LU501709B1

LU501709B1 - Field emission cathode based on graphene/metamaterial composite nanostructure and preparation method thereof

Info

Publication number: LU501709B1
Application number: LU501709A
Authority: LU
Inventors: Ji Xu
Original assignee: Nanjing Univ Of Information Science And Technology
Priority date: 2022-03-24
Filing date: 2022-03-24
Publication date: 2022-09-26

Abstract

The invention provides a field emission cathode based on graphene/metamaterial composite nanostructures and a preparation method thereof, wherein the graphene/metamaterial composite nanostructures comprise patterned vertical carbon nanotube arrays or patterned microtip arrays and graphene materials compounded with them. According to the invention, by combining novel two-dimensional materials with metamaterial structures such as patterned carbon nanotubes, microtip arrays and the like, the electrostatic shielding effect on the cathode surface can be effectively avoided, the edge effect is fully utilized to compress the potential barrier on the cathode surface, and the threshold of energy required for electron emission is reduced; the top graphene material can achieve the prefocusing effect on the emitted electrons and enhance the electric field intensity at the top of the emitter, thus improving the emission efficiency and current density of the field emission cathode.

Description

DESCRIPTION LU501709 Field emission cathode based on graphene/metamaterial composite nanostructure and preparation method thereof

TECHNICAL FIELD The invention relates to a novel nano-field emission cathode combining graphene with metamaterial structures such as carbon nanotubes or metal microtip arrays and a preparation method thereof, which is mainly applied to electron sources by utilizing the excellent electron emission capability of metamaterial structures and the prefocusing characteristics of graphene, and belongs to the field of vacuum nano electronic devices.

BACKGROUND Field electron emission is to apply a strong electric field on the surface of an object to reduce the surface potential barrier and accelerate electrons, making it easier for electrons to jump out of the cathode surface. Field emission cathode has the characteristics of fast start-up, low energy consumption, long service life and easy compact design. Therefore, the field emission cathode has an important application prospect in the field of electron source with high brightness and good coherence. The cathode materials of traditional field emission cathodes generally use alkali metal materials with low work function or III-V semiconductor materials with negative electron affinity. However, in the process of preparation, storage and use, the requirements for environmental cleanliness are very high, which requires ultra-high vacuum environment, and it is easy to be polluted during use, and its service life is not long. Therefore, the experimental difficulty and use cost of this field emission cathode are very high. With the development of micro-nano processing technology, the field emission cathode materials and structures are diversified, and it is easier to realize compact and integrated design. Metamaterial is a kind of artificial electromagnetic material which is composed of sub-wavelength periodic micro-nano structure and has extraordinary physical characteristics that natural materials do not have. The peculiar properties of metamaterials come from their precise geometric structure and size. Among them, the microstructure has a size smaller than the wavelength it acts on, so it can exert influence on waves. Metamaterials is an interdisciplinary subject, including electronic engineering, condensed matter physics, microwave, optoelectronics, classical optics, materials science, semiconductor science and nanotechnology, etc. The singular nature of metamaterials makes it have a wide application prospect, such as antenna with highJ501709 receiving rate, radar reflector, earthquake warning and electron beam evaporation source, etc. Unlike the traditional field emission cathode array, metamaterial electron source has smaller characteristic size, which requires higher periodicity and uniformity of the structure, so it is necessary to master the patterning and etching process with higher precision.

SUMMARY Based on the above problems, the present invention provides a field emission cathode based on graphene/metamaterial composite nanostructure and a preparation method thereof. In order to achieve the above purpose, the method adopted by the invention is that a field emission cathode based on graphene/metamaterial composite nanostructures comprises a base material, wherein patterned vertical carbon nanotube arrays or patterned microtip arrays and graphene materials compounded with the patterned vertical carbon nanotube arrays are arranged on the base material. As an improvement of the present invention, the patterned shape structure includes a periodically ordered patterned structure composed of rectangle, cone or circle; the size of the patterning is

0.1-1 mm, and the duty ratio is 0.1-0.5. As an improvement of the present invention, the patterned vertical carbon nanotube array is grown on the patterned catalytic layer. As an improvement of the present invention, the patterned catalytic layer includes a first metal plating layer and a second metal plating layer on the first metal plating layer; the first metal plating layer comprises aluminum, and the thickness of the first metal plating layer is 10-20 nm; the second metal plating layer includes iron, and the thickness of the second metal plating layer is 5-10 nm. As an improvement of the present invention, the patterned microtip array includes metal materials and semiconductor materials; the size of the graphene material is 1-1.5 cm”. The invention also discloses a field emission cathode based on graphene/metamaterial composite nanostructure, which comprises the following steps when a patterned vertical carbon nanotube array is arranged on the base material: (1) spin coating photoresist on a base material and patterning;

(2) sputtering a catalytic layer and removing excess photoresist to obtain a patterned catalytk&/501 709 layer structure; (3) transferring graphene onto the patterned catalytic layer by wet method; (4) growing vertical carbon nanotubes on the patterned catalytic layer structure; as an improvement of the present invention, the catalytic layer is formed by DC sputtering or RF sputtering, and the catalytic layer is one or both of aluminum catalytic layer and iron catalytic layer.

As an improvement of the present invention, the growth of vertical carbon nanotubes includes thermal chemical vapor deposition or plasma enhanced chemical vapor deposition.

The invention also discloses another preparation method of the field emission cathode based on the graphene/metamaterial composite nanostructure, and the preparation method of the patterned microtip array comprises the following steps: (1) depositing a metal film on a base material; (2) preparing a patterned metal microtip array structure; (3) transfer graphene to the metal microtip array structure by wet method.

As an improvement of the present invention, the deposited metal film is prepared by thermal evaporation or electron beam evaporation.

The method for preparing the patterned metal microtip array structure adopts a focused ion beam etching method.

The invention has the beneficial effects that: (1) taking graphene as the cathode structure of electron emission, graphene can pre-focus the electron emission, which can reconstruct the electric field distribution, make the electron emission more concentrated in the initial stage of electron emission, reduce the divergence angle of electron beam and improve the focusing performance of electron beam; (2) combining graphene with metamaterials such as carbon nanotube array or microtip array, making full use of the unique advantages of metamaterials and their corresponding structural design in the application of cathode electron source, such as high conductivity and electron mobility, and good environmental stability, which makes the required vacuum condition lower and effectively improves the electron emission performance of cathode; (3) the field emission cathode of the present invention has the advantages of compactness and miniaturization, the cathode silicon substrate is about 1.5x1.5 cm“, and the surface cathode emission material is about 1x1 cm”. With the preparation method of the invention, a mok&/501709 efficient and stable field emission cathode can be prepared.

BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a schematic diagram of the preparation process of patterned carbon nanotube array field emission cathode based on graphene/metamaterial composite nanostructures designed by an embodiment of the present invention. Fig. 2 is a 3D structural schematic diagram of a patterned carbon nanotube array field emission cathode based on graphene/metamaterial composite nanostructures designed in an embodiment of the present invention. Fig. 3 is a schematic diagram of the preparation process of patterned metal microtip array field emission cathode based on graphene/metamaterial composite nanostructures designed in an embodiment of the present invention. Fig. 4 is a 3D structural schematic diagram of the patterned metal microtip array field emission cathode based on graphene/metamaterial composite nanostructures designed in an embodiment of the present invention. In the figure, 1, substrate, 2, photoresist, 3, catalytic layer, 4, graphene, 5, carbon nanotubes, 6, metal microtip.

DESCRIPTION OF THE INVENTION In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention will be described in detail below with reference to specific embodiments, so that the above-mentioned and other objects, features and advantages of the present invention will become clearer, in which the words indicating directions such as up, down, left, right, etc. are only for the position of the shown structure in the corresponding figures. Embodiment 1 The embodiment of the invention provides a method for preparing the patterned carbon nanotube array field emission cathode based on graphene/metamaterial composite nanostructure of the invention. Referring to Fig. 1, the patterned carbon nanotube array field emission cathode based on graphene/metamaterial composite nanostructure of the invention is prepared on a substrate material, such as a silicon wafer or a quartz substrate with a transparent conductive layer. In this embodiment, the substrate material is a heavily doped n-type silicon wafer, and the speciflé/501709 preparation method is as follows: (1) clean that silicon substrate: first, remove the surface oxide, and then use ultrasonic cleaning to clean the surface. (2) photolithography: spin-coating photoresist (positive glue) with spin-coating homogenizer, process parameters: rotating speed 4,000 r/min, time 1 min; bake at 100°C for 2 min; ultraviolet exposure for 3 min; (3) sputtering catalytic layer: coating aluminum (Al) on the photoetched silicon wafer by magnetron sputtering coater.

The technological parameters are: RF current 100 mA, voltage 500 V, time 2 min; iron (Fe) sputtering, process parameters: 100 W, 1 min.

The sputtered aluminum film is about 10 nm and the sputtered iron film is about 5 nm. (4) degreasing: after sputtering, the photoresist on the silicon wafer is soaked and cleaned with acetone to obtain a patterned catalytic layer; (5) transferring graphene: graphene is transferred to the patterned catalytic layer by wet method; (6) growing carbon nanotubes: carbon nanotubes are grown by thermal CVD.

The process parameters are as follows: growth temperature 750°C, pressure 2,000 Pa, hydrogen flow rate 100 sccm, acetylene flow rate 50 sccm, and growth time 20 min.

Finally, the patterned carbon nanotube array field emission cathode based on the graphene/metamaterial composite nanostructure is obtained.

Compared with the prior art, the patterned carbon nanotube array field emission cathode based on the graphene/metamaterial composite nanostructure of the present invention is a structure combining graphene materials and patterned carbon nanotubes, and the patterned carbon nanotube array field emission cathode based on the graphene/metamaterial composite nanostructure of the present invention effectively avoids the electrostatic shielding effect on the cathode surface, and makes full use of the edge effect to make the field strength of the effective emission part of the cathode surface stronger under the same macroscopic field strength, thereby more effectively compressing the cathode surface barrier and more effectively.

On the one hand/501709 graphene has extremely high potential and unique advantages in the field emission cathode application, such as good conductivity and ultra-high electron mobility; On the other hand, carbon nanotubes also have unique advantages in the application of cathode electron source, such as high conductivity and electron mobility, good environmental stability and low work function.

In addition, a more efficient and stable field emission cathode can be prepared by using the preparation method of the invention.

Embodiment 2 This embodiment provides a patterned carbon nanotube array field emission cathode based on graphene/metamaterial composite nanostructures, as shown in Fig. 1 and Fig. 2. The novel nanostructured field emission cathode is fabricated on a substrate 1, and includes a patterned catalytic layer 3, patterned carbon nanotubes 5 formed on the catalytic layer 3, and graphene 4 on the carbon nanotubes 5. In addition, the lower surface of the substrate 1 is coated with conductive silver paste or gallium indium solder as a conductive electrode for applying voltage.

In this embodiment, the material of the substrate 1 is preferably a heavily doped n-type silicon wafer, but it is not limited to this, and may also be other types of silicon wafers or indium tin oxide (ITO) conductive glass, for example.

The lower surface of the substrate 1 is coated with conductive silver paste or gallium indium solder as the conductive electrode for applying voltage.

On the upper surface of the substrate 1, a patterned catalytic layer 3 is formed at intervals.

The catalytic layer 3 is deposited by photolithography and coating process, for example, and includes a first metal plating layer and a second metal plating layer on the first metal plating layer, wherein the first metal plating layer is preferably aluminum (Al), and the thickness of the first metal plating layer is in the range of 10-20 nm, preferably about 20 nm; the second metal plating layer is preferably iron (Fe), and the thickness of the second metal plating layer is 5-10 nm.

The shapes of the patterned structures include gratings, rectangles, rings, etc.

The pattern size is 0.1-1 mm, preferably 0.5 mm, and the duty ratio is 0.1-0.5. In this embodiment, the patterned shape is a rectangle of 0.2 mm*0.2 mm with a pitch of 0.4 mm; the patterned structure includes a periodic ordered patterned structure composed of at least one of grating, rectangle, triangle, ring, square ring or hexagon.

Graphene 4 is transferred on the catalytic layer 3, for example, by wet method.

LU501709 Patterned carbon nanotubes 5 are grown on the catalytic layer 3 by, for example, thermal chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD). The height of the carbon nanotubes 5 is about 40 um, and the shape of the patterned structure of the carbon nanotubes 5 is the same as that of the catalytic layer 3. Embodiment 3 The embodiment of the invention provides a method for preparing a patterned metal microtip array field emission cathode based on graphene/metamaterial composite nanostructures, as shown in Fig. 3. The novel nanostructured field emission cathode based on graphene metamaterials of the present invention is prepared on a substrate material, such as a silicon wafer or indium tin oxide (ITO) conductive glass, etc.

In this embodiment, the substrate material 1s a heavily doped N-type silicon wafer, and its specific preparation method is as follows: (1) clean that silicon substrate: first, remove the surface oxide, and then use ultrasonic cleaning to clean the surface; (2) thermal evaporation metal film: gold plating (Au) is carried out on the cleaned silicon wafer by thermal evaporation coater, and the technological parameters are: current of 10 A, time of 5 min; after plating, the thickness of Au is about 500 nm; (3) etching the gold film: the focused ion beam process is used to etch the metal microtip array structure; (4) transferring graphene: graphene is transferred to the metal microtip array by wet method.

Finally, the patterned metal microtip array field emission cathode based on graphene/metamaterial composite nanostructure is obtained.

Embodiment 4 This embodiment provides a patterned metal microtip array field emission cathode based on graphene/metamaterial composite nanostructures, as shown in Fig. 3 and Fig. 4. The novel nanostructured field emission cathode is fabricated on a substrate 1, and comprises a patterned metal microtip array 6 and graphene 4 transferred on the metal pillar array 6. In addition, the lower surface of the substrate 1 is coated with conductive silver paste or gallium indium solde#/501709 as a conductive electrode for applying voltage.

In this embodiment, the material of the substrate 1 is preferably a heavily doped n-type silicon wafer, but it is not limited to this, and it can also be other types of silicon wafers or a quartz substrate with a transparent conductive layer, for example.

On the upper surface of the substrate 1, a layer of patterned metal micro-tip arrays 6 are formed at intervals, for example, by coating deposition and ion beam etching, and the metal micro-tip arrays 6 are selected from gold (Au), and the thickness of the metal micro-tip arrays 6 is in the range of 150-200 nm, preferably about 200 nm.

Graphene is transferred on the metal pillar array 6. What have been described above are only the embodiments of the present invention.

It should be pointed out here that ordinary technicians in this field can make improvements without departing from the inventive concept, but these are within the scope of protection of the present invention.

Claims

CLAIMS LU501709 I. A field emission cathode based on graphene/metamaterial composite nanostructures, characterized by comprising a base material, wherein patterned vertical carbon nanotube arrays or patterned microtip arrays and graphene materials compounded with them are arranged on the base material.
2. The field emission cathode based on graphene/metamaterial composite nanostructure according to claim 1, characterized in that the patterned shape structure comprises a periodically ordered patterned structure composed of rectangle, cone or circle; the size of the patterning 1s

0.1-1 mm, and the duty ratio is 0.1-0.5.
3. The field emission cathode based on graphene/metamaterial composite nanostructure according to claim 1, characterized in that the patterned vertical carbon nanotube array is grown on the patterned catalytic layer.
4. The field emission cathode based on graphene/metamaterial composite nanostructure according to claim 3, characterized in that the patterned catalytic layer comprises a first metal plating layer and a second metal plating layer on the first metal plating layer; the first metal plating layer comprises aluminum, and the thickness of the first metal plating layer is 10-20 nm; the second metal plating layer includes iron, and the thickness of the second metal plating layer is 5-10 nm.
5. The field emission cathode based on graphene/metamaterial composite nanostructure according to claim 1, characterized in that the patterned microtip array comprises metal materials and semiconductor materials; the size of the graphene material is 1-1.5 cm”.
6. A field emission cathode based on graphene/metamaterial composite nanostructure, characterized in that when a patterned vertical carbon nanotube array is arranged on the base material, it comprises the following steps: (1) spin coating photoresist on a base material and patterning; (2) sputtering a catalytic layer and removing excess photoresist to obtain a patterned catalytic layer structure; (3) transferring graphene onto the patterned catalytic layer by wet method; (4) growing vertical carbon nanotubes on the patterned catalytic layer structure.
7. The preparation method of field emission cathode based on graphene/metamaterial composiké/501709 nanostructure according to claim 6, characterized in that the catalytic layer is formed by DC sputtering or RF sputtering, and the catalytic layer is one or both of aluminum catalytic layer and iron catalytic layer.
8. The preparation method of field emission cathode based on graphene/metamaterial composite nanostructure according to claim 6, characterized in that growing vertical carbon nanotubes comprises thermochemical vapor deposition or plasma enhanced chemical vapor deposition.
9. A method for preparing a field emission cathode based on graphene/metamaterial composite nanostructures, characterized in that the method for preparing the patterned microtip array comprises the following steps: (1) depositing a metal film on a base material; (2) preparing a patterned metal microtip array structure; (3) transferring graphene to the metal microtip array structure by wet method.
10. The preparation method of field emission cathode based on graphene/metamaterial composite nanostructure according to claim 9, characterized in that the deposited metal film is prepared by thermal evaporation or electron beam evaporation; the method for preparing the patterned metal microtip array structure adopts a focused ion beam etching method.