M1-phase VO2 nanosheet, preparation thereof and application of M1-phase VO2 nanosheet in memristor

Abstract

The invention belongs to the field of semiconductor materials, and particularly relates to an M1-phase VO2 nanosheet, preparation of the M1-phase VO2 nanosheet and application of the M1-phase VO2 nanosheet in a memristor, the M1-phase VO2 nanosheet is obtained by conducting thermal transformation treatment on a VSe2 nanosheet, and the atmosphere in the thermal transformation treatment process is mixed gas of protective gas and oxygen with the volume ratio being 1500-3000; the temperature of thermal transformation is 320-580 DEG C; the thermal transformation time is 5 to 65 minutes. Innovative research shows that the VSe2 nanosheets are subjected to thermal transformation in the mixed atmosphere, and combined control of thermal transformation temperature, time and atmosphere is further matched, so that synergy can be realized, and the VO2 nanosheets with high M1 phase crystal phase purity can be obtained with high selectivity. In addition, research also shows that the M1-phase VO2 nanosheet prepared by the method disclosed by the invention can meet the preparation requirements of the memristor, and can obtain excellent performance such as circulation and switch ratio.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of two-dimensional materials, and particularly relates to the field of memristor materials. TECHNICAL BACKGROUND

[0002] In the era of big data and Internet of Things (IoT), massive amounts of sensory data such as images, speech, and videos need to be processed in real time by hardware with higher energy efficiency. At the same time, the demand for parallel processing and multitasking capabilities in the computing field is also growing. However, Von Neumann architecture computer systems based on traditional Complementary Metal-Oxide-Semiconductor (CMOS) technology have been difficult to fully meet these needs [1] . Therefore, the industry is actively exploring emerging computing paradigms such as In-Memory Computing and Neuromorphic Computing to break through the limitations of traditional computing architectures and achieve higher computing performance and energy efficiency.

[0003] In recent years, new types of semiconductor devices such as Resistive Random Access Memory (RRAM) [2] , Phase Change Memory (PCRAM) [3] , and Insulator-Metal Transition (MIT) devices [4] have become ideal candidates for simulating artificial synapses or neurons due to their significant advantages in integration density and performance. These devices not only enable more efficient hardware implementation of SNNs, but also provide new possibilities for optimization of neuromorphic computing systems. At the same time, optimization and innovation research for spiking neural network algorithms continues to advance to fully exploit the computing potential of new hardware. Among the many memristor materials, Mott memristors are of great interest due to their unique Insulator-Metal Transition (Mott Transition)

[0004] characteristics. As early as 1937 [5] , De Boer et al. found that traditional band theory could not explain the insulating properties of certain transition metal oxides. Mott's electron correlation theory, proposed in 1949, successfully explained this phenomenon, and such materials are therefore referred to as Mott insulators [6] . Research has shown that Mott insulators not only exhibit unconventional insulating behavior, but also undergo significant electrical and magnetic property mutations under external stimuli. This insulator-metal transition is defined as the Mott Transition [7] . Among them, vanadium dioxide (VO2) is a typical representative with a phase transition temperature close to room temperature (~ 68 ℃), a resistance change of up to 4 orders of magnitude during phase transition, and a reversible transition that can be controlled by heat, electricity, light, stress, and other means [8] . VO2 These characteristics, combined with its simple preparation and single component, make it have broad application prospects in the fields of thermochromic, electronic devices and neuromorphic computing.

[0005] References

[0006] [1]Wong H S P, Salahuddin S. Memory leads the way to better computing[J]. Nature Nanotechnology, 2015, 10(3): 191-194 [2]Wang Z, Joshi S, Savel’ev S, et al. Fully memristive neural networks for pattern classification with unsupervised learning[J]. Nature Electronics, 2018, 1(2): 137- 145. [3]Tuma T, Pantazi A, Le Gallo M, et al. Stochastic phase-change neurons[J]. Nature Nanotechnology, 2016, 11(8): 693-699. [4]Zhang X, Zhuo Y, Luo Q, et al. An artificial spiking afferent nerve based on Mott memristors for neurorobotics[J]. Nature Communications, 2020, 11(1). [5]Boer J H d, Verwey E J W. Semi-conductors with partially and with completely filled 3d-lattice bands[J]. Proceedings of the Physical Society, 1937, 49(4S): 59. [6]Mott N F. The Basis of the Electron Theory of Metals, with Special Reference to the Transition Metals[J]. Proceedings of the Physical Society Section A, 1949, 62(7): 416. [7]Mott N F. Metal-Insulator Transition[J]. Reviews of Modern Physics, 1968, 40(4): 677-683. [8]Eyert V. The metal‐insulator transitions of VO2: A bandtheoretical approach[J]. Annalen der Physik, 2002, 514(9): 650-704 SUMMARY

[0007] In view of the prior art, the present application provides a preparation method of M1 phase VO2 nanosheets, aiming to prepare M1 phase VO2 nanosheets with high purity phase and suitable for the application requirements of memristors.

[0008] The second object of the present application is to provide M1 phase VO2 nanosheets prepared by the preparation method.

[0009] The third object of the present application is to provide the application of the M1 phase VO2 nanosheets in the preparation of memristors.

[0010] The fourth object of the present application is to provide a memristor comprising the M1 phase VO2 nanosheets of the present application.

[0011] Vanadium element in +4 valence state (VO2) shows unique chemical instability, and its outer electron configuration 3d1 makes it have significant valence state adjustability. From the analysis of atomic bonding theory, V 4+ ions in VO2 can be further oxidized to V 5+ ((V2O5), or reduced to V 3+ ((V2O3). This valence instability leads to the coexistence of various vanadium oxide mixtures in actual material systems, including non-stoichiometric V6O 13 , metastable β-VO2 and various crystal face oriented polycrystalline structures, such as (110), (011), (101) and the like. In view of this problem, the present application provides the following solutions:

[0012] A preparation method of M1 phase VO2 nanosheet is obtained by heat transformation treatment of VSe2 nanosheet, wherein the atmosphere of the heat transformation treatment process is a mixed gas of a protective gas and oxygen in a volume ratio of 1500-3000; the temperature of the heat transformation is 320-580 DEG C; and the time of the heat transformation is 5-65 min.

[0013] The present application innovatively shows that the VSe2 nanosheet is heat transformed in the mixed atmosphere, and the heat transformation temperature, time and atmosphere are jointly controlled, so that the high M1 phase crystal phase purity VO2 nanosheet can be obtained with high selectivity. In addition, the research also shows that the M1 phase VO2 nanosheet prepared by the method of the present application can meet the preparation requirements of the memristor, and excellent cycle, switching ratio and other performances can be obtained.

[0014] In the present application, the VSe2 nanosheet can be prepared based on known means, for example, the VSe2 nanosheet is prepared by PVD or CVD method.

[0015] In the present application, the CVD preparation process of the VSe2 nanosheet is that VCl3 and Se powder are volatilized and CVD deposited in a carrier gas to prepare the VSe2 material.

[0016] The purity of VCl3 and Se powder raw material is greater than 99%.

[0017] Preferably, the weight ratio of VCl3 and Se powder is 5-10:10; further can be 6-8:10.

[0018] Preferably, the volatilization temperature of VCl3 is 550-650 DEG C, and further can be 570-590 DEG C.

[0019] Preferably, the volatilization temperature of Se powder is 360-400 DEG C.

[0020] Preferably, the carrier gas includes a protective gas and hydrogen. The protective gas is at least one of nitrogen, inert gas, etc.

[0021] Preferably, in the carrier gas, the flow rate of the protective gas is 50-100 sccm, and the flow rate of hydrogen is 1-5 sccm.

[0022] In the present application, the temperature of the CVD deposition is 550-650 DEG C, and further can be 590-620 DEG C.

[0023] Preferably, the time of the CVD deposition is 5-15 min.

[0024] In the present application, the substrate of the CVD deposition is not particularly required, for example, can be a 280nm thick SiO2 / Si substrate.

[0025] The application innovatively performs the transformation treatment on the VSe2 nanosheet, and the M1 phase VO2 nanosheet can be induced by combining control of transformation conditions.

[0026] In the application, the protective gas in the mixed gas is at least one of nitrogen and inert gas.

[0027] Preferably, the volume ratio of the protective gas-oxygen in the mixed gas is 2000-2500:1.

[0028] The temperature of the thermal transformation is 320-340 DEG C, and the time of the thermal transformation is 55-65 min;

[0029] The temperature of the thermal transformation is 360-390 DEG C, and the time of the thermal transformation is 35-45 min;

[0030] The temperature of the thermal transformation is 400-450 DEG C, and the time of the thermal transformation is 15-25 min;

[0031] The temperature of the thermal transformation is 510-550 DEG C, and the time of the thermal transformation is 5-15 min.

[0032] The application research shows that the M1 phase VO2 nanosheet can be obtained by transforming at 400-450 DEG C for 15-25 min.

[0033] The application also provides the M1 phase VO2 nanosheet prepared by the preparation method.

[0034] The preparation method can endow the prepared material with special physicochemical characteristics, and the material with the characteristics has excellent performance in the preparation of the memristor.

[0035] The application also provides the application of the M1 phase VO2 nanosheet prepared by the preparation method to the preparation of the memristor.

[0036] In the application, the M1 phase VO2 nanosheet can be made into a required memristor based on known means.

[0037] For example, a preparation method of a horizontal double-terminal VO2 memristor, the synthesized M1 phase VO2 nanosheet is subjected to electron beam exposure and metal evaporation processes, and a horizontal double-terminal VO2 memristor is successfully prepared. The memristor device can still maintain good cycle stability in 3000 cycles, wherein the maximum device switching ratio can reach 320, the fastest on-state time is 30 mu s, and the fastest off-state time is 20 mu s.

[0038] Preferably, the metal is pure Au.

[0039] The application also provides a preparation method of a vertical double-terminal VO2 memristor, which comprises the following steps: transferring the obtained M1 phase VO2 nanosheet to a bottom gold electrode, and then transferring a top gold electrode, thereby successfully preparing a vertical double-terminal VO2 memristor. The memristor device can still maintain good cycle stability in 300 cycles.

[0040] The application also provides an application of a VO2 memristor, which comprises the horizontal double-terminal VO2 memristor, and by applying a pulse voltage to both ends of VO2, the response of a living being under pain stimulation can be simulated, and the VO2 memristor can be used as a pain receptor of a nervous system.

[0041] The application also provides a memristor comprising the M1 phase VO2 nanosheet prepared by the preparation method.

[0042] The memristor described in the application can comprise other components and structures known in the art in addition to the M1 phase VO2 nanosheet material described in the application.

[0043] Advantages

[0044] 1. The VSe2 nanosheet is subjected to thermal transformation in the mixed atmosphere, and the thermal transformation temperature, time and atmosphere are jointly controlled, so that the M1 phase VO2 nanosheet with high crystalline phase purity can be obtained with high selectivity.

[0045] 2. The M1 phase VO2 nanosheet is innovatively used to prepare a memristor, which has excellent adaptability and can exhibit excellent performance, for example, the obtained planar memristor has a cycle stability of >3100 times, the switching ratio is up to 320, and the vertical structure memristor has a fast response speed (on-off time <50 mu s).

[0046] 3. Application expansion: the VO2 memristor is applied to bionic pain perception, and provides a hardware basis for neuromorphic engineering. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 An atmospheric pressure chemical vapor deposition device for preparing VSe2 two-dimensional material;

[0048] Figure 2 A schematic diagram of the experimental apparatus for the thermal transformation and oxidation of VSe2 obtained in Example 1-1 to VO2;

[0049] Figure 3 Optical photographs of the sample before and after thermal transformation in Example 1-1;

[0050] Figure 4 X-ray photoelectron spectroscopy characterization of VSe2 in Example 1-1;

[0051] Figure 5 X-ray photoelectron spectroscopy characterization of VO2 in Example 1-1;

[0052] Figure 6 The scanning transmission electron microscopy energy dispersive spectroscopy characterization of VO2 in Example 1-1;

[0053] Figure 7 These are Raman characterization images of the thermal transformation at 420 °C for different times in Examples 1-2;

[0054] Figure 8 These are Raman characterization images of oxidation times at different temperatures in Examples 1-2;

[0055] Figure 9 VO obtained by oxidation under different oxygen pressures in Examples 1-3 x Raman characterization diagram;

[0056] Figure 10 VO2+ obtained by oxygen Plasma oxidation in Comparative Example 1-1 x Raman characterization diagram;

[0057] Figure 11 This is a flowchart illustrating the fabrication of the planar double-ended Au / VO2 / Au memristor in Example 2-1;

[0058] Figure 12 The electrical test diagram of the planar double-ended Au / VO2 / Au memristor in Example 2-1 is shown.

[0059] Figure 13 The resistive switching performance test diagram of the planar double-ended Au / VO2 / Au memristor in Example 2-1 is shown.

[0060] Figure 14 The IV characteristic curve of the planar double-ended Au / VO2 / Au memristor with maximum switching ratio in Example 2-1;

[0061] Figure 15 This is a flowchart illustrating the fabrication of the vertically dual-terminal Au / VO2 / Au memristor in Example 2-2;

[0062] Figure 16Figure for electrical and resistive switching test of vertical dual-terminal Au / VO2 / Au memristor in Example 2-2;

[0063] Figure 17 I-V characteristic curve of planar dual-terminal Au / V2O5 / Au device in Comparative Example 2-1;

[0064] Figure 18 Mechanism of action of nociceptor in Example 3-1;

[0065] Figure 19 Switching time of planar dual-terminal Au / VO2 / Au memristor in Example 3-1 and I-V characteristic curve of device for nociceptor;

[0066] Figure 20 Characteristic test chart of planar dual-terminal Au / VO2 / Au memristor in Example 3-1 applied to nociceptor. DETAILED DESCRIPTION

[0067] The application will be further described in the following examples, but the application is not limited to the following content.

[0068] An alternative scheme of the application provides a two-dimensional VSe2 nanosheet which can be prepared based on known methods, for example, an alternative method, and the synthesis conditions of the two-dimensional VSe2 nanosheet are as follows:

[0069] In this study, VSe2 nanosheets were prepared in a double-zone tube furnace using an atmospheric pressure chemical vapor deposition (APCVD) system. First, 100 mg of selenium powder and 70 mg of vanadium trichloride were accurately weighed and placed in clean ceramic boats. The selenium powder was placed in the upstream temperature zone of the quartz tube, and the vanadium trichloride was placed at the junction of the two temperature zones. A polished SiO2 / Si substrate was placed 10 mm downstream of the VCl3 ceramic boat. Before the formal growth, the system was purged with 1200 sccm of high-purity argon for 10 minutes to completely remove H2O and O2 in the reaction chamber. Then, 80 sccm of Ar and 2.5 sccm of H2 were used as carrier gas, and the upstream temperature zone was heated to 370-380 ℃ and the downstream temperature zone was heated to 570-590 ℃ within 25 min, and then kept constant for 10 min to allow the VSe2 nanosheets to grow fully. After the reaction, the sample was obtained after the furnace was naturally cooled to room temperature.

[0070] In an alternative scheme for preparing VO2 from the prepared VSe2 nanosheets, the VSe2 nanosheets are placed in the center region of a tube furnace and sealed, and then subjected to thermal transformation treatment in a mixed gas of a protective gas and oxygen at a volume ratio of 1500-3000. Argon gas at 30 sccm is used as the protective gas, the temperature is raised to 420 DEG C within 20 min and maintained for 20 min. After the furnace body is naturally cooled to room temperature, VO2 nanosheets are obtained. This process does not require pre-washing of the gas, and the conversion of VSe2 to VO2 is achieved by controlling the oxidation environment.

[0071] In an alternative scheme for preparing a planar double-end Au / VO2 / Au memristor, the planar double-end Au / VO2 / Au memristor is prepared using VO2 obtained by thermal transformation of VSe2 nanosheets as a functional layer. First, PMMA is spin-coated on a SiO2 / Si substrate and subjected to two uniform gelation and baking treatments to form a uniform electron beam resist layer. Then, pattern marking is performed by an electron beam exposure system, and after treatment with a specific ratio of isopropyl alcohol / ultra-pure water developer and pure isopropyl alcohol fixer for 30 s each, the marked pattern is dried with nitrogen. Finally, a 60 nm gold thin film is deposited by thermal evaporation, and after soaking in acetone to remove excess metal, a complete planar double-end electrode structure is obtained.

[0072] In an alternative scheme for preparing a planar double-end Au / VO2 / Au memristor, the planar double-end Au / VO2 / Au memristor is prepared using VO2 obtained by thermal transformation of VSe2 nanosheets as a functional layer. First, PMMA is spin-coated on a SiO2 / Si substrate and subjected to two uniform gelation and baking treatments to form a uniform electron beam resist layer. Then, pattern marking is performed by an electron beam exposure system, and after treatment with a specific ratio of isopropyl alcohol / ultra-pure water developer and pure isopropyl alcohol fixer for 30 s each, the marked pattern is dried with nitrogen. Finally, a 60 nm gold thin film is deposited by thermal evaporation, and after soaking in acetone to remove excess metal, a complete planar double-end electrode structure is obtained.

[0073] In the present application, the deposition process can be realized on existing equipment, as long as the temperature control mode is met.

[0074] In the present application, the material described in the present application can be prepared into a device based on known methods.

[0075] In the present application, the ratio of the protective gas-oxygen is allowed to have a reasonable error, for example, the volume ratio of the protective gas-oxygen is X(±20):1, wherein X is 1500-3000.

[0076] 1. A method for preparing pure M1 phase VO2

[0077] Example 1-1

[0078] Step 1: Preparation of VSe2 two-dimensional material

[0079] The experimental device for the VSe2 two-dimensional material is shown in Figure 1 The present study used an atmospheric pressure chemical vapor deposition (APCVD) system to prepare VSe2 nanosheets in a double-temperature zone tube furnace. First, 100 mg of selenium powder and 70 mg of vanadium trichloride were accurately weighed and placed in clean ceramic boats. The selenium powder was placed in the upstream temperature zone of the quartz tube, and the vanadium trichloride was placed at the junction of the two temperature zones, with the polished SiO2 / Si substrate facing downwards and placed 10 mm downstream from the VCl3 ceramic boat. Before the formal growth, the system was purged with 1200 sccm of high-purity argon for 10 minutes to completely remove H2O and O2 in the reaction chamber. Then, using 80 sccm of Ar and 2.5 sccm of H2 as the carrier gas, the upstream temperature zone was heated to 370-380 ℃ and the downstream temperature zone (where VCl3 is volatilized and deposited) was heated to 570-590 ℃ within 25 min, and then kept at constant temperature for 10 min to allow the VSe2 nanosheets to grow fully. After the reaction was completed, the sample was obtained after the furnace was naturally cooled to room temperature.

[0080] Step 2: Preparation of M1 phase-VO2 nanosheets

[0081] Figure 2 The experimental device for the thermal transformation oxidation of VSe2 prepared in Example 1-1 is shown in the figure. The prepared VSe2 nanosheets were placed in the center region of the tube furnace and sealed, and then subjected to thermal transformation treatment under an Ar-oxygen mixture with a volume ratio of 2200:1, wherein the flow rate of the mixture was 30 sccm, and the temperature was increased to 420 ℃ within 20 min and maintained for 20 min. After the furnace was naturally cooled to room temperature, M1-VO2 nanosheets were obtained. Figure 3 The optical images of the samples before and after thermal transformation are shown in the figure. It can be seen that there is a clear color change. Figure 4 The XPS characterization of VSe2 nanosheets is shown in the figure. The fitting analysis shows that Figure 4 The XPS characteristic peaks of V 2p, O 1s, and Se 3d are consistent with the reported results of VSe2. It can be clearly observed that there is only one 1s peak for SiO2 and 53.9 eV (3d 3 / 2two distinct peaks were observed, which were in perfect agreement with the reported Se 2- characteristic binding energy data. In addition, the sub-peaks at 54.5 eV and 55.4 eV corresponded to the adsorbed Se on the SiO2 / Si substrate. The energy spectrum analysis of the V 2p orbitals revealed the mixed valence characteristics of the V element in the sample. The test results showed the presence of two chemical states of vanadium ions: (1) V 3+ The corresponding characteristic peaks were located at 513.4 eV (2p 3 / 2 ) and 521.2 eV (2p 1 / 2 ) (blue markers); (2) V 4+ The characteristic peaks of V 3 / 2 were observed at 516.4 eV (2p 1 / 2 ) and 523.2 eV (2p 3+ ) (yellow markers), which might be due to the residual use of VCl3 as a precursor. The corresponding Si-O bond. The purple spectrum peak, Se 3d energy level was at a binding energy of 53.1 eV (3d 5 / 2 .

[0082] Figure 5 XPS characterization of M1-VO2 nanosheets, the fitting analysis showed that the 2p 4+ and 2p 3 / 2 binding energy peaks of V 1 / 2 in VO2 were located at 515.8 eV and 523.4 eV, respectively. In addition, the peak at a binding energy of 529.5 eV corresponded to the O 1s of the V-O bond in VO2, while the peak at 532.5 eV belonged to the O 1s of the Si-O bond. Notably, the characteristic peak of Se had completely disappeared, indicating that the Se element in the sample had been completely removed. Through XPS characterization, we can confirm that VSe2 has been oxidized to the oxide of V 4+ , i.e., VO2.

[0083] Figure 6 Scanning transmission electron microscopy image of M1-VO2 nanosheets. Figure 6 a presents the high-angle annular dark-field imaging (HAADF) results of VO2 nanosheets, together with Figure 6 b and c show the V, O element energy spectrum (EDS) area distribution analysis. The test data show that the V element and O element present a uniform spatial distribution characteristic in the nanosheet region, which is in perfect agreement with the morphology characteristics observed by low-magnification scanning transmission electron microscopy, fully confirming the highly uniform distribution characteristics of the two elements in the prepared nanosheets.

[0084] Figure 7Raman characterization of VO2 after thermal transformation at 420 ℃ for different time, by systematically studying the influence of different thermal transformation time on the sample at 420 ℃, we observed the following evolution rules: first, the VSe2 characteristic peak at 207 cm -1 gradually weakened until disappeared with the prolongation of thermal transformation time; at the same time, the characteristic Raman peaks (193 cm -1 , 223 cm -1 and 613 cm -1 ) of VO2 began to appear. In the initial stage of oxidation, the signals of other characteristic peaks of VO2 were weak. With the prolongation of thermal transformation time to 10 min, the VSe2 nanosheet basically completed the oxidation transformation. In order to ensure that the oxidation reaction is fully carried out, we further prolong the thermal transformation time to 20 min. After 20 min of thermal transformation treatment, not only all the characteristic peaks of VO2 are clearly visible, but also excellent crystallinity is exhibited.

[0085] Example 1-2

[0086] Compared with Example 1-1, the only difference is that the time and temperature of thermal transformation are changed, and the experimental groups are as follows:

[0087] Group A: the temperature of thermal transformation is 320 ℃, and the holding time at the thermal transformation temperature is 60 min;

[0088] Group B: the temperature of thermal transformation is 380 ℃, and the holding time at the thermal transformation temperature is 40 min;

[0089] Group C: the temperature of thermal transformation is 520 ℃, and the holding time at the thermal transformation temperature is 10 min;

[0090] Group D: the temperature of thermal transformation is 550 ℃, and the holding time at the thermal transformation temperature is 5 min.

[0091] Figure 8 It is shown that the time required for complete oxidation has a significant negative correlation with the temperature of thermal transformation. Specifically, at a lower temperature (320 ℃), a thermal transformation treatment of up to 60 min is required, but the crystallinity of the obtained sample is poor; while increasing the thermal transformation temperature to 550 ℃, only 5 min is required to complete the oxidation process. This temperature-time dependence provides an important basis for accurately controlling the oxidation process of VSe2. It is worth pointing out that when the temperature is lower than 300 ℃, even if the thermal transformation time is continued to be delayed, the crystallinity of the obtained VO2 nanosheet is also poor.

[0092] Example 1-3

[0093] The difference compared with Example 1-1 is only that the atmosphere of thermal transformation is changed, and the experimental groups are respectively:

[0094] Group A: the volume ratio of Ar:O2 in the atmosphere of thermal transformation is 200:1;

[0095] Group B: the volume ratio of Ar:O2 in the atmosphere of thermal transformation is 1000:1;

[0096] Group C: the volume ratio of Ar:O2 in the atmosphere of thermal transformation is 1500:1;

[0097] Group D: the volume ratio of Ar:O2 in the atmosphere of thermal transformation is 2300:1;

[0098] Other operations and parameters are the same as those in Example 1.

[0099] Figure 9 VO obtained by thermal transformation with different oxygen contents x Raman characterization. Through systematic research under different Ar / O2 mixing ratios (400:1, 1000:1, 1500:1 and 2300:1), we found that the oxygen partial pressure has a decisive influence on the oxidation product. During the experiment of each group, we used high-purity argon (1200 sccm, 10 min) to pretreat the reaction system in order to eliminate the interference of residual oxygen as much as possible. Raman spectrum analysis shows that pure VO2 phase is not obtained in groups A and B; pure VO2 phase is obtained in group D.

[0100] Comparative Example 1-1

[0101] The VSe2 nanosheet was oxidized by oxygen Plasma. Before oxidation, we evacuated the cavity to eliminate the interference of residual oxygen as much as possible, Figure 10 a is oxidized by Plasma for 20 min, Figure 10 b is oxidized by Plasma for 50 min, and the characterization fully shows that the substance obtained by oxidation by this method is not M1 phase VO2.

[0102] 2. Preparation of Au / VO2 / Au memory resistor

[0103] Example 2-1

[0104] Figure 11For the preparation process of the planar Au / VO2 / Au memristor, the preparation steps are as follows: the planar Au / VO2 / Au memristor is prepared by using VSe2 nanosheet converted VO2 as a functional layer. First, PMMA is spin-coated on the SiO2 / Si substrate and treated with two uniform glue and baking processes to form a uniform electron beam resist layer. Then, the pattern is marked by an electron beam exposure system, and after being treated with a specific ratio of isopropyl alcohol / ultra-pure water developer and pure isopropyl alcohol fixer for 30 s each, the marked pattern is dried with nitrogen. Finally, a 60 nm gold thin film is deposited by thermal evaporation, and after soaking in acetone to remove excess metal, a complete planar double electrode structure is obtained.

[0105] Figure 12 For the electrical test of the planar double-end memristor. The optical micrograph of the planar Au / VO2 / Au memristor shows that the channel length is accurately controlled at 700 nm (L=700 nm) Figure 12 a). The electrical test is carried out by Keithley 4200 semiconductor parameter analyzer combined with probe station, using step voltage scanning strategy of 0 V→n V→0 V. The initial test shows that the I-V curve is completely coincident in the range of 0-1 V, indicating that the device state is stable. When the voltage increases to 3.68 V, the SET process (HRS→LRS) occurs, and when the voltage decreases to 0.69 V, the RESET process (LRS→HRS) is completed, forming the first complete hysteresis curve (Forming process). Set the upper limit of 1 mA current to protect the device, and the subsequent cycle test uses the scanning sequence of 0 V→3 V→0 V→-3 V→0 V, and the threshold voltage V TH = ±2.28 V (SET process) and the holding voltage V H = ±0.69 V (RESET process), which confirms that the device has a symmetric bipolar switching characteristic and belongs to a typical volatile threshold memristor.

[0106] Figure 13 For the resistance switching performance test of the planar double-end memristor. The planar Au / VO2 / Au memristor exhibits excellent resistance switching stability after 3100 consecutive voltage scanning tests (0 V→3 V→0 V→-3 V→0 V). The test data shows that: the holding voltage V H = ±0.69 V fluctuates within a range of less than ±0.03 V in 2900 cycles; the threshold voltage V TH= ±2.49 ±0.21 V Good symmetry is maintained, but a slight upward trend with the increase of cycle number, which may be related to the accumulation of defect states. At 0.72 V read voltage, the LRS shows extremely high stability, and the HRS has a slight fluctuation but still maintains the order of magnitude of stability. The device maintains a stable switching ratio of about 38 times throughout the test process, which confirms its excellent reliability and practical potential.

[0107] Figure 14 The maximum switching ratio achieved for this structure of the memristor is 320.

[0108] Example 2-2

[0109] Compared with Example 2-1, the only difference is that Example 2-2 is a vertical double-end structure of the memristor.

[0110] Figure 15 The preparation process of the vertical double-end Au / VO2 / Au memristor, for example, uses PDMS as a transfer medium to realize the precise transfer of VO2 nanosheets through its temperature-sensitive adhesion characteristics. First, the PDMS film is pressed onto the surface of the substrate where VO2 is grown, and after peeling off, part of the nanosheets are attached to the PDMS. Then, at 80 ℃, the PDMS is aligned with the pre-prepared 60 nm gold electrode and kept for 2 min, so that the VO2 nanosheets are reliably transferred to the bottom electrode. The top electrode is prepared by evaporating a 60 nm gold film on another substrate and treating it with HMDS vapor for 7 min to improve the surface properties. After spin-coating a PMMA protective layer, the same PDMS transfer technique is used to accurately align and transfer the gold electrode to the top of the VO2 nanosheets to form a vertical structure at 80 ℃. Finally, the sample is immersed in chloroform for 1 min to remove the PMMA residue, and after nitrogen blowing dry, the complete vertical double-end Au / VO2 / Au memristor is obtained.

[0111] Figure 16 The resistive switching performance test of the vertical double-end Au / VO2 / Au memristor. Similar to Example 2-1, the Au / VO2 / Au memristor with a vertical double-end structure exhibits the same resistive switching characteristics. The electrical test is carried out by Keithley 4200 semiconductor parameter analyzer combined with probe station, using a step voltage scanning strategy of 0 V→n V→0 V. The initial test shows that the I-V curves are completely coincident in the range of 0-1 V, indicating that the device state is stable. Figure 16a The schematic diagram of the test method is shown, and the two probes are in contact with the top and bottom gold electrodes during the test. The electrical performance test of the forming, SET and RESET processes is carried out in turn. Fig. 16b shows the I-V characteristic curve of the forming process, and the inset is the optical micrograph of the vertical structure of the memristor prepared by the two-step transfer method, which clearly shows the typical "sandwich" structure formed by the electrode and the VO2 nanosheet. The vertical structure memristor exhibits excellent symmetric resistive switching characteristics and cycle stability in 300 cycle tests Figure 16 c}.

[0112] Comparative Example 2-1

[0113] Compared with Example 2-1, the only difference is that the functional material in Comparative Example 2-1 is V2O5 obtained by thermal transformation under the oxygen condition of Group A in Example 1-3. Figure 17 is the I-V characteristic curve of the planar double-end Au / V2O5 / Au device, which has no resistive switching characteristics, and under the same voltage conditions, the current is one thousandth of that of the device in Example 2-1.

[0114] 3. Application of horizontal double-end Au / VO2 / Au memristor (Example 2-1)

[0115] Example 3-1

[0116] Figure 18 is a schematic diagram of a nociceptor, showing the mechanism of action of a nociceptor.

[0117] Figure 19 is the electrical performance of the planar double-end Au / VO2 / Au memristor. The response threshold characteristics of the device not only depend on the stimulus intensity, but also closely related to the stimulus duration. According to physiological research, human nociceptors need at least 0.015 s of stimulation to produce pain perception. To meet this biological characteristic requirement, we designed and prepared Au / VO2 / Au memristors and systematically characterized their dynamic response characteristics. As shown in Fig. 19a, under the test conditions of 0.3 V working voltage and 50 μs pulse width, the device exhibits excellent switching performance: the on-state time is 30 μs, and the off-state time is 20 μs. This ultrafast switching characteristic enables it to accurately simulate the transient response behavior of biological nociceptors, providing an ideal hardware foundation for building high-performance neuromorphic pain perception systems.

[0118] Figure 20 is the characteristic study of the nociceptor based on the memristor. This study successfully simulates the key characteristics of biological nociceptors through Au / VO2 / Au memristors. Figure 19b is the I-V characteristic curve of the memristor for the nociceptor. The activation threshold is measured to be 0.6 V / 50 μs with the pulse amplitude (0.1-0.8 V, increasing by 0.1 V for each pulse) and width (5, 10, 20, 30, 50, 100, 200 μs) representing the stimulation intensity and duration, respectively. The device exhibits typical nociceptive relaxation characteristics: the response amplitude of a detection pulse (0.3 V) decreases with the increasing interval time (100 μs-100 ms) after a 0.8 V stimulation. More importantly, the nociceptive sensitization is successfully induced by applying suprathreshold stimuli (0.8, 1.2, 1.8 V), which is manifested as the decrease of the threshold voltage (from 0.6 V to 0.4 V) and the enhancement of the response current, precisely mimicking the two major clinical features of allodynia and hyperalgesia. This artificial nociceptive system based on VO2 phase transition provides a new paradigm for the study of pain mechanisms and quantitative diagnosis.

Claims

1. A method for preparing M1 phase VO2 nanosheets, characterized in that, The material was obtained by thermal transformation of VSe2 nanosheets. The atmosphere of the thermal transformation process was a mixture of protective gas and oxygen with a volume ratio of 1500~3000; the thermal transformation temperature was 320~580 ℃; and the thermal transformation time was 5~65 min.

2. The method for preparing M1 phase VO2 nanosheets as described in claim 1, characterized in that, The VSe2 nanosheets were prepared by PVD or CVD methods.

3. The method for preparing M1 phase VO2 nanosheets as described in claim 2, characterized in that, The CVD preparation process of VSe2 nanosheets is as follows: VCl3 and Se powder are volatilized and CVD deposition is carried out in a carrier gas to obtain the VSe2 material.

4. The method for preparing M1 phase VO2 nanosheets as described in claim 3, characterized in that, The weight ratio of VCl3 to Se powder is 5~10:10; Preferably, the volatilization temperature of VCl3 is 550~650℃, and more preferably 570~590℃; Preferably, the volatilization temperature of Se powder is 360~400℃; Preferably, the carrier gas includes a protective gas and hydrogen; Preferably, in the carrier gas, the flow rate of the protective gas is 50~100 sccm, and the flow rate of the hydrogen is 1~5 sccm; In this invention, the CVD deposition temperature is 550~650 ℃, and can be further 590~620 ℃; Preferably, the CVD deposition time is 5 to 15 minutes.

5. The method for preparing M1 phase VO2 nanosheets as described in claim 1, characterized in that, The temperature for thermal transformation is 320~340 ℃, and the time for thermal transformation is 55~65 min; The temperature for thermal transformation is 360~390 ℃, and the time for thermal transformation is 35~45 min; The temperature for thermal transformation is 400~450 ℃, and the time for thermal transformation is 15~25 min; The temperature for thermal transformation is 510~550 ℃, and the time for thermal transformation is 5~15 min.

6. The method for preparing M1 phase VO2 nanosheets as described in claim 1, characterized in that, In the mixed gas, the protective gas is at least one of nitrogen and an inert gas.

7. The method for preparing M1 phase VO2 nanosheets as described in claim 6, characterized in that, In the gas mixture, the volume ratio of protective gas to oxygen is 2000~2500:

1.

8. An M1 phase VO2 nanosheet prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the M1 phase VO2 nanosheets prepared by the method according to any one of claims 1 to 7, characterized in that, It is used to prepare memristors.

10. A memristor, characterized in that, It includes M1 phase VO2 nanosheets prepared by the preparation method according to any one of claims 1 to 7.

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