WO2008013343A1

WO2008013343A1 - Diamond/carbon nano-materials hybrid film and the fabrication method thereof

Info

Publication number: WO2008013343A1
Application number: PCT/KR2006/005363
Authority: WO
Inventors: Jae-Kap Lee; John Phillip
Original assignee: Korea Institute Of Science And Technology
Priority date: 2006-07-27
Filing date: 2006-12-08
Publication date: 2008-01-31
Also published as: KR100797775B1

Abstract

A diamond/carbon nano-material hybrid film is a novel carbon material in which a diamond film is formed at one surface thereof and carbon nano-material is formed at another surface thereof at the atomic level. In a CVD (Chemical Vapor Deposition) diamond synthesis process, layered micro particles are used as matrix and a CVI synthesis technique is employed to provide dual gas chemistry conditions in which a diamond phase is stabilized at an upper surface of a matrix particle layer and a graphite phase is stabilized at a lower surface thereof, thereby fabricating the hybrid film. Also, porous sacrificial matrix particles are used as a matrix, non-deposition portions, at which the diamond or carbon nano-material is not deposited, are formed on the particles during the synthesis process, and the matrix is removed by a capillary-enhanced etching. Accordingly, a diamond/carbon nano-material hybrid film in the form of a free-standing film can be fabricated. This hybrid film has a large surface area and characteristics in which the diamond and the graphite are merged with each other (electrical anisotropy). Also, this method is provided for fabricating a carbon nano-material film well-aligned on a silicon or a metallic or ceramic plate, and for mass producing carbon nano-material in the form of a free-standing film.

Description

DIAMOND/CARBON NANO-MATE RIALS HYBRID FILM AND THE FABRICATION METHOD THEREOF

TECHNICAL FIELD The present invention relates to a diamond/carbon nano material hybrid film, and more particularly, to a diamond/carbon nano material hybrid film having a diamond on one surface and carbon nano materials on the other surface, and a fabrication method thereof.

BACKGROUND ART

The background technology of the present invention is a technology of synthesizing a CVD diamond and a CVD carbon nano material (graphite nano flake). The process of synthesizing the CVD diamond activates a gas (mostly, methane) in a vacuum vessel by using heat or plasma, and synthesizes a diamond on a surface of a matrix (or substrate) in the form of a polycrystalline film. The typical synthesis condition is a deposition (substrate) temperature of 500 to 800°C and a gas pressure of 40 to 200Torr. Generally, the CVD diamond film is deposited on the matrix (substrate) at a thickness of a few nm to a few mm. When the CVD diamond film is adhered to the matrix as in an insert tool or a drill (direct coating), a few tens μm of thin film is used, and when the CVD diamond film is separated from the matrix as a free-standing film, a few μm to a few mm of thick film is used. The technology of synthesizing the CVD diamond has been steadily developed with the development and improvement of various apparatuses and methods for synthesizing the diamond. Currently, it is possible to fabricate a diamond film on a large area up to 4"-8" in diameter where thickness is in the range of 0.5-1.0 mm. The CVD diamond is applied to various fields such as a wear resistant tool, an optical window and a substrate material. In another background technology of the present invention, synthesis conditions of plasma CVD graphite nano flakes (or carbon nano flakes) include a temperature of 350 to 55O⁰C and a pressure below 10Torr. That is, the synthesis conditions are lower than the synthesis conditions of the diamond [S. K. Srivastava, et. al., Thin Solid Films 492 (2005) 124-130]. The graphite nano flakes have chemical stability, electrical conductivity and a large specific surface area. Therefore, the graphite nano flakes are applicable to the electronic and electrochemical fields like carbon nano tubes. But, the related researches still remain at the early stage. On the other hand, the synthesis conditions of the carbon nano tubes are similar to the aforementioned conditions.

Plasma characteristics are considerably influenced by pressure. A high density plasma (or thermal plasma) is generated over a few tens Torr and is used for synthesizing a diamond, and a low density plasma (or low temperature plasma) is generated below IOTorr and is used for synthesizing a graphite nano material. The high density plasma has a relatively small volume, but shows higher deposition rate because it generates more radicals relatively. Also it can synthesize materials that are normally formed in the low density plasma. That is, the graphite nano material can be synthesized in the condition for diamond deposition (high density plasma). The diamond which is an allotrope of graphite is a high pressure phase of carbon (over a few ten thousands air pressure). Nevertheless, the diamond can be grown at the CVD condition (a few tens to 200Torr). It is well known that presence of atomic hydrogen(H) formed by heat or plasma energy is critical for growth of unstable diamond. Atomic hydrogen forms dangling bond to carbon atom(C) on the growth surface of the diamond in the CVD conditions, and makes diamond stable. For diamond growth, at least a quantity of atomic hydrogen is necessary. If concentration of atomic hydrogen is insufficient, poor diamond in crystallinity containing graphitic phases is formed. This suggests that graphite can grow in the condition for diamond growth if concentration of atomic hydrogen is low enough.

The diamond has the highest thermal conductivity, chemical stability and hardness among the existing materials, so that it can be used in various fields, including an electrode material in the electrochemical field due to excellent chemical stability. The diamond for the electrode material should be conductive and has a large specific surface area. Normal CVD diamond is, however, an insulator and is a film type which has a small specific surface area. As a result, the use of the diamond in this field is limitative.

The graphite nano flakes are usable for the electrochemical field due to chemical stability, electrical conductivity and a large specific surface area. The graphite nano flakes having similar physical properties to those of the carbon nano tubes have a lower aspect ratio of shape than the carbon nano tubes, and thus are well aligned on a matrix (substrate) and are very physically stable. Although actively investigated, they have not been put into the practical use. In general, similarly to the diamond, the graphite nano flakes are deposited on a flat matrix (substrate, generally, Si, but SiO₂, AI₂O₃ and various metals such as Mo, Zr, Ti, Hf, Nb, W, Ta, Cu and 304 stainless steel can be used). The main problems of the graphite nano flakes in the electrochemical field application (electrode material) are that the substrate may react with an acid or an organic solution used as an electrolyte, and that the graphite nano flakes cannot be easily prepared in the form of free-standing particles.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a new diamond/carbon nano material (graphite nano flake) hybrid film which has not been reported yet.

Another object of the present invention is to fabricate a diamond/matrix/graphite nano material composite which improves electrochemical stability, increases a surface area and efficiently arranges graphite nano materials, by using a conventional CVD diamond deposition process where (a) layer(s) of micro particles are used as a matrix instead of a general flat type matrix (substrate) to induce dual gas chemistry, the condition for diamond (high atomic H concentration) on the top surface of the matrix particle layer (namely, plasma contact portion) and the condition for graphite nano material (low atomic H concentration) on the bottom surface of the matrix particle layer (plasma non- contact portion, namely, empty spaces between the matrix particle layer and a plate (see Fig. 1(b)).

Still another object of the present invention is to provide a fabrication method of a carbon hybrid film having micron size hollow spheres (cavities) inside, a diamond on its top surface and carbon nano materials (graphite nano flakes) on its bottom surface, by preparing a composite by using micron size (0.1 to 1 ,000μm) porous sacrificial particles as matrix particles, putting the composite into etchant for matrix, and removing the porous matrix particles by capillary-enhanced etching. Yet another object of the present invention is to at least double synthesis efficiency of a diamond film by introducing a controlled chemical vapor infiltration (CVI) diamond synthesizing technology.

To achieve these and other advantages, according to a first aspect of the present invention, there is provided a diamond/matrix/carbon nano material composite hybrid film, wherein a diamond film is formed on one surface of a matrix and a carbon nano material film is formed on the other surface thereof.

According to a second aspect of the present invention, there is provided a diamond/carbon nano material hybrid film, which has a diamond film on one surface, a carbon nano material film on the other surface, and a matrix-removed space inside.

According to a third aspect of the present invention, there is provided a fabrication method of a diamond/matrix/carbon nano material composite hybrid film, including the steps of: preparing a sample set obtaining spaces between a substrate and matrix particles and between the matrix particles by laminating a particle phase matrix on the substrate; putting the sample set into a vessel of an apparatus for synthesizing a CVD diamond; and depositing a diamond film at the upper portion of the matrix particle layer in contact with a plasma and depositing a carbon nano material film at the other side of the matrix particle layer.

According to a fourth aspect of the present invention, there is provided a fabrication method of a diamond/carbon nano material hybrid film, including the steps of: preparing a sample set where (a) layer(s) of porous matrix particles are laminated on a substrate; putting the sample set into a vessel of an apparatus for synthesizing a CVD diamond; preparing a diamond/matrix/carbon nano material composite by depositing a diamond film at the upper portion of the matrix particle layer in contact with a plasma and depositing carbon nano materials at the lower portion of the layer where a small part is free from the carbon nano materials (uncoated zone); putting the composite into an etchant for the matrix, infiltrating the etchant into the inside of the matrix particles through the uncoated zones, and removing the porous matrix particles by capillary-enhanced etching.

According to a fifth aspect of the present invention, there is provided a fabrication method of a carbon nano material/matrix composite, including the steps of: preparing a sample set where several layers of porous matrix particles are laminated on a substrate; putting the sample set into a vessel of an apparatus for synthesizing a CVD diamond; and forming graphite nano materials or carbon nano tubes at least on the surfaces of the particles in the middle and lower portions of the matrix particle layer. Preferably, the deposition condition is out of those of CVD diamond, that is, a pressure of 1 to 60Torr and a deposition temperature of the matrix particle layer of 400 to 600°C. According to a sixth aspect of the present invention, there is provided a fabrication method of free-standing film type carbon nano materials, including the steps of: preparing a sample set where several layers of porous matrix particles are laminated on a substrate; putting the sample set into a vessel of an apparatus for synthesizing a CVD diamond; and forming graphite nano materials or carbon nano tubes at least on the surfaces of the particles in the middle and lower portions of the matrix particle layer, where a small part which was the contact points between inter-particles or between lowermost particles and the substrate is uncoated; and putting the composite into an etchant for the matrix, infiltrating the etchant into the inside of the matrix particles through the uncoated zones, and removing the porous matrix particles by capillary-enhanced etching.

According to a seventh aspect of the present invention, there is provided a fabrication method of a carbon nano material film/substrate composite, including the steps of: preparing a sample set where a layer of particles are laminated on a substrate; putting the sample set into a vessel of an apparatus for synthesizing a CVD diamond; synthesizing a diamond/matrix/carbon nano material composite by depositing a diamond film at the upper portion of the matrix particle layer in contact with a plasma, and depositing carbon nano materials on the substrate where gas chemistry is ideal for graphite(carbon nano materials) due to sparse of atomic hydrogen; and obtaining a substrate on which carbon nano materials are deposited (carbon nano material/substrate composite) by removing the diamond/matrix/carbon nano material composite from the substrate. Here the composite can be removed spontaneously due to difference of thermal expansion coefficient between the composite and the substrate.

EFFECT OF THE INVENTION

In accordance with the present invention, the diamond/carbon nano material (graphite nano flake) hybrid film can be fabricated by using the laminated porous silica spheres as the matrix and duplicating gas chemistry near the sample.

The diamond/graphite nano flake hybrid film has electrical anisotropy and a large specific surface area. In addition, this film has a light weight, chemical stability and high thermal conductivity. Therefore, the carbon hybrid film can be applied to a high efficient electrode in the electrochemical field (for secondary cell or ultrahigh capacitance capacitor), a semiconductor or FED device. Also, the present invention provides the method for fabricating the carbon nano material film well arranged on a plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

Fig. 1 shows a fabrication process of a diamond/carbon nano material hybrid film in accordance with the present invention; and

Fig. 2 shows texture photographs of the diamond/carbon nano material hybrid film fabricated by the process of Fig. 1.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The following three processes are carried out to achieve the objects of the present invention.

1 ) Sample preparation : This step prepares a sample set (matrix particle layer/metal plate) by laminating at least one layer of a particle typed matrix on a plate, instead of a plate type matrix used for general CVD diamond synthesis.

2) Synthesis of diamond/matrix/graphite nano material composite : This step fabricates a diamond/matrix/carbon nano material composite hybrid film by putting the prepared sample set into an apparatus for CVD diamond synthesis and/or CVI diamond synthesis for a predetermined time.

3) Matrix particle etching : This step removes the matrix particles in the composite hybrid film to fabricate diamond/carbon nano material hybrid film. The sacrificial particles are nano-porous for capillary-enhanced etching.

The diamond/matrix/carbon nano material composite can be fabricated by the first and second steps.

In addition, the carbon hybrid film(diamond/graphite nano materials) having micron size(0.1 to 1 ,000μm) cavities inside, the diamond on its top surface and the graphite nano materials on its bottom surface can be fabricated by throughout all the three steps. The sample preparation process includes a pretreatment of the matrix particles( normally porous silica spheres) 1. The pretreatment, which is identical to the general method for synthesizing the CVD diamond, is for easy diamond nucleation on the particles, and is forming scratches or residues to be sites for diamond nucleation on the surface of the matrix by ultrasonically vibrating a beaker containing the matrix particles and diamond power agents(<a few μm) in alcohol. After the pretreatment, the silica spheres are filtered by a sieve, washed with alcohol, and dried. The silica spheres of at least a layer are evenly laminated on a plate 2 (substrate: silicon, molybdenum, tungsten or copper), thereby obtaining a sample set (Fig. 1(a)).

The fabrication method of the diamond/matrix/carbon nano material composite hybrid film is similar to the general method for synthesizing the CVD diamond. The prepared sample set is put into a plasma 3 enhanced CVD diamond synthesizing vacuum vessel, and a process of synthesizing a diamond is carried out (Fig. 1(b)). Preferably, a diamond synthesis pressure ranges from 40 to 200Torr and a deposition temperature of the top surface of the sample set ranges from 600 to 900°C. Here, the diamond is deposited on the top surfaces of the sample (matrix particle layer) contacting the plasma, thereby forming eventually a diamond film which merge the particles lying on the top of the sample. Conversely, the lower portion of the sample is isolated from the plasma by the diamond film and forms gas chemistry different from that at the upper portion thereof. Concentration of radicals, C2H₂, CH₃ (known as radicals for diamond) and atomic H (known to stabilize the diamond phase) decreases. Especially, the reduction of concentration of atomic H interferes the growth of the diamond, and provides ideal gas chemistry for carbon nano materials instead. In this synthesis of the composite, micron size uncoated zones 4-3, in which the diamond film and/or the carbon nano materials are not synthesized, are formed at the bottommost surface of the laminated matrix particles and at the contact portions between the particles in the other region. In addition, the diamond film deposited on the surfaces of the silica spheres can have nano to micron size gaps naturally formed in the process of forming the polycrystalline film from the nuclei particles. Also, pores can be formed in the empty spaces between the particles during the synthesis. The uncoated zones, the gaps and pores become paths for the etchant going into the composite and each matrix particle. After the synthesis, the composite peeled off spontaneously from the metal plate due to the difference of thermal expansion coefficient between the composite and the plate during cooling of the plate. Preferably, a ratio of the thermal expansion coefficient of the composite to the thermal expansion coefficient of the metal plate is over 5. In the case that copper is used as the plate, if the thermal expansion coefficient of the diamond is 1 , the thermal expansion coefficient of the copper is about 10. The copper metal plate expanded during the synthesis at 600-900⁰C is shrunken after the synthesis where temperature decreases down to room temperature. So the composite can be naturally separated from the plate.

The matrix particles can be removed by etching the composite in an etchant only for the matrix. If the matrix is Siθ₂, where SiC layers can be formed between the matrix particles and diamond films during the synthesis, a hydrofluoric acid(HF) or boiling Murakami solution can be used as the etchant. When the hydrofluoric acid is used, the silica matrix particles are etched, but the SiC layers are remained because they are not susceptible to hydrofluoric acid. When the boiling Murakami solution is used as the etchant, the SiC can be removed together with the matrix particles. If silica particles are nano-porous, the etching process is much easier due to capillary-enhanced effect (capillary- enhanced etching. After the etching, the resulting structure is washed with water and alcohol, respectively, thereby fabricating the diamond/carbon nano material hybrid film.

To fabricate the diamond/carbon nano material (graphite nano flake) hybrid film, a sample set, that pretreated porous silica spheres of 10 to 30μm diameter are densely dispersed at one or two layers partially on a 4" diameter of copper plate, is placed on an anode (substrate holder) of a multi-cathode DC plasma CVD diamond synthesizing apparatus, and synthesized for 3 hours under the conditions of 15kW of power, 10% methane in hydrogen gas, IOOTorr of pressure and 200sccm of gas flow. In this apparatus, the sample set placed on the anode in which cooling water is circulating, is heated by plasma energy. The temperature of the top surface of the sample is maintained at about 800°C. It is expected that the temperature of the bottom surface of the sample (not measurable) is lower than that of the top surface of the sample by a few tens to 100°C. In this condition, a growth speed of a CVD diamond film on top surface of sample is about 10μm/h. After the synthesis, the silica matrix was removed by putting the diamond/silica/carbon nano flake composite in the boiling Murakami solution for 10 minutes. As a result, a diamond/graphite nano flake hybrid film was obtained. According to the SEM observation result of the hybrid film, as shown in Fig.

2, the nano crystalline diamond film is formed on the top surface of the film, and the leaf-shaped nano flakes are formed on the bottom surface thereof along the contours of the silica matrix particles. According to the XRD analysis result of the rear surface of the hybrid film, a peak is formed when 2Θ is about 26°, 44° and 72°. The 26° peak corresponds to (002) surface of the graphite, and the 44° and 72° peaks correspond to (111 ) and (220) surfaces of the diamond. That is, the materials formed on the bottom surface of the carbon hybrid film are graphite nano flakes having a graphite structure. In the hybrid film, the diamond and the graphite nano flakes are coupled in an atomic level because there is no an intermediate phase between the two materials. According to the electrical property of the film, the graphite nano material side has a specific resistance of about 10^'3Ω cm (conductive), and the diamond side was insulator. This means that the hybrid film has an electrically anisotropic property.

In the hybrid film, the diamond and the graphite nano-flakes are connected to each other at the atomic level at their boundaries. Since the graphite nano-flake layer of the hybrid film is an electrical conductor and the diamond film is an electrical nonconductor, the hybrid film has the characteristics of a nonconductor in its vertical direction. That is, the hybrid film has electrical anisotropy. Also, the hybrid film has a large surface area. Concerning the spatial distribution of the graphite nano-flakes, their surface area may be larger than that of a carbon nano- tube. In addition, the hybrid film is light in weight, and has high thermal conductivity along with being chemically stabilized. Hence, this novel diamond/carbon nano-material hybrid film can be used for highly efficient electrode materials (secondary cells or electrodes for ultra-capacitor) in the battery field, for supports in the an electrochemical field, heat-emitting diodes, semiconductor devices and electron emitting electrode materials, and the like. By changing the process conditions, various diamond/carbon nano material hybrid films can be fabricated. Carbon nano tubes can be formed instead of the graphite nano flakes. Here, another pretreatment, scattering nano particles of a transition metal such as Ni, Co, Fe which are catalyst for the carbon nano tubes onto the matrix silica particles, is needed. The synthesis condition of the carbon nano tubes, a pressure of 1 to 40Torr and a temperature of 400 to 800°C, is much similar to that of the graphite nano flakes. A dense diamond thick film which does not have pores can be grown on the top surface of the sample by extending the synthesis time. The surface morphology of the diamond film and the layer thickness, shape (tube, flake, etc.), density and length of the graphite nano materials are controllable by adjusting the size of the matrix particles, the lamination thickness and the deposition temperature of the plate. Also conductive diamond film can be formed by boron doping in the synthesis.

Furthermore, the diamond/matrix/carbon nano-material composite hybrid film can be obtained as a final result without performing the third step among the aforementioned steps. In this case, the porous matrix particles do not have to be used and also non-deposition portions are not required on the matrix particles.

In addition, the present invention provides a fabrication method of a carbon nano material film well arranged on a plate such as silicon, metal or ceramic. That is, spaces formed between the laminated particles and the plate maintains gas chemistry conditions at which a graphite phase can be grown. Accordingly, carbon nano-materials having a graphite phase (sp² bonded) can be grown both on a rear surface of the matrix (i.e., silica particle layer) and on the plate 4-2. Therefore, when separating the composite of the diamond/silica/carbon nano-material (formed on the surface of the silica spheres) from the plate, the carbon nano-material deposited on the plate remains in the form of a film, such that carbon nano-materials well-aligned on the plate can be obtained. The removal of the composite from the plate can simply be done by using a material having a great thermal expansion coefficient. The synthesis temperature (i.e., temperature of the plate) is about 600 to 900⁰C . Accordingly, the composite (usually diamond) film can automatically be removed during the cooling process of the plate after completing the synthesis process, due to the thermal stress by aring from the difference in the thermal expansion coefficients between the composite film (the thermal expansion coefficient of diamond is as small as 1 ^χ10^"6/^°C) and the plate used (usually metal, and the thermal expansion coefficient thereof is several to tens times greater than that of diamond).

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and preferred embodiments. In the preferred embodiments of the present invention, the carbon nano-material is graphite nano-flakes (or carbon nano-sheets) (refer to FIG. 2). However, it can be carbon nano tubes according to changes in the synthesis conditions. Also, the preferred embodiments of the present invention adopt a metallic plate as a mother substrate, but a ceramic plate can also be used therefor.

Fig. 1 shows a fabrication process of a diamond/carbon nano material hybrid film in accordance with the present invention. A sample set is prepared by laminating pretreated porous silica sphere 1 particles serving as a matrix on a plate 2 (Fig. 1(a)). A diamond film 4-1 and carbon nano materials 4-2 are synthesized in a plasma 3 enhanced CVD apparatus, thereby fabricating a diamond/silica/carbon nano material composite 4 (Fig. 1(b)). The carbon nano- material can be synthesized on the surface of the silica spheres which are placed at a rear surface of the layered matrix (the carbon nano-material which were synthesized at this portion is contained in the composite), and also be deposited on the plate 2.

In this process, micron size uncoated zones 4-3 on which the carbon nano material is not deposited can be formed at the bottommost surfaces of the laminated particles and the contact portions between the particles. The porous silica matrix is removed by capillary-enhanced etching by putting the diamond/silica/carbon nano material composite into a hydrofluoric acid or boiling Murakami solution 5 (Fig. 1(c)), thereby obtaining a diamond/carbon nano material hybrid film 7 having cavities 7-1 inside.

Fig. 2 shows surface morphologies of the diamond/carbon nano material (graphite nano flake) hybrid film. A nano crystalline diamond film is formed on the top surface of the film, and the contours of the silica matrix particles are formed on the bottom surface thereof along, showing pentagonal or hexagonal shape due to over growth of the graphite nano flakes on the spherical matrix particles. As shown in the amplified photograph, each particle has a hole 7-3. As shown in the more amplified photograph, the surfaces of the particles consist of the leaf-shaped nano flakes 4-2. The nano flakes have a thickness below about 100nm and a length of a few μm. The present invention will now be explained in more detail by the following examples. These examples are not intended to be limiting. Example 1

A sample set prepared by dispersively laminating pretreated porous silica spheres (25 to 30μm diameter) of at least one layer on a copper plate having a diameter of 4" was put into a multi-cathode DC plasma CVD diamond synthesizing apparatus, and synthesized for 3 hours under the conditions of 15kW of power, 10% methane in hydrogen gas, IOOTorr of pressure and 200sccm of gas flow. A temperature of the top surface of the sample was maintained at about 800°C. Here, a growth rate of the CVD diamond film was about 10μm/h. After the synthesis, a black diamond/silica/carbon nano material (graphite nano flake) composite film spontaneously separated from the copper plate.

According to SEM observation of the composite film, a continuous diamond film morphology having boundaries appeared on its top surface, while clear silica matrix particle contours were observed on its bottom surface. The contours were composed of petal-shaped graphite nano flakes. Uncoated zones having a diameter of a few μm were also observed at the centers of each contour. The uncoated zones were the contact points between silica spheres and the copper plate. According to the electrical property of the film, the graphite nano material side was conductive with a specific resistance of about 10^"3Ω cm and the diamond side was insulator.

Example 2

The silica matrix was removed by putting the composite film fabricated in

Example 1 into a boiling Murakami solution for 10 minutes, thereby obtaining a diamond/graphite nano flake hybrid film. According to SEM observation, holes having a size of a few μm appeared at the centers of the matrix particle contours on the bottom surface of the composite film. These holes were the uncoated zones. The electrical property of the film was identical to that of Example 1.

Example 3

The sample set prepared by the same method as that described in Examples was synthesized for 50 hours in the same conditions as those of Example 1. A fabricated diamond/silica/graphite nano material composite had a thickness of about 600μm. A growth surface revealed the typical CVD diamond film morphology, mixture of (100) and (111 ) planes, with grain boundaries of a few tens to hundred μm in size. Morphology of fraphite nano flakes formed on the bottom surface of the film was similar to those of Example 1. According to the electrical property of the film, the graphite nano material side was conductive with a specific resistance of about 10^"3Ω cm and the diamond side was insulator.

Example 4 A sample set prepared by laminating pretreated porous silica spheres (10 to 30μm diameter) by about ten layers on a copper plate having a diameter of 4" was put into a DC plasma CVD apparatus, and synthesized for 3 hours under the conditions of 1OkW of power, 20% methane in hydrogen gas, 40Torr of pressure and 200ccm of gas flow. A temperature of the top surface of the sample was about 600°C, and a temperature of the bottom surface thereof was lower by a few tens ⁰C (in this condition, a diamond film was not formed).

According to the SEM observation result of the composite, a diamond film was not deposited on its top surface, clear silica matrix particle contours were formed at its middle and lower portions, and petal-shaped graphite nano flakes were formed on its bottom surfaces. Example 5

The silica matrix was removed by putting the composite fabricated in

Example 4 into a boiling Murakami solution for 10 minutes, thereby obtaining free- standing carbon nano materials film. According to the SEM observation, holes of a few μm in size were formed at the centers of the contour of matrix particles on its bottom surface. The film shows a specific resistance of about 10^"3Ω-cm.

Normally, the graphite nano flakes are synthesized on a silicon substrate. According to the general method, carbon nano materials formed on the silicon substrate have a thickness below 1 μm, and yield is low. However, in the case that the matrix particles are laminated on the plate by several layers, mass- production is possible due to the large surface area for growth of the carbon nano materials as a in Example 4 or 5,and yield is high.

Example 6

To synthesize graphite nano flakes vertically aligned on a plate, a CVD experiment was carried out for 2 hours in the same conditions as those of Example 1. After the experiment, the diamond/silica/carbon nano flake composite was removed. According to the SEM observation having a diameter of 4", graphite nano flakes were confirmed to be vertically aligned to the plate. The graphite nano flake film had a thickness of about 1 μm, and each nano flake had a size of a few nm and a thickness of 10 to 20nm. In accordance with the present invention, the gas chemistry was evenly maintained in the wide region of the plate because graphite nano flakes obtained were aligned on a plate at a uniform thickness.

Claims

What is claimed is:

1. A diamond/matrix/carbon nano material composite film, wherein a diamond film is formed on one surface of a matrix and a carbon nano material film is formed on the other surface thereof.

2. A diamond/carbon nano material hybrid film, wherein a diamond film is formed on one surface, a carbon nano material film is formed on the other surface, and a matrix-removed space is formed inside.

3. The hybrid film of claim 2, wherein a plurality of holes are formed on the surface of the carbon nano material film.

4. A method for fabricating a diamond/matrix/carbon nano material composite hybrid film comprising: preparing a sample set where matrix particles are laminated at least by a layer on a substrate and spaces are ensured between the substrate and the matrix particles and between the matrix particles; putting the sample set into an apparatus for synthesizing CVD diamond; and fabricating a diamond/matrix/carbon nano material composite hybrid film where its upper portion is a diamond film and its lower portion is carbon nano material film.

5. The method of claim 4, wherein the matrix particles are porous particles of a ceramic material or a metallic material.

6. The method of claim 4, wherein the size of the matrix particles ranges 10nm to 2mm.

7. The method of claim 4, which performs a pretreatment of forming scratches or residues on the surfaces of the matrix particles, by putting the matrix particles into a beaker containing alcohol in which diamond powder agents are dispersed, and vibrating the beaker in an ultrasonic bath for a predetermined time.

8. The method of claim 4, wherein a ratio of a thermal expansion coefficient of the hybrid film to a thermal expansion coefficient of the substrate is over 5.

9. The method of any one of claims 4 to 8, wherein a synthesis pressure of the vessel of the apparatus for synthesizing the CVD diamond ranges from 40 to 200Torr, and a deposition temperature of the top surface of the sample set ranges from 600 to 900⁰C.

10. A method for fabricating a diamond/carbon nano material hybrid film, comprising: preparing a sample set where porous matrix particles are laminated at least by a layer on a substrate and spaces are ensured between the substrate and the matrix particles and between the matrix particles; putting the sample set into an apparatus for synthesizing CVD diamond; fabricating a diamond/matrix/carbon nano material composite hybrid film where its upper portion is a diamond film and its lower portion is carbon nano material film; and removing the porous matrix particles by capillary-enhanced etching by putting the composite film into an etchant.

11. The method of claim 10, wherein the porous matrix particles are irregular-shaped, simple spherical or hollow spherical particles.

12. The method of claim 10, wherein the size of the matrix particles ranges 10nm to 2mm.

13. The method of claim 10, wherein the porous matrix particles consist of metal oxides containing at least one of SiO₂, AI₂O₃ and BaTiO₃.

14. The method of claim 10, which performs a pretreatment of forming scratches or residues on the surfaces of the matrix particles, by putting the matrix particles into a beaker containing alcohol in which diamond powder agents are dispersed, and vibrating the beaker in an ultrasonic bath for a predetermined time.

15. The method of claim 10, wherein the porous matrix particles comprise SiO₂, and a hydrofluoric acid is used as the etchant to remove the porous matrix particles, leaving a SiC layer formed between the porous matrix particles and the diamond film, where capillary-enhanced etching is working.

16. The method of claim 10, wherein the porous matrix particles comprise SiO₂, and a boiling Murakami solution is used as the etchant to remove both the SiC layer and the porous matrix particles at the same time, where capillary-enhanced etching is working.

17. The method of claim 10, wherein a ratio of a thermal expansion coefficient of the hybrid film to a thermal expansion coefficient of the substrate is over 5.

18. The method of any one of claims 10 to 17, wherein a synthesis pressure of the vessel of the apparatus for synthesizing the CVD diamond ranges from 40 to 200Torr, and a deposition temperature of the top surface of the sample set ranges from 600 to 900°C.

19. A method for fabricating a carbon nano material/matrix composite, comprising: preparing a sample set where matrix particles are laminated at least by a layer on a substrate and spaces are ensured between the substrate and the matrix particles and between the matrix particles; putting the sample set into an apparatus for synthesizing CVD diamond; and fabricating a carbon nano materials/matrix composite at least at the middle and lower portions of the matrix particle layer.

20. The method of claim 19, wherein the carbon nano materials are formed on the surfaces of the laminated matrix particles.

21. The method of claim 19, wherein the matrix particles are porous particles formed of a ceramic material or a metallic material.

22. The method of claim 19, wherein the size of the matrix particles ranges 10nm to 2mm.

23. The method of claim 19, which performs a pretreatment of forming scratches or residues on the surfaces of the matrix particles, by putting the matrix particles into a beaker containing alcohol in which diamond powder agents are dispersed, and vibrating the beaker in an ultrasonic bath for a predetermined time.

24. The method of claim 19, wherein a ratio of a thermal expansion coefficient of the composite to a thermal expansion coefficient of the substrate is over 5.

25. The method of any one of claims 19 to 24, wherein a synthesis pressure of the vessel of the apparatus for synthesizing the CVD diamond ranges from 1 to 60Torr, and a deposition temperature of the bottom surface of the matrix particle layer ranges from 400 to 800°C.

26. A method for fabricating a free-standing film type carbon nano materials, comprising: preparing a sample set where porous matrix particles are laminated at least by a layer on a substrate and spaces are ensured between the substrate and the matrix particles and between the matrix particles; putting the sample set into an apparatus for synthesizing CVD diamond; fabricating a carbon nano materials/matrix composite film at least at the middle and lower portions of the matrix particle layers; and removing the porous matrix particles by capillary-enhanced etching by putting the composite film into an etchant.

27. The method of claim 26, wherein the porous matrix particles are irregular-shaped, simple spherical or hollow spherical particles.

28. The method of claim 26, wherein the size of the matrix particles ranges 10nm to 2mm.

29. The method of claim 26, wherein the porous matrix particles consist of metal oxides containing at least one of SiO₂, AI₂O₃ and BaTiθ₃.

30. The method of claim 26, which performs a pretreatment of forming scratches or residues on the surfaces of the porous matrix particles, by putting the matrix particles into a beaker containing alcohol in which diamond powder agents are dispersed, and vibrating the beaker in an ultrasonic bath for a predetermined time.

31. The method of claim 26, wherein a ratio of a thermal expansion coefficient of the composite to a thermal expansion coefficient of the substrate is over 5.

32. The method of any one of claims 26 to 31 , wherein a synthesis pressure of the vessel of the apparatus for synthesizing the CVD diamond ranges from 1 to 60Torr, and a deposition temperature of the bottom surface of the matrix particle layer ranges from 400 to 800°C.

33. A method for fabricating carbon nano materials well aligned on a substrate, comprising: preparing a sample set where matrix particles are laminated at least by a layer on a substrate and spaces are ensured between the substrate and the matrix particles and between the matrix particles; putting the sample set into an apparatus for synthesizing CVD diamond; depositing carbon nano materials on the substrate at least at the middle and lower portions of the matrix particle layers; and obtaining carbon nano materials well aligned vertically to the substrate, by removing any composites formed above the substrate.