KR101214044B1

KR101214044B1 - Manufacture method of CNT-Metal homogeneous film for electron field emission

Info

Publication number: KR101214044B1
Application number: KR1020100116129A
Authority: KR
Inventors: 허승헌
Original assignee: 한국세라믹기술원
Priority date: 2010-11-22
Filing date: 2010-11-22
Publication date: 2012-12-20
Also published as: KR20120054813A

Abstract

The present invention provides a CNT-metal mixed film for field emission by accelerating a mixed powder of CNT (carbon nanotube) and metal by vacuum expansion principle (aerosol deposition method: AD method) and then impinging on a substrate. It relates to a method of uniformly forming and an aerosol deposition apparatus for carrying out such a method.
The present invention is an aerosol chamber having a gas inlet; A low vacuum deposition chamber having a substrate disposed therein; And a transport tube having one end communicating with the aerosol chamber and the other end inserted into the deposition chamber and open toward the substrate. A pretreatment step of applying mechanical collision energy to the CNT-metal mixed powder by an aerosol deposition apparatus configured to include; (b) aerosolizing the pre-treated CNT-metal mixed powder into the aerosol chamber and injecting a transport gas directly into the CNT-metal mixed powder; And (c) depositing the aerosol on the substrate by accelerating the aerosol with a vacuum expansion principle and discharging the aerosol through the transport tube into the deposition chamber. It provides a method for producing a field emission CNT-metal mixed film implemented by.

Description

Manufacture method of CNT-Metal homogeneous film for electron field emission

The present invention provides a CNT-metal mixed film for field emission by accelerating a mixed powder of CNT (carbon nanotube) and metal by vacuum expansion principle (aerosol deposition method: AD method) and then impinging on a substrate. It relates to a method of uniformly forming and an aerosol deposition apparatus for carrying out such a method.

In the method of coating the powder on the substrate, the thermal spraying method is a method of obtaining a coating material by activating the substrate powder at high temperature by using plasma or thermal energy and spraying the compressed air of high temperature and high pressure through a nozzle to directly spray on the substrate. This thermal spraying method has been widely used in ceramic coatings for aircraft and large structures. However, work must be done in fireproof clothing in an enclosed space, and there are serious disadvantages of noise pollution, sparks, air pollution and energy waste. Recently, the coating method of metal nanoparticles using the cold spray method, which has been developed by the thermal spraying method, has gained much attention. This is related to the direct wiring of metal nanoparticles, and similarly to the thermal spraying method, compressed air is sprayed through a nozzle and metal particles are hit at a high speed at room temperature to form a coating. At this time, the compressed gas container is heated to several hundred degrees to obtain a high pressure gas, but the powder activation process is not performed as in the thermal spraying method. This requires very high acceleration due to the resistive gas pressure of the deposition part, which requires a unique nozzle design, high temperature and high pressure compressed gas retention technology, and severe noise generation during coating.

A method of manufacturing a field emission emitter in which a carbon nanotube (hereinafter referred to as 'CNT') film is formed on a cathode electrode such as a back light unit (BLU), a field emission display (FED), a surface light emitting source, and an X-ray source. CVD (Chemical Vapor Deposition) method. The CVD method is a method in which a catalyst is formed on a cathode electrode and a substrate is heated so that the CNTs grow in the catalyst portion while the hydrocarbon precursor is broken by thermal-chemical action. Most CNTs grow in the catalyst section and grow perpendicular to the cathode. However, vertically grown CNTs are prone to collapse and have the disadvantage of requiring additional catalytic process and expensive CVD equipment techniques.

Meanwhile, a method of dispersing in a liquid phase through chemical treatment of CNTs, or mixing a polymer or a photo resist and coating the cathode is very inexpensive and is currently used by many companies. In particular, CNT-Ag high-dispersion paste manufacturing, screen printing on the electrode and heat treatment to form a CNT field emission emitter technology is currently the most used technology in the industry. Ag serves as an electrical and physical binder between the electrode and the CNT. However, this too, the high temperature sintering and the remaining organic matter of the paste still remains a problem to be solved.

The aerosol deposition (AD) technique used in the present invention is based on the principle of vacuum expansion and its roots are based on cluster beam sources that are widely used in the basic sciences. Supersonic cluster sources achieve accelerations of 10 ³ to 10 ⁴ m / s by spraying gases into the chamber in a vacuum or pulsed state. Aerosol deposition, on the other hand, uses heavier powders, so it does not gain tremendous acceleration like a cluster source, but it can produce a good deposition film even at subsonic speeds. An example is a 4 nm powder aerosol deposition method (Huh et. Al. Appl. Phys. Lett. 91, 093118, 2007). This paper introduces the fact that 4nm particles are accelerated to about 200m / s by the vacuum expansion principle and collide on the silicon substrate, so that the direct bonding between particle-substrate and particle-particle is achieved. The aerosol deposition method is much quieter than the thermal spraying method or the cold spray method and is an environmentally friendly energy saving process technology compared to the CVD, PVD, thermal spraying method and the cold spray method. Unlike the cluster source, it can be implemented with low vacuum technology.

The present invention is to produce an Electron Field Emission (Electron Field Emission) method by accelerating the CNT-metal mixed powder by the vacuum expansion principle (applied by the AD method) and then impinged on the electrode. Although the AD method is a very general and simple method for forming a thin film (see FIG. 1), serious process problems occur when forming a thin film using a CNT powder and a metal powder simultaneously. That is, a separate chamber for aerosolizing the CNT-metal mixed powder should be provided separately. The following two problems typically occur.

(1) Uniform aerosolization problem of CNT powder and metal powder (hereinafter 'Problem 1')

The problem is that the specific gravity of CNT is very small compared to metal, and the shape of metal powder is spherical, but the shape of CNT powder is linear, so the behavior of metal powder and CNT powder in aerosol state is very different. It happens because Therefore, when the mixture of the CNT powder and the metal powder is simply aerosolized, phase separation occurs (upper CNT, lower metal), so that the CNT is first aerosolized and discharged (see the left figure of FIG. 2). This problem has been overlooked as it may be difficult to observe in small area, and it is very serious in in-line or roll-to-roll large-area coating, and CNT-based film is formed at the beginning of coating and metal-based film is formed in the middle of coating. It is difficult to expect a CNT field emission membrane.

(2) The problem of discharging aerosol to the deposition chamber at a certain concentration (hereinafter 'Problem 2')

When the CNT-metal mixed powder aerosol is continuously sent from the aerosol chamber to the deposition chamber, a problem arises in that powders are deposited at the bottom corner of the aerosol chamber (see FIG. 3). In other words, due to the combination of gravity and friction force, the powder is settled or stagnated and accumulated in the lower side of the aerosol chamber (the corner of the aerosol chamber). In this case, the mixed powder accumulated in the corner is intermittently discharged into the deposition chamber with agglomeration, which causes a great obstacle in obtaining a uniform CNT-ceramic mixed film. This phenomenon creates a uniform aerosol and makes it difficult to deliver a certain concentration of aerosol to the thickening chamber.

The present invention aims to provide a method and apparatus capable of depositing a uniform CNT-metal mixed film in large areas by solving the above two problems.

In the present invention, the following means is applied to solve the above-mentioned problem.

1. In order to solve the 'problem 1', a pretreatment step of applying energy to the CNT-metal mixed powder by a mechanical method before the aerosol deposition (AD) process is performed. As the pretreatment step, 1) a ball milling method and 2) a high speed blading method (Blading: blades rotating at high speed such as a mixer (5,000 to 15,000 rpm) in the present invention) may be selectively applied. By this pretreatment step 1) cutting and dispersing CNT twisted like a thread, 2) improving the bonding strength of CNT-metal mixed powder (CNT also increases the effect of wrapping metal powder), 3) uniform CNT- The effect of forming the metal mixed powder aerosol can be obtained (see the right figure of FIG. 2).

2. In order to solve the problem 2, the powder raw materials are constantly moved by supplying new physical kinetic energy from the outside before the powder loses kinetic energy and stops by using a physical method. As the above 'physical method', 1) a collision (see FIG. 4) using a rotational force of a magnet and 2) a blowing (gas collision) (see FIG. 5) through a gas shower may be applied. At this time, the gas shower can be a variety of directions, various sizes and in some cases can be configured to rotate by the power source can control the gas injection direction.

Through the present invention, a large area field emission film having a uniformity of CNT powder and metal powder can be formed in a large area, and thus can be variously used for producing high quality CNT BLU, FED, surface light emitting source, X-ray source at low energy cost. Can be.

1 is a schematic diagram of an aerosol deposition apparatus.
2 is a schematic diagram of the aerosolization state when the pre-treatment step for the CNT-metal (Ag) mixed powder is not performed and is performed.
FIG. 3 is a schematic diagram of a problem occurring in the aerosol chamber over time when the CNT-metal mixed powder aerosol is continuously sent from the aerosol chamber to the deposition chamber.
4 is a schematic view of an aerosol chamber provided with a magnet rotor.
5 is a schematic view of an aerosol chamber having a gas inlet configured in the form of a shower formed with a plurality of micropores.
6 is an electron micrograph taken after ball milling the CNT-Ag mixed powder.
7 is an electron micrograph taken after mixing the CNT-Ag mixed powder at rpm 10,000 for 10 minutes.
8 is an electron micrograph of a CNT-Ag mixed film formed on an aluminum substrate by a method provided by the present invention.
9 is a graph showing an XRD pattern of a CNT-Ag mixed film formed on an aluminum substrate.
10 is a graph showing data of measuring field emission properties of a CNT-Ag mixed film formed on an aluminum substrate.

The present invention is an aerosol chamber having a gas inlet; A low vacuum deposition chamber having a substrate disposed therein; And a transport tube having one end communicating with the aerosol chamber and the other end inserted into the deposition chamber and open toward the substrate. A pretreatment step of applying mechanical collision energy to the CNT-metal mixed powder by an aerosol deposition apparatus configured to include; (b) aerosolizing the pre-treated CNT-metal mixed powder into the aerosol chamber and injecting a transport gas directly into the CNT-metal mixed powder; And (c) depositing the aerosol on the substrate by accelerating the aerosol with a vacuum expansion principle and discharging the aerosol through the transport tube into the deposition chamber. It provides a method for producing a field emission CNT-metal mixed film implemented by.

At this time, any of the transition metals such as Ag, Au, Al, Zn, Pd, Sn, Pt, Fe, Co, Ni, W, Mo or lanthanum-based metal may be used as the metal mixed with CNT.

In the step (a), the pretreatment step of applying mechanical collision energy may use a ball milling method or a blading method. The blading method is a method of applying mechanical collision energy by blade rotation, and the blade is preferably rotated at a speed of 5,000 ~ 15,000rpm.

In addition, the inner bottom surface of the aerosol chamber is provided with a magnet rotor that can be rotated by a power source, in the step (b) to perform the operation of rotating the magnet rotor together in the aerosol chamber mixing CNT-metal The powder can be prevented from laminating.

In addition, the gas inlet of the aerosol chamber is configured in the form of a shower with a plurality of micropores, in this case, the step (b) is a gas inlet of the shower type by introducing the gas into the entire area of the aerosol chamber, aerosol chamber It is possible to prevent the CNT-metal mixed powder from laminating on the bottom.

In addition, the substrate may be a metal substrate or a transparent conductive film.

The present invention is an aerosol chamber having a gas inlet; A low vacuum deposition chamber having a substrate disposed therein; And a transport tube having one end communicating with the aerosol chamber and the other end inserted into the deposition chamber and open toward the substrate. It is configured to include, and the inner bottom surface of the aerosol chamber provides aerosol deposition apparatus, characterized in that provided with a magnet rotor that can be rotated by a power source.

In addition, the present invention includes an aerosol chamber having a gas inlet; A low vacuum deposition chamber having a substrate disposed therein; And a transport tube having one end communicating with the aerosol chamber and the other end inserted into the deposition chamber and open toward the substrate. It is configured to include, the gas inlet is provided with an aerosol deposition apparatus, characterized in that configured in the form of a shower formed with a plurality of micropores. The size and direction of the gas shower can be adjusted according to the conditions, and in some cases, the gas shower can be configured to rotate by power supply.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As described above, as the metal that can be mixed with CNT in the present invention, all of transition metals or lanthanide series metals may be used, but preferably Ag, Au, Al, Zn, Pd, Sn, Pt, Fe, Co, Ni, W, Mo and the like can be applied, it is expected that the thin film consisting of a mixed powder of these metal powders and CNTs have good interfacial properties. Hereinafter, the present invention will be described in detail with reference to an embodiment to which Ag (silver) of the above metal is applied.

The amount of CNT included in the CNT-metal mixed powder can be adjusted according to the physical properties of the film finally produced. In the method for producing a CNT-metal mixed film for field emission according to the present invention, before aerosolizing the CNT-metal mixed powder, a pretreatment step (step (a)) is performed to apply mechanical collision energy. In the embodiment to be described below in order to maximize the effect of the present invention, CNT and Ag powder is ball milled for 24 hours after mixing in a 1: 1 volume ratio. After 24 hours of ball milling, the CNT-Ag mixed powder was black, and by electron microscopic observation, it was found that most of CNT adhered to Ag powder or wrapped Ag powder. It can be seen that (see Figure 6). This phenomenon can be interpreted as CNT wrapped Ag powder by mechanical kinetic energy by ball milling, CNT stuck between Ag powder, or CNT pressed on Ag powder surface, and the effect of van der Waals attraction Can also be interpreted as

These phenomena are similarly expressed when mechanical impact energy is applied externally, such as ball milling. Therefore, the conventional ball milling, bead ball milling, high energy ball milling, high energy mixer, etc., as well as the blading method can be applied It may be. In the case of the blading method, the blade is rotated at a speed of 5,000 to 15,000 rpm. FIG. 7 is an electron micrograph of a CNT-Ag mixed powder after blazing at 10,000 rpm for 10 minutes. FIG.

The aerosol deposition apparatus used in the CNT-metal mixed film manufacturing method for electric field emission provided by the present invention, and also achieves the claims of the present invention, as shown in Figure 1 aerosol chamber 10, the deposition chamber 20 and It is comprised including the transport pipe 30. Steps (b) and (c) of the method for preparing the field emission CNT-metal mixed film are performed using the aerosol deposition apparatus.

The aerosol chamber 10 is introduced with a CNT-metal mixed powder 1 pretreated by ball milling or blading. The transport gas 2 is injected into the aerosol chamber 10 through the gas inlet 11. The gas inlet 11 may be equipped with a flow rate control unit 12 to supply a certain amount of transport gas. When the transport gas is injected into the CNT-metal mixed powder located at the bottom of the aerosol chamber 10, the CNT-metal mixed powder particles are blown to the gas phase, thereby forming an aerosol 3 (step (b)). If the above step (a) is not performed, as shown in the left figure of FIG. 2, phase separation occurs due to a difference in density and shape when aerosolized, and CNTs are first discharged, thereby making it impossible to manufacture a uniform CNT-metal mixed film. do. However, the CNT-metal mixed powder particles which have undergone the above-described step (a) (pretreatment by ball milling or blading) are uniform CNT- due to the adhesion between the CNT-metals (Ag) as shown in the right figure of FIG. It becomes a metal (Ag) mixed powder aerosol. This pretreatment step is a necessary process technology for large area continuous coating such as in-line or roll-to-roll.

CNT-metal mixed powder aerosol (3) formed through the steps (a) and (b) as described above is a transport pipe 30 by the pressure difference between the aerosol chamber 10 and the deposition chamber 20 in a low vacuum state After passing through the deposition chamber 20 at high speed, the aerosol is deposited on the substrate to form a CNT-metal mixed film for field emission (step (c)). An injection end of the aerosol may be controlled by combining various injection nozzles 31 having different cross-sectional areas and shapes at the end of the transport pipe 30 introduced into the deposition chamber 20. The aerosol accelerated at high speed is deposited upon the substrate 21. As the substrate 21, a metal substrate (in the embodiment, an aluminum substrate is used) or a transparent conductive film may be used. The substrate 21 may be fixed to the holder 22, and the holder 15 may be coupled to the height adjusting unit 16 to adjust the distance between the substrate 21 and the injection nozzle 31. The critical velocity for the aerosol 3 to be injected and deposited on the substrate is 150 m / sce or more. The gas in the deposition chamber 20 remaining after the aerosol 3 is deposited on the substrate may be discharged through the exhaust 24 as shown in FIG. 1.

However, as the process proceeds to steps (b) and (c), the CNT-metal mixed powder begins to accumulate in the corners of the interior of the aerosol chamber 10, and thus the volume of the CNT-metal mixed powder thus accumulated. When becomes large, discharge of powder lump state may occur intermittently, and serious problem arises in uniform thin film formation.

In order to solve this problem, as shown in FIG. 4, the magnet rotor 13 which can be rotated by a power source is coupled to the inner bottom surface of the aerosol chamber, and the magnet rotor is rotated to rotate the CNT-metal mixed powder. To prevent them from accumulating in every corner of the aerosol chamber. In some cases, several small magnets may be installed as the rotor, and one long rod magnet may be used as the rotor.

In addition, the gas inlet for supplying the transport gas into the aerosol chamber in the form of a shower with a plurality of micropores as shown in Figure 5 by blowing the transport gas to every corner of the aerosol chamber CNT-metal mixed powder to gravity This can prevent phenomena such as settling down or losing kinetic energy. The gas inlet of this type can be configured to be provided at the upper end or side portion of the aerosol chamber, and in some cases may be provided at the bottom. Further, depending on the conditions, the size of the shower-type gas inlet, the size and number of fine pores, the transport gas injection direction, etc. may be adjusted, or in some cases, the shower-type gas inlet may be rotated. In this case, in the step (b), a rotary air stream of a transport gas is formed in the aerosol chamber so that the CMT-metal powders are not laminated to the aerosol chamber bottom.

8 is an electron micrograph of a CNT-Ag mixed film formed on an aluminum substrate by a method provided by the present invention. As shown in the photograph, it can be seen that a significant amount of CNTs are incorporated into the Ag film, and a film in which CNTs and Ag are uniformly mixed can be obtained by the ball milling effect. 9 shows the XRD pattern of the CNT-Ag mixed film formed on the aluminum substrate, it can be seen that all of Al, Ag, CNT is detected. 10 is data of measuring field emission properties of the CNT-Ag mixed film formed on the aluminum substrate. The result of the measurement of the resulting film (Original (blue)) and the result of pretreatment using the taping method (Tape method (red)) were compared. Through the taping method treatment, it can be seen that electrons are emitted at a low voltage. This is because the phenomenon that the CNT tip stands perpendicular to the electrode by the taping method is increased.

In addition, when the CNT-Ag mixed membrane prepared through the present invention was simply heat treated at 400 ° C. or lower, the field emission property was improved by 10 to 20% from the result shown in FIG. 10, which removes debris of CNTs and thus interfaces the membrane. It is interpreted that the physical properties are improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Therefore, the claims of the present invention include modifications and variations that fall within the true scope of the present invention.

1: CNT-metal mixed powder 2: Transport gas
3: aerosol 4: exhaust gas
10: aerosol chamber
11 gas inlet 11 ': shower-type gas inlet
12: flow rate control unit 13: magnet rotor
20: deposition chamber
21: substrate 22: holder
23: height adjustment 24: exhaust
30: pipeline
31: injection nozzle
100: aerosol deposition apparatus

Claims

An aerosol chamber having a gas inlet; A low vacuum deposition chamber having a substrate disposed therein; And a transport tube having one end communicating with the aerosol chamber and the other end inserted into the deposition chamber and open toward the substrate. Method for producing a field emission CNT-metal mixed film carried out in each of the following steps by an aerosol deposition apparatus configured to include.
(a) pretreatment step of applying mechanical collision energy to the CNT-metal mixed powder by blade rotation;
(b) aerosolizing the pre-treated CNT-metal mixed powder into the aerosol chamber and injecting a transport gas directly into the CNT-metal mixed powder; And
(c) depositing the aerosol on the substrate by accelerating the aerosol with a vacuum expansion principle and discharging the aerosol through the transport tube into the deposition chamber;

In claim 1,
The metal is Ag, Au, Al, Zn, Pd, Sn, Pt, Fe, Co, Ni, W and Mo, characterized in that the field emission CNT-metal mixed film manufacturing method.

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In claim 1,
The blade is a method for producing a field emission CNT-metal mixed film, characterized in that for rotating at a speed of 5,000 ~ 15,000rpm.

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In claim 1,
The substrate is a method for producing a field emission CNT-metal mixed film, characterized in that the metal substrate or a transparent conductive film.

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