Diamond electrode, method for manufacturing a diamond electrode, and electrochemical measuring device

Abstract

To provide a diamond electrode that has reduced crystal defects and improved in-plane uniformity and a method for producing such a diamond electrode, and an electrochemical measurement device including such a diamond electrode.SOLUTION: A method for producing a diamond electrode includes an attachment step for attaching nano diamond particles 3a to the surface of a substrate 2, and a deposition step for depositing a diamond thin film 4 on the surface of the substrate 2 on which the nano diamond particles 3a have been attached, wherein the diamond thin film 4 includes a p-type dopant and at least one element of tungsten, tantalum and rhenium, and the concentration of the p-type dopant is 2×1020 cm-3 to 3×1022 cm-3.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a diamond electrode having a diamond thin film, a method for manufacturing a diamond electrode, and an electrochemical measuring device using a diamond electrode. [Background technology]

[0002] Conventionally, electrochemical measurements such as cyclic voltammetry using a diamond electrode with a diamond thin film as the working electrode have been known (see, for example, Patent Document 1). Electrochemical measurements using a diamond thin film as the electrode material have the advantage of a wide potential window in which oxygen and hydrogen are not generated from the test solution, a small background current flowing within the potential window, and the ability to measure minute amounts of the test solution within a wide potential window. On the other hand, because diamond is chemically extremely stable, the catalytic activity of the surface of the diamond electrode is low, and there is a problem that substances that can be oxidized on a metal electrode are difficult to oxidize directly on a diamond electrode.

[0003] Patent Document 1 discloses a method for producing a diamond electrode by first depositing a conductive diamond thin film, and then ion-implanting one element selected from the group consisting of gold, platinum, silver, palladium, ruthenium, rhodium, and iridium as a catalyst onto the surface of the conductive diamond thin film. In Patent Document 1, a diamond electrode thus produced and containing a metallic element on its surface is used as a working electrode to electrochemically analyze and measure the concentration of arsenic and arsenic compounds contained in a test solution. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2006-98281 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in Patent Document 1, in addition to the diamond thin film forming process, an ion implantation process is required. Further, in order to recover the crystal defects induced in the diamond thin film by ion implantation, a high-temperature heat treatment process is additionally required after the ion implantation process, resulting in a problem of high manufacturing cost. Also, when ion-implanting a metal element into a polycrystalline diamond thin film, there is an issue that the implanted metal element does not become uniform in the plane. There was room for further improvement in order to stably manufacture a diamond electrode with high in-plane uniformity of the metal element.

[0006] Therefore, an object of the present invention is to provide a diamond electrode having few crystal defects and good in-plane uniformity, a method for manufacturing the diamond electrode, and an electrochemical measurement device using the diamond electrode.

Means for Solving the Problems

[0007] The diamond electrode of the present invention has a diamond thin film containing a p-type dopant and at least one element of tungsten, and tantalum or rhenium on the surface and inside, and the concentration of the p-type dopant is 2×10 ~3×10 , -3 , -3 , cm , cm , 22 cm -3 ~3×10 22 cm -3 is.

[0008] The method for manufacturing a diamond electrode of the present invention includes a film forming process of forming a diamond thin film containing a p-type dopant and at least one element of tungsten, and tantalum or rhenium on the surface of the diamond electrode, and the concentration of the p-type dopant is 2×10 20 cm -3 ~3×10 22 cm -3 is. 。 Another method for manufacturing a diamond electrode according to the present invention comprises a p-type dopant and tungsten, wherein the concentration of the p-type dopant is 2 × 10⁻⁶. 20 cm -3 <00​​​ The process includes a film deposition step in which a diamond thin film is deposited on the surface of a diamond electrode, wherein the diamond thin film is deposited by a thermal filament CVD apparatus equipped with a thermal filament made of tungsten, and the concentration of tungsten contained in the diamond thin film is controlled by the temperature of the thermal filament and the substrate on which the diamond thin film is grown. .

[0009] The electrochemical measuring device of the present invention uses a diamond electrode as described in any one of claims 1 to 3 as the working electrode. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a diamond electrode with few crystal defects and good in-plane uniformity, a method for manufacturing a diamond electrode, and an electrochemical measuring device using a diamond electrode. [Brief explanation of the drawing]

[0011] [Figure 1] An explanatory diagram showing the configuration of the main part of a diamond electrode according to one embodiment of the present invention. [Figure 2] Flowchart of a method for manufacturing a diamond electrode according to one embodiment of the present invention [Figure 3] (a)(b) Explanatory diagram of the manufacturing process of a diamond electrode according to one embodiment of the present invention. [Figure 4] An explanatory diagram showing the configuration of an electrochemical measuring device according to one embodiment of the present invention. [Figure 5] Figure showing the main parameters of examples and comparative examples of the diamond electrode of the present invention. [Figure 6] (a) Figure showing the cyclic voltammogram of Example 1 (a) Figure showing the scanning electron microscope image [Figure 7] (a) Figure showing the cyclic voltammogram of Example 2 (b) Figure showing the scanning electron microscope image [Figure 8] (a) Figure showing the cyclic voltammogram of Example 3 (b) Figure showing the scanning electron microscope image [Figure 9] (a) Figure showing the cyclic voltammogram of Example 4 (b) Figure showing the scanning electron microscope image [Figure 10] (a) Figure showing the cyclic voltammogram of Comparative Example 1 (b) Figure showing the cyclic voltammogram of Comparative Example 2 [Modes for carrying out the invention]

[0012] An embodiment of the present invention will be described in detail below with reference to the drawings. The configurations, shapes, etc. described below are illustrative examples for illustrative purposes and can be modified as appropriate depending on the specifications of the diamond electrode and electrochemical measuring device. In addition, the drawings used in the following description may be partially enlarged, and the dimensions and proportions of each component may not be the same as in reality. In the following, all corresponding elements in the drawings are denoted by the same reference numeral, and redundant explanations are omitted. Also, numerical ranges indicated using "~" in this specification include the numerical values ​​indicated before and after it.

[0013] First, the structure of the diamond electrode 1 will be explained with reference to Figure 1. The diamond electrode 1 has a nanodiamond layer 3 and a diamond thin film 4 on the upper surface of the substrate 2. The substrate 2 is formed of single-crystal diamond, heterodiamond, silicon (Si), molybdenum (Mo), or niobium (Nb). The nanodiamond layer 3 is composed of aggregated nanodiamond particles 3a (see Figure 3) with a size of several nanometers.

[0014] The diamond thin film 4 is formed by diamond particles 4a (see Figure 3) created by chemical vapor deposition (CVD) using nanodiamond particles 3a of the nanodiamond layer 3 as seeds. Suitable chemical vapor deposition methods include thermal filament CVD, microwave plasma CVD, or DC plasma CVD. The thickness of the diamond thin film 4 is 0.5 μm to 1 mm (preferably 1 μm or more). The diamond particles 4a contain a p-type dopant and at least one metallic element (transition metal) of tungsten (W), tantalum (Ta), or rhenium (Re) on their surface and within their interior.

[0015] The diamond particles 4a contain boron (B) as a p-type dopant. The concentration of the p-type dopant is 2 × 10⁻¹⁰, which is the concentration at which the diamond thin film 4 exhibits metallic properties. 20 cm -3 ~3×10 22 cm -3(Preferably 2.5 × 10 20 cm -3 The above values ​​are set. Also, the concentration of the metal element is 1 × 10 18 cm -3 ~2×10 21 cm -3 (Preferably 2 × 10 18 cm -3 The above settings are used. As a result, when the diamond electrode 1 is used as the working electrode of the electrochemical measuring device 10 (see Figure 4), it exhibits good characteristics as a working electrode, such as a wide potential window and low background current. Thus, the diamond electrode 1 has a diamond thin film 4 which contains a p-type dopant and at least one metal element of tungsten, tantalum, or rhenium not only on the surface that comes into contact with the test solution, but also inside which it does not come into contact with the test solution.

[0016] Next, the manufacturing method of the diamond electrode 1 will be explained following the flow chart in Figure 2 and with reference to Figure 3. First, nanodiamond particles 3a are attached to the surface of the substrate 2, including the upper surface, to form a nanodiamond layer 3 (ST1: attachment step) (Figure 3(a)). In the attachment step (ST1), for example, the substrate 2 is immersed in a solution containing nanodiamond particles 3a to attach (aggregate) the nanodiamond particles 3a to the surface of the substrate 2.

[0017] Next, a diamond thin film 4 containing a p-type dopant and at least one metal element, such as tungsten (W), tantalum (Ta), or rhenium (Re), is deposited on the surface of the substrate 2 to which the nanodiamond particles 3a are attached (ST2: film deposition process) (Figure 3(b)). As a result, a diamond thin film 4 uniformly containing a p-type dopant and at least one metal element, such as tungsten (W), tantalum (Ta), or rhenium (Re), is deposited on the surface of the diamond electrode 1.

[0018] The diamond thin film 4 is formed by growing diamond particles 4a using nanodiamond particles 3a attached to the upper surface of the substrate 2 as a seed, for example, by the thermal filament CVD method. Film formation by the thermal filament CVD method is achieved using a thermal filament CVD apparatus equipped with multiple thermal filaments made of transition metals such as tungsten (W), tantalum (Ta), or rhenium (Re).

[0019] When forming a diamond thin film 4 using a thermal filament CVD apparatus, first, a substrate 2 on which a nanodiamond layer 3 is formed is placed in the chamber of the apparatus, and then the chamber is evacuated to a predetermined pressure (several Pas). Next, in the thermal filament CVD apparatus, the thermal filament and the substrate 2 are heated to predetermined temperatures, and methane (CH4) gas, hydrogen (H2) gas, and hydrogen-diluted trimethylboron (TMB) gas are introduced at predetermined flow rates to grow diamond particles 4a on the nanodiamond layer 3 and form a diamond thin film 4.

[0020] While the diamond thin film 4 is growing, metallic elements contained in the thermal filament leach into the deposition gas, and these metallic elements are incorporated into the diamond particles 4a. For example, if a thermal filament made of tungsten (W) is used, the tungsten elements are incorporated into the grown diamond particles 4a.

[0021] The temperatures of the thermal filament and substrate 2, the flow rates of each gas, and the pressure inside the chamber are determined by the quality of the diamond particles 4a being grown and the deposition rate. The concentration of the metal element is controlled by the temperatures of the thermal filament and substrate 2. The concentration of the p-type dopant is controlled by the ratio of hydrogen-diluted trimethylboron (TMB) gas to the deposition gas. The thickness of the diamond thin film 4 is controlled by the time the diamond particles 4a are grown.

[0022] When forming a diamond thin film 4 by microwave plasma CVD or DC plasma CVD, in addition to methane (CH4) gas, hydrogen (H2) gas, and hydrogen-diluted trimethylboron (TMB) gas, a gas containing transition metals such as tungsten (W), tantalum (Ta), or rhenium (Re) is introduced into the apparatus at a predetermined flow rate. That is, in the film deposition process (ST2), a diamond thin film 4 containing p-type dopants and metal elements substantially uniformly on the surface and inside is deposited in a gas containing carbon (C), p-type dopants, and metal elements.

[0023] When a diamond thin film 4 is deposited on a substrate 2 on which a nanodiamond layer 3 has been formed on its upper surface by an adhesion process (ST1) using a film deposition process (ST2), the diamond thin film 4 becomes a polycrystalline diamond thin film composed of multiple diamond particles 4a. Furthermore, when a diamond thin film 4 is deposited on a substrate 2 made of single-crystal diamond, or on a substrate 2 on which single-crystal diamond has been formed on its upper surface using a film deposition process (ST2), the diamond thin film 4 becomes a single-crystal diamond thin film. When depositing single-crystal diamond, the adhesion process (ST1) is omitted.

[0024] Next, with reference to Figure 4, an electrochemical measuring device 10 using a diamond electrode 1 as the working electrode will be described. The electrochemical measuring device 10 is composed of a diamond electrode 1, a counter electrode 13, and a reference electrode 14, which are working electrodes partially immersed in the test solution 12 stored in the measuring cell 11; a potentiostat 16 connected to the diamond electrode 1, the counter electrode 13, and the reference electrode 14 via wiring 15; and a control device 17 such as a PC that controls the potentiostat 16.

[0025] For the counter electrode 13, for example, platinum (Pt), carbon (C), stainless steel, gold (Au), diamond, and tin oxide (SnO2) can be used. For the reference electrode 14, standard hydrogen electrodes, silver-silver chloride electrodes (Ag / AgCl), mercury-silver chloride electrodes (Hg / AgCl), palladium-hydrogen electrodes (Pd / H), and saturated calomel electrodes (SCE) can be used.

[0026] The control device 17 controls the potentiostat 16 to apply a voltage between the diamond electrode 1 (working electrode) and the counter electrode 13 to measure the potential between the diamond electrode 1 and the reference electrode 14, or to control the current between the diamond electrode 1 and the counter electrode 13 to measure the potential between the diamond electrode 1 and the reference electrode 14, thereby performing electrochemical measurements. Examples of electrochemical measurements that can be performed include cyclic voltammetry, chronoamperometry, and differential pulse voltammetry.

[0027] Next, examples and comparative examples of the diamond electrode 1 of the present invention will be described with reference to Figures 5 to 10. The table in Figure 5 shows the main film deposition conditions, X-ray analysis (XRD) results, and cyclic voltammetry measurement results using the electrochemical measuring device 10 for Examples 1 to 4 and Comparative Examples 1 to 2 of the diamond electrode 1. The diamond thin films 4 of the diamond electrode 1 in Examples 1 to 4 and Comparative Examples 1 to 2 were all deposited using a thermal filament CVD apparatus equipped with multiple thermal filaments made of tungsten (W).

[0028] In Figure 5, "CH4", "H2", and "TMB / H2" represent the flow rates of methane (CH4) gas, hydrogen (H2) gas, and hydrogen-diluted trimethylboron (TMB) gas during film formation, respectively. "B / C" is the ratio of boron (B) to carbon (C) in the film formation gas. The concentration of the p-type dopant in the diamond thin film 4 can be estimated from this "B / C". "Pressure" is the pressure of the film formation gas during film formation. "W amount" is the amount (ratio) of tungsten (W) in the diamond thin film 4 measured by energy-dispersive X-ray analysis (EDX). The concentration of tungsten in the diamond thin film 4 can be calculated from this "W amount".

[0029] "I 220 / I 111 " and "I 400 / I 111 " is the ratio of the intensity of the diffracted X-rays of the diamond thin film 4 measured by X-ray diffraction (XRD), and the crystalline state of the diamond thin film 4 can be estimated from this ratio. 220 / I111 From this, the ratio of diamond particles 4a having (220) faces to diamond particles 4a having (111) faces can be estimated. 400 / I 111 From this, the ratio of diamond particles 4a having (400) faces to diamond particles 4a having (111) faces can be estimated.

[0030] In Figure 5, "BG current" and "potential window" represent the background current and potential window when the redox reaction was evaluated by cyclic voltammetry using an electrochemical measuring device 10, with the diamond electrode 1 of Examples 1-4 and Comparative Examples 1-2 as the working electrode, the silver-silver chloride electrode (Ag / AgCl) as the reference electrode 14, and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. In Examples 1-4 and Comparative Examples 1-2, the area of ​​the diamond electrode 1 immersed in the test solution 12 was 0.38 cm². 2 The background current is the current value flowing through the working electrode (diamond electrode 1) when its potential is 0V. The potential window is the voltage range in which the current flowing through the working electrode (diamond electrode 1) is between -100μA and 100μA.

[0031] The "Judgment" indicates whether the diamond electrode 1 of Examples 1-4 and Comparative Examples 1-2 exhibits good (good) or poor (unsatisfactory) characteristics as a working electrode for cyclic voltammetry. In this example, a background current of 10 μA or less and a potential window of 2.5 V or more are judged as good (good). In other words, the diamond electrode 1 of Examples 1-4 exhibits good characteristics as a working electrode for cyclic voltammetry, while the diamond electrode 1 of Comparative Examples 1-2 exhibits unsuitable characteristics as a working electrode for cyclic voltammetry.

[0032] (Example 1) Next, the manufacturing method of Example 1 of the diamond electrode 1 will be described. The substrate 2 is a silicon (Si) substrate having a (100) surface. In the deposition step (ST1), nanodiamond particles 3a are deposited on the surface of the substrate 2 by immersion in a solution containing nanodiamond particles 3a. In the film formation step (ST2), a diamond thin film 4 is formed using a thermal filament CVD apparatus equipped with multiple thermal filaments made of tungsten (W).

[0033] In the film deposition process (ST2), methane (CH4) gas was introduced into the chamber of the thermal filament CVD apparatus at a flow rate of 60 sccm, hydrogen (H2) gas at 2000 sccm, and hydrogen-diluted trimethylboron (10%) gas at 1 sccm, and the pressure inside the chamber was adjusted to 15 Torr. Subsequently, the tungsten filament was maintained at 2200°C by electric heating, and a polycrystalline diamond thin film (diamond thin film 4) with a thickness of approximately 2 μm was grown over a film deposition period of 10 hours.

[0034] In Figure 5, a peak originating from tungsten was detected by energy-dispersive X-ray spectroscopy (EDX). Since the tungsten content (W content) of diamond thin film 4 is 0.03%, the concentration of tungsten in diamond thin film 4 is 5.3 × 10⁻⁶. 19 cm -3 This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the deposition gas (B / C) is 0.16%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 2.8 × 10⁻⁶. 20 cm -3 It is presumed that...

[0035] Figure 6(b) shows a scanning electron microscope (SEM) image of the diamond thin film 4 of the diamond electrode 1 in Example 1. The SEM image and X-ray analysis (XRD) results (Figure 5) indicate that the diamond thin film 4 has few vacancies and crystal defects, and that a high-quality polycrystalline diamond thin film has been formed.

[0036] Figure 6(a) shows the cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using the diamond electrode 1 of Example 1 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. The background current at a voltage of 0 V was 4.16 μA and the potential window was 3.01 V, indicating that the diamond electrode 1 of Example 1 exhibits good characteristics as the working electrode of the electrochemical measuring device 10.

[0037] (Example 2) Next, the manufacturing method for Example 2 of the diamond electrode 1 will be described. In Example 2, the substrate 2, the conditions for the deposition process (ST1), and the film formation gas and pressure conditions for the film formation process (ST2) are the same as in Example 1, except that the temperature of the substrate 2 in the film formation process (ST2) is higher than in Example 1.

[0038] In Figure 5, a peak originating from tungsten was detected by energy-dispersive X-ray spectroscopy (EDX), and since the tungsten content (W content) of diamond thin film 4 is 0.28%, the concentration of tungsten element in diamond thin film 4 is 4.9 × 10⁻⁶. 20 cm -3 This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the deposition gas (B / C) is 0.16%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 2.8 × 10⁻⁶. 20 cm -3 It is presumed that...

[0039] Figure 7(b) shows a scanning electron microscope (SEM) image of the diamond thin film 4 of the diamond electrode 1 in Example 2. The SEM image and X-ray analysis (XRD) results (Figure 5) indicate that the diamond thin film 4 has few vacancies and crystal defects, and that a high-quality polycrystalline diamond thin film has been formed.

[0040] Figure 7(a) shows the cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using the diamond electrode 1 of Example 2 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. The background current at a voltage of 0 V was 4.30 μA and the potential window was 3.00 V, indicating that the diamond electrode 1 of Example 2 also exhibits good characteristics as the working electrode of the electrochemical measuring device 10.

[0041] (Example 3) Next, the manufacturing method for Example 3 of the diamond electrode 1 will be described. In Example 3, the substrate 2, the conditions for the deposition process (ST1), and the temperature of the substrate 2 in the film formation process (ST2) are the same as in Example 1. The flow rates of methane (CH4) gas and hydrogen (H2) gas in the film formation process (ST2) are the same as in Example 1, and hydrogen-diluted trimethylboron (10%) gas is introduced at a flow rate of 2 sccm, and the pressure in the chamber is adjusted to 15 Torr. In other words, in Example 3, the concentration of the p-type dopant in the diamond thin film 4 is higher than in Example 1.

[0042] In Figure 5, a peak originating from tungsten was detected by energy-dispersive X-ray spectroscopy (EDX), and since the tungsten content (W content) of the diamond thin film 4 is 0.04%, the concentration of tungsten in the diamond thin film 4 is 7.0 × 10⁻⁶. 20 cm -3 This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the film deposition gas (B / C) is 0.32%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 5.6 × 10 20 cm -3 It is presumed that...

[0043] Figure 8(b) shows a scanning electron microscope (SEM) image of the diamond thin film 4 of the diamond electrode 1 in Example 3. The SEM image and X-ray analysis (XRD) results (Figure 5) indicate that the diamond thin film 4 has few voids or crystal defects, and that a high-quality polycrystalline diamond thin film has been formed. From the SEM image, the particle size of the diamond particles 4a is estimated to be an average of 1 μm.

[0044] Figure 8(a) shows the cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using the diamond electrode 1 of Example 3 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. The background current at a voltage of 0 V was 5.38 μA and the potential window was 2.94 V, indicating that the diamond electrode 1 of Example 3 also exhibits good characteristics as the working electrode of the electrochemical measuring device 10.

[0045] (Example 4) Next, the manufacturing method for Example 4 of the diamond electrode 1 will be described. In Example 4, the substrate 2, the conditions for the adhesion process (ST1), and the conditions for the film formation process (ST2) are all the same as in Example 1, and the reproducibility of the manufacturing process has been confirmed.

[0046] In Figure 5, a peak originating from tungsten was detected by energy-dispersive X-ray analysis (EDX). The tungsten content (W content) of diamond thin film 4 was 0.02%, which is the same as in Example 1, and the concentration of tungsten element in diamond thin film 4 was 3.5 × 10⁻⁶. 20 cm -3 This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the deposition gas (B / C) is 0.16%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 2.8 × 10⁻⁶. 20 cm -3 It is presumed that...

[0047] Figure 9(b) shows a scanning electron microscope (SEM) image of the diamond thin film 4 of the diamond electrode 1 in Example 4. The SEM image and X-ray analysis (XRD) results (Figure 5) are equivalent to those of Example 1, indicating that the diamond thin film 4 has few vacancies and crystal defects, and that a high-quality polycrystalline diamond thin film is formed with good reproducibility.

[0048] Figure 9(a) shows the cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using diamond electrode 1 from Example 4 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. The background current at 0V was 4.30 μA and the potential window was 3.09 V, which is equivalent to Example 1, and diamond electrode 1 from Example 4 also showed good characteristics as the working electrode of the electrochemical measuring device 10. Thus, Example 1 and Example 4 showed equivalent composition and characteristics, and reproducibility was confirmed.

[0049] (Comparative Examples 1 and 2) Next, the manufacturing methods for Comparative Examples 1 and 2 of the diamond electrode 1 will be described. The manufacturing conditions for Comparative Examples 1 and 2 are the same. In Comparative Examples 1 and 2, the substrate 2, the conditions for the deposition process (ST1), and the temperature of the substrate 2 in the film formation process (ST2) are the same as in Example 1. In Comparative Examples 1 and 2, the flow rates of methane (CH4) gas and hydrogen (H2) gas in the film formation process (ST2) are the same as in Example 1, and hydrogen-diluted trimethylboron (10%) gas is introduced at a flow rate of 0.5 sccm, and the pressure in the chamber is adjusted to 15 Torr. In other words, the concentration of the p-type dopant in the diamond thin film 4 is lower in Comparative Examples 1 and 2 than in Example 1.

[0050] In Figure 5, both Comparative Example 1 and Comparative Example 2 show peaks originating from tungsten by energy-dispersive X-ray analysis (EDX). Since the tungsten content (W content) of the diamond thin film 4 in Comparative Example 1 is 0.14%, the concentration of tungsten element in the diamond thin film 4 is 2.5 × 10⁻⁶. 20 cm -3 This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the film deposition gas (B / C) is 0.08%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 1.4 × 10⁻⁶. 20 cm -3 It is estimated that the tungsten content (W content) of the diamond thin film 4 in Comparative Example 2 is 0.06%, and therefore the concentration of tungsten element in the diamond thin film 4 is 1.1 × 10⁻⁶. 20 cm -3This is calculated as follows. Also, since the ratio of boron (B) to carbon (C) in the film deposition gas (B / C) is 0.08%, the concentration of the p-type dopant (boron concentration) in the diamond thin film 4 is 1.4 × 10⁻⁶. 20 cm -3 It is presumed that...

[0051] Figure 10(a) is a cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using diamond electrode 1 of Comparative Example 1 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. Figure 10(b) is a cyclic voltammogram obtained when the oxidation-reduction reaction was evaluated by cyclic voltammetry using diamond electrode 1 of Comparative Example 2 as the working electrode and 0.1 mol / l sulfuric acid (0.1 M) as the test solution 12. In both Comparative Example 1 and Comparative Example 2, the potential window was 2.5 V or less, and the background current was large, failing to meet the performance requirements as the working electrode of the electrochemical measuring device 10.

[0052] From the above results, in order for the diamond electrode 1 to meet the performance requirements as the working electrode of the electrochemical measuring device 10, the diamond thin film 4 must contain a p-type dopant and tungsten (W) element on its surface and internally. Furthermore, the concentration of the p-type dopant (boron concentration) should be 1.4 × 10⁻⁶. 20 cm -3 This is insufficient, and the degree to which it exhibits metallic properties (for example, 2.8 × 10) 20 cm -3 It is necessary to have a high level of ) [Industrial applicability]

[0053] The present invention provides a diamond electrode with few crystal defects and good in-plane uniformity, and the diamond electrode and electrochemical apparatus using the diamond electrode are useful in the field of electrochemical measurement. [Explanation of symbols]

[0054] 1. Diamond electrode 2 circuit boards 3a Nanodiamond particles 4. Diamond thin film 10 Electrochemical measuring device

Claims

1. The diamond thin film contains a p-type dopant and at least one element, tungsten, and tantalum or rhenium, on its surface and inside. The concentration of the aforementioned p-type dopant is 2 × 10 ２０ cm －３ ~3 x 10 ２２ cm －３ This is a diamond electrode.

2. The concentration of the aforementioned element is 1 × 10 １８ cm －３ ~2 x 10 ２１ cm －３ The diamond electrode according to claim 1.

3. The diamond electrode according to claim 1, wherein the diamond thin film is formed in a gas containing carbon, the p-type dopant, and the element.

4. A method for manufacturing a diamond electrode, comprising a film-forming step of forming a diamond film containing a p-type dopant, tungsten, and at least one element of tantalum or rhenium on the surface of the diamond electrode, wherein the concentration of the p-type dopant is 2×10 ２０ cm －３ to 3×10 ２２ cm －３ .

5. The method for manufacturing a diamond electrode according to claim 4, wherein in the film formation step, the diamond thin film is formed by a thermal filament CVD apparatus comprising a thermal filament made of tungsten and at least one of the thermal filaments made of tantalum or rhenium.

6. The dopant contains a p-type dopant and tungsten, and the concentration of the p-type dopant is 2 × 10⁻⁶. ２０ cm －３ ~3 x 10 ２２ cm －３ The process includes a film deposition step in which a thin diamond film is deposited on the surface of a diamond electrode. A method for manufacturing a diamond electrode, wherein in the film formation step, the diamond thin film is formed by a thermal filament CVD apparatus equipped with a thermal filament made of tungsten, and the concentration of tungsten contained in the diamond thin film is controlled by the temperature of the thermal filament and the substrate on which the diamond thin film is grown.

7. The process further includes an adhesion step in which nanodiamond particles are attached to the surface of the substrate. A method for manufacturing a diamond electrode according to any one of claims 4 to 6, wherein in the film formation step, the diamond thin film is formed on the surface of the substrate to which the nanodiamond particles are attached.

8. The method for manufacturing a diamond electrode according to claim 7, wherein in the deposition step, the substrate is immersed in a solution containing the nanodiamond particles to deposit the nanodiamond particles onto the surface of the substrate.

9. A method for manufacturing a diamond electrode according to claim 4 or 5, wherein in the film formation step, the diamond thin film is formed in a gas containing carbon, the p-type dopant, and the element.

10. An electrochemical measuring device that uses a diamond electrode according to any one of claims 1 to 3 as the working electrode.

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