Electrode and electrochemical measurement system

Abstract

An electrode 10 is provided with a carbon film 20 having sp2 bonds and sp3 bonds. The ratio of sp3 bonds in the carbon film 20 is 0.3-0.45 inclusive, and the full width at half maximum of the G band is 135 cm-1 to 220 cm-1 inclusive.

Description

[Technical Field]

[0001] This invention relates to electrodes and electrochemical measurement systems. [Background technology]

[0002] One electrochemical measurement technique known as stripping voltammetry involves reducing and concentrating (depositing) metal ions present in low concentrations in an aqueous solution on the surface of an electrode, then oxidizing and dissolving the reduced and concentrated metal, and measuring the metal ions in the aqueous solution with high sensitivity based on the current value at this time.

[0003] Patent Document 1 describes a base material and sp arranged on one side of the thickness direction of the base material. 2 Binding and sp 3 An electrode is disclosed, comprising a conductive carbon layer having bonds, characterized in that the oxygen concentration ratio to carbon is 0.07 or less on one side in the thickness direction of the conductive carbon layer.

[0004] According to the electrode described in Patent Document 1, for example, in stripping voltammetry, the target metal can be sufficiently reduced and concentrated, and reliably oxidized and dissolved, thereby increasing the signal current. Furthermore, in cyclic voltammetry, the target hydrogen peroxide can be sufficiently reduced at a lower potential, thereby increasing sensitivity. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-56205 [Overview of the project] [Problems that the invention aims to solve]

[0006] The metal detection characteristics in electrochemical measurements are influenced by the background current or signal current of stripping voltammetry, as well as the negative potential window. Specifically, a lower background current and a higher signal current in stripping voltammetry result in better metal detection sensitivity, and a wider negative potential window results in a wider range of detectable metals.

[0007] However, Patent Document 1 does not mention the background current or signal current of stripping voltammetry, nor the negative potential window. Therefore, there is room for improvement from the viewpoint of obtaining the desired metal detection characteristics.

[0008] The present invention was made to solve the above problems and aims to provide an electrode with low background current in stripping voltammetry and excellent metal detection sensitivity. Furthermore, the present invention aims to provide an electrochemical measurement system equipped with the above electrode. [Means for solving the problem]

[0009] The electrode of the present invention is sp 2 Binding and sp 3 The carbon film comprises a bonded carbon film, and the sp in the carbon film 3 The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. -1 More than 220cm -1 The following applies:

[0010] The electrochemical measurement system of the present invention is equipped with the electrode of the present invention. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an electrode with low background current in stripping voltammetry and excellent metal detection sensitivity. Furthermore, according to the present invention, it is possible to provide an electrochemical measurement system equipped with the above electrode. [Brief explanation of the drawing]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an embodiment of the electrode of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the electrochemical measurement system of the present invention. [Figure 3] FIG. 3 is the C1s spectrum of XPS in Example 1. [Figure 4] FIG. 4 is the Raman spectrum of Raman spectroscopy in Example 1. [Figure 5] FIG. 5 is the SV waveform of lead in Example 1. [Figure 6] FIG. 6 is a graph showing the concentration dependence of the oxidation current of lead in Example 1. [Figure 7] FIG. 7 is the SV waveform of zinc in Example 8.

MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, the electrode and the electrochemical measurement system of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied without changing the gist of the present invention. Combinations of two or more of the individual desirable configurations of the present invention described in the following embodiments are also within the scope of the present invention.

[0014] The drawings shown below are schematic diagrams, and their dimensions, aspect ratios, scales, etc. may be different from those of actual products.

[0015] FIG. 1 is a cross-sectional view schematically showing an embodiment of the electrode of the present invention.

[0016] The electrode 10 shown in FIG. 1 includes a carbon film 20. As shown in FIG. 1, the electrode 10 preferably further includes a base substrate 30. In that case, the carbon film 20 is disposed on one main surface of the base substrate 30.

[0017] The carbon film 20 has sp 2 bonding and sp 3It is formed from carbon atoms that have bonds. In other words, the carbon film 20 is a film having a graphite structure and a diamond structure. As a result, the carbon film 20 has good conductivity.

[0018] At electrode 10, sp in the carbon film 20 3 The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. -1 More than 220cm -1 The following characteristics apply:

[0019] sp in carbon film 20 3 The ratio of bonds is sp 2 The number of bonded atoms and sp 3 sp for the sum of the number of bonded atoms 3 The ratio of the number of atoms bonded together (sp 3 / sp 2 +way 3 This means sp in carbon film 20. 3 The bonding ratio is determined from the sp2c ratio obtained from the C1s spectrum acquired by performing X-ray photoelectron spectroscopy (XPS) on the carbon film 20. 2 Binding and sp 3 The peak area of ​​the bond can be calculated.

[0020] The full width at half maximum (FWHM) of the G band in the carbon film 20 is used as an indicator of the degree of crystallinity. A higher FWHM of the G band indicates a lower degree of crystallinity, while a lower FWHM of the G band indicates a higher degree of crystallinity. The FWHM of the G band in the carbon film 20 can be calculated by performing Raman spectroscopy on the carbon film 20 and separating the peaks into the G band and D band from the Raman spectrum obtained.

[0021] sp 3 The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. -1 More than 220cm -1 The carbon film 20 described below exhibits low background current in stripping voltammetry and excellent metal detection sensitivity.

[0022] The background current in stripping voltammetry is generated by the desorption of water molecules, etc. 2 The π electrons of the bonded carbon function as adsorption sites, therefore sp 3 It is thought that background current can be reduced in film structures with a high bond ratio and a low number of π electrons.

[0023] On the other hand, sp in carbon film 20 3 If the bonding ratio is too high, the conductivity of the carbon film 20 will decrease, making it difficult to use as an electrode. Furthermore, sp in the carbon film 20 3 If the bonding ratio is too high, the internal stress of the carbon film 20 increases, making it more prone to peeling from the underlying substrate 30.

[0024] Furthermore, if the full width at half maximum (FMAX) of the G band in the carbon film 20 is too high, the conductivity of the carbon film 20 will decrease, making it difficult to use as an electrode. In addition, if the full width at half maximum (FMAX) of the G band in the carbon film 20 is too high, the crystallite size (La) will be less than three times the intercarbon bond distance of the six-membered carbon ring (0.14 nm), and it will no longer be possible to define it as a carbon film with nanoscale crystals.

[0025] At electrode 10, sp in the carbon film 20 3 The binding ratio is between 0.3 and 0.42, and the G-band full width at half maximum is 135 cm. -1 More than 210cm -1 The following is preferable:

[0026] sp 3 The binding ratio is between 0.3 and 0.42, and the G-band full width at half maximum is 135 cm. -1 More than 210cm -1 In the carbon film 20 described below, the signal current in stripping voltammetry is high, and it exhibits excellent metal detection sensitivity.

[0027] The oxidation current is proportional to the size of the electrode area where reduction and concentration are active in stripping voltammetry. 2 Since the surface exposure of bonded carbons corresponds to the area of ​​reduction and concentration, to some extent sp2 It is thought that creating a film structure with a high bonding ratio can increase the signal current.

[0028] At electrode 10, sp in the carbon film 20 3 The binding ratio is between 0.34 and 0.37, and the G-band full width at half maximum is 185 cm. -1 More than 210cm -1 The following is more preferable:

[0029] sp 3 The binding ratio is between 0.34 and 0.37, and the G-band full width at half maximum is 185 cm. -1 More than 210cm -1 In the carbon film 20 described below, the negative potential window is wide, and many metal species can be detected.

[0030] The negative potential window refers to the potential at which the reduction reaction of water occurs, and is related to the ease with which electrons are donated from the electrode to water molecules. The carriers of conductive carbon are sp 2 Because it originates from clusters formed by bonding, a smaller cluster size and fewer electron carriers make electron donation less likely, thus widening the negative potential window.

[0031] Furthermore, when the negative potential window is wide, the reduction and concentration of metals with high reduction potentials, such as zinc, is less likely to compete with the reduction reaction of water. Therefore, it is thought that reproducible detection becomes possible.

[0032] The thickness of the carbon film 20 is not particularly limited, but from the viewpoint of film formation, the thickness of the carbon film 20 is preferably 5 nm or more, and more preferably 10 nm or more. On the other hand, from the viewpoint of thin film formation and handling, the thickness of the carbon film 20 is preferably 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less.

[0033] The thickness of the carbon film 20 can be calculated by measuring the X-ray reflectance of the carbon film 20. For measuring the X-ray reflectance, for example, a multi-purpose X-ray diffractometer SmartLab (manufactured by Rigaku) ​​can be used.

[0034] The carbon film 20 may contain other additives (including other elements) in addition to carbon. Furthermore, the carbon film 20 may be composed of multiple layers with different structures, compositions, and additive concentrations. Alternatively, the carbon film 20 may have a configuration in which the structure, composition, and additive concentrations change in a stepwise manner.

[0035] If the electrode 10 includes a base substrate 30, the base substrate 30 has a sheet shape or a film shape. The base substrate 30 supports the carbon film 20.

[0036] Examples of the base substrate 30 include inorganic substrates and organic substrates.

[0037] Examples of inorganic substrates include silicon substrates and glass substrates.

[0038] Examples of organic substrates include polymer films. Examples of polymer film materials include polyester resins (e.g., polyethylene terephthalate, polyethylene naphthalate), acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins (e.g., polycycloolefin polymers), (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins.

[0039] The base substrate 30 is preferably conductive. Examples of conductive base substrates 30 include conductive inorganic substrates such as conductive silicon substrates.

[0040] Although the carbon film 20, which has a film structure suitable for metal detection, may have low conductivity, by using a conductive substrate 30, it becomes possible to extract the current generated by the electrochemical reaction on the surface of the carbon film 20 from the substrate 30, thus allowing it to be used as an electrode. Furthermore, since the resistance of the carbon film and the underlying substrate are high, if IR drop is present, the potential on the electrode surface may drop below the applied potential, and the apparent oxidation potential may shift to the higher potential side. Therefore, it is preferable that the oxidation potential of the reactant measured by cyclic voltammetry does not shift to the higher potential side due to the IR drop during current extraction.

[0041] In this context, "conductivity" means, for example, that the volume resistivity is less than 0.02 Ωcm.

[0042] The thickness of the base substrate 30 is not particularly limited, but is, for example, 2 μm or more, preferably 20 μm or more, while on the other hand, is, for example, 1000 μm or less, preferably 500 μm or less.

[0043] The electrode 10 shown in Figure 1 consists of a carbon film 20 and a substrate 30, but may further include one or more functional layers between the carbon film 20 and the substrate 30, or on the other main surface of the substrate 30. Examples of functional layers include a gas barrier layer, a conductive layer, an adhesion layer, and a surface smoothing layer.

[0044] A method for manufacturing the electrode 10 shown in Figure 1 includes, for example, the steps of preparing a base substrate 30 and forming a carbon film 20 on one main surface of the base substrate 30.

[0045] In the process of preparing the base substrate 30, for example, a known or commercially available substrate is prepared. If necessary, one main surface of the prepared substrate may be subjected to surface treatment, cleaning treatment, etc.

[0046] In the process of forming the carbon film 20, the carbon film 20 is deposited on one main surface of the substrate 30.

[0047] The film deposition process is selected to control the structure of the carbon film 20 and is not particularly limited. Examples include pulsed laser deposition (PLD), chemical vapor deposition (CVD), sputtering, paste printing of carbon materials, and carbonization of various organic materials (polyimide, liquid crystal polymer, epoxy, lignin, polyamide, phenolic resin, etc.).

[0048] The electrode of the present invention can be used as various types of electrodes. Preferably, the electrode of the present invention can be used as an electrode for electrochemical measurements, and more specifically, as a working electrode for stripping voltammetry.

[0049] On one main surface of the electrode of the present invention, an insulating layer patterned into a desired shape may be provided, from the viewpoint of adjusting the exposed surface (electrode surface) of the carbon film. Alternatively, the entire electrode or the carbon film may be patterned into a desired shape. Examples of insulating layers include the polymer film mentioned above as the base substrate.

[0050] The following describes in detail an electrochemical measurement system equipped with the electrodes of the present invention. Such an electrochemical measurement system is also one of the present inventions.

[0051] The electrochemical measurement system of the present invention comprises, for example, a working electrode, a reference electrode, a potentiometer for measuring the electromotive force between these electrodes, and an aqueous solution (electrolyte). The electrode of the present invention is preferably used as the working electrode.

[0052] Figure 2 is a schematic diagram showing an example of the electrochemical measurement system of the present invention.

[0053] The electrochemical measurement system 100 shown in Figure 2 comprises a working electrode 110, a reference electrode 120, a counter electrode (counter electrode) 130, a potentiostat 140 for controlling the potentials of these electrodes, an ammeter (not shown as it is incorporated into the potentiostat 140) for measuring the current flowing between the working electrode 110 and the counter electrode 130, and an aqueous solution 150.

[0054] Examples of the working electrode 110 include the electrode 10 shown in Figure 1, which is an example of the electrode of the present invention.

[0055] Examples of reference electrodes 120 include silver / silver chloride electrodes, saturated calomel electrodes, and standard hydrogen electrodes.

[0056] Examples of counter electrodes 130 include platinum electrodes, gold electrodes, and nickel electrodes.

[0057] Aqueous solution 150 can be an aqueous solution containing the object to be measured.

[0058] In the electrochemical measurement system 100 shown in Figure 2, for example, stripping voltammetry is performed using the electrode of the present invention as the working electrode 110.

[0059] The target of measurement in stripping voltammetry is metal ions. Examples of heavy metal ions include iron ions, lead ions, gold ions, platinum ions, silver ions, copper ions, chromium ions, cadmium ions, mercury ions, zinc ions, arsenic ions, manganese ions, cobalt ions, nickel ions, molybdenum ions, tungsten ions, tin ions, bismuth ions, uranium ions, and plutonium ions.

[0060] As described above, in the electrode of the present invention, sp in the carbon film 3 The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. -1 More than 220cm -1 The following is the reason: Therefore, the background current of stripping voltammetry is low, resulting in excellent metal detection sensitivity.

[0061] This specification discloses the following:

[0062] <1> sp 2 Binding and sp 3 A carbon film having bonds, Spa 3 The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. -1 More than 220cm -1 The electrodes are as follows.

[0063] <2> Spa 3 The binding ratio is between 0.3 and 0.42, and the G-band full width at half maximum is 135 cm. -1 More than 210cm -1 The following is: <1> The electrodes described above.

[0064] <3> Spa 3 The binding ratio is between 0.34 and 0.37, and the G-band full width at half maximum is 185 cm. -1 More than 210cm -1 The following is: <2> The electrodes described above.

[0065] <4> Further equipped with a base substrate, The carbon film is arranged on one main surface of the above-mentioned substrate. <1> ~ <3> The electrode described in one of the following.

[0066] <5> The above substrate is conductive. <4> The electrodes described above.

[0067] <6> <1> ~ <5> An electrochemical measurement system comprising an electrode described in any one of the following.

[0068] <7> Stripping voltammetry is performed using the above electrode as the working electrode. <6> The electrochemical measurement system described above. [Examples]

[0069] The following are examples that more specifically disclose the electrodes of the present invention. However, the present invention is not limited to these examples.

[0070] <Example 1> [Deposition of carbon films] A 200 nm thick carbon film was formed on a 350 μm thick conductive silicon substrate using pulsed laser deposition (PLD). In PLD, a pulsed laser is irradiated onto a graphite target placed in a chamber, causing the target to instantaneously evaporate and generate a plume. Active particles in the plume reach the substrate and recondense to form a carbon film.

[0071] The film structure of the carbon film can be controlled by the PLD conditions. Specifically, by changing the way carbon atoms are released and the energy after they reach the substrate, the film structure of the carbon film (degree of crystallinity and sp) can be controlled by the deposition conditions. 3 The binding ratio can be controlled.

[0072] The conditions for this embodiment are as follows: Target material: Graphite Laser wavelength: Nd:YAG laser (266nm) Laser density: 2.54 J / cm² 2 Repeat frequency: 10Hz Deposition atmosphere: Vacuum (2.0 × 10⁻⁶) -7 Torr) Substrate temperature: 400℃

[0073] [Evaluation of carbon film structure] X-ray photoelectron spectroscopy (XPS) was performed on this carbon film.

[0074] Figure 3 shows the C1s spectrum of XPS in Example 1.

[0075] From the obtained C1s spectrum, sp 2 Binding and sp 3 The peak area of ​​the bond is calculated, sp 3 The bonding ratio was calculated. In Example 1, sp 3 The binding ratio was 0.32.

[0076] Next, Raman spectroscopy was performed.

[0077] Figure 4 shows the Raman spectrum obtained from Raman spectroscopy in Example 1.

[0078] The obtained Raman spectra were separated into G-band and D-band peaks, and the full width at half maximum (FWHM) of the G-band, an indicator of the degree of crystallization, was calculated. In Example 1, the FWHM of the G-band was 136 cm⁻¹. -1 That was the case. 2 The cluster size La due to bonding is estimated to be approximately 1.5 nm, indicating that it is amorphous carbon with nanoscale crystals.

[0079] The measurement and analysis conditions are as follows: [XPS] Measurement equipment: X-ray photoelectron spectrometer PHI XPS-1600R (manufactured by ULVAC) X-ray source: MgKα (1253.6eV), 15kV, 400W Removal angle: 45 degrees Measurement area: Φ800μm Analysis conditions: Baseline subtraction using the Shirley method and peak separation using Voigt functions (Gauss 0.7, Lorentz 0.3). [Raman spectroscopy] Measurement device: Fluorescence-avoiding laser Raman spectrophotometer RMP-510RS (manufactured by JASCO Corporation) Light source: Nd:YVO4 semiconductor laser (532nm), 20mW Grating: 900g / mm Measurement area: Magnification 20x, working distance 12mm, numerical aperture 0.40 Analysis conditions: Baseline subtraction using a linear function and peak separation using a Gaussian function.

[0080] [Evaluation of lead detection characteristics of carbon films] The carbon film was used as the working electrode, silver chloride as the reference electrode, and platinum wire as the counter electrode, and was set up in an electrochemical measurement cell (plate electrode evaluation cell kit, BAS). Acetate buffer solution containing lead chloride (pH 5.6) was poured in so that each electrode was immersed, and the cell was connected to a potentiostat (Model 600E, BAS).

[0081] The lead ion concentration is 1 × 10 -7 M, 5×10 -7 M, 1×10 -6 M, 2×10 -6 The solutions were prepared to achieve the M standard, and stripping voltammetry (SV) was performed on each solution. Specifically, first, a voltage was applied to the carbon film with a reduction potential of -1.4V and a deposition time of 300 seconds. This reduced and concentrated the lead ions in the low-concentration lead chloride aqueous solution onto the carbon film surface. Next, linear sweep voltammetry was performed with a sweep rate of 200mV / s to oxidize and dissolve the concentrated lead.

[0082] Figure 5 shows the SV waveform of lead in Example 1. Figure 6 is a graph showing the concentration dependence of the oxidation current of lead in Example 1.

[0083] In Example 1, the background current (BG current) of the SV was 25 μA / cm². 2 The slope of the lead calibration curve is 19 μA / μM·cm. 2 This was the case. Furthermore, the current value at 0V in the SV waveform was defined as the SV BG current.

[0084] <Example 2> The sample was fabricated under the same conditions as in Example 1, except that the substrate temperature was changed to room temperature (RT). The same evaluation of the film structure and lead detection characteristics as in Example 1 was performed.

[0085] <Example 3> The atmosphere is nitrogen (1.0 × 10 -2 The sample was prepared under the same conditions as in Example 1, except that Torr was changed. The same evaluation of the film structure and lead detection characteristics as in Example 1 was performed.

[0086] <Comparative Example 1> The atmosphere is argon (1.0 x 10 -2 The sample was prepared under the same conditions as in Example 1, except that Torr was changed. The same evaluation of the film structure and lead detection characteristics as in Example 1 was performed.

[0087] <Comparative Example 2> A 70 μm thick carbon film was formed on a 125 μm thick polyimide film using laser carbonization. Laser carbonization is a phenomenon in which organic materials such as resins are transformed into a graphite structure by laser energy.

[0088] The film structure of the carbon film can be controlled by the laser irradiation conditions. Specifically, by changing the amount of heat applied to the surface of a resin such as polyimide depending on the laser wavelength, the film structure of the carbon film (degree of crystallinity and sp) can be controlled. 3 The bonding ratio can be controlled. By using the laser carbonization method, carbon films with a high degree of crystallinity, which are difficult to deposit using the PLD method, can be fabricated.

[0089] The conditions for Comparative Example 2 were as follows. After preparation, the same evaluation of the film structure and lead detection characteristics as in Example 1 was performed. Irradiation material: Kapton® (manufactured by Toray DuPont) Laser equipment: 3-axis CO2 laser marker / head ML-Z9510 (manufactured by Keyence Corporation) Laser wavelength: 10.6 μm Laser output: 6W Atmosphere: Atmosphere Sweep speed: 250mm / s Sweep interval: 100μm

[0090] <Comparative Example 3> A 50 μm thick carbon film was formed on a 125 μm thick polyimide film using a laser carbonization method. The film structure was controlled by using a different laser wavelength than in Comparative Example 2.

[0091] The conditions for Comparative Example 3 were as follows. After preparation, the same evaluation of the film structure and lead detection characteristics as in Example 1 was performed. Irradiation material: Kapton® (manufactured by Toray DuPont) Laser device: 3-Axis Hybrid Laser Marker MD-X1000 (manufactured by Keyence Corporation) Laser wavelength: 1064nm Laser output: 5W Atmosphere: Atmosphere Sweep speed: 250mm / s Sweep interval: 25μm

[0092] Table 1 summarizes the film deposition conditions, film structure indicators, and lead detection characteristics for Examples 1-3 and Comparative Examples 1-3. In Table 1, carbon films in which lead oxidation current could not be detected are marked with "-".

[0093] [Table 1]

[0094] The BG current of SV in Examples 1-3 was an order of magnitude smaller than the BG current of SV in Comparative Examples 1-3, and the oxidation current of lead was confirmed. Therefore, sp in the carbon film 3 The binding ratio is between 0.3 and 0.45, and the G-band FWHM is 135 cm⁻¹. -1 More than 220cm -1 The following conditions indicate high detection sensitivity and suitability for metal detection.

[0095] As mentioned above, the BG current in SV is generated by the desorption of water molecules, etc. 2 The π electrons of the bonded carbon function as adsorption sites, therefore sp 3 It is thought that a film structure with a higher bond ratio and lower crystallinity, resulting in fewer π electrons, can lower the background current.

[0096] <Example 4> Laser density of 3.57 J / cm² 2 The sample was prepared under the same conditions as in Example 2, except for the changes made to the other components. The same evaluation of the film structure and lead detection characteristics as in Example 1 was performed.

[0097] <Example 5> After film deposition under the same conditions as in Example 2, annealing treatment was performed in the same chamber (substrate temperature: 400°C, atmosphere: vacuum (2.0 × 10)). -7 The sample was prepared by adding Torr (time: 1 hr). The same evaluation of the film structure and lead detection characteristics as in Example 1 was performed.

[0098] <Example 6> After film formation under the same conditions as in Example 3 except that the substrate temperature was changed to room temperature (R.T.), annealing treatment (substrate temperature: 400 °C, atmosphere: vacuum (2.0×10 -7 Torr), time: 1 hr) was added in the same chamber and the sample was fabricated. The evaluation of the film structure and the evaluation of the lead detection characteristics were carried out in the same manner as in Example 1.

[0099] <Example 7> After film formation under the same conditions as in Comparative Example 1 except that the substrate temperature was changed to room temperature (R.T.), annealing treatment (substrate temperature: 400 °C, atmosphere: vacuum (2.0×10 -7 Torr), time: 1 hr) was added in the same chamber and the sample was fabricated. The evaluation of the film structure and the evaluation of the lead detection characteristics were carried out in the same manner as in Example 1.

[0100] The film formation conditions, the indexes of the film structure, and the lead detection characteristics of Examples 1 to 7 are summarized in Table 2.

[0101]

Table 2

[0102] The slopes of the calibration curves for lead in Examples 1, 3, 4, 6, and 7 were 1.5 times or more the slopes of the calibration curves for lead in Examples 2 and 5. Therefore, when the proportion of sp 3 bonding in the carbon film is 0.3 or more and 0.42 or less, and the FWHM of the G band is 135 cm -1 or more and 210 cm -1 or less, it can be said that the detection sensitivity is higher and it is suitable for metal detection.

[0103] As described above, the oxidation current is proportional to the size of the electrode area where the reduction concentration of SV is active. Since the surface exposed portion of the highly reactive sp 2 bonded carbon corresponds to the area of reduction concentration, it is considered that the slope of the calibration curve can be increased in a film structure having a large amount of carbon with sp 2 bonding.

[0104] <Example 8> The laser density was 2.65 J / cm 2It was fabricated under the same conditions as in Example 2 except for the change. In addition to the evaluation of the film structure and the detection characteristics of lead as in Example 1, the following evaluation of the detection characteristics of zinc was carried out.

[0105] [Evaluation of the Detection Characteristics of Zinc in the Carbon Film] Using the same setup as in the evaluation of the detection characteristics of lead in Example 1, the detection characteristics of zinc were evaluated. For the detection of metals with a large reduction potential such as zinc, it is necessary to make the reduction potential of SV significantly negative, so the reduction reaction of water competes and the reproducibility tends to decrease. Therefore, the width of the negative potential window and the reproducibility of the oxidation current of zinc were evaluated. Note that when the negative potential window is wide, it is less affected by the reduction reaction of water.

[0106] The evaluation of the potential window was carried out by cyclic voltammetry at a scan rate of 50 mV / s in 0.05 M sulfuric acid. The negative potential at which the current density reaches 5×10 -4 A / cm 2 was defined as the negative potential window. The evaluation of the reproducibility of the oxidation current of zinc was carried out by preparing a zinc ion concentration of 1×10 -5 M and performing stripping voltammetry (SV) three times. Except for changing the reduction potential to -2.0 V, it was the same as in Example 1.

[0107] Figure 7 is the SV waveform of zinc in Example 8.

[0108] In Example 8, the negative potential window was -1.4 V, and the oxidation currents of zinc measured three times were 47 μA / cm 2 , 50 μA / cm 2 , 50 μA / cm 2 and highly reproducible measurements were possible.

[0109] [Example 9] It was fabricated under the same conditions as in Example 2 except for changing the film-forming chamber and changing the laser density to 0.91 J / cm 2 . In addition to the evaluation of the film structure and the detection characteristics of lead as in Example 1, the evaluation of the detection characteristics of zinc as in Example 8 was carried out.

[0110] For Examples 1, 3, 4, 6, and 7, the same evaluation of zinc detection characteristics as in Example 8 was added, and the film deposition conditions, film structure indicators, and lead detection characteristics are summarized in Table 3. The criteria for reproducible detection of zinc were as follows. ○: The variation from the average of three measured oxidation currents is within 5%. ×: The variation from the average of three measured oxidation currents is 5% or more, or no oxidation current is detected.

[0111] [Table 3]

[0112] In Examples 4, 8, and 9, the negative potential window was 0.2V wider than in Examples 1, 3, 6, and 7, enabling reproducible detection of zinc. Therefore, sp in carbon films 3 The binding ratio is between 0.34 and 0.37, and the G-band FWHM is 185 cm⁻¹. -1 More than 210cm -1 The following conditions indicate a wider range of detectable metal species and make the device more suitable for metal detection.

[0113] As mentioned above, the negative potential window refers to the potential at which the reduction reaction of water occurs, and is related to the ease with which electrons are donated from the electrode to water molecules. The carriers of conductive carbon are sp 2 Because the reaction originates from bonded clusters, smaller cluster sizes and fewer electron carriers make electron donation less likely, resulting in a wider negative potential window. Furthermore, a wider negative potential window means that the reduction and concentration of metals with high reduction potentials, such as zinc, is less likely to compete with the reduction reaction of water, thus ensuring reproducibility.

[0114] <Example 10> The sample was prepared under the same conditions as in Example 8, except that the substrate was changed to a polyimide film (Kapton®, manufactured by Toray DuPont). When the film structure was evaluated in the same way as in Example 1, it was similar to Example 8, where the substrate was a conductive silicon substrate. On the other hand, the electrode resistance was high, making electrochemical measurements difficult.

[0115] From the above, as shown in Examples 1 to 9, a carbon film formed on a conductive substrate can be used as an electrode for electrochemical measurements even if the carbon film is thin. If the conductivity of the carbon film is low, a carbon film with a thickness of 200 nm alone will have high electrode resistance, making it difficult to use as an electrode for electrochemical measurements on its own. Therefore, by using a conductive substrate, it becomes possible to draw out the current generated by the electrochemical reaction on the surface of the carbon film from the substrate, and thus it can be used as an electrode. [Explanation of symbols]

[0116] 10 electrodes 20 Carbon film 30 Substrate 100 Electrochemical Measurement Systems 110 Working electrode 120 Reference electrode 130 Counter electrode (counter electrode) 140 potentiostats 150 Aqueous solution

Claims

1. sp ２ Bonding and sp ３ A carbon film having bonds, sp in the carbon film ３ The binding ratio is between 0.3 and 0.45, and the G-band full width at half maximum is 135 cm. －１ 220cm or more －１ The electrodes are as follows.

2. sp in the carbon film ３ The binding ratio is between 0.3 and 0.42, and the G-band full width at half maximum is 135 cm. －１ 210cm or more －１ The electrode according to claim 1, which is as follows:

3. The proportion of sp ３ bonding in the carbon film is 0.34 or more and 0.37 or less, and the full width at half maximum of the G band is 185 cm －１ or more and 210 cm －１ or less. The electrode according to claim 2.

4. Further equipped with a base substrate, The electrode according to any one of claims 1 to 3, wherein the carbon film is disposed on one main surface of the substrate.

5. The electrode according to claim 4, wherein the base substrate is conductive.

6. An electrochemical measurement system comprising the electrode described in any one of claims 1 to 3.

7. The electrochemical measurement system according to claim 6, wherein stripping voltammetry is performed using the electrode as the working electrode.

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