CN109801819B - A composite nano-cold cathode structure with high stable electron emission and preparation method - Google Patents

Abstract

The invention discloses a composite nano-cold cathode structure with high stable electron emission and a preparation method. The composite nano-cold cathode structure includes a substrate; a low-dimensional nano-cold cathode prepared upright on the substrate; a two-dimensional thin film material covered on the tip of the low-dimensional nano cold cathode; a support for regulating the geometric curvature of the tip of the two-dimensional thin film material structure. The advantage of this structure is that the surface of the two-dimensional thin film material has no dangling bond structure to obtain a clean emission surface. In addition, by adjusting the geometric curvature of the tip of the two-dimensional thin film material, the transport process of the emitted electrons can be controlled, making them become hot electrons with higher energy, thus having a lower turn-on electric field. The cleaner surface and reduced surface potential barrier enable the composite low-dimensional nanocold cathode to achieve highly stable electron emission.

Description

A composite nano-cold cathode structure with high stable electron emission and preparation method

technical field

The invention relates to the technical field of vacuum microelectronics. In particular, the invention relates to a composite nano-cold cathode structure with high stability of electron emission, and more particularly to a preparation method of a composite nano-cold cathode with high stability of electron emission.

Background technique

Cold cathode electron sources have the advantages of high brightness, good coherence, and easy integration, so they have important applications in high-precision electron microscopes, flat-panel X-ray sources, flat-panel displays, and parallel electron beam etching. However, the inherent emission current instability of cold cathodes limits its development.

Generally speaking, the instability of cold cathode is mainly related to two aspects. One is the surface adsorption and desorption process, which is mainly related to surface dangling bonds and surface charges. At present, the adsorption molecules are mainly removed as much as possible by heating the cold cathode at high temperature (such as Field emission microscopy of carbon nanotube caps). However, the high-temperature heating method has a great limitation on the melting point of the materials used in the electron source structure, and when the temperature drops to the normal operating temperature, the residual gas will still be adsorbed on the cold cathode.

Another factor is the formation of atomic-scale protrusions on the surface structure under strong electric fields, which induce changes in the local electric field. According to the field emission theory, the higher the surface barrier of a cold cathode, the more sensitive its emission current is to changes in the electric field, therefore, the electric field disturbance will cause greater current fluctuation.

SUMMARY OF THE INVENTION

The present invention provides a composite nano-cold cathode structure with highly stable electron emission in order to overcome at least one of the above-mentioned defects in the prior art.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

The composite nano-cold cathode structure of the present invention includes a substrate, a low-dimensional nano-cold cathode prepared on the substrate, a two-dimensional thin film material covered on the tip of the low-dimensional nano cold cathode, and a tip for adjusting the geometric curvature of the two-dimensional thin film material The geometric curvature of the tip of the two-dimensional thin film material is smaller than that of the tip of the low-dimensional nanostructure.

The substrate can be a planar structure such as a silicon wafer or glass, or a tapered structure such as a tungsten needle. The support structure can be a low-dimensional nanocold cathode array, or a porous structure such as an integrated insulating layer or a separated ceramic.

According to geometry, when the geometric curvature of the tip of the two-dimensional thin film material is smaller than that of the low-dimensional nanostructure tip, the tip can be in close contact, otherwise a dangling structure will be formed at the tip, which is not conducive to the generation of hot electrons and the stable emission of electrons.

Preferably, the substrate is a planar substrate or a tapered substrate. The substrate can be a flat substrate such as glass, ceramics, silicon, etc., or a tapered substrate such as a tungsten needle tip, a nickel needle tip, or a gold needle tip. Among them, the planar substrate is suitable for the manufacture of cold cathode electron source arrays, and the tapered substrate is suitable for the manufacture of cold cathode point electron source devices.

Preferably, the support structure can be the low-dimensional nano-cold cathode array itself, and further, it can also be an additionally prepared integrated or separated pore-like structure. Among them, the support structure composed of the low-dimensional nano-cold cathode array itself and the integrated hole-like structure is suitable for the fabrication of electron source arrays, while the use of the separated hole-like structure as the support structure is suitable for the fabrication of point electron source devices. The support structure of the low-dimensional nano-cold cathode array itself has the advantages of simple structure and easy fabrication, but it has certain requirements on the aspect ratio of the low-dimensional nano-cold cathode. If the aspect ratio is too large, the two-dimensional thin film material is easily overwhelmed. 3D nano-cold cathode, and the integrated pore-like structure can reduce the gravity of the low-dimensional nano-cold cathode from the 2D thin film material itself and the pressure during its transfer process.

Preferably, the integrated hole-like structure can be composed of insulating films such as silicon dioxide, silicon nitride or aluminum oxide, or metal films such as chromium, tungsten, and copper.

Preferably, the separated porous structure can be composed of ceramics or metals such as copper, aluminum, iron and the like. Since electrons are mainly injected into 2D thin film materials through low-dimensional nanocold cathodes, the supporting structures can be either conductors or insulators.

The invention also provides a method for preparing a composite nanostructure with highly stable electron emission, which includes cleaning the substrate, fabricating a low-dimensional nano-cold cathode and a supporting structure of equal or near equal height, and then transferring the two-dimensional thin film material to a low-dimensional low-dimensional cold cathode. Nano-cold cathodes and support structures.

Preferably, the low-dimensional nano-cold cathodes can be quasi-one-dimensional nanostructures such as nanowires, nanorods, nanocones, two-dimensional nanostructures such as vertical graphene and nanowalls, and spindt cold cathodes, and the materials thereof can be zinc oxide, Tungsten oxide, copper oxide, silicon, carbon, molybdenum, nickel, tungsten, etc.

Preferably, the two-dimensional thin film material may be composed of one or more materials such as graphene, molybdenum disulfide, molybdenum diselenide, tungsten disulfide, tungsten diselenide and other transition metal sulfides, hexagonal boron nitride and the like.

The principle of improving the electron emission stability of the present invention is to use the clean surface of the two-dimensional thin film material. The two-dimensional thin film material has no surface dangling bonds, which reduces the adsorption and desorption process of the surface, and the thermal electron energy generated by the electron transport process is reduced. surface barrier, thereby improving the stability of electron emission.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention has a wide range of applications. The support structure formed by the low-dimensional nano-cold cathode array itself and the integrated hole-like structure is suitable for the production of electron source arrays, while the use of the separated hole-like structure as the support structure is suitable for point electrons. Fabrication of source devices. The electron-emitting composite nano-cold cathode structure is suitable for application in vacuum point electron sources and flat plate electron source arrays.

(2) The composite nano-cold cathode structure of the present invention has the advantages of simple structure and high operability.

(3) The present invention utilizes the surface-free dangling bond structure of the two-dimensional thin film material to obtain a clean emission surface. In addition, by regulating the geometric curvature of the tip of the two-dimensional thin film material, the transport process of the emitted electrons can be controlled, making them become hot electrons with higher energy, thus having a lower turn-on electric field. The cleaner surface and reduced surface potential barrier enable the composite low-dimensional nanocold cathode to achieve highly stable electron emission.

Description of drawings

Figure 1 is a schematic structural diagram of a composite low-dimensional nano-cold cathode on the basis of different substrates;

2 is a schematic diagram of the fabrication process of the composite nano-cold cathode structure shown in (a) in FIG. 1 in Example 1;

3 is a schematic diagram of the fabrication process of the composite nano-cold cathode structure shown in (b) in FIG. 1 in Example 1;

4 is a schematic diagram of the fabrication process of the composite nano-cold cathode structure shown in (c) in FIG. 1 in Example 1;

Figure 5 is a schematic structural diagram of a composite low-dimensional nano-cold cathode with a tip curvature of two-dimensional thin film material greater than/less than that of a low-dimensional nanostructure tip;

Fig. 6 is the simulation result of the surface energy band bending of single-layer tungsten diselenide thin films with different thicknesses under the applied electric field of 2.5V/nm;

FIG. 7 is a scanning electron microscope photograph and a stability test result of the actually fabricated composite nano-cold cathode structure.

Description of reference numerals

Substrate 1; low-dimensional nano-cold cathode 2; two-dimensional thin film material 3; support structure 4.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms “upper”, “lower”, “left” and “right” , "top", "bottom", "inside", "outside" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or It is implied that the referred device or element must have a specific orientation, be constructed and operate in a specific orientation, so the terms describing the positional relationship in the drawings are for illustrative purposes only and should not be construed as limitations on this patent.

In addition, if there are terms such as "first" and "second", they are only used for descriptive purposes, and are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used for Indicate or imply the relative importance and quantity of the indicated means, elements or components, but should not be construed as indicating or implying relative importance.

Example 1

As shown in Figure 1, the structural schematic diagrams of three kinds of composite low-dimensional nano-cold cathodes based on different substrates and using nanowires as low-dimensional cold cathode materials are given.

The basic structure of the cold cathode includes a substrate 1 , a low-dimensional nano-cold cathode 2 , a two-dimensional thin film material 3 and a support structure 4 .

In (a) of FIG. 1, the substrate 1 is a planar structure, and the supporting structure is the low-dimensional nano-cold cathode array itself; in (b) of FIG. 1, the substrate 1 is a planar structure, and the supporting structure is an integrated insulating layer pinhole ; In (c) of FIG. 1 , the substrate 1 is a tapered structure, and the supporting structure is a separate ceramic mesh/copper mesh.

Example 2

Schematic diagram of the fabrication process of the composite nano-cold cathode structure based on FIG. 1 .

As shown in FIG. 2 , FIG. 2 shows a flow chart of the fabrication of the composite nano-cold cathode structure in (a) of FIG. 1 . First prepare a planar substrate 1 ((a) in FIG. 2 ); then prepare low-dimensional nano-cold cathodes 2 with vertical and equal heights on it, and a plurality of low-dimensional nano-cold cathodes 2 form a low-dimensional nano-cold cathode array (Fig. 2(b)); finally, transfer the two-dimensional thin film material 3 to the low-dimensional nano-cold cathode 2 (Fig. 2(c)). The low-dimensional nano-cold cathode of equal height ensures that the geometric curvature of the tip of the two-dimensional thin film material is smaller than that of the nanowire tip.

As shown in FIG. 3 , FIG. 3 shows a flow chart of the fabrication of the composite nano-cold cathode structure in (b) of FIG. 1 . First prepare a flat substrate 1 ((a) in FIG. 3 ); then deposit an insulating layer film 4 thereon ((b) in FIG. 3 ); hole ((c) in Figure 3); then prepare a low-dimensional nano-cold cathode 2 with the same height as the insulating layer film in the small hole ((d) in Figure 3); finally transfer the two-dimensional thin film material 3 to the small hole. into the hole and draped on the nanowire ((e) in Figure 3). Keeping the same height between the nanowire and the insulating layer film ensures that the geometric curvature of the tip of the two-dimensional thin film material is smaller than that of the nanowire tip.

As shown in FIG. 4 , FIG. 4 shows a flow chart of the fabrication of the composite nano-cold cathode structure in (c) of FIG. 1 . First prepare a cone-shaped substrate 1 ((a) in FIG. 4 ); then prepare low-dimensional nano-cold cathodes 2 thereon ((b) in FIG. 4 ); then prepare a ceramic mesh with small holes/ Copper mesh 4 ((c) in Figure 4); then transfer the two-dimensional thin film material 3 into the pores ((d) in Figure 4); finally place the ceramic mesh/copper mesh 4 in a low-dimensional nano-cold cathode 2 and move until they touch ((e) in Figure 4). During the movement, it is necessary to ensure that the geometric curvature of the tip of the two-dimensional thin film material is smaller than that of the nanowire tip.

The fabrication of the composite nano-cold cathode structure based on other low-dimensional nano-cold cathodes in the present invention can be performed according to the basic steps of the above examples. It should be specially pointed out that the composite nano-cold cathode structures in Figure 1(a), Figure 1(b) and Figure 1(c) are not limited to the single emitter shown in the figure, It can also be applied to large area emitter array structures.

Example 3

Figure 5 is the simulation result of the surface band bending of the composite low-dimensional nanocold cathode with the tip curvature of the two-dimensional thin film material greater than/less than the tip curvature of the low-dimensional nanostructure.

As shown in Fig. 5, the schematic diagrams of the structures in which the geometrical curvature of the tip of the two-dimensional thin film material is larger than or smaller than the geometrical curvature of the tip of the nanowire are listed respectively. According to the geometry, the 2D thin film material in Fig. 5(b) is in close contact with the nanowire tip at the tip, while the 2D thin film material in Fig. 5(a) forms a dangling structure at the tip.

Figure 6 shows the simulation results of the surface energy band bending of single-layer tungsten diselenide films with different thicknesses under an applied electric field of 2.5 V/nm; Band bending under V/nm electric field. Among them, (a) in FIG. 6 is the simulation result of a single-layer tungsten diselenide thin film with a thickness of 0.7 nm. (b) in Figure 6 is the simulation result of bulk tungsten diselenide with a thickness of 700 nm. From the results, it can be seen that the surface potential energy is only about 0.13 eV for the monolayer film, while for the bulk shape , and its surface potential energy is about 1.4 eV.

5 and 6, in the structure of (a) in FIG. 5, the tip of the two-dimensional thin film material is suspended, so the emitted electrons are only accelerated by the osmotic electric field in the c-axis direction of the two-dimensional thin film material. Therefore, the energy of the penetration electric field is the surface potential energy of the monolayer film, as shown in (a) in Figure 6, that is, 0.13 eV. In the structure in (b) of Figure 5, the tip of the two-dimensional material is in close contact with the nanowire, so the emitted electrons can be injected into the two-dimensional material through the nanowire under the osmotic electric field. Therefore, the energy of its penetrating electric field can be approximated as the surface potential energy of the bulk shape, as shown in (b) in Figure 6, that is, 1.4 eV. It can be seen that the structure in (b) of Fig. 5 can obtain higher energy emitted electrons and thus have a lower surface barrier.

Example 4

This example presents the fabrication process, electron microscope scanning and stability test of a composite low-dimensional nano-cold cathode using zinc oxide nanowires as a quasi-one-dimensional low-dimensional nano-cold cathode and a single-layer tungsten diselenide film as a two-dimensional film material result.

The specific production steps are shown in Figure 2. First, the silicon wafer substrate was ultrasonically cleaned with acetone, ethanol and deionized water for 30 minutes, respectively. After drying with nitrogen, a zinc film with a thickness of 1 micron was prepared on a silicon wafer substrate by electron beam evaporation technology. The silicon wafers are then thermally oxidized in a tube furnace in an atmospheric environment. The temperature of the tube furnace was first raised from room temperature to 470°C and then held at 470°C for 3 hours. After the silicon wafer is naturally cooled, the zinc film will grow into a low-dimensional nano-cold cathode array of zinc oxide. Then, the monolayer tungsten diselenide thin film was transferred to the low-dimensional nano-cold cathode array by organosol-assisted method. Finally, the silicon wafer samples were placed in a vacuum tube furnace to rapidly heat up to 450 °C and held for 2 hours to remove the organosol.

We carried out scanning electron microscopy observations on the as-prepared composite nanocold cathode structures. FIG. 7 is a scanning electron microscope photograph and a stability test result of the actually fabricated composite nano-cold cathode structure.

As shown in FIG. 7, (a) in FIG. 7 is a picture of the composite nano-cold cathode structure observed by scanning electron microscope. Among them, the white arrow points to the tip position of the tungsten diselenide and the zinc oxide nanowire in contact. It can be seen that tungsten diselenide covers the nanowire relatively flatly, and the geometric curvature of tungsten diselenide is smaller than that of the tip of the nanowire. (b) in FIG. 7 is the field emission stability test result of the structure. It can be seen that the field emission stability of the cold cathode is very good with a volatility as low as 0.79% in the test time of 300 seconds.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (8)

1. a composite nano-cold cathode structure of highly stable electron emission, is characterized in that, comprises: (1) Substrate; (2) a low-dimensional nano-cold cathode prepared on the above-mentioned substrate; (3) a two-dimensional thin film material covering the tip of the above-mentioned low-dimensional nano-cold cathode; (4) a support structure for adjusting the geometric curvature of the tip of the two-dimensional thin film material, the support structure and the low-dimensional nano-cold cathode have the same height, and the support structure includes an integrated pore structure or a separate pore structure; (5) The geometric curvature of the tip of the two-dimensional thin film material is smaller than the geometric curvature of the tip of the low-dimensional nano-cold cathode, and the tip of the two-dimensional thin-film material is in close contact with the low-dimensional nano-cold cathode. 2 . The composite nano-cold cathode structure with high stability of electron emission according to claim 1 , wherein the substrate is a planar substrate or a tapered substrate. 3 . 3 . The composite nano-cold cathode structure with high stability of electron emission according to claim 1 , wherein the low-dimensional nano-cold cathode is an upright quasi-one-dimensional low-dimensional nano-cold cathode or an upright two-dimensional low-dimensional nano-cold cathode. 4 . 4 . The composite nano-cold cathode structure with high stability of electron emission according to claim 1 , wherein the material of the integrated porous structure comprises an insulating film or a metal film. 5 . 5 . The composite nano-cold cathode structure with high stability of electron emission according to claim 1 , wherein the material of the isolated pore structure comprises ceramic or metal. 6 . 6. a preparation method of the composite nano-cold cathode structure of high stable electron emission according to claim 1, is characterized in that, comprises the following steps: (1) clean the substrate; (2) Preparation of low-dimensional nano-cold cathodes and supporting structures of equal height; (3) Transfer the two-dimensional thin film material to the above-mentioned low-dimensional nano-cold cathode. 7. The preparation method of the composite nano-cold cathode structure of high stable electron emission according to claim 6, wherein the low-dimensional nano-cold cathode comprises zinc oxide, tungsten oxide, copper oxide, molybdenum oxide, silicon, silicon carbide , one or more materials of boron, carbon, molybdenum, nickel, tungsten. 8. the preparation method of the composite nano-cold cathode structure of high stable electron emission according to claim 6, is characterized in that, described two-dimensional thin film material comprises graphene, molybdenum disulfide, molybdenum diselenide, tungsten disulfide, disulfide Tungsten Selenide and other transition metal sulfides, one or more of hexagonal boron nitride.

Images