Preparation method of metal-containing graphite-diamond composite film field emission cathode

Abstract

The invention belongs to the technical field of material chemical preparation, and particularly relates to a preparation method of a metal-containing graphite-diamond composite film field emission cathode. In the process of preparing the graphite-diamond composite film through an MPCVD method, a liquid carbon source and a metal source are introduced into plasma, and then a monocrystalline silicon wafer subjected to diamond grinding and seed crystal is used as a substrate to prepare the metal-containing graphite-diamond composite film. According to the preparation method, a metal source is successfully introduced into the graphite-diamond composite film, and no new phase is generated. The electronic structure of the composite film can be regulated and controlled by introducing a metal source into the graphite-diamond composite film, and by taking an iron source as an example, the surface work function of the composite film can be reduced by about 1.5 eV, and the field emission performance of the composite film is remarkably enhanced: the starting field intensity is reduced to 1.1 V / mu m from 4.0 V / mu m, and the emission current density is improved to 15.8 mA / cm < 2 > at 2.8 V / mu m from 13mA / cm < 2 > at 8.8 V / mu m.

Description

Technical Field

[0001] The invention belongs to the technical field of material chemical preparation, and in particular relates to a method for preparing a metal-containing graphite-diamond composite film field emission cathode. Background Art

[0002] Vacuum micro (nano) electronic devices play an irreplaceable role in information communication and military applications due to their high frequency and high power. These scientific and technological application demands drive the continuous improvement of the performance of vacuum micro (nano) electronic devices, which puts higher requirements on the quality of the device's electron beam source. Therefore, the development of field emission cold cathode materials with low turn-on field strength and high current density has become the key to the iterative upgrade of vacuum micro (nano) electronic devices. In recent years, semiconductor materials represented by graphite-diamond composite films have become a hot spot in the research of field emission cold cathode materials, which is mainly due to the effective combination of the high aspect ratio and high conductivity of graphite sheets and the low effective work function and high chemical inertness of diamond. However, the current field emission performance of graphite-diamond composite films has not yet reached the level of practical application, and there is still a lot of room for improvement.

[0003] The field emission process of graphite-diamond composite film mainly involves the electron transfer process in the film and the emission process of tunneling over the potential barrier on the film surface. The former is mainly related to the electron transport characteristics, and the latter is mainly related to the surface work function. Therefore, how to effectively control the electron transport characteristics and surface work function of the composite film is the key to enhancing the field emission performance of the composite film. The microstructure of a typical graphite-diamond composite film can be regarded as composed of diamond nanowires or diamond nanoparticles intercalated in graphite sheets. The current mainstream method to enhance the field emission performance is to control the microstructure of graphite-diamond composite thin films. On the one hand, it focuses on controlling and optimizing the phase ratio, distribution, surface morphology, etc. in the composite film, and on the other hand, it focuses on controlling the grain boundary microstructure of the composite film. A large number of research results show that changing the preparation process such as microwave plasma chemical vapor deposition (MPCVD) temperature and time can effectively control the content ratio, size distribution, and surface morphology of the graphite phase and diamond phase in the composite film. This microstructure control method can enhance the electron transport of the composite film to a certain extent, but it is difficult to effectively adjust the surface work function of the composite film, resulting in a higher field emission start-up field strength. On the other hand, grain boundary microstructure regulation is mainly focused on composite films with a high content of diamond phase. By replacing part of the argon with nitrogen, the grain boundary size is widened. At high nitrogen content, a novel nanowire core / shell structure is even formed, thereby reducing the tunneling barrier of electron emission. However, the microwave activation efficiency of nitrogen molecules is low, and the doping amount and doping efficiency of nitrogen atoms in composite films are limited, resulting in low electron transport and field emission performance of composite films.

[0004] From the above, it can be seen that it is difficult to achieve effective regulation of the electron transport properties and surface work function of the composite film simply by controlling and optimizing the microstructure of the graphite-diamond composite film. Therefore, it is urgent to break through the limitations of the existing microstructure regulation mode and develop new strategies and methods for regulating the electron transport properties and surface work function of the graphite-diamond composite film. Summary of the invention

[0005] To this end, the present application provides a metal-containing graphite-diamond composite film and a preparation method thereof, which adopts the method of simultaneously introducing a metal source during the growth of the composite film by the MPVCD method to achieve the preparation of the metal-containing graphite-diamond composite film, so that the metal is evenly dispersed in the composite film, and the field emission performance of the composite film (the turn-on field strength is reduced and the emission current density is increased) is greatly improved.

[0006] To this end, the first technical solution of the present application discloses a method for preparing a metal-containing graphite-diamond composite film, which is an MPCVD method, in which a saturated liquid carbon source and a saturated liquid metal source are introduced into a plasma, and a graphite-diamond composite film is deposited on the surface of a pretreated single crystal silicon substrate.

[0007] Furthermore, the saturated liquid carbon source is n-butylamine; and the saturated liquid metal source is a saturated ethanol solution of iron acetylacetonate, nickel acetylacetonate, or cerium acetylacetonate.

[0008] Furthermore, the plasma is H2 or Ar.

[0009] Furthermore, the method for preparing the pre-treated single crystal silicon substrate is as follows: grinding a high-conductivity single crystal silicon wafer with diamond powder and seeding the wafer to obtain a single crystal silicon substrate.

[0010] Furthermore, the seed crystal is obtained by placing a ground single crystal silicon wafer in a diamond powder suspension and ultrasonicating for 30-90 minutes.

[0011] Furthermore, the diamond powder is ground until uniform and dense scratches appear on the surface of the single crystal silicon wafer.

[0012] Furthermore, the diamond powder has a particle size of 50-200 nm.

[0013] Furthermore, in the MPCVD method, the microwave power is 3-3.5 kW, the working gas pressure is maintained at 8-10 kPa, the growth temperature is 750-950° C., and the growth time is 1-3 h.

[0014] And, a metal-containing graphite-diamond composite film prepared according to the above preparation method.

[0015] Beneficial effects of the present application: The present application prepares an iron-containing graphite-diamond composite film by introducing a liquid carbon source and a metal source into a plasma during the preparation of a graphite-diamond composite film by the MPCVD method, and then using a single crystal silicon wafer that has been diamond-ground and seeded as a substrate. The preparation method successfully introduces a metal source into the graphite-diamond composite film without the generation of a new phase. The introduction of a metal source into the graphite-diamond composite film can regulate the electronic structure of the composite film. Taking an iron source as an example, the surface work function of the composite film can be reduced by about 1.5 eV, and its field emission performance can be significantly enhanced: the turn-on field strength is reduced from 4.0 V / μm to 1.1 V / μm, and the emission current density is reduced from 13 mA / cm 2 @8.8V / μm increased to 15.8mA / cm 2 @2.8V / μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 SEM scans of iron-containing graphite-diamond composite films at different temperatures;

[0017] Attached Figure 2 This is a graph showing the emission performance of iron-containing graphite-diamond composite films. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0020] The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples were purchased from commercial channels, and the purity of the reagents was basically LC-MS grade or LC grade. At the same time, quality control measures were introduced into the experimental process to ensure the quality of the data results.

[0021] In the present application, the term "MPCVD" refers to a microwave plasma chemical vapor deposition device, which is a conventional device used to prepare graphite-diamond composite films, using H2 or Ar as plasma.

[0022] The first embodiment of the present application discloses a method for preparing a metal-containing graphite-diamond composite film, which is an MPCVD method, wherein a saturated liquid carbon source and a saturated liquid metal source are introduced into a plasma, and a graphite-diamond composite film is deposited on the surface of a pretreated single crystal silicon substrate.

[0023] In this embodiment, the saturated liquid carbon source is n-butylamine. Since n-butylamine contains nitrogen, it helps to regulate the surface morphology of the composite film into staggered nanosheets. The metal source is a metal-containing component that can be in a saturated liquid state, such as saturated ethanol solutions of iron acetylacetonate, nickel acetylacetonate, and cerium acetylacetonate. The purpose is to simultaneously introduce metals during the growth of the composite film, thereby regulating its electronic structure and achieving improved field emission performance.

[0024] In this embodiment, the introduction of the saturated liquid carbon source and the saturated liquid metal source into the plasma is specifically as follows: the saturated liquid carbon source and the saturated liquid metal source are respectively packed into two stainless steel containers and sealed in a constant temperature water bath with independently adjustable temperature; after the air pressure in the sealed container is stabilized, the MPCVD connection valve is opened, and the inherent air pressure difference between the stainless steel container (high air pressure) and the MPCVD deposition chamber (low air pressure) is used to introduce n-butylamine and metallic iron into the plasma; the plasma is preferably H2 or Ar.

[0025] In this embodiment, the method for preparing the pre-treated single crystal silicon substrate is as follows: grinding a high-conductivity single crystal silicon wafer with diamond powder and seeding the wafer to obtain a single crystal silicon substrate, so that an initial crystal nucleus exists during the deposition process. The seeding wafer is obtained by placing the ground single crystal silicon wafer in a diamond powder suspension and ultrasonicating for 30-90 minutes. The diamond powder is ground until uniform and dense scratches appear on the surface of the single crystal silicon wafer.

[0026] In this embodiment, in the MPCVD method, the microwave power is 3.5 kW, the working gas pressure is maintained at 10 kPa, the growth temperature is 850° C., and the growth time is 2 hours. It should be noted that MPCVD is a conventional device for preparing graphite-diamond composite films, and its application mechanism and specific application method are known to those skilled in the art, and this application does not make any special restrictions here.

[0027] The specific effects of the technical solution of the present application will be described below in conjunction with the accompanying drawings and specific embodiments.

[0028] Example 1 Preparation of Iron-Containing Graphite-Diamond Composite Film

[0029] S1. Ultrasonic cleaning of (100) oriented highly conductive single crystal silicon with acetone and anhydrous ethanol in turn to remove organic impurities such as surface grease, grinding of its surface with 200nm diamond powder until uniform and dense scratches appear, ultrasonication of the ground silicon substrate in a suspension made of 200nm diamond powder for 1h (to achieve seeding), and finally cleaning with anhydrous ethanol for multiple times and drying to serve as the substrate for the growth of graphite-diamond composite film.

[0030] S2. Put the liquid organic small molecule n-butylamine with a certain saturated vapor pressure into a sealed stainless steel container and place it in a constant temperature water bath as a carbon source for composite film deposition. Prepare a saturated ethanol solution of iron acetylacetonate, and also put it into another sealed stainless steel container and place it in a constant temperature water bath as a metallic iron source for composite film deposition. The temperature between the two liquid sources (constant temperature water bath) is independently adjustable. After the air pressure in the two stainless steel containers is stable, open the connecting valve, and use the inherent air pressure difference between the stainless steel container (high air pressure) and the MPCVD deposition chamber (low air pressure) to introduce n-butylamine and metallic iron into H2 or Ar plasma, and use microwave plasma chemical vapor deposition equipment to deposit graphite-diamond composite film on the surface of the treated single crystal silicon substrate. The microwave power is 3.5kW, the working air pressure is maintained at 10kPa, the growth temperature is 850℃, and the growth time is 2h, and a graphite-diamond composite film containing metallic iron can be obtained.

[0031] Example 2 Preparation of Iron-Containing Graphite-Diamond Composite Film

[0032] The preparation method is the same as that in Example 1, except that the growth temperature in Example 2 is 750°C.

[0033] Example 3 Preparation of Iron-Containing Graphite-Diamond Composite Film

[0034] The preparation method is the same as that in Example 1, except that the growth temperature in Example 3 is 950°C.

[0035] Test Example 1 Microstructure Observation

[0036] The iron-doped graphite-diamond composite film prepared in Example 1-3 was subjected to SEM scanning to obtain the following SEM scanning images: Figure 1 As shown (where a is 750°C, b is 850°C, and c is 950°C).

[0037] Test Example 2: Launch Performance Test

[0038] like Figure 2 The figure shows the emission performance of the iron-containing graphite-diamond composite film prepared in Example 1. The composite film is tested for field emission performance using a DC field emission test device. The test is performed when the vacuum degree of the cavity reaches 3.0×10-5Pa. In the experiment, the anode is quartz glass coated with ITO, the cathode is the composite film, and the distance between the positive and negative electrodes is 280m.

[0039] like Figure 2 As shown, (a) is the full spectrum of XPS (X-ray photoelectron spectroscopy), from which we can see the Fe2p peak, O1s peak, and C1s peak, indicating that the composite film contains F, C, and O elements. (b) is the C1s narrow spectrum, indicating that C is mainly composed of sp3-C (diamond phase) and sp2-C (graphite). (c) is the Fe2p narrow spectrum, indicating that the composite film contains Fe elements. (d) is the XRD (X-ray diffraction) diagram, black represents pure graphite-diamond composite film, and red represents iron-containing graphite-diamond composite film. This figure shows that the introduction of iron into the composite film will not generate a new phase, and the composite film The film is still mainly composed of diamond phase and graphite phase. (e) is the UPS (ultraviolet photoelectron spectroscopy) diagram. Black represents pure graphite-diamond composite film, and red represents iron-containing graphite-diamond composite film. From this figure, it can be calculated that the surface work function of pure graphite-diamond composite film is 21.2-16.6=4.6eV, and the surface work function of iron-containing graphite-diamond composite film is 21.2-18.1=3.1eV, indicating that the surface work function of the composite film is significantly reduced after the introduction of iron, which helps to improve the field emission performance. (f) is the field emission performance diagram, which gives the field emission starting field strength and emission current density values.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. The embodiments of the present invention and the features in the embodiments can be arbitrarily combined with each other without conflict. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an iron-doped graphite-diamond composite film, characterized in that: The method is an MPCVD method, in which a saturated liquid carbon source and a saturated liquid metal source iron source are introduced into plasma, and a graphite-diamond composite film is deposited on the surface of a pretreated single crystal silicon substrate.

2. The preparation method according to claim 1, characterized in that: The saturated liquid carbon source is n-butylamine; the saturated liquid metal source is an ethanol saturated solution of iron acetylacetonate, nickel acetylacetonate or cerium acetylacetonate.

3. The preparation method according to claim 1, characterized in that: The plasma is H2 or Ar.

4. The preparation method according to claim 1, characterized in that: The method for preparing the pre-treated single crystal silicon substrate comprises the following steps: grinding a high-conductivity single crystal silicon wafer with diamond powder and seeding the wafer to obtain the single crystal silicon substrate.

5. The preparation method according to claim 4, characterized in that: The seed crystal is obtained by placing a ground single crystal silicon wafer in a diamond powder suspension and ultrasonicating for 30-90 minutes.

6. The preparation method according to claim 4, characterized in that: The diamond powder is ground until uniform and dense scratches appear on the surface of the single crystal silicon wafer.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The particle size of the diamond powder is 50-200nm.

8. The preparation method according to claim 1, characterized in that: In the MPCVD method, the microwave power is 3-3.5 kW, the working gas pressure is maintained at 8-10 kPa, the growth temperature is 750-950° C., and the growth time is 1-3 h.

9. A metal-containing graphite-diamond composite film prepared according to any one of the preparation methods of claims 1-8.

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