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 conductiv

Description

TECHNICAL FIELD

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

[0002] Conductive diamond has excellent properties such as high electric conductivity and thermal conductivity, high hardness, and high durability against acid and alkali. A technique of using the conductive diamond for an electrode by utilizing these properties has been considered.

[0003] For example, PTL 1 discloses a diamond electrode in which a thin film consisting of diamond fine grains is deposited on a base material consisting of a wire composed of a metal. CITATION LIST PATENT LITERATURE

[0004] PTL 1: Japanese Patent Laying-Open No. 2011-174822 SUMMARY OF INVENTION

[0005] A diamond electrode according to the present disclosure is a diamond electrode comprising: a conductive diamond member having a bar shape; and a metal member having a bar shape and electrically connected to the conductive diamond member, wherein a diamond content ratio of the conductive diamond member is 80 volume% or more. BRIEF DESCRIPTION OF DRAWINGS

[0006] [Fig. 1] Fig. 1 is a diagram illustrating a representative exemplary configuration of a diamond electrode according to a first embodiment. [Fig. 2A] Fig. 2A is a cross sectional view along a line I-I of Fig. 1. [Fig. 2B] Fig. 2B is a side view of a diamond member of the diamond electrode according to the first embodiment. [Fig. 3 A] Fig. 3 A is a diagram for illustrating a method of producing the diamond electrode according to the first embodiment. [Fig. 3B] Fig. 3B is a diagram for illustrating the method of producing the diamond electrode according to the first embodiment. [Fig. 3C] Fig. 3C is a diagram for illustrating the method of producing the diamond electrode according to the first embodiment. [Fig. 3D] Fig. 3D is a diagram for illustrating the method of producing the diamond electrode according to the first embodiment. [Fig. 3E] Fig. 3E is a diagram for illustrating the method of producing the diamond electrode according to the first embodiment. [Fig. 4] Fig. 4 is a diagram illustrating a representative exemplary configuration of a diamond electrode according to a second embodiment. [Fig. 5A] Fig. 5A is a diagram for illustrating a method of producing the diamond electrode according to the second embodiment. [Fig. 5B] Fig. 5B is a diagram for illustrating the method of producing the diamond electrode according to the second embodiment. [Fig. 5C] Fig. 5C is a diagram for illustrating the method of producing the diamond electrode according to the second embodiment. [Fig. 6] Fig. 6 is a diagram illustrating a representative exemplary configuration of a diamond electrode according to a third embodiment. [Fig. 7A] Fig. 7A is a diagram for illustrating a method of producing the diamond electrode according to the third embodiment. [Fig. 7B] Fig. 7B is a diagram for illustrating the method of producing the diamond electrode according to the third embodiment. [Fig. 8] Fig. 8 is a diagram illustrating a representative exemplary configuration of a diamond electrode according to a fourth embodiment. [Fig. 9A] Fig. 9A is a diagram for illustrating a method of producing the diamond electrode according to the fourth embodiment. [Fig. 9B] Fig. 9B is a diagram for illustrating the method of producing the diamond electrode according to the fourth embodiment. [Fig. 9C] Fig. 9C is a diagram for illustrating the method of producing the diamond electrode according to the fourth embodiment. DETAILED DESCRIPTION

[0007] [Problem to be Solved by the Present Disclosure] When a thin film consists of diamond fine grains as in PTL 1, clearances, so-called pinholes, are present between the diamond fine grains. When the pinholes are present, coverage of a base material with the thin film is decreased to result in decreased electric conductivity. In order to reduce the pinholes and improve the coverage, it is necessary to attain small grain sizes of the diamond fine grains.

[0008] However, when the grain sizes of the diamond fine grains are made small, a ratio of SP2 bonds in the thin film becomes larger than a ratio of SP3 bonds therein. Thus, the thin film cannot sufficiently have the above-described excellent properties of the conductive diamond, with the result that a cyclic voltammetry property (hereinafter, also referred to as "CV property") of the electrode tend to be decreased.

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

[0010] [Advantageous Effect of the Present Disclosure] According to the present disclosure, it is possible to provide a diamond electrode having an excellent CV property.

[0011] [Description of Embodiments] First, embodiments of the present disclosure will be listed and described. (1) A diamond electrode according to the present disclosure is a diamond electrode comprising: a conductive diamond member having a bar shape; and a metal member having a bar shape and electrically connected to the conductive diamond member, wherein a diamond content ratio of the conductive diamond member is 80 volume% or more.

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

[0013] (2) In (1), the conductive diamond member may include a first region exposed to outside, a maximum value D of a diameter of a circumscribed circle of a cross section of the first region may be 0.3 mm or less, the cross section may be a cross section for which an extending direction of the conductive diamond member is regarded as a normal direction, and a resistivity of the conductive diamond member may be 1000 Q cm or less.

[0014] According to this, since the conductive diamond member is very thin and is sufficiently small, the diamond electrode including the conductive diamond member can be used for a probe for a minute portion, an electrochemical biosensor, and a probe for supplying electric power to a cell. Moreover, when measurement is performed inside a cell by using the diamond electrode, an in-vivo substance can be detected with high sensitivity.

[0015] (3) In (2), a ratio L / D of a length L of the first region along the extending direction to the D may be 1 or more. According to this, the probe can be inserted deep inside a measurement sample and an area of contact with the measurement sample is increased, thereby improving the sensitivity of the diamond electrode.

[0016] (4) In any one of (1) to (3), the conductive diamond member may include a first end portion on the metal member side and a second end portion on a side opposite to the first end portion, a diameter d2 of a maximum inscribed circle of the conductive diamond member on the second end portion side may be smaller than a diameter dl of a maximum inscribed circle of the conductive diamond member on the first end portion side, and the d2 may be 0.05 mm or less. Each of the dl and the d2 may be measured by observing the conductive diamond member laterally.

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

[0018] (5) In any one of (1) to (4), the conductive diamond member may consist of diamond, and a boron content ratio of the diamond may be 10 ppm or more and 50000 ppm or less.

[0019] According to this, the electric conductivity of the conductive diamond member is improved, thereby exhibiting a function as a sensor.

[0020] (6) In any one of (1) to (5), in a Raman spectrum of the conductive diamond member, a percentage (I2 / I3)x 100 of a peak intensity 12 of a peak having a full width at half maximum of more than 50 cm'1 at a wave number of 1545 cm'1 or more and 1600 cm'1 or less with respect to a peak intensity 13 of a peak having a full width at half maximum of 20 cm’1 or less at a wave number of 1320 cm’1 or more and 1340 cm’1 or less may be 30% or less.

[0021] According to this, in the diamond electrode including the conductive diamond member, leakage current becomes small, thereby improving detection sensitivity.

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

[0023] According to this, it is suitable in observing only an electrochemical property of the diamond because an electrochemical property of another material is not included.

[0024] (8) In any one of (1) to (7), the metal member may have a pipe shape. According to this, the conductive diamond member can be inserted into a through hole of the metal member so as to connect them. That is, the thin bar-shaped diamond and the thin bar-shaped metal can be firmly connected together.

[0025] (9) In (7), the insulating member may consist of polyimide. According to this, a thin film of the insulating member can be formed so as to realize electric insulation at a low temperature of 300°C or less.

[0026] (10) In (7), the insulating member may consist of a crosslinked fluororesin. According to this, the thin film of the insulating member can be formed so as to realize electric insulation at a low temperature of 300°C or less. Further, the insulating member can maintain durability even in strong acidity or alkalinity.

[0027] (11) In any one of (7), (9) and (10), an average thickness of the insulating member may be 5 pm or more and 50 pm or less. According to this, it is possible to maintain a state of bar with about the same thinness as that of a bar-shaped electrode not covered with an insulating member while maintaining electric insulation at about 10 V or less.

[0028] (12) In any one of (1) to (11), the conductive diamond member may consist of single-crystal diamond. According to this, even when the content ratio of the impurity is the same as that in a polycrystalline diamond, the electric conductivity can be larger than that of the polycrystalline diamond. This is due to the following reason: in the single-crystal diamond, carriers supplied by an acceptor impurity and a donor impurity can be avoided from being disappeared due to grain boundaries, thereby avoiding electric resistance from being increased due to contact resistance.

[0029] (13) In any one of (1) to (11), the conductive diamond member may consist of poly crystalline diamond, and an average grain size of the polycrystalline diamond may be larger than a diameter d2 of a maximum inscribed circle of the conductive diamond member on a second end portion side of the conductive diamond member opposite to a first end portion of the conductive diamond member on the metal member side.

[0030] According to this, the diamond at the tip on the second end portion side is substantially uniformly a single crystal, with the result that the electric conductivity can be increased due to the same reason as in (12) above.

[0031] (14) In any one of (1) to (11), the conductive diamond member may consist of nano polycrystalline diamond. According to this, the strength at the central portion of the bar-shaped diamond becomes stronger than that of a single crystal that is likely to be cleaved, thereby producing a strong bar-shaped diamond electrode that is not broken even when pierced into a solid such as a cell.

[0032] [Details of Embodiments of the Present Disclosure] Specific examples of the diamond electrode according to the present disclosure will be described below with reference to figures. In the figures of the present disclosure, the same reference characters represent the same or corresponding portions. Further, a dimensional relation such as a length, a width, a thickness, or a depth is appropriately changed for clarity and simplification of the figures, and therefore do not necessarily represent an actual dimensional relation.

[0033] In the present specification, the expression "A to B" means the lower and upper limits of a range (i.e., A or more and B or less), and when no unit is indicated for A and a unit is indicated 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 described as each of lower and upper limits of a numerical range, it is assumed that a combination of any one numerical value described as the lower limit and any one numerical value described as the upper limit is also disclosed. For example, in the case where al or more, bl or more, and cl or more are each described as the lower limit and a2 or less, b2 or less, and c2 or less are each described as the upper limit, it is assumed that al or more and a2 or less, al or more and b2 or less, al or more and c2 or less, bl or more and a2 or less, bl or more and b2 or less, bl or more and c2 or less, cl or more and a2 or less, cl or more and b2 or less, and cl or more and c2 or less are disclosed.

[0035] The present embodiment will be described more specifically with reference to examples. However, the present embodiment is not limited by these examples.

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

[0037] As shown in Fig. 1, a diamond electrode 1 includes: a conductive diamond member 2 having a bar shape; and a metal member 3 having a bar shape and electrically connected to conductive diamond member 2, wherein a diamond content ratio of conductive diamond member 2 is 80 volume% or more. The description "80 volume% or more" expresses that the conductive diamond member is substantially constituted of conductive diamond, and expresses that the volume ratio of another material is less than 20 volume%. For example, in an observation of a cross section of a bar-shaped diamond, when a material other than the conductive diamond is less than 20 area% in its cross sectional area, there is a high possibility that "the diamond content ratio of the conductive diamond member is 80 volume% or more". Strictly, an integral value thereof is vol urn e% along a direction of the shape of bar. When another material having a bar shape is covered with diamond, a product having a diamond content ratio of less than 80 volume% can be produced; however, with this method, the diamond electrode of the present invention in which the "the diamond content ratio of the conductive diamond member is 80 volume% or more" cannot be produced. This is because it is not a minute electrode to which the present invention is applied.

[0038] The diamond electrode of the present disclosure can have an excellent CV property because the diamond content ratio of the diamond member is 80 volume% or more and the diamond electrode of the present disclosure can have the excellent property of diamond.

[0039] <Structure> Diamond electrode 1 according to the first embodiment includes: conductive diamond member 2 having the bar shape; and metal member 3 having the bar shape and electrically connected to conductive diamond member 2. Metal member 3 has a pipe shape provided with a through hole extending from one end portion to the other end portion thereof, and a portion of conductive diamond member 2 on the first end portion 2a side is inserted in the through hole on the one end portion (hereinafter, also referred to as third-A end portion) side of metal member 3. Since the metal member has such a pipe shape, the metal member can be firmly connected to the conductive diamond having the bar shape. The strength can also be adjusted by adjusting the length of the connection portion. A brazing material 5 is disposed between metal member 3 and conductive diamond member 2. The brazing material is in contact with both metal member 3 and conductive diamond member 2, and electrically connects metal member 3 and conductive diamond member 2. Since the metal member has the pipe shape, electric connection with small contact resistance can be attained. The contact resistance can also be made low by adjusting the length of the connection portion. First end portion 2a of conductive diamond member 2 and third-A end portion 3a of metal member 3 may be in contact with each other. The connection portion between conductive diamond member 2 and metal member 3 is covered with an insulating member 4. The conductive diamond member is preferably in contact with the metal member because the whole of the diamond electrode can be maintained to be thin. Although there is such a drawback that the strength of the connection portion is insufficient, the connection strength can be supplemented and the contact resistance can be reduced by obliquely cutting both the bar shapes to increase the cross sectional areas, rather than vertical cross sections. Here, a portion expressed as the bar shape includes a needle-shaped portion having a tip that is gradually tapered. This is because it is effective that the conductive diamond member has a needle shape in an actual application.

[0040] An angle (hereinafter, also referred to as "connection angle") between an extending direction of conductive diamond member 2 and an extending direction of metal member 3 may be 5° or less. One often wishes to deliver the diamond electrode to a sensing portion straightly. It is important that a trajectory through which the tip of the diamond electrode has passed is also followed by the remaining portion of the diamond electrode. Therefore, a smaller connection angle is more favorable. When the connection angle is 5° or less and the conductive diamond member has a length of 5 mm, a deviation (deviation (displacement) between the end portion on the diamond member side and the end portion on the metal member side when the diamond electrode is viewed from the second end portion 2b side of the conductive diamond member) is restricted to a width of 0.43 mm or less. When the connection angle is 3° or less, the deviation is restricted to a width of 0.26 mm or less. When the connection angle is 1° or less, the deviation is restricted to a width of 0.087 mm or less. When the deviation has a width of 0.5 mm or more, the diamond electrode cannot be pointed at a target site for measurement, with the result that it is difficult to implement intended measurement.

[0041] <Conductive Diamond Member> In the present disclosure, the diamond content ratio of conductive diamond member 2 is 80 volume% or more. Thus, the conductive diamond member can have the excellent property of diamond, and can therefore have the excellent CV property.

[0042] The lower limit of the diamond content ratio of the conductive diamond member is 80 volume% or more, preferably 85 volume% or more, more preferably 90 volume% or more, more preferably 95 volume% or more, and further preferably 98 volume% or more. The upper limit of the diamond content ratio of the conductive diamond member is preferably 100 volume% or less. The diamond content ratio of the conductive diamond member is preferably 80 volume% or more and 100 volume% or less, more preferably 90 volume% or more and 100 volume% or less, and further preferably 98 volume% or more and 100 volume%. Conventionally, it has been generally proposed to grow diamond on a bar-shaped metal so as to produce a barshaped diamond; however, in this case, the diamond content ratio is less than 80 volume%. When the diamond content ratio is small, a pinhole may be generated in a diamond-covered portion to exhibit a property of the metal member, with the result that the property of the bar-shaped diamond is deteriorated in that case. This can be prevented by attaining the content ratio of 80 volume% or more.

[0043] A method of measuring the diamond content ratio of the conductive diamond member is as follows. The conductive diamond member is cut at 10 locations and the cross sections at the 10 locations are subjected to an element analysis for the sake of classification into areas (carbon areas) each consisting of carbon atoms and areas (areas other than carbon) each including atoms other than carbon. A percentage A of the total area of the carbon areas of the cross sections at the 10 locations with respect to the total area of the cross sections at the 10 locations is calculated. The percentage A corresponds to the diamond content ratio of the conductive diamond member. The 10 locations can be calculated by selecting cross sectional areas obtained by substantially equally cutting the conductive diamond member with portions at 10 pm from the both ends of the conductive diamond member being included. The cutting is performed using laser but causes a diamond portion to be changed into a non-diamond, and therefore the measurement needs to be performed after performing treatment for removing the non-diamond. Specifically, the treatment for removing is performed in a hot mixed acid liquid obtained by heating a mixed acid in which concentrated sulfuric acid and concentrated nitric acid are mixed at a volume ratio of 3:1.

[0044] The carbon areas are substantially diamond in most cases; however, when the carbon areas have a portion that is not diamond, the diamond content ratio of the conductive diamond member is measured with the areas being divided into a diamond area consisting of diamond and an area consisting of a material other than diamond by Raman spectroscopy instead of the element analysis. Specifically, a cross section of the conductive diamond member is produced by laser cutting and polishing, Raman spectroscopy measurement is performed so as to divide the areas into an area in which a peak of 1332±2 cm'1 is present and an area in which the peak is not present so as to create a two-dimensional distribution, thereby obtaining a distribution of presence of diamond. The average of area ratios (the area in which diamond is present / the whole of the area) at five different locations are taken, thereby determining the diamond content ratio (volume ratio) of the conductive diamond member.

[0045] The conductive diamond member can consist of diamond and an inevitable impurity. Examples of the inevitable impurity include silicon, aluminum, molybdenum, tungsten, tantalum, iron, nickel, cobalt, and the like. The content ratio of the inevitable impurity is preferably an atomic density of 100 ppm or less. The content ratio of the inevitable impurity is measured by secondary ion mass spectrometry (SIMS).

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

[0047] The resistivity of the conductive diamond member is preferably 1000 Q cm or less. Thus, the sensitivity of the diamond electrode is improved. When measurement is performed inside a cell by using the diamond electrode, an in-vivo substance can be detected with high sensitivity.

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

[0049] As shown in Fig. 2A, conductive diamond member 2 preferably includes a first region 21 exposed to outside, and a maximum value D of a diameter of a circumscribed circle Cl of a cross section of first region 21 is preferably 0.3 mm or less. Here, the cross section is a cross section when the first region is cut along a plane for which an extending direction of the diamond member from first end portion 2a toward second end portion 2b of the conductive diamond member is regarded as a normal direction. According to this, since the diamond member is sufficiently small, the diamond electrode including the diamond member can be used for a probe for a minute portion, an electrochemical biosensor, and a probe for supplying electric power to a cell.

[0050] For example, when a cell is measured using the diamond electrode, local information can be collected without breaking the cell. Therefore, a correlation between a disease and an in-vivo substance can be accurately measured.

[0051] The upper limit of the maximum value D is preferably 0.3 mm or less, more preferably 0.1 mm or less, and further preferably 0.075 mm or less. The lower limit of the maximum value D is not particularly limited, and can be, for example, 0.01 mm or more from the viewpoint of production. 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 further 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 first region 21 with an optical microscope or a scanning electron microscope.

[0053] A ratio L / D of a length L of first region 21 along the extending direction (direction indicated by an arrow Al in Fig. 1) to the maximum value D is preferably 1 or more. According to this, the probe can be inserted deep inside a measurement sample, and an area of contact with the measurement sample is increased, thereby 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 further preferably 10 or more. The upper limit of the ratio L / D is not particularly limited, and can be, for example, 20 or less from the viewpoint of production. 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 further 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, further preferably 0.5 mm or more, and further preferably 1.0 mm or more. The upper limit of the length L is not particularly limited, and can be, for example, 20 mm or less from the viewpoint of production. 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 further preferably 1.0 mm or more and 5.0 mm or less.

[0056] As shown in Fig. 2B, conductive diamond member 2 includes first end portion 2a on the metal member 3 side and second end portion 2b on the side opposite to first end portion 2a, a diameter d2 of a maximum inscribed circle C2 of conductive diamond member 2 on the second end portion 2b side is smaller than a diameter dl of a maximum inscribed circle C3 of conductive diamond member 2 on the first end portion 2a side, and the diameter d2 is preferably 0.1 mm or less, more preferably 0.05 mm or less, and further preferably 0.03 mm or less. According to this, since the diamond member is sufficiently small, the diamond electrode including the diamond member can be used for a probe for a minute portion, an electrochemical biosensor, and a probe for supplying electric power to a cell.

[0057] Here, each of the diameter dl and the diameter d2 is measured by observing conductive diamond member 2 laterally. Maximum inscribed circle C2 of conductive diamond member 2 on the second end portion 2b side means a maximum circle that can be drawn inside a region surrounded by the outer edge of conductive diamond member 2 when the second end portion 2b side of conductive diamond member 2 is observed laterally. Maximum inscribed circle C3 of conductive diamond member 2 on the first end portion 2a side means a maximum circle that can be drawn inside a region surrounded by the outer edge of conductive diamond member 2 when the first end portion 2a side of conductive diamond member 2 is observed laterally. When the size of maximum inscribed circle C2 differs depending on a direction in which conductive diamond member 2 is observed, each of the diameter dl and the diameter d2 is measured in a direction in which the diameter of maximum inscribed circle C2 is the largest.

[0058] The upper limit of the diameter d2 is preferably 0.05 mm or less, more preferably 0.03 mm or less, and further preferably 0.01 mm or less. The lower limit of the diameter d2 is not particularly limited, and can be, for example, 0.0001 mm or more from the viewpoint of production. 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 further preferably 0.001 mm or more and 0.01 mm or less.

[0059] The diameter dl 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 further preferably 0.05 mm or more and 0.1 mm or less.

[0060] From first end portion 2a toward second end portion 2b, the cross sectional area of conductive diamond member 2 may be unchanged or may be monotonously decreased. From the viewpoint of production, the cross sectional area is preferably monotonously decreased, and from the viewpoint of the strength of the structure and the viewpoint of use, the cross sectional area is more preferably unchanged from first end portion 2a to a predetermined position between first end portion 2a and second end portion 2b in the length L and decreased monotonously from the predetermined position to 2b. Here, the cross sectional area is the area of a cross section exposed when cut along the plane for which the direction from first end portion 2a toward second end portion 2b is regarded as a normal line.

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

[0062] The conductive diamond member preferably consists of diamond, and the boron content ratio of the diamond is preferably 10 ppm or more and 50000 ppm or less. Thus, the electric conductivity of the conductive diamond member is improved. The boron content ratio of the diamond is preferably 10 ppm or more and 50000 ppm or less, more preferably 200 ppm or more and 50000 ppm or less, and further preferably 2000 ppm or more and 50000 ppm or less. Here, the conductive diamond member can include an impurity other than diamond as long as the effects of the present disclosure are not impaired.

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

[0064] The conductive diamond member may consist mainly of diamond. In a Raman spectrum of the conductive diamond member, a percentage (I2 / I3)x 100 of a peak intensity 12 of a peak having a full width at half maximum of more than 50 cm'1 at a wave number of 1545 cm'1 or more and 1600 cm'1 or less with respect to a peak intensity 13 of a peak having a full width at half maximum of 20 cm’1 or less at a wave number of 1320 cm'1 or more and 1340 cm'1 or less is preferably 30% or less. In the diamond electrode including the conductive diamond member, leakage current is small and detection sensitivity is improved. The peak having the full width at half maximum of 20 cm'1 or less at the wave number of 1320 cm'1 or more and 1340 cm'1 or less is a peak originated from diamond. The peak having the full width at half maximum of more than 50 cm'1 at the wave number of 1545 cm'1 or more and 1600 cm' 1 or less is considered to be a peak originated from a graphite-like structure. Excitation light laser for the Raman spectroscopy measurement is typically excitation light of 530 nm, and the measurement is preferably performed under such conditions that an objective lens has a magnification of 20 times or more and a laser power density is9*106 W / cm2.

[0065] The upper limit of the percentage (12 / 13)* 100 is preferably 30% or less, preferably 20% or less, more preferably 10% or less, and further preferably 5% or less. The lower limit of the percentage (12 / 13)* 100 is not particularly limited, and can be, for example, 0% or more. The percentage (12 / 13)* 100 is preferably 0% or more and 30% or less, more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less.

[0066] The Raman spectrum is measured by a microscopic Raman spectrometer. The measurement is performed at a room temperature (20°C or more and 25°C or less) using, as excitation light, laser having a wavelength of 532 nm.

[0067] The angle between the extending direction of conductive diamond member 2 and the extending direction of metal member 3 is preferably 5° or less. That is, diamond electrode 1 preferably has a bar shape as a whole. According to this, diamond electrode 1 is suitably inserted straightly into a minute portion such as a cell or is suitably inserted through a narrow clearance. The angle is more preferably 0° or more and 2° or less, and further preferably 0° or more and 1° or less.

[0068] The conductive diamond member preferably consists of single-crystal diamond. According to this, it is suitable in increasing the electric conductivity as compared with that of poly crystalline diamond having the same amount of impurity.

[0069] The conductive diamond member may consist of polycrystalline diamond, and an average grain size of the polycrystalline diamond may be larger than the diameter d2 of the maximum inscribed circle of the conductive diamond member on the second end portion side opposite to the first end portion side on the metal member side. According to this, the portion of the conductive diamond member at its tip on the second end portion 2b side is substantially uniformly a single crystal, and it is suitable in increasing the electric conductivity as compared with a case where the conductive diamond member consists of polycrystalline diamond having the same amount of impurity and having a grain size smaller than the diameter d2.

[0070] The conductive diamond member preferably consists of nano polycrystalline diamond. According to this, it is suitable in maintaining a large mechanical strength of the thin conductive diamond member. This is due to the following reason: in the case of single-crystal diamond, the thin conductive diamond member may be cleaved and therefore unable to maintain necessary strength.

[0071] The average grain size of the nano poly crystalline diamond is preferably 5 nm or more and 2000 nm or less, more preferably 10 nm or more and 500 nm or less, and further preferably 20 nm or more and 100 nm or less.

[0072] The average grain size of the nano polycrystalline diamond can be found by an intercept method employing a scanning electron microscope (SEM). Specifically, the scanning electron microscope is first used to observe the nano polycrystalline diamond at a magnification of 1000 times to 100000 times so as to obtain a SEM image.

[0073] Next, a circle is drawn on the SEM image and then eight straight lines are drawn from the center of the circle to the outer circumference of the circle in a radial manner (in such a manner that intersecting angles between the straight lines become substantially equal to one another). In this case, the observation magnification and the diameter of the circle are preferably set such that the number of diamond grains (crystal grains) on each straight line becomes about 10 to 50.

[0074] Then, the number of times each of the straight lines crosses the crystal grain boundaries of the diamond grains is counted, the length of the straight line is divided by the number of times the straight line crosses the crystal grain boundaries so as to determine an average intercept length, and a numerical value obtained by multiplying the average intercept length by 1.128 is regarded as the first average grain size. It should be noted that the first average grain size is determined for each of five SEM images in the above procedure, and the average value of these first average grain sizes is regarded as the average grain size.

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

[0076] The material of metal member 3 is preferably a material that has strength to stand by itself even with a diameter of 0.1 mm, that is not corroded, and that is readily processed, such as a stainless steel wire or a tungsten wire.

[0077] Metal member 3 of the first embodiment has the pipe shape. According to this, conductive diamond member 2 can be inserted into the through hole of metal member 3. The shape of the metal member is not limited to the pipe shape. For example, only one end portion side of metal member 3 may have a hollow structure in which a hole into which the conductive diamond member can be inserted is formed, and the other end portion side thereof may have a solid structure. The outer shape of the metal member is not limited to the cylindrical shape. For example, the outer shape can be a truncated cone shape, an elliptical cone shape, a truncated elliptical cone shape, a pyramid shape, or a truncated pyramid shape.

[0078] The magnitude of a level difference at the connection portion between metal member 3 and conductive diamond member 2 is preferably 100 pm or less, more preferably 75 pm or less, and further preferably 50 pm or less. According to this, it is possible to obtain an effect of smoothly connecting metal member 3 and conductive diamond member 2 to form one bar shape, i. e., an effect of allowing for insertion without resistance due to being caught at the level difference when piercing it into a cell or the like. Here, the magnitude of the level difference corresponds to the half of a difference between the outer diameter of metal member 3 and the outer diameter of conductive diamond member 2. As long as the level difference falls within the above numerical range, insulating member 4 can be smoothly connected without interruption.

[0079] <Insulating Member> The connection portion between conductive diamond member 2 and metal member 3 is covered with insulating member 4. Here, the connection portion is a portion at which the above-described level difference between conductive diamond member 2 and metal member 3 is caused. According to this, it is possible to obtain such an effect that metal member 3 is not exposed to outside and electrochemical current is not generated in metal member 3. Moreover, it is possible to obtain such an effect that the insulating member smoothly connects conductive diamond member 2 and metal member 3 at the level difference so as to form a smooth connection portion. The insulating member may cover half or more of conductive diamond member 2 from the connection portion at the level difference in the extending direction of conductive diamond member 2, or may cover half or more of metal member 3 from the connection portion at the level difference in the extending direction of metal member 3. The length of the insulating member can be appropriately set based on the design of a measurement apparatus as long as the structure is such that only conductive diamond member 2 is in contact with an electrolyte to be measured and metal member 3 is not in direct contact therewith and is in an insulated state.

[0080] Examples of the material of the insulating member include polyimide, crosslinked fluororesin, and Teflon (registered trademark)-based resin. One of these materials may be used or two or more of these materials may be used.

[0081] The insulating member preferably consists of polyimide. According to this, the insulating member can be formed at a lower temperature, and a portion remaining not to be covered can be reduced even when the insulating member is thin. The insulating member preferably consists of a crosslinked fluororesin. According to this, the insulating member is formed at a higher temperature, covers thickly, and realizes benefits of acid resistance and alkali resistance. The crosslinked fluororesin refers to a resin obtained by improving adhesion of a fluororesin through application of electron beam or the like, or a resin in which a molecular chain of CF in the fluororesin is branched / crosslinked.

[0082] The average thickness of the insulating member is preferably 5 pm or more and 50 pm or less. According to this, it is possible to obtain an effect of securing insulation at a potential of 10 V and smoothly covering the level difference between conductive diamond member 2 and metal member 3. The average thickness of the insulating member is more preferably 10 pm or more and 40 pm or less, and further preferably 10 pm or more and 30 pm or less.

[0083] A method of measuring the average thickness of the insulating member is as follows. In a cross section obtained by cutting, along an imaginary plane for which the extending direction of the metal member is regarded as a normal line, the region in which the metal member of the diamond electrode and the insulating member covering the metal member are present, the outer diameter of the whole of the insulating member covering metal member 3 and the outer diameter of metal member 3 are observed with a micrometer or a microscope, and the average thickness of the insulating member is calculated from half of a difference therebetween.

[0084] <Method of Producing Diamond Electrode> A method of producing the diamond electrode according to the first embodiment will be described with reference to Figs. 1 and 3A to 3E.

[0085] A diamond plate 20 consisting of conductive diamond is prepared (see Fig. 3A). Diamond plate 20 can be produced, for example, in the following manner: a boron-added polycrystalline diamond having a thickness of 50 pm or more and 500 pm or less is synthesized on a silicon substrate by a general CVD method, and the silicon substrate is then removed. Moreover, diamond plate 20 can also be produced in the following manner: Ir or Pt is epitaxially grown on a single-crystal sapphire or single-crystal MgO substrate, a heterojunction boron-added single-crystal diamond is synthesized thereon, and the heterogeneous substrate is removed. Further, diamond plate 20 can also be produced in the following manner: a boron-added single-crystal diamond is homoepitaxially grown on a single-crystal diamond substrate having an insulating property and the single-crystal diamond of the seed substrate is separated by laser. The diamond content ratio of the diamond plate thus obtained is 100 volume%. The average thickness of the diamond plate is preferably 50 pm or more and 500 pm or less. The diamond plate may be any of a homoepitaxial single-crystal diamond, a heteroepitaxial diamond, and a polycrystalline diamond. It should be noted that the diamond content ratio of the diamond plate is not limited to 100 volume%, and may be, for example, 80 volume% or more. In this case, examples of the component other than diamond in the diamond plate include tungsten, tantalum, iron, nickel, cobalt, and silicon.

[0086] In the CVD method, the diamond content ratio of the diamond plate can be 100 volume%, whereas in a diamond obtained by the sintering method, the diamond content ratio can be 80 volume% because a metal of a binder is contained. In either case, the diamond is the main component and a bonding state of the diamond is dominant, with the result that the bonding strength is large. The binder metal can be subjected to surface treatment so as not to be exposed at the surface. On the other hand, when the diamond is synthesized by the CVD method with a metal wire being located at the center, the diamond content ratio is usually less than 80 volume%. The bonding of diamond deposited by the CVD method is not necessarily strong. Since the metal is exposed from a weak portion thereof, the electrochemical property is deteriorated when used for a long period of time.

[0087] Next, diamond plate 20 is cut by laser processing, thereby obtaining conductive diamond member 2 having the bar shape (see Fig. 3B). Laser application conditions can be, for example, as follows: a focal spot diameter of 3 to 50 pm and a pulse energy of 10 to 50 pj.

[0088] Metal member 3 is prepared (see Fig. 3C). In the production method of the first embodiment, metal member 3 has the pipe shape.

[0089] Next, brazing material 5 is provided in the through hole of metal member 3 on the one end portion side (see Fig. 3D). The brazing material may be provided from the hole on the opposite side. Alternatively, the brazing material may be suctioned from the hole on the opposite side. The brazing material located outside the hole and other than the brazing material provided in the hole is preferably wiped off.

[0090] Next, conductive diamond member 2 is inserted into the end portion side of metal member 3 on which brazing material 5 is provided. Thus, conductive diamond member 2 and metal member 3 are electrically connected to each other via brazing material 5, and conductive diamond member 2 is fixed to metal member 3. By heating the brazing material at a predetermined temperature, the brazing material is melted and firmly joins conductive diamond member 2 and metal member 3 together. The brazing material may be an active silver wax. This is because a Ti activator joins the both more firmly. Alternatively, the brazing material may be a Ag or Cu powder. This is because such a powder is not melted and is sintered at a predetermined temperature to join the both together. It should be noted that it is essential that the predetermined temperature is equal to or less than the melting point of metal member 3.

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

[0092] Insulating member 4 is preferably formed by spray coating. More preferably, the insulating member formed by the spray coating is subjected to heat treatment at 100°C or more.

[0093] [Second Embodiment] A diamond electrode according to one embodiment (hereinafter, also referred to as "second embodiment") of the present disclosure will be described with reference to Fig. 4. As shown in Fig. 4, a diamond electrode 1 includes: a conductive diamond member 2 having a bar shape; and a metal member 3 having a bar shape and electrically connected to conductive diamond member 2, wherein a diamond content ratio of conductive diamond member 2 is 80 volume% or more.

[0094] Diamond electrode 1 of the second embodiment can have basically the same configuration as that of the first embodiment except for the structure of metal member 3 and the method of connecting conductive diamond member 2 and metal member 3. Hereinafter, the differences from the first embodiment will be described.

[0095] In diamond electrode 1 of the second embodiment, metal member 3 has a solid bar shape, and includes a third-A end portion 3a disposed on the conductive diamond member 2 side and a third-B end portion 3b on a side opposite to third-A end portion 3a. First end portion 2a of conductive diamond member 2 and third-A end portion 3a of metal member 3 face each other. Brazing material 5 is disposed between first end portion 2a of conductive diamond member 2 and third-A end portion 3a of metal member 3. Brazing material 5 is in contact with both metal member 3 and conductive diamond member 2, and electrically connects metal member 3 and conductive diamond member 2. A part of first end portion 2a of conductive diamond member 2 and a part of third-A end portion 3a of metal member 3 may be in contact with each other. In Fig. 4, conductive diamond member 2 and metal member 3 are shown to be joined to each other at their surfaces substantially perpendicular to the axial direction. However, both of them may have inclined surfaces in the axial direction, and may be joined to each other at the inclined surfaces. This is more preferable because a joining area can be large to result in large joining strength and large electric conductivity of the joining. Here, even when the surfaces to be joined are inclined with respect to the axial direction, it is preferable that the axial direction of diamond member 2 and the axial direction of metal member 3 at the time of joining are at 5° or less and are substantially straight lines.

[0096] The diameter of metal member 3 can be appropriately set depending on a purpose of use. For example, the thickness 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 further preferably 0.03 mm or more and 0.1 mm or less. When the thickness is less than 0.01 mm, the rigidity of metal member 3 itself becomes too small and diamond member 2 cannot be pushed forward from rearward, which is not preferable. When the thickness is more than 0.3 mm, it becomes difficult to insert it into a minute portion such as a cell through a clearance.

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

[0098] Brazing material 5 can further cover the outer peripheral surface of conductive diamond member 2 in the vicinity of first end portion 2a and the outer peripheral surface of metal member 3 in the vicinity of third-A end portion 3a. Here, the outer peripheral surface in the vicinity of first end portion 2a means a region on the outer peripheral surface of conductive diamond member 2 where a distance from first end portion 2a is 0.9 times or less, more preferably 0.3 times or less, and further preferably 0.1 times or less as large as the length of conductive diamond member 2. The vicinity of third-A end portion 3a means a region on the outer peripheral surface of metal member 3 where a distance from third-A end portion 3a is 0.9 times or less, more preferably 0.3 times or less, and further preferably 0.1 times or less as large as the length of metal member 3.

[0099] Diamond electrode 1 according to the second embodiment can further include an insulating member 4 that covers the connection portion between conductive diamond member 2 and metal member 3. In Fig. 4, insulating member 4 covers brazing material 5 entirely.

[0100] <Method of Producing Diamond Electrode> A method of producing the diamond electrode according to the second embodiment will be described with reference to Figs. 4 and 5A to 5C.

[0101] Conductive diamond member 2, metal member 3, and a connection assistance device 8 are prepared (see Fig. 5A). Conductive diamond member 2 is prepared by the method described in the production method of the first embodiment. As metal member 3, a solid bar-shaped member composed of a metal is prepared.

[0102] Connection assistance device 8 has a tubular shape provided with a through hole extending from one end portion to the other end portion thereof. The material of connection assistance device 8 can be, for example, Teflon (registered trademark), resin, or aron ceramic. This is because the diamond member and the metal member can be removed therefrom in a subsequent step without damaging them. The size of the cross section of the through hole when cut along a plane for which the extending direction of the through hole is regarded as a normal line is not particularly limited as long as conductive diamond member 2 and metal member 3 can be inserted and brazing material 5 can be provided on the outer peripheral surface of each of conductive diamond member 2 and metal member 3. The size of the cross section of the through hole is preferably, for example, 1.1 times or more and 1.5 times or less as large as the larger one of the cross sectional area of first end portion 2a of conductive diamond member 2 and the cross sectional area of third-A end portion 3a of metal member 3. Brazing material 5 is provided in the through hole of connection assistance device 8.

[0103] Next, conductive diamond member 2 is inserted into the through hole, on the one end portion side, of connection assistance device 8 provided with brazing material 5. Metal member 3 is inserted into the through hole, on the other end portion side, of connection assistance device 8 (see Fig. 5B). On this occasion, it is preferable to remove brazing material 5 pushed out from the through hole.

[0104] After brazing material 5 is solidified or is subjected to heat treatment for the sake of solidification, connection assistance device 8 is removed (see Fig. 5C). Connection assistance device 8 can be removed, for example, by physically sliding it when a material that does not adhere to the connection assistance device is used. Alternatively, connection assistance device 8 can be removed by burning it in oxygen. Alternatively, connection assistance device 8 can be removed by placing it in water.

[0105] Brazing material 5 is covered with insulating member 4, thereby obtaining diamond electrode 1 of the second embodiment (see Fig. 4).

[0106] [Third Embodiment] A diamond electrode according to one embodiment (hereinafter, also referred to as "third embodiment") of the present disclosure will be described with reference to Fig. 6. As shown in Fig. 6, a diamond electrode 1 includes: a conductive diamond member 2 having a bar shape; and a metal member 3 having a bar shape and electrically connected to conductive diamond member 2, wherein a diamond content ratio of conductive diamond member 2 is 80 volume% or more.

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

[0108] <Method of Producing Diamond Electrode> A method of producing the diamond electrode according to the third embodiment will be described with reference to Figs. 6, 7A, and 7B.

[0109] Conductive diamond member 2, metal member 3, and brazing material 5 are prepared (see Fig. 7A). First end portion 2a of the conductive diamond member and third-A end portion 3 a of metal member 3 are opposed to each other with brazing material 5 being interposed therebetween. On this occasion, each of first end portion 2a and third-A end portion 3a is disposed in contact with brazing material 5.

[0110] Brazing material 5 is subjected to electric discharging processing so as to join conductive diamond member 2 and metal member 3 (see Fig. 7B). The electric discharging is generated between conductive diamond member 2 and metal member 3. Brazing material 5 is covered with an insulating member 4, thereby obtaining diamond electrode 1 of the third embodiment (see Fig. 6).

[0111] [Fourth Embodiment] A diamond electrode according to one embodiment (hereinafter, also referred to as "fourth embodiment") of the present disclosure will be described with reference to Fig. 8. As shown in Fig. 8, a diamond electrode 1 includes: a conductive diamond member 2 having a bar shape; and a metal member 3 having a bar shape and electrically connected to conductive diamond member 2, wherein a diamond content ratio of conductive diamond member 2 is 80 volume% or more.

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

[0113] In diamond electrode 1 of the fourth embodiment, metal member 3 has a solid bar shape, and includes third-A end portion 3a disposed on the conductive diamond member 2 side and third-B end portion 3b on a side opposite to third-A end portion 3a. First end portion 2a of conductive diamond member 2 and third-A end portion 3a of metal member 3 face each other. An adhesive agent 6 is disposed between first end portion 2a of conductive diamond member 2 and third-A end portion 3a of metal member 3. Adhesive agent 6 is in contact with both metal member 3 and conductive diamond member 2, and physically connects metal member 3 and conductive diamond member 2. A part of first end portion 2a of conductive diamond member 2 and a part of third-A end portion 3a of metal member 3 may be in contact with each other.

[0114] Adhesive agent 6 can further cover the outer peripheral surface of conductive diamond member 2 in the vicinity of first end portion 2a and the outer peripheral surface of metal member 3 in the vicinity of third-A end portion 3a. Here, the outer peripheral surface in the vicinity of first end portion 2a means a region on the outer peripheral surface of conductive diamond member 2 where a distance from first end portion 2a is 0.9 times or less, more preferably 0.3 times or less, and further preferably 0.1 times or less as large as the length of conductive diamond member 2. The vicinity of third-A end portion 3a means a region on the outer peripheral surface of metal member 3 where a distance from third-A end portion 3a is 0.9 times or less, more preferably 0.3 times or less, and further preferably 0.1 times or less as large as the length of metal member 3.

[0115] Diamond electrode 1 according to the fourth embodiment further includes a metal coating 7 that continuously covers a part of conductive diamond member 2 on the first end portion 2a side, adhesive agent 6, and a part of metal member 3 on the third-A end portion 3a side. Metal coating 7 is in contact with conductive diamond member 2, adhesive agent 6 and metal member 3. Thus, conductive diamond member 2 and metal member 3 are electrically connected by metal coating 7. As metal coating 7, gold, platinum, titanium, zirconium, niobium, molybdenum, tungsten, or the like can be used.

[0116] Diamond electrode 1 according to the fourth embodiment can further include an insulating member 4 that covers conductive diamond member 2, adhesive agent 6, and metal member 3. In Fig. 8, insulating member 4 entirely covers conductive diamond member 2, adhesive agent 6, and metal member 3.

[0117] <Method of Producing Diamond Electrode> A method of producing the diamond electrode according to the fourth embodiment will be described with reference to Figs. 8 and 9A to 9C.

[0118] Conductive diamond member 2, metal member 3, and adhesive agent 6 are prepared (see Fig. 9A). First end portion 2a of conductive diamond member 2 and third-A end portion 3 a of metal member 3 are opposed to each other with adhesive agent 6 being interposed therebetween. On this occasion, each of first end portion 2a and third-A end portion 3a is disposed in contact with adhesive agent 6 (see Fig. 9B).

[0119] After conductive diamond member 2 and metal member 3 are fixed by adhesive agent 6, metal coating 7 is formed to continuously cover a part of conductive diamond member 2 on the first end portion 2a side, adhesive agent 6, and a part of metal member 3 on the third-A end portion 3a side (see Fig. 9C). Metal coating 7 can be formed by using a sputtering method, an electron beam evaporation method, or the like. Since the formation of metal coating 7 is for the purpose of electrical connection, it is sufficient to perform the formation on one side, but the formation may be performed twice from both the front and rear sides or may be performed three times in three directions.

[0120] Conductive diamond member 2, metal coating 7, and metal member 3 are covered with insulating member 4, thereby obtaining diamond electrode 1 of the fourth embodiment (see Fig. 8). Examples

[0121] The following types of conductive diamond plates were prepared. The first one is a boron-added polycrystalline diamond produced by the CVD method (Example 1), the second one is a boron-added single-crystal diamond produced by the CVD method (Example 2), and the third one is a boron-added nano polycrystalline diamond produced by a high-pressure method (Example 3). These three conductive diamond plates were preferable because the boron could be contained substantially uniformly in the substrate. Further, a conductive diamond plate consisting of a sintered diamond was prepared (Example 4).

[0122] [Example 1] In Example 1, the conductive diamond plate consisting of the poly crystalline diamond was prepared. As the poly crystalline diamond that can be used for each sample, a boron-added diamond plate that stands by itself was produced in the following manner: a boron-added diamond having a thickness of 50 pm to 300 pm was synthesized on a silicon substrate by the CVD method and the silicon substrate was removed with hydrofluoric-nitric acid. The diamond was produced by introducing methane gas into hydrogen and decomposing it in microwave plasma. Alternatively, the diamond could also be produced by thermal decomposition with a hot filament heated to 2000°C. The impurity boron was added by adding a small amount of trimethylboron. These are not particularly different from a general synthesis method. Since a substrate in the form of a 10 mm square was used as the silicon substrate, the conductive diamond plate could be produced to have a size of a 10 mm square. In a sample for which "W" is described in the column "Other Material" in Table 1, a thin wire of W (tungsten) with a diameter of about 17 pm was partially embedded at the time of the diamond synthesis (sample 19). On the other hand, W in the form of each of a strip with a width of 8 pm and a thickness of 2 pm and a strip with a width of 1 pm and a thickness of 0.1 pm was partially evaporated and embedded therein (sample 18 and sample 17). When the diamond was later laser-cut into a thin needle shape, this thin wire was embedded inside the needle-shaped diamond without the thin wire being exposed to the surface. Such a structure can provide an effect of making the diamond pliable and preventing the diamond from being readily broken. If the W is exposed to the surface, a CV property as a sensor is deteriorated, and therefore, if the W is exposed to the surface, the exposed W could be covered and completely embedded by additionally performing CVD growth of diamond for a short period of time after forming the diamond into the needle shape.

[0123] Next, a conductive diamond member having a bar shape was cut out by a laser processing machine from the conductive diamond having the plate shape. The conductive diamond member was cut out from the diamond having a plate thickness of 50 pm so as to have a width of 50 pm, and the conductive diamond member was cut out from diamond having a plate thickness of 100 pm so as to have a width of 100 pm. At this point of time, the width of the diamond to be cut is adjusted in accordance with the plate thickness so as to form a bar in the form of a 50 pm square or 100 pm square prism, with the result that the length of the side of the prism could be adjusted. Even when the cross section was not exactly square but was trapezoidal, there was no significant problem. The length is 10 mm, which corresponds to the length of one side of the substrate. A desired length can be obtained by cutting with laser. In order to produce a bar having a diameter of 100 pm, the length of the diagonal was 100 pm when the thickness was 70 pm and the width was 70 pm, thereby producing a bar to which a circle having a diameter of 100 pm is circumscribed.

[0124] Next, cutting was performed by the laser obliquely from a position corresponding to 1 / 3 of the bar toward the tip thereof, the bar was further rotated by 90° about the axis of the bar, and cutting was performed in a similar manner by the laser obliquely from the position corresponding to 1 / 3 of the bar toward the tip thereof. As a result, there was obtained a conductive diamond member having a quadrangular pyramid shape with the tip as an apex. The tip had a tip diameter of 5 pm. A tip diameter of 5 pm or less could also be produced by adjusting a margin for cutting by the laser. When the needle-shaped bar having the tip diameter of 5 pm was etched laterally with an ion beam in two directions with rotation of 90°, the bar could also be sharpened to have a tip diameter of 0.7 pm. The tip diameter could be adjusted to 3 pm, 1.2 pm, and 0.7 pm by changing the etching time to 20 minutes, 40 minutes, and 60 minutes.

[0125] Thereafter, the periphery of the conductive diamond member was subjected to hot mixed-acid treatment, ion beam etching, or hydrogen plasma treatment to remove a graphite component adhered due to the laser processing. This was confirmed by taking a peak ratio in Raman spectroscopy.

[0126] Next, a SUS pipe, which has an inner diameter corresponding to the outer diameter of the conductive diamond and has a length of 5 cm, was prepared, a small amount of silver paste was suctioned from one opening of the pipe, and the conductive 5 diamond was inserted by 2 mm into the end portion thereof in which the silver paste had been introduced, drying was performed, and annealing was performed on a hot plate at 250°C for 1 hour. In this way, the conductive diamond could be fixed to the SUS pipe in such a state that the conductive diamond could not be readily removed even when shaken. Electric conduction was also realized without problem. 10

[0127] Next, the tip of 3 mm of the conductive diamond, and the rear portion of 1 cm of the SUS pipe with no diamond attached thereto were masked, and remaining portions were coated with polyimide by a spraying method. Since each of the needle-shaped conductive diamond and the SUS pipe was rotated by 120° on this occasion, the entire periphery thereof could be coated. Thereafter, drying was performed in an oven 15 at a temperature of 120°C. Thus, diamond electrodes of samples 1 to 19 including the diamond members having the specifications described in Tables 1 and 2 were obtained. Table 1 Conductive Diamond Member Production Method Crystal Grain Dia meter Diamond Content Ratio Other Material Boron Content Ratio Resistivity I2 / I3 pm volume% PPm Q-cm Sample 1 CVD Polycrystal 50.0 100.00 - 5500 0.002 0.020 Sample 2 CVD Polycrystal 40.0 100.00 - 5500 0.002 0.040 Sample 3 CVD Polycrystal 30.0 100.00 - 5500 0.002 0.020 Sample 4 CVD Polycrystal 50.0 100.00 - 5500 0.002 0.030 Sample 5 CVD Polycrystal 30.0 100.00 - 5500 0.002 0.040 Sample 6 CVD Polycrystal 60.0 100.00 - 5500 0.002 0.020 Sample 7 CVD Polycrystal 40.0 100.00 - 5500 0.002 0.040 Sample 8 CVD Polycrystal 30.0 100.00 - 5500 0.002 0.040 Sample 9 CVD Polycrystal 20.0 100.00 - 5500 0.002 0.020 Sample 10 CVD Polycrystal 40.0 100.00 - 2200 0.080 0.006 Sample 11 CVD Polycrystal 50.0 100.00 - 1000 0.300 0.006 Sample 12 CVD Polycrystal 50.0 100.00 - 250 5.000 0.004 Sample 13 CVD Poly crystal 60.0 100.00 - 15 50.000 0.002 Sample 14 CVD Polycrystal 50.0 100.00 - 9 200.000 0.002 Sample 15 CVD Polycrystal 0.3 100.00 - 5000 0.002 0.600 Sample 16 CVD Polycrystal 0.3 100.00 - 10 150.000 0.350 Sample 17 CVD Polycrystal 40.0 99.99 w 5500 0.002 0.020 Sample 18 CVD Polycrystal 50.0 98.00 w 5500 0.002 0.020 Sample 19 CVD Polycrystal 80.0 70.00 w 5500 0.002 0.020 Table 2 Conductive Diamond Member Maximum Value of Diameter of Circumscribed Circle (D) Length of First Region (L) Ratio L / D Diameter of Maximum Inscribed Circle on First End Portion Side (d1) Diameter of Maximum Inscribed Circle on Second End Portion Side (d2) mm mm mm mm Sample 1 0.05 5.0 100.00 0.05 0.01 Sample 2 0.07 5.0 71.43 0.07 0.02 Sample 3 0.10 1.0 10.00 0.10 0.03 Sample 4 0.15 1.2 8.00 0.15 0.02 Sample 5 0.20 1.0 5.00 0.20 0.03 Sample 6 0.20 0.6 3.00 0.20 0.04 Sample 7 0.30 1.0 3.33 0.30 0.05 Sample 8 0.40 1.0 2.50 0.40 0.06 Sample 9 1.50 1.0 0.67 1.50 0.10 Sample 10 0.05 5.0 100.00 0.05 0.01 Sample 11 0.05 5.0 100.00 0.05 0.01 Sample 12 0.05 5.0 100.00 0.05 0.01 Sample 13 0.05 5.0 100.00 0.05 0.01 Sample 14 0.05 5.0 100.00 0.05 0.01 Sample 15 0.07 5.0 71.43 0.07 0.02 Sample 16 0.07 5.0 71.43 0.07 0.02 Sample 17 0.05 5.0 100.00 0.05 0.01 Sample 18 0.05 5.0 100.00 0.05 0.01 Sample 19 0.05 5.0 100.00 0.05 0.01

[0130] The cyclic voltammetry properties of the completed thin needle-shaped diamond electrodes with the conductive diamonds were evaluated. The results are shown in Table 3. In the tables of the present disclosure, leakage current indicates a current value at a low potential (potential window) in CV measurement. In the tables of the present disclosure, A, B, C and D in the column "Signal Detection" of the "CV Measurement" indicate as follows. A: signal detectable. B: signal detectable in part of species. C: signal detectable, but signal undetectable at low temperature. D: signal undetectable.

[0131] The diamond electrode of each of the samples was inserted into a plurality of cells having different sizes (a brain cell of a mouse and a brain cell of a pig) so as to evaluate easiness of insertion and damage states of the cells. The results are shown in Table 3. In the tables of the present disclosure, A, B, C and D in the column "Easiness" of "Insertion into Cell" indicate as follows. A: very easy to insert into cell. B: easy to insert into cell. C: insertable into cell. D: insertable into cell, but difficult to insert into small cell.

[0132] In the tables of the present disclosure, A, B and C in the column "Damage of Cell" of "Insertion into Cell" indicate as follows. A: cell not damaged. B: cell partially damaged. C: cell entirely damaged. Table 3 Insertion into Cell CV Measurement Easiness Damage of Cell Signal Detection Leakage Current pA Sample 1 A A A 0.03 Sample 2 A A A 0.04 Sample 3 B B A 0.15 Sample 4 A A A 0.08 Sample 5 B B A 0.30 Sample 6 C B A 3.00 Sample 7 C B A 3.00 Sample 8 D C B 30.00 Sample 9 D C B 60.00 Sample 10 A A A 0.03 Sample 11 A A A 0.02 Sample 12 A A A 0.01 Sample 13 A A A 0.01 Sample 14 A A C <0.00001 Sample 15 A A A >10 Sample 16 A A C <0.00001 Sample 17 A A A 0.03 Sample 18 A A A 0.02 Sample 19 A A D >100

[0134] [Example 2] In Example 2, the conductive diamond plate consisting of the single-crystal diamond was prepared. As the single-crystal diamond, first, a type lb diamond in the form of a 10 mm square was prepared by a high-pressure synthesis method. On the substrate, 3 1016 cm’2 of carbon ions were implanted at 350 keV, and 50 um of a non- doped single-crystal diamond was synthesized thereon. After synthesizing the singlecrystal diamond, the ion-implanted layer was removed by applying voltage in pure water, thereby preparing a non-doped single-crystal diamond plate that stands by itself. A boron-added diamond having a thickness of 50 pm to 300 pm was epitaxially synthesized using the non-doped single-crystal diamond as a substrate. A boron-added diamond that stands by itself with the non-doped substrate attached thereto was produced. The diamond was produced by introducing methane gas into hydrogen and decomposing it in microwave plasma. Alternatively, the diamond could be produced by thermal decomposition with a hot filament heated to 2000°C. The impurity boron was added by adding a small amount of trimethylboron. These are not particularly different from a general synthesis method. Since a single-crystal substrate in the form of a 10 mm square was used as the substrate, a plate having a size of 10 mm square could also be produced as the conductive diamond substrate. The non-doped singlecrystal diamond was attached but could be removed in the next laser process. In sample 25, a thin wire of W (tungsten) with a diameter of about 19 pm was partially embedded at the time of the diamond synthesis. When the diamond was later laser-cut into a thin needle shape, the thin wire was embedded inside the needle-shaped diamond without the thin wire being exposed to the surface.

[0135] Next, a diamond having a bar shape was cut out by a laser processing machine from the conductive diamond having the plate shape. The diamond having a bar shape was cut out from diamond having a plate thickness of 50 pm so as to have a width of 50 pm, and the diamond having the bar shape was cut out from the diamond having a plate thickness of 100 pm so as to have a width of 100 pm. However, since the non-doped single-crystal diamond is attached at the beginning, the non-doped single-crystal diamond portion has to be finally removed by laser. By doing so, the single-crystal bar could be formed in the form of a 50 pm square or 100 pm square prism. The width of the diamond to be cut was adjusted in accordance with the plate thickness, with the result that the length of the side of the prism could be adjusted. Even when the cross section was not exactly square but was trapezoidal, there was no significant problem. The length is 10 mm, which corresponds to the length of one side of the substrate. A desired length can be obtained by cutting with laser. In order to produce a bar having a diameter of 100 pm, the length of the diagonal was 100 pm when the thickness was 70 pm and the width was 70 pm, thereby producing a bar to 5 which a circle having a diameter of 100 pm is circumscribed.

[0136] In the same manner as in Example 1, it was also possible to produce a bar having a quadrangular pyramid shape having its tip as an apex, a bar having a tip diameter of 5 pm or less, and a bar having a tip diameter of 0.7 pm. Moreover, a graphite component adhered by laser processing could be removed in the same manner 10 as in Example 1. Further, in the same manner as in Example 1, an electrode in which the conductive diamond and the SUS pipe are structurally and electrically connected to each other could be produced, and an insulating coating was similarly obtained. Thus, diamond electrodes of samples 20 to 25 having the specifications described in Tables 4 and 5 were obtained. 15

[0137] [Table 4] Table 4 Conductive Diamond Member Production Method Crystal Grain Diameter Plane Orientation Diamond Content Ratio Other Material Boron Content Ratio Resistivity I2 / I3 pm volume% ppm Q-cm Sample 20 CVD Single Crystal - (100) 100 - 3500 0.002 0.001 Sample 21 CVD Single Crystal - (100) 100 - 3500 0.002 0.001 Sample 22 CVD Single Crystal - (100) 100 - 3500 0.002 0.001 Sample 23 CVD Single Crystal - (110) 100 - 2000 0.003 0.001 Sample 24 CVD Single Crystal - (111) 100 - 5000 0.001 0.001 Sample 25 CVD Single Crystal - (100) 70 w 5000 0.001 0 Table 5 Conductive Diamond Member Maximum Value of Diameter of Circumscribed Circle (D) Length of First Region (L) Ratio L / D Diameter of Maximum Inscribed Circle on First End Portion Side (d1) Diameter of Maximum Inscribed Circle on Second End Portion Side (d2) mm mm mm mm Sample 20 0.05 5 100.00 0.05 0.01 Sample 21 0.07 5 71.43 0.07 0.02 Sample 22 0.50 5 10.00 0.50 0.08 Sample 23 0.05 5 100.00 0.05 0.02 Sample 24 0.05 5 100.00 0.05 0.02 Sample 25 0.05 5 100.00 0.05 0.02

[0139] The cyclic voltammetry properties of the completed thin needle-shaped 5 diamond electrodes with the conductive diamonds were evaluated. The results are shown in Table 6.

[0140] The diamond electrode of each of the samples was inserted into a plurality of cells having different sizes (a brain cell of a mouse and a brain cell of a pig) so as to evaluate easiness of insertion and damage states of the cells. The results are shown in 10 Table 6. Table 6 Insertion into Cell CV Measurement Easiness Damage of Cell Signal Detection Leakage Current pA Sample 20 A A A 0.01 Sample 21 A A A 0.01 Sample 22 D C B 50 Sample 23 A A A 0.01 Sample 24 A A A 0.01 Sample 25 A A D >100

[0142] [Example 3] 5 In Example 3, a conductive diamond plate consisting of nano polycrystalline diamond was prepared. Regarding the conductive nano polycrystalline diamond produced by the high-pressure high-temperature method (HPHT), boron is added to graphite to be directly converted, an entirely conductive nano polycrystalline diamond can be accordingly synthesized, and the nano polycrystalline diamond formed in the 10 form of a bulk was sliced into a plate shape using laser, thereby producing a plate material of the conductive nano polycrystalline diamond. In a sample 35, a thin wire of W (tungsten) with a diameter of about 19 pm was partially embedded at the time of the diamond synthesis. When the diamond was later laser-cut into a thin needle shape, this thin wire was embedded inside the needle-shaped diamond without the thin 15 wire being exposed to the surface. The diamond electrode in the form of the thin diamond needle can be produced in the same manner as in each of Example 1 and Example 2. Diamond electrodes of samples 30 to 35 having the specifications described in Tables 7 and 8 were obtained. Table 7 Conductive Diamond Member Production Method Crystal Grain Diameter Diamond Content Ratio Other Material Boron Content Ratio Resistivity 12 / 13 pm volume% PPm fl-cm Sample 30 HPHT Polycrystal 1200 100 - 3000 0.02 0.01 Sample 31 HPHT Polycrystal 500 100 - 3000 0.04 0.02 Sample 32 HPHT Polycrystal 100 100 - 3000 0.03 0.03 Sample 33 HPHT Polycrystal 10 100 - 200 20 0.01 Sample 34 HPHT Polycrystal 100 100 - 8 500 0.01 Sample 35 HPHT Polycrystal 100 70 w 8 500 0.01

[0144] [Table 8] 5 Table 8 Conductive Diamond Member Maximum Value of Diameter of Circumscribed Circle (D) Length of First Region (L) Ratio L / D Diameter of Maximum Inscribed Circle on First End Portion Side (d1) Diameter of Maximum Inscribed Circle on Second End Portion Side (d2) mm mm mm mm Sample 30 0.05 5 100.00 0.05 0.01 Sample 31 0.07 5 71.43 0.07 0.02 Sample 32 0.09 5 55.56 0.09 0.01 Sample 33 0.05 5 100.00 0.05 0.02 Sample 34 0.05 5 100.00 0.05 0.02 Sample 35 0.05 5 100.00 0.05 0.02

[0145] The cyclic voltammetry properties of the completed thin needle-shaped diamond electrodes with the conductive diamonds were evaluated. The results are shown in Table 9. 10

[0146] The diamond electrode of each of the samples was inserted into a plurality of cells having different sizes (a brain cell of a mouse and a brain cell of a pig) so as to evaluate easiness of insertion and damage states of the cells. The results are shown in Table 9.

[0147] [Table 9] 5 Table 9 Insertion into Cell CV Measurement Easiness Damage of Cell Signal Detection Leakage Current pA Sample 30 A A A 0.05 Sample 31 A A A 0.03 Sample 32 A A A 0.04 Sample 33 A A A 0.01 Sample 34 A A C <0.00001 Sample 35 A A D >100

[0148] [Example 4] In Example 4, a conductive diamond plate consisting of sintered diamond was prepared. The sintered diamond was produced in the following manner: powder 10 diamond was calcined and solidified with a Co binder by the high-pressure method. In addition to the Co binder, boron was added to and contained in the diamond. The sintered diamond was polished into a thin plate shape, and cutting was performed thinly using laser, with the result that a diamond electrode in the form of a thin diamond needle could be produced in the same manner as in each of Examples 1 to 3. The thin 15 needle-shaped diamond was covered with diamond on its surface by a vapor phase synthesis method so as not to expose the Co binder. Diamond electrodes of samples 40 to 42 having the specifications described in Tables 10 and 11 were obtained. Table 10 Conductive Diamond Member Production Method Crystal Grain Diameter Diamond Content Ratio Other Material Boron Content Ratio Resistivity I2 / I3 pm volume% PPm Q-cm Sample 40 HPHT Poly crystal 15 90 Co 5500 0.002 0.02 Sample 41 HPHT Poly crystal 1 80 Co 5500 0.002 0.02 Sample 42 HPHT Poly crystal 0.5 70 Co 5500 0.002 0.02

[0150] [Table 11] 5 Table 11 Conductive Diamond Member Maximum Value of Diameter of Circumscribed Circle (D) Length of First Region (L) Ratio L / D Diameter of Maximum Inscribed Circle on First End Portion Side (d1) Diameter of Maximum Inscribed Circle on Second End Portion Side (d2) mm mm mm mm Sample 40 0.09 5 55.56 0.09 0.03 Sample 41 0.09 5 55.56 0.09 0.03 Sample 42 0.09 5 55.56 0.09 0.03

[0151] The cyclic voltammetry properties of the completed thin needle-shaped diamond electrodes with the conductive diamonds were evaluated. The results are shown in Table 12. 10

[0152] The diamond electrode of each of the samples was inserted into a plurality of cells having different sizes (a brain cell of a mouse and a brain cell of a pig) so as to evaluate easiness of insertion and damage states of the cells. The results are shown in Table 12. Table 12 Insertion into Cell CV Measurement Easiness Damage of Cell Signal Detection Leakage Current pA Sample 40 B B A 0.50 Sample 41 B B A 4.00 Sample 42 B B D >100

[0154] Although the embodiments and examples of the present disclosure have been 5 described as described above, it is also initially expected to appropriately combine or variously modify the configurations of the above-described embodiments and examples. The embodiments and examples disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms 10 of the claims, rather than the embodiments and examples described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. dcucdempc ciPMC t ict KErEKLNCL SKtNS LISI

[0155] 1 diamond electrode; 2 conductive diamond member; 2a first end portion; 2b 15 second end portion; 3 metal member; 3a third-A end portion; 3b third-B end portion; 4 insulating member; 5 brazing material; 6 adhesive agent; 7 metal coating; 8 connection assistance device; 21 first region; 20 diamond plate; Cl circumscribed circle; C2, C3 maximum inscribed circle.

Claims

1. A diamond electrode comprising: a conductive diamond member having a bar shape; and a metal member having a bar shape and electrically connected to the conductive diamond member, whereina diamond content ratio of the conductive diamond member is 80 volume% ormore.

2. The diamond electrode according to claim 1, whereinthe conductive diamond member includes a first region exposed to outside,a maximum value D of a diameter of a circumscribed circle of a cross section of the first region is 0.3 mm or less,the cross section is a cross section for which an extending direction of the conductive diamond member is regarded as a normal direction, anda resistivity of the conductive diamond member is 1000 Q cm or less.

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

4. The diamond electrode according to any one of claims 1 to 3, whereinthe conductive diamond member includes a first end portion on the metal member side and a second end portion on a side opposite to the first end portion, a diameter d2 of a maximum inscribed circle of the conductive diamond member on the second end portion side is smaller than a diameter dl of a maximum inscribed circle of the conductive diamond member on the first end portion side,the d2 is 0.05 mm or less, andeach of the dl and the d2 is measured by observing the conductive diamond member laterally.

5. The diamond electrode according to any one of claims 1 to 4, whereinthe conductive diamond member consists of diamond, anda boron content ratio of the diamond is 10 ppm or more and 50000 ppm or less.

6. The diamond electrode according to any one of claims 1 to 5, wherein in a Raman spectrum of the conductive diamond member, a percentage (I2 / I3)x 100 of a peak intensity 12 of a peak having a full width at half maximum of more than 50 cm'1 at a wave number of 1545 cm'1 or more and 1600 cm'1 or less with respect to a peak intensity 13 of a peak having a full width at half maximum of 20 cm'1 or less at a wave number of 1320 cm'1 or more and 1340 cm'1 or less is 30% or less.

7. The diamond electrode according to any one of claims 1 to 6, whereinan angle between an extending direction of the conductive diamond member and an extending direction of the metal member is 5° or less, anda 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 7, wherein the metal member has a pipe shape.

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

10. The diamond electrode according to claim 7, wherein the insulating member consists of a crosslinked fluororesin.

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

12. The diamond electrode according to any one of claims 1 to 11, 5 wherein the conductive diamond member consists of single-crystal diamond.

13. The diamond electrode according to any one of claims 1 to 11, whereinthe conductive diamond member consists of polycrystalline diamond, and10 an average grain size of the polycrystalline diamond is larger than a diameter d2of a maximum inscribed circle of the conductive diamond member on a second end portion side of the conductive diamond member opposite to a first end portion of the conductive diamond member on the metal member side.15

14. The diamond electrode according to any one of claims 1 to 11,wherein the conductive diamond member consists of nano polycrystalline diamond.INTERNATIONAL SEARCH REPORT International application No. PCT / JP2024 / 022570A. CLASSIFICATION OF SUBJECT MATTER GOIN27 / 30(2006.01)1 FI: G01N27 / 30 B According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) G01N27 / 00-27 / 49, G01N33 / 48-33 / 98, C12M1 / 00-3 / 10, C12Q1 / 00-3 / 00, A61B5 / 00-5 / 22 Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched Published examined utility model applications of Japan 1922-1996 Published unexamined utility model applications of Japan 1971-2024 Registered utility model specifications of Japan 1996-2024 Published registered utility model applications of Japan 1994-2024 Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. X A A JP 2012-080787 A (SUMITOMO ELECTRIC INDUSTRIES, LTD.) 26 April 2012 (2012-04-26) claims, paragraphs [0020], [0024], [0034]-[0036], fig. 1 US 2020 / 0303236 Al (BOARD OF TRUSTEES OF MICHIGAN STATE UNIVERSITY) 24 September 2020 (2020-09-24) entire text, all drawings 1, 12-14 2-11 1-14 A US 2015 / 0250421 Al (ADVANCED DIAMOND TECHNOLOGIES, INC.) 10 September 2015 (2015-09-10) entire text, all drawings 1-14 A JP 2018-155728 A (TOKYO UNIVERSITY OF SCIENCE FOUNDATION) 04 October 2018 (2018-10-04) entire text, all drawings 1-14 | V | Further documents are listed in the continuation of Box C. | V | See patent family annex. * Special categories of cited documents: “A” document defining the general state of the art which is not considered to be of particular relevance “D” document cited by the applicant in the international application ‘4E” earlier application or patent but published on or after the international filing date *4L” document which may throw doubts on priority claim(s) or which is cited to establish the publication date of another citation or other special reason (as specified) “O” document referring to an oral disclosure, use, exhibition or other means “P” document published prior to the international filing date but later than the priority date claimed “T” later document published after the international filing date or priority date and not in conflict with the application but cited to understand the principle or theory underlying the invention “X” document of particular relevance; the claimed invention cannot be considered novel or cannot be considered to involve an inventive step when the document is taken alone “Y” document of particular relevance; the claimed invention cannot be considered to involve an inventive step when the document is combined with one or more other such documents, such combination being obvious to a person skilled in the art document member of the same patent family Date of the actual completion of the international search 08 August 2024 Date of mailing of the international search report 27 August 2024 Name and mailing address of the ISA / JP Japan Patent Office (ISA / JP) 3-4-3 Kasumigaseki, Chiyoda-ku, Tokyo 100-8915 Japan Authorized officer Telephone No.

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