Diamond electrode

Abstract

This diamond electrode comprises a rod-like conductive diamond member, and a rod-like metal member electrically connected to the conductive diamond member, wherein the diamond content of the conductive diamond member is at least 80 vol%.

Description

Diamond electrodes

[0001] The present disclosure relates to a diamond electrode. This application claims priority to Japanese Patent Application No. 2023-115406, filed on July 13, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Conductive diamond has excellent properties such as high electrical and thermal conductivity, high hardness, and high resistance to acids and alkalis. Taking advantage of these properties, technologies for using conductive diamond as electrodes are being investigated.

[0003] For example, Patent Document 1 discloses a diamond electrode in which a thin film made of diamond particles is deposited on a substrate made of a metal wire.

[0004] JP 2011-174822 A

[0005] The diamond electrode of the present disclosure is a diamond electrode comprising a rod-shaped conductive diamond member and a rod-shaped metal member electrically connected to the conductive diamond member, wherein the diamond content of the conductive diamond member is 80% by volume or more.

[0006] FIG. 1 is a diagram illustrating a typical configuration example of a diamond electrode according to embodiment 1. FIG. 2A is a cross-sectional view taken along line II in FIG. 1. FIG. 2B is a side view of a diamond member of the diamond electrode according to embodiment 1. FIG. 3A is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 1. FIG. 3B is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 1. FIG. 3C is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 1. FIG. 3D is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 1. FIG. 3E is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 1. FIG. 4 is a diagram illustrating a typical configuration example of a diamond electrode according to embodiment 2. FIG. 5A is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 2. FIG. 5B is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 2. FIG. 5C is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 2. FIG. 6 is a diagram illustrating a typical configuration example of a diamond electrode according to embodiment 3. FIG. 7A is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 3. FIG. 7B is a diagram illustrating a method for manufacturing a diamond electrode according to embodiment 3. FIG. 8 is a diagram illustrating a typical configuration example of a diamond electrode according to embodiment 4. Fig. 9A is a diagram for explaining a method for manufacturing a diamond electrode according to embodiment 4. Fig. 9B is a diagram for explaining a method for manufacturing a diamond electrode according to embodiment 4. Fig. 9C is a diagram for explaining a method for manufacturing a diamond electrode according to embodiment 4.

[0007] [Problem to be Solved by the Present Disclosure] When a thin film is made of diamond fine particles, as in Patent Document 1, gaps, so-called pinholes, exist between the diamond fine particles. The presence of pinholes reduces the coverage of the substrate with the thin film and reduces conductivity. In order to reduce pinholes and improve coverage, it is necessary to reduce the particle size of the diamond fine particles.

[0008] However, when the particle size of the diamond particles is reduced, the SP in the thin film ２ The bond ratio is SP ３As a result, the thin film cannot fully exhibit the excellent properties of conductive diamond, and the cyclic voltammetry properties (hereinafter also referred to as "CV properties") of the electrode tend to deteriorate.

[0009] Therefore, an object of the present disclosure is to provide a diamond electrode having excellent CV characteristics.

[0010] [Advantages of the Present Disclosure] According to the present disclosure, it is possible to provide a diamond electrode having excellent CV characteristics.

[0011] [Explanation of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and explained. (1) The diamond electrode of the present disclosure is a diamond electrode comprising a rod-shaped conductive diamond member and a rod-shaped metal member electrically connected to the conductive diamond member, wherein the diamond content of the conductive diamond member is 80% by volume or more.

[0012] According to the present disclosure, it is possible to provide a diamond electrode having excellent CV characteristics.

[0013] (2) In the above (1), the conductive diamond member may include a first region exposed to the outside, the maximum diameter D of the circumscribed circle of the cross section of the first region may be 0.3 mm or less, the cross section may be normal to the extension direction of the conductive diamond member, and the resistivity of the conductive diamond member may be 1000 Ω·cm or less.

[0014] According to this, the conductive diamond member is very thin and small enough, so that the diamond electrode including the conductive diamond member can be used as a probe for a minute part, an electrochemical biosensor, and a probe for supplying electricity to a cell. Furthermore, when the diamond electrode is used for intracellular measurement, it can detect biological substances with high sensitivity.

[0015] (3) In the above (2), the ratio L / D of the length L of the first region along the extension direction to D may be equal to or greater than 1. This allows the probe to be inserted deep into the measurement sample, increasing the contact area with the measurement sample and improving the sensitivity of the diamond electrode.

[0016] (4) In any of the above (1) to (3), the conductive diamond member includes a first end portion on the metal member side and a second end portion opposite the first end portion, and the diameter d2 of the largest inscribed circle on the second end portion side is smaller than the diameter d1 of the largest inscribed circle on the first end portion side, and the diameter d2 may be 0.05 mm or less. The diameters d1 and d2 are measured by observing the conductive diamond member from the side.

[0017] According to this, since the conductive diamond member is sufficiently small, a diamond electrode including the diamond member can be used as a probe for a minute part, an electrochemical biosensor, and a probe for supplying electricity to a cell.

[0018] (5) In any one of the above (1) to (4), the conductive diamond member may be made of diamond, and the boron content of the diamond may be 10 ppm or more and 50,000 ppm or less.

[0019] This improves the electrical conductivity of the conductive diamond member, allowing it to function as a sensor.

[0020] (6) In any one of the above (1) to (5), the Raman spectrum of the conductive diamond member has a wave number of 1320 cm －１ 1340cm or more －１ The full width at half maximum that exists below is 20 cm －１ The wave number 1545 cm for the peak intensity I3 of the following peak －１ More than 1600cm －１ The full width at half maximum that exists below is 50 cm －１ The percentage (I2 / I3)×100 of the peak intensity I2 of the peak exceeding may be 30% or less.

[0021] According to this, the diamond electrode including the conductive diamond member has a small leakage current and an improved detection sensitivity.

[0022] (7) In any of the above (1) to (6), the angle between the extension direction of the conductive diamond member and the extension direction of the metal member may be 5° or less, and the connection portion between the conductive diamond member and the metal member may be covered with an insulating member.

[0023] This is suitable for observing only the electrochemical properties of diamond, without including the electrochemical properties of other materials.

[0024] (8) In any of the above (1) to (7), the metal member may be pipe-shaped. In this case, the conductive diamond member can be inserted into the through-hole of the metal member to connect them. In other words, a thin rod-shaped diamond and a thin rod-shaped metal can be firmly connected.

[0025] (9) In the above (7), the insulating member may be made of polyimide, which allows a thin insulating member to be formed so as to achieve electrical insulation at a low temperature of 300° C. or less.

[0026] (10) In the above (7), the insulating member may be made of a cross-linked fluororesin. This allows a thin insulating member to be formed so as to achieve electrical insulation at a low temperature of 300° C. or less. Furthermore, the insulating member can maintain its durability even in strong acidic or alkaline environments.

[0027] (11) In any of the above (7), (9), and (10), the insulating member may have an average thickness of 5 μm to 50 μm, which allows the electrode to maintain electrical insulation at approximately 10 V or less and maintain a rod-like shape with a similar thinness to that of a rod-shaped electrode not covered with an insulating member.

[0028] (12) In any of the above (1) to (11), the conductive diamond member may be made of single-crystal diamond. This allows for a higher electrical conductivity than polycrystalline diamond, even if the impurity content is the same as that of polycrystalline diamond. This is because single-crystal diamond can avoid the loss of carriers supplied by acceptor impurities and donor impurities due to grain boundaries, and can avoid an increase in electrical resistance due to contact resistance.

[0029] (13) In any of (1) to (11) above, the conductive diamond member may be made of polycrystalline diamond, and the average grain size of the polycrystalline diamond may be larger than the diameter d2 of the largest inscribed circle at the second end side opposite to the first end side of the conductive diamond member on the metal member side.

[0030] This makes the diamond at the tip on the second end side almost a single crystal, and for the same reason as in (12) above, the electrical conductivity can be increased.

[0031] (14) In any of the above (1) to (11), the conductive diamond member may be made of nano-polycrystalline diamond. This makes the strength of the center of the rod-shaped diamond stronger than that of a single crystal, which is easily cleaved, and makes it possible to produce a strong rod-shaped diamond electrode that will not break even when pierced into a solid such as a cell.

[0032] [Details of the embodiment of the present disclosure] Specific examples of the diamond electrode of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same parts or corresponding parts. In addition, the dimensional relationship of length, width, thickness, depth, etc. has been changed appropriately for the purpose of clarifying and simplifying the drawings, and does not necessarily represent the actual dimensional relationship.

[0033] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0034] In the present disclosure, when one or more numerical values ​​are recited as the lower limit and the upper limit of a numerical range, a combination of any one numerical value recited as the lower limit and any one numerical value recited as the upper limit is also considered to be disclosed. For example, when a1 or more, b1 or more, and c1 or more are recited as the lower limit and a2 or less, b2 or less, and c2 or less are recited as the upper limit, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are considered to be disclosed.

[0035] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0036] [Embodiment 1] A diamond electrode according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figs. 1, 2A and 2B.

[0037] As shown in FIG. 1 , the diamond electrode 1 comprises a rod-shaped conductive diamond member 2 and a rod-shaped metal member 3 electrically connected to the conductive diamond member 2, and the conductive diamond member 2 has a diamond content of 80% or more by volume. The phrase "80% or more by volume" indicates that the conductive diamond member is composed almost entirely of conductive diamond, with other materials accounting for less than 20% by volume. For example, if the cross section of a rod-shaped diamond member is observed to contain less than 20% by area of ​​materials other than conductive diamond, it is highly likely that the "diamond content of the conductive diamond member is 80% or more by volume." Strictly speaking, the integral value along the rod direction is the volume percentage. While diamond coating on a rod-shaped material can produce a diamond content of less than 80% by volume, this method cannot produce the diamond electrode of the present invention in which the "diamond content of the conductive diamond member is 80% or more by volume." This is because it does not result in the fine electrodes that the present invention applies to.

[0038] The diamond electrode of the present disclosure has a diamond content of 80% by volume or more in the diamond member, and can have the excellent properties of diamond, and therefore can have excellent CV characteristics.

[0039] <Structure> The diamond electrode 1 of embodiment 1 comprises a rod-shaped conductive diamond member 2 and a rod-shaped metal member 3 electrically connected to the conductive diamond member 2. The metal member 3 is pipe-shaped with a through-hole extending from one end to the other, and a portion of the first end 2a of the conductive diamond member 2 is inserted into the through-hole at one end (hereinafter also referred to as the third A end) of the metal member 3. The pipe-shaped metal member enables a strong connection with the rod-shaped conductive diamond. Furthermore, the strength can be adjusted by adjusting the length of the connection portion. A brazing filler metal 5 is disposed between the metal member 3 and the conductive diamond member 2. The brazing filler metal is in contact with both the metal member 3 and the conductive diamond member 2, electrically connecting the metal member 3 and the conductive diamond member 2. The pipe-shaped metal member enables an electrical connection with low contact resistance. The length of the connection portion can also be adjusted to further reduce contact resistance. The first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3 may be in contact. The connection portion between the conductive diamond member 2 and the metal member 3 is covered with an insulating member 4. The conductive diamond member is in contact with the metal member, which is preferable because it allows the entire diamond electrode to be kept thin. Although there is a drawback in that the strength of the connection portion is insufficient, by cutting both rod-shaped members obliquely rather than vertically to increase the cross-sectional area, the connection strength can be compensated for and the contact resistance can be reduced. Here, the expression "rod-shaped" also includes needle-shaped members whose tips gradually become thinner. This is because in actual applications, it is effective for the conductive diamond member to be needle-shaped.

[0040] The angle between the extension direction of the conductive diamond member 2 and the extension direction of the metal member 3 (hereinafter also referred to as the "connection angle") may be 5° or less. It is often desirable to deliver this diamond electrode straight to the sensing portion. It is important that the remaining portion follows the trajectory of the tip. Therefore, the smaller the connection angle, the better. If the connection angle is 5° or less, when the conductive diamond member is 5 mm long, the deviation is within 0.43 mm (the deviation (deviation) between the end of the diamond member side and the end of the metal member side when viewing the diamond electrode from the second end 2b side of the conductive diamond member). If the angle is 3° or less, the deviation is within 0.26 mm. If the angle is 1° or less, the deviation is within 0.087 mm. If the deviation is 0.5 mm or more, it is difficult to aim at the measurement site, making it difficult to achieve the desired measurement.

[0041] <Conductive Diamond Member> In the present disclosure, the conductive diamond member 2 has a diamond content of 80 volume % or more. This allows the conductive diamond member to have the excellent properties of diamond, and therefore excellent CV characteristics.

[0042] The lower limit of the diamond content of the conductive diamond member is 80 vol% or more, preferably 85 vol% or more, more preferably 90 vol% or more, more preferably 95 vol% or more, and even more preferably 98 vol% or more. The upper limit of the diamond content of the conductive diamond member is preferably 100 vol% or less. The diamond content of the conductive diamond member is preferably 80 vol% or more and 100 vol% or less, more preferably 90 vol% or more and 100 vol% or less, and even more preferably 98 vol% or more and 100 vol%. Conventionally, it has been proposed to grow diamond on a rod-shaped metal to produce a rod-shaped diamond, but in this case, the diamond content is less than 80 vol%. If the diamond content is low, pinholes may occur in the diamond coating, which may reveal the characteristics of the metal member, resulting in deterioration of the characteristics. This can be prevented by setting the content to 80 vol% or more.

[0043] The method for measuring the diamond content of a conductive diamond member is as follows. The conductive diamond member is cut at 10 locations, and the 10 cross sections are subjected to elemental analysis to classify them into areas consisting of carbon atoms (carbon areas) and areas containing atoms other than carbon (non-carbon areas). The percentage A of the total area of ​​the carbon areas of the 10 cross sections relative to the total area of ​​the 10 cross sections is calculated. Percentage A corresponds to the diamond content of the conductive diamond member. The 10 locations can be calculated by selecting approximately equal cross-sectional areas, including 10 μm portions from both ends of the conductive diamond member. Cutting is performed using a laser, but since the diamond portions are transformed into non-diamonds, measurement is required after a process to remove the non-diamonds. Specifically, the removal process is performed in a heated mixed acid solution made by heating a mixed acid of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1.

[0044] In most cases, the carbon area is almost entirely made of diamond, but if there is also a portion of the carbon area that is not diamond, the diamond content of the conductive diamond member is measured by separating the area into diamond and non-diamond areas by Raman spectroscopy instead of elemental analysis. Specifically, a cross section of the conductive diamond member is prepared by laser cutting and polishing, and Raman spectroscopy is measured to obtain a diamond content of 1332±2 cm －１ By dividing the area into areas where a peak exists and areas where no peak exists and creating a two-dimensional distribution, it is possible to obtain a distribution where diamonds exist, and by averaging the area ratio (area where diamonds exist / total area) at five different locations, the diamond content (volume fraction) of the conductive diamond member can be determined.

[0045] The conductive diamond member may be composed of diamond and unavoidable impurities. Examples of the unavoidable impurities include silicon, aluminum, molybdenum, tungsten, tantalum, iron, nickel, and cobalt. The content of the unavoidable impurities is preferably 100 ppm atomic density or less. The content of the unavoidable impurities is measured by secondary ion mass spectrometry (SIMS).

[0046] Examples of components other than diamond contained in the conductive diamond member include tungsten, tantalum, iron, nickel, and cobalt.

[0047] The resistivity of the conductive diamond member is preferably 1000 Ω·cm or less. This improves the sensitivity of the diamond electrode. When the diamond electrode is used for intracellular measurement, it can detect biological substances with high sensitivity.

[0048] The upper limit of the resistivity of the conductive diamond member is preferably 1000 Ω cm or less, more preferably 100 Ω cm or less, more preferably 10 Ω cm or less, more preferably 1 Ω cm or less, more preferably 0.1 Ω cm or less, and even more preferably 0.01 Ω cm or less. The lower limit of the resistivity of the conductive diamond member is not particularly limited, but can be, for example, 0.0001 Ω cm or more. The resistivity of the conductive diamond member is preferably 0.0001 Ω cm or more to 1000 Ω cm or less, more preferably 0.0001 Ω cm or more to 10 Ω cm or less, more preferably 0.0001 Ω cm or more to 0.1 Ω cm or less, and even more preferably 0.0001 Ω cm or more to 0.01 Ω cm or less.

[0049] As shown in Fig. 2A, the conductive diamond member 2 includes a first region 21 exposed to the outside, and the maximum diameter D of the circumscribing circle C1 of the cross section of the first region 21 is preferably 0.3 mm or less. Here, the cross section is a cross section when the first region is cut by a plane having a normal to the extension direction of the diamond member from the first end 2a to the second end 2b of the conductive diamond member. According to this, since the diamond member is sufficiently small, a diamond electrode including the diamond member can be used as a probe for a minute part, an electrochemical biosensor, and a probe for supplying electricity to a cell.

[0050] For example, when cells are measured using the diamond electrode, local information can be collected without destroying the cells, allowing accurate measurement of the correlation between diseases and substances in the body.

[0051] The upper limit of the maximum value D is preferably 0.3 mm or less, more preferably 0.1 mm or less, and even more preferably 0.075 mm or less. The lower limit of the maximum value D is not particularly limited, but from the viewpoint of manufacturing, it can be set to, for example, 0.01 mm or more. The maximum value D is preferably 0.01 mm or more and 0.3 mm or less, more preferably 0.01 mm or more and 0.1 mm or less, and even more preferably 0.01 mm or more and 0.075 mm or less.

[0052] The maximum value D is measured by observing the cross section of the first region 21 with an optical microscope or a scanning electron microscope.

[0053] It is preferable that the ratio L / D of the length L along the extension direction of the first region 21 (the direction indicated by the arrow A1 in FIG. 1 ) to the maximum value D is equal to or greater than 1. This allows the probe to be inserted deep inside the measurement sample, increasing the contact area with the measurement sample and improving the sensitivity of the diamond electrode.

[0054] The lower limit of the ratio L / D is preferably 1 or more, more preferably 3 or more, more preferably 5 or more, more preferably 8 or more, and even more preferably 10 or more. The upper limit of the ratio L / D is not particularly limited, but from the viewpoint of production, it can be, for example, 20 or less. The ratio L / D is preferably 1 or more and 20 or less, more preferably 3 or more and 20 or less, more preferably 5 or more and 20 or less, and even more preferably 10 or more and 20 or less.

[0055] The lower limit of the length L is preferably 0.01 mm or more, more preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.0 mm or more. The upper limit of the length L is not particularly limited, but may be set to, for example, 20 mm or less from the viewpoint of manufacturing. The length L is preferably 0.01 mm or more and 20 mm or less, more preferably 0.1 mm or more and 10 mm or less, and even more preferably 1.0 mm or more and 5.0 mm or less.

[0056] 2B, the conductive diamond member 2 includes a first end 2a on the metal member 3 side and a second end 2b opposite to the first end 2a, and the diameter d2 of the largest inscribed circle C2 on the second end 2b side is smaller than the diameter d1 of the largest inscribed circle C3 on the first end 2a side, and the diameter d2 is preferably 0.1 mm or less, more preferably 0.05 mm or less, and even more preferably 0.03 mm or less. According to this, since the diamond member is sufficiently small, a diamond electrode including the diamond member can be used as a probe for a minute part, an electrochemical biosensor, and a probe for supplying electricity to a cell.

[0057] Here, the diameters d1 and d2 are measured by observing the conductive diamond member 2 from the side. The maximum inscribed circle C2 on the second end 2b side of the conductive diamond member 2 means the largest circle that can be drawn within the area surrounded by the outer edge of the conductive diamond member 2 when the second end 2b side of the conductive diamond member 2 is observed from the side. The maximum inscribed circle C3 on the first end 2a side of the conductive diamond member 2 means the largest circle that can be drawn within the area surrounded by the outer edge of the conductive diamond member 2 when the first end 2a side of the conductive diamond member 2 is observed from the side. If the size of the maximum inscribed circle C2 varies depending on the direction in which the conductive diamond member 2 is observed, the diameters d1 and d2 are measured in the direction in which the diameter of the maximum inscribed circle C2 is largest.

[0058] The upper limit of the diameter d2 is preferably 0.05 mm or less, more preferably 0.03 mm or less, and even more preferably 0.01 mm or less. The lower limit of the diameter d2 is not particularly limited, but may be set to 0.0001 mm or more from the viewpoint of manufacturing, for example. The diameter d2 is preferably 0.0001 mm or more and 0.05 mm or less, more preferably 0.0005 mm or more and 0.03 mm or less, and even more preferably 0.001 mm or more and 0.01 mm or less.

[0059] The diameter d1 is preferably 0.05 mm or more and 0.3 mm or less, more preferably 0.05 mm or more and 0.2 mm or less, and even more preferably 0.05 mm or more and 0.1 mm or less.

[0060] The cross-sectional area of ​​the conductive diamond member 2 may be constant or may decrease monotonically from the first end 2a to the second end 2b. From the viewpoint of manufacturing, it is preferable that it decreases monotonically, and from the viewpoints of structural strength and use, it is more preferable that it is constant from the first end 2a of length L to a predetermined position between the first end 2a and the second end 2b, and then decreases monotonically from the predetermined position to 2b. Here, the cross-sectional area is the area of ​​the cross section exposed when cut along a plane having a normal line extending from the first end 2a to the second end 2b.

[0061] The shape of the conductive diamond member is not particularly limited as long as it can be used as an electrode, and may be, for example, a cone, a truncated cone, an elliptical cone, a truncated elliptical cone, a pyramid, or a truncated pyramid.

[0062] The conductive diamond member is made of diamond, and the boron content of the diamond is preferably 10 ppm or more and 50,000 ppm or less. This improves the electrical conductivity of the conductive diamond member. The boron content of the diamond is preferably 10 ppm or more and 50,000 ppm or less, more preferably 200 ppm or more and 50,000 ppm or less, and even more preferably 2,000 ppm or more and 50,000 ppm or less. Here, the conductive diamond member can contain impurities other than diamond within a range that does not impair the effects of the present disclosure.

[0063] The boron content of the diamond is measured by secondary ion mass spectrometry (SIMS).

[0064] The conductive diamond member may be mainly made of diamond. In the Raman spectrum of the conductive diamond member, －１ 1340cm or more －１ The full width at half maximum that exists below is 20 cm －１ The wave number 1545 cm for the peak intensity I3 of the following peak －１ More than 1600cm －１ The full width at half maximum that exists below is 50 cm －１The percentage (I2 / I3) x ​​100 of the peak intensity I2 of the peak exceeding the wavenumber 1320 cm is preferably 30% or less. A diamond electrode including the conductive diamond member has a small leakage current and improved detection sensitivity. －１ 1340cm or more －１ The full width at half maximum that exists below is 20 cm －１ The following peak is derived from diamond: Wavenumber 1545 cm －１ More than 1600cm －１ The full width at half maximum that exists below is 50 cm －１ The peaks exceeding this are thought to be peaks derived from graphite-like structures. The excitation laser for Raman spectroscopy is typically 530 nm, with an objective lens of 20x or more and a laser power density of 9x10 ６ W / cm ２ It is preferable to measure under the following conditions.

[0065] The upper limit of the percentage (I2 / I3) x ​​100 is preferably 30% or less, preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit of the percentage (I2 / I3) x ​​100 is not particularly limited, but can be, for example, 0% or more. The percentage (I2 / I3) x ​​100 is preferably 0% or more and 30% or less, more preferably 0% or more and 10% or less, and even more preferably 0% or more and 5% or less.

[0066] The Raman spectrum is measured using a micro-Raman spectrometer at room temperature (20° C. to 25° C.) using a laser with a wavelength of 532 nm as excitation light.

[0067] The angle between the extension direction of the conductive diamond member 2 and the extension direction of the metal member 3 is preferably 5° or less. That is, the diamond electrode 1 is preferably rod-shaped as a whole. This makes it suitable for straight insertion into a minute part such as a cell or for insertion through a narrow gap. The angle is more preferably 0° or more and 2° or less, and even more preferably 0° or more and 1° or less.

[0068] The conductive diamond member is preferably made of single crystal diamond, which is suitable for increasing electrical conductivity compared to polycrystalline diamond even with the same amount of impurities.

[0069] The conductive diamond member is made of polycrystalline diamond, and the average grain size of the polycrystalline diamond may be larger than the diameter d2 of the largest inscribed circle at the second end side opposite to the first end side of the conductive diamond member on the metal member side. In this way, the tip portion on the second end side 2b of the conductive diamond member becomes almost a single crystal, which is suitable for increasing the electrical conductivity compared to when the conductive diamond member is made of polycrystalline diamond with a grain size smaller than the diameter d2, even with the same amount of impurities.

[0070] The conductive diamond member is preferably made of nano-polycrystalline diamond, which is suitable for maintaining high mechanical strength of the thin conductive diamond member, because if a single crystal diamond is used, the thin conductive diamond member may cleave and not maintain the required strength.

[0071] The average particle size of the nano-polycrystalline diamond is preferably 5 nm or more and 2000 nm or less, more preferably 10 nm or more and 500 nm or less, and even more preferably 20 nm or more and 100 nm or less.

[0072] The average grain size of nano-polycrystalline diamond can be determined by a cross-section method using a scanning electron microscope (SEM). Specifically, the nano-polycrystalline diamond is first observed using a scanning electron microscope at a magnification of 1,000 to 100,000 times to obtain an SEM image.

[0073] Next, a circle is drawn on the SEM image, and eight straight lines are drawn radially from the center of the circle (so that the intersecting angles between each line are approximately equal) to the periphery of the circle. In this case, the observation magnification and the diameter of the circle are preferably set so that the number of diamond particles (crystal particles) placed on each line is approximately 10 to 50.

[0074] Next, count the number of crossings of the grain boundary of diamond grains for each of the above-mentioned straight lines, and calculate the average intercept length by dividing the length of the straight line by the number of crossings, and multiply this average intercept length by 1.128 to obtain the value that is the first average grain size.In addition, calculate the first average grain size for each of the five SEM images by the above-mentioned procedure, and the average value of these first average grain sizes is the average grain size.

[0075] <Metal Member> In the present disclosure, the metal member 3 is electrically connected to the conductive diamond member 2. The metal member 3 and the conductive diamond member 2 may be in contact with each other, or may be electrically connected via a brazing material 5. As the brazing material, for example, silver paste, solder, silver solder, etc. may be used.

[0076] The material of the metal member 3 is preferably a stainless steel wire, a tungsten wire, or the like, which has enough strength to stand on its own even with a diameter of 0.1 mm, is corrosion-resistant, and is easy to process.

[0077] The metal member 3 in embodiment 1 is pipe-shaped. This allows the conductive diamond member 2 to be inserted into the through-hole of the metal member 3. The shape of the metal member is not limited to a pipe-shaped one. For example, only one end side of the metal member 3 may have a hollow structure with a hole formed therein into which the conductive diamond member can be inserted, and the other end side may have a solid structure. The outer shape of the metal member is not limited to a cylinder. For example, it may be a truncated cone, an elliptical cone, an elliptical truncated cone, a pyramid, or a truncated pyramid.

[0078] The size of the step at the connection part between the metal member 3 and the conductive diamond member 2 is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. This makes it possible to smoothly connect the metal member 3 and the conductive diamond member 2 to form a single rod-like member, that is, to obtain the effect that when piercing a cell or the like, the step does not get caught and can be inserted without resistance. Here, the size of the step corresponds to half the difference between the outer diameter of the metal member 3 and the outer diameter of the conductive diamond member 2. If the step is within the above numerical range, the insulating member 4 can be connected smoothly without interruption.

[0079] <Insulating member> The connection portion between the conductive diamond member 2 and the metal member 3 is covered with an insulating member 4. Here, the connecting portion is the portion where the above-mentioned step between the conductive diamond member 2 and the metal member 3 occurs. This has the effect of preventing the metal member 3 from being exposed to the outside and preventing electrochemical current from being generated in the metal member 3. In addition, the insulating member smoothly connects the step between the conductive diamond member 2 and the metal member 3, and has the effect of forming a smooth connecting portion. The insulating member may cover more than half of the extension direction of the conductive diamond member 2 from the connection portion of the step, or may cover more than half of the extension direction of the metal member 3. As long as the structure is such that only the conductive diamond member 2 comes into contact with the electrolyte to be measured and the metal member 3 does not come into direct contact with it and is insulated, the length of the insulating member can be appropriately set based on the design of the measuring device.

[0080] Examples of materials for the insulating member include polyimide, cross-linked fluororesin, and Teflon (registered trademark)-based resins. These materials may be used alone or in combination of two or more.

[0081] The insulating member is preferably made of polyimide. This allows it to be formed at a lower temperature and reduces residual coating even when the insulating member is thin. The insulating member is preferably made of cross-linked fluororesin. This allows it to be formed at a higher temperature and achieves the benefits of acid and alkali resistance even when the insulating member is thickly coated. Cross-linked fluororesin refers to a fluororesin whose adhesion has been improved using electron beam irradiation or the like, or a resin in which the CF molecular chains in the fluororesin are branched and cross-linked.

[0082] The average thickness of the insulating member is preferably 5 μm or more and 50 μm or less, which ensures insulation at a potential of 10 V and provides the effect of smoothly covering the steps between the conductive diamond member 2 and the metal member 3. The average thickness of the insulating member is more preferably 10 μm or more and 40 μm or less, and even more preferably 10 μm or more and 30 μm or less.

[0083] The average thickness of the insulating member is measured as follows: In a cross section obtained by cutting the region where the metal member of the diamond electrode and the insulating member covering the metal member are present along an imaginary plane normal to the direction in which the metal member extends, the overall outer diameter of the insulating member covering the metal member 3 and the outer diameter of the metal member 3 are observed with a micrometer or microscope, and the average thickness is calculated from half the difference between them.

[0084] <Method for Manufacturing Diamond Electrode> The method for manufacturing a diamond electrode according to the first embodiment will be described with reference to FIG. 1 and FIGS. 3A to 3E.

[0085] A diamond plate 20 made of conductive diamond is prepared (see FIG. 3A). The diamond plate 20 can be fabricated, for example, by synthesizing a boron-doped polycrystalline diamond with a thickness of 50 μm to 500 μm on a silicon substrate using a conventional CVD method and then removing the silicon substrate. Alternatively, the diamond plate 20 can be fabricated by epitaxially growing Ir or Pt on a single-crystal sapphire or single-crystal MgO substrate, synthesizing a heterojunction boron-doped single-crystal diamond thereon, and then removing the heterosubstrate. Alternatively, the diamond plate can be fabricated by homoepitaxially growing a boron-doped single-crystal diamond on an insulating single-crystal diamond substrate and then laser-separating the seed substrate single-crystal diamond. The diamond content of the resulting diamond plate is 100% by volume. The average thickness of the diamond plate is preferably 50 μm to 500 μm. The diamond plate may be homoepitaxial single-crystal diamond, heteroepitaxial diamond, or polycrystalline diamond. The diamond content of the diamond plate is not limited to 100% by volume, but can be, for example, 80% by volume or more. In this case, components other than diamond contained in the diamond plate include, for example, tungsten, tantalum, iron, nickel, cobalt, and silicon.

[0086] With the CVD method, the diamond content of the diamond plate can be 100% by volume, but with sintered diamonds, the diamond content can be 80% by volume due to the inclusion of a binder metal. In either case, diamond is the main component, and the bonding between the diamonds is the main factor, resulting in high bond strength. The binder metal can also be surface-treated to prevent it from being exposed on the surface. On the other hand, when diamonds are synthesized using the CVD method with a metal wire at the center, the diamond content is generally less than 80% by volume. The bond between diamonds deposited using the CVD method is not necessarily strong. Metal is exposed at weak points, resulting in deterioration of electrochemical properties over long periods of use.

[0087] Next, the diamond plate 20 is cut out by laser processing to obtain a rod-shaped conductive diamond member 2 (see FIG. 3B). The laser irradiation conditions can be, for example, a focused beam diameter of 3 to 50 μm and a pulse energy of 10 to 50 μJ.

[0088] A metal member 3 is prepared (see FIG. 3C). In the manufacturing method of the first embodiment, the metal member 3 has a pipe shape.

[0089] Next, the through hole on one end side of the metal member 3 is filled with brazing filler metal 5 (see FIG. 3D). The brazing filler metal may be filled by pushing it in from the hole on the opposite side, or by suction from the hole on the opposite side. It is preferable to wipe off any brazing filler metal other than the brazing filler metal filled in the hole.

[0090] Next, the conductive diamond member 2 is inserted into the end of the metal member 3 filled with the brazing material 5. This electrically connects the conductive diamond member 2 and the metal member 3 via the brazing material 5, and also fixes the conductive diamond member 2 to the metal member 3. The brazing material melts and firmly joins the conductive diamond member 2 and the metal member 3 when heated at a predetermined temperature. The brazing material may be activated silver brazing, as the Ti activator bonds them more firmly. Alternatively, the brazing material may be Ag or Cu powder, as this bonds them by sintering at a predetermined temperature without melting. However, it is essential that the predetermined temperature be below the melting point of the metal member 3.

[0091] Next, the connection portion between the metal member 3 and the conductive diamond member 2 is covered with an insulating member 4, thereby obtaining the diamond electrode 1 of the first embodiment (see FIG. 1).

[0092] The insulating member 4 is preferably formed by spray coating. It is more preferable to subject the insulating member formed by spray coating to a heat treatment at 100° C. or higher.

[0093] [Embodiment 2] A diamond electrode according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") will be described with reference to Fig. 4. As shown in Fig. 4, the diamond electrode 1 comprises a rod-shaped conductive diamond member 2 and a rod-shaped metal member 3 electrically connected to the conductive diamond member 2, and the diamond content of the conductive diamond member 2 is 80% by volume or more.

[0094] The diamond electrode 1 of embodiment 2 can basically have the same configuration as embodiment 1, except for the structure of the metal member 3 and the method of connecting the conductive diamond member 2 and the metal member 3. Below, we will explain the differences from embodiment 1.

[0095] In the diamond electrode 1 of embodiment 2, the metal member 3 is solid and rod-shaped, and includes a third A end 3a located on the conductive diamond member 2 side and a third B end 3b opposite the third A end 3a. The first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3 face each other. A brazing filler metal 5 is disposed between the first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3. The brazing filler metal 5 contacts both the metal member 3 and the conductive diamond member 2, electrically connecting the metal member 3 and the conductive diamond member 2. A portion of the first end 2a of the conductive diamond member 2 and a portion of the third A end 3a of the metal member 3 may contact each other. In FIG. 4, the conductive diamond member 2 and the metal member 3 are depicted as being joined at a surface approximately perpendicular to the axial direction. However, both may have surfaces oblique to the axial direction and be joined at an oblique surface. This is more preferable because it increases the joining area, thereby increasing the joining strength and electrical conductivity of the joint. Here, even if the surfaces to be joined are inclined with respect to the axial direction, it is preferable that the axial direction of the diamond member 2 and the axial direction of the metal member 3 when joined are within 5° and are substantially straight.

[0096] The diameter of the metal member 3 can be set appropriately depending on the application. For example, it is preferably 0.01 mm or more and 0.3 mm or less, more preferably 0.02 mm or more and 0.2 mm or less, and even more preferably 0.03 mm or more and 0.1 mm or less. If it is less than 0.01 mm, the rigidity of the metal member 3 itself becomes too small, making it impossible to push the diamond member 2 forward from the rear, which is not preferable. If it is greater than 0.3 mm, it becomes difficult to insert it through gaps in minute parts such as cells.

[0097] The angle formed between the extending direction of the conductive diamond member 2 and the extending direction of the metal member 3 is 5° or less.

[0098] The brazing material 5 can further cover the outer peripheral surface near the first end 2a of the conductive diamond member 2 and the outer peripheral surface near the 3A end 3a of the metal member 3. Here, the outer peripheral surface near the first end 2a means a region on the outer peripheral surface of the conductive diamond member 2 that is a distance from the first end 2a within 0.9 times, more preferably within 0.3 times, and even more preferably within 0.1 times the length of the conductive diamond member 2. The vicinity of the 3A end 3a means a region on the outer peripheral surface of the metal member 3 that is a distance from the 3A end 3a within 0.9 times, more preferably within 0.3 times, and even more preferably within 0.1 times the length of the metal member 3.

[0099] The diamond electrode 1 of the second embodiment can further include an insulating member 4 that covers the connection portion between the conductive diamond member 2 and the metal member 3. In FIG. 4, the insulating member 4 covers the entire brazing material 5.

[0100] <Method for Manufacturing Diamond Electrode> The method for manufacturing a diamond electrode according to the second embodiment will be described with reference to FIG. 4 and FIGS. 5A to 5C.

[0101] A conductive diamond member 2, a metal member 3, and a connection assistant 8 are prepared (see FIG. 5A). The conductive diamond member 2 is prepared by the method described in the manufacturing method of embodiment 1. The metal member 3 is prepared as a solid rod made of metal.

[0102] The connection aid 8 is cylindrical with a through hole extending from one end to the other. The material of the connection aid 8 can be, for example, Teflon (registered trademark), resin, or Aron ceramic. This is because it can be removed in a subsequent process without damaging the diamond member or the metal member. The cross-sectional size of the through hole when cut along a plane normal to the extension direction of the through hole is not particularly limited, as long as it is large enough to allow the insertion of the conductive diamond member 2 and the metal member 3 and to provide the brazing material 5 on the outer peripheral surfaces of each of the conductive diamond member 2 and the metal member 3. The cross-sectional size of the through hole is preferably 1.1 to 1.5 times the larger of the cross-sectional areas of the first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3. The brazing material 5 is filled into the through hole of the connection aid 8.

[0103] Next, the conductive diamond member 2 is inserted into the through-hole at one end of the connection aid 8 filled with the brazing material 5. The metal member 3 is inserted into the through-hole at the other end of the connection aid 8 (see FIG. 5B). At this time, it is preferable to remove the brazing material 5 that protrudes from the through-hole.

[0104] After the brazing material 5 has hardened, or after heat treatment to harden it, the connection aid 8 is removed (see FIG. 5C). The connection aid 8 can be removed by physically sliding it if a material that does not adhere to the connection aid is used, or by burning it in oxygen, or by soaking it in water.

[0105] The brazing material 5 is covered with the insulating member 4 to obtain the diamond electrode 1 of the second embodiment (see FIG. 4).

[0106] [Embodiment 3] A diamond electrode according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 3") will be described with reference to Fig. 6. As shown in Fig. 6, the diamond electrode 1 comprises a rod-shaped conductive diamond member 2 and a rod-shaped metal member 3 electrically connected to the conductive diamond member 2, and the diamond content of the conductive diamond member 2 is 80% by volume or more.

[0107] The diamond electrode 1 of the third embodiment can basically have the same configuration as that of the second embodiment.

[0108] <Method for Manufacturing Diamond Electrode> A method for manufacturing a diamond electrode according to the third embodiment will be described with reference to FIGS. 6, 7A, and 7B.

[0109] A conductive diamond member 2, a metal member 3, and a brazing material 5 are prepared (see FIG. 7A). The first end 2a of the conductive diamond member and the third A end 3a of the metal member 3 are opposed to each other with the brazing material 5 interposed therebetween. At this time, the first end 2a and the third A end 3a are arranged so as to be in contact with the brazing material 5.

[0110] The brazing material 5 is subjected to electrical discharge machining to join the conductive diamond member 2 and the metal member 3 (see FIG. 7B). An electrical discharge is generated between the conductive diamond member 2 and the metal member 3. The brazing material 5 is covered with the insulating member 4 to obtain the diamond electrode 1 of the third embodiment (see FIG. 6).

[0111] [Embodiment 4] A diamond electrode according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 4") will be described with reference to Fig. 8. As shown in Fig. 8, the diamond electrode 1 comprises a rod-shaped conductive diamond member 2 and a rod-shaped metal member 3 electrically connected to the conductive diamond member 2, and the diamond content of the conductive diamond member 2 is 80% by volume or more.

[0112] The diamond electrode 1 of embodiment 4 can have the same configuration as embodiment 1 except for the structure of the metal member 3 and the method of connecting the conductive diamond member 2 and the metal member 3. Below, the differences from embodiment 1 will be described.

[0113] In the diamond electrode 1 of embodiment 4, the metal member 3 is solid and rod-shaped, and includes a third A end 3a arranged on the conductive diamond member 2 side, and a third B end 3b opposite the third A end 3a. The first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3 face each other. An adhesive 6 is arranged between the first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3. The adhesive 6 is in contact with both the metal member 3 and the conductive diamond member 2, and physically connects the metal member 3 and the conductive diamond member 2. A portion of the first end 2a of the conductive diamond member 2 and a portion of the third A end 3a of the metal member 3 may be in contact.

[0114] The adhesive 6 can further cover the outer peripheral surface near the first end 2a of the conductive diamond member 2 and the outer peripheral surface near the 3A end 3a of the metal member 3. Here, the outer peripheral surface near the first end 2a means a region on the outer peripheral surface of the conductive diamond member 2 that is a distance from the first end 2a within 0.9 times, more preferably within 0.3 times, and even more preferably within 0.1 times the length of the conductive diamond member 2. The vicinity of the 3A end 3a means a region on the outer peripheral surface of the metal member 3 that is a distance from the 3A end 3a within 0.9 times, more preferably within 0.3 times, and even more preferably within 0.1 times the length of the metal member 3.

[0115] The diamond electrode 1 of embodiment 4 further includes a metal coating 7 that continuously covers a portion of the first end 2a side of the conductive diamond member 2, the adhesive 6, and a portion of the third A end 3a side of the metal member 3. The metal coating 7 is in contact with the conductive diamond member 2, the adhesive 6, and the metal member 3. Thus, the conductive diamond member 2 and the metal member 3 are electrically connected by the metal coating 7. The metal coating 7 can be made of gold, platinum, titanium, zirconium, niobium, molybdenum, tungsten, or the like.

[0116] The diamond electrode 1 of embodiment 4 may further include an insulating member 4 that covers the conductive diamond member 2, adhesive 6, and metal member 3. In Fig. 8, the insulating member 4 covers all of the conductive diamond member 2, adhesive 6, and metal member 3.

[0117] <Method for Manufacturing Diamond Electrode> A method for manufacturing a diamond electrode according to the fourth embodiment will be described with reference to FIG. 8 and FIGS. 9A to 9C.

[0118] A conductive diamond member 2, a metal member 3, and an adhesive 6 are prepared (see FIG. 9A). The first end 2a of the conductive diamond member 2 and the third A end 3a of the metal member 3 are placed opposite each other with the adhesive 6 sandwiched therebetween. At this time, the first end 2a and the third A end 3a are placed so as to be in contact with the adhesive 6 (see FIG. 9B).

[0119] After the conductive diamond member 2 and the metal member 3 are fixed with the adhesive 6, a metal coating 7 is formed so as to continuously cover a part of the first end 2a side of the conductive diamond member 2, the adhesive 6, and a part of the third A end 3a side of the metal member 3 (see FIG. 9C ). The metal coating 7 can be formed by sputtering, electron beam evaporation, or the like. Since the purpose is electrical connection, one side is sufficient, but it may also be formed twice from both the front and back sides, or three times from three directions.

[0120] The conductive diamond member 2, the metal coating 7 and the metal member 3 are covered with the insulating member 4 to obtain the diamond electrode 1 of the fourth embodiment (see FIG. 8).

[0121] The following types of conductive diamond plates were prepared: one was a boron-doped polycrystalline diamond produced by CVD (Example 1), the second was a boron-doped single-crystal diamond produced by CVD (Example 2), and the third was a boron-doped nano-polycrystalline diamond produced by high-pressure (Example 3). These three conductive diamond plates were preferable because they allowed for the boron to be contained almost uniformly in the substrate. Furthermore, a conductive diamond plate made of sintered diamond was prepared (Example 4).

[0122] Example 1 In Example 1, conductive diamond plates made of polycrystalline diamond were prepared. The polycrystalline diamond used in each sample was synthesized by CVD on a silicon substrate, where boron-doped diamond was deposited to a thickness of 50 μm to 300 μm. The silicon substrate was then removed with nitric acid and fluorofluoride to create a free-standing boron-doped diamond plate. Diamond was produced by introducing methane gas into hydrogen and decomposing it in a microwave plasma. Alternatively, diamond could be produced by thermal decomposition using a hot filament heated to 2000°C. The boron impurity was added by adding trace amounts of trimethylboron. These methods are no different from conventional synthesis methods. A 10 mm square silicon substrate was used, allowing the production of conductive diamond plates of 10 mm square size. For the sample marked "W" in the "Other Materials" column of Table 1, thin tungsten (W) wires approximately 17 μm in diameter were partially embedded during diamond synthesis (Sample 19). In addition, strips of tungsten (W) with a width of 8 μm and a thickness of 2 μm, and strips of tungsten (W) with a width of 1 μm and a thickness of 0.1 μm were partially vapor-deposited and embedded inside the diamond (Sample 18, Sample 17). When the diamond was later laser-cut into thin needle-like shapes, these thin strips were embedded inside the needle-like diamond without being exposed on the surface. This structure provides flexibility to the diamond, preventing it from easily breaking. If W were exposed on the surface, its CV characteristics as a sensor would deteriorate. However, if W were to be exposed on the surface, additional CVD growth of diamond for a short period after cutting the diamond into needle-like shapes could cover the exposed W and completely embed it.

[0123] Next, a rod-shaped conductive diamond member was cut from the plate-shaped conductive diamond using a laser processing machine. A 50 μm width was cut from a diamond with a plate thickness of 50 μm, and a 100 μm width was cut from a diamond with a plate thickness of 100 μm. At this point, the width of the diamond to be cut could be adjusted according to the plate thickness to obtain a 50 μm square or 100 μm square prism rod, thereby adjusting the side length of the prism. Even if the cross section was not exactly square but trapezoidal, there was no significant problem. The length was 10 mm, the length of one side of the substrate. It was also possible to cut it to the desired length using a laser. To produce a rod with a diameter of 100 μm, a thickness of 70 μm and a width of 70 μm resulted in a diagonal length of 100 μm, and a rod with a circumscribed diameter of 100 μm could be produced.

[0124] Next, the rod was laser cut diagonally from one-third of the way down toward the tip, then rotated another 90° around its axis. The laser was then used to cut diagonally from one-third of the way down toward the tip. This resulted in a square pyramidal conductive diamond member with the tip at the apex. The tip had a tip diameter of 5 μm. By adjusting the laser cutting allowance, tip diameters of less than 5 μm could also be fabricated. By rotating a needle-shaped rod with a tip diameter of 5 μm further by 90° and etching it with an ion beam from two sides, the tip diameter could be sharpened to 0.7 μm. By varying the etching time from 20, 40, or 60 minutes, the tip diameter could be adjusted to 3 μm, 1.2 μm, or 0.7 μm.

[0125] After that, by treating the conductive diamond member with hot mixed acid treatment, ion beam etching, or hydrogen plasma treatment, the graphite components that had adhered during the laser processing could be removed. This was confirmed by taking the peak ratio of Raman spectroscopy.

[0126] Next, a 5cm long SUS pipe with an inner diameter matching the outer diameter of the conductive diamond was prepared, a small amount of silver paste was sucked into one end of the pipe, and the conductive diamond was inserted 2mm into the end containing the silver paste, dried, and annealed on a hot plate at 250°C for 1 hour. In this way, the conductive diamond was fixed to the SUS pipe in a state where it would not easily come off even if shaken. Electrical conductivity was also achieved without any problems.

[0127] Next, a 3 mm tip of the conductive diamond and a 1 cm rear portion of the SUS pipe where no diamond was attached were masked, and the remaining portion was coated with polyimide using a spray method. At this time, the needle-shaped conductive diamond and the SUS pipe were rotated 120° at a time, so that the entire periphery could be coated. After this, they were dried at a temperature of 120°C in an oven. In this way, diamond electrodes Samples 1 to 19 containing diamond members with the specifications listed in Tables 1 and 2 were obtained.

[0128]

[0129]

[0130] The cyclic voltammetry characteristics of the completed thin needle-shaped diamond electrode with conductive diamond were evaluated. The results are shown in Table 3. In the tables of this disclosure, the leakage current indicates the current value at a low potential (potential window) of the CV measurement. In the tables of this disclosure, A, B, C, and D in the "Signal Detection" column of "CV Measurement" indicate the following: A: Signal detectable. B: Signal detectable for some species. C: Signal detectable, but signal becomes undetectable at low temperatures. D: Signal undetectable.

[0131] The diamond electrodes of each sample were inserted into multiple cells of different sizes (rat brain cells, pig brain cells) to evaluate the ease of insertion and the state of cell damage. The results are shown in Table 3. In the table of this disclosure, A, B, C, and D in the "Ease" column of "Cell Insertion" indicate the following: A: Very easy to insert into cells. B: Easy to insert into cells. C: Possible to insert into cells. D: Possible to insert into cells, but difficult for small cells.

[0132] In the tables of the present disclosure, A, B, and C in the "Cell Damage" column of "Insertion into Cells" indicate the following: A: No cell damage. B: Partial cell damage. C: Complete cell damage.

[0133]

[0134] [Example 2] In Example 2, a conductive diamond plate made of single-crystal diamond was prepared. First, a 10 mm square Ib type single-crystal diamond was prepared by high-pressure synthesis. Carbon was then deposited on the substrate at 350 keV at a concentration of 3 × 10 １６ cm －２ Ion implantation was performed, and a 50 μm thick non-doped single-crystal diamond was synthesized on top. After synthesizing the single-crystal diamond, the ion-implanted layer was removed by applying a voltage in pure water, resulting in a free-standing non-doped single-crystal diamond plate. Using the non-doped single-crystal diamond as a substrate, boron-doped diamonds with thicknesses of 50 μm to 300 μm were epitaxially synthesized. Free-standing boron-doped diamonds with a non-doped substrate were fabricated. Diamonds were fabricated by introducing methane gas into hydrogen and decomposing it in a microwave plasma. Alternatively, they could be fabricated by thermal decomposition using a hot filament heated to 2000°C. The boron impurity was added by adding a trace amount of trimethylboron. These methods are no different from conventional synthesis methods. A 10 mm square single-crystal substrate was used as the substrate, allowing for the fabrication of a 10 mm square conductive diamond plate. The non-doped single-crystal diamond was removed using the subsequent laser process. In Sample 25, a thin wire of W (tungsten) with a diameter of approximately 19 μm was partially embedded during diamond synthesis. When the diamond was later cut into thin needle-like shapes by laser cutting, this thin wire was embedded inside the needle-like diamond without being exposed on the surface.

[0135] Next, diamond rods were cut from the conductive diamond plates using a laser processing machine. 50 μm widths were cut from 50 μm thick diamond plates, and 100 μm widths were cut from 100 μm thick diamond plates. However, since undoped single-crystal diamond was initially attached, the undoped single-crystal diamond portion had to be removed with a laser at the end. This resulted in the formation of 50 μm or 100 μm square prismatic single-crystal rods. The side length of the prismatic rods could be adjusted by adjusting the width of the diamond cut according to the plate thickness. Even if the cross section was not exactly square but trapezoidal, this did not pose a significant problem. The length was 10 mm, the length of one side of the substrate. Desired lengths could also be achieved by laser cutting. To produce a rod with a diameter of 100 μm, a thickness of 70 μm and a width of 70 μm resulted in a diagonal length of 100 μm, and a circumscribed diameter of 100 μm could be produced.

[0136] As in Example 1, it was possible to fabricate square pyramidal shapes with a tip at the apex, tip diameters of 5 μm or less, and tip diameters of 0.7 μm. Also, as in Example 1, it was possible to remove graphite components attached by laser processing. Furthermore, as in Example 1, it was possible to fabricate electrodes in which a conductive diamond and a SUS pipe were structurally and electrically connected, and an insulating coating was also possible. As a result, diamond electrodes Samples 20 to 25 with the specifications listed in Tables 4 and 5 were obtained.

[0137]

[0138]

[0139] The cyclic voltammetry characteristics of the completed thin needle-shaped diamond electrode with conductive diamond were evaluated, and the results are shown in Table 6.

[0140] The diamond electrodes of each sample were inserted into cells of different sizes (mouse brain cells, pig brain cells) to evaluate the ease of insertion and the state of cell damage. The results are shown in Table 6.

[0141]

[0142] Example 3 In Example 3, a conductive diamond plate made of nano-polycrystalline diamond was prepared. Conductive nano-polycrystalline diamond was synthesized by high-pressure, high-temperature (HPHT) by adding boron to the graphite used for direct conversion, resulting in the synthesis of entirely conductive nano-polycrystalline diamond. The bulk nano-polycrystalline diamond was then sliced ​​into plates using a laser to produce conductive nano-polycrystalline diamond plates. In Sample 35, a thin tungsten (W) wire approximately 19 μm in diameter was partially embedded during diamond synthesis. When the diamond was later laser-cut into thin needle-like shapes, this thin wire was embedded within the needle-like diamond without being exposed on the surface. Similar to Examples 1 and 2, thin needle-like diamond electrodes could be fabricated. Diamond electrodes were obtained for Samples 30 to 35, with the specifications listed in Tables 7 and 8.

[0143]

[0144]

[0145] The cyclic voltammetry characteristics of the completed thin needle-shaped diamond electrode with conductive diamond were evaluated, and the results are shown in Table 9.

[0146] The diamond electrodes of each sample were inserted into cells of different sizes (mouse brain cells, pig brain cells) to evaluate the ease of insertion and the state of cell damage. The results are shown in Table 9.

[0147]

[0148] [Example 4] In Example 4, a conductive diamond plate made of sintered diamond was prepared. Powdered diamond was sintered with a Co binder using a high-pressure method to produce sintered diamond. In addition to the Co binder, boron was added and incorporated into the diamond. The sintered diamond was polished into a thin plate and thinly cut with a laser, and thin, needle-shaped diamond electrodes were produced in the same manner as in Examples 1 to 3. The surface of the thin, needle-shaped diamond was coated with diamond using a vapor-phase synthesis method to prevent the Co binder from being exposed. Diamond electrodes of Samples 40 to 42 with the specifications listed in Tables 10 and 11 were obtained.

[0149]

[0150]

[0151] The cyclic voltammetry characteristics of the completed thin needle-shaped diamond electrode with conductive diamond were evaluated. The results are shown in Table 12.

[0152] The diamond electrodes of each sample were inserted into cells of different sizes (mouse brain cells, pig brain cells) to evaluate the ease of insertion and the state of cell damage. The results are shown in Table 12.

[0153]

[0154] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0155] 1 Diamond electrode, 2 Conductive diamond member, 2a First end, 2b Second end, 3 Metal member, 3a Third A end, 3b Third B end, 4 Insulating member, 5 Brazing material, 6 Adhesive, 7 Metal coating, 8 Connection aid, 21 First region, 20 Diamond plate, C1 Circumscribed circle, C2, C3 Maximum inscribed circle.

Claims

1. The device comprises a rod-shaped conductive diamond member and a rod-shaped metal member electrically connected to the conductive diamond member. A diamond electrode wherein the diamond content of the conductive diamond member is 80 volume% or more.

2. The conductive diamond member includes a first region exposed to the outside, The maximum value D of the circumscribed circle of the cross-section of the first region is 0.3 mm or less. The cross-section is a cross-section whose normal direction is the extending direction of the conductive diamond member, The diamond electrode according to claim 1, wherein the resistivity of the conductive diamond member is 1000 Ω·cm or less.

3. The diamond electrode according to claim 2, wherein the ratio L / D of the length L of the first region along the extending direction to D is 1 or more.

4. The conductive diamond member includes a first end on the metal member side and a second end on the opposite side of the first end. The diameter d2 of the largest inscribed circle at the second end is smaller than the diameter d1 of the largest inscribed circle at the first end. The aforementioned d2 is 0.05 mm or less. The diamond electrode according to any one of claims 1 to 3, wherein d1 and d2 are measured by observing the conductive diamond member from the side.

5. The conductive diamond member is made of diamond. The diamond electrode according to any one of claims 1 to 3, wherein the boron content of the diamond is 10 ppm or more and 50,000 ppm or less.

6. In the Raman spectrum of the conductive diamond member, wavenumber 1320 cm⁻¹ －１ 1340cm or more －１ The following examples have a full width at half maximum of 20 cm. －１ The following peak intensity I3 corresponds to wavenumber 1545 cm⁻¹. －１ More than 1600cm －１ The following have a full width at half maximum of 50 cm. －１ The diamond electrode according to any one of claims 1 to 3, wherein the percentage of peak intensity I2 of a peak exceeding (I2 / I3) × 100 is 30% or less.

7. The angle between the extending direction of the conductive diamond member and the extending direction of the metal member is 5° or less. The diamond electrode according to any one of claims 1 to 3, wherein the connection portion between the conductive diamond member and the metal member is covered with an insulating member.

8. The diamond electrode according to any one of claims 1 to 3, wherein the metal member is pipe-shaped.

9. The diamond electrode according to claim 7, wherein the insulating member is made of polyimide.

10. The diamond electrode according to claim 7, wherein the insulating member is made of a cross-linked fluororesin.

11. The diamond electrode according to claim 7, wherein the average thickness of the insulating member is 5 μm or more and 50 μm or less.

12. The conductive diamond member is made of single-crystal diamond, as described in any one of claims 1 to 3.

13. The conductive diamond member is made of polycrystalline diamond. The diamond electrode according to any one of claims 1 to 3, wherein the average grain size of the polycrystalline diamond is greater than the diameter d2 of the maximum inscribed circle on the second end opposite to the first end on the metal member side of the conductive diamond member.

14. The conductive diamond member is made of nanocrystalline diamond, as described in any one of claims 1 to 3, for the diamond electrode.