Laminate, method for manufacturing a laminate, and method for increasing the superconducting transition temperature.

Abstract

To provide a laminate with a structure that persistently compresses an object such as an oxide superconducting material, and to provide a method for manufacturing the same and a method for raising a superconducting transition temperature.SOLUTION: A laminate includes a diamond-like carbon (DLC) film on an object including a material selected from an oxide superconducting material and a conductive material, where the object is a pattern-like thin film that is formed on a wire, a sheet material, or a substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a laminate, a method for manufacturing a laminate, and a method for increasing the superconducting transition temperature. [Background technology]

[0002] Superconductivity is a phenomenon in which a material loses its electrical resistance below a certain transition temperature Tc. Currently, efforts are being made to conserve energy and reduce CO2 emissions in order to achieve carbon neutrality and the SDGs, and superconductivity is attracting attention as a phenomenon that can solve these problems. For example, in terms of energy conservation, resistance-free power transmission lines that utilize the superconducting state are expected. In addition, other applications of superconductivity include linear motor cars that enable high-speed travel, magnetic resonance imaging (MRI) that can precisely image the inside of the human body, and quantum computers that enable parallel computing.

[0003] It is known that some superconductors exhibit an increase in Tc when pressure is applied; this phenomenon is called the pressure effect. For example, Patent Document 1 discloses a high-pressure generator used to investigate the pressure effect of superconductors.

[0004] Furthermore, Patent Document 2 discloses an oxide superconducting composite long body formed by depositing an oxide superconductor on a long metal substrate via a buffer layer made of a diamond-like carbon thin film. According to Patent Document 2, by providing a buffer layer, it is possible to prevent the interdiffusion between atoms in the substrate and the oxide superconducting material that occurs during heat treatment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-187612 [Patent Document 2] Japanese Patent Application Publication No. 02-243781 [Overview of the project] [Problems that the invention aims to solve]

[0006] From the perspective of industrial applications of superconductivity, various methods are being considered to increase the Tc (transistor temperature). One such method is the pressure effect described above. However, it is difficult to apply pressure to wiring in quantum computers, for example, that is wired under liquid nitrogen using a large press. Therefore, there is a need for a method that can obtain the pressure effect without using mechanical compression equipment.

[0007] The present invention aims to solve the above problems and to provide a laminate with a structure that continuously applies pressure to an object such as an oxide superconducting material, a method for manufacturing the same, and a method for raising the superconducting transition temperature. [Means for solving the problem]

[0008] The present invention includes the following embodiments. [1] A laminate comprising a diamond-like carbon (DLC) film on an object containing a material selected from oxide superconducting materials and conductive materials, A laminate in which the object is a wire, a sheet, or a patterned thin film formed on a substrate. [2] The laminate according to [1], wherein the object is a patterned thin film formed on a substrate, and the patterned thin film has a repeating pattern. [3] The laminate according to [2], wherein the repeating pattern is stripe-shaped or tile-shaped. [4] The laminate according to [2] or [3], wherein the line width of the thin film is 0.5 to 500 μm. [5] The laminate according to any one of [2] to [4], wherein the thickness of the thin film is 0.05 to 5 μm. [6] The laminate according to [1], wherein the object is a wire with a major axis of cross-section of 50 mm or less. [7] The laminate according to [1], wherein the object is a sheet material and the DLC film is provided on at least one surface of the sheet material. [8] The laminate according to [7], wherein a compressive stress is generated in a range of about 1 / 3 of the thickness from the surface of the sheet material opposite to the DLC film. [9] The laminate according to any one of [1] to [8], wherein the thickness of the DLC film is 0.05 to 5 μm.

[10] The laminate according to any one of [1] to [9], wherein the DLC film has a compressive internal stress of 20 MPa or more.

[11] The laminate according to any one of [1] to

[10] , wherein the material is an oxide superconducting material.

[12] The laminate according to

[11] , wherein the oxide superconducting material is a cuprate superconductor.

[13] The laminate according to

[11] or

[12] , having a superconducting transition temperature 0.5 K or higher than that of an object without a DLC film.

[14] The laminate according to any one of [1] to

[10] , wherein the material is a conductive material, the object is a patterned thin film, and the pattern constitutes a circuit pattern.

[15] A method for manufacturing a laminate according to any one of [1] to

[14] , comprising: preparing an object containing a material selected from an oxide superconducting material and a conductive material; forming a DLC film on the object.

[16] The method for manufacturing a laminate according to claim 15, wherein the formation of the DLC film is performed by a vapor phase growth method.

[17] The method for manufacturing a laminate according to

[15] , wherein the formation of the DLC film is performed by a Filtered Cathodic Vacuum Arc method.

[18] A method for increasing the superconducting transition temperature of an object, comprising coating the object containing an oxide superconducting material with DLC.

[19] The object is a sheet material, and the process includes coating at least one surface of the sheet material with DLC. A method for increasing the superconducting transition temperature of an object as described in

[18] , wherein compressive stress is generated in a range of approximately 1 / 3 of the thickness of the sheet material from the side opposite to the DLC film.

[20] A method for increasing the superconducting transition temperature of an object according to

[18] or

[19] , wherein the DLC film coating is performed by the Filtered Cathodic Vacuum Arc method. [Effects of the Invention]

[0009] The present invention provides a laminate structure for continuously applying pressure to an object such as an oxide superconducting material, a method for manufacturing the same, and a method for increasing the superconducting transition temperature. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing an example of a laminate according to the first embodiment. [Figure 2] This is a schematic cross-sectional view used to illustrate the pressurization of an object within a laminate. [Figure 3] This is a perspective view showing an example of an object according to the first embodiment. [Figure 4] This is a schematic cross-sectional view showing an example of a laminate according to the first embodiment. [Figure 5] This is a schematic cross-sectional view showing an example of a laminate according to the second embodiment. [Figure 6] This is a schematic cross-sectional view showing an example of a laminate according to the second embodiment. [Figure 7] These are schematic cross-sectional and front views showing an example of a laminate according to the third embodiment. [Figure 8] This is a schematic cross-sectional view used to illustrate the pressurization of an object within a laminate. [Figure 9]This is a schematic front view showing an example of a laminate according to the third embodiment. [Figure 10] This is a schematic cross-sectional view showing an example of a laminate according to the third embodiment. [Figure 11] This is a schematic diagram of the FCVA method. [Figure 12] This is the result of structural evaluation using a laser microscope. [Figure 13] This is a laser microscope image showing the pattern shape of a YBCO thin film. [Figure 14] This is the Raman spectrum of a DLC film. [Figure 15] This is a schematic cross-sectional view illustrating the parameters of Stoney's formula. [Figure 16] This graph shows the evaluation of the superconductivity of thin films. [Figure 17] This is a graph showing the film thickness of DLC films. [Modes for carrying out the invention]

[0011] The embodiments for carrying out the invention will be described below with reference to the drawings. In each embodiment, identical components are denoted by the same reference numerals, and their descriptions are omitted or simplified. For clarity, the following descriptions and drawings are simplified as appropriate, and the scale of each component may differ significantly. In this specification, terms such as "parallel," "perpendicular," "orthogonal," and "identical," which specify shapes, geometric conditions, and their degrees, shall not be interpreted strictly, but shall be interpreted to include a range that can be expected to function similarly. The "~" symbol indicating a numerical range includes the numbers before and after it as the lower and upper limits, unless otherwise specified.

[0012] [Laminated structure] First, the laminate of this disclosure will be outlined with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing an example of the laminate of the first embodiment described later. Figure 2 is a schematic cross-sectional view used to explain the pressurization of the object in the laminate of Figure 1. For illustrative purposes, the warp in Figure 2 is exaggerated to an extreme degree. The laminate 100 shown in Figure 1 has an object 10 in the shape of a sheet, and a DLC film 20 is provided on the sheet-shaped object 10.

[0013] DLC is made of spruce of carbon. 2 join,sp 3 DLC is an amorphous carbon film composed of bonds and hydrogen atoms. Depending on the ratio of the above bonds and hydrogen atoms, DLC has an internal stress (residual stress) of about 10 MPa to 20 GPa. Therefore, in the laminate 100, a sustained compressive force is generated in the DLC film 20, and pressure is applied to the object 10 in the direction of arrow 30 in Figure 2. This causes a pressure effect on the object 10, and if the object 10 is an oxide superconducting material, the transition temperature Tc increases, and if the object 10 is a conductive material, the electrical resistance decreases. Furthermore, because DLC possesses properties such as high hardness, low coefficient of friction, high wear resistance, and gas barrier properties, it also functions as a protective film for object 10.

[0014] Examples of materials constituting object 10 include oxide superconducting materials and conductive materials. Examples of conductive materials include metals, conductive carbon, and indium tin oxide (ITO). As the oxide superconducting material, a suitable material can be selected from among materials capable of exhibiting superconductivity. Since the transition temperature Tc tends to increase due to the pressure effect, copper oxide superconducting materials containing copper oxide are preferred as the oxide superconducting material. Among copper oxide superconducting materials, those represented by the following stoichiometric compositional formulas (1) to (8) are preferred. (1) YBa2Cu3O (7-δ) (YBCO) (2) Bi2Sr2Ca (n-1) Cu n O (2n+4+δ) (3) (Bi,Pb)2Sr2Ca (m-1) Cu m O (2n+4+δ) (BSCCO) (4) CuBa2Ca2Cu3O (10-δ) (5) Ba2Ca2Cu3O 6.8 F 1.2 (6) HgBa2Ca2Cu3O (8+δ) (Hg-1223) (7) HgBa2CaCu2O (6+δ) (Hg-1212) (8) HgBa2CuO (4+δ) (Hg-1201) However, n is 1, 2 or 3, m is 2 or 3, and δ is a number between 0 and 1.

[0015] Among the above, the copper oxide superconducting material is preferably a superconducting material represented by any of the above (1) to (5) that does not contain mercury, and a superconducting material represented by any of the above (1) to (3) that has a relatively high Tc and can be used at liquid nitrogen temperature (77K) is more preferable. For example, the above YBCO and BSCCO are high-temperature superconductors with a Tc of 77K or higher. However, depending on purity, environment, conditions, etc., the problem is that superconductivity does not occur in the YBCO and BSCCO at 77K. As will be described later, the laminate of the present disclosure can increase the transition temperature Tc by 0.5K or more, preferably 2.0K or more, and these materials can be used at liquid nitrogen temperature even when they contain impurities or under a wide range of conditions. Hereinafter, specific embodiments will be described.

[0016] <First Embodiment> The laminate of the first embodiment is a laminate in which object 10 is in the form of a sheet. As shown in Figure 1 above, it is sufficient to have a DLC film 20 on at least the sheet-like object 10, and it may also have other layers. Figure 4 is a schematic cross-sectional view showing another example of the laminate of the first embodiment. The laminate of Figure 4 comprises an adhesive layer 12, a reinforcing material 14, and a DLC film 20 on object 10. One example of the adhesive layer 12 is solder. The reinforcing material 14 can be, for example, glass, a metal plate, etc. The shape of object 10 is not particularly limited and may be square in front view (in the +z direction in Figure 1), elongated as shown in the example in Figure 3, or even rectangular.

[0017] When object 10 is elongated, the width W (short length) is not particularly limited, but can be, for example, about 0.01 to 500 mm, and is preferably 0.1 to 100 mm from the viewpoint of handling. The length L (length) of object 10 is not particularly limited and can be, for example, about 0.1 to 1000 mm, with 0.5 to 500 mm being preferable from the standpoint of handling. However, the length of object 10 shall be longer than its width. Furthermore, the thickness T of object 10 is preferably 0.001 to 10 mm, and more preferably 0.005 to 5 mm.

[0018] If object 10 is an oxide superconducting material, the molding method for object 10 is not particularly limited and can be appropriately selected from known methods for molding ceramics. Specific examples of molding methods include extrusion molding, injection molding, pressure molding, casting, and tape molding.

[0019] In the first embodiment, the thickness of the DLC film 20 is preferably 0.05 to 5 μm, preferably 0.1 to 2 μm, and more preferably 0.2 to 1.5 μm, from the viewpoint of pressure effect.

[0020] The method for depositing the DLC film 20 should preferably be selected considering the required magnitude of internal stress. Specific examples of DLC film deposition methods include chemical vapor deposition (CVD) methods such as plasma CVD, vacuum deposition, sputtering, ion plating, arc plasma deposition using an arc plasma gun (APG), and PVD methods such as filtered cathodic vacuum arc (FCVA). According to the above CVD method, a DLC film containing a relatively high amount of hydrogen can be deposited, resulting in a relatively soft film. Furthermore, according to the above PVD method, a DLC film containing a relatively low amount of hydrogen or no hydrogen at all can be deposited, resulting in a DLC film with high internal stress. Among these, the FCVA method can eliminate droplets generated during arc discharge, allowing for the deposition of a harder film, i.e., a DLC film with high internal stress.

[0021] <Second Embodiment> Next, the laminate of the second embodiment will be described with reference to Figures 5 and 6. Figures 5 and 6 are schematic cross-sectional views showing an example of the laminate of the second embodiment. In the laminate of the second embodiment, the object 10 is a laminate of wire material. The laminate 100 shown in Figure 5 has a DLC film 20 on the surface of a long, round wire-shaped object 10 in the Y-axis direction. The laminate 100 shown in Figure 6 has a DLC film 20 on the surface of a rectangular wire-shaped object 10. In both laminates, pressure is applied to the object 10 in the direction of the center.

[0022] In the wire-shaped object 10, the major axis (diameter in the case of a round object) is not particularly limited, but for example, it should be 50 mm or less, and from the viewpoint of handling, 0.01 to 5 mm is preferred, and 0.05 to 1 mm is preferred.

[0023] In the second embodiment, the thickness of the DLC film 20 is preferably 0.05 to 5 μm, preferably 0.1 to 2 μm, and more preferably 0.2 to 1.5 μm, from the viewpoint of pressure effect.

[0024] <Third Embodiment> Next, the laminate of the third embodiment will be described with reference to Figure 7. Figure 7 is a schematic cross-sectional view and a front view showing an example of the laminate of the third embodiment. The laminate of the third embodiment is a patterned thin film in which object 10 is formed on a substrate. The laminate 100 shown in Figure 7 comprises a patterned object 10 formed on a substrate 40 and a DLC film 20. In the laminate 100 of the third embodiment, as shown in Figure 8, the DLC that has entered the grooves applies pressure to the patterned object 10 in the direction of arrow 30.

[0025] The pattern shape of the thin film is not particularly limited, but a repeating pattern is preferred because it is easier to obtain a uniform pressure effect. Specifically, a stripe pattern as shown in Figure 7 or a tile pattern as shown in Figure 9 is preferred. On the other hand, if a conductive material is used as object 10, a circuit pattern may be formed. Furthermore, the grooves (spaces) formed in the thin film do not need to reach the substrate 40, and may have an uneven pattern as shown in Figure 10. The depth of the grooves should be 30% or more of the thickness of the film-like object 10, preferably 50% or more, and more preferably 70% or more.

[0026] The line width L of the thin film is not particularly limited, but from the viewpoint of pressure effect, it is preferably 0.5 to 500 μm, more preferably 0.8 to 400 μm, and even more preferably 1 to 300 μm. Furthermore, from the viewpoint of pressure effect, the space width S is preferably 0.01 to 500 μm, more preferably 0.05 to 200 μm, and even more preferably 0.1 to 100 μm. From the viewpoint of pressure effect, the thickness of the thin film is preferably 0.05 to 20 μm, more preferably 0.1 to 15 μm, and even more preferably 0.2 to 5 μm.

[0027] The material of the substrate 40 is not particularly limited and can be appropriately selected from known materials such as glass, ceramics, metals, and silicon substrates, depending on the application of the laminate.

[0028] When object 10 is an oxide superconducting material, the method for forming the film-like object 10 is not particularly limited and can be appropriately selected from known methods for forming ceramics. Specific examples of forming methods include chemical vapor deposition (CVD) and sputtering. Furthermore, the patterning method can be appropriately selected from known methods, specifically, etching methods such as wet etching and dry etching, and laser patterning.

[0029] The laminates of each of the above embodiments can, for example, achieve a superconducting transition temperature 0.5K or higher than an object of the same shape but without a DLC film, preferably 1.0K or higher, and more preferably 2.0K or higher.

[0030] This disclosure further provides a method for manufacturing a laminate and a method for increasing the superconducting transition temperature of an object. Since the specific method is as described above, a detailed explanation is omitted here. [Examples]

[0031] The present invention will be described more specifically below with reference to examples and comparative examples. However, this description is not intended to limit the present invention.

[0032] [Example 1: Manufacturing of a laminate containing a patterned thin film] First, an MgO substrate with a YBCO (formula (1) above) film deposited on it was prepared. Details of the substrate are shown in Table 1. A stripe-like pattern, as shown in Figure 7, was formed by irradiating this substrate with laser light. Specifically, a YAG laser was used, and the patterning was performed by irradiating the substrate twice under the conditions of power 50W, scan speed 50mm / s, and Q switch 50Hz.

[0033] [Table 1]

[0034] Next, a DLC film was deposited using the FCVA method. Figure 11 shows a schematic diagram of the FCVA method. In the FCVA method, carbon ions are generated from a graphite target by arc discharge under a vacuum atmosphere. In addition to carbon ions, impurities such as droplets are also included in the product, but these are removed by an electromagnetic space filter with a bent structure, so only the ions that pass through the filter are used for film deposition, making it possible to create a high-quality film. The film deposition conditions are shown in Table 1. Note that in this example, the DLC film is used to apply compressive stress to YBCO, so sp 3 Conditions were set for forming a film with a high bonding ratio. The film formation conditions are shown in Table 2.

[0035] [Table 2]

[0036] <Evaluation Method> The following equipment was used for the evaluation. (Laser microscope) A laser microscope was used to measure the surface roughness and surface profile of YBCO films, and the film thickness, surface roughness, and surface profile of DLC films. The laser microscope used was a laser confocal optical system. (Raman spectroscopy) Raman spectroscopy was used to evaluate the structure of the DLC film. In Raman spectroscopy, the structure can be evaluated by irradiating the sample with laser light and detecting the Raman scattered light generated at that time. A Raman microscope XploRa from Horiba, Ltd. was used, and measurements were taken at a wavelength of 532 nm. (Measurement of electrical resistivity) One phenomenon that indicates superconductivity is occurring is when electrical resistance becomes zero. To observe this, we measured voltage and current at four terminals.

[0037] <Results and Discussion> (Evaluation of the composition and structure of thin films) A YBCO thin film that had undergone laser patterning was structurally evaluated using a laser microscope. As shown in Figure 12, the width S of the patterned grooves was approximately 57 μm and the depth was approximately 230 μm, and from Figure 13, it was confirmed that the line width L of the YBCO thin film was 220 μm. These dimensions are as designed. No grooves were formed on the MgO substrate, which has high transmittance to laser light, and only the YBCO in the laser-irradiated area was removed.

[0038] (Evaluation of the tissue and structure of DLC membranes) The carbon film formed on YBCO was measured using a Raman microscope. The results are shown in Figure 14. From this, 1000 cm² -1 ~2000cm -1 A broad peak characteristic of DLC was observed, confirming that the film deposited on the surface was DLC.

[0039] (Stress evaluation of DLC film) In addition to the above examples, DLC was deposited on a linear YBCO thin film, the surface strain was observed using a laser microscope, and the stress of the YBCO thin film was calculated using Stoney's equation (equation (I) below).

[0040]

number

[0041] The conditions for the Si substrate and thin film used are as follows: E s = 131 GPa ν = 0.266 b = 1.0 × 10 3 μm L = 2.0 × 10 4 μm d = 0.2 μm Using this method, the stress on the DLC film is estimated to be around 11 GPa.

[0042] (Evaluation of superconductivity in thin films) Using the four-terminal method, the resistivity of the YBCO thin film in the laminate fabricated in Example 1 was measured to confirm whether a superconducting state was achieved. Sample A was the sample up to patterning, and Sample B was the sample with DLC deposition (Example 1). The resistivity was measured for each. As shown in Figure 16, which illustrates the temperature dependence of resistivity, the temperature of Sample A, which did not have DLC deposition, was 85.8K, while the transition temperature of Sample B, which had DLC deposition, was 87.6K, confirming an increase in the transition temperature. This is thought to be because the compressive stress from the DLC applied to the patterned YBCO parallel to the substrate surface created a steady-state pressure effect.

[0043] [Example 2: Fabrication of a laminate containing a long oxide superconducting material] As the oxide superconducting material, a wire of BSCCO represented by the above formula (3) was used (length 25 mm × width 4.5 mm × thickness 0.4 mm). A reinforcing material was soldered to one side of the wire. Multiple samples were prepared, and the surface (reinforcement material) of the DLC film was polished with sandpaper. DLC films were then deposited on each sample under the following conditions, aiming for a film thickness of 1 μm. For the FCVA method, film deposition was performed under the following three conditions, varying the film thickness. [Table 3]

[0044] Figure 17 shows the film thickness of each sample. DLC film was deposited on almost the entire surface of all samples, and pressurization of BSCCO was confirmed. Table 4 shows the compressive stress of the DLC film and the Tc of the BSCCO for the samples in which DLC film was deposited by the FCVA method. Samples 60 and 45 showed an increase in Tc of 0.5K and 1.2K, respectively, compared to the superconducting transition temperature before DLC film deposition. [Table 4] [Industrial applicability]

[0045] According to the present invention, it is possible to raise the superconducting critical temperature of a superconducting thin film that exhibits a pressure effect without using mechanical compression equipment, enabling applications in resistance-free power transmission lines, linear motor cars, MRI, quantum computers, and other fields that utilize the superconducting state. [Explanation of Symbols]

[0046] 10: Object, 20: DLC film, 30: Pressurization, 40: Substrate, 100: Laminate.

Claims

1. A laminate comprising a diamond-like carbon (DLC) film on an object containing a material selected from oxide superconducting materials and conductive materials, The object is a thin film with a pattern having grooves or spaces, formed on a substrate. A laminate in which DLC is embedded in the aforementioned grooves or spaces.

2. The laminate according to claim 1, wherein the depth of the grooves formed in the thin film is 30% or more of the thickness of the thin film.

3. The laminate according to claim 1, wherein the patterned thin film has a stripe-like or tile-like repeating pattern.

4. The laminate according to claim 1, wherein the material is a conductive material and the patterned thin film constitutes a circuit pattern.

5. The laminate according to claim 1, wherein the line width of the thin film is 0.5 to 500 μm.

6. The laminate according to claim 1, wherein the thickness of the thin film is 0.05 to 5 μm.

7. The laminate according to claim 1, wherein the space or groove width of the thin film is 0.01 to 500 μm.

8. The laminate according to claim 1, wherein the thickness of the DLC film is 0.05 to 5 μm.

9. The laminate according to claim 1, wherein the DLC film has a compressive internal stress of 20 MPa or more.

10. The laminate according to claim 1, wherein the material is an oxide superconducting material.

11. The laminate according to claim 10, wherein the oxide superconducting material is a copper oxide superconductor.

12. The laminate according to claim 10, wherein the superconducting transition temperature is 0.5 K or higher than that of an object without a DLC film.

13. A method for manufacturing a laminate according to claim 1, As an object containing a material selected from oxide superconducting materials and conductive materials, a patterned thin film having grooves or spaces formed on a substrate is prepared, A method for manufacturing a laminate, comprising forming a DLC film on the aforementioned object.

14. The method for manufacturing a laminate according to claim 13, wherein the DLC film is formed by vapor phase growth.

15. The method for manufacturing a laminate according to claim 13, wherein the DLC film is formed by a Filtered Cathodic Vacuum Arc method.

16. This includes coating an object containing an oxide superconducting material with DLC, A method for increasing the superconducting transition temperature of an object, wherein the object is a thin film in the shape of a pattern having grooves or spaces formed on a wire or a substrate.

17. A method for increasing the superconducting transition temperature of an object according to claim 16, wherein the DLC coating is performed by a filtered cathode vacuum arc method.

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