CN102394204B - Field electron emission source - Google Patents

Abstract

A field emission electron source includes a conductive substrate and a carbon nanotube needle point. The carbon nanotube tip is a carbon nanotube bundle structure, and the carbon nanotube bundle structure includes a plurality of carbon nanotubes extending along the axis direction of the carbon nanotube tip and connected end to end. The carbon nanotube tip has a first end and a second end opposite to the first end, the first end of the carbon nanotube tip is electrically connected to the conductive substrate, and the top of the second end of the carbon nanotube tip is a prominent carbon nanotubes.

Description

field emission electron source

technical field

The invention relates to a field emission electron source, in particular to a field emission electron source based on carbon nanotubes.

Background technique

The field emission electron source works at low temperature or room temperature. Compared with the thermal emission electron source in the electric vacuum device, it has the advantages of low energy consumption, fast response speed and low discharge. Therefore, the field emission electron source is used to replace the thermal emission in the electric vacuum device. Electron sources have become a hotspot of research.

Carbon Nanotube (CNT) is a new type of carbon material discovered by Japanese researcher Iijima in 1991, see "Helical Microtubules of Graphitic Carbon", S. Iijima, Nature, vol.354, p56 (1991) . Carbon nanotubes have excellent electrical conductivity, good chemical stability and large aspect ratio, and they have a tip surface area that is almost close to the theoretical limit (the smaller the tip surface area, the more concentrated its local electric field), so carbon nanotubes in the field The field of emitting vacuum electron sources has potential application prospects. Current research shows that carbon nanotubes are one of the best known field emission materials. Its tip size is only a few nanometers to tens of nanometers, it has a low turn-on voltage, can transmit a large current density, and the current is stable. ,long lasting. Therefore, carbon nanotubes are an excellent source of point electrons, and can be used in electron emission components of electron emission displays, scanning electron microscopes (Scanning Electron Microscope), and transmission electron microscopes (Transmission Electron Microscope).

Existing carbon nanotube field emission electron sources generally include a conductive substrate and a carbon nanotube, one end of the carbon nanotube is used as a field emission tip, and the other end of the carbon nanotube is electrically connected with the conductive substrate, see "Growth of single-walled Carbon nanotubes on the given Locations for AFM Tips", Wang Rui , Acta Physico-Chimica Sinica, vol. 23, p565 (2007).

However, due to the small size of a single carbon nanotube, the process of electrically connecting a single carbon nanotube to a conductive substrate often requires the assistance of expensive equipment atomic force microscope and scanning tunneling microscope, making this method of combining a single carbon nanotube The preparation process of the field emission electron source formed by the electrical connection of the tube and the conductive substrate is complex and costly. This field emission electron source structure is composed of a single carbon nanotube electrically connected to the substrate. Due to the small size of the single carbon nanotube, its contact area with the substrate is small, resulting in the gap between the carbon nanotube and the substrate. The binding force is small, it is easy to fall off, and it is difficult to withstand a large electric field force, so that the life of this field emission electron source is short. Also because the contact area between a single carbon nanotube and the conductive substrate is small, the heat generated by the carbon nanotube when forming a field emission current is not easy to spread out, and the field emission current that this field emission electron source can withstand is small. Moreover, because the preparation process of this field emission electron source is complex and expensive, the cost of this field emission electron source is relatively high.

Therefore, it is indeed necessary to provide a field emission electron source, which has good field emission performance, can withstand a large electric field force, has a long life, and can carry a large field emission current.

Contents of the invention

A field emission electron source, which includes a conductive substrate, the field emission electron source further includes a carbon nanotube needle point, the carbon nanotube needle point is a carbon nanotube bundle structure, and the carbon nanotube bundle structure includes a plurality of A carbon nanotube with a nanotube tip axially oriented and connected end to end, the carbon nanotube tip has a first end and a second end opposite to the first end, the first end of the carbon nanotube tip is electrically connected to the conductive substrate connected, the top of the second end of the carbon nanotube tip is a protruding carbon nanotube.

Compared with the prior art, the field emission electron source has the following advantages: First, the carbon nanotube tip used is a carbon nanotube bundle structure composed of a plurality of carbon nanotubes connected by van der Waals force, and the tip has only one Carbon nanotubes, the carbon nanotubes at the tip are firmly fixed by other surrounding carbon nanotubes through van der Waals force, so the carbon nanotubes at the tip can withstand a large electric field force; The carbon nanotube bundle structure is connected to the conductive substrate, and the base area of the carbon nanotube tip and the conductive substrate is relatively large, so the heat generated by field emission current heating can also be conducted out through the surrounding carbon nanotubes in a timely and effective manner, so the field The electron emitting source can carry a large field emission current.

Description of drawings

Fig. 1 is a schematic structural diagram of a field emission electron source according to an embodiment of the technical solution.

Fig. 2 is a schematic diagram of the structure of the carbon nanotube tip in Fig. 1 .

Fig. 3 is a scanning electron micrograph of the carbon nanotube tip of the embodiment of the technical solution.

Fig. 4 is a transmission electron micrograph of the carbon nanotube tip of the embodiment of the technical solution.

Fig. 5 is a flowchart of a method for manufacturing a field emission electron source according to an embodiment of the technical solution.

Fig. 6 is a photo of the carbon nanotube film of the embodiment of the technical solution after being treated with an organic solvent.

Fig. 7 is a schematic diagram of a carbon nanotube wire current heating device according to an embodiment of the technical solution.

Fig. 8 is a schematic diagram of a carbon nanotube wire according to an embodiment of the technical solution.

Fig. 9 is a schematic diagram of the carbon nanotube wire of the embodiment of the technical solution after the carbon nanotube wire is fused.

Fig. 10 is a photo of the carbon nanotube wire of the embodiment of the technical solution when it is heated to an incandescent state.

Fig. 11 is a Raman spectrum diagram of the carbon nanotube tip obtained in the embodiment of the technical solution.

Fig. 12 is a schematic flowchart of a method for arranging carbon nanotube needle tips on a conductive substrate according to an embodiment of the technical solution.

Fig. 13 is a schematic diagram of an optical fiber coated with silver glue according to an embodiment of the technical solution.

FIG. 14 is a schematic flowchart of a method for fixing carbon nanotube needle tips with conductive glue according to an embodiment of the technical solution.

Fig. 15 is a graph showing the relationship between field emission voltage and current of the field emission electron source provided by the embodiment of the technical solution.

Detailed ways

The field emission electron source and its preparation method of the technical solution will be described in detail below in conjunction with the accompanying drawings.

Referring to FIG. 1 , FIG. 2 , FIG. 3 and FIG. 4 , the embodiment of the technical solution provides a field emission electron source 10 , which includes a carbon nanotube tip 12 and a conductive substrate 14 .

The carbon nanotube tip 12 includes a first end 122 and a second end 124 opposite to the first end 122, the first end 122 of the carbon nanotube tip 12 is electrically connected to the conductive substrate 14, and the carbon nanotube tip 12 is electrically connected to the conductive substrate 14. The second end 124 of 12 is used to emit electrons. The carbon nanotube tip 12 has a length of 0.01 mm to 1 mm and a diameter of 1 micron to 20 microns.

The carbon nanotube tip 12 is a carbon nanotube bundle structure, and the carbon nanotube bundle structure includes a plurality of carbon nanotubes 126 extending along the axial direction of the carbon nanotube tip 12 and connected end to end, and the carbon nanotubes 126 pass through The van der Waals forces are tightly coupled with each other. The second end 124 of the carbon nanotube tip 12 is a kind of conical shape, the diameter of the second end 124 of the carbon nanotube tip 12 gradually decreases along the direction away from the first end 122, and the top of the second end 124 includes a protruding The carbon nanotube 126 , the carbon nanotube 126 is the electron emitting end 128 .

The carbon nanotubes 126 connected end to end are single-walled carbon nanotubes with a diameter of 0.5 nanometers to 50 nanometers, double-walled carbon nanotubes with a diameter of 1 nanometer to 50 nanometers, and multi-walled carbon nanotubes with a diameter of 1.5 nanometers to 50 nanometers. tube or any combination thereof. The lengths of the end-to-end carbon nanotubes 126 are all in the range of 10 microns to 5000 microns. The protruding carbon nanotube 126 of the second end 124 of the carbon nanotube tip 12 is used as the electron emission end 128 of the field emission electron source. The length and diameter of the carbon nanotubes 126 at the end 128 are smaller than the other carbon nanotubes 126 in the carbon nanotube tip 12 .

The conductive base 14 is made of conductive material, such as copper, tungsten, gold, molybdenum, platinum and so on. The conductive base 14 can be designed into other shapes according to actual needs, such as a cone, a small column or a truncated cone. The conductive base 14 can also be an insulating base with a conductive thin film formed on its surface.

The first end 122 of the carbon nanotube tip 12 is electrically connected to the conductive matrix 14 through intermolecular force. It can be understood that the carbon nanotube tip 12 and the conductive base 14 can also be connected by conductive glue. The positional relationship between the carbon nanotube tip 12 and the conductive substrate 14 is not limited, it is only necessary to ensure that the first end 122 of the carbon nanotube tip 12 is electrically connected to the conductive substrate 14, such as: the carbon nanotube tip 12 and the conductive substrate 14. The included angle of the conductive base 14 is an acute angle, the included angle between the carbon nanotube tip 12 and the conductive base 14 is a right angle or the axes of the carbon nanotube tip 12 and the conductive base 14 are parallel to each other.

The field emission electron source has the following advantages: First, the carbon nanotube tip used is a carbon nanotube bundle structure composed of a plurality of carbon nanotubes connected by van der Waals force, and the tip has only one carbon nanotube, and the tip is The carbon nanotubes are firmly fixed by other surrounding carbon nanotubes through van der Waals force, so the carbon nanotubes at the tip can withstand a large electric field force; It is connected to the conductive substrate, so the heat generated by field emission current heating can also be conducted through the surrounding carbon nanotubes in a timely and effective manner, so the field emission electron source can carry a large field emission current; third, the carbon nanotubes Only one protruding carbon nanotube is used as the field emission tip in the needle tip, and the diameter of the carbon nanotube is less than 5 nanometers, so the width of the electron beam formed by the field emission electron source is small and the resolution is high.

Please refer to Fig. 5, Fig. 6, Fig. 7 and Fig. 8. The embodiment of the technical solution provides a method for preparing the above-mentioned field emission electron source, which specifically includes the following steps:

Step 1: providing a carbon nanotube film, the carbon nanotubes in the carbon nanotube film are extended and arranged along the same direction.

The preparation method of the carbon nanotube film comprises the following steps:

Firstly, a carbon nanotube array formed on a substrate is provided. Preferably, the array is a superparallel carbon nanotube array.

In this embodiment, the preparation method of the carbon nanotube array adopts the chemical vapor deposition method, and its specific steps include: (a) providing a flat substrate, which can be a P-type or N-type silicon substrate, or a silicon substrate with an oxide layer formed on it. Silicon substrate, this embodiment preferably adopts a 4-inch silicon substrate; (b) uniformly form a catalyst layer on the surface of the substrate, and the catalyst layer material can be selected from iron (Fe), cobalt (Co), nickel (Ni) or any One of the combined alloys; (c) annealing the above-mentioned substrate with the catalyst layer in the air at 700°C to 900°C for about 30 minutes to 90 minutes; (d) placing the treated substrate in a reaction furnace, under protection Heating to 500°C to 740°C in a gas environment, and then introducing a carbon source gas to react for about 5 minutes to 30 minutes to grow a carbon nanotube array with a height greater than 100 microns. The carbon nanotube array is a pure carbon nanotube array formed by a plurality of carbon nanotubes growing parallel to each other and perpendicular to the substrate. The carbon nanotube array has substantially the same area as the aforementioned substrate. By controlling the growth conditions above, the super-aligned carbon nanotube array basically does not contain impurities, such as amorphous carbon or residual catalyst metal particles.

In this embodiment, the carbon source gas can be selected from acetylene, ethylene, methane and other chemically active hydrocarbons. The preferred carbon source gas in this embodiment is acetylene; the protective gas is nitrogen or an inert gas, and the preferred protective gas in this embodiment for argon gas.

It can be understood that the carbon nanotube array provided in this embodiment is not limited to the above preparation method. The carbon nanotube array provided in this embodiment is one of a single-wall carbon nanotube array, a double-wall carbon nanotube array, and a multi-wall carbon nanotube array.

Secondly, a stretching tool is used to pull carbon nanotubes from the carbon nanotube array to obtain a carbon nanotube film.

The preparation of the carbon nanotube film specifically includes the following steps: (a) selecting a plurality of carbon nanotube segments with a certain width from the above-mentioned carbon nanotube array. In this embodiment, an adhesive tape with a certain width is preferably used to contact the carbon nanotube array to Selecting a plurality of carbon nanotube segments with a certain width; (b) Stretching the plurality of carbon nanotube segments at a certain speed along a direction substantially perpendicular to the growth direction of the carbon nanotube array to form a continuous carbon nanotube film.

During the above-mentioned stretching process, while the multiple carbon nanotube segments are gradually detached from the substrate along the stretching direction under the action of tension, due to the van der Waals force, the selected multiple carbon nanotube segments are separated from other carbon nanotube segments respectively. The carbon nanotubes are pulled out continuously end to end to form a carbon nanotube film. The carbon nanotube film includes a plurality of end-to-end connected carbon nanotube segments extending in an orientation. The extending direction of the carbon nanotubes in the carbon nanotube film is substantially parallel to the stretching direction of the carbon nanotube film.

Step 2, provide a first electrode 22 and a second electrode 24, and fix the two ends of the above-mentioned carbon nanotube film on the first electrode 22 and the second electrode 24 respectively, in this carbon nanotube film, carbon nanotubes from the second electrode The first electrode 22 extends toward the second electrode 24 .

A certain distance is maintained between the first electrode 22 and the second electrode 24 , and they are insulated from each other. One end of the carbon nanotube film along its stretching direction is tiled and adhered to the first electrode 22 and electrically connected to the first electrode 22, and the other end of the carbon nanotube film along its stretching direction is tiled and adhered On the second electrode 24 and electrically connected to the second electrode 24, the middle of the carbon nanotube film is suspended and stretched. Since the carbon nanotube film itself has a certain viscosity, the two ends of the carbon nanotube film can be directly adhered to the first electrode 22 and the second electrode 24 respectively, or the carbon nanotube film can be bonded by conductive glue such as silver glue. The two ends of the electrode are adhered to the first electrode 22 and the second electrode 24 respectively.

The first electrode 22 and the second electrode 24 are made of conductive materials, such as copper, tungsten, gold, molybdenum, platinum, ITO glass and the like. The shapes of the first electrode 22 and the second electrode 24 are not limited, it is only necessary to ensure that the first electrode 22 and the second electrode 24 have a flat surface so that the two ends of the carbon nanotube film can be tiled and adhered respectively. In this embodiment, the shape of the first electrode 22 and the second electrode 24 is a cuboid. The distance between the first electrode 22 and the second electrode 24 is 50 microns-2 mm, preferably 320 microns in this embodiment.

In step three, a plurality of carbon nanotube wires 28 are formed by treating the carbon nanotube film with an organic solvent.

The organic solvent is dropped on the surface of the carbon nanotube film through a test tube to infiltrate the entire carbon nanotube film. It is also possible to immerse the above-mentioned carbon nanotube film together with the first electrode 22 and the second electrode 24 into a container containing an organic solvent. The organic solvent is a volatile organic solvent, such as ethanol, methanol, acetone, dichloroethane or chloroform, and ethanol is preferably used in this embodiment. After the organic solvent volatilizes, under the effect of the surface tension of the volatile organic solvent, the end-to-end connected carbon nanotube segments in the carbon nanotube film will partially gather into a plurality of carbon nanotube wires 28 . The carbon nanotube wire 28 includes a plurality of carbon nanotubes 126 extending axially along the carbon nanotube wire 28 and connected end to end. Both ends of the carbon nanotube wire 28 are vertically connected to the first electrode 22 and the second electrode 28 respectively. The carbon nanotube wire 28 has a diameter of 1 μm-20 μm and a length of 0.05 mm-2 mm.

Step 4: heating and fusing the carbon nanotube wire 28 with electric current to obtain a plurality of carbon nanotube needle points 12 .

This step can be carried out under a vacuum environment or an environment protected by an inert gas, and it specifically includes the following steps:

First, referring to Fig. 7, Fig. 8 and Fig. 9, the first electrode 22, the second electrode 24 and the carbon nanotube wire 28 connected with the two electrodes are placed in a reaction chamber 20, and the reaction chamber 20 includes a visible Window (not shown in the figure), the internal pressure of the reaction chamber 20 is in a vacuum state lower than 1×10 ^-1 Pa, and the vacuum degree inside the reaction chamber 20 in this embodiment is preferably preferably 2×10 ^-5 Pa.

The interior of the reaction chamber 20 can be filled with an inert gas instead of the vacuum environment, such as helium or argon, so as to prevent the structure damage of the carbon nanotubes 28 due to oxidation during the fusing process.

Secondly, a voltage is applied between the first electrode 22 and the second electrode 24 , and a current is passed through to heat and fuse the carbon nanotube wire 28 .

Those skilled in the art should understand that the voltage applied between the first electrode 22 and the second electrode 24 is related to the diameter and length of the carbon nanotube wire 28 . In this embodiment, the carbon nanotube wire 28 has a diameter of 2 microns and a length of 300 microns, and a DC voltage of 40 volts is applied between the first electrode 22 and the second electrode 24 . The carbon nanotube wire 28 is heated to a temperature of 2000K to 2400K under the action of Joule heat, and the heating time is less than 1 hour. During the vacuum direct current heating process, the current passing through the carbon nanotube wire 28 will gradually increase, but the current will soon decrease until the carbon nanotube wire 28 is fused. Please refer to Fig. 10, before fusing, bright spots will appear in the middle of each carbon nanotube wire 28. The carbon nanotube wire 28 itself conducts to the direction of the first electrode 22 or the second electrode 24 respectively, and the middle position of the carbon nanotube wire 28 is farthest away from the first electrode 22 or the second electrode 24, so that the temperature there is the highest, Therefore, a bright spot appears, so the middle position of the carbon nanotube wire 28 is most likely to be disconnected. After each carbon nanotube wire 28 is fused from the bright spot, two facing carbon nanotube needle points 12 are formed, and the carbon nanotube needle point 12 includes a first end 122 and a second end opposite to the first end 122 124, wherein the first end 122 is fixed on the first electrode 22 or the second electrode 124, and the second end 124 is suspended. The carbon nanotube tip 12 includes a plurality of carbon nanotubes 126 extending along the axial direction of the carbon nanotube tip 12 and connected end to end, and the carbon nanotubes 126 are closely combined with each other by van der Waals force. The second end 124 of the carbon nanotube tip 12 is conical, the diameter of the second end 124 gradually decreases along the direction away from the first end 122, and the top of the second end 124 is a protruding carbon nanotube 126. The carbon nanotubes 126 are the electron emitting ends 128 . The carbon nanotube tip 12 has a length of 0.01 mm to 1 mm and a diameter of 1 micron to 20 microns.

The vacuum fusing method adopted in this embodiment avoids the contamination of the port when the carbon nanotube 28 is mechanically cut, and the mechanical strength of the carbon nanotube 28 will be improved during the heating process, so that it has better mechanical properties.

Please refer to FIG. 11 , which is a Raman spectrum diagram of the second end 124 of the carbon nanotube tip 12 . It can be seen from the figure that after heat treatment, the defect peak of the second end 124 of the carbon nanotube tip 12 is significantly lower than that of the carbon nanotube wire 28 without heat treatment. That is to say, the quality of the carbon nanotubes 126 at the second end 124 of the carbon nanotube tip 12 is greatly improved during the fusing process. On the one hand, this is due to the fact that the defects of carbon nanotubes are reduced after heat treatment, and on the other hand, because the graphite layer rich in defects is easy to collapse at high temperature, leaving some high-quality graphite layers, this result leads to the electron emission end 128 The carbon nanotubes 126 have a smaller diameter than other carbon nanotubes 126 in the carbon nanotube tip 12 .

Step 5: transfer and arrange the carbon nanotube tip 12 on the conductive substrate 14 to obtain the field emission electron source 10 .

Please refer to FIG. 12 , the method for transferring the carbon nanotube tip 12 to the conductive substrate 14 specifically includes the following steps:

First, fix the conductive base 14 on a three-dimensional moving mechanism.

The three-dimensional moving mechanism can precisely control its moving direction and moving distance through a computer, so that the conductive base 14 can move precisely in three-dimensional space.

Secondly, the conductive base 14 is moved so that the conductive base 14 is in contact with a carbon nanotube tip 12 , and the carbon nanotube tip 12 is bent to form a certain stress at the bend of the carbon nanotube tip 12 .

The above steps are carried out with the aid of an optical microscope in order to clearly observe the distance between the carbon nanotube tip 12 and the conductive substrate 14 and the state of the carbon nanotube tip 12 .

Finally, a current is applied between the conductive substrate 14 and the carbon nanotube tip 12 to fuse the carbon nanotube tip 12 , and the fused carbon nanotube tip 12 is fixed on the conductive substrate 14 to form a field emission electron source.

Described electric current can be direct current also can be alternating current, and its magnitude is 5-30 milliamps, and it can be understood that the magnitude of electric current is related to the diameter of carbon nanotube needle point 12, and in the present embodiment, the diameter of carbon nanotube needle point 12 is 3 µm and the current is 10 mA.

After the above steps, the carbon nanotube tip 12 and the conductive matrix 14 are bonded by intermolecular force to form a field emission electron source 10 .

Due to the smaller size of the carbon nanotube tip 12, if the carbon nanotube tip 12 is removed from the electrode by mechanical means, and then the carbon nanotube tip 12 is adhered to the conductive substrate 14, it is easy to remove the carbon nanotube tip 12. 12 damaged and difficult to handle. The vacuum current fusing method adopted in this technical solution will not damage the carbon nanotube tip 12, and the process of removing the carbon nanotube tip 12 from the electrode and adhering to the conductive substrate 14 can be completed in one step, and the operation is simple.

Please refer to FIG. 13 and FIG. 14 , the preparation method of the above-mentioned field emission electron source 10 can further fix the carbon nanotube tip 12 and the conductive substrate 14 through the conductive glue after the sixth step, which specifically includes the following steps:

First, a support body 16 is provided, and a certain thickness of conductive glue 18 is coated on one end of the support body 16 .

The support body 16 is used to support the conductive glue 18, which is a linear structure with a diameter of 50-200 microns. The material of the support body 16 is a hard material. Preferably, the support body 16 is a 125 micron diameter. optical fiber.

The conductive glue 18 is coated on one end of the support body 16 with a thickness of 5-50 microns. Preferably, the conductive glue 18 is silver glue with a thickness of 20 microns.

Secondly, the other end of the support body 16 that is not coated with the conductive glue 18 is fixed on a three-dimensional moving mechanism (not shown).

The three-dimensional moving mechanism can precisely control its moving direction and moving distance through a computer, so that the supporting body 16 can move precisely in three-dimensional space.

Again, the field emission electron source 10 is brought into contact with the end of the support body 16 coated with the conductive glue, and part of the conductive glue 18 is adhered to the position where the carbon nanotube tip 12 is in contact with the conductive matrix 14 .

The above steps were carried out under an optical microscope. Since the conductive glue 18 is in the slurry state, the carbon nanotube tip 12 and part of the conductive matrix 14 are immersed in the conductive glue 18, and then, the support body 16 or the field emission electron source 10 is slowly moved to separate the support body 16 from the field emission electron source 10 , at this time, since the conductive adhesive 18 is in a slurry state, when the support body 16 and the field emission electron source 10 are separated, the conductive adhesive 18 presents a drawing shape, until the filamentous conductive adhesive 18 is pulled off, and part of the conductive adhesive 18 adheres In the field emission electron source 10 , the carbon nanotube tip 12 is in contact with the conductive base 14 . In the process of separating the conductive glue 18 and the field emission electron source 10 , due to the certain intermolecular force between the carbon nanotube tip 12 and the conductive matrix 14 , the carbon nanotube tip 12 will not fall off from the conductive matrix 14 .

Finally, the field emission electron source 10 adhered with the conductive glue 18 is dried, and then the field emission electron source 10 is sintered at a certain temperature for a period of time.

In this embodiment, the field emission electron source 10 adhered with silver colloid is placed in a heating furnace, and dried at a temperature of 80-120° C. for 30 minutes to 2 hours under nitrogen, inert gas or vacuum state, and then Raise the temperature to 350-500°C, sinter for 20 minutes to 1 hour, and then cool to room temperature.

In the above-mentioned sintering process, the organic components in the silver colloid are removed at high temperature, and the silver colloid is solidified, so that the carbon nanotube tip 12 is fixed on the conductive substrate 14, and the carbon nanotube tip 12 is firmly combined with the conductive substrate 14, so that The field emission electron source 10 can withstand relatively large electric field force. Please refer to FIG. 15 , the field emission electron source 10 prepared in this embodiment can emit a current above 20 microamperes.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included within the scope of protection claimed by the present invention.

Claims (8)

1. A field emission electron source, which comprises a conductive substrate, is characterized in that, the field emission electron source further comprises a carbon nanotube needle point, and the carbon nanotube needle point is a carbon nanotube bundle structure, and the carbon nanotube bundle shape The structure includes a plurality of carbon nanotubes extending along the axial direction of the carbon nanotube needle point and connected end to end. The carbon nanotube needle point includes a first end and a second end opposite to the first end. The first end of the carbon nanotube needle point The end is electrically connected with the conductive substrate, and the top of the second end of the carbon nanotube tip includes a protruding carbon nanotube. 2 . The field emission electron source according to claim 1 , wherein the carbon nanotube tip has a length of 0.01 mm to 1 mm and a diameter of 1 micron to 20 microns. 3 . The field emission electron source according to claim 1 , wherein the plurality of carbon nanotubes in the carbon nanotube tip are connected by van der Waals force. 4 . 4. The field emission electron source as claimed in claim 1, wherein the carbon nanotubes connected end to end are single-wall carbon nanotubes, double-wall carbon nanotubes, multi-wall carbon nanotubes or a mixture of any combination thereof . 5. field emission electron source as claimed in claim 4 is characterized in that, the diameter of described single-wall carbon nanotube is 0.5 nanometer-50 nanometer, and the diameter of double-wall carbon nanotube is 1 nanometer-50 nanometer, multi-wall The diameter of the carbon nanotubes is 1.5 nanometers to 50 nanometers, and the lengths of the end-to-end carbon nanotubes are all 10 micrometers to 5000 micrometers. 6 . The field emission electron source according to claim 1 , wherein the length of the protruding carbon nanotube at the top of the second end of the carbon nanotube needle tip is 10 micrometers to 1000 micrometers, and its diameter is less than 5 nanometers. 7. The field emission electron source according to claim 1, wherein the first end of the carbon nanotube tip is electrically connected to the conductive substrate through intermolecular force. 8 . The field emission electron source according to claim 1 , wherein the first end of the carbon nanotube tip is electrically connected to the conductive substrate through conductive glue.