JP2008074690A - Porous diamond film and method of forming the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous diamond film having a most suitable form as a base material for a chemical electrode or the like applied to electrochemical reaction and a useful method of efficiently forming the diamond film. <P>SOLUTION: The porous diamond film is formed by forming to disperse many fine pores each having a square or rectangular cross section parallel to the surface of a high orientational diamond film and extending in the direction vertical to the surface on the surface of the high orientational diamond film having mainly ä100} crystal plane. The porous diamond film is formed by depositing one of metal element of Fe, Co, Ni or Pt on the high orientational diamond film mainly having ä100} plane and heating in a reducing atmosphere containing hydrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a porous diamond film useful as a material such as an electrode applied to an electrochemical reaction, and a useful method for efficiently producing such a diamond film.

  The electrolysis process uses clean electrical energy to control the chemical reaction on the electrode surface to separate and purify hydrogen, oxygen, ozone, hydrogen peroxide, etc. from aqueous solutions, salt electrolysis, electroplating, It is applied in various fields such as industrial electrolysis techniques such as metal extraction. In recent years, organic pollutants can be indirectly decomposed or directly adsorbed on electrodes to be electrolyzed, so that they are also used as wastewater treatment.

  In the oxidation reaction at the anode in electrolysis, it is known that an acid agent (organic chlorine, ozone, etc.) effective for water treatment is generated, and some active species such as OH radicals are also generated. Is called by names such as activated water, functional water, ionic water, and sterilized water, and is widely used.

  As described above, the electrolysis process is applied in various fields, but it has been pointed out that sufficient reaction may not proceed depending on the electrode material used. For example, in an anodic oxidation reaction by electrolysis in an aqueous solution, an electrolysis product using water as a raw material is generated. When an electrode catalyst having high reactivity with respect to discharge of water is used, a target substance is generated. Therefore, a situation occurs in which the oxidation of other coexisting substances does not proceed easily.

  As a catalyst material for an electrode for electrolysis (anode), lead oxide, tin oxide, white metal elements and oxides thereof, carbon, and the like are known. Of these, platinum and iridium are considered in consideration of corrosion resistance and the like. The white metal elements such as are mainly used. In addition, as a material for the electrode base material, a material having good corrosion resistance such as a valve metal such as titanium or an alloy thereof is selectively used. However, even if these materials are used, it is known that the electrode is consumed depending on the current density and the processing time and flows out into the solution, and an electrode material with better corrosion resistance is desired. It is a fact. In addition, graphite and amorphous carbon have been conventionally used as a material for an electrode material, but it is known that there is a significant consumption when used as an anode material.

  Since diamond is excellent in thermal conductivity, strength, and chemical stability with respect to the various substances described above, it is expected to be useful as a material for the electrode material as described above. Diamond is also considered promising as a material for semiconductor devices and energy conversion elements because it is possible to control electrical conductivity by ion doping. For example, Patent Document 1 discloses that a diamond electrode provided with conductivity by ion implantation is applied as a sensor. Patent Document 2 also proposes a technique in which platinum fine particles are supported on a diamond surface doped with boron (B) and imparted conductivity to be used for an electrochemical electrode.

  As described above, diamond is expected to be applied in various fields. However, when applied as an electrode for electrolysis, the reaction efficiency is improved as compared with the case where a conventional electrode material is applied. Depending on the application field, a long life may not be achieved and a sufficient response may be difficult. The cause of this situation is that the existence density of active sites on the diamond surface is less than that of other electrode materials, and the surface properties are large due to the appearance of crystal planes. It is considered that the actual current density is increased, and electrode consumption due to electrolysis is likely to proceed at an early stage.

  For this reason, various techniques for forming as many holes as possible by forming a large number of holes on the diamond surface have been proposed. As such a technique, for example, Patent Document 3 discloses a method of placing anodized alumina on a diamond substrate as a mask and forming pores having the same arrangement as the mask on the diamond substrate by plasma etching. Although this technique has an advantage that regular and uniform holes can be formed, it is considered that the cost is relatively high because advanced condition control is required in the mask processing and plasma etching processes.

  In Patent Document 4, metal particles deposited on the diamond layer are heat-treated in a reducing atmosphere to promote a carbon reduction reaction using the metal particles as a catalyst, and fine pores are formed on the surface of the diamond layer. A method of forming is disclosed. This method is useful in that a diamond layer or diamond particles having micropores formed at or near the atomic level can be obtained. However, diamond targeted by this technique is a relatively complex polycrystal whose diamond fine particles or crystal plane cannot be specified, and cannot be said to be an optimum form when considering application as an electrode material. Also, the shape and distribution of the micropores to be formed cannot be said to have a suitable shape as an electrode material.

As another method for making the diamond surface porous, a method of etching the diamond surface by heat-treating the diamond at a temperature of 500 ° C. or higher in an oxygen atmosphere is also known. In such a method of etching without using a catalyst, it is considered that micropores are formed starting from crystal defects such as dislocations, and micropores etched using this (ie, “etch pits”). ) May determine the surface density of dislocations and defects. This dislocation does not exist uniformly even in one crystal plane, and naturally, if the dislocation density in the crystal is low, the etch pit density is also low. Therefore, when such a method is applied, it is not possible to form micropores with high density at almost equal intervals only by selecting a specific crystal plane, and to obtain porous diamond having a form useful as an electrode material. I can't.
JP 58-1060379 A JP 2004-235080 A JP 2000-1393 A JP 2006-183102 A

  In the case of applying porous diamond to an electrode material, it is an optimal form that the micropores formed on the surface thereof are formed at equal intervals and extending in the vertical direction. It is the actual situation that no porous diamond having such a shape has been obtained.

  For example, if polycrystalline or fine-grained diamond whose crystal plane cannot be specified is used as a starting material for producing porous diamond, the distribution and shape of the pores are random, and the surface area cannot be predicted or designed in advance. In such porous diamond, it is of course difficult to control the number density of the catalyst supported for each micropore. Even if the shape and distribution are uniform locally, the crystal plane is generally inclined so that the micropore formation direction is generally not vertical. Application to materials and the like becomes difficult.

  The present invention has been made paying attention to the above-mentioned circumstances, and the object thereof is a porous diamond film having an optimum form as a material for a chemical electrode or the like applied to an electrochemical reaction, and such a diamond film. It is in providing the useful method for manufacturing efficiently.

  The porous diamond film of the present invention that has achieved the above object is a highly oriented diamond film having a {100} crystal plane as a main component and a micropore having a square or rectangular cross section parallel to the surface. The present invention has a gist in that a large number of dispersions are formed so as to extend in a direction perpendicular to the surface.

  As a more specific form of the porous diamond film, the fine holes may have a long side average length of 5 to 50 nm and an average interval between the fine holes of 5 to 50 nm.

  In producing the porous diamond film as described above, any metal element of Fe, Co, Ni and Pt is attached to the surface of the highly oriented diamond film mainly composed of {100} crystal planes. After that, heat treatment may be performed in a reducing atmosphere containing hydrogen.

  In carrying out this method, the following requirements are satisfied: (a) the adhesion amount of the metal element is equivalent to 1 to 10 atomic layers, and (b) the heat treatment temperature is 600 to 1000 ° C. It is preferable to do.

  In the present invention, after a metal element of any one of Fe, Co, Ni and Pt is attached to the surface of a highly oriented diamond film mainly composed of {100} crystal planes, a reducing atmosphere containing hydrogen By heat-treating with the above, it is possible to efficiently produce a product in which a large number of micropores having a square or rectangular cross section parallel to the surface of the diamond film are formed in a dispersed manner at almost equal intervals so as to extend in a direction perpendicular to the surface. The obtained porous diamond film is extremely useful as a material for electrode materials and the like.

  In order to solve the above-mentioned problems, the present inventors have conducted research from various angles with the aim of realizing a porous diamond film having an optimum form as a material such as an electrode material. As a result, a highly oriented diamond film mainly composed of {100} crystal planes is used as a material (diamond film) for forming micropores, and any one of Fe, Co, Ni, and Pt is formed on the diamond film surface. If the metal element is attached and heat-treated in a reducing atmosphere containing hydrogen, the micropores having a square or rectangular cross section parallel to the diamond film surface extend at a substantially equal interval so as to extend in a direction perpendicular to the surface. It was found that a multi-pore diamond film having a desired form was obtained by forming a large number of dispersions, and the present invention was completed.

  In this porous diamond film, the shape of the micropores formed in a large number on the surface thereof is a square or a rectangle (rectangular) in cross section parallel to the diamond film surface. It becomes an “inverted quadrangular pyramid”. The shape of the micropores varies depending on the heat treatment conditions described later. For example, when the heat treatment time is shortened, the micropores have a shape reflecting the “inverted pyramid shape” as it is. Further, when the heat treatment time is lengthened, the hole shape up to the inverted quadrangular pyramid portion near the bottom surface becomes a rectangular column shape having a surface (side surface) substantially perpendicular to the diamond film surface. In addition, the “square column shape” includes a square or rectangular cross section parallel to the diamond film surface.

  In the porous diamond film of the present invention, the fine pores formed on the surface include any of the above-mentioned forms, but in the present invention, these are collectively referred to as “a cross section parallel to the surface of the porous diamond film is a square. Or it is a rectangle ". In any form, the calculation of the individual surface area can be performed geometrically easily from the shape. Further, since the micropores are formed with substantially the same size and at almost equal intervals, the error in the calculation of the surface area over the whole is very small. Because of this, it is important to know the correlation between the surface area and the processing capacity, such as electrodes for electrochemical sensors that detect the ion concentration in the liquid. Products with good quality can be produced.

  If the surface area is just the same, it is possible to use the surface as a flat surface without forming micropores, but it is desirable to increase the surface area for applications using such surface reactions. This is well known. In addition, there is an application in which a specific surface reaction is promoted by supporting a catalyst such as platinum (Pt) or nickel (Ni) on the diamond surface. Even in the case of application to such a use, the catalyst is easily fixed and is not easily detached due to the presence of a large number of micropores rather than a flat surface.

  This is because, at the bottom of the micropores, the flow of water hitting the surface makes it difficult to apply a force in the direction of peeling the catalyst from the diamond of the base material, that is, the shear direction, and the contact area with the diamond increases. . Further, fine catalyst particles can be distributed with high density and almost evenly, and can be isolated from adjacent particles. As a result, when expensive platinum or the like is used as a catalyst, the adhesion mass can be minimized, and the manufacturing cost can be reduced.

  The depth of the fine hole can be increased by extending the heat treatment time. For example, a hole penetrating to the back side of the diamond film can be formed. The size of the hole can be increased by increasing the amount of metal element deposited (deposition amount). As for the size of the micropores, the average length of the long sides is preferably about 5 to 50 nm, and the average interval between the micropores is preferably 5 to 50 nm. As an index indicating the size of the fine holes, the average length of the long side is based on the premise that a hole having a rectangular cross section is formed. In this case, the short side is almost equal to the long side, and when the cross-sectional shape is a square, it means the length of one side. Moreover, the space | interval between micropores means the shortest distance from the center point of one micropore to the center point of another micropore.

  In order to form the porous diamond film as described above, any metal element of Fe, Co, Ni and Pt is attached to the surface of a highly oriented diamond film mainly composed of {100} crystal planes. After that, heat treatment may be performed in a reducing atmosphere containing hydrogen. Next, the manufacturing conditions will be described.

  First, the diamond film used as a raw material in the present invention needs to be a highly oriented diamond film mainly composed of {100} crystal planes, and a manufacturing method thereof will be described later. For example, JP-A-2006-176389 discloses Discloses a method for producing a {100} crystal plane oriented diamond film having a grain size of 30 μm or more. In addition, the “100th crystal plane oriented diamond film with a maximum grain size of 100 μm” was realized in the “Proceedings of the 65th JSAP Conference on Applied Physics (2004)” (p.506, 3a-ZB-6). Has been. The diamond film used in the present invention can be formed by applying these techniques. Note that the fact that the {100} crystal plane is mainly used does not require that all the crystal planes of the highly oriented diamond film are (100) planes. For example, the present invention is applicable even if the (100) plane is 70% or more. Means you can.

  Although it is necessary to adhere any metal element of Fe, Co, Ni and Pt to the surface of the highly oriented diamond film as described above by, for example, a vapor deposition method (hereinafter represented by “vapor deposition”). The metal element immediately after the vapor deposition becomes a film when the vapor deposition amount is sufficiently large. In this state, the vapor deposition amount can be defined by the film thickness. On the other hand, when the deposition amount of the metal element is very small, it is expected that the particles are in an irregular shape by a high resolution electron microscope. That is, when the deposition amount of the metal element is very small, the deposition amount (film thickness) varies depending on the location, and the deposition amount cannot be defined by the film thickness. Therefore, the thickness when it is assumed that the film has a constant thickness (uniform film) is defined in atomic layer units (amount equivalent to the atomic layer) and is defined as the deposition amount (attachment amount). Thus, the atomic layer unit has an advantage that the deposition amount can be applied as it is to metals having different atomic radii.

  At the same time as the heat treatment temperature is raised in an atmosphere containing hydrogen, spontaneous aggregation of the metal element occurs, and the metal element changes into dispersed fine particles. The size of the fine particles can be controlled by the amount of deposition, and increases when the amount of deposition is large. However, when the deposition amount is larger than the equivalent amount of 10 atomic layers, the variation in size becomes remarkable. Further, when the amount is less than the equivalent amount of one atomic layer, the number density decreases and the variation in the interval becomes remarkable. From such a point of view, it is preferable that the metal element is deposited in an amount corresponding to an amount equivalent to 1 to 10 atomic layers, and in this range, the size and the distance between them are all within the range of 5 to 30 nm. Highly precise micropores can be formed.

  Such a phenomenon applies only to the flat {100} crystal plane obtained by the crystal growth of diamond, and other crystal planes such as the {111} crystal plane, the so-called off-plane slightly inclined from the {100} crystal plane, In the case of {100} crystal planes, the same phenomenon does not generally occur with low flatness or with different materials. This was thought to be due to the difference in wettability between the diamond {100} crystal plane and other planes.

  By the way, about the atmosphere at the time of heat treatment, it is necessary to set it as "reducing atmosphere containing hydrogen" as described above, but as a gas forming such an atmosphere, hydrogen is contained at about 3 to 30% by volume at room temperature, A mixed gas in which the balance is an inert gas (for example, nitrogen gas) can be used.

  Moreover, it is preferable that the heat processing temperature is about 600-1000 degreeC. When this temperature is lower than 600 ° C., the reaction treatment time becomes longer and impractical, and when it exceeds 1000 ° C., the treatment time can be shortened, but the formation of micropores proceeds excessively. The mechanical strength of the diamond film tends to decrease, and the diamond film may be corroded or embrittled by hydrogen.

  The porous diamond film of the present invention detects low reflection surfaces, prism plates, photonic materials, electron emission surfaces, and special material gases, as well as various electrode materials used for electrolysis and ion detection in solution. It can be applied to a gas sensor or the like. In addition, technical application as a gate surface of a field effect transistor is also possible (for example, 4p-ZB-4 of “Proceedings of the 65th JSAP Conference on Applied Physics” p.519-520), light, ion It can be used as a sensor material sensitive to proteins, amino acids, DNA, gas and the like.

  Further, the porous diamond film of the present invention can be used directly, or can be produced by transferring the fine pores by pressing a plastic material against it. In this case, the protrusions corresponding to the fine holes having the characteristic shape as described above can be formed in a state of being densely distributed at substantially equal intervals. In addition to the chemical electrode surface used for electrolysis and ion detection in solution, the application field of the molding material thus formed with protrusions is a low reflection surface, prism plate, photonic material, electron emission surface, Examples include a probe and a tip of an electric measurement probe.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Example 1]
An oriented diamond film (polycrystalline diamond film) mainly composed of {100} crystal planes as a material for the porous diamond of the present invention was produced by the following method.

  (1) Using a microwave plasma CVD apparatus having a clean (100) plane wafer of single crystal silicon as a substrate and having a quartz tube chamber, a mixed gas of 5% methane and hydrogen (remainder) is supplied at a pressure of 25 Torr (3.3 kPa). ), Flow rate: Plasma was formed by applying microwaves while flowing under the condition of 100 SCCM (Standard Cubic Centimeter per minute). A substrate placed on a molybdenum plate was placed near the end of the plasma, and a tungsten net was placed on the opposite end. At this time, a terminal is provided outside each device and connected to a direct current power source (DC power source). The microwave output was adjusted, and a DC bias of 150 to 200 V was applied by a DC power source while keeping the substrate at 650 ° C. The substrate side was set to a negative potential. This state was maintained for 10 to 15 minutes.

  (2) Thereafter, the conditions were switched to conditions of 2% methane, 98% hydrogen, pressure 50 Torr (6.7 kPa), gas flow rate: 100 SCCM, substrate temperature: 800 ° C., and held for 5 to 10 hours. At this point, when the surface is observed with a scanning electron microscope (SEM), a diamond film (continuous film) having a surface shape in which the direction perpendicular to the substrate is oriented in the <100> direction and the {111} plane appears predominantly is obtained. It was confirmed that it was formed. That is, when focusing on the surface of one crystal grain, a so-called pyramid-like quadrangular pyramid shape appears, and it has been confirmed that the four slopes are {111} planes based on equilateral triangles. . The average grain size of one crystal grain becomes larger as the holding time is longer, but was 2 to 4 μm in the range of 5 to 10 hours.

  (3) Thereafter, the conditions were switched to methane 1%, oxygen 0.5%, hydrogen 98.5%, gas flow rate 100 SCCM, substrate temperature: 850 ° C. and held for 5 to 10 hours. As a result, a diamond thin film having a total film thickness of about 30 μm was synthesized.

  When the surface of the diamond thin film was observed with an SEM, it was confirmed that the surface was covered with a crystal plane based on a square or rectangle parallel to the substrate (that is, {100} crystal plane). The average grain size of one crystal grain increases as the holding time in the above steps (2) and (3) increases, but one crystal is in the range of 5 to 10 hours in both steps (2) and (3). The average particle size of the grains was 3 to 30 μm. In any case, it is covered with a {100} crystal plane that is substantially parallel to the entire substrate surface, and the difference in height between adjacent particles is 0.1 to 0.5 μm, so that there are few steps. As a whole, it could be regarded as a flat surface.

  FIG. 1 shows an electron micrograph of the surface of the diamond film produced by setting the holding times in the above steps (2) and (3) to 5 hours and 5 hours, respectively.

  FIG. 2 shows an electron micrograph of the surface of the diamond film produced with the holding times of the above step (2) and step (3) being 10 hours and 10 hours, respectively.

  The orientation of the obtained diamond film was investigated by X-ray diffraction (XRD), positive-point X-ray diffraction (polar-XRD), and backscattered electron diffraction (EBSP), and is shown in FIG. It was confirmed that diamond particles corresponding to an area of 90% or more of the uppermost surface of the diamond film were oriented within 10% from the <001> direction. In the diamond film shown in FIG. 2, it was confirmed that diamond particles corresponding to an area of 95% or more of the uppermost surface were oriented within 10% from the <001> direction.

  Next, Co was deposited on the surface of the diamond thin film shown in FIG. 1 by a vacuum deposition method in an amount equivalent to about 5 atomic layers, and then heated at 900 ° C. for 2 hours under a hydrogen (10%)-nitrogen mixed gas stream. As a result of observing the surface properties of the diamond film using an SEM, Co particles excavated the {100} plane of the diamond film, and a large number of fine holes extending in a direction perpendicular to the diamond film surface were dispersedly formed. It was confirmed that 90% or more of the fine holes were 10 to 20 nm in size, and were almost uniform, and the shape (cross-sectional shape) was almost all square or rectangular. Moreover, there were few things which seemed that the adjacent micropores were partially connected, and most of them became independent forms. The interval between the micropores on average was 23 nm. The surface property of the diamond film obtained at this time is shown in FIG.

  As is apparent from the SEM observation, almost all the {100} crystal planes of the diamond film are changed to micropores, and the shape of the micropores can be approximated as a half shape of an octahedron. Based on this, it can be calculated that the surface area has increased by about √3 times. When this diamond film is observed with a backscattered electron image, diamond and Co on the substrate appear to have different contrasts (Co is observed as a bright white spot), but Co is present in almost all of the diamond micropores. I understood. The reflected electron image at this time is shown in FIG.

  By comparing FIG. 3 and FIG. 4, it is considered that micropores were formed as a result of the catalytic reaction caused by Co particles on the diamond film surface. In this catalytic reaction, it is considered that carbon atoms on the diamond surface in contact with Co easily dissolve at high temperatures, diffuse in Co, combine with hydrogen, and are released from the Co surface as hydrocarbon gas such as methane gas.

[Example 2]
The experiment was performed under the same conditions as in Example 1 except that Ni was used instead of Co as the vapor deposition metal element. As a result of observing the surface properties of the diamond film using an SEM, Ni particles excavated the {100} plane of the diamond film, and a large number of fine holes extending in a direction perpendicular to the diamond film surface were dispersedly formed. It was confirmed that As for the size of the micropores, 90% or more is 5 to 15 nm, which is almost uniform, and the shape (cross-sectional shape) is almost all square or rectangular. Moreover, there were few things which seemed that the adjacent micropores were partially connected, and most of them became independent forms. The interval between the micropores on average was 32 nm. The surface property of the diamond film obtained at this time is shown in FIG.

  As is apparent from the SEM observation, the depth of the micropores is shallower than when Co particles are used, the size of the Ni fine particles is substantially the same as the size of the pores, and the number density is slightly lower. The shape of the micropore is approximated as a half of an octahedron, and the original {100} plane remains as it is in the region of approximately 3/4, so the surface area is approximately (3/4 + 1/4 × √3) times. It can be calculated as increasing. When this diamond film is observed with a backscattered electron image, the substrate diamond and Ni appear to have different contrasts as described above (Ni is observed as a bright white spot), but Ni is almost all of the diamond micropores. It was found to exist. The reflected electron image at this time is shown in FIG.

  A few relatively large holes were observed on the diamond film surface, but there were many cases where there were no Ni particles. Here, it is considered that the dislocation originally present in the diamond crystal is a starting point and the etching progresses in a hydrogen atmosphere. On the other hand, it was thought that most of the fine holes were formed by Ni fine particles.

[Example 3]
The experiment was performed under the same conditions as in Example 1 except that Pt was used instead of Co as the vapor deposition metal element and the heating temperature was 1000 ° C. As a result of observing the surface properties of the diamond film using an SEM, it was found that Pt particles excavated the {100} plane of the diamond film, and a large number of fine holes extending in a direction perpendicular to the diamond film surface were dispersedly formed. It was confirmed that The micropores were 90% or more in 5-15 nm, almost uniform, and the shape (cross-sectional shape) was almost all square or rectangular. Moreover, there were few things which seemed that the adjacent micropores were partially connected, and most of them became independent forms. The interval between the micropores on average was 13 nm. The surface properties of the diamond film obtained at this time are shown in FIG.

  As is clear from the SEM observation, the depth of the micropores is almost the same as when Co particles are used, the size of the fine Pt particles and the size of the pores are almost the same, and the number density is high. Further, the increase rate of the surface area can be calculated as about √3 times as in the case of Example 1. When this diamond film is observed with a backscattered electron image, the diamond and Pt of the substrate appear to have different contrasts as described above (Pt is observed as a bright white point), but Pt is almost all of the fine pores of the diamond. It was found to exist. The reflected electron image at this time is shown in FIG.

[Example 4]
In all of the diamond film production steps, a diamond film was formed under the same conditions as in Example 1 except that 10 ppm of diborane was mixed in the source gas, and fine holes were formed in this diamond film in the same manner as in the example. did. As a result, a porous diamond film having electrical conductivity could be produced.

[Comparative Example 1]
Of the steps for producing an oriented diamond film (polycrystalline diamond film) mainly composed of {100} crystal planes described in Example 1, the diamond film consisting only of {111} planes by the step (2). Can do. An attempt was made to form micropores using this diamond film. When the surface morphology of the sample using Ni as the vapor deposition metal element was observed using SEM, the surface was etched, but the shape was a disordered shape with many grooves, {100 } Each micropore as seen on the surface did not form a dispersed shape independently. Further, when the backscattered electron image was observed, regularity was not recognized between the location where the Ni particles were present and the etched portion. The surface properties of the diamond film obtained at this time are shown in FIG. 9 (drawing substitute micrograph).
FIG. 10 shows a backscattered electron image of the diamond film.

  In the above Examples 1 to 3, the case where Co, Ni and Pt are used as the metal elements to be attached to the diamond film surface is shown, but this is the case where Fe is used as the metal element instead of Co, Ni and Pt. However, although there are some differences in the size, depth, and number density of the fine holes, a large number of fine holes can be dispersedly formed on the surface of the diamond film.

FIG. 2 is a drawing-substituting electron micrograph showing the surface of a diamond film produced by setting the holding times of step (2) and step (3) in Example 1 to 5 hours and 5 hours, respectively. FIG. 2 is a drawing-substituting electron micrograph showing the surface of a diamond film produced with the holding times of Step (2) and Step (3) of Example 1 being 10 hours and 10 hours, respectively. 2 is a drawing-substituting electron micrograph showing the surface properties of a porous diamond film in which fine pores are formed on the surface of the diamond film by Co particles. FIG. 4 is a drawing-substituting photograph showing a result of observing a portion corresponding to FIG. 3 with a reflected electron image. 2 is a drawing-substituting electron micrograph showing the surface properties of a porous diamond film having fine pores formed on the diamond film surface by Ni particles. 6 is a drawing-substituting photograph showing a result of observing a portion corresponding to FIG. 5 with a reflected electron image. 2 is a drawing-substituting electron micrograph showing the surface properties of a porous diamond film in which fine pores are formed on the diamond film surface by Pt particles. 8 is a drawing-substituting photograph showing a result of observing a portion corresponding to FIG. 7 with a reflected electron image. 2 is a drawing-substituting electron micrograph showing the surface properties of a porous diamond film when micropores are attempted to be formed in a diamond film consisting only of {111} planes. FIG. 10 is a drawing-substituting photograph showing a result of observing a portion corresponding to FIG. 9 with a reflected electron image. FIG.

Claims (5)

  A large number of fine holes having a square or rectangular cross section parallel to the surface are formed on the surface of a highly oriented diamond film mainly composed of {100} crystal faces so as to extend in a direction perpendicular to the surface. A porous diamond film characterized by being a material.   2. The porous diamond film according to claim 1, wherein the fine holes have an average long side length of 5 to 50 nm and an average distance between the fine holes of 5 to 50 nm.   In producing the porous diamond film according to claim 1 or 2, any one of Fe, Co, Ni and Pt is formed on the surface of the highly oriented diamond film mainly composed of {100} crystal planes. A method for producing a porous diamond film, wherein the element is attached and then heat-treated in a reducing atmosphere containing hydrogen.   The manufacturing method according to claim 3, wherein the adhesion amount of the metal element is equivalent to 1 to 10 atomic layers.   The manufacturing method according to claim 3 or 4, wherein the heat treatment temperature is 600 to 1000 ° C.