Method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, ferromagnetic graphene and application thereof

Abstract

The application belongs to the field of advanced material technology, and relates to a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, ferromagnetic graphene and application thereof. The method is as follows: 3 or more layers of copper-based graphene are folded densely by a mechanical method, and then at least 10 cycles of rapid cooling and heating are performed, and the ferromagnetic graphene is obtained; the process of rapid cooling and heating is as follows: the copper-based graphene after being folded densely is placed in a cold trap environment of 70-120K for cooling, and then is rapidly placed in an environment of room temperature and above for heating. Through the pretreatment method of mechanical folding and continuous rapid cooling and heating, strong and tough ferromagnetic property is observed in large-size graphene (centimeter scale), and the Curie temperature is 100K to room temperature and above. The ferromagnetic graphene in the application is applied to the fields of flexible electronic devices and wearable artificial intelligence.

Description

Technical Field

[0001] This invention belongs to the field of advanced materials technology, and relates to a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, ferromagnetic graphene and its applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Graphene possesses exceptional carrier mobility, spin diffusion length, and a nontrivial band structure. Introducing ferromagnetism into graphene would significantly expand its applications in flexible electronics, wearable artificial intelligence, and spintronics. However, the unique π-bond structure in graphene, and the pseudospins of the AB sublattice mutually compensating due to lattice symmetry, lead to intrinsic sp... 2 Structural graphene exhibits diamagnetism due to the lack of local magnetic moments.

[0004] According to the inventors' research, current studies on breaking the aforementioned symmetry and introducing local magnetic moments include: defective graphene treated with electron beam irradiation exhibits paramagnetism at low temperatures (<50K) and diamagnetic behavior at high temperatures; partial functionalization of atoms or chemical groups induces changes in the band structure of graphene, thereby making it ferromagnetic; ferromagnetism can also be observed in graphene with serrated boundaries through scanning tunneling microscopy; furthermore, ferromagnetism can be achieved in intrinsic graphene through doping with magnetic elements and through the magnetic proximity effect of magnetic substrates; room-temperature ferromagnetism can be obtained in highly reduced graphene oxide through non-equilibrium pulsed laser annealing; and ferromagnetism has also been observed in twisted bilayer and trilayer graphene. However, due to the very weak coupling between these introduced local magnetic moments, the observed ferromagnetic order can only be maintained at very low temperatures or in powder form. Therefore, a new method is needed to introduce strong intrinsic ferromagnetic order into large-size sheet graphene. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, ferromagnetic graphene and its applications. The ferromagnetic graphene prepared by the method of the present invention can maintain its strong ferromagnetic order at close to 100K or even above room temperature.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In the first aspect, a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering is provided, which involves mechanically folding three or more layers of copper-based graphene into dense layers and then cycling through rapid cooling and heating at least 10 times to obtain the desired graphene.

[0008] The rapid cooling and heating process is as follows: the densely folded graphene is placed in a cold trap environment of 70-120K for cooling, and then rapidly placed in an environment at or above room temperature for heating.

[0009] The stress engineering is generated by the combined effect of the aforementioned mechanical folding and rapid cooling and heating cycle.

[0010] Secondly, a ferromagnetic graphene is obtained by the aforementioned method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering.

[0011] Thirdly, the above-mentioned ferromagnetic graphene is used in flexible electronic devices or wearable artificial intelligence.

[0012] The beneficial effects of this invention are as follows:

[0013] This invention achieves a paramagnetic to ferromagnetic transition in large-scale (centimeter-scale) graphene with three or more layers through the synergistic effect of mechanical folding and rapid cooling-heating cycles. The Curie temperature of the ferromagnetic graphene can reach nearly 100K, and can even be maintained above room temperature. This has practical value for the development and application of two-dimensional flexible magnetoelectronic materials.

[0014] This invention exhibits high chemical stability compared to other two-dimensional ferromagnetic materials (such as Fe3GeTe2, Fe3GaTe2, CrTe2, etc.), maintaining its structure and electromagnetic properties even at room temperature and high temperatures while resisting oxidation. This contributes to improving the durability of materials in practical applications.

[0015] The stress engineering introduction method of the present invention is simple and helps to reduce the cost of development and application.

[0016] This invention, combining Raman spectroscopy, XPS, STEM, and EELS results, reveals that under the synergistic stress of mechanical folding and rapid cooling / heating, delocalized carbon atoms promote localized sp atoms in graphene. 3 The formation of C-C bonds produces sp 3 Graphene, thus enabling it to maintain long-range ferromagnetic order, while also possessing the advantages of stability and toughness. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The images show the magnetic properties of graphene in Examples 1 and 2 of this invention: (a) Magnetic properties of ~6-layer graphene after mechanical folding and rapid cooling-heating (MF-RCH) cycling; (b) Detailed magnetic properties of ~6-layer graphene in MF-RCH at different temperatures; (c) Detailed magnetic properties of ~6-layer graphene in MF-RCH, with insets showing the coercivity of ~6-layer graphene in MF-RCH; (d) Magnetic properties of ~10-layer graphene in the initial state; (e) Magnetic properties of ~10-layer graphene in MF-RCH; (f) Detailed magnetic properties of ~10-layer graphene in MF-RCH.

[0019] Figure 2 The images show Raman and X-ray photoelectron spectra of graphene in Examples 1 and 2 of this invention; (a) Raman spectra of graphene in the initial state, MF, RCH and MF-RCH processes; (b) X-ray photoelectron spectra of graphene in the initial state and (c) MF-RCH of graphene in the 6-layer graphene; (d) XPS of graphene in the initial state and (e) MF-RCH of graphene in the 10-layer graphene.

[0020] Figure 3 The images show scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) in Example 1 of this invention: (a) STEM image of 6-layer graphene; (b) STEM image of 6-layer graphene after mechanical folding and rapid cooling-heating (MF-RCH); (c) EELS image of the K absorption edge of C in the initial state of 6-layer graphene; and (d) EELS image of MF-RCH 6-layer graphene.

[0021] Figure 4 The following are three-dimensional images of the surface morphology of the copper-based six-layer graphene in Example 1 of the present invention: (a) initial state; (b) after mechanical folding (MF); (c) after continuous rapid cooling and heating (RCH); and (d) after the mechanical folding and rapid cooling and heating (MF-RCH) processes. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] Given that the ferromagnetic order of ferromagnetic graphene provided by existing methods can only be maintained at very low temperatures, in order to solve the above-mentioned technical problems, this invention proposes a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, ferromagnetic graphene and its applications.

[0025] A typical embodiment of the present invention provides a method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering. The method involves mechanically folding three or more layers of copper-based graphene into dense layers, and then cyclically performing at least 10 rapid cooling and heating cycles to obtain the graphene.

[0026] The rapid cooling and heating process is as follows: first, the densely folded copper-based graphene is placed in a cold trap environment of 70-120K for cooling, and then it is rapidly placed in an environment at or above room temperature for heating.

[0027] The room temperature and above mentioned in this invention refer to indoor environments or temperatures higher than indoor environments, generally 285-400K.

[0028] The copper-based graphene described in this invention refers to graphene with copper as its substrate.

[0029] In some embodiments, the number of layers of copper-based graphene is 3 to 20. For example, the number of layers can be any value among 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20.

[0030] In some embodiments, the copper-based graphene has a size of 0.5 × 0.5 cm. 2 Up to 10×10cm 2 .

[0031] In some embodiments, the folding process involves rolling the copper-based graphene into a cylindrical shape and then flattening it.

[0032] In some embodiments, the folding process is performed in a cleanroom environment.

[0033] In some embodiments, the folding tool used during the folding process must not contain transition metals. Folding tools that do not contain transition metals in this invention include, for example, non-magnetic tweezers.

[0034] In some embodiments, the 70-120K cold trap environment is a cold trap at liquid nitrogen temperature.

[0035] In some embodiments, the ambient temperature of the cooling cold trap is 75-100K.

[0036] In some embodiments, the temperature is lowered to match the ambient temperature of the cold trap, and then raised to room temperature or above. The room temperature or above is preferably 285-320K.

[0037] In some embodiments, the rapid cooling and heating cycle is repeated 10-200 times.

[0038] In some embodiments, the cooling time is 1-30 seconds. The heating time is 1-30 seconds.

[0039] A second embodiment of the present invention provides a ferromagnetic graphene obtained by the above-described method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering.

[0040] In some embodiments, in the Raman spectrum, at 1300-1400 cm⁻¹ -1 A D peak exists at 1300-1350 cm⁻¹. Preferably, it is located at 1300-1350 cm⁻¹. -1 A D peak exists at this location.

[0041] In some embodiments, the ferromagnetic graphene contains sp 3 CC bonds. Specifically, sp in X-ray photoelectron spectroscopy. 3 The integrated intensity of the C-C bonds accounts for approximately 10.00-20.00% of the total C-C peak intensity, preferably 15.00-20.00%. During the preparation process, as the number of layers in the raw graphene increases, the sps of the prepared ferromagnetic graphene increases. 3 As the integral strength of the C-C bond gradually increases, the temperature at which its strong ferromagnetic order is maintained also increases.

[0042] In some embodiments, the Curie temperature range of the ferromagnetic graphene is 100-500K.

[0043] A third embodiment of the present invention provides an application of the above-mentioned ferromagnetic graphene in flexible electronic devices or wearable artificial intelligence.

[0044] The flexible electronic devices described in this invention include, but are not limited to, printed electronics, flexible displays, flexible sensors, and flexible logic and storage.

[0045] The wearable artificial intelligence described in this invention includes, but is not limited to, smart bracelets, smartwatches, smart glasses, smart helmets, smart headphones, smart shoes, and therapeutic wearable medical devices.

[0046] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0047] Example 1

[0048] (1) Folding 6 layers of copper-based graphene into a dense roll using mechanical methods:

[0049] In a cleanroom environment, using non-magnetic tweezers, six layers of copper-based graphene (2×4cm) were first placed... 2The graphene is rolled into a cylindrical shape and then flattened to obtain mechanically folded (MF) 6-layer graphene, denoted as MF 6-layer graphene. This MF 6-layer graphene is non-ferromagnetic.

[0050] (2) Rapid cooling and heating cycle:

[0051] The MF 6-layer graphene was first placed in a cold trap at liquid nitrogen temperature (77K) to cool to 77K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 298K at room temperature. This process was repeated 50 times to obtain ferromagnetic graphene, denoted as MF-RCH 6-layer graphene. The Curie temperature of this ferromagnetic graphene is approximately 100K.

[0052] Compare with Example 1-1:

[0053] (1) Folding two layers of copper-based graphene into a dense roll using mechanical methods:

[0054] In a cleanroom environment, using non-magnetic tweezers, two layers of copper-based graphene (4×4cm) were first placed... 2 The graphene was rolled into a cylindrical shape and then flattened. The folded sample was labeled as mechanically folded (MF) graphene.

[0055] (2) Rapid cooling and heating cycle:

[0056] The MF graphene was first placed in a cold trap at liquid nitrogen temperature (77K) to cool to 77K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 298K at room temperature. This process was repeated 50 times. The resulting graphene was designated as MF-RCH 2-layer graphene, which is non-ferromagnetic.

[0057] Compare with Example 1-2:

[0058] 6-layer copper-based graphene cyclic rapid cooling and heating:

[0059] Six layers of copper-based graphene were first placed in a cold trap at liquid nitrogen temperature (78K) to cool to 78K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 298K at room temperature. This process was repeated 100 times. The resulting graphene was denoted as RCH 6-layer graphene, which is non-ferromagnetic.

[0060] Example 2

[0061] (1) Folding 10 layers of copper-based graphene into a dense roll using mechanical methods:

[0062] In a cleanroom environment, using non-magnetic tweezers, 10 layers of copper-based graphene (3×3cm) were first placed... 2 The graphene is rolled into a cylindrical shape and then flattened to obtain mechanically folded (MF) 10-layer graphene, denoted as MF 10-layer graphene. This MF 10-layer graphene is non-ferromagnetic.

[0063] (2) Rapid cooling and heating cycle:

[0064] MF 10-layer graphene was first placed in a cold trap at liquid nitrogen temperature (80K) to cool to 80K (avoiding direct contact between graphene and liquid nitrogen), and then heated to 300K at room temperature (300K). This process was repeated 70 times to obtain ferromagnetic graphene, denoted as MF-RCH 10-layer graphene. The Curie temperature of this ferromagnetic graphene is greater than 300K.

[0065] Compare with Example 2-1:

[0066] (1) Folding single-layer copper-based graphene into dense rolls using mechanical methods:

[0067] In a cleanroom environment, using non-magnetic tweezers, a single layer of copper-based graphene (3×5cm) was first placed... 2 The graphene is rolled into a cylindrical shape and then flattened to obtain mechanically folded (MF) monolayer graphene, denoted as MF 1-layer graphene. This MF 1-layer graphene is non-ferromagnetic.

[0068] (2) Rapid cooling and heating cycle:

[0069] The MF 1-layer graphene was first placed in a cold trap at liquid nitrogen temperature (80K) to cool to 80K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 300K at room temperature (300K). This process was repeated 70 times to obtain ferromagnetic graphene, denoted as MF-RCH10-layer graphene. The Curie temperature of this ferromagnetic graphene is greater than 300K.

[0070] Compare with Example 2-2:

[0071] 10-layer copper-based graphene cyclic rapid cooling and heating:

[0072] Ten layers of copper-based graphene were first placed in a cold trap at liquid nitrogen temperature (79K) to cool to 79K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 295K at room temperature. This process was repeated 120 times. The resulting graphene was designated as RCH10-layer graphene, which is non-ferromagnetic.

[0073] Example 3

[0074] (1) Folding eight layers of copper-based graphene into a dense roll using mechanical methods:

[0075] In a cleanroom environment, using non-magnetic tweezers, first place 8 layers of copper-based graphene (3×3cm) 2 The graphene is rolled into a cylindrical shape and then flattened to obtain mechanically folded (MF) 8-layer graphene, denoted as MF 8-layer graphene. This MF 8-layer graphene is non-ferromagnetic.

[0076] (2) Rapid cooling and heating cycle:

[0077] The MF 8-layer graphene was first placed in a cold trap at liquid nitrogen temperature (81K) to cool to 81K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 296K at room temperature. This process was repeated 90 times to obtain ferromagnetic graphene, denoted as MF-RCH 8-layer graphene. The Curie temperature of this ferromagnetic graphene is approximately 270K.

[0078] Compare with Example 3-1:

[0079] Rapid cooling and heating cycle:

[0080] Eight layers of copper-based graphene were first placed in a cold trap at liquid nitrogen temperature (82K) to cool to 82K ​​(avoiding direct contact between the graphene and liquid nitrogen), and then heated to 298K at room temperature. This process was repeated 80 times. The resulting graphene was denoted as RCH 8-layer graphene, which is non-ferromagnetic.

[0081] Compare with Example 3-2:

[0082] (1) Folding 8 layers of PET-based graphene into a dense roll using mechanical methods:

[0083] In a cleanroom environment, using non-magnetic tweezers, 8 layers of copper-based graphene (4×3cm) were first placed... 2 The graphene is transferred onto a flexible polyester (PET) substrate to form an 8-layer PET-based graphene. Then, the 8-layer PET-based graphene is rolled into a cylindrical shape using non-magnetic tweezers and flattened to obtain mechanically folded (MF) 8-layer graphene, denoted as MF 8-layer graphene.

[0084] (2) Rapid cooling and heating cycle:

[0085] The MF 8-layer graphene prepared in step (1) was first placed in a cold trap at liquid nitrogen temperature (78K) to cool to 78K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 294K at room temperature. This process was repeated 150 times. The resulting graphene was denoted as MF-RCH 8-layer graphene, which is non-ferromagnetic.

[0086] Example 4:

[0087] (1) Folding 15 layers of copper-based graphene into a dense roll using mechanical methods:

[0088] In a cleanroom environment, using non-magnetic tweezers, 15 layers of copper-based graphene (6×6cm) were first placed... 2 The graphene is rolled into a cylindrical shape and then flattened to obtain mechanically folded (MF) 15-layer graphene, denoted as MF 15-layer graphene. This MF 8-layer graphene is non-ferromagnetic.

[0089] (2) Rapid cooling and heating cycle:

[0090] MF 15-layer graphene was first placed in a cold trap at liquid nitrogen temperature (81K) to cool to 81K (avoiding direct contact between the graphene and liquid nitrogen), and then heated to 296K at room temperature. This process was repeated 90 times to obtain ferromagnetic graphene, denoted as MF-RCH 18-layer graphene. The Curie temperature of this ferromagnetic graphene is approximately 296K.

[0091] In this invention, atomic force microscopy (AFM) and Raman spectroscopy were used to estimate the thickness and number of layers of graphene. The AFM measurements were performed by transferring copper-based graphene onto a polished silica substrate. Subsequently, the graphene samples underwent mechanical folding, continuous rapid cooling (liquid nitrogen temperature) followed by heating to room temperature, and a combination of both methods, resulting in graphene samples labeled as MF, RCH, or MF-RCH graphene, respectively. Their magnetism was then investigated using a vibrating sample magnetometer (VSM) in a superconducting quantum interference device (SQUID).

[0092] In Example 1 and its control examples, only diamagnetism was observed in the initial state, MF, and RCH-6-layer graphene, in addition to weak paramagnetism at low temperatures. However, MF-RCH-6-layer graphene exhibited weak ferromagnetism at low temperatures (below 100 K), and hysteresis characteristics appeared in the MH curves of the samples at 2 K, 50 K, and 75 K, indicating the presence of ferromagnetism, while exhibiting diamagnetism at 300 K. At 2 K, the coercivity of MF-RCH-6-layer graphene reached ~74 Oe, and the remanence was ~0.002 μemu·cm. -2 ,like Figure 1 As shown in a-1c. Figure 1 The inset of c shows the coercivity as a function of temperature, indicating that the Curie temperature of MF-RCH ~6-layer graphene is close to 100K.

[0093] In Example 2 and its comparative example, the magnetic properties of ~10 layers of graphene are as follows: Figure 1 As shown in d-1f. The initial sample exhibits diamagnetism at room temperature. Figure 1 d), while the magnetic susceptibility of the sample becomes positive at low temperatures, and the magnetization reaches saturation after 8 kOe. However, after the MF-RCH process, the MH curve of ~10 layers of graphene shows obvious hysteresis behavior between 2 K and 300 K. Figure 1 e). Compared to the initial sample, the saturation magnetization increases significantly. This is illustrated by the magnified MH curve in the low magnetic field region ( Figure 1 As shown in f), coercivity and remanence decrease with increasing temperature. Even so, when the temperature rises to 300 K, there is still a coercivity of about 45 Oe and a remanence of about 0.004 μe·cm. -2 Residual magnetism.

[0094] In Examples 1 to 3 of this invention, the MF-RCH method demonstrates a certain degree of reliability and probability in generating ferromagnetism in graphene. Examples 1 to 3 each investigated 50 independent experiments. Among these, 12 groups of MF-RCH graphene with up to 6 layers exhibited significant ferromagnetism, with Curie temperatures ranging from 50K to 100K; while 17 groups of MF-RCH graphene with up to 10 layers exhibited strong and robust ferromagnetism, with more than half of these exhibiting Curie temperatures above 300K.

[0095] In both Examples 1 and 2, Raman excitation was performed using 633 nm light. The signal results for MF and RCH-6-layer graphene were the same as those for the pristine sample, at 1583 cm⁻¹. -1 There is a G peak at 2720cm. -1 There is a 2D peak at that location. In ferromagnetic MF-RCH samples, besides sp... 2 In addition to the main phonon mode of graphene—the G peak—there is a peak at approximately 1330 cm⁻¹. -1 A non-negligible D peak appeared. Similarly, a significant D peak was observed in the MF-RCH ~10-layer graphene sample that underwent the paramagnetic-ferromagnetic transition, while no D peak characteristic was observed in the MF-RCH ~2-layer graphene sample that did not undergo the ferromagnetic transition.

[0096] The X-ray photoelectron spectroscopy (XPS) results for Examples 1 and 2 are as follows: Figure 2 Only sp2 at 284.5 eV was observed in the initial state sample. 2 CC bonds are present, but for MF-RCH graphene, significant sp bonds at 285.6 eV are observed in both ~6-layer and ~10-layer graphene. 3 The CC key explains ~1330cm -1 Raman Peak, because of SP 3 The vibration frequency of CC is exactly 1330 cm⁻¹. -1 sp 3 The integrated intensities of the CC fitting peaks were 10.71% and 15.97%, respectively, indicating that the sp content in MF-RCH graphene increases with the increase of graphene layer thickness. 3 The proportion of C-C bonds increased. For ~2-layer graphene, no sp bonds were observed in either the initial state sample or the MF-RCH sample. 3 CC peak.

[0097] The STEM and corresponding EELS (electron energy loss spectroscopy) results in Example 1 show that the initial state of the ~6-layer graphene consists of a low-energy AB-type stacked structure and some locally metastable AA-type stacked structures. Figure 3 a) Composition. In AB-stacked graphene, the interatomic spacing between C atoms was measured to be... This is different from typical sp 2 The CC key length matches perfectly. And for... Figure 3 In graphene a, the AA-type stacked graphene forms a triangular lattice with a nearest neighbor spacing of [missing information]. Therefore, the calculated lattice constant (CC bond length) is also... The ~6-layer graphene treated with MF-RCH also exhibited triangular lattice characteristics. Figure 3 b). Within the area circled by the dashed line, the distance between the light spots is approximately... Approaching AB stack sp 3 The spacing of the CC structure, while the distance outside the region is close to With AB stacking sp 2 The typical spacing values ​​of the CC structure are consistent, indicating that the MF-RCH process leads to the critical phase transition of graphene.

[0098] sp in graphene in Example 1 3 The phase transition can also be verified using high-resolution electron energy loss spectroscopy (HR-EELS) of the K absorption edge of C. For example... Figure 3 As shown in Figure c, in the initial state of ~6 layers of graphene, the HR-EELS of the K absorption edge of C shows a weak π* absorption peak at 284.6 eV and a broad σ* absorption band starting at 292.4 eV, which is consistent with sp 2 Characteristics of graphene / graphite. However, in HR-EELS of MF-RCH ~ 6-layer graphene, the π* peak at 284.6 eV was observed to be weakened to some extent, while the σ* absorption band became stronger, and a significant blue shift was observed from 292.4 eV to 292.7 eV. Analysis of the fitted curves of the π* and σ* absorption edges suggests that within a locally selected range near the fold, sp... 3 The proportion of CC structures is as high as 18.5%, such as Figure 3 As shown in d.

[0099] In Examples 1 and 2, the surface structure of the copper-based MF-RCH graphene exhibits sharp protrusions, within a 2×2 μm area. 2 Within this range, the maximum protrusion is less than 10 nm, revealing the smoothness of the original graphene surface. Figure 4 a). Figure 4 b shows the surface of MF-6 layer graphene, which also exhibits a near-initial ultraflat surface. In contrast, due to the mismatch in thermal expansion coefficients between graphene and the copper substrate, the RCH process generates significant strain and produces a certain degree of wrinkling. Figure 4 c). Previous studies have also reported this type of thermally induced wrinkled structure. Since no ferromagnetism was observed after the RCH process, it can be inferred that this strain is insufficient to support a sufficient ferromagnetic structure within the scope of this embodiment. Figure 4 Figure d shows the surface of a MF-RCH ~6-layer graphene. Numerous wrinkles and raised peaks can be observed after the MF-RCH process, caused by the different coefficients of thermal expansion of the graphene and the copper substrate; the peak sizes (height and diameter) differ by tens of nanometers. MF can locally pin the wrinkled graphene, while the RCH process generates enormous stress, resulting in strain and peaks on the graphene.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering, characterized in that, The copper-based graphene with three or more layers is densely folded using mechanical methods, and then subjected to at least 10 cycles of rapid cooling and heating to obtain the desired product. The rapid cooling and heating process is as follows: First, the densely folded copper-based graphene is placed in a cold trap environment of 70-120 K for cooling, and then it is rapidly placed in a room temperature environment for heating. The copper-based graphene refers to graphene with copper as its substrate; The copper-based graphene has a size of 0.5 × 0.5 cm. 2 Up to 10 × 10 cm 2 .

2. The method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering as described in claim 1, characterized in that, Copper-based graphene has 3 to 20 layers.

3. The method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering as described in claim 1, characterized in that, The folding process involves rolling the copper-based graphene into a cylindrical shape and then flattening it.

4. The method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering as described in claim 1, characterized in that, The folding process is carried out in a cleanroom environment; Alternatively, the folding tools used during the folding process must not contain transition metals.

5. The method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering as described in claim 1, characterized in that, Cool down to the same temperature as the cold trap environment, then heat up to the same temperature as room temperature; Alternatively, the rapid cooling and heating cycle may be 10-200 times.

6. A ferromagnetic graphene, characterized in that, It is obtained by the method for preparing large-size room-temperature ferromagnetic graphene based on stress engineering as described in any one of claims 1-5.

7. The ferromagnetic graphene as described in claim 6, wherein the Curie temperature is 100-500 K.

8. The application of the ferromagnetic graphene as described in claim 6 or 7 in flexible electronic devices or wearable artificial intelligence devices.

9. The application of the ferromagnetic graphene as described in claim 8 in flexible electronic devices or wearable artificial intelligence devices, characterized in that, The flexible electronic device is a printed electronics, flexible display, flexible sensor, or flexible logic and storage; Alternatively, the wearable AI device may be a smart bracelet, smartwatch, smart glasses, smart helmet, smart headphones, or therapeutic wearable medical device.

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