A Periodically Ferroelectric-Polarization-Induced WSe₂-Like Superlattice and Its Preparation Method

Abstract

The present invention discloses a preparation method of a WSe2-like superlattice induced by periodic ferroelectric polarization, including spin-coating a P(VDF-TrFE) organic solution on a silicon substrate, and then annealing to obtain a P(VDF-TrFE) ferroelectric thin film; scribing on the surface of the P(VDF-TrFE) ferroelectric thin film to obtain a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure; transferring a WSe2 thin film to the surface of the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure through a two-dimensional transfer process; and performing ferroelectric polarization induction on the WSe2 thin film through the electrostatic field generated by the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure, so that the WSe2 thin film forms a superlattice-like energy band structure. This preparation method realizes the rapid, efficient and simple construction of the energy band structure of the van der Waals superlattice. The present invention also discloses a WSe2-like superlattice induced by periodic ferroelectric polarization.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterials, and particularly relates to a periodic ferroelectric polarization-induced WSe2-like superlattice and a preparation method thereof. Background Art

[0002] Two-dimensional transition metal dichalcogenides (TMDCs) are quasi-two-dimensional structured layered materials with a graphene-like hexagonal honeycomb formed by transition metal atoms and chalcogen atoms. Due to the weak van der Waals force between layers, TMDCs can form van der Waals superlattices (vdWSLs) through layer-by-layer transfer and stacking. Due to their unique crystal structure and electronic structure, vdWSLs have unique physical and chemical properties similar to and different from graphene, such as layer-dependent direct / indirect bandgap transitions, long carrier relaxation lifetimes, high carrier mobilities, superconducting properties, two-dimensional ferroelectric / ferromagnetic, moiré excitons, rich multi-physical field coupling properties, etc. Functional devices based on vdWSLs have excellent device performance, including source-drain currents exceeding 100 microamperes, on-off ratios as high as 10 7 and rectification ratios as high as 10 5 . Up to now, vdWSLs have shown great application potential in the fields of optoelectronics, biology, energy, etc., and have become new materials that have attracted much attention in the academic and industrial circles.

[0003] The preparation of vdWSLs usually adopts the combination of mechanical exfoliation and layer-by-layer transfer mode, chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), intercalation method, etc. The preparation of vdWSLs by combining mechanical exfoliation and layer-by-layer transfer often requires a large amount of manpower and may introduce defects such as air impurities during the artificial exfoliation and transfer process, which is not conducive to large-scale device integration. During the preparation of vdWSLs, after a layer of TMDCs is nucleated and grown by CVD and MOCVD methods, the vertical growth or lateral growth of the next layer of TMDCs is continued by switching chemical vapor sources, changing gas flow parameters, adjusting reaction temperature, etc., which generally requires continuous deposition or multi-step reactions. Such preparation processes have extremely high requirements for kinetic growth control under thermal equilibrium conditions, or inevitably introduce temperature disturbances, uniform nucleation, thermally induced material erosion, etc. between reaction steps, which is not conducive to the preparation of vdWSLs. If high-quality vdWSLs with 3-5 alternating cycles are to be grown, CVD and MOCVD methods need to grow continuously for 10 days day and night, which is time-consuming and the yield is also limited. The intercalation method allows the insertion of active components such as atoms, ions, molecules, etc. into the vdW gap to form unique embedded vdWSLs, but is limited to lithium or passivating molecules. The intercalated layer generally does not have direct optical, electronic or magnetic functions, nor can it have an electronic coupling effect with the TMDCs support layer. Therefore, the intercalated layer only acts as a passivation layer to expand the layer spacing of the TMDCs support layer, thereby decoupling the electronic interaction between the original support layers. The vdWSLs prepared by the above preparation methods generally have a short alternating cycle and a limited yield, and cannot achieve the efficient preparation of high-order vdWSLs with a large number of alternating cycles. If the continuous stacking or multi-step reaction process is still used, due to problems such as low yield and material damage, the preparation difficulty of high-order vdWSLs will increase exponentially with the increase in the number of alternating cycles. Summary of the Invention

[0004] The present application provides a preparation method for a periodic ferroelectric polarization-induced WSe2-like superlattice. The preparation method is simple and efficient, and realizes the rapid, efficient and simple construction of the energy band structure of the van der Waals superlattice.

[0005] The present application provides a preparation method for a periodic ferroelectric polarization-induced WSe2-like superlattice, including:

[0006] Spin-coat a P(VDF-TrFE) organic solution on a silicon substrate, and then anneal it to obtain a P(VDF-TrFE) ferroelectric thin film;

[0007] Perform scribing on the surface of the P(VDF-TrFE) ferroelectric thin film to obtain a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure;

[0008] The WSe2 thin film is transferred onto the surface of a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure through a two-dimensional transfer process. The WSe2 thin film is induced by the electrostatic field generated by the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure, so that the WSe2 thin film forms a band structure similar to a superlattice.

[0009] The embodiment of the present application also provides scribing on the surface of the P(VDF-TrFE) ferroelectric thin film by using an atomic force microscope tip. The specific steps are as follows:

[0010] The scanning area for each scribing of the atomic force microscope tip, the offset of the atomic force microscope tip in the X-direction or Y-direction movement, and the scribing times threshold are set respectively;

[0011] After the atomic force microscope tip completes one scribing according to the set scanning area, it is moved to the target position according to the offset of the X-direction or Y-direction movement to perform the next scribing until the scribing stops after reaching the scribing times threshold, and a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure is obtained;

[0012] Wherein, after moving the atomic force microscope tip to the target position according to the set offset of the X-direction or Y-direction movement each time, the voltage on the atomic force microscope tip is reset. The voltage value of the reset voltage is the same as the voltage value during the previous scribing, and the voltage direction is opposite to the voltage direction during the previous scribing.

[0013] The present invention sets appropriate voltage, offset of X and Y directions, so that the tip can scribe a periodic ferroelectric domain structure on the surface of the P(VDF-TrFE) ferroelectric thin film. A periodic depolarization field is generated by the P(VDF-TrFE) ferroelectric thin film with the periodic ferroelectric domain structure. The electrostatic field provided by the depolarization field induces the WSe2 thin film to form a band structure similar to a superlattice. The rapid, efficient and simple construction of the van der Waals superlattice band structure is realized by the above method.

[0014] The voltage applied to the atomic force microscope tip is -10 - +10V.

[0015] The offset of the X-direction movement is -5 - +5μm; the offset of the Y-direction movement is -5 - +5μm.

[0016] In a preferred embodiment, after each scribing of the scanning area is completed, the voltage on the tip is adjusted from a positive voltage or a negative voltage to 0V, and then the adjusted tip is moved to the position where it was when starting to scribe the scanning area.

[0017] The thickness of the P(VDF-TrFE) ferroelectric thin film is 20 nm - 300 nm. A suitable thickness can obtain better polarized ferroelectric domains. During the depolarization process, a suitable periodic electrostatic field can be generated to induce the WSe2 thin film, enabling the WSe2 thin film to form a band structure similar to a superlattice.

[0018] The periodic ferroelectric domain structure is obtained by the periodic arrangement of ferroelectric domains. The width of the ferroelectric domain is 500 nm - 5 μm, and the length is 1 μm - 5 μm.

[0019] The P(VDF-TrFE) organic solution includes P(VDF-TrFE) and a polar solvent. The polar solvent is diethyl carbonate, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, or methyl ethyl ketone. The mass fraction of P(VDF-TrFE) in the P(VDF-TrFE) organic solution is 0.5% - 5%.

[0020] The molar ratio of TrFE in the P(VDF-TrFE) is 20% - 50%, and the rest is VDF.

[0021] The P(VDF-TrFE) organic solution is spin-coated on a silicon substrate. Among them, the spin-coating process is: the spin-coating speed is 300 - 800 rpm for 3 - 5 s, and then the spin-coating speed is increased to 2000 - 3000 rpm for 20 - 50 s. The volume of the spin-coated P(VDF-TrFE) organic solution is 40 μL - 100 μL.

[0022] Furthermore, the silicon substrate spin-coated with the P(VDF-TrFE) organic solution is annealed. Among them, the annealing process is: the annealing temperature is 120 - 140 °C, and the annealing time is 0.5 - 12 h.

[0023] The silicon substrate is a P-type Si, which is a heavily doped conductive semiconductor material with a SiO2 thickness of 285 nm - 300 nm and a resistivity of 0.001 - 0.005 Ω·cm.

[0024] The P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure is in the β phase, and its morphology is a woven network. A periodic ferroelectric domain structure with periodically arranged out-of-plane upward and out-of-plane downward polarization directions is obtained by writing.

[0025] The WSe2 thin film is transferred to the surface of the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure through a two-dimensional transfer process, including:

[0026] The mechanically exfoliated WSe2 film is transferred onto the P(VDF-TrFE) ferroelectric film with a periodically ferroelectric domain structure by dry or wet methods. The transfer medium is a PDMS film, and with the assistance of heat baking to soften the PDMS film, the adhered WSe2 film is transferred onto the surface of the P(VDF-TrFE) ferroelectric film.

[0027] This application also provides a periodically ferroelectric polarization-induced WSe2-like superlattice prepared by using the preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] In the present invention, by scribing a periodically ferroelectric domain structure on the surface of the P(VDF-TrFE) ferroelectric film, based on the depolarization field generated by the P(VDF-TrFE) ferroelectric film with the obtained periodically ferroelectric domain structure, a periodic electrostatic field is provided to the WSe2 film attached to the surface of the P(VDF-TrFE) ferroelectric film. The bandgap of the WSe2 film is regulated by the periodic electrostatic field, and then a superlattice-like energy band structure is induced. Compared with the high-temperature, high-pressure and other generation processes required for preparing van der Waals superlattices in the prior art, this application can realize the rapid, efficient and simple construction of the energy band structure of van der Waals superlattices. Description of the Drawings

[0030] Figure 1 It is a flowchart of the preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice provided in Embodiment 1 of the present invention;

[0031] Figure 2 It is a scanning route map of the tip of the atomic force microscope in the X direction provided in Embodiment 1 of the present invention;

[0032] Figure 3 It is a morphology diagram of the P(VDF-TrFE) ferroelectric film provided in Embodiment 1 of the present invention;

[0033] Figure 4 It is a schematic flow diagram of the preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice provided in Embodiment 1 of the present invention;

[0034] Figure 5 It is a scanning route map of the tip of the atomic force microscope in the Y direction provided in Embodiment 2 of the present invention;

[0035] Figure 6 It is a programmable ferroelectric domain structure schematic diagram of the periodically ferroelectric domain structure of the P(VDF-TrFE) ferroelectric film provided in the embodiment of the present invention;

[0036] Figure 7A diagram for regulating the bandgap of a two-dimensional semiconductor by the inversion of ferroelectric domains under an external electric field provided by an embodiment of the present invention. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. It should be noted that, without conflict, the features in the following embodiments and implementation manners can be combined with each other.

[0038] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the technical field to which they belong. In addition, it can be understood that the terms defined in a commonly used dictionary should be understood to have a meaning consistent with the context of the relevant field, and should not be understood in an idealized or overly formal sense.

[0039] In this embodiment, by using the tip of an atomic force microscope to write a periodic ferroelectric domain structure on a P(VDF-TrFE) ferroelectric thin film, the P(VDF-TrFE) ferroelectric thin film has a periodic electrostatic field. The bandgap of the WSe2 thin film attached to the surface of the P(VDF-TrFE) ferroelectric thin film is regulated through this periodic electrostatic field, thereby inducing the formation of a band structure similar to a superlattice. To achieve the above goal, this embodiment provides a preparation method for a WSe2-like superlattice induced by periodic ferroelectric polarization, as Figure 1 shown, including:

[0040] (1) Spin-coat a P(VDF-TrFE) organic solution on a silicon substrate, and then perform annealing to obtain a P(VDF-TrFE) ferroelectric thin film;

[0041] (2) Write on the surface of the P(VDF-TrFE) ferroelectric thin film through the tip of an atomic force microscope (AFM tip) to obtain a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure;

[0042] (3) Transfer the WSe2 thin film to the surface of the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure through a two-dimensional transfer process; the electrostatic field generated by the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure is used to induce the WSe2 thin film to form a band structure similar to a superlattice.

[0043] As Figure 6 shown in a to c, by utilizing the programmability that ferroelectric domains can be inverted under an external electric field, asFigure 7 As shown, the bandgap of the two-dimensional semiconductor can be adjusted as needed at any time, and it is compatible with the current semiconductor process, enabling the fabrication of novel semiconductor devices with optoelectronic detection, storage, and logic operation functions.

[0044] Example 1

[0045] This example provides a method for preparing a WSe2-like superlattice induced by periodic ferroelectric polarization, including:

[0046] Step (1): Weigh 0.2 g of P(VDF-TrFE) powder and pour it into a sample bottle containing 8 g of diethyl carbonate, stir until the P(VDF-TrFE) powder is completely dissolved to obtain a P(VDF-TrFE) organic solution with a mass fraction of 2.4%, where the VDF / TrFE molar ratio is 70:30.

[0047] Step (2): Use a pipette to take 40 μL of the P(VDF-TrFE) organic solution prepared in step (1) and drop it onto a cleaned P-type Si substrate of 1 cm × 1 cm. The P-type Si substrate has a SiO2 layer with a thickness of 285 nm and a resistivity of 0.001 - 0.005 Ω·cm. Set the initial rotation speed to 500 rpm and the initial spin-coating time to 3 s, and the formal spin-coating speed to 2000 rpm and the formal spin-coating time to 30 s.

[0048] Step (3): Put the P(VDF-TrFE) spin-coated on the silicon wafer in step (2) into a vacuum oven for annealing crystallization. The annealing temperature is 135 °C and the annealing time is 4 h to obtain a crystallized P(VDF-TrFE) ferroelectric thin film with a thickness of 130 nm.

[0049] Step (4): Place the P(VDF-TrFE) ferroelectric thin film under the tip of an atomic force microscope, as Figure 2 shown, to prepare a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure in the X direction, as Figure 3 shown. The specific steps are as follows:

[0050] Step (4.1): Apply a voltage signal with an amplitude of 10 V to the tip of the atomic force microscope. Set the scanning area for the first writing to X = 1 μm and Y = 5 μm. The values of this scanning area are scalar values. After the scanning is completed, an out-of-plane upward ferroelectric domain is obtained. Set the tip voltage to 0 V, and then move the tip of the atomic force microscope to the position where the tip of the atomic force microscope was located at the start of this step's scanning.

[0051] Step (4.2): Set the X-direction movement offset to +1 μm and the Y-direction movement offset to 0 μm. Move the atomic force microscope tip to the target position. Set the voltage from 0 V to -10 V. Set the scanning area for the second scribing as X = 1 μm and Y = 5 μm. The values of this scanning area are scalar values. After the scanning is completed, an out-of-plane downward ferroelectric domain is obtained. Set the tip voltage to 0 V. Then, move the atomic force microscope tip to the position where the atomic force microscope tip was located at the start of the scanning in this step.

[0052] Step (4.3): Continue to repeat steps (4.1)-(4.2) two times to obtain three pairs of periodically arranged ferroelectric domain structures with upward and downward polarization directions adjacent to each other. At this time, each ferroelectric domain is 1 μm long and 5 μm wide.

[0053] Step (5): As shown in (a)-(d) of Figure 4 Transfer the mechanically exfoliated monolayer WSe2 film to the P(VDF-TrFE) ferroelectric film scribed with the periodic ferroelectric domain structure by dry method. The transfer medium is a PDMS film. Assist with heat baking to soften the PDMS film and transfer the adhered WSe2 film to the surface of the P(VDF-TrFE) ferroelectric film.

[0054] Step (6): As shown in (e) of Figure 4 The P(VDF-TrFE) ferroelectric film scribed with ferroelectric domains by the atomic force microscope probe generates a periodic depolarization field. The electrostatic field provided by this depolarization field regulates the bandgap of WSe2 and induces WSe2 to form a superlattice-like energy band structure.

[0055] Example 2

[0056] Step (1): Weigh 0.3 g of P(VDF-TrFE) powder and pour it into a sample bottle containing 8 g of diethyl carbonate. Stir until the P(VDF-TrFE) powder is completely dissolved to obtain a P(VDF-TrFE) organic solution with a mass fraction of 3.6%, where the molar ratio of VDF / TrFE is 70:30.

[0057] Step (2): Use a pipette to take 40 μL of the P(VDF-TrFE) organic solution prepared in step (1) and drop it onto a cleaned P-type Si substrate of 1 cm × 1 cm for spin coating. The P-type Si substrate has a SiO2 with a thickness of 285 nm and a resistivity of 0.001 - 0.005 Ω·cm. Set the initial rotation speed to 500 rpm and the initial spin coating time to 3 s. The formal spin coating speed is 3000 rpm and the formal spin coating time is 30 s.

[0058] Step (3): Place the P(VDF-TrFE) ferroelectric film spin-coated on the silicon wafer in a vacuum oven for annealing crystallization at an annealing temperature of 135 °C and an annealing time of 4 h to obtain the crystallized P(VDF-TrFE) ferroelectric film;

[0059] Step (4): Place the P(VDF-TrFE) ferroelectric film under the tip of an atomic force microscope, as Figure 5 shown, to prepare a P(VDF-TrFE) ferroelectric film with a periodic ferroelectric domain structure in the Y direction. The specific steps are as follows:

[0060] Step (4.1): Apply a voltage signal with an amplitude of 10 V to the tip of the atomic force microscope. Set the scanning area for the first writing as X = 5 μm and Y = 1 μm. The values of this scanning area are scalar values. After the scanning is completed, an out-of-plane upward ferroelectric domain is obtained. Set the voltage of the atomic force microscope tip to 0 V, and then move the atomic force microscope tip to the position where it was at the start of the scanning in this step.

[0061] Step (4.2): Set the offset in the X direction to 0 μm and the offset in the Y direction to -1 μm. Move the atomic force microscope tip to the target position. Set the voltage from 0 V to -10 V. Set the scanning area (scalar value) for the second writing as X = 5 μm and Y = 1 μm. After the scanning is completed, an out-of-plane downward ferroelectric domain is obtained. Set the tip voltage to 0 V, and then move the atomic force microscope tip to the position where it was at the start of the scanning in this step.

[0062] Step (4.3): Continue to repeat steps (4.1) - (4.2) 2 times to obtain 3 pairs of periodically adjacent ferroelectric domain structures with upward and downward polarization directions. At this time, each ferroelectric domain is 5 μm long and 1 μm wide.

[0063] Step (5): Transfer the mechanically exfoliated monolayer WSe2 film to the P(VDF-TrFE) ferroelectric film inscribed with a periodic ferroelectric domain structure by dry transfer. The transfer medium is a PDMS film. With the assistance of heat baking, soften the PDMS film and transfer the adhered WSe2 film to the surface of the P(VDF-TrFE) ferroelectric film;

[0064] Step (6): The P(VDF-TrFE) ferroelectric film inscribed by the atomic force microscope probe generates a periodic depolarization field. The electrostatic field provided by this depolarization field regulates the bandgap of WSe2 and induces WSe2 to form a band structure similar to a superlattice.

[0065] Example 3

[0066] Step (1): Weigh 0.1 g of P(VDF-TrFE) powder and pour it into a sample bottle containing 8 g of diethyl carbonate. Stir until the P(VDF-TrFE) powder is completely dissolved to obtain a P(VDF-TrFE) organic solution with a mass fraction of 1.2%, where the molar ratio of VDF / TrFE is 70:30.

[0067] Step (2): Use a pipette to take 40 μL of the P(VDF-TrFE) organic solution prepared in step (1) and drop it onto a cleaned P-type Si substrate with a size of 1 cm × 1 cm for spin coating. The P-type Si substrate has a SiO2 layer with a thickness of 285 nm and a resistivity of 0.001 - 0.005 Ω·cm. Set the initial rotation speed to 500 rpm, the initial spin coating time to 3 s, the formal spin coating speed to 2500 rpm, and the formal spin coating time to 30 s.

[0068] Step (3): Put the P(VDF-TrFE) spin-coated on the silicon wafer in step (2) into a vacuum oven for annealing crystallization. The annealing temperature is 135 °C and the annealing time is 4 h to obtain a crystallized P(VDF-TrFE) ferroelectric thin film.

[0069] Step (4): Place the P(VDF-TrFE) ferroelectric thin film under the tip of an atomic force microscope to prepare a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure in the X direction. The specific steps are as follows:

[0070] Step (4.1): Apply a voltage signal with an amplitude of 10 V to the tip of the atomic force microscope. Set the scanning area for the first scribing to X = 2 μm, Y = 2 μm. The values of this scanning area are scalar values. After the scanning is completed, set the tip voltage to 0 V, and then move the tip of the atomic force microscope to the position where it was at the start of the scanning in this step.

[0071] Step (4.2): Set the offset in the X direction to +1 μm and the offset in the Y direction to 0 μm. Move the tip of the atomic force microscope to the target position. Set the voltage from 0 V to -10 V. Set the scanning area (scalar value) for the second scribing to X = 2 μm, Y = 2 μm. After the scanning is completed, set the tip voltage to 0 V, and then move the tip of the atomic force microscope to the position where it was at the start of the scanning in this step.

[0072] Step (4.3): Continue to repeat steps (4.1) - (4.2) twice to obtain three pairs of periodically ferroelectric domain structures with adjacent upward and downward polarization directions. At this time, each ferroelectric domain is 2 μm long and 2 μm wide. Step (5): Transfer the mechanically exfoliated monolayer WSe2 film onto the P(VDF-TrFE) ferroelectric film inscribed with the periodic ferroelectric domain structure by dry transfer. The transfer medium is a PDMS film, assisted by heat baking to soften the PDMS film and transfer the adhered WSe2 film onto the surface of the P(VDF-TrFE) ferroelectric film.

[0073] Step (6): The P(VDF-TrFE) ferroelectric film inscribed with ferroelectric domains by an atomic force microscope probe generates a periodic depolarization field. The electrostatic field provided by this depolarization field regulates the bandgap of WSe2 and induces the formation of a superlattice-like energy band structure in WSe2.

[0074] Example 4

[0075] Step (1): Weigh 0.1 g of P(VDF-TrFE) powder and pour it into a sample bottle containing 8 g of diethyl carbonate, stir until the P(VDF-TrFE) powder is completely dissolved to obtain a P(VDF-TrFE) organic solution with a mass fraction of 1.2%, where the molar ratio of VDF / TrFE is 70:30.

[0076] Step (2): Use a pipette to take 40 μL of the P(VDF-TrFE) organic solution prepared in step (1) and drop it onto a cleaned P-type Si substrate of 1 cm × 1 cm for spin coating. The P-type Si substrate has a SiO2 layer with a thickness of 285 nm and a resistivity of 0.001 - 0.005 Ω·cm. Set the initial rotation speed to 500 rpm, the initial spin coating time to 3 s, the formal spin coating speed to 2500 rpm, and the formal spin coating time to 30 s.

[0077] Step (3): Put the P(VDF-TrFE) spin-coated on the silicon wafer in a vacuum oven for annealing crystallization. The annealing temperature is 135 °C and the annealing time is 4 h to obtain the crystallized P(VDF-TrFE) ferroelectric film.

[0078] Step (4): Place the P(VDF-TrFE) ferroelectric film under the tip of an atomic force microscope to prepare a P(VDF-TrFE) ferroelectric film with a periodic ferroelectric domain structure in the X direction. The specific steps are as follows:

[0079] Step (4.1): Apply a voltage signal with an amplitude of 5 V to the tip of the atomic force microscope. Set the scanning area for the first writing as X = 5 μm and Y = 5 μm. The values of this scanning area are scalar values. After the scanning is completed, set the tip voltage to 0 V. Then, move the tip of the atomic force microscope to the position where it was at the start of the scanning in this step.

[0080] Step (4.2): Set the offset in the X - direction movement as +1 μm and the offset in the Y - direction movement as 0 μm. Move the tip of the atomic force microscope to the target position. Set the voltage from 0 V to -5 V. Set the scanning area (scalar value) for the second writing as X = 5 μm and Y = 5 μm. After the scanning is completed, set the tip voltage to 0 V. Then, move the tip of the atomic force microscope to the position where it was at the start of the scanning in this step.

[0081] Step (4.3): Continue to repeat steps (4.1)-(4.2) 4 times to obtain 5 pairs of periodically arranged ferroelectric domains with opposite polarization directions (upward and downward). At this time, each ferroelectric domain has a length of 5 μm and a width of 5 μm.

[0082] Step (5): Transfer the mechanically exfoliated single - layer WSe2 film onto the P(VDF - TrFE) ferroelectric film with periodically written ferroelectric domains by dry transfer method. The transfer medium is a PDMS film. With the assistance of heat baking to soften the PDMS film, transfer the adhered WSe2 film onto the surface of the P(VDF - TrFE) ferroelectric film.

[0083] Step (6): The P(VDF - TrFE) ferroelectric film scribed by the atomic force microscope probe generates a periodic depolarization field. The electrostatic field provided by this depolarization field regulates the bandgap of WSe2 and induces WSe2 to form a superlattice - like energy band structure.

[0084] Research shows that the bandgap of TMDCs can be regulated by an externally applied electric field, such as narrowing the bandgap or shifting the energy band position. Ferroelectrics with spontaneous polarization characteristics can provide depolarization fields with upward or downward polarization directions as electrostatic fields through ferroelectric domains to regulate the bandgap of two - dimensional materials. When the ferroelectric domains are periodically arranged, the generated periodic depolarization field will induce WSe2 to form a superlattice - like energy band structure. Therefore, by using the periodic ferroelectric domain structure to regulate the intrinsic bandgap of two - dimensional materials, a new type of two - dimensional superlattice material with a superlattice - like energy band structure can be prepared, which is expected to solve the current preparation problems of vdWSL.

[0085] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present application. Obviously, those skilled in the art can make various changes and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A preparation method of a periodically ferroelectric polarization-induced WSe2-like superlattice, characterized in that, Including: Spin-coat a P(VDF-TrFE) organic solution on a silicon substrate, and then perform annealing to obtain a P(VDF-TrFE) ferroelectric thin film; Perform scribing on the surface of the P(VDF-TrFE) ferroelectric thin film to obtain a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure; Transfer the WSe2 thin film to the surface of the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure through a two-dimensional transfer process. Induce the WSe2 thin film through the electrostatic field generated during the depolarization process of the P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure, so that the WSe2 thin film forms a band structure similar to a superlattice.

2. The preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice according to claim 1, characterized in that Use the tip of an atomic force microscope to perform scribing on the surface of the P(VDF-TrFE) ferroelectric thin film. The specific steps are as follows: Set the scanning area for each scribing of the atomic force microscope tip, the offset of the atomic force microscope tip in the X-direction or Y-direction movement, and the scribing times threshold respectively; After the atomic force microscope tip performs the first scribing on the set scanning area, move the atomic force microscope tip to the target position according to the offset in the X-direction or Y-direction movement for the next scribing until the scribing times threshold is reached and then stop scribing to obtain a P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure; Among them, each time after moving the atomic force microscope tip to the target position according to the set offset in the X-direction or Y-direction movement, reset the voltage on the atomic force microscope tip. The reset voltage value is the same as the voltage value during the previous scribing, and the voltage direction is opposite to the voltage direction during the previous scribing.

3. The preparation method of the periodically ferroelectrically polarized induced WSe2-based superlattice according to claim 2, characterized in that, The voltage applied to the tip of the atomic force microscope is -10 - +10V.

4. The preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice according to claim 2, wherein The offset in the X-direction movement is -5 - +5μm; the offset in the Y-direction movement is -5 - +5μm.

5. The preparation method of the periodically ferroelectrically polarized induced WSe2-based superlattice according to claim 2, characterized in that, After each completion of scribing the scanning area, set the voltage on the tip of the atomic force microscope to 0V, and then move the atomic force microscope tip with the adjusted voltage to the position where it was when starting to scribe the scanning area.

6. The preparation method of the periodically ferroelectrically polarized induced WSe2-like superlattice according to claim 1, characterized in that, The P(VDF-TrFE) ferroelectric thin film with a periodic ferroelectric domain structure is in the β-phase, and its morphology is a woven network. A periodic ferroelectric domain structure with periodically arranged out-of-plane upward and out-of-plane downward polarization directions is obtained through scribing.

7. The preparation method of the periodically ferroelectric polarization-induced WSe2-like superlattice according to claim 1, wherein, The thickness of the P(VDF-TrFE) ferroelectric thin film is 20nm - 300nm.

8. The method for preparing a periodic ferroelectric polarization-induced WSe2-like superlattice according to claim 1, characterized in that, The P(VDF-TrFE) organic solution includes P(VDF-TrFE) and a polar solvent. The polar solvent is diethyl carbonate, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone or methyl ethyl ketone. The mass fraction of P(VDF-TrFE) in the P(VDF-TrFE) organic solution is 0.5% - 5%.

9. The preparation method of the periodically ferroelectrically polarized induced WSe2-like superlattice according to claim 1, wherein, Anneal the silicon substrate spin-coated with the P(VDF-TrFE) organic solution. Among them, the annealing process is: the annealing temperature is 120 - 140°C, and the annealing time is 0.5 - 12h.

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