JP7160053B2 - Carbon film and its deposition method - Google Patents

Description

The present invention relates to carbon films and the like.

Carbon materials take various forms depending on the bonding state and arrangement structure of carbon (C), and exhibit unique physical properties (characteristics) according to each form. By using a carbon material in an appropriate form, desired properties, functions, and the like can be imparted to the member. In particular, since the properties of a member largely depend on the surface properties, a predetermined carbon film is often formed on the surface of the member.

As an example, a carbon film having excellent conductivity and corrosion resistance is formed on the electrode-side surface of a metal separator for fuel cells. There is a description related to this in Patent Document 1.

Japanese Patent No. 5217243 Japanese Patent No. 3962420 JP-A-2005-97113

Cancado, K. Takai, T. Enoki, M. Endo, Y. A. Kim, H. Mizusaki, A. Jorio, L. N. Coelho, R. Magalhaes-Paniago and M. A. Pimenta, Applied Physics Letters, 88, 163106 (2006).

Patent Document 1 proposes a conductive amorphous carbon film (also referred to simply as "DLC (Diamond-like Carbon) film"). A DLC film is generally formed by σ-bonding carbon (Csp ³ ) in sp ³ hybrid orbitals, and is close to diamond and hard, but has low electrical conductivity. Therefore, in the DLC film of Patent Document 1, conductivity is ensured by increasing the π-bonds due to carbon (Csp ² ) in sp ² hybrid orbitals. However, Patent Document 1 does not refer to the specific form of the DLC film, the nano-size level structure, and the like. The DLC film of Patent Document 1 is formed by a plasma CVD method under high vacuum.

Patent Literatures 2 and 3 describe carbon nanowalls, although their uses are not clear. A carbon nanowall is a wall-like carbon nanostructure that rises almost vertically from the surface of a substrate and has a two-dimensional spread ([0006] of Patent Document 2, [0006] of Patent Document 3, etc.).

The carbon nanowalls of Patent Literatures 2 and 3 are characterized in that they stand directly on the substrate surface without intervening a metal catalyst. A diagram of such carbon nanowalls is shown in FIG.

However, in carbon nanowalls standing directly on the base material surface, the corrosive liquid may enter the base material side through the adjacent walls (gap) and corrode the base material surface. For this reason, a carbon film composed of such carbon nanowalls is not suitable as a conductive carbon film covering at least the electrode-side surface of a fuel cell separator used in a corrosive environment.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a new carbon film or the like having a structure different from that of the conventional ones.

As a result of intensive research to solve this problem, the inventors of the present invention succeeded in obtaining a carbon film with a new structure in which the forms of graphene contained in each region (layer) are different. Developing this result led to the completion of the present invention described below.

《Carbon film》
The present invention is a carbon film having a first layer containing flat graphene and a second layer formed on the first layer and containing arc-shaped graphene.

The carbon film of the present invention contains graphene in which ^Csp2 is bound, and itself is excellent in corrosion resistance and conductivity. In addition, the carbon film of the present invention can also improve the corrosion resistance, electrical conductivity, etc. of the substrate on which it is formed. This is considered to be due to the following reasons.

The first layer on the lower layer side (substrate side) is formed along the substrate surface with flat graphene. Therefore, the first layer serves as a barrier layer that inhibits contact between the surface of the base material and corrosive substances, and suppresses corrosion and oxidation of the base material (including generation of a passivation film, etc.).

The second layer on the upper layer side (surface side) increases the (specific) surface area of the carbon film due to arc-shaped graphene. Therefore, when the second layer comes into contact with another member (gas diffusion layer, etc.) or a reactant (reactant gas, etc.), it contributes to an increase in the contact area between the two and an accompanying improvement in contact conductivity.

<<Method of Forming Carbon Film>>
(1) The above-described carbon film can be formed by any method, but for example, plasma of a raw material gas containing a hydrocarbon gas is ejected onto the surface to be treated in an environment near atmospheric pressure, and the surface to be treated is It can also be obtained by the method of forming the above-described carbon film on the surface. The present invention can also be understood as a method for forming such a carbon film.

In this case, the film can be formed without preparing a high-vacuum atmosphere or the like, and a coated member (for example, a fuel cell separator) having a carbon film formed on the surface to be treated can be efficiently produced at low cost. In addition, according to this film forming method, a carbon film can be applied to a base material (non-metallic material such as resin, ceramics, etc.) that is not electrically conductive (conductive).

(2) The film forming method described above may be performed using, for example, the following plasma apparatus. That is, it has an introduction section to which the raw material gas is supplied, and a first insulator, a first electrode, a second insulator, and a second electrode that are arranged downstream of the introduction section and stacked in order from the upstream side. and a communication hole penetrating through the first insulator, the first electrode, the second insulator and the second electrode from the upstream side to the downstream side, and connecting the first electrode and the second electrode. It is a plasma device that applies a voltage to eject the plasma of the raw material gas from the communication hole.

《Covering material》
The present invention provides a coated member (conductive member) having a base material and a carbon film covering at least a part of the surface of the base material, or a coating formed by forming a carbon film on the surface of the base material to be treated by the method described above. It is also grasped as a member. Such a coated member can be improved in electrical conductivity, corrosion resistance, etc. by the carbon film.

An example of the covering member is a fuel cell separator. The substrate is, for example, a metal substrate such as titanium (alloy) or stainless steel. The carbon film formed on the substrate (electrode side, gas diffusion layer side) has a film thickness of, for example, 10 to 1000 nm, 25 to 300 nm, or further 50 to 100 nm.

"others"
(1) The "carbon film" referred to in this specification may be C as a main component. Suffice it to say, for example, C should be contained in an amount of 70 atomic % (at %) or more, 80 at % or more, further 90 at % or more with respect to the entire carbon film. The carbon film contains, for example, H, etc., in addition to C, although it depends on the raw material gas.

(2) The "conductivity" of the carbon film is indexed by contact resistivity, for example. The contact resistivity is, dare I say, 500 mΩ/cm ² or less, 50 mΩ/cm ² or less, 10 mΩ/cm ² or less, or even 5 mΩ/cm ² or less.

(3) “Around atmospheric pressure” in this specification is, dare I say, a range of atmospheric pressure (P) that satisfies 0.01P ₀ ≤ P ≤ 1.1P ₀ with respect to atmospheric pressure (P ₀ ). .

(4) "x to y" as used herein includes the lower limit value x and the upper limit value y unless otherwise specified. A new range such as “a to b” can be established as a new lower or upper limit of any numerical value included in the various numerical values or numerical ranges described herein. Unless otherwise specified, "x to ynm" as used herein means xnm to ynm. The same applies to other unit systems (mΩ/cm ² , kHz, sccm, mm, etc.).

It is a schematic diagram showing an example of the carbon film of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an outline of a plasma apparatus as an example in a cross section of a main part; It is a photograph showing plasma actually generated by the plasma device. 4 is a Raman spectrum of a film according to sample 1; 3 is an HRTEM image obtained by observing a film cross section of Sample 1. FIG. It is explanatory drawing which shows typically the measuring method of contact resistance. 1 is a schematic diagram showing a conventional carbon film (carbon nanowall); FIG.

The components of the present invention may be supplemented with one or more optional components selected from herein. The contents described in this specification apply not only to the carbon film and its film forming method, but also to the coated member and its manufacturing method as appropriate. Even a method component can be a material component. Which embodiment is the best depends on the target, required performance, and the like.

《Graphene/Graphite》
Graphene is a constituent unit of graphite, and is a one-atom-thick sheet-like material having a basic structure of a six-membered ring structure in which ^Csp2 is bonded in a hexagonal lattice.

(1) The presence or absence of graphene can be determined from the Raman spectrum of the carbon film. The Raman spectrum is obtained by Raman spectroscopy, and the Raman shift, which is the wave number difference between the incident light (excitation light, Rayleigh scattered light) and the Raman scattered light, is plotted on the horizontal axis (cm ⁻¹ ), and the scattering FIG. 2 is a diagram with Raman intensity on the vertical axis.

When graphene exists, a peak called G-band appears near 1580 cm ⁻¹ on the Raman spectrum. The number of graphene stacks is indexed by, for example, the shift amount of the peak position of the G band. Looking at the Stokes line side where the scattering intensity is strong (the same applies hereinafter), the peak position shifts to the low frequency side (the side where the wavenumber of the Raman shift increases) as the number of layers increases. Note that the number of stacked layers of graphene may be grasped from the 2D band (G′: G prime), which is a peak appearing near 2700 cm ⁻¹ .

Graphene may contain a lattice defect or the like in which Csp ² is bonded in a pentagonal or heptagonal lattice in the basic structure. Disorders and defects in the structure are known from the D-band, which is a peak appearing near 1360 cm ⁻¹ on the Raman spectrum derived from them.

If we dare to say each band range, for example, G band: 1570 to 1620 cm ^-1 and D band: 1340 to 1380 cm ^-1 may be used.

(2) The form of graphene can be grasped by observing the cross section of the carbon film with an electron microscope or the like. For the electron microscope, for example, a transmission electron microscope (TEM) or a high-resolution transmission electron microscope (HRTEM) may be used.

In the cross section of the carbon film, the graphene that appears to be linear (linear) is referred to herein as “flat” graphene, and the graphene that appears to be curved (arcuate) is referred to herein as “arc”. called graphene. In terms of three-dimensional space, flat graphene can have a substantially planar shape, and arc-shaped graphene can have a curved surface (curved surface).

《Carbon film》
(1) Crystallite size Graphene contained in a carbon film is usually in a laminated state and is considered to form graphite crystals. The size of each crystal is evaluated by the crystallite size (La/nm) defined by the following formula (Formula 1).
La ₌ 560·( _ID / _IG ) ⁻¹ /EL ⁴ (Formula 1)
where, E _L : Energy of excitation laser (eV)
I _D : Peak value of D band
_IG : Peak value of _G band Note that ID and IG are the peak values on the Stokes line side of the Raman spectrum (wavelength of excitation light: _532.05 nm).

The graphite contained in each layer preferably has a crystallite size of, for example, 10 nm or more, 15 nm or more, or further 20 nm or more. The upper limit of the crystallite size may be, for example, 100 nm or less, or 50 nm or less. The larger the crystallite size, the higher the corrosion resistance (including oxidation resistance, passivation film formation, etc.) and contact conductivity of the substrate coated with the carbon film. However, if the crystallite size becomes excessively large, the arc-shaped graphene is reduced, the specific surface area is also reduced, and the contact conductivity may be lowered.

In this specification, the crystallite size is evaluated by Equation 1 above, regardless of the graphite crystallite size directly observed by HRTEM or the like. Formula 1 is described in detail in Non-Patent Document 1 mentioned above.

(2) Raman spectrum Depending on the crystallinity of graphite contained in the carbon film, the half width of the G band is, for example, 100 cm ^-1 or less, 80 cm ^-1 or less, or 65 cm ^-1 or less. As for the lower limit, the half width may be, for example, 20 cm ⁻¹ or more, or 40 cm ⁻¹ or more. It should be noted that the “half width” referred to in this specification is the full width at half maximum determined based on the Raman spectrum. The carbon film of the present invention is considered to have higher crystallinity than the conventional conductive DLC film from the crystallite size and half width. However, the carbon film of the present invention may be generally called crystalline or amorphous.

A carbon film does not necessarily consist only of complete graphene, and peaks other than the G band (D band, 2D band, etc.) may also appear on its Raman spectrum. At this time, the intensity ratio (I _D /I _G ), which is the ratio of the peak value (I _D ) of the D band to the peak value (I _G ) of the G band, is, for example, 0.6 to 1.4, 1 to 1 .3 and 1.1 to 1.2.

(3) Layers The morphology of each layer constituting the carbon film is schematically shown in FIG. Each layer will be described below. Although FIG. 1 shows only representative layers according to the present invention for convenience of explanation, the carbon film of the present invention may have other layers.

The first layer preferably contains planar graphene and has a planar or curved shape extending along the substrate surface. The dense coating of the first layer on the substrate surface prevents contact between corrosive substances (e.g., acidic corrosive liquids, corrosive gases, etc.) and the substrate surface, thereby suppressing chemical changes (alteration) on the substrate surface. be. The thickness of the first layer is, for example, 1-100 nm or even 3-20 nm.

The second layer includes arc-shaped graphene, and its surface (the substrate side (the first layer side) is the back surface) has an uneven shape in which, for example, open curved depressions are distributed. The second layer increases the specific surface area of the carbon film and can improve the contact between the carbon film and other members or reactants.

The recess may have any specific shape, and may be, for example, substantially hemispherical, substantially cylindrical with a bottom, or the like. The center of the recess may be planar or curved. Conversely, the ends of the depressions may stand upright toward the first layer. This increases electron mobility from the surface of the carbon film to the substrate. In addition, dare to say, "vertical" means that the angle formed by the tangent line at the outermost surface end of the depression and the first layer (substrate surface) is approximately perpendicular (30 ° to 150 °, 45 ° to 135 ° and even 60 ° ~120°).

The opening size of the depression (maximum opening width on the surface side) is, for example, 1 to 100 nm, further 3 to 20 nm. The thickness of the second layer is, for example, 1-500 nm, 5-100 nm or even 10-50 nm.

In addition, in the transition region from the first layer to the second layer (for example, the connection region from the upper surface side of the first layer to the lower surface side of the depression of the second layer), flat graphene and / or arc-shaped graphene, Alternatively, there may be an intermediate layer (connection layer, filling layer) composed of a laminate (graphite) (see FIG. 1).

<<Method of forming film>>
An example of forming a carbon film using a plasma apparatus will be described below.

(1) The plasma device ejects plasma from a communication hole passing through, for example, a first insulator, a first electrode, a second insulator, and a second electrode, which are stacked in order from the upstream side. Plasma is generated by discharge between the inner peripheral surface of the first electrode and the inner peripheral surface of the second electrode exposed in the communication hole. Plasma (electrons, radicals, ions, etc. formed by ionization of gas molecules) generated in the communicating hole is pushed out by the flow of the raw material gas (air current) introduced from the upstream end of the communicating hole, and flows downstream of the communicating hole. It is drawn out (ejected) from the end port. According to such a plasma apparatus, unlike a dielectric barrier discharge apparatus or the like, it is possible to generate plasma with a large discharge current and a high current density. Therefore, efficient plasma processing can be performed even on the surface to be processed of the work (base material) in an atmosphere near the atmospheric pressure. It should be noted that upstream and downstream referred to in this specification are along the direction of flow of source gas or plasma.

Each electrode is made of metal such as stainless steel, iron, copper, titanium, tungsten, and aluminum. The insulator is made of, for example, ceramics, quartz, glass, polytetrafluoroethylene, polyimide (eg Kapton), or the like. For ceramics, for example, alumina (Al ₂ O ₃ ), aluminum nitride (AlN), boron nitride (BN), etc., which are also excellent in heat resistance, can be used.

The thickness of each electrode is, for example, 1-30 mm or even 5-15 mm. The thickness of each insulator is, for example, 0.1-20 mm or even 1-10 mm. In particular, the thickness of the first insulator (the distance between the first electrode and the second electrode) is preferably 0.1 to 5 mm, more preferably 0.5 to 3 mm. If the thickness is too small, the insulator will partially break down and the discharge will become unstable. Its thickness may be large, but if it is too large, the discharge voltage will increase and the equipment cost of the power supply will increase.

The second electrode may have the same potential as the work (or the stage on which it is placed), or may be given a bias potential. If the potential difference between the two is appropriate, the plasma is efficiently guided to the surface of the workpiece to be processed without causing electrical discharge between the lower surface of the second electrode and the workpiece. The lower surface side (work side) of the second electrode may be covered with an insulator (film). When no bias potential is applied, the second electrode, the stage (or workpiece), the housing (chamber) surrounding them, and the like may all be grounded.

The shape, arrangement, etc. of the communication holes are appropriately adjusted. The cross-section of the communication hole may be, for example, circular or slit-like (elliptical, oval, rectangular, etc.). The hole diameter of the round hole is, for example, φ0.1 to 10 mm, or φ0.5 to 5 mm. The size of the slit-like hole may be, for example, a maximum width of 0.1 to 10 mm, preferably 0.5 to 5 mm, and a maximum length of 20 to 200 mm, preferably 40 to 120 mm. An excessively small communicating hole may be clogged by film formation for a long time. An excessively large communication hole shortens the length of plasma blowout.

One or more communication holes may be provided. If there are a plurality of communication holes, the arrangement of each communication hole may be regular or irregular.

(2) The raw material gas contains at least a carbon source gas. A carbon source gas is, for example, a hydrocarbon gas containing one or more of methane, ethane, propane, ethylene, acetylene, and the like. The raw material gas may contain nitrogen gas, rare gas (He, Ne, Ar, Kr, Xe, etc.) in addition to the carbon source gas. In particular, the raw material gas is preferably a mixed gas of a carbon source gas (such as methane) and a rare gas (such as Ar).

The flow rate of the raw material gas can be appropriately adjusted according to film formation conditions (film thickness, applied voltage, size of communicating holes, etc.). The flow rate of the carbon source gas may be, for example, 30 to 2000 sccm in total (standard conditions: 1 atm×0° C./same below), and further preferably 50 to 300 sccm. The flow rate of the rare gas may be, for example, 100 to 3000 sccm, or even 200 to 1000 sccm. If the amount of the carbon source gas is too small, the film formability will deteriorate. Each gas can be more, but the surplus gas increases. Note that the raw material gas may contain a small amount of impurities (such as oxygen).

(3) A voltage required for plasma generation is applied between the electrodes from a power source. The applied voltage may be a DC voltage, an AC voltage, or a pulse voltage. The AC voltage or pulse voltage may have a frequency of, for example, 1 kHz to 50 kHz, or 5 kHz to 20 kHz.

The applied voltage (the voltage difference from the maximum value to the minimum value/peak to peak value) is preferably 200 to 2000V, further 400 to 1000V, for example. Typically, a positive or negative high voltage is applied to the first electrode with respect to the second electrode. The second electrode may be grounded, for example.

(4) The distance (interval) from the lower end opening of the communicating hole to the work may be, for example, 0.1 to 20 mm, further preferably 0.5 to 10 mm. By appropriately adjusting the gap, a desired carbon film can be stably formed.

A carbon film can be formed on the surface of the workpiece under atmospheric pressure, but at least the periphery of the workpiece may be under sub-atmospheric pressure. As a result, it is possible to prevent the material gas, plasma, and the like used in the process from leaking or diffusing to the outside, and maintaining a suitable working environment. Therefore, it is preferable that the carbon film is formed in a containment chamber (chamber or the like) evacuated by a draft device, a vacuum pump, or the like.

If the surface to be treated is heated to, for example, 300 to 700° C. or even 350 to 650° C., a dense carbon film with less H can be formed. If the heating temperature is too low, the effect is poor, and if the heating temperature is too high, deterioration of the base material, reaction between the carbon film and the base material, etc. may occur.

The temperature of the surface to be processed is adjusted, for example, by a heater or the like incorporated in the stage on which the workpiece is placed. Further, by moving the stage relative to the communication hole along the planar direction of the workpiece, the carbon film can be efficiently formed over a wide range.

The surface to be treated may be subjected to pretreatment such as purification or roughening before the carbon film is formed. Pretreatment may be done using the plasma apparatus described above. For example, pretreatment may be performed in which plasma containing no carbon source gas is jetted onto the surface to be treated.

《Covering material》
A coated member in which a carbon film is formed on the surface of a base material to be processed is used not only in the electric/electronic field but also in the mechanical field, the chemical field, and the like. The base material of the covering member is appropriately selected, and may be, for example, metal or resin.

A representative example of the coated member according to the present invention is a fuel cell separator (also referred to as "metal separator" or simply "separator") made of a metal substrate having a carbon film on the electrode side surface. Metal separators have higher strength than conventional carbon separators, and are superior in electrical conductivity, gas shielding properties, and gas channel (groove) moldability, and contribute to cost reduction and miniaturization of fuel cells.

As the metal substrate, a highly corrosion-resistant metal (stainless steel-based substrate, titanium-based substrate, aluminum-based substrate, etc.) that forms a protective film such as a passive film (oxide film) is used. However, the protective film formed on the surface of the metal separator generally increases the contact resistance with the gas diffusion layer (GDL), which in turn can reduce the power generation efficiency (output) of the fuel cell.

The carbon film (particularly the first layer) of the present invention prevents contact between the acidic corrosive liquid that produces or grows such a protective film and the surface of the metal substrate, thereby reducing the contact resistance between the separator and the gas diffusion layer. It can contribute to stabilization. Note that the acidic corrosive liquid is mainly produced as an acidic liquid from humidifying water supplied to the electrolyte of the fuel cell and water (by-product) generated during the operation of the fuel cell.

Moreover, since the carbon film of the present invention (especially the second layer) has a large surface area, the contact area with the gas diffusion layer (GDL) tends to be large. In this respect as well, the carbon film of the present invention can contribute to reducing and stabilizing the contact resistance between the separator and the gas diffusion layer. Thus, if a metal separator having at least the electrode-side surface coated with the carbon film of the present invention is used, it is possible to reduce the cost of the fuel cell and stabilize the output.

The fuel cell can be of any type. Fuel cells include polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and the like. Polymer electrolyte fuel cells are used in automobiles and the like because they are highly efficient, can operate at low temperatures, and can be miniaturized.

By the way, a polymer electrolyte fuel cell has a solid polymer electrolyte membrane disposed approximately in the center of each cell, an anode (negative electrode, fuel electrode) on one side, and a cathode (negative electrode, fuel electrode) on the other side for each cell. positive electrode and oxygen (air) electrode). Each electrode is formed by stacking a catalyst layer, a gas diffusion layer, and a separator in order from the electrolyte membrane side. The catalyst layer is formed by, for example, carrying Pt—Ru (on the anode side) or Pt (on the cathode side) on carbon fine particles. The gas diffusion layer is made of, for example, a (PAN-based) carbon fiber nonwoven fabric. The separator functions as a gas supply, current collector, outer wall structure, and the like.

A sample (coated member) was prepared by forming a carbon film on the surface of a substrate under atmospheric pressure, and the carbon film was subjected to Raman spectroscopic analysis, cross-sectional observation, and contact resistivity measurement. While showing such a specific example, the present invention will be described more specifically below.

《Plasma Device》
FIG. 2A shows an outline (partial cross section) of a plasma apparatus S (simply referred to as "apparatus S") used for forming a carbon film. For convenience of explanation, each direction of up and down, front and rear, or left and right is the direction of the arrow shown in the drawing.

The apparatus S includes a raw material gas introduction section 1 , a plasma generation section 2 , and a power source 6 . FIG. 2A also shows the workpiece w placed on the stage 3 with a built-in heater.

In the generator 2, an insulating plate 211 (first insulator), an electrode plate 221 (first electrode), an insulating plate 212 (second insulator), and an electrode plate 222 (second electrode) are laminated in order from above. Become. The generator 2 also has nozzles 20 (communication holes) penetrating in the vertical direction. The nozzle 20 has an elongated shape (slit shape) extending in the left-right direction (longitudinal direction) at substantially the center in the front-rear direction (width direction) of the generation unit 2 .

When a high voltage is applied from the power source 6 between the electrode plates 221 and 222, discharge occurs between the inner peripheral surface 221a and the inner peripheral surface 222a of the nozzle 20, generating plasma p within the nozzle 20. do. The plasma p is pushed by the airflow (raw material gas flow) in the nozzle 20 from upstream to downstream and jets out from the lower end opening 20b of the nozzle 20 .

《Plasma Generation》
The following device S was actually manufactured as a prototype. The electrode plates 221 and 222 are made of rolled stainless steel (SUS304), and the insulating plates 211 and 212 are made of sintered alumina (Al ₂ O ₃ ). The thickness of the electrode plate 221 was 2 mm, the thickness of the electrode plate 222 was 1 mm, the thickness of the insulating plate 211 was 2 mm, and the thickness of the insulating plate 212 was 1 mm. The opening of the nozzle 20 was 1 mm×25 mm. A pulse power source was used as the power source.

Nitrogen gas was supplied to the introduction portion 1 and a pulse voltage (600 V (Peak to Peak value), frequency 6 kHz, rectangular wave) was applied between the electrode plates 221 and 222 . When the lower surface side of the electrode plate 222 was observed, as shown in FIG. 2B, purple glow discharge was observed at the lower end opening 20b of the nozzle 20, and generation (ejection) of plasma p was confirmed.

《Production of samples》
Film formation was carried out under the conditions shown in Table 1 using the prototype apparatus S.

A pure titanium plate (100 mm×110 mm×t0.1 mm) was used as the work w. The workpiece w was heated by the built-in heater of the stage 3.

A mixed gas of methane gas (hydrocarbon gas) and argon gas (rare gas) was used as the source gas. The heating temperature of the workpiece w was set to 500°C. The distance between the lower surface of the electrode plate 222 (lower end opening 20b of the nozzle 20) and the processed surface wa of the workpiece w was set to 4 mm.

The plasma p of the raw material gas generated by using the apparatus S in this way was irradiated to the surface to be processed wa of the workpiece w in an environment near atmospheric pressure for 30 minutes. At this time, the lower end opening 20b of the nozzle 20 was reciprocated (scanned) over a range of 36 mm with respect to the surface to be processed wa at a relative speed of 0.06 mm/sec.

《Analysis/Observation》
(1) Film Structure The film of Sample 1 was analyzed using a Raman spectrometer (NRS-3200 manufactured by JASCO Corporation/wavelength of excitation light: 532.05 nm). The obtained Raman spectrum is shown in FIG.

From the Raman spectrum of each sample, the wave number of each peak value and the ratio (I _D /I _G ) of these peak values were determined for the G band and D band. For the G band, the half width of the peak was also obtained. These results are summarized in Table 1.

(2) TEM
A cross section of the film of Sample 1 was observed with a field emission transmission electron microscope (JEM-2100F manufactured by JEOL Ltd.), and the TEM image and HRTEM image shown in FIG. 4 were obtained. For cross-sectional observation, a TEM sample produced by a focused ion beam composite processing observation device (FIB-SEM/ NB5000 manufactured by Hitachi High-Technologies Corporation) was further processed using a low-energy ion milling device (Gentle Mill manufactured by Nihon Physitec Co., Ltd.). It was carried out using a sliced sample.

"measurement"
(1) For the film of sample 1, the initial contact resistivity (before the corrosion test) was determined as follows. As shown in FIG. 5, carbon paper is placed on the upper surface side (film side) of the sample. They are sandwiched between two copper plates. At this time, pressure was applied vertically between the copper plates at 1.47 MPa. In addition, each surface of the copper plate in contact with the sample and the carbon paper was plated with gold.

A constant current (I) of 1 A was supplied between the copper plates from a DC power source. After 60 seconds from the start of pressurization between the copper plates, the potential difference (V) between the substrate of the sample and the carbon paper was measured. The contact resistivity was determined by dividing the electrical resistance value (R=V/I) between the two thus calculated by the contact area of 4 cm ² (2 cm×2 cm) between the sample and the carbon paper. The contact resistivity is also shown in Table 1. The contact resistivity of the substrate alone (workpiece w) before film formation was 3 mΩ·cm ² .

(2) The contact resistivity was similarly measured for the film of sample 1 after the corrosion test. The contact resistivity is also shown in Table 1. In the corrosion test, a sample (4 cm ² : 2 cm × 2 cm) was immersed in an aqueous sulfuric acid solution (pH 3) containing 30 ppm F and 10 ppm Cl, and a constant potential (0.9 V) was applied for 8 hours. kept it. The contact resistivity was measured after the sample after the corrosion test was washed with water and dried.

"evaluation"
(1) Film Structure From the Raman spectrum shown in FIG. 3 and Table 1, it was confirmed that the film of each sample was a carbon film having a G band.

As is clear from FIG. 3, the carbon film of Sample 1 has a sharp peak and is highly crystalline.

As is clear from FIG. 4, the carbon film of sample 1 consists of a graphite layer (first layer) containing flat graphene extending parallel to the substrate interface and arc-shaped graphene formed thereon. It was confirmed to have a graphite layer (second layer/dashed box).

(2) Crystallite size By substituting the intensity ratio (I _D /I _G ): 1.16 obtained from the Raman spectrum and the excitation laser energy (E _L ): 2.33 (eV) into the above-described formula 1, The crystallite size (La) was approximately 16.3 nm.

(3) Contact Resistivity As is clear from Table 1, the carbon film of Sample 1 had a low contact resistivity, and the contact resistivity hardly changed even after the corrosion test.

From the above, it was confirmed that the carbon film of the present invention has a new film structure and can impart stable conductivity even to substrates in corrosive environments.

S plasma device 1 introduction part 2 generation part 20 nozzle (communication hole)
211 insulating plate (first insulator)
212 insulating plate (second insulator)
221 electrode plate (first electrode)
222 electrode plate (second electrode)
w work

Claims (10)

a first layer containing flat graphene;
a second layer formed on the first layer and containing arc-shaped graphene opened on the surface side ;
A carbon film having 2. The carbon film according to claim 1, comprising graphite having a crystallite size of 15 nm or more. 3. The carbon film according to claim 1, wherein the second layer has an uneven surface formed by distribution of open curved depressions. 4. The carbon film according to claim 3, wherein the end of said depression stands upright toward said first layer. The carbon membrane according to any one of claims 1 to 4, which is formed on at least the electrode-side surface of a fuel cell separator. Plasma of a raw material gas containing a hydrocarbon gas is ejected onto the surface to be treated which is in an environment near atmospheric pressure and heated to 300 to 700° C., and the surface to be treated is exposed to any one of claims 1 to 5. A method for depositing the described carbon film. 7. The method of forming a carbon film according to claim 6, wherein the raw material gas further contains a rare gas. an introduction section to which the raw material gas is supplied;
a generation section disposed downstream of the introduction section and having a first insulator, a first electrode, a second insulator and a second electrode stacked in order from the upstream side;
a communication hole that penetrates the first insulator, the first electrode, the second insulator, and the second electrode from the upstream side to the downstream side;
8. The method of forming a carbon film according to claim 6 or 7, wherein a plasma device is used to apply a voltage to the first electrode and the second electrode to eject plasma of the raw material gas from the communicating hole. a base material;
The carbon film according to any one of claims 1 to 5, which covers the substrate surface;
A covering member having a 10. The covering member according to claim 9, which is a fuel cell separator.

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