Low-evaporation three-layer film cathode assembly for space traveling wave tube and preparation method of low-evaporation three-layer film cathode assembly

Abstract

The invention relates to the field of electron tubes, and discloses a low-evaporation three-layer film cathode assembly for a space traveling wave tube, which comprises a tungsten substrate positioned on a substrate; the first layer of rhenium film and the rhenium film cover the tungsten substrate; the carbon nanotube composite material layer is deposited on the rhenium film; the second osmium-tungsten film is deposited on the carbon nanotube layer; the third osmium-ruthenium film is deposited on the osmium-tungsten film; wherein the thicknesses of the rhenium film, the carbon nanotube layer, the osmium-tungsten film and the osmium-ruthenium film are respectively controlled to be 0.5-2 mu m, 10-50 nm, 50-200 nm and 20-100 nm, and the carbon nanotube composite material layer is obtained by growing on the rhenium film through chemical vapor deposition. By adopting the osmium-tungsten and osmium-ruthenium films with high crystallinity and the optimized carbon nanotube composite material layer, the electron emission efficiency of the cathode assembly is remarkably improved, so that the energy required by electron emission is reduced, and the electron output quantity under the same working condition is increased.

Description

Technical Field

[0001] The invention relates to the technical field of electron tubes, in particular to a low-evaporation, three-layer film cathode assembly for a space traveling wave tube and a preparation method thereof. Background Art

[0002] Space traveling wave tubes are indispensable core components in satellite systems such as communication navigation and data transmission, and have the function of microwave power amplification. The cathode assembly is the core component of the space traveling wave tube. As an electron source, it emits electrons and interacts with signals. It must not only ensure the smoothness of electronic signals in space and air-to-ground communications, but also ensure the on-orbit life and high reliability of the traveling wave tube. The film layer on the cathode emission surface directly affects the ability and life of emitting electrons, and the electron emission active substances on the non-emitting surface directly affect the insulation reliability of the traveling wave tube. At present, space traveling wave tubes mainly use M-type cathodes (impregnated diffusion cathodes covered with a layer of precious metal film), the cathode emission surface is covered with a layer of precious metal film, and the side non-emitting surface is not physically shielded. There is alloying of the emission film layer and evaporation of the side active substances, which affects the insulation reliability of the traveling wave tube. In addition, with the increase of the frequency band, the size of the space traveling wave tube is smaller, and its electron optics are easily affected by the emission performance of the cathode surface and the distance between the cathode assembly and the accessory components, and there is no effective space (such as cathode-coating distance <0.2mm) for mechanical structure design to shield the evaporation of the active substances on the cathode side.

[0003] Traditional traveling wave tube cathodes usually use single-layer metal or alloy materials, such as tungsten or tungsten-based composite materials. Although these materials have good electron emission performance, they have some significant limitations when facing extreme space environments (such as high temperature, high radiation and vacuum):

[0004] High evaporation rate at high temperature: In a high-temperature working environment, traditional materials are prone to evaporation, resulting in the gradual consumption of cathode materials, affecting the long-term stability and life of the cathode.

[0005] Low electron emission efficiency: As the usage time increases, the cathode surface may cause the electron emission efficiency to decrease due to material degradation.

[0006] Poor environmental adaptability: Traditional cathode materials are sensitive to changes in environmental conditions, especially in extreme vacuum and radiation environments, and are prone to performance fluctuations. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a low-evaporation, three-layer film cathode assembly for a space traveling wave tube and a preparation method thereof, which solves the problem that traditional materials of traditional space traveling wave tubes are prone to evaporation in a high-temperature working environment, resulting in gradual consumption of cathode materials and affecting the long-term stability and life of the cathode.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A low evaporation, three-layer film cathode assembly for a space traveling wave tube, comprising:

[0009] a tungsten substrate disposed on a substrate;

[0010] A first layer of rhenium film and molybdenum film covering a tungsten substrate;

[0011] a carbon nanotube composite layer deposited on a rhenium film;

[0012] a second osmium-tungsten film deposited on the carbon nanotube layer;

[0013] a third osmium-ruthenium film deposited on the osmium-tungsten film;

[0014] The thickness of each layer of material is as follows: the thickness of the rhenium film is controlled between 0.5-2 μm, the thickness of the carbon nanotube layer is 10-50 nm, the thickness of the osmium tungsten film is 50-200 nm, and the thickness of the osmium ruthenium film is 20-100 nm.

[0015] Preferably, the carbon nanotube composite material layer is grown on a rhenium film by chemical vapor deposition, the temperature during the chemical vapor deposition process is 600-800°C, methane is used as a carbon source, and hydrogen is used as a carrier gas. During the chemical vapor deposition process, the flow rate of methane is controlled to be 0.1-0.5sccm, and the flow rate of hydrogen is controlled to be 5-20sccm, ensuring that the growth rate of the carbon nanotubes is 1-5nm per hour.

[0016] Preferably, the first layer of rhenium film and molybdenum film is deposited on a tungsten substrate by magnetron sputtering technology, and the sputtering parameters are: substrate temperature 200°C, sputtering power 120W, gas pressure 2Pa, and rhenium film thickness control formula:

[0017]

[0018] Where D is the self-diffusion coefficient of rhenium, t is the sputtering time, F is the sputtering flow rate, and ρ is the density of rhenium.

[0019] Preferably, the osmium tungsten film is deposited on the carbon nanotube composite material layer by pulsed DC sputtering technology, with a pulse parameter of 100 ns per time and a pulse frequency of 1 kHz. The film thickness and bonding strength control formula is:

[0020]

[0021] Where K is the interface strength adjustment coefficient, γ is the surface tension of the material, L is the material contact length, and d is the film thickness.

[0022] Preferably, the space traveling wave tube uses a low evaporation, three-layer film cathode assembly, wherein the osmium ruthenium film is deposited on the osmium tungsten film by pulsed DC sputtering technology, with a pulse parameter of 100ns per time and a pulse frequency of 1kHz.

[0023] Preferably, the cathode assembly passes a long-term high temperature and high voltage test, and the electron emission performance thereof decays by no more than 20% of the initial performance after 1000 hours of testing.

[0024] Preferably, the cathode assembly is tested in a simulated space environment, and its stability can meet the requirement of continuous operation for more than 2000 hours under vacuum conditions.

[0025] Preferably, the growth rate of the carbon nanotube composite material layer during chemical vapor deposition is 1-5 nm per hour, ensuring the uniformity and stability of the composite layer. The surface roughness of the carbon nanotube composite material layer of the cathode assembly does not exceed 10 nm, ensuring the uniformity and consistency of electron emission.

[0026] A method for preparing a low evaporation, three-layer film cathode assembly for a space traveling wave tube comprises the following steps:

[0027] Step 1: Pre-treat the surface of the tungsten substrate to ensure that the surface is clean and flat;

[0028] Step 2: using physical vapor deposition technology to deposit a rhenium film with good bonding properties on the pretreated tungsten substrate;

[0029] Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film using chemical vapor deposition technology, and controlling the growth conditions to achieve uniformity and stability;

[0030] Step 4: Pulsed DC sputtering.

[0031] Preferably, the preparation method further comprises the following detailed steps:

[0032] Step 1: Pre-treat the surface of the tungsten substrate to ensure the surface is clean and flat, including:

[0033] Mechanical polishing is used to remove the oxide layer and impurities on the surface of the tungsten substrate;

[0034] The tungsten substrate was cleaned with a mixed solution of ethanol and deionized water in an ultrasonic cleaner to ensure that there were no visible impurities and organic residues;

[0035] The tungsten substrate was thermally annealed in a high-purity argon atmosphere at 950°C for 2 hours to release internal stress and improve crystal integrity.

[0036] Step 2: Depositing a rhenium film on the pretreated tungsten substrate using physical vapor deposition technology, wherein:

[0037] The sputtering parameters included substrate temperature 200 °C, sputtering power 120 W, and gas pressure 2 Pa;

[0038] The thickness of the rhenium film is precisely adjusted by controlling the sputtering time and flow rate, and the thickness is controlled between 0.5-2μm;

[0039] Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film using chemical vapor deposition technology, specifically including:

[0040] Set the temperature of the chemical vapor deposition furnace to 750°C;

[0041] Methane was used as the carbon source with a flow rate of 0.2 sccm, and hydrogen was used as the carrier gas and activation gas with a flow rate of 10 sccm;

[0042] The growth rate of carbon nanotubes was ensured to be 1-5 nm per hour. The entire reaction was carried out under low pressure conditions, with the total pressure maintained at 500 mTorr.

[0043] Step 4: Depositing an osmium tungsten film and an osmium ruthenium film in sequence by pulsed DC sputtering technology, wherein:

[0044] The deposition parameters of the osmium-tungsten film and the osmium-ruthenium film included a pulse width of 100 ns and a pulse frequency of 1 kHz;

[0045] The thickness of the osmium tungsten film is 50-200nm, and the thickness of the osmium ruthenium film is 20-100nm;

[0046] Ensure that the film has clear layers and good crystallinity, and optimize the film's bonding strength and thickness by controlling sputtering conditions and material properties.

[0047] The present invention provides a low evaporation, three-layer film cathode assembly for a space traveling wave tube and a preparation method thereof. It has the following beneficial effects:

[0048] 1. The present invention significantly improves the electron emission efficiency of the cathode assembly by adopting high-crystallinity osmium tungsten and osmium ruthenium films and optimized carbon nanotube composite material layers. The introduction of osmium tungsten and osmium ruthenium films reduces the work function of the cathode and optimizes the energy state distribution of the electron escape surface, thereby reducing the energy required for electron emission and increasing the electron output under the same working conditions. In addition, the high conductivity of carbon nanotubes provides a low-impedance transmission path for electrons, further enhancing the collective emission effect of electrons. On the basis of the traditional M-type cathode emission film layer, a rhenium film-osmium tungsten film-osmium ruthenium film sandwich emission film structure is adopted. While improving the film quality, the alloying of the osmium tungsten film can be reduced, so that the cathode emission system is always in the optimal work function state, the alloying of the cathode emission layer is reduced, and the service life is increased, so that the traveling wave tube can work more stably during its entire service life.

[0049] 2. The present invention adopts a multilayer film structure, especially the introduction of a carbon nanotube layer on a rhenium substrate and the covering of osmium tungsten and osmium ruthenium films, which effectively protects the cathode material from direct erosion by high-energy particles and radiation, and significantly extends the service life of the cathode. The carbon nanotube layer acts as a stable buffer layer, which not only improves the thermal stability of the cathode, but also reduces thermal stress through its unique nanostructure, preventing the rapid degradation of the material at high temperatures. These design optimizations ensure that the cathode maintains stability and reliability for a longer time under extreme working conditions of high pressure and high temperature. Based on the traditional M-type cathode, a special mold is designed. By coating the non-emitting surface of the cathode with rhenium and molybdenum metal film layers, the diffusion of molybdenum metal to the cathode substrate can be suppressed, and the diffusion and evaporation of the cathode's emitting active substances can also be suppressed. At the same time, it does not affect the emission performance of the cathode substrate and the change in the electron optical state caused by the change in the cathode focusing distance, and fully improves the reliability of the traveling wave tube cathode focusing insulation.

[0050] 3. The present invention effectively controls the deposition process of osmium tungsten and osmium ruthenium films by introducing multi-pulse sputtering technology into the cathode design, so that the films have higher crystallinity and better interface quality. Multi-pulse technology intermittently adjusts the energy output during the deposition process, which helps to reduce the internal stress generated during material deposition, thereby avoiding cracks or peeling that may occur in the film during long-term use. The application of this technology significantly improves the mechanical strength and structural integrity of the film, providing additional physical protection for the cathode assembly.

[0051] 4. The cathode assembly of the present invention has excellent high temperature resistance and radiation resistance through a carefully designed three-layer film structure, enabling it to work stably under extreme conditions in the space environment. The high melting point and excellent chemical stability of the osmium tungsten and osmium ruthenium films enable the cathode to resist the effects of high-energy particles and severe thermal cycles, maintaining performance consistency and reliability. This environmental corrosion resistance is indispensable in space traveling wave tubes and other aerospace devices, ensuring the long-term and effective operation of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a three-dimensional diagram of depositing two layers of thin film on the side wall of the immersion diffusion cathode blank of the present invention;

[0053] Figure 2 It is a schematic diagram of depositing three layers of thin film on the emitting surface of the immersion diffusion cathode of the present invention;

[0054] Figure 3 It is a schematic diagram of the state after the surface of the cathode coating of the present invention is scratched;

[0055] Figure 4 A schematic diagram of a low evaporation, three-layer film impregnation diffusion cathode assembly of the present invention;

[0056] Figure 5 The figure is a flow chart of the method of the present invention.

[0057] Among them, 1. rhenium film; 2. osmium tungsten film; 3. osmium ruthenium film; 4. molybdenum film. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] Embodiment 1:

[0060] Please see attached Figure 1 - Attachment Figure 4 The embodiment of the present invention provides a low evaporation, three-layer film cathode assembly for a space traveling wave tube, comprising:

[0061] a tungsten substrate disposed on a substrate;

[0062] A first layer of rhenium film 1 and molybdenum film 4 covering the tungsten substrate;

[0063] a carbon nanotube composite material layer deposited on the rhenium film 1;

[0064] a second osmium tungsten film 2 deposited on the carbon nanotube layer;

[0065] a third osmium ruthenium film 3 deposited on the osmium tungsten film 2;

[0066] The thickness of each material layer is as follows: the thickness of the rhenium film 1 is controlled between 0.5-2 μm, the thickness of the carbon nanotube layer is 10-50 nm, the thickness of the osmium tungsten film 2 is 50-200 nm, and the thickness of the osmium ruthenium film 3 is 20-100 nm.

[0067] The carbon nanotube composite material layer is grown on a rhenium film by chemical vapor deposition. The temperature during the chemical vapor deposition process is 600-800°C, methane is used as a carbon source, and hydrogen is used as a carrier gas. During the chemical vapor deposition process, the flow rate of methane is controlled to be 0.1-0.5sccm, and the flow rate of hydrogen is controlled to be 5-20sccm, ensuring that the growth rate of the carbon nanotubes is 1-5nm per hour.

[0068] The first layer of rhenium film 1 and molybdenum film 4 are deposited on a tungsten substrate by magnetron sputtering technology. The sputtering parameters are: substrate temperature 200°C, sputtering power 120W, gas pressure 2Pa, and rhenium film thickness control formula:

[0069]

[0070] Where D is the self-diffusion coefficient of rhenium, t is the sputtering time, F is the sputtering flow rate, and ρ is the density of rhenium.

[0071] The osmium tungsten film 2 is deposited on the carbon nanotube composite material layer by pulsed DC sputtering technology. The pulse parameters are 100ns per time and the pulse frequency is 1kHz. The film thickness and bonding strength control formula are:

[0072]

[0073] Where K is the interface strength adjustment coefficient, γ is the surface tension of the material, L is the material contact length, and d is the film thickness.

[0074] The space traveling wave tube uses a low evaporation, three-layer film cathode assembly, wherein the osmium ruthenium film 3 is deposited on the osmium tungsten film 3 by pulsed DC sputtering technology, with a pulse parameter of 100ns per time and a pulse frequency of 1kHz.

[0075] The cathode assembly has passed long-term high temperature and high voltage testing, and its electron emission performance has a performance degradation of no more than 20% of the initial performance after 1000 hours of testing.

[0076] The cathode assembly was tested in a simulated space environment and its stability was found to meet the requirement of continuous operation for more than 2,000 hours under vacuum conditions.

[0077] The growth rate of the carbon nanotube composite material layer during chemical vapor deposition is 1-5nm per hour, which ensures the uniformity and stability of the composite layer. The surface roughness of the carbon nanotube composite material layer of the cathode assembly does not exceed 10nm, ensuring the uniformity and consistency of electron emission.

[0078] Please see attached Figure 5 , a method for preparing a low evaporation, three-layer film cathode assembly for a space traveling wave tube, comprising the following steps:

[0079] Step 1: Pre-treat the surface of the tungsten substrate to ensure that the surface is clean and flat;

[0080] Step 2: using physical vapor deposition technology to deposit a rhenium film with good bonding properties on the pretreated tungsten substrate;

[0081] Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film using chemical vapor deposition technology, and controlling the growth conditions to achieve uniformity and stability;

[0082] Step 4: Deposit osmium tungsten film and osmium ruthenium film in sequence through pulsed DC sputtering technology to ensure that the film layers are clear and have good crystallinity.

[0083] The preparation method further comprises the following detailed steps:

[0084] Step 1: Pre-treat the surface of the tungsten substrate to ensure the surface is clean and flat, including:

[0085] Mechanical polishing is used to remove the oxide layer and impurities on the surface of the tungsten substrate;

[0086] The tungsten substrate was cleaned with a mixed solution of ethanol and deionized water in an ultrasonic cleaner to ensure that there were no visible impurities and organic residues;

[0087] The tungsten substrate was thermally annealed in a high-purity argon protection environment at a temperature of 950°C for 2 hours to release internal stress and improve crystal integrity.

[0088] Step 2: Depositing a rhenium film 1 on the pretreated tungsten substrate using physical vapor deposition technology, wherein:

[0089] The sputtering parameters included substrate temperature 200 °C, sputtering power 120 W, and gas pressure 2 Pa;

[0090] The thickness of the rhenium film 1 is precisely adjusted by controlling the sputtering time and flow rate, and the thickness is controlled between 0.5-2 μm.

[0091] Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film 1 using chemical vapor deposition technology, specifically comprising:

[0092] Set the temperature of the chemical vapor deposition furnace to 750°C;

[0093] Methane was used as the carbon source with a flow rate of 0.2 sccm, and hydrogen was used as the carrier gas and activation gas with a flow rate of 10 sccm;

[0094] To ensure that the growth rate of carbon nanotubes is 1-5 nm per hour, the entire reaction is carried out under low pressure conditions, and the total pressure is maintained at 500 mTorr.

[0095] Step 4: Depositing the osmium tungsten film 2 and the osmium ruthenium film 3 in sequence by pulsed DC sputtering technology, wherein:

[0096] The deposition parameters of the osmium-tungsten film 2 and the osmium-ruthenium film 3 include a pulse width of 100 ns and a pulse frequency of 1 kHz;

[0097] The thickness of the osmium tungsten film 2 is 50-200 nm, and the thickness of the osmium ruthenium film 3 is 20-100 nm;

[0098] Ensure that the film has clear layers and good crystallinity, and optimize the film's bonding strength and thickness by controlling sputtering conditions and material properties.

[0099] The molybdenum film 4 is introduced in the present invention based on its excellent mechanical strength and high temperature stability. Molybdenum is a metal with an extremely high melting point, which can maintain the stability of physical properties under extreme temperature conditions. In the cathode of the space traveling wave tube, the functions of the molybdenum film are as follows:

[0100] The molybdenum film 4, as a layer of structural reinforcement material, can effectively enhance the mechanical stability of the entire cathode assembly and resist deformation and stress under high temperature.

[0101] The molybdenum film 4 can slow down the evaporation and degradation of other materials in a high temperature environment, thereby extending the service life of the cathode.

[0102] Optimizing electron emission performance: Molybdenum has a low electron work function, which helps to form a stable electron emission layer on the cathode surface and improve the overall emission efficiency.

[0103] The preparation of the molybdenum film 4 adopts the following steps:

[0104] Material selection: High purity Mo target material is selected to ensure the quality of the deposited Mo film 4.

[0105] Physical vapor deposition (PVD): Deposit the molybdenum film on the carbon nanotube composite layer using magnetron sputtering or electron beam evaporation techniques. Control the deposition parameters (such as power, pressure, temperature) to optimize the uniformity and adhesion of the film.

[0106] Thickness and uniformity control: The thickness of the molybdenum film 4 is usually controlled within the range of 10-100 nm, and the precise control of thickness is ensured by adjusting the deposition time and power.

[0107] Integration of Molybdenum Membrane 4 in Cathode Assembly

[0108] Molybdenum film 4 is the third layer of material, located between the carbon nanotube composite material layer and the osmium tungsten film. This structural design not only optimizes the functionality of each layer of material, but also ensures the synergistic effect of the entire cathode assembly in terms of electron emission and durability. The introduction of molybdenum film 4 provides an additional protective layer for the cathode assembly, which is essential for maintaining long-term stability in the harsh space environment.

[0109] Step 1: Pretreatment of tungsten substrate

[0110] In this embodiment, the pretreatment of the tungsten substrate is the first step in preparing an efficient electron emission cathode. A tungsten plate with a purity higher than 99.95% is selected and first mechanically polished to remove the oxide layer and impurities on the surface. Thereafter, the tungsten substrate is placed in an ultrasonic cleaner and thoroughly cleaned with a mixed solution of ethanol and deionized water to ensure that there are no visible impurities and organic residues. The cleaned tungsten substrate needs to be thermally annealed in an environment protected by high-purity argon gas, with the temperature set at 950°C for 2 hours to release internal stress and improve its crystal integrity, providing a uniform and stable substrate for subsequent thin film deposition.

[0111] Step 2: Deposition of rhenium film

[0112] In this embodiment, the deposition of the rhenium film is carried out by magnetron sputtering technology. The pre-treated tungsten substrate is placed in a magnetron sputtering device, and a rhenium target with a purity of 99.99% is used. During the sputtering process, the substrate temperature is controlled at 200°C to promote the adhesion and smoothness of the rhenium film. The sputtering gas pressure is set to 3×10 -3 Torr, using pure argon as the sputtering atmosphere. The sputtering power is set to 150W to ensure uniform rhenium film deposition rate and consistent film thickness. The deposition time is usually 30 minutes to form a continuous rhenium film with a thickness of about 1.5μm. The uniform deposition of the rhenium film in this process is crucial to ensure the uniform growth of the carbon nanotube composite layer.

[0113] Step 3: Growth of carbon nanotube composite layer

[0114] In this embodiment, the growth of the carbon nanotube composite material layer is carried out by chemical vapor deposition technology. The tungsten substrate covered with rhenium film is placed in a chemical vapor deposition furnace and the temperature is adjusted to 750°C. Methane is used as a carbon source, the flow rate is controlled at 0.2sccm, and hydrogen is used as a carrier and activation gas, and the flow rate is controlled at 10sccm. The entire reaction is carried out under low pressure conditions, and the total pressure is maintained at 500mTorr. By accurately controlling the ratio of methane and hydrogen and the reaction time (about 60 minutes), the uniform growth of the carbon nanotube layer is achieved, and its thickness is about 30nm. The introduction of the carbon nanotube layer significantly improves the thermal stability and electron emission efficiency of the cathode, and provides an ideal structural support for the subsequent deposition of osmium tungsten and osmium ruthenium films.

[0115] Step 4: Deposition of Osmium-Tungsten and Osmium-Ruthenium Thin Films

[0116] In this embodiment, the deposition of osmium tungsten and osmium ruthenium films is carried out by pulsed DC sputtering technology. First, the osmium tungsten film is deposited by adjusting to the pulsed DC sputtering mode in the chemical vapor deposition equipment, the pulse frequency is set to 1kHz, the pulse width is 100ns, the sputtering power is 200W, and the duration is 20 minutes, forming an osmium tungsten film with a thickness of about 100nm. Subsequently, under the same conditions, an osmium ruthenium target is used to deposit an osmium ruthenium film with a thickness of about 50nm. The introduction of these two layers of metal films not only further reduces the work function of the cathode, but also increases its chemical and thermal stability in extreme environments.

[0117] Role of rhenium film: As a substrate layer, the rhenium film provides a stable working surface, and its low work function is conducive to the easy emission of electrons.

[0118] Carbon nanotube composite material layer: The carbon nanotube layer not only enhances the stability of the structure, but also has excellent thermal conductivity and electron transport due to its unique nanostructure, and can serve as an efficient transmission channel for electrons.

[0119] Osmium tungsten and osmium ruthenium films: These two layers of metal films further reduce the electron escape work function, improve the emission efficiency, and provide good chemical stability and heat resistance, resisting the erosion of high temperature and radiation environment.

[0120] Improved electron emission efficiency: The multilayer structure significantly improves the electron emission efficiency, especially at low voltages.

[0121] Extended cathode life: By reducing the evaporation rate and enhancing physical stability, the cathode of the present invention has a longer service life than conventional cathodes.

[0122] Adaptability to extreme environments: The cathode of the present invention can withstand the harsh space environment, including high temperature and radiation, and is suitable for high-end equipment such as space traveling wave tubes.

[0123] In a preferred embodiment, the temperature gradient controls the growth of carbon nanotubes.

[0124] In this preferred embodiment, the temperature gradient control technology is introduced into the growth process of carbon nanotubes to promote the growth of higher quality carbon nanotubes and better structural consistency. The specific steps are as follows:

[0125] In the chemical vapor deposition setup, the heating zone of the chemical vapor deposition furnace is divided into two parts, the temperature of the front zone is set at 780°C, and the temperature of the rear zone is gradually reduced to 720°C. This temperature gradient helps control the growth rate and structural orientation of carbon nanotubes, thereby improving the uniformity of the carbon nanotube layer and the electron transport performance.

[0126] By introducing this temperature gradient during the chemical vapor deposition process, the uniformity of the carbon nanotube layer is significantly improved, thereby ensuring a more efficient electron transport pathway through the carbon nanotube layer and reducing the possibility of local hot spots and electron blockage.

[0127] This optimization not only improves the quality of the carbon nanotube layer, but also further enhances the overall emission performance and reliability of the cathode by improving the uniformity of electron transport.

[0128] In a preferred embodiment, the multi-pulse sputtering technique is used to deposit osmium-tungsten and osmium-ruthenium thin films.

[0129] In this preferred embodiment, the deposition of osmium tungsten and osmium ruthenium thin films uses multi-pulse sputtering technology to improve the density and uniformity of the thin films. The specific steps are as follows:

[0130] Based on pulsed DC sputtering, a double-pulse sputtering mode is introduced, in which a short secondary pulse is inserted between each main pulse, the width of the secondary pulse is 10ns, and the power is 50% of the main pulse. This double-pulse technology helps to redistribute the deposited energy during the deposition process, reduce the internal stress of the film, and improve the crystallinity of the film.

[0131] The osmium tungsten film was first deposited in double pulse mode, followed by the osmium ruthenium film under the same conditions. This method resulted in a smoother interface between the films and significantly enhanced bonding between the films.

[0132] Through this multi-pulse sputtering technology, the structural stability and electron emission performance of osmium tungsten and osmium ruthenium films have been further improved, especially the performance stability under long-term or high-load working conditions has been significantly enhanced.

[0133] In a preferred embodiment, the comprehensive implementation steps are:

[0134] Step 1: High-precision pretreatment of tungsten substrate

[0135] The tungsten substrate is surface polished by automated polishing equipment to ensure a high degree of flatness and smoothness.

[0136] The polished tungsten substrate was ultrasonically cleaned in a mixed solution of ultrapure water and ethanol to remove all possible surface contamination.

[0137] During the high-temperature annealing process, temperature gradient control is introduced to gradually reduce the temperature from one end of the tungsten substrate to the other, from 950°C to 900°C, in order to optimize the crystal structure and reduce internal stress.

[0138] Step 2: Precise deposition of rhenium film:

[0139] The sputtering parameters were precisely controlled using a magnetron sputtering device, in which the rhenium target was uniformly sputtered in an argon atmosphere.

[0140] The film thickness is monitored in real time during the sputtering process to ensure that the rhenium film thickness is uniform, usually controlled at 1.5μm, with an error of no more than ±0.1μm.

[0141] Step 3: Optimized Growth of Carbon Nanotube Layers

[0142] A temperature gradient was introduced during the chemical vapor deposition process, gradually decreasing from 750°C to 700°C, and a mixed gas of methane and hydrogen was used to grow a uniform and highly conductive carbon nanotube layer on the rhenium film.

[0143] During the growth process, the structure and alignment of carbon nanotubes are optimized by precisely controlling the gas flow and pressure.

[0144] Step 4: Multi-pulse sputtering deposition of Osmium-Tungsten and Osmium-Ruthenium thin films

[0145] On the carbon nanotube layer, the osmium tungsten and osmium ruthenium films were deposited using double-pulse DC sputtering technology. Double-pulse sputtering technology provides more detailed energy control, reduces internal stress, and enhances the crystallinity and interface bonding of the film.

[0146] The sputtering parameters are as follows: the main pulse power is 200 W, the duration is 100 ns, and the secondary pulse power is 100 W, the duration is 50 ns, to ensure the uniformity and high quality of the O-T and O-Ru films.

[0147] Comparative Example 1:

[0148] Single layer tungsten cathode

[0149] Step content:

[0150] Material selection: High-purity tungsten (purity>99.95%) is selected as the cathode material to ensure its stability during electron emission.

[0151] Surface treatment: The tungsten rod is machined, ground and polished to obtain a smooth surface and reduce surface defects.

[0152] Heat treatment: High temperature treatment is performed in a vacuum furnace to remove gas inclusions in tungsten and improve the crystal quality of tungsten.

[0153] Deposition: The processed tungsten material is directly used as the cathode, usually formed by arc discharge or evaporation deposition.

[0154] Comparative Example 2:

[0155] Tungsten-rhenium alloy cathode

[0156] Step content:

[0157] Alloy preparation: Tungsten and rhenium are mixed in a specific ratio (such as 90% tungsten and 10% rhenium) and the alloy material is prepared by smelting or mechanical alloying technology.

[0158] Casting and processing: The alloy material is cast into the cathode shape and machined to obtain the required geometric dimensions and surface roughness.

[0159] Surface treatment: Polish and clean the alloy surface to remove surface oxide layer and impurities.

[0160] Comparative Example 3:

[0161] Tungsten Carbide Cathode

[0162] Step content:

[0163] Material selection: Choose tungsten and a carbon source (such as graphite powder) for mixing.

[0164] Synthesis: The mixture is reacted and synthesized at high temperature to form tungsten carbide (WC), usually in a high temperature atmosphere furnace.

[0165] Molding: The synthesized tungsten carbide powder is molded into a cathode shape by pressing and sintering methods.

[0166] Surface treatment: The sintered tungsten carbide is surface polished to improve its smoothness and emission performance.

[0167] Experimental Group:

[0168] Example group: using the three-layer film structure cathode described in the present invention (tungsten substrate, rhenium film, CNT composite material layer, osmium tungsten film and osmium ruthenium film).

[0169] Comparison group 1: single-layer tungsten cathode.

[0170] Comparison group 2: tungsten-rhenium alloy cathode.

[0171] Comparison group 3: tungsten carbide cathode.

[0172] Test parameters:

[0173] Electron emission efficiency: The electron emission current of each group of cathodes under standard conditions is measured using electron beam testing equipment.

[0174] High temperature tolerance: Each group of cathodes was tested for continuous operation in a simulated vacuum and high temperature environment, and performance changes were recorded.

[0175] Life test: Long-term operation test to observe the performance degradation of each cathode after 2000 hours of continuous operation.

[0176] Environmental adaptability: Each set of cathodes is placed in high radiation and extreme temperature cycle tests to check the stability of their structure and performance.

[0177] Experimental methods

[0178] Material preparation: The corresponding cathode was prepared according to the preparation method of each example and comparative group.

[0179] Performance Testing:

[0180] Preliminary electron emission tests were performed using an electron beam emitter, with the same acceleration voltage and measurement current set.

[0181] The long-term temperature resistance test was carried out in a high-temperature thermal vacuum chamber with the temperature set to 500°C and the duration being 1000 hours.

[0182] Conduct electron emission performance decay test and record the initial performance and performance data after 2000 hours.

[0183] Conduct environmental adaptability tests to simulate space environmental conditions, such as radiation intensity and temperature cycles.

[0184]

[0185] Table 1

[0186] annotation:

[0187] Electron emission efficiency: measured in terms of current density (mA / cm 2 ) indicates that the higher the value, the better the electron emission performance.

[0188] High temperature tolerance: The rate of change of performance after running at high temperature. The lower the rate of change, the better the high temperature resistance.

[0189] Life test: The performance decay rate after long-term operation. The lower the decay rate, the longer the life.

[0190] As can be seen from the table above, the cathode of the present invention outperforms conventional cathode technology in all test aspects. In particular, in the electron emission efficiency and life tests, the cathode of the present invention shows significant performance advantages. These data support the significant improvement of the present invention in improving the performance of space traveling wave tube cathodes.

[0191] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low evaporation, three-layer film cathode assembly for a space traveling wave tube, characterized in that: include: a tungsten substrate disposed on a substrate; A first layer of rhenium film (1) and molybdenum film (4) covering the tungsten substrate; A carbon nanotube composite material layer deposited on the rhenium film (1); a second osmium tungsten film (2) deposited on the carbon nanotube layer; a third osmium ruthenium film (3) deposited on the osmium tungsten film (2); The thickness of each material layer is: the thickness of the rhenium film (1) is controlled between 0.5-2 μm, the thickness of the carbon nanotube layer is 10-50 nm, the thickness of the osmium tungsten film (2) is 50-200 nm, and the thickness of the osmium ruthenium film (3) is 20-100 nm.

2. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The carbon nanotube composite material layer is grown on a rhenium film by chemical vapor deposition. The temperature during the chemical vapor deposition process is 600-800°C. Methane is used as a carbon source and hydrogen is used as a carrier gas. During the chemical vapor deposition process, the flow rate of methane is controlled to be 0.1-0.5sccm and the flow rate of hydrogen is controlled to be 5-20sccm to ensure that the growth rate of the carbon nanotubes is 1-5nm per hour.

3. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The first layer of rhenium film (1) and molybdenum film (4) are deposited on a tungsten substrate by magnetron sputtering technology. The sputtering parameters are: substrate temperature 200° C., sputtering power 120 W, gas pressure 2 Pa. The thickness control formula of the rhenium film (1) is: where D is the self-diffusion coefficient of rhenium, t is the sputtering time, F is the sputtering flow rate, and ρ is the density of rhenium.

4. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The osmium tungsten film (2) is deposited on the carbon nanotube composite material layer by pulsed DC sputtering technology, with pulse parameters of 100 ns per time and a pulse frequency of 1 kHz. The film thickness and bonding strength control formula is: Where K is the interface strength adjustment coefficient, γ is the surface tension of the material, L is the material contact length, and d is the film thickness.

5. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 3, characterized in that: The space traveling wave tube uses a low evaporation, three-layer film cathode assembly, wherein the osmium ruthenium film (3) is deposited on the osmium tungsten film (2) by pulse direct current sputtering technology, the pulse parameters are 100ns once, and the pulse frequency is 1kHz.

6. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The cathode assembly has passed a long-term high-temperature and high-voltage test, and its electron emission performance has a performance degradation of no more than 20% of the initial performance after 1000 hours of testing.

7. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The cathode assembly is tested in a simulated space environment, and its stability can meet the requirement of continuous operation for more than 2000 hours under vacuum conditions.

8. A low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 1, characterized in that: The growth rate of the carbon nanotube composite material layer during chemical vapor deposition is 1-5 nm per hour, ensuring the uniformity and stability of the composite layer. The surface roughness of the carbon nanotube composite material layer of the cathode assembly does not exceed 10 nm, ensuring the uniformity and consistency of electron emission.

9. A method for preparing a low evaporation, three-layer film cathode assembly for a space traveling wave tube, according to a low evaporation, three-layer film cathode assembly for a space traveling wave tube as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Pre-treat the surface of the tungsten substrate to ensure that the surface is clean and flat; Step 2: using physical vapor deposition technology to deposit a rhenium film (1) having good bonding properties on the pretreated tungsten substrate; Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film (1) using chemical vapor deposition technology, and controlling the growth conditions to achieve uniformity and stability; Step 4: Deposit an osmium tungsten film and an osmium ruthenium film (3) in sequence by pulsed DC sputtering technology to ensure that the film layers are clear and have good crystallinity.

10. The method for preparing a low evaporation, three-layer film cathode assembly for a space traveling wave tube according to claim 9, characterized in that: The preparation method further comprises the following detailed steps: Step 1: Pre-treat the surface of the tungsten substrate to ensure the surface is clean and flat, including: Mechanical polishing is used to remove the oxide layer and impurities on the surface of the tungsten substrate; The tungsten substrate was cleaned with a mixed solution of ethanol and deionized water in an ultrasonic cleaner to ensure that there were no visible impurities and organic residues; The tungsten substrate was thermally annealed in a high-purity argon atmosphere at 950°C for 2 hours to release internal stress and improve crystal integrity. Step 2: Depositing a rhenium film (1) on the pretreated tungsten substrate using a physical vapor deposition technique, wherein: The sputtering parameters included substrate temperature 200 °C, sputtering power 120 W, and gas pressure 2 Pa; The thickness of the rhenium film (1) is precisely adjusted by controlling the sputtering time and flow rate, and the thickness is controlled between 0.5-2 μm; Step 3: growing a carbon nanotube composite material layer on the surface of the rhenium film (1) using chemical vapor deposition technology, specifically comprising: Set the temperature of the chemical vapor deposition furnace to 750°C; Methane was used as the carbon source with a flow rate of 0.2 sccm, and hydrogen was used as the carrier gas and activation gas with a flow rate of 10 sccm; The growth rate of carbon nanotubes was ensured to be 1-5 nm per hour. The entire reaction was carried out under low pressure conditions, with the total pressure maintained at 500 mTorr. Step 4: sequentially depositing an osmium tungsten film (2) and an osmium ruthenium film (3) by pulsed DC sputtering technology, wherein: The deposition parameters of the osmium tungsten film (2) and the osmium ruthenium film (3) include a pulse width of 100 ns and a pulse frequency of 1 kHz; The thickness of the osmium tungsten film (2) is 50-200 nm, and the thickness of the osmium ruthenium film (3) is 20-100 nm; Ensure that the film has clear layers and good crystallinity, and optimize the film's bonding strength and thickness by controlling sputtering conditions and material properties.

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