.

[0069] Example 1

[0070] A method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, comprising the following steps: Dispersing 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treating for 30 min to form a uniform 2H-WS2 solution; dropping the 2H-WS2 solution onto a SiN substrate chip and naturally drying to obtain multiple independent 2H-WS2 nanosheet crystals; mounting the entire SiN substrate chip onto a sample rod and inserting it into a transmission electron microscope; using software to control the heating to 1000 °C at a heating rate of 5 °C / s, and simultaneously performing electron beam irradiation during the high-temperature treatment (both the high-temperature treatment and electron beam irradiation are operated under vacuum, the same below), and the electron beam energy is 3.35 A / cm 2 , observing that after the combined action of high-temperature treatment and electron beam irradiation for 3 min on two 2H-WS2 nanosheet crystals with an orientation angle of 11°, the two 2H-WS2 nanosheet crystals come into contact, and atomic rearrangement occurs in the contact area, and the phase changes to 1T-phase WS2, that is, 1T-WS2 nanosheets are obtained.

[0071] Figure 2 Figure for comparing WS2 nanosheets before and after the reaction in Example 1, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b is the 1T-WS2 nanosheet after the reaction. From Figure 2 it can be seen that after two adjacent 2H-WS2 nanosheet crystals come into contact after being treated by high temperature and electron beam irradiation, the contact area changes to the 1T phase.

[0072] Example 2

[0073] A method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, comprising the following steps: Dispersing 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treating for 30 min to form a uniform 2H-WS2 solution; dropping the 2H-WS2 solution onto a SiN substrate chip and naturally drying to obtain multiple independent 2H-WS2 nanosheet crystals; mounting the entire SiN substrate chip onto a sample rod and inserting it into a transmission electron microscope; using software to control the heating to 800 °C at a heating rate of 5 °C / s, and simultaneously performing electron beam irradiation during the high-temperature treatment, and the electron beam energy is 3.35 A / cm 2 , observing that after the combined action of high-temperature treatment and electron beam irradiation for 3 min on two 2H-WS2 nanosheet crystals with an orientation angle of 13°, the two 2H-WS2 nanosheet crystals come into contact, and atomic rearrangement occurs in the contact area, and the phase changes to 1T-phase WS2, that is, 1T-WS2 nanosheets are obtained.

[0074] Figure 3 Figure for comparing WS2 nanosheets before and after the reaction in Example 2, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b is the 1T-WS2 nanosheet after the reaction. From Figure 3It can be seen that after two adjacent 2H-WS2 nanosheet crystals come into contact after being treated with high temperature and electron beam irradiation, the contact area changes to the 1T phase.

[0075] Example 3

[0076] A method for controllably regulating the growth of 2H-WS2 to 1T-WS2 includes the following steps: Disperse 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treat it for 30 min to form a uniform 2H-WS2 solution; Drop the 2H-WS2 solution onto a SiN substrate chip and let it dry naturally to obtain multiple independent 2H-WS2 nanosheet crystals; Mount the entire SiN substrate chip onto a sample rod and insert it into a transmission electron microscope; Use software to control the heating to 1000 °C at a heating rate of 5 °C / s, and at the same time perform electron beam irradiation during the high-temperature treatment, with the electron beam energy being 3.35 A / cm 2 , Observe that after two 2H-WS2 nanosheet crystals with an orientation angle of 12° are subjected to high-temperature treatment and electron beam irradiation together for 3 min, the two 2H-WS2 nanosheet crystals come into contact, and atomic rearrangement occurs in the contact area, changing to the 1T-phase WS2, that is, 1T-WS2 nanosheets are obtained;

[0077] Subsequently, continue to bring the 1T-WS2 nanosheets into contact with the surrounding 2H-WS2 nanosheet crystals, use software to control the heating to 1000 °C at a heating rate of 5 °C / s, and at the same time perform electron beam irradiation during the high-temperature treatment, with the electron beam energy being 300 keV. Observe that after the 1T-WS2 nanosheets and 2H-WS2 nanosheet crystals with an orientation angle of 13° are subjected to high-temperature treatment and electron beam irradiation together for 3 min, the 1T-WS2 nanosheets and 2H-WS2 nanosheet crystals come into contact. Through the way of contact diffusion, the 2H-WS2 nanosheet crystals are further transformed into 1T-WS2 nanosheets, changing to the 1T-phase WS2, that is, large-area 1T-WS2 nanosheets are obtained.

[0078] Figure 4 Figure for comparing WS2 nanosheets before and after the reaction in Example 3, where the left figure shows adjacent 1T-WS2 nanosheets and 2H-WS2 nanosheet crystals before the reaction, and the right figure shows the large-area 1T-WS2 nanosheets after the reaction. From Figure 4 It can be seen that after the 1T-WS2 nanosheets and the surrounding 2H-WS2 nanosheet crystals come into contact after being treated with high temperature and electron beam irradiation, the contact area all changes to the 1T phase, forming large-area 1T-WS2 nanosheets, which are more conducive to practical applications and expand the application scope.

[0079] Example 4

[0080] A method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, comprising the following steps: dispersing 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treating for 30 min to form a uniform 2H-WS2 solution; dropping the 2H-WS2 solution onto a SiN substrate chip and naturally drying to obtain a plurality of independent 2H-WS2 nanosheet crystals; mounting the entire SiN substrate chip on a sample rod and inserting it into a transmission electron microscope; using software to control the heating to 1000 °C at a heating rate of 5 °C / s, and simultaneously performing electron beam irradiation during the high-temperature treatment, with an electron beam energy of 3.35 A / cm 2 , observing that after 3 min of the combined action of high-temperature treatment and electron beam irradiation on two 2H-WS2 nanosheet crystals with an orientation angle of 11°, the two 2H-WS2 nanosheet crystals come into contact, and atomic rearrangement occurs in the contact area, transforming into 1T-phase WS2, that is, obtaining 1T-WS2 nanosheets;

[0081] Subsequently, continue to contact the 1T-WS2 nanosheets with the surrounding 2H-WS2 nanosheet crystals, use software to control the heating to 1000 °C at a heating rate of 5 °C / s, and simultaneously perform electron beam irradiation during the high-temperature treatment, with an electron beam energy of 3.35 A / cm 2 , observing that after 3 min of the combined action of high-temperature treatment and electron beam irradiation on a 1T-WS2 nanosheet and a 2H-WS2 nanosheet crystal with an orientation angle of 8°, the 1T-WS2 nanosheet and the 2H-WS2 nanosheet crystal come into contact, and through the way of contact diffusion, the 2H-WS2 nanosheet crystal is further transformed into a 1T-WS2 nanosheet, transforming into 1T-phase WS2, that is, obtaining a large-area 1T-WS2 nanosheet.

[0082] Figure 5 Figure for comparing WS2 nanosheets before and after the reaction in Example 4, where the left figure shows adjacent 1T-WS2 nanosheets and 2H-WS2 nanosheet crystals before the reaction, and the right figure shows the large-area 1T-WS2 nanosheets after the reaction. From Figure 5 it can be seen that after the 1T-WS2 nanosheets and the surrounding 2H-WS2 nanosheet crystals are in contact after high-temperature and electron beam irradiation treatment, the contact area is uniformly transformed into the 1T phase, forming large-area 1T-WS2 nanosheets, which are more conducive to practical applications and expand the application scope.

[0083] Comparative Example 1

[0084] Disperse 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treat for 30 min to form a uniform 2H-WS2 solution; drop the 2H-WS2 solution onto a SiN substrate chip and allow it to dry naturally to obtain multiple independent 2H-WS2 nanosheet crystals; mount the entire SiN substrate chip onto a sample rod and insert it into a transmission electron microscope; use software to control the heating to 1000 °C at a heating rate of 5 °C / s, and simultaneously perform electron beam irradiation during the high-temperature treatment, with an electron beam energy of 3.35 A / cm 2 After observing two 2H-WS2 nanosheet crystals with an orientation angle close to parallel for 3 min under the combined action of high-temperature treatment and electron beam irradiation, the two 2H-WS2 nanosheet crystals contacted, and no atomic rearrangement occurred in the contact area, resulting in a large-area 2H-WS2 nanosheet.

[0085] Figure 6 Figure for comparing WS2 nanosheets before and after the reaction of Comparative Example 1, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b is the 2H-WS2 nanosheet after the reaction. From Figure 6 As can be seen, after two adjacent 2H-WS2 nanosheet crystals contacted after high-temperature and electron beam irradiation treatment, no atomic rearrangement occurred in the contact area, nor did it transform into the 1T phase. After the two 2H-WS2 nanosheet crystals contacted, they combined to form a large-area 2H-WS2 nanosheet.

[0086] Comparative Example 2

[0087] Change the high-temperature treatment temperature. The technical solution is as follows: A method for controllably adjusting the growth of 2H-WS2 to 1T-WS2 includes the following steps: Disperse 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treat for 30 min to form a uniform 2H-WS2 solution; drop the 2H-WS2 solution onto a SiN substrate chip and allow it to dry naturally to obtain multiple independent 2H-WS2 nanosheet crystals; mount the entire SiN substrate chip onto a sample rod and insert it into a transmission electron microscope; use software to control the heating to 700 °C at a heating rate of 5 °C / s, and simultaneously perform electron beam irradiation during the high-temperature treatment, with an electron beam energy of 3.35 A / cm 2 After observing two 2H-WS2 nanosheet crystals with an orientation angle of 17° for 3 min under the combined action of electron beam irradiation, the two 2H-WS2 nanosheet crystals did not move, and thus no contact phase change could occur.

[0088] Figure 7 Figure for comparing WS2 nanosheets before and after the reaction of Comparative Example 2, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b is the 2H-WS2 nanosheet after the reaction. From Figure 7It can be seen that after two adjacent 2H-WS2 nanosheet crystals are subjected to a high temperature of 700 °C for 3 min and electron beam irradiation, the two nanosheets do not move, and it is impossible to promote the movement of two adjacent grains on the SiN substrate chip at this temperature, and thus contact is generated.

[0089] Comparative Example 3

[0090] Without electron beam irradiation, the technical solution is as follows: a method for controllably adjusting the growth of 2H-WS2 to 1T-WS2, comprising the following steps: dispersing 1 g of 2H-phase WS2 in 100 mL of ethanol (95%) and ultrasonically treating for 30 min to form a uniform 2H-WS2 solution; dropping the 2H-WS2 solution onto the SiN substrate chip and naturally drying to obtain a plurality of independent 2H-WS2 nanosheet crystals; mounting the entire SiN substrate chip on a sample rod and inserting it into a transmission electron microscope; using software to control the heating to 1000 °C at a heating rate of 5 °C / s, and observing that after two 2H-WS2 nanosheet crystals with an orientation angle of 13° are subjected to high-temperature treatment for 3 min, the two 2H-WS2 nanosheet crystals come into contact, and the two grains fuse in the contact area, and no phase change occurs.

[0091] Figure 8 FIG. is a comparison diagram of WS2 nanosheets before and after the reaction in Comparative Example 3, where a are two adjacent 2H-WS2 nanosheet crystals before the reaction, and b are 2H-WS2 nanosheets after the reaction. From Figure 8 It can be seen that after two adjacent 2H-WS2 nanosheet crystals are in contact after high-temperature treatment, only fusion occurs in the contact area, and no phase change phenomenon occurs. After the two 2H-WS2 nanosheet crystals are in contact, they combine to form a large-area 2H-WS2 nanosheet.

[0092] Figure 9 FIG. is a high-resolution picture of the 1T-phase WS2 nanosheet prepared in Example 3. No other impurities and heterophases are found under the electron microscope, which proves that the 1T-WS2 nanosheet obtained by the method of the present invention is pure and environmentally friendly without pollution.

[0093] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for controllably regulating the growth of 2H-WS2 to 1T-WS2, characterized in that: The following steps are involved: Dispersing 2H phase WS2 in a solvent to obtain a 2H-WS2 solution; dropping the 2H-WS2 solution onto a SiN substrate chip and drying it to obtain a plurality of independent 2H-WS2 nanosheet crystals; simultaneously subjecting any two of the 2H-WS2 nanosheet crystals to high temperature treatment and electron beam irradiation, observing the phase transition process by transmission electron microscopy to obtain 1T-WS2 nanosheets; The condition for the phase transition process to occur is that the orientation angle between two 2H-WS2 nanosheet crystals is >10°.

2. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 1, characterized in that: The solvent is ethanol.

3. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 1, characterized in that: There needs to be contact between any two of the 2H-WS2 nanosheet crystals.

4. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 1, characterized in that: The steps also include: the generated 1T-WS2 nanosheets continue to contact with the surrounding 2H-WS2 nanosheet crystals, undergo phase transformation under the combined action of high temperature treatment and electron beam irradiation, and generate large-area 1T-WS2 nanosheets.

5. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 4, characterized in that: The condition for the phase transition to occur is that the orientation angle between the 1T-WS2 nanosheet and the 2H-WS2 nanosheet crystal is an arbitrary value.

6. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 1, characterized in that: The specific operation steps of the high temperature treatment include: heating to 800-1000° C. at a heating rate of 5-15° C. / s, and keeping the temperature at this temperature for 2-3 minutes.

7. The method for controllably regulating the growth of 2H-WS2 to 1T-WS2 according to claim 1, characterized in that: The parameters of the electron beam irradiation are: the electron beam energy is 1-5A / cm 2 , the irradiation time is 2-3min.

8. A 1T-WS2 nanosheet film prepared by the method of claim 4.

9. A use of the 1T-WS2 nanosheet film as claimed in claim 8 in the preparation of electronic devices.

10. An application of the 1T-WS2 nanosheet film as claimed in claim 8 in the hydrogen production reaction by water electrolysis.

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