Laminate, method for manufacturing laminate, and method for raising 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] The present disclosure relates to stacks, methods for making stacks, and methods for increasing the superconducting transition temperature. [Background technology]

[0002] Superconductivity is a phenomenon in which a material loses 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, there are high hopes for resistance-free power transmission lines that utilize the superconducting state. Other applications of superconductivity include linear motor cars, which enable high-speed travel; magnetic resonance imaging (MRI), which can precisely image the inside of the human body; and quantum computers, which enable parallel computing.

[0003] It is known that some superconductors have an increase in Tc when pressure is applied, which is called the pressure effect. For example, Patent Document 1 discloses a high-pressure generating apparatus used to investigate the pressure effect of superconductors.

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

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-187612 [Patent Document 2] Japanese Patent Application Publication No. 02-243781 Summary of the Invention [Problem to be solved by the invention]

[0006] From the perspective of industrial applications of superconductivity, various methods for increasing Tc are being considered. One method is the pressure effect described above. However, it is difficult to apply pressure to the wiring of quantum computers, which are wired under liquid nitrogen, using a large press. Therefore, a method for achieving the pressure effect without using mechanical compression equipment is needed.

[0007] The present invention is devised to solve the above-mentioned problems, and aims to provide 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. [Means for solving the problem]

[0008] The present invention includes the following aspects. [1] A laminate comprising a diamond-like carbon (DLC) film on an object including a material selected from an oxide superconducting material and an electrically conductive material, A laminate, wherein 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 a striped or tiled pattern. [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 having a cross-sectional major axis 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 compressive stress is generated in a range of approximately 1 / 3 of the thickness of the sheet material from the surface opposite the DLC film. [9] The laminate according to any one of [1] to [8], wherein the DLC film has a thickness of 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 copper oxide superconductor.

[13] The laminate according to

[11] or

[12] , which has a superconducting transition temperature that is 0.5 K or more higher than that of an object not having 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 producing a laminate according to any one of [1] to

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

[16] 16. The method for producing a laminate according to claim 15, wherein the DLC film is formed by vapor deposition.

[17] The method for producing a laminate according to

[15] , wherein the DLC film is formed by a filtered cathodic vacuum arc method.

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

[19] the object is a sheet material, and coating at least one surface of the sheet material with DLC; A method for increasing the superconducting transition temperature of an object according to

[18] , which comprises generating compressive stress in a range of approximately one-third of the thickness of the sheet material from the surface opposite the DLC film.

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

[18] or

[19] , wherein the coating of the DLC film is carried out by a filtered cathodic vacuum arc method. [Effects of the Invention]

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

[0010] [Figure 1] FIG. 2 is a schematic cross-sectional view showing an example of a laminate according to the first embodiment. [Figure 2] 1 is a schematic cross-sectional view used to explain that an object in a stack is pressurized. FIG. [Figure 3] FIG. 2 is a perspective view showing an example of an object according to the first embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view showing an example of a laminate according to the first embodiment. [Figure 5] FIG. 10 is a schematic cross-sectional view showing an example of a laminate according to a second embodiment. [Figure 6] FIG. 10 is a schematic cross-sectional view showing an example of a laminate according to a second embodiment. [Figure 7] 10A and 10B are a schematic cross-sectional view and a front view showing an example of a laminate according to a third embodiment. [Figure 8] 1 is a schematic cross-sectional view used to explain that an object in a stack is pressurized. FIG. [Figure 9]FIG. 10 is a schematic front view showing an example of a laminate according to a third embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view showing an example of a laminate according to a third embodiment. [Figure 11] FIG. 1 is a schematic diagram of the FCVA method. [Figure 12] These are the results 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 a Raman spectrum of the DLC film. [Figure 15] FIG. 1 is a schematic cross-sectional view for explaining parameters of the Stoney formula. [Figure 16] 1 is a graph showing superconductivity evaluation of a thin film. [Figure 17] 1 is a graph showing the film thickness of a DLC film. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same components in each embodiment are designated by the same reference numerals, and their description will be omitted or simplified. For clarity of explanation, the following description and drawings will be simplified as appropriate, and the scale of each component may differ significantly. Terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "perpendicular," "orthogonal," and "identical," are not to be construed as being limited to their strict meanings, but rather as including the range of degrees to which similar functions can be expected. Unless otherwise specified, "~" indicating a range of values ​​includes the values ​​before and after it as the lower and upper limits.

[0012] [Laminate] First, the laminate of the present disclosure will be outlined with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing an example of a laminate of a first embodiment described below. Figure 2 is a schematic cross-sectional view used to explain that an object in the laminate of Figure 1 is pressurized. For the purpose of explanation, the warpage in Figure 2 is extremely exaggerated. In the laminate 100 shown in FIG. 1, an object 10 is in the form of a sheet, and a DLC film 20 is provided on the sheet-like object 10 .

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

[0014] Examples of materials that can be used to form the object 10 include oxide superconducting materials and conductive materials, such as metals, conductive carbon, and indium tin oxide (ITO). The oxide superconducting material can be appropriately selected from materials capable of exhibiting superconductivity. In view of the fact that the transition temperature Tc is easily increased by the pressure effect, a copper oxide superconducting material containing copper oxide is preferred as the oxide superconducting material. Among them, the copper oxide superconducting materials preferably have stoichiometric composition formulas represented by the following formulas (1) to (8). (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) Here, n is 1, 2 or 3, m is 2 or 3, and δ is a number from 0 to 1.

[0015] Of the above copper oxide superconducting materials, those which do not contain mercury and are represented by any of (1) to (5) above are preferred, and those which have a relatively high Tc and can be used at the liquid nitrogen temperature (77 K) and are represented by (1) to (3) above are preferred. For example, the above-mentioned YBCO and BSCCO are high-temperature superconductors with a Tc of 77 K or higher. However, depending on the purity, environment, conditions, etc., the problem with YBCO and BSCCO is that they do not superconduct at 77 K. As will be described later, the laminate of the present disclosure can increase the transition temperature Tc by 0.5 K or more, preferably by 2.0 K or more, making it possible to use these materials at liquid nitrogen temperatures even when they contain impurities or under a wide range of conditions. Specific explanations are given below with reference to embodiments.

[0016] First Embodiment In the laminate of the first embodiment, the object 10 is a sheet-like laminate. As shown in FIG. 1 above, it is sufficient that the laminate has at least a DLC film 20 on the sheet-like object 10, and other layers may also be included. FIG. 4 is a schematic cross-sectional view showing another example of the laminate of the first embodiment. The laminate of FIG. 4 has an adhesive layer 12, a reinforcing material 14, and a DLC film 20 on the object 10. An example of the adhesive layer 12 is solder. Furthermore, an example of the reinforcing material 14 is glass, a metal plate, or the like. The shape of the object 10 is not particularly limited, and may be square when viewed from the front (+z direction in Figure 1), elongated as shown in the example of Figure 3, or may be rectangular wire-like.

[0017] When the object 10 is long, 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 ease of handling. The length L (long dimension) of the object 10 is not particularly limited and can be, for example, about 0.1 to 1000 mm, and is preferably 0.5 to 500 mm from the viewpoint of ease of handling. However, the length of the object 10 is longer than the width. The thickness T of the object 10 is preferably 0.001 to 10 mm, and more preferably 0.005 to 5 mm.

[0018] When the object 10 is an oxide superconducting material, the molding method of the 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, slip casting, tape casting, etc.

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

[0020] The method for forming the DLC film 20 is preferably selected taking into consideration the magnitude of the required internal stress, etc. Specific examples of methods for forming the DLC film 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). The CVD method can form a DLC film that contains a relatively large amount of hydrogen, resulting in a relatively soft film. The PVD method can form a DLC film that contains relatively little or no hydrogen, resulting in a DLC film with high internal stress. The FCVA method, among others, can eliminate droplets generated during arc discharge and form a harder film, i.e., a DLC film with high internal stress.

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

[0022] The major axis (diameter in the case of a round material) of the wire-shaped object 10 is not particularly limited, but may be, for example, 50 mm or less, and is preferably 0.01 to 5 mm, more preferably 0.05 to 1 mm, from the viewpoint of handleability.

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

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

[0025] The pattern shape of the thin film is not particularly limited, but a repeating pattern is preferred in that it is easier to obtain a uniform pressure effect, and specifically, a stripe pattern as shown in Fig. 7 or a tile pattern as shown in Fig. 9 is preferred. On the other hand, when a conductive material is used as the 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 Fig. 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. 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 intended use of the laminate.

[0028] When the 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, and specific examples include etching methods such as wet etching and dry etching, and laser patterning.

[0029] The laminates of the above embodiments can increase the superconducting transition temperature by 0.5 K or more, preferably by 1.0 K or more, and more preferably by 2.0 K or more, compared to an object of the same shape that does not have a DLC film.

[0030] The present disclosure further provides a method for manufacturing a laminate and a method for increasing the superconducting transition temperature of an object, the specific methods of which are as described above and therefore will not be described in detail here. [Example]

[0031] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0032] [Example 1: Production of a laminate including a patterned thin film] First, an MgO substrate on which a YBCO film (formula (1) above) was formed was prepared. Details of the substrate are shown in Table 1. This substrate was irradiated with laser light to form the stripe pattern shown in Figure 7. Specifically, a YAG laser was used, and the laser was irradiated twice to form the pattern under the conditions of a power of 50 W, a scan speed of 50 mm / s, and a Q-switch of 50 Hz.

[0033] [Table 1]

[0034] Next, a DLC film was formed by 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 in a vacuum atmosphere. The product contains impurities such as droplets in addition to carbon ions, but these are removed by an electromagnetic space filter with a bent structure, so only ions that pass through the filter are used for film formation, making it possible to create a high-quality film. The film formation conditions are shown in Table 1. In this example, the DLC film is used to apply compressive stress to YBCO, so sp 3 The conditions for forming a film with a high bonding ratio were set as shown in Table 2.

[0035] [Table 2]

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

[0037] <Results and Discussion> (Evaluation of thin film composition and structure) The structure of the laser-patterned YBCO thin film was 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 Figure 13 confirmed that the line width L of the YBCO thin film was 220 μm. These are the dimensions as designed. No grooves were formed in the MgO substrate, which has a high transmittance to laser light, and only the YBCO in the areas irradiated by the laser was removed.

[0038] (Evaluation of the structure and texture of DLC films) The carbon film formed on the YBCO was measured using a Raman microscope. The results are shown in Figure 14. -1 ~2000cm -1 Since a broad peak characteristic of DLC was observed, it was confirmed that the film formed on the surface was DLC.

[0039] (Stress evaluation of DLC film) Separately from the above example, DLC was formed on a linear YBCO thin film, the surface distortion was observed using a laser microscope, and the stress of the YBCO thin film was calculated using Stoney's formula (the following formula (I)).

[0040]

number

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

[0042] (Superconductivity evaluation of thin films) Using the four-probe method, the resistivity of the YBCO thin film in the laminate produced in Example 1 was measured to confirm whether a superconducting state had been achieved. The sample that had been patterned was designated Sample A, and the sample with DLC film (Example 1) was designated Sample B. Resistivity measurements were performed on each. As shown in Figure 16, the temperature change in resistivity was 85.8 K for Sample A without DLC film, while the transition temperature was 87.6 K for Sample B with DLC film, confirming an increase in the transition temperature. This is thought to be due to the compressive stress applied by the DLC parallel to the substrate surface to the patterned YBCO, which created a steady pressure effect.

[0043] [Example 2: Production 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. Several of these were prepared, and the DLC film deposition surface (reinforcement material) was polished with sandpaper, and a DLC film was deposited on each under the following conditions, aiming for a film thickness of 1 μm. Note that for the FCVA method, deposition was carried out under the following three conditions, with the film thickness varied. [Table 3]

[0044] The film thickness of each sample is shown in Figure 17. A DLC film was formed over almost the entire surface of each sample, and pressure was confirmed on the BSCCO. Table 4 shows the compressive stress of the DLC film and the Tc of the BSCCO for the samples with the DLC film formed by the FCVA method. Samples 60 and 45 showed that the Tc increased by 0.5 K and 1.2 K, respectively, compared to the superconducting transition temperature before the DLC film was formed. [Table 4] [Industrial Applicability]

[0045] According to the present invention, it is possible to increase the superconducting critical temperature of a superconducting thin film that has a pressure effect without using a mechanical compression device, and this invention can be applied to resistance-free power transmission lines that utilize the superconducting state, linear motor cars, MRI, quantum computers, etc. [Explanation of symbols]

[0046] 10: object, 20: DLC film, 30: pressure, 40: substrate, 100: laminate.

Claims

1. 1. A laminate comprising a diamond-like carbon (DLC) film on an object comprising a material selected from an oxide superconducting material and an electrically conductive material, A laminate, wherein the object is a wire, a sheet, or a patterned thin film formed on a substrate.

2. The laminate according to claim 1 , wherein the object is a patterned thin film formed on a substrate, the patterned thin film having a repeating pattern.

3. The laminate of claim 2 , wherein the repeating pattern is a striped or tiled pattern.

4. 3. The laminate according to claim 2, wherein the line width of the thin film is 0.5 to 500 μm.

5. 3. The laminate according to claim 2, wherein the thickness of the thin film is 0.05 to 5 μm.

6. The laminate according to claim 1 , wherein the object is a wire having a cross-sectional major axis of 50 mm or less.

7. The laminate according to claim 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 claim 7 , wherein compressive stress is generated in a range of about one-third of the thickness of the sheet material from the surface opposite to the DLC film.

9. 2. The laminate according to claim 1, wherein the DLC film has a thickness of 0.05 to 5 μm.

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

11. The stack of claim 1 , wherein the material is an oxide superconducting material.

12. 12. The stack of claim 11, wherein the oxide superconducting material is a copper oxide superconductor.

13. The laminate according to claim 11, wherein the superconducting transition temperature is 0.5 K or more higher than that of an object not having a DLC film.

14. The laminate according to claim 1 , 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 producing the laminate according to any one of claims 1 to 14, providing an object comprising a material selected from an oxide superconducting material and an electrically conductive material; and depositing a DLC film on the object.

16. The method for manufacturing a laminate according to claim 15, wherein the DLC film is formed by vapor deposition.

17. The method for producing a laminate according to claim 15, wherein the DLC film is formed by a filtered cathodic vacuum arc method.

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

19. the object is a sheet material, and coating at least one surface of the sheet material with DLC; 20. The method for increasing the superconducting transition temperature of an object as set forth in claim 18, further comprising: inducing compressive stress in a range of approximately one-third of the thickness of the sheet material from the surface opposite the DLC film.

20. 20. The method of claim 18, wherein the DLC coating is applied by a Filtered Cathodic Vacuum Arc process.

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