Graphene-coated barium-tungsten cathode and preparation method thereof
阅读说明：本技术 一种石墨烯覆膜钡钨阴极及其制备方法 (Graphene-coated barium-tungsten cathode and preparation method thereof ) 是由 樊鹤红 杜航 包正强 孙小菡 于 2020-06-08 设计创作，主要内容包括：本发明公开了一种石墨烯覆膜钡钨阴极及其制备方法,所述石墨烯覆膜钡钨阴极包括石墨烯层和B型钡钨阴极层,B型钡钨阴极层的上表面覆石墨烯层,B型钡钨阴极层置于支撑筒内,支撑筒内的B型钡钨阴极层下设置灯丝。所述制备方法包括以下步骤：(1)制备B型钡钨阴极；(2)在衬底生长石墨烯一侧覆TRT,通过溶液腐蚀去除衬底,保留石墨烯,将覆有石墨烯的TRT清洗,烘干；(3)在温控台上放置石墨烯/TRT膜,B型钡钨阴极倒置其上,控制温度达到TRT热剥离温度,再将阴极取开,石墨烯附着在阴极表面。本发明有利于降低钡钨阴极表面逸出功,估计逸出功可达1.9eV以下,相比B型阴极,可以提升发射能力,或降低工作温度以延长阴极使用寿命。(The invention discloses a graphene-coated barium-tungsten cathode and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a B-type barium-tungsten cathode; (2) covering a TRT on one side of the substrate where the graphene grows, removing the substrate through solution corrosion, reserving the graphene, cleaning the TRT covered with the graphene, and drying; (3) and placing the graphene/TRT film on a temperature control table, inverting the B-type barium-tungsten cathode, controlling the temperature to reach the TRT thermal stripping temperature, taking the cathode away, and attaching the graphene to the surface of the cathode. The invention is beneficial to reducing the work function of the surface of the barium-tungsten cathode, the work function is estimated to be less than 1.9eV, and compared with a B-type cathode, the emission capability can be improved, or the working temperature is reduced to prolong the service life of the cathode.)
1. A graphene coated barium-tungsten cathode is characterized in that: including graphite alkene layer (1) and B type barium tungsten cathode layer (2), the upper surface of B type barium tungsten cathode layer (2) covers graphite alkene layer (1), B type barium tungsten cathode layer arranges in support section of thick bamboo (3), set up the filament under B type barium tungsten cathode layer (2) in the support section of thick bamboo (3).
2. The graphene-coated barium-tungsten cathode according to claim 1, characterized in that: the graphene layer (1) is single-layer or double-layer graphene.
3. The graphene-coated barium-tungsten cathode according to claim 1, characterized in that: the graphene layer is characterized by further comprising a grid (4), wherein the grid (4) is isolated from the graphene layer (1) through an insulating medium layer (5) or vacuum.
4. The graphene-coated barium-tungsten cathode according to claim 3, wherein: the grid (4) is annular or net-shaped.
5. The graphene-coated barium-tungsten cathode according to claim 1, characterized in that: when the anode is used as an electron source in a thermo-photo comprehensive emission vacuum electronic device, the anode adopts a net structure, so that cathode excitation light can be incident to the cathode from the back of the anode.
6. The graphene-coated barium-tungsten cathode according to claim 1, characterized in that: when the cathode excitation light is used as an electron source in a thermo-photo integrated emission vacuum electronic device, the wavelength of the cathode excitation light is shorter than 690 nanometers.
7. The preparation method of the graphene-coated barium-tungsten cathode according to claim 1, characterized by comprising the following steps:
(1) preparing a B-type barium-tungsten cathode;
(2) covering a TRT on one side of a substrate where graphene grows, then corroding by a corrosive solution, removing the substrate, reserving the graphene on the TRT, cleaning the TRT covered with the graphene in deionized water, and drying;
(3) and (3) placing the graphene/TRT film obtained in the step (2) on a temperature control table, inverting the B-type barium-tungsten cathode on the film, controlling the temperature of the temperature control table to reach a TRT thermal stripping temperature, losing the TRT viscosity, removing the cathode, and attaching the graphene to the surface of the cathode to obtain the graphene-coated barium-tungsten cathode (6).
8. The method for preparing the graphene-coated barium-tungsten cathode according to claim 7The preparation method is characterized by comprising the following steps: the corrosive solution is FeCl3And (3) solution.
Technical Field
The invention relates to the technical field of microwave vacuum electronics, in particular to a graphene coated barium-tungsten cathode and a preparation method thereof.
Background
Vacuum electronic devices have been widely used in various devices and systems such as various power microwave systems, precision detection devices, etc. for communication, display, medical CT, nondestructive detection, particle accelerators, free electron lasers, electron microscopes, etc. because of their characteristics of high frequency, high output power, etc. The cathode is used as an electron source of a vacuum microelectronic device, and the emission capability of the cathode directly influences the performance indexes of the device and a system. The hot cathode has the obvious advantages of large emission current, long service life and the like, and is widely applied. Further improvement of the emission capability or extension of the cathode life is a constant development direction of cathodes.
The interdiffusion between the M-type cathode surface film layer and the substrate material can significantly change the cathode surface work function, and the optimal ratio is maintained during the preparation and use processes. An M-type cathode in the existing hot cathode is a cathode with better emission capability and service life, lower work function is realized by coating a layer of osmium or iridium or ruthenium thin film on the surface of a B-type or S-type cathode, the emission capability is improved, but the work function of the surface of the M-type cathode is greatly related to the component ratio of the film layer on the surface of the cathode, the mutual diffusion of the film layer on the surface of the cathode and base metal under the thermal working condition can cause the change of the components on the surface of the cathode, the change of the work function on the surface of the cathode and the change of the emission current density under the same working condition are caused, and the mutual diffusion between the surface of the cathode and the base in the using process influences the working stability and the service life of the M-type.
Disclosure of Invention
The purpose of the invention is as follows: in order to improve the emission performance of the cathode, simplify the preparation process and improve the working stability, the invention aims to provide the graphene coated barium tungsten cathode for improving the emission capability and the working stability, and the invention also aims to provide the preparation method of the graphene coated barium tungsten cathode with simple process.
The technical scheme is as follows: the graphene-coated barium-tungsten cathode comprises a graphene layer and a B-type barium-tungsten cathode layer, wherein the upper surface of the B-type barium-tungsten cathode layer is coated with the graphene layer, the B-type barium-tungsten cathode layer is arranged in a supporting cylinder, and a filament is arranged below the B-type barium-tungsten cathode layer in the supporting cylinder to form a hot cathode.
The graphene layer is single-layer or double-layer graphene. The graphene layer is isolated from the grid electrode through an insulating medium layer or vacuum. The grid is annular or mesh-shaped.
The graphene-coated barium-tungsten cathode can be used as an electron source in a hot cathode vacuum electronic device and a hot-photocathode vacuum electronic device. When the graphene-coated barium-tungsten cathode is used as an electron source in a heat-light comprehensive emission vacuum electronic device, the anode adopts a net structure, so that cathode excitation light can be incident to the cathode from the back of the anode. When the graphene-coated barium-tungsten cathode is used as an electron source in a thermal-optical integrated emission vacuum electronic device, the wavelength of cathode excitation light is shorter than 690 nanometers.
The preparation method of the graphene coated barium-tungsten cathode comprises the following steps:
(1) preparing a B-type barium-tungsten cathode;
(2) covering TRT on one side of the substrate to grow graphene, and then passing through FeCl3Corroding with a corrosive solution, removing the substrate, reserving the graphene on the TRT, cleaning the TRT coated with the graphene in deionized water, and drying;
(3) and (3) placing the graphene/TRT film obtained in the step (2) on a temperature control table, inverting the B-type barium-tungsten cathode on the film, controlling the temperature of the temperature control table to reach a TRT thermal stripping temperature, enabling the TRT to lose viscosity, then removing the cathode, and enabling the graphene to be attached to the surface of the cathode to obtain the graphene-coated barium-tungsten cathode.
In addition, the surface emission of the cathode can be adjusted by adding a grid on the surface of the cathode, the grid adopts a ring-shaped or net-shaped structure, the grid and the cathode are isolated by an insulating layer medium or vacuum, and the adjustment of the emission capability of the cathode can be realized by adjusting the voltage of the grid.
Has the advantages that: compared with the prior art, the invention has the following remarkable characteristics:
1. the surface work function of the barium-tungsten cathode can be reduced, and compared with a B-type cathode, the emission capability can be improved, or the working temperature can be reduced to prolong the service life of the cathode;
2. compared with an M-type cathode, the graphene is adopted to replace the surface coating of the M-type cathode, so that the preparation process is simplified, the stability is enhanced, and the cost is reduced.
3. With the additional gate, the cathode emission capability can be adjusted by adjusting the gate voltage.
Drawings
FIG. 1 is a schematic structural view of the present invention;
fig. 2 is a schematic structural diagram of the gate of the present invention.
Detailed Description
In the following examples, the starting materials were all available as received.
The position relationship between the graphene-coated barium-tungsten cathode 6 and the
A schematic diagram of a graphene-coated barium-tungsten cathode gate control structure and a position relation with an
The measured value of the (unsaturated) emission current density of the graphene-coated barium-tungsten cathode 6 reaches 0.235A/cm under the working temperature condition of 1080K and the cathode-anode spacing of 1-2mm when the cathode-anode voltage is 160V2The work function is estimated to be not more than 1.9 eV. The literature (Work function distribution for a B category and an M category earlyin life (From: T.J.Grant, Technical Digest, 1986 IEDM).1986 IEEE.)) showed that the work function of B-type barium-tungsten cathode was about 2.1eV, and the work function of M-type cathode was about 1.95 eV; the work function of the domestic Os-coated film M-type cathode can reach about 1.87 eV; thus, it is possible to provideThe graphene coated barium-tungsten cathode 6 provided by the invention has better emission performance than a B-type cathode (about 2.1 eV) and is not inferior to an M-type cathode (about 1.9 eV). Experience has shown that the working life can be doubled for every 10 ℃ reduction in the working temperature of the hot cathode. Therefore, the reduction of the operating temperature at the same emission current density of the low-work-function cathode 6 can effectively improve the lifetime.
Based on the experience of graphene preparation, a graphene film is not suitable for directly growing on a tungsten substrate, so that the graphene needs to be coated on the surface of a barium-tungsten cathode in a transfer mode, but the contact with liquid needs to be avoided in consideration of the specificity of the cathode, and therefore, the graphene coating on the surface of the barium-tungsten cathode is carried out by a two-step transfer method of intermediate transfer-Thermal Release Tape (TRT) dry transfer. In the case of using a TRT-based graphene finished product, the first transfer step is not required, and only direct dry transfer is required. The preparation method of the graphene-coated barium-tungsten cathode 6 specifically comprises the following steps:
in the first step, a commercial graphene film is transferred from a substrate (such as a copper substrate) to a TRT (TRT transfer method) by an intermediary transfer method, the TRT is covered on the side of the substrate where graphene is grown, and then the TRT is passed through a solution (such as FeCl)3Solution) etching to remove the substrate while keeping the graphene on the TRT, then cleaning the TRT coated with the graphene in deionized water, and then drying;
and secondly, placing a graphene/TRT film on a temperature control table, inverting the B-type barium-tungsten cathode on the temperature control table, controlling the temperature of the temperature control table to reach a TRT thermal stripping temperature, removing the cathode, and attaching graphene to the surface of the cathode to obtain the graphene-coated barium-tungsten cathode 6.
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