Preparation method of low-dimensional insulating ferromagnetic LaCoO3 self-supporting film

Abstract

The invention provides a preparation method of a low-dimensional insulating ferromagnetic LaCoO3 self-supporting thin film. According to the preparation method, the Ru-based perovskite oxide thin film SrRuO3 (SRO) is inserted to serve as the buffer layer, the problem that the LaCoO3 thin film cannot be stripped from any substrate can be solved, further, the Ru-based perovskite oxide thin film SRO on the surface can be rapidly dissolved within 10 seconds through an electrochemical voltage applying method, and the performance of the LaCoO3 thin film is improved. Therefore, the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film with a clean surface can be efficiently obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating ferromagnetic material preparation, and in particular relates to a method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film. Background Art

[0002] Transition metal oxides, especially those with perovskite structure (ABO3), play an important role in many research fields due to their strong correlation and flexible adjustability. LaCoO3 is a typical perovskite oxide with strong electron correlation. The correlation effect makes its thin film form have insulating ferromagnetism when subjected to tensile strain.

[0003] Insulating ferromagnetic materials have potential applications in many new magnetic devices, such as dissipative quantum spintronic devices and magnetic tunnel junctions. With the increasing maturity of complex oxide epitaxy technology, the preparation of high-quality LaCoO3 films has been achieved. However, in the field of semiconductors or quantum information devices, the demand for the integration of functional oxides with other materials is growing. LaCoO3 films epitaxially grown on single-crystalline oxide substrates are restricted by the strong ionic or covalent bonds between the film and the substrate interface, which limits their integration with other low-dimensional materials. If it is combined with existing silicon-based semiconductor technology, it is expected to further promote the application of LaCoO3 films in devices. However, it is impossible to obtain high-quality single-crystalline LaCoO3 films directly on silicon substrates, which will cause the insulating ferromagnetism to deteriorate or even disappear. Therefore, the premise for preparing devices is to obtain high-quality LaCoO3 self-supporting films.

[0004] At present, selectively dissolving the sacrificial layer between the film and the substrate to peel off the film is one of the methods to obtain high-quality self-supporting oxide films. In recent years, researchers have reported a variety of sacrificial layer materials, such as Sr3Al2O6, Sr4Al2O7, SrCoO 2.5 ,La 0.7 Sr 0.3 MnO3, etc. Among them, the use of water-soluble sacrificial layer materials Sr3Al2O6 and Sr4Al2O7 to obtain self-supporting oxide films is relatively common. The characteristics of these water-soluble sacrificial layers are wide application range, easy dissolution and high efficiency. Since scholars first used Sr3Al2O6 as a sacrificial layer to prepare self-supporting perovskite oxide films in 2016, the Sr3Al2O6 sacrificial layer has received widespread attention in the field of oxide films and heterojunctions, and there has been an increasing number of high-quality research works based on self-supporting films. Later, some scholars reported a new Sr4Al2O7 sacrificial layer with a supertetragonal structure that is more water-soluble. The Sr4Al2O7 sacrificial layer is also suitable for the preparation of a variety of self-supporting oxide thin film materials, such as LaNiO3, La 0.7 Ca 0.3Materials such as MnO3, SrTiO3, SrRuO3 and SrSnO3. The discovery of the Sr4Al2O7 water-soluble sacrificial layer has further promoted the development of the field of self-supporting oxide films. Although the water-soluble sacrificial layer materials Sr3Al2O6 and Sr4Al2O7 are suitable for the preparation of a variety of self-supporting oxide films, researchers have achieved a series of innovative results based on these two typical water-soluble sacrificial layers. However, the research on self-supporting films still faces many problems. First, the structural mismatch between Sr3Al2O6 and Sr4Al2O7 and the target oxide material often affects the dissolution rate of the sacrificial layer, such as the difference in lattice parameters and symmetry. In addition, for different materials, the difference in film growth conditions and sacrificial layers will also affect the stripping efficiency of the film. The above factors may be the main reason why the insulating ferromagnetic LaCoO3 self-supporting film has not been successfully prepared so far. Therefore, it is still necessary to develop a new method for preparing low-dimensional insulating ferromagnetic LaCoO3 self-supporting films. Summary of the invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film. The preparation method of the present invention can solve the problem that the LaCoO3 film cannot be peeled off from any substrate by inserting a Ru-based perovskite oxide film SRO as a buffer layer. Furthermore, the present invention can quickly dissolve the Ru-based perovskite oxide film SRO on the surface (within 10 seconds) through an electrochemical voltage application method, thereby efficiently obtaining a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film with a clean surface.

[0006] The invention also provides a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film.

[0007] The first aspect of the present invention provides a method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, the preparation method comprising the following steps:

[0008] S1: A water-soluble sacrificial layer film SAO, a Ru-based perovskite oxide film SRO and a LaCoO3 film LCO are sequentially grown on the substrate surface to form a rigid film with a structure of substrate / SAO / SRO / LCO;

[0009] S2: After a protective film layer is attached to the surface of the LaCoO3 film, a rigid film having a structure of substrate / SAO / SRO / LCO / protective film layer is formed, and the water-soluble sacrificial layer film SAO is dissolved to achieve the shedding of the substrate, thereby obtaining a rigid film having a structure of SRO / LCO / protective film layer;

[0010] S3: applying voltage to the Ru-based perovskite oxide film SRO to electrochemically peel off the Ru-based perovskite oxide film SRO to obtain a film with a structure of LCO / protective film layer, and removing the protective film layer to obtain a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film.

[0011] A technical solution in the method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film of the present invention has at least the following beneficial effects:

[0012] The preparation method of the present invention can solve the problem that the LaCoO3 film cannot be peeled off from any substrate by inserting a Ru-based perovskite oxide film SRO as a buffer layer. Furthermore, the present invention can quickly dissolve the Ru-based perovskite oxide film SRO on the surface (within 10 seconds) through an electrochemical voltage application method, thereby efficiently obtaining a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film with a clean surface.

[0013] The present invention proposes a method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, by growing a water-soluble sacrificial layer and a Ru-based perovskite oxide film as a buffer layer on a substrate, and using an electrochemical stripping technique to efficiently dissolve the buffer layer, thereby successfully achieving the stripping of the LaCoO3 film. This method can effectively solve the problem that the LaCoO3 film cannot be stripped from the substrate, maintain the high quality and functionality of the film, has the advantages of high efficiency, low cost and easy industrialization, and can be extended to the preparation of other oxide films, promoting its application in the fields of quantum spin electronics, magnetic storage devices, etc.

[0014] According to some embodiments of the present invention, in step S1, the substrate used for thin film growth includes a perovskite single crystal substrate.

[0015] According to some embodiments of the present invention, the perovskite single crystal substrate includes LaAlO3, (La, Sr)(Al, Ta)O3 substrate.

[0016] According to some embodiments of the present invention, in step S1, the water-soluble sacrificial layer film SAO includes a Sr3Al2O6 film or a Sr4Al2O7 film.

[0017] According to some embodiments of the present invention, in step S1, the process parameters for growing the water-soluble sacrificial layer SAO film include: film growth temperature of 700-800°C, oxygen partial pressure of 0.05-0.15 Pa, laser energy density of 1-2 J / cm 2 .

[0018] According to some embodiments of the present invention, in step S1, the Ru-based perovskite oxide film includes a SrRuO3 film or a CaRuO3 film.

[0019] According to some embodiments of the present invention, the process parameters for growing Ru-based perovskite oxide thin films SRO include: film growth temperature 650-750°C, oxygen partial pressure 10-15 Pa, laser energy density 1-2 J / cm 2 .

[0020] According to some embodiments of the present invention, the process parameters for growing LaCoO3 thin film-LCO include: film growth temperature of 650-750°C, oxygen partial pressure of 10-15 Pa, laser energy density of 1-2 J / cm 2 .

[0021] According to some embodiments of the present invention, step S1 further includes cooling the temperature to room temperature at a rate of 10° C. / min after the growth of the LaCoO 3 thin film LCO is completed.

[0022] According to some embodiments of the present invention, the thickness of the water-soluble sacrificial layer thin film SAO is 20-40 nm.

[0023] According to some embodiments of the present invention, the Ru-based perovskite oxide thin film SRO has a thickness of 10 to 30 nm.

[0024] According to some embodiments of the present invention, in step S2, the protective film layer includes a polydimethylsiloxane (PDMS) film.

[0025] According to some embodiments of the present invention, in step S2, the method for dissolving the water-soluble sacrificial layer film SAO includes: soaking a rigid film having a structure of substrate / SAO / SRO / LCO / protective film layer in deionized water, and the water-soluble sacrificial layer film SAO is dissolved during the soaking process.

[0026] According to some embodiments of the present invention, the soaking time is 4 to 8 hours.

[0027] According to some embodiments of the present invention, in step S3, the electrochemical stripping method includes: connecting a working electrode to the Ru-based perovskite oxide thin film SRO, forming a three-electrode system with a counter electrode and a reference electrode, inserting the three-electrode system into an alkaline solution, applying a positive voltage to the working electrode, and the Ru-based perovskite oxide thin film SRO is dissolved.

[0028] According to some embodiments of the present invention, the target voltage value of the applied positive voltage is 1.55 V (vs RHE).

[0029] According to some embodiments of the present invention, the time for applying the positive voltage is 5 to 10 seconds.

[0030] According to some embodiments of the present invention, in step S3, the electrochemical stripping method further comprises: after the Ru-based perovskite oxide film SRO is dissolved, taking out the sample from the alkaline solution and washing and drying it.

[0031] The second aspect of the present invention provides a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, which is prepared by the preparation method of the first aspect of the present invention.

[0032] One of the technical solutions of the present invention regarding the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film has at least the following beneficial effects:

[0033] First, the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film of the present invention has a good crystal structure, can retain the unique electronic and magnetic characteristics of the LaCoO3 film, and has excellent insulating ferromagnetism, which makes it potentially applicable in quantum spin electronics, magnetic tunnel junctions and other new magnetic devices. Secondly, due to its self-supporting characteristics, the film does not need to rely on the substrate, which enhances the flexibility in device integration. The structure of the self-supporting film can also reduce the performance degradation caused by the stress and mismatch generated at the interface with the substrate, thereby ensuring its stability and reliability in long-term use. In addition, since the film has good surface quality and high electron mobility, it can also effectively improve device performance and meet the needs of high-quality heterogeneous integration.

[0034] According to some embodiments of the present invention, the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film grows along the

[001] crystal orientation.

[0035] According to some embodiments of the present invention, the thickness of the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film is 10 to 30 nm.

[0036] According to some embodiments of the present invention, the out-of-plane lattice parameter c of the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film is BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the preparation strategy of LaCoO3 self-supporting films.

[0038] Figure 2 It is a physical picture of LaCoO3 self-supporting film, an image under an optical microscope, and an X-ray diffraction θ-2θ linear scanning curve.

[0039] Figure 3 These are the XRD test results of the sample in Example 2 before and after soaking in water and after electrochemical treatment (1.20 V).

[0040] Figure 4These are the XRD test results of the sample in Example 3 before and after soaking in water and after electrochemical treatment (2.10 V), and the optical microscopic image of the LaCoO3 self-supporting film obtained at a voltage of 2.10 V.

[0041] Figure 5 These are the XRD test results of the sample of Comparative Example 1 before and after soaking in water.

[0042] Figure 6 These are the XRD test results of the sample of Example 2 before and after soaking in water and after electrochemical treatment (1.60 V). DETAILED DESCRIPTION

[0043] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0044] In a first aspect, some embodiments of the present invention provide a method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, the preparation method comprising the following steps:

[0045] S1: A water-soluble sacrificial layer film SAO, a Ru-based perovskite oxide film SRO and a LaCoO3 film LCO are sequentially grown on the substrate surface to form a rigid film with a structure of substrate / SAO / SRO / LCO;

[0046] S2: After the protective film layer is attached to the surface of the LaCoO3 film, a rigid film with a structure of substrate / SAO / SRO / LCO / protective film layer is formed, and the water-soluble sacrificial layer film SAO is dissolved to realize the shedding of the substrate, thereby obtaining a rigid film with a structure of SRO / LCO / protective film layer;

[0047] S3: By applying voltage to the Ru-based perovskite oxide film SRO, the Ru-based perovskite oxide film SRO is electrochemically stripped to obtain a film with a structure of LCO / protective film layer. By removing the protective film layer, a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film can be obtained.

[0048] It can be understood that the preparation method of the present invention can solve the problem that the LaCoO3 film cannot be peeled off from any substrate by inserting the Ru-based perovskite oxide film SRO as a buffer layer. Furthermore, the present invention can quickly dissolve the Ru-based perovskite oxide film SRO on the surface (within 10 seconds) by an electrochemical voltage addition method, thereby efficiently obtaining a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film with a clean surface. The preparation method of the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film proposed by the present invention has multiple beneficial effects. In addition to inserting the Ru-based perovskite oxide film SRO as a buffer layer and accelerating the peeling by electrochemical methods, specifically, it also includes the following advantages:

[0049] 1. Efficient stripping and structural integrity are guaranteed. It can be understood that the method of the present invention adopts electrochemical stripping technology (rapidly dissolving the SRO film by applying voltage), which can efficiently dissolve the Ru-based perovskite oxide film (SRO) on the surface in a short time (within 10 seconds), so that the LaCoO3 film can be quickly stripped from the bottom layer and maintain the integrity of the LaCoO3 film. Traditional physical stripping methods are often time-consuming and easy to damage the film, while electrochemical stripping can accurately control the dissolution process under mild conditions, avoiding the loss of film quality caused by physical stress and thermal stress in traditional methods.

[0050] 2. In terms of the optimization of the buffer layer, the Ru-based perovskite oxide film SRO is introduced as a buffer layer to effectively solve the problem that the LaCoO3 film cannot be directly peeled off from the substrate. The SRO film not only provides a better lattice match for LaCoO3 and reduces the structural mismatch between the substrate and LaCoO3, but also plays a protective role in the peeling process through its low electrical conductivity and chemical stability, avoiding damage to the LaCoO3 film during the peeling process. In addition, the SRO buffer layer helps to optimize the growth conditions of the LaCoO3 film, improve the surface quality and crystal structure of the film, and further improve the functional properties of the LaCoO3 film, especially its insulating ferromagnetism.

[0051] 3. In terms of efficient utilization of the water-soluble sacrificial layer, this method uses a water-soluble sacrificial layer (such as SAO) as a separation layer between the film and the substrate, which has the advantages of fast dissolution and simple processing. The water-soluble sacrificial layer does not require complex chemical treatment or high-temperature treatment and can be removed by water dissolution in a short time, reducing complex operations and potential damage to the film. This method is particularly suitable for the preparation of oxide films because the water-soluble sacrificial layer can effectively prevent damage to the film by other solvents or chemicals. In addition, the water-soluble sacrificial layer can effectively control the accuracy of the stripping process during the stripping process, so that the structure of the LaCoO3 film will not be damaged by external forces and its functional characteristics can be retained to the greatest extent.

[0052] 4. In terms of improving film quality and stability, this preparation method can not only efficiently strip the film but also ensure the high quality of the LaCoO3 film after stripping through the optimization of multiple steps (such as the introduction of the buffer layer and electrochemical stripping). The surface of the LaCoO3 film can remain relatively intact and does not require further treatment or repair, further improving the stability of the film and its reliability for long-term use.

[0053] 5. Promoted the combination of LaCoO3 film and silicon-based technology. Traditionally, due to the lattice mismatch between LaCoO3 film and silicon-based materials, it is impossible to grow high-quality LaCoO3 film directly on a silicon substrate. The present invention effectively overcomes this problem by providing a low-dimensional self-supporting LaCoO3 film. In this way, LaCoO3 film can achieve better performance in devices integrated with silicon-based materials, providing a new technical path for the application of LaCoO3 film in the fields of quantum information, magnetic storage devices, etc.

[0054] 6. Lower cost and industrial potential. The material selection (such as water-soluble sacrificial layer) and steps (such as electrochemical stripping) in this method are relatively mature technologies. Compared with traditional methods, it has lower cost and higher industrial production potential. The combination of water-soluble sacrificial layer and electrochemical stripping makes this method efficient and operable, reducing the dependence on expensive equipment and complex processes, and is particularly suitable for application in industrial production.

[0055] 7. Potential versatility and wide application. The LaCoO3 self-supporting film provided by the present invention has high-quality insulating ferromagnetic properties and can be applied to various magnetic devices, such as magnetic tunnel junctions, quantum spin electronic devices, etc. In addition, the preparation method is not only applicable to LaCoO3, but can also be extended to the preparation of other types of perovskite oxide films, with wide applicability and versatility.

[0056] Therefore, the preparation method of the present invention successfully solves multiple technical problems in the preparation of low-dimensional insulating ferromagnetic LaCoO3 self-supporting films through innovative electrochemical stripping technology, optimized buffer layer design and efficient water-soluble sacrificial layer utilization. This method not only improves the quality and stability of LaCoO3 films, but also promotes their application in silicon-based semiconductors and other new device fields.

[0057] It should be noted that, in the present invention, "self-supporting" refers to the existence of the film independently of the substrate, capable of self-support and maintaining its performance, and suitable for further application or integration.

[0058] In combination with the first aspect, in some embodiments of the present invention, in step S1, the substrate used for thin film growth includes a perovskite single crystal substrate.

[0059] In combination with the first aspect, in some embodiments of the present invention, the perovskite single crystal substrate includes a LaAlO3 or (La, Sr)(Al, Ta)O3 substrate.

[0060] In combination with the first aspect, in some embodiments of the present invention, in step S1, the water-soluble sacrificial layer film SAO includes a Sr3Al2O6 film or a Sr4Al2O7 film.

[0061] Sr3Al2O6 film or Sr4Al2O7 film is used as a water-soluble sacrificial layer material. The "mismatch" between their crystal structure, lattice constant and symmetry and the structure of the target oxide film material refers to the inconsistency between the crystal structure of these two materials and the target oxide (such as LaCoO3), which may have an adverse effect on the film stripping and growth process. Sr3Al2O6 has a cubic structure and a lattice parameter of The pseudocubic lattice parameters are Sr4Al2O7 has a supertetragonal structure and the lattice parameters are The pseudocubic lattice parameters are LaCoO3 is a rhombohedral perovskite oxide with a lattice parameter of Therefore, the differences in structure and lattice parameters may affect the dissolution degree of the sacrificial layer, resulting in the inability to obtain LaCoO3 free-standing films using Sr3Al2O6 and Sr4Al2O7 sacrificial layers.

[0062] In combination with the first aspect, in some embodiments of the present invention, in step S1, a water-soluble sacrificial layer thin film SAO is grown on a commercial

[001] oriented SrTiO3 (STO) substrate using pulsed laser deposition (PLD) technology.

[0063] In combination with the first aspect, in some embodiments of the present invention, in step S1, the process parameters for growing the water-soluble sacrificial layer SAO film include: film growth temperature of 700-800°C, oxygen partial pressure of 0.05-0.15 Pa, laser energy density of 1-2 J / cm 2 .

[0064] In combination with the first aspect, in some embodiments of the present invention, in step S1, the process parameters for growing the water-soluble sacrificial layer SAO film include: film growth temperature of 750°C, oxygen partial pressure of 0.1 Pa, laser energy density of 1.5 J / cm 2 .

[0065] In combination with the first aspect, in some embodiments of the present invention, in step S1, the Ru-based perovskite oxide film SRO includes a SrRuO3 film or a CaRuO3 film.

[0066] In combination with the first aspect, in some embodiments of the present invention, the process parameters for growing Ru-based perovskite oxide thin film SRO include: film growth temperature 650-750°C, oxygen partial pressure 10-15 Pa, laser energy density 1-2 J / cm 2 .

[0067] In combination with the first aspect, in some embodiments of the present invention, the process parameters for growing Ru-based perovskite oxide thin film SRO include: film growth temperature of 700°C, oxygen partial pressure of 13Pa, laser energy density of 1J / cm 2 .

[0068] In combination with the first aspect, in some embodiments of the present invention, the process parameters for growing LaCoO3 thin film-LCO include: film growth temperature of 650-750°C, oxygen partial pressure of 10-15 Pa, laser energy density of 1-2 J / cm 2 .

[0069] In combination with the first aspect, in some embodiments of the present invention, the process parameters for growing LaCoO3 thin film-LCO include: film growth temperature of 700°C, oxygen partial pressure of 13Pa, laser energy density of 1.6J / cm 2 .

[0070] In combination with the first aspect, in some embodiments of the present invention, step S1 further includes cooling the temperature to room temperature at a rate of 10° C. / min after the growth of the LaCoO 3 thin film LCO is completed.

[0071] In combination with the first aspect, in some embodiments of the present invention, the thickness of the water-soluble sacrificial layer film SAO is 20-40 nm.

[0072] In combination with the first aspect, in some embodiments of the present invention, the thickness of the water-soluble sacrificial layer film SAO is any value of 20 nm, 30 nm, 40 nm, or a range formed by any two of them, such as 30 to 40 nm.

[0073] In combination with the first aspect, in some embodiments of the present invention, the thickness of the Ru-based perovskite oxide film SRO is 10 to 30 nm.

[0074] In combination with the first aspect, in some embodiments of the present invention, the thickness of the Ru-based perovskite oxide film SRO is any value of 10 nm, 20 nm, 30 nm, or a range formed by any two of them, such as 20 to 30 nm.

[0075] In combination with the first aspect, in some embodiments of the present invention, in step S2, the protective film layer includes a polydimethylsiloxane (PDMS) film.

[0076] In combination with the first aspect, in some embodiments of the present invention, in step S2, the method for dissolving the water-soluble sacrificial layer film SAO includes: soaking a rigid film having a structure of substrate / SAO / SRO / LCO / protective film layer in deionized water, and the water-soluble sacrificial layer film SAO is dissolved during the soaking process.

[0077] In combination with the first aspect, in some embodiments of the present invention, the soaking time is 4 to 8 hours.

[0078] In combination with the first aspect, in some embodiments of the present invention, the soaking time is any one of 4h, 5h, 6h, 7h and 8h, or a range formed by any two of them, such as 6h to 8h.

[0079] It can be understood that when the water-soluble sacrificial layer SAO film is dissolved, the substrate is also peeled off. After the substrate is peeled off, the sample can be picked up with tweezers and blown dry with dry nitrogen.

[0080] In combination with the first aspect, in some embodiments of the present invention, in step S3, the method of electrochemical stripping includes: connecting the working electrode to the Ru-based perovskite oxide film SRO, forming a three-electrode system with the counter electrode and the reference electrode, inserting the three-electrode system into an alkaline solution, applying a positive voltage to the working electrode, and the Ru-based perovskite oxide film SRO is dissolved.

[0081] In combination with the first aspect, in some embodiments of the present invention, the three-electrode system refers to a working electrode, a counter electrode Pt, and a reference electrode Ag / AgCl.

[0082] In combination with the first aspect, in some embodiments of the present invention, the alkaline solution may be a 0.1 mol / L KOH solution.

[0083] In combination with the first aspect, in some embodiments of the present invention, the target voltage value of the applied positive voltage is 1.55V (vsRHE).

[0084] In combination with the first aspect, in some embodiments of the present invention, the positive voltage is applied for a time of 5 to 10 seconds.

[0085] The time for applying the positive voltage is 5 to 10 seconds because the Ru-based perovskite oxide film SRO can be completely dissolved within 5 to 10 seconds.

[0086] It should be noted that since the LCO film is underneath the Ru-based perovskite oxide film SRO and is relatively insulating, applying a voltage of 1.55V is not enough to affect the LCO film. Therefore, after the Ru-based perovskite oxide film SRO is completely dissolved, the sample is taken out of the alkaline solution, the surface is cleaned with deionized water, and then blown dry with dry nitrogen to obtain the LCO self-supporting film.

[0087] It should also be noted that SRO is an orthorhombic perovskite oxide with a pseudocubic lattice parameter of The lattice constant size is located in LCO and SAO Therefore, the SRO film can provide a relatively stable interface between LCO and the sacrificial layer (SAO), reducing the stress caused by structural mismatch. This matching can promote the growth of LCO film and also provide support for the subsequent stripping process.

[0088] It should also be noted that by introducing the SRO buffer layer, the sacrificial layer (such as SAO) can be made more orderly during the dissolution process without causing damage to the LCO film. In addition, SRO has good conductivity, which is beneficial to the current distribution in the subsequent electrochemical stripping process.

[0089] In combination with the first aspect, in some embodiments of the present invention, in step S3, the electrochemical stripping method further includes: after the Ru-based perovskite oxide film SRO is dissolved, taking out the sample from the alkaline solution and washing and drying it.

[0090] It should be noted that, as required, the LaCoO3 film LCO can be transferred to the target substrate, and the protective film layer can be removed to obtain a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film. For example, when transferring to a Si substrate, the LaCoO3 film surface in LaCoO3 / PDMS can be inverted on the Si substrate, and then they are placed on a heating table and heated to 80°C. The heating time is about 10 minutes to transfer the LaCoO3 film to the Si substrate.

[0091] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0092] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0093] Unless otherwise specified, "room temperature" in the present invention means 25°C±5°C.

[0094] Unless otherwise specified, "about" in the present invention means that the allowable error is within ±2%.

[0095] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0096] Example 1

[0097] A method for preparing low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, the process is referenced Figure 1 As shown, specifically:

[0098] (1) Preparation of rigid films: First, a 30 nm Sr3Al2O6 sacrificial layer film was grown on a commercial

[001] oriented SrTiO3 (STO) substrate using pulsed laser deposition (PLD) technology. The film growth temperature was 750 °C, the oxygen partial pressure was 0.1 Pa, and the laser energy density was 1.5 J / cm 2 Then, a 20nm SrRuO3 film was grown on the Sr3Al2O6 film. The film growth temperature was 700℃, the oxygen partial pressure was 13Pa, and the laser energy density was 1.0J / cm 2 Then, LaCoO3 film was grown on the SrRuO3 film. The film growth temperature was 700℃, the oxygen partial pressure was 13Pa, and the laser energy density was 1.6J / cm 2 After the film growth is completed, the temperature is lowered to room temperature at a rate of 10°C / min to obtain LCO / SRO / SAO / STO rigid films.

[0099] (2) Dissolution of the sacrificial layer: First, a polydimethylsiloxane (PDMS) film is attached to the surface of the LCO / SRO / SAO / STO rigid film. Then, the rigid film with PDMS is placed in a culture dish filled with deionized water. After waiting for 6 hours, the SAO can be dissolved by water and the STO single crystal substrate will fall off. The SRO / LCO / PDMS sample is picked up with tweezers and blown dry with dry nitrogen.

[0100] (3) Electrochemical stripping of the buffer layer: The SRO film on the surface of the SRO / LCO / PDMS sample is connected to the working electrode of the electrochemical workstation to form a three-electrode system with the counter electrode Pt and the reference electrode Ag / AgCl, and then the three electrodes are inserted into a beaker containing a 0.1 mol / L KOH solution. A positive voltage of 1.55 V (vs RHE) is applied to the working electrode, and the SRO film on the surface begins to dissolve. The SRO film can be completely dissolved within 5 to 10 seconds. Since the LCO film is under the SRO film and is relatively insulating, applying a voltage of 1.55 V is not enough to affect the LCO film. Therefore, after the SRO is completely dissolved, the sample is removed from the KOH solution, the surface is cleaned with deionized water, and then blown dry with dry nitrogen to obtain a LCO self-supporting film.

[0101] Figure 2 In the figure, the blue box in a is a physical picture of the LaCoO3 self-supporting film. It can be seen that the LCO self-supporting film attached to PDMS is very complete.

[0102] Figure 2 In the figure, b is a LaCoO3 self-supporting film under an optical microscope. It can be seen that although there are a few wrinkles (caused by the adhesion of the PDMS underneath), the LaCoO3 self-supporting film has good integrity and high quality.

[0103] Figure 2 In the figure, c is the X-ray diffraction θ-2θ linear scanning curve of LCO / SRO / SAO / STO rigid film, SRO / LCO / PDMS self-supporting film and LCO / PDMS self-supporting film. It can be seen that the films obtained in the three processes of rigid film preparation, sacrificial layer dissolution and electrochemical stripping of buffer layer have good crystallinity, no impurities, and grow along the

[001] crystal orientation. The out-of-plane lattice parameter c of the LCO self-supporting film finally obtained is The lattice parameters of LaCoO3 in bulk form The results are basically consistent within the error range.

[0104] Therefore, the present invention successfully obtains high-quality LaCoO3 self-supporting single crystal films, which provides an important prerequisite for transferring LaCoO3 films to other materials and integrating them with them.

[0105] Example 2

[0106] The difference from Example 1 is that the applied voltage for the low voltage electrochemical stripping of SRO / LCO / PDMS is 1.20 V (vsRHE).

[0107] XRD results are as follows Figure 3 Reference Figure 3It can be seen that at a voltage of 1.20 V, the crystal structure of the SRO / LCO film is basically unchanged, that is, the SRO film on the surface is not dissolved. Therefore, a pure LCO free-standing film cannot be obtained when the applied voltage is 1.20 V.

[0108] Example 3

[0109] The difference from Example 1 is that the high voltage electrochemical stripping of SRO / LCO / PDMS is performed with an applied voltage of 2.10 V (vs RHE). Figure 4 As shown in a, at a voltage of 2.10 V, the diffraction peak of the SRO film disappears, that is, the SRO film on the surface dissolves at this voltage, and thus a LCO free-standing film is obtained.

[0110] However, excessively high voltage causes certain damage to the LCO film, such as Figure 4 Therefore, when the LCO self-supporting film is obtained by electrochemical method, the applied voltage should not be too large, and the applied voltage should be 1.55V to 1.60V (vs RHE), otherwise the surface of the LCO self-supporting film will be damaged.

[0111] Comparative Example 1

[0112] The difference from Example 1 is that the LaCoO3 film is grown directly on the Sr3Al2O6 and Sr4Al2O7 sacrificial layers, and the method does not use the SrRuO3 buffer layer. Figure 5 As shown, the XRD results indicate that the LaCoO3 films of LaCoO3 / Sr3Al2O6 / SrTiO3 and LaCoO3 / Sr4Al2O7 / SrTiO3 cannot be detached from the substrate after being soaked in water (for one week), so this method cannot obtain LaCoO3 self-supporting films.

[0113] Comparative Example 2

[0114] The difference from Example 1 is that other oxide materials are selected as the buffer layer between LCO and SAO. 0.7 Sr 0.3 MnO3(LSMO) as buffer layer. Figure 6 As shown in the XRD results, it can be seen that LCO / LSMO self-supporting films can be obtained by using LSMO as a buffer layer, but it is difficult to make it into Figure 1In the electrochemical device shown, when a voltage of 1.60 V (vsRHE) is applied, the crystal structure of the film is basically unchanged, that is, the LSMO on the LSMO / LCO / PDMS surface does not dissolve when a voltage is applied. Therefore, although the film can be peeled off from the substrate using LSMO as a buffer layer between LCO and SAO, a pure LCO self-supporting film cannot be obtained by electrochemical methods.

[0115] The present invention has been described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for preparing a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film, characterized in that: The preparation method comprises the following steps: S1: A water-soluble sacrificial layer film SAO, a Ru-based perovskite oxide film SRO and a LaCoO3 film LCO are sequentially grown on the substrate surface to form a rigid film with a structure of substrate / SAO / SRO / LCO; S2: After a protective film layer is attached to the surface of the LaCoO3 film LCO, a rigid film having a structure of substrate / SAO / SRO / LCO / protective film layer is formed, and the water-soluble sacrificial layer film SAO is dissolved to achieve the shedding of the substrate, thereby obtaining a rigid film having a structure of SRO / LCO / protective film layer; S3: By applying voltage to the Ru-based perovskite oxide film SRO, the Ru-based perovskite oxide film SRO is electrochemically stripped to obtain a film with a structure of LCO / protective film layer. The protective film layer is removed to obtain a low-dimensional insulating ferromagnetic LaCoO3 self-supporting film.

2. The preparation method according to claim 1, characterized in that: In step S1, the process parameters for growing the water-soluble sacrificial layer SAO film include: film growth temperature of 700-800°C, oxygen partial pressure of 0.05-0.15 Pa, laser energy density of 1-2 J / cm 2 ; and / or, the process parameters for growing Ru-based perovskite oxide thin films SRO include: film growth temperature 650-750°C, oxygen partial pressure 10-15 Pa, laser energy density 1-2 J / cm 2 ; and / or, the process parameters for growing LaCoO3 thin film LCO include: film growth temperature 650-750°C, oxygen partial pressure 10-15Pa, laser energy density 1-2J / cm 2 .

3. The preparation method according to claim 2, characterized in that: Step S1 also includes cooling the temperature to room temperature at a rate of 10° C. / min after the LaCoO 3 thin film LCO is grown.

4. The preparation method according to claim 1, characterized in that: In step S1, the substrate includes a perovskite single crystal substrate.

5. The preparation method according to claim 1, characterized in that: The thickness of the water-soluble sacrificial layer film SAO is 20-40 nm; and / or the thickness of the Ru-based perovskite oxide film SRO is 10-30 nm.

6. The preparation method according to claim 1, characterized in that: In step S2, the method for dissolving the water-soluble sacrificial layer film SAO includes: soaking a rigid film having a structure of substrate / SAO / SRO / LCO / protective film layer in deionized water, wherein the water-soluble sacrificial layer film SAO is dissolved during the soaking process; and / or the soaking time is 4 to 8 hours.

7. The preparation method according to claim 1, characterized in that: In step S3, the electrochemical stripping method includes: connecting the working electrode to the Ru-based perovskite oxide film SRO, forming a three-electrode system with the counter electrode and the reference electrode, inserting the three-electrode system into an alkaline solution, applying a positive voltage to the working electrode, and dissolving the Ru-based perovskite oxide film SRO; and / or, the target voltage value of applying the positive voltage is 1.55V (vs RHE); and / or, the time for applying the positive voltage is 5 to 10s.

8. The preparation method according to claim 1, characterized in that: In step S3, the electrochemical stripping method further comprises: after the Ru-based perovskite oxide film SRO is dissolved, taking out the sample from the alkaline solution and washing and drying it.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The low-dimensional insulating ferromagnetic LaCoO3 self-supporting film grows along the [001] crystal orientation.

10. The preparation method according to any one of claims 1 to 8, characterized in that: The thickness of the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film is 10 to 30 nm; and / or the out-of-plane lattice parameter c of the low-dimensional insulating ferromagnetic LaCoO3 self-supporting film is

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