Preparation method of two-dimensional MoS2 / In2Se3 Van der Waals heterojunction thin film and application of two-dimensional MoS2 / In2Se3 Van der Waals heterojunction thin film in photoelectric synaptic device

Abstract

The invention discloses a preparation method of a two-dimensional MoS2 / In2Se3 Van der Waals heterojunction thin film and application of the two-dimensional MoS2 / In2Se3 Van der Waals heterojunction thin film in a photoelectric synapse device, and belongs to the technical field of photoelectric synapse devices.The preparation method comprises the steps that annealing treatment is conducted on a c-plane sapphire substrate, and a substrate surface with steps is formed; growing a MoS2 film on the c-plane sapphire substrate with the step by adopting a chemical vapor deposition method; an amorphous In2Se3 thin film is deposited on the surface of the MoS2 thin film at the room temperature through magnetron sputtering, and a MoS2 / In2Se3 composite thin film is obtained; the obtained composite film is placed in a hydrogen-argon mixed atmosphere to be annealed, amorphous In2Se3 is converted into alpha-In2Se3 crystals, the MoS2 / In2Se3 van der Waals heterojunction film is obtained, the film has the characteristics of good interface contact, large size and the like, the film is applied to a photoelectric synaptic device, and a technological foundation is laid for a sensing, storage and calculation integrated artificial vision array.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic synaptic device technology, specifically relating to a method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film and its application in optoelectronic synaptic devices. Background Technology

[0002] With the rapid development of IoT and AI technologies, traditional CMOS image sensing systems, due to the physical separation of detectors, processors, and memory, suffer from redundant data conversion and transmission, leading to bandwidth, storage, and power consumption bottlenecks. This makes them unable to meet the demands of real-time, high-energy-efficiency processing of massive image data. In contrast, the human retina can perform information detection, storage, and preprocessing in parallel with extremely low energy consumption, transmitting only compressed key features to the brain's visual cortex for deep analysis. This efficient mechanism inspires researchers to mimic biological neurons, directly integrating sensing, storage, and computation functions at the sensor end to construct neuromorphic visual devices with photoelectric synaptic properties. This enables the realization of an integrated sensing, storage, and computation artificial vision system, providing crucial hardware support for real-time, high-energy-efficiency applications such as autonomous driving and drone visual navigation.

[0003] To achieve these goals, existing technologies have drawn inspiration from biological vision mechanisms, proposing various innovative device solutions. For example, inspired by human four-color vision, broadband neuromorphic visual synapse devices based on two-dimensional WSe2 / three-dimensional GaN heterojunctions have achieved simultaneous sensing and processing in the ultraviolet-visible bands, demonstrating high accuracy in image recognition tasks. Mimicking the functional differentiation of retinal cells, reconfigurable sensors based on GaN nanowires can control their operating modes through gate voltage, making them suitable for image enhancement or dynamic action recognition. Further multimodal sensing systems can simultaneously analyze light and electrical signals, exhibiting brain-like multisensory fusion potential in scenarios such as intelligent traffic monitoring and emotion classification. However, for these devices to move towards wafer-level arrays, they must simultaneously meet two prerequisites: large size and good interface contact. Otherwise, laboratory-level performance indicators are difficult to translate into deployable chip-level systems. System-level requirements first impose a rigid constraint on large size: applications such as autonomous driving and drones require 1 cm². 2Even pixel arrays of several inches are needed to ensure spatial resolution, frame rate, and edge computing power. If the heterojunction film only maintains micron-level islands, the chip will lose its total pixel scale due to a large number of blank pixels, and the costs of subsequent packaging, alignment, and interconnection will also increase exponentially. The physical mechanism of the device further requires good interface contact: the updating of photoelectric synapse weights depends on the photogenerated carrier-interface separation-defect trapping-conductivity modulation chain, and the interface quality directly determines the fate of the carriers. Once there is residual photoresist, polymer, or lattice mismatch at the interface, deep level traps will be introduced, resulting in decreased responsivity, smaller memory window, increased power consumption, and deterioration of array uniformity, thereby weakening the core characteristics of synapse weights being trainable, storable, and stable. Process scalability also requires the simultaneous achievement of large size and good interface: mechanical peeling / transfer can obtain local high-quality heterojunctions, but lacks the ability to scale up; chemical vapor deposition or epitaxial growth has wafer-level potential, but often causes interface damage due to lattice / thermal expansion mismatch. Therefore, the combination of centimeter-scale two-dimensional material growth and interface engineering has been recognized by the field as a key bottleneck, and the degree of breakthrough directly determines whether the device can move from laboratory performance indicators to production line mass production.

[0004] Therefore, there is an urgent need in this field for a two-dimensional material heterojunction thin film preparation scheme that can achieve atomic-level interface integrity at the centimeter scale and is suitable for sensor-memory-computing integrated neuromorphic vision systems, in order to break through the current technical bottlenecks and truly realize the large-scale production and application of optoelectronic synaptic device arrays. Summary of the Invention

[0005] Based on the shortcomings of the aforementioned background technology, this invention addresses the core technical bottlenecks of traditional mechanical peel-and-transfer processes in the fabrication of two-dimensional material heterojunctions, such as the unavoidable introduction of impurities, device performance degradation, and limitations on large-scale array expansion. It proposes a method for fabricating two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin films and their application in optoelectronic synaptic devices. Using stepped c-plane sapphire as a substrate, chemical vapor deposition, magnetron sputtering, and annealing processes are sequentially employed to grow MoS2 / α-In2Se3 van der Waals heterojunction thin films with atomically flat interlayers, no dangling bonds, and centimeter-scale dimensions on the sapphire substrate. These films are then further applied to optoelectronic synaptic devices, laying the technological foundation for the large-scale fabrication of high-quality, large-size heterojunction thin films and the development of integrated sensing, storage, and computing artificial vision arrays.

[0006] To achieve the above-mentioned objectives, an embodiment provides a method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film, comprising the following steps: Step 1: Anneal the c-plane sapphire substrate to form a stepped substrate surface that is conducive to the subsequent preparation of MoS2 thin films; Step 2: MoS2 thin film is grown on a stepped c-plane sapphire substrate using chemical vapor deposition: sulfur powder is placed in the first temperature zone, and a mixture of MoO3 and NaCl powder is placed in the second temperature zone. The substrate is inverted on top of the mixed powder. Inert gas is used as the carrier gas. The temperature and holding time of each temperature zone are controlled to prepare the MoS2 thin film. Step 3: On the surface of the MoS2 thin film, an amorphous In2Se3 thin film is deposited by magnetron sputtering at room temperature to obtain a MoS2 / In2Se3 composite thin film; Step 4: Anneal the obtained MoS2 / In2Se3 composite film in a hydrogen-argon mixed atmosphere to transform the amorphous In2Se3 into α-In2Se3 crystal, thus obtaining the MoS2 / In2Se3 van der Waals heterojunction film.

[0007] Silica substrates cannot form steps through annealing, making it difficult to control the orientation of MoS2 during growth and easily leading to the formation of multiple grain boundaries and poor film quality. Therefore, this invention selects a c-plane sapphire substrate. By introducing steps through a specific oblique cut on the c-plane of the sapphire (e.g., oblique cut along the A-axis, C / A), the energy degeneracy state during nucleation can be broken. The formed step edges promote the nucleation of MoS2 domains in a single orientation and epitaxially grow along the step-dominant direction, ultimately splicing them into a large-area thin film. Without steps, multi-orientation nucleation leads to the formation of high-density grain boundaries, resulting in poor film continuity and making large-area growth difficult. In addition, a sulfur-rich environment can suppress the formation of reverse grain domains, further optimizing the nucleation conditions. Using this method, the formation of internal grain boundaries in MoS2 can be minimized or even eliminated by controlling the crystal orientation, further improving its electrical, optical, and mechanical properties.

[0008] As a preferred embodiment of the present invention, the inert gas is preferably argon, which can effectively remove elements such as carbon, oxygen, and nitrogen from the environment, and does not participate in the reaction or introduce impurities, which is beneficial for obtaining high-purity films.

[0009] As a preferred embodiment of the present invention, the annealing process in step 1 is as follows: the central temperature zone is heated to 600-1000°C within 20-60 minutes, then heated to 1100-1400°C within 80 minutes, held at that temperature for 180-300 minutes, and then cooled to 700-800°C at a rate of 5-20°C / min, and then cooled to room temperature in the furnace. The entire annealing process is carried out in an atmospheric atmosphere, and after natural cooling to room temperature, a c-plane sapphire substrate with steps is obtained.

[0010] As a preferred embodiment of the present invention, the thickness of the MoS2 layer is 1-10 nm. In step 2, during the preparation of MoS2 by chemical vapor deposition, the argon flow rate is adjusted to 50-70 sccm during the growth stage, and the horizontal distance between the substrate and the mixed powder is 0.5-2.0 cm and the vertical distance is 0.5-1.0 cm. The first temperature zone is heated to 180°C, and the second temperature zone is heated to 700-900°C and held for 10-20 min.

[0011] As a preferred embodiment of the present invention, the amorphous In2Se3 film has a thickness of 1-20 nm and completely covers the surface of the MoS2 film layer. In step 3, during the preparation of the amorphous In2Se3 film by magnetron sputtering, the sputtering gas is argon, the distance from the target to the substrate is 50-150 mm, the pressure in the sputtering chamber is 0.3-3.0 Pa, the deposition power is 10-30 W, and the film deposition time is 5-30 min.

[0012] In step 4, the annealing process reduces the surface energy of the MoS2 film and enhances atomic diffusion, promoting the crystallization of the amorphous In2Se3 film into a highly crystalline α-In2Se3 film. Ultimately, α-In2Se3 is vertically stacked on the MoS2 surface by van der Waals forces, avoiding defects caused by interfacial chemical bonding and lattice mismatch. During growth, α-In2Se3 and MoS2 form a specific band arrangement, thereby achieving coupling between ferroelectric and semiconductor properties. Furthermore, under inert atmosphere protection, the MoS2 / In2Se3 van der Waals heterojunction film heterostructure obtained after magnetron sputtering and annealing exhibits cleanliness and stability, providing a foundation for carrier separation and transport optimization in optoelectronic devices.

[0013] As a preferred embodiment of the present invention, in step 4, the hydrogen-argon mixed atmosphere used for annealing the MoS2 / In2Se3 composite film is a mixture of 50 sccm argon and 5 sccm hydrogen. The annealing temperature is as follows: the heating rate is 5-30 °C / min, the reaction apparatus is heated to 450-550 °C and held for 30-120 min, and after the holding time, it is slowly cooled to room temperature at a rate of 3-6 °C / min to ensure that the crystallization is α-In2Se3 film. The most stable phase at room temperature is the α phase. Controlling the heating rate, holding time, and cooling rate is beneficial to the slow crystallization of the amorphous film, improving the crystallization quality, and forming a high-quality MoS2 / In2Se3 van der Waals heterojunction film.

[0014] To achieve the above-mentioned objectives, the embodiments also provide a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film, which is prepared by the above method.

[0015] To achieve the above-mentioned objectives, the embodiments also provide an application of a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film in optoelectronic synaptic devices. The above-mentioned MoS2 / In2Se3 van der Waals heterojunction thin film is transferred to a SiO2 / Si substrate, wherein the MoS2 layer contacts the surface of the SiO2 / Si substrate. The heterojunction array material is obtained by inductively coupled plasma etching. Gold electrodes are fabricated on the surface of the α-In2Se3 layer of the heterojunction array material to construct an arrayed two-electrode field-effect device.

[0016] In the fabrication of dual-electrode field-effect devices, the prepared gold electrode is not transferred to the heterojunction, but the thin film is transferred first and then the gold electrode is constructed. This is to form a better ohmic contact between the deposited gold electrode and the channel material. If the electrode is prepared first and then the material is transferred, impurities are easily introduced at the interface between the heterojunction and the gold electrode during the transfer process, thereby reducing the device performance.

[0017] In a preferred embodiment of the present invention, the SiO2 / Si substrate has a SiO2 layer thickness of 200-500 nm, a MoS2 layer thickness of 1-10 nm, an α-In2Se3 layer thickness of 1-20 nm, and a gold electrode thickness of 30-100 nm. Typically, the gold electrode thickness is controlled within tens of nanometers. Excessively thin gold electrodes can easily affect electrical performance during testing and are prone to damage when using a probe station.

[0018] As a preferred embodiment of the present invention, the gold electrode is generated in situ on the surface of the α-In2Se3 layer of the heterojunction array material by laser direct writing lithography, metallization evaporation and other processes.

[0019] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages: First, a stepped substrate surface is formed by annealing the c-plane sapphire, which enables better growth of large-area MoS2 films. MoS2 has a low surface energy, and the amorphous In2Se3 deposited on the MoS2 film is more likely to nucleate and crystallize during the annealing process, which is beneficial for preparing large-area, interface-clean, and impurity-free two-dimensional MoS2 / In2Se3 van der Waals heterojunction films.

[0020] The optoelectronic device fabricated based on the above-mentioned two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film possesses photodetection, storage, and computing functions, and achieves an optical on / off ratio of 10 under 532 nm laser irradiation. 7Furthermore, the off-state current increases with increasing optical power. Under optical pulse stimulation, the device also exhibits non-volatile photoresponse; the photocurrent remains effectively maintained after the optical stimulation ends. After applying two consecutive optical pulses, there is a significant double-pulse facilitation phenomenon, which can effectively mimic the short-term enhancement behavior in synaptic plasticity. By extending the illumination time, it can simulate the long-term enhancement behavior of synapses, which has great application value in the field of integrated sensing, storage, and computing devices. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the preparation method of the two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film provided in the embodiment; Figure 2 This is a schematic diagram of the growth experimental apparatus and principle for preparing MoS2 thin films using the chemical vapor deposition (CVD) process provided in the embodiments; Figure 3 These are optical microscopic images of the MoS2 thin film grown on a sapphire substrate provided in the embodiments; Figure 4 These are optical micrographs of the MoS2 / In2Se3 van der Waals heterojunction thin films provided in the embodiments; Figure 5 These are XRD patterns of the MoS2 / In2Se3 van der Waals heterojunction thin film before and after annealing, provided in the examples; Figure 6 The Raman spectra of MoS2, α-In2Se3 and MoS2 / In2Se3 van der Waals heterojunction films provided in the examples; Figure 7 The example provides an arrayed optoelectronic device based on a MoS2 / In2Se3 van der Waals heterojunction thin film. Figure 8 This is a schematic diagram of the MoS2 / In2Se3 van der Waals heterojunction optoelectronic device structure provided in the embodiment; Figure 9 The examples show the transfer curves of the device under dark conditions and under irradiation with 532 nm lasers of different powers. Figure 10 The device provided in the example exhibits a two-pulse facilitation phenomenon under optical pulses; Figure 11The embodiment describes the transition behavior of the device from short-term enhancement to long-term enhancement under different time-dependent light pulse stimulation. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0024] Example 1: Preparation of two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin films like Figure 1 As shown in the embodiment, a method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film includes the following steps: S1, the c-plane sapphire substrate is annealed to form a stepped substrate surface.

[0025] In this embodiment, to obtain a sapphire substrate with a stepped c-plane, the sapphire substrate was sequentially ultrasonically cleaned in acetone, ethanol, and deionized water, dried with nitrogen, placed in a clean alumina crucible, and transferred to a high-temperature tube furnace; under atmospheric conditions, the central temperature zone was raised to 800°C within 40 minutes. o C, then 5 o The rate of C / min increased to 1150 within 80 minutes. o C, keep warm for 240 min, then at 5 o Cool down to 800°C / min o C, and finally cooled to room temperature in the furnace to obtain a c-plane sapphire substrate with atomic steps.

[0026] Figure 2 This diagram illustrates the fabrication of MoS2 thin films using chemical vapor deposition (CVD). A stepped c-plane sapphire serves as the growth substrate on which the MoS2 film is grown. The mechanism primarily relies on the manipulation of the degenerate nucleation energy state through substrate surface step engineering. By introducing steps into a specific obliquely cut c-plane of the sapphire (e.g., along the A-axis, C / A), the degenerate energy state during nucleation is broken. The resulting step edges promote the nucleation of MoS2 domains in a single orientation, leading to epitaxial growth along the step-dominant direction and ultimately forming a large-area film. Furthermore, a sulfur-rich environment can suppress the formation of reverse-oriented domains, further optimizing the nucleation conditions. This method allows for the control of crystal orientation, minimizing or even eliminating the formation of internal grain boundaries in MoS2, thereby improving its electrical, optical, and mechanical properties.

[0027] S2, MoS2 thin films are grown on a stepped c-plane sapphire substrate using chemical vapor deposition.

[0028] In this embodiment, 250 mg of sulfur powder (analytical grade) was weighed and placed in the center of a quartz boat in the first temperature zone. Separately, 1 mg of MoO3 (analytical grade) and 0.5 mg of NaCl (analytical grade) were ground evenly and placed into a double-opening quartz boat. A molecular sieve was used to cover the surface to control the precursor release rate. The substrate obtained in step S1 was placed upside down on top of the mixed powder, maintaining a horizontal distance of 1.0 cm and a vertical distance of 0.8 cm between the center of the substrate and the powder. The quartz boat was then fixed in the center of the second temperature zone. After continuously introducing 200 sccm of argon gas for 30 min to purge residual air, a segmented heating program was initiated: the second temperature zone was heated to 800℃ at 40℃ / min and held for 15 min; the first temperature zone was initially maintained at room temperature, and when the second temperature zone reached 650℃, it was simultaneously heated to 180℃ at 40℃ / min to achieve timing matching of sulfur vapor and MoO3. During the growth stage, the argon gas flow rate was adjusted to 60 sccm. After the reaction, the furnace was cooled to room temperature, and the substrate with a uniformly layered MoS2 film on its surface was removed.

[0029] Figure 3 This is an optical microscope image of a MoS2 thin film grown on the c-plane of sapphire. The entire image area contains a uniform MoS2 thin film with a large area and high flatness.

[0030] S3, on the surface of the MoS2 thin film, an amorphous In2Se3 thin film is deposited by magnetron sputtering at room temperature to obtain a MoS2 / In2Se3 composite thin film.

[0031] In this embodiment, an amorphous In2Se3 layer was deposited on a substrate with a pre-grown MoS2 thin film using radio frequency magnetron sputtering to form a MoS2 / In2Se3 composite thin film. Argon gas was used as the sputtering gas. Throughout the sputtering process, an radio frequency power supply was used for film sputtering. The film was deposited at room temperature, and no bias voltage was applied to the substrate. Sputtering conditions: radio frequency power of 15 W, argon atmosphere of 0.4 Pa, target-substrate distance of 130 mm, room temperature deposition for 30 min, and pre-sputtering for 10 min to ensure target surface cleanliness and avoid initial component contamination of the sputtered film. No bias voltage was applied to the substrate.

[0032] S4. The obtained MoS2 / In2Se3 composite film is annealed in a hydrogen-argon mixed atmosphere to transform amorphous In2Se3 into α-In2Se3 crystal, thus obtaining MoS2 / In2Se3 van der Waals heterojunction film.

[0033] After sputtering, the sample was placed in a tube furnace and heated to 500°C at 10°C / min in a mixed atmosphere of 50 sccm Ar and 5 sccm H2, held for 60 min, and then slowly cooled to room temperature at 5°C / min to crystallize the amorphous In2Se3 layer into α-In2Se3 crystals, thereby forming an atomically clean and centimeter-scale continuous MoS2 / In2Se3 van der Waals heterojunction.

[0034] Figure 4 These are optical microscope images of MoS2 / In2Se3 heterojunction thin films. Based on the magnetron sputtered thin film, an amorphous In2Se3 film was transformed into an α-In2Se3 crystalline film using annealing and recrystallization. The main growth mechanism involves reducing surface energy and enhancing atomic diffusion on the MoS2 film surface, promoting the crystallization of the amorphous In2Se3 film into a highly crystalline film. Ultimately, α-In2Se3 is vertically stacked on the MoS2 surface by van der Waals forces, avoiding defects caused by interfacial chemical bonding and lattice mismatch. During growth, α-In2Se3 and MoS2 form a specific band arrangement, thereby achieving coupling between ferroelectric and semiconductor properties. Furthermore, under inert atmosphere protection, the MoS2 / In2Se3 van der Waals heterojunction interface obtained after magnetron sputtering and annealing exhibits cleanliness and stability, providing a foundation for carrier separation and transport optimization in optoelectronic devices.

[0035] Figure 5 To compare the XRD test results of In2Se3 thin film before and after annealing, it was found that the film was in an amorphous state before annealing and no diffraction peaks appeared. After annealing, main diffraction peaks such as (004), (006), and (0010) appeared, proving that the amorphous α-In2Se3 thin film of the material crystallized to form α-In2Se3 crystals.

[0036] Figure 6 For Raman spectral characterization of MoS2 films, α-In2Se3 films, and MoS2 / In2Se3 van der Waals heterojunction films, the characteristic peak of MoS2 film is located at 381 cm⁻¹. -1 and 405 cm -1 The characteristic peaks of the α-In2Se3 thin film are located at 92 cm⁻¹. -1 104 cm -1 181 cm -1 200 cm -1 The Raman peaks of the two materials were superimposed in the heterojunction, and no other impurity peaks appeared, confirming that the prepared MoS2 / α-In2Se3 heterojunction has high quality and good crystallinity.

[0037] Example 2: Fabrication of Electrode Field-Effect Devices In this embodiment, the MoS2 / In2Se3 van der Waals heterojunction film prepared in Example 1 was transferred integrally to a SiO2 / Si substrate using PMMA-assisted wet transfer technology. A 10×10 array pattern was defined using ICP etching, followed by the fabrication of gold electrodes through laser direct writing lithography, electron beam evaporation, and lift-off processes to construct an arrayed two-electrode field-effect device. The device structure, from bottom to top, consists of a SiO2 / Si substrate, a 2 nm MoS2 layer, a 20 nm α-In2Se3 layer, and a 60 nm gold electrode. The gold electrode forms an ohmic contact with the α-In2Se3 layer, completing the fabrication of the heterojunction photosynapse array.

[0038] Figure 7 To transfer MoS2 / In2Se3 heterojunction thin films onto the surface of SiO2 / Si substrates, heterojunction array materials are obtained through ICP etching, and arrayed dual-electrode field-effect devices are constructed on SiO2 / Si substrates using processes such as laser direct writing lithography and metallization evaporation.

[0039] Figure 8 This is a schematic diagram of a cross-section of a single device. The MoS2 layer is in direct contact with the SiO2 / Si substrate, and α-In2Se3 covers the MoS2 layer to form a heterojunction. The gold electrode is in direct contact with the α-In2Se3 layer.

[0040] Figure 9 To test the transfer curves of the electrode field-effect device under different irradiation powers of a 532 nm laser, the heterojunction exhibits n-type semiconductor transfer characteristics. As the optical power increases, the source and drain currents of the device gradually increase, and the off-state current rises significantly under illumination. At an incident optical power of 270 μW, a maximum current close to 10 μW can be generated. 7 Optical switching ratio.

[0041] Figure 10 The test results were obtained by applying two continuous optical pulses with a pulse width of 0.5 s to the device. The current of the second optical pulse was increased based on the current of the first optical pulse, showing obvious double-pulse facilitation. After the optical pulse ended, the device maintained the photocurrent for a period of time, which can effectively mimic the short-term enhancement behavior in synaptic plasticity.

[0042] Figure 11 The test results of applying single laser pulses to the device for different durations show that as the illumination time increases, the photocurrent of the device continuously increases, and the steady-state current level also gradually increases, indicating that the synaptic weight gradually increases. By extending the pulse stimulation time, the device can effectively mimic the transition behavior from short-term enhancement to long-term enhancement in synaptic plasticity.

[0043] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film, characterized in that, Includes the following steps: Step 1: Anneal the c-plane sapphire substrate to form a stepped substrate surface; Step 2: MoS2 thin film is grown on a stepped c-plane sapphire substrate using chemical vapor deposition: sulfur powder is placed in the first temperature zone, and a mixture of MoO3 and NaCl powder is placed in the second temperature zone. The substrate is inverted on top of the mixed powder. Inert gas is used as the carrier gas. The temperature and holding time of each temperature zone are controlled to prepare the MoS2 thin film. Step 3: On the surface of the MoS2 thin film, an amorphous In2Se3 thin film is deposited by magnetron sputtering at room temperature to obtain a MoS2 / In2Se3 composite thin film; Step 4: Anneal the obtained MoS2 / In2Se3 composite film in a hydrogen-argon mixed atmosphere to transform the amorphous In2Se3 into α-In2Se3 crystal, thus obtaining the MoS2 / In2Se3 van der Waals heterojunction film.

2. The method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 1, characterized in that, In step 1, the annealing process is as follows: the central temperature zone is heated to 600-1000℃ within 20-60 min, then heated to 1100-1400℃ within 80 min, held for 180-300 min, and then cooled to 700-800℃ at a rate of 5-20℃ / min, and then cooled to room temperature in the furnace.

3. The method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 1, characterized in that, The thickness of the MoS2 layer is 1-10 nm. In step 2, during the preparation of MoS2 by chemical vapor deposition, the argon flow rate is adjusted to 50-70 sccm during the growth stage, and the horizontal distance between the substrate and the mixed powder is 0.5-2.0 cm and the vertical distance is 0.5-1.0 cm. The first temperature zone is heated to 180℃ and the second temperature zone is heated to 700-900℃ and held for 10-20 min.

4. The method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 1, characterized in that, The amorphous In2Se3 film has a thickness of 1-20 nm and completely covers the surface of the MoS2 film. In step 3, during the preparation of the amorphous In2Se3 film by magnetron sputtering, the sputtering gas is argon, the distance from the target to the substrate is 50-150 mm, the pressure in the sputtering chamber is 0.3-3.0 Pa, the deposition power is 10-30 W, and the film deposition time is 5-30 min.

5. The method for preparing a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 1, characterized in that, In step 4, the hydrogen-argon mixed atmosphere used for annealing the MoS2 / In2Se3 composite film is a mixture of 50 sccm argon and 5 sccm hydrogen. The annealing temperature is as follows: the heating rate is 5-30 ℃ / min, the reaction apparatus is heated to 450-550 ℃ and held for 30-120 min. After the holding time, it is slowly cooled to room temperature at a rate of 3-6 ℃ / min to ensure that the amorphous In2Se3 crystallizes into α-In2Se3 crystals.

6. A two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film, characterized in that, The thin film is prepared by the method described in any one of claims 1-5.

7. An application of a two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film in optoelectronic synaptic devices, characterized in that, The MoS2 / In2Se3 van der Waals heterojunction thin film of claim 6 is transferred to a SiO2 / Si substrate, wherein the MoS2 layer contacts the surface of the SiO2 / Si substrate, and the heterojunction array material is obtained by inductively coupled plasma etching. A gold electrode is fabricated on the surface of the α-In2Se3 layer of the heterojunction array material, thereby constructing an arrayed dual-electrode field-effect device.

8. The application of the two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 7 in photoelectric synaptic devices, characterized in that, In the SiO2 / Si substrate, the SiO2 layer has a thickness of 200-500 nm, the MoS2 layer has a thickness of 1-10 nm, the α-In2Se3 layer has a thickness of 1-20 nm, and the gold electrode has a thickness of 30-100 nm.

9. The application of the two-dimensional MoS2 / In2Se3 van der Waals heterojunction thin film according to claim 7 in photoelectric synaptic devices, characterized in that, The gold electrode is generated in situ on the surface of the α-In2Se3 layer of the heterojunction array material by laser direct writing lithography or metallization evaporation.

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