A field emission cathode paste and a field emission cathode and a method for manufacturing the same

Abstract

This application discloses a field emission cathode paste and a field emission cathode and its preparation method, relating to the technical field of field emission cathodes. The paste includes a dispersant, a cold cathode emission material, conductive particles, and a thickener. The dispersant includes terpineol, ethylene glycol, and glycerol. This application improves the formulation of the dispersant by combining terpineol, ethylene glycol, and glycerol. Terpineol ensures the printing leveling properties of the paste; ethylene glycol enhances the wetting and dispersing ability of carbon nanotubes and inhibits agglomeration; and glycerol moderately increases the viscosity of the system to prevent the paste from dripping after printing. The three components synergistically balance viscosity, dispersibility, and the thermal decomposition characteristics of the organic carrier, reducing the turn-on electric field of the field emission cathode and improving the emission current and current emission stability.

Description

Technical Field

[0001] This application relates to the technical field of field emission cathodes, specifically to a field emission cathode paste and a field emission cathode and its preparation method. Background Technology

[0002] In recent years, field emission cold cathodes have attracted increasing attention due to their performance advantages, especially carbon nanotube materials, which possess advantages such as miniaturization, low turn-on electric field, fast response speed, low power consumption, and the ability to operate at room temperature. In practical applications, carbon nanotubes are usually coated in the form of field emission paste to achieve cathode fabrication.

[0003] Traditional pastes typically consist of cold cathode emitter materials, conductive fillers, dispersants, and thickeners. To improve the turn-on electric field, emission current, and current emission stability, process optimization is often performed on aspects such as the specifications of the cold cathode emitter material, the composition ratio of the conductive filler, and the composition ratio of each component in the paste. The selection of dispersants and thickeners is particularly challenging, as their organic properties vary greatly due to differences in melting point, viscosity, and solubility. Optimizing the paste involves a complex formulation system with extremely high processing difficulty. A qualified paste formulation has a significant positive impact on the long-term stability and reliability of the device. Summary of the Invention

[0004] In a first aspect, this application provides a field emission cathode slurry, the slurry comprising a dispersant, a cold cathode emission material, conductive particles, and a thickener; Dispersants include terpineol, ethylene glycol, and glycerol.

[0005] In some optional embodiments of the first aspect of this application, the volume fraction of terpineol is 50% to 65%, the volume fraction of ethylene glycol is 20% to 25%, and the volume fraction of glycerol is 10% to 30%, based on the total volume of the dispersant.

[0006] In some optional embodiments of the first aspect of this application, the volume fraction of terpineol is 60%, the volume fraction of ethylene glycol is 20%, and the volume fraction of glycerol is 20% based on the total volume of the dispersant.

[0007] In some optional embodiments of the first aspect of this application, the mass ratio of cold cathode emitting material to dispersant is 1:(150~300), the mass ratio of conductive particles to dispersant is 1:(20~40), and the mass ratio of thickener to dispersant is 1:(80~120).

[0008] In some optional embodiments of the first aspect of this application, the cold cathode emitting material includes carbon nanotubes and graphene.

[0009] In some optional embodiments of the first aspect of this application, the length of the carbon nanotube is 50 μm to 100 μm and the diameter of the carbon nanotube is 10 nm to 30 nm.

[0010] In some optional embodiments of the first aspect of this application, the cold cathode emitting material includes at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0011] In some optional embodiments of the first aspect of this application, the graphene monolayer thickness is 0.55nm~1.2nm, the graphene diameter is 0.5μm~3μm, and the number of graphene layers is 1~5.

[0012] In some optional embodiments of the first aspect of this application, the conductive particles are selected from at least one of copper, titanium, cobalt, molybdenum, iron, nickel and silver.

[0013] In some optional embodiments of the first aspect of this application, the conductive particles are selected from at least one of nickel-copper alloy, nickel-silver alloy, copper-silver alloy, copper-molybdenum alloy, copper-silver-titanium alloy, and iron-cobalt alloy.

[0014] In some optional embodiments of the first aspect of this application, the particle size of the conductive particles is 50 nm to 100 nm.

[0015] A second aspect of this application provides a method for preparing a field emission cathode, using the field emission cathode paste described above, the method comprising the following steps: The field emission cathode paste is coated onto the conductive electrode and then degassed and activated to obtain the field emission cathode.

[0016] In some optional embodiments of the second aspect of this application, the preparation steps of the field emission cathode paste include: The conductive particles are mixed with a dispersant to form a first slurry; The cold cathode emission material is mixed with the first slurry to form the second slurry; The thickener is mixed with the second slurry to form a field emission cathode slurry.

[0017] In some optional embodiments of the second aspect of this application, mixing conductive particles with a dispersant to form a first slurry includes: mixing the conductive particles and the dispersant, and then ball milling them for 60 min to 80 min at a ball milling speed of 300 r / min to 550 r / min and a ball milling power of 250 W to 350 W to form the first slurry.

[0018] In some optional embodiments of the second aspect of this application, mixing the cold cathode emitting material with the first slurry to form the second slurry includes: mixing the cold cathode emitting material with the first slurry and ball milling for 180 min to 240 min at a ball milling speed of 400 r / min to 500 r / min and a ball milling power of 300 W to 400 W to form the second slurry.

[0019] In some optional embodiments of the second aspect of this application, mixing the thickener with the second slurry to form a field emission cathode slurry includes: mixing the thickener with the second slurry and ball milling for 120 min to 180 min at a ball milling speed of 500 r / min to 600 r / min and a ball milling power of 350 W to 450 W to form a field emission cathode slurry.

[0020] In some optional embodiments of the second aspect of this application, the degassing activation process includes: The conductive electrode coated with field emission cathode paste is degassed by vacuum heat treatment, and then the cold cathode emission material is distributed in a vertically upward direction.

[0021] In some optional embodiments of the second aspect of this application, the field emission cathode paste is applied to the conductive electrode by screen printing.

[0022] A third aspect of this application provides a field emission cathode, which is prepared by the above-described method for preparing a field emission cathode.

[0023] Beneficial effects: The field emission cathode paste provided in the first aspect of this application improves the dispersant formulation by combining terpineol, ethylene glycol, and glycerol. Terpineol ensures the printing leveling properties of the paste; ethylene glycol enhances the wetting and dispersing ability of carbon nanotubes and inhibits agglomeration; and glycerol moderately increases the viscosity of the system to prevent the paste from dripping after printing. The three components work synergistically to balance viscosity, dispersibility, and the thermal decomposition characteristics of the organic carrier, thereby reducing the turn-on electric field of the field emission cathode and improving the emission current and current emission stability. Attached Figure Description

[0024] Figure 1 This is a SEM image of the cathode with a scale bar of 500 nm from Embodiment 1 of this application; Figure 2 This is a SEM image of the cathode body with a scale bar of 1 μm in Example 2 of this application; Figure 3 This is a SEM image of the cathode body with a scale bar of 1 μm in Example 3 of this application; Figure 4 This is a SEM image of the cathode with a scale bar of 500 nm, as shown in Comparative Example 1 of this application. Figure 5 This is a SEM image of the cathode body with a scale bar of 20 μm, which is Comparative Example 2 of this application; Figure 6 This is a SEM image of the cathode body with a scale bar of 2 μm, which is Comparative Example 2 of this application; Figure 7 This is a SEM image of the cathode with a scale bar of 500 nm, as shown in Comparative Example 3 of this application. Figure 8 This is a SEM image of the cathode body with a scale bar of 20 μm, which is Comparative Example 4 of this application; Figure 9 This is the IV curve of the 100μm diameter cathode in Embodiment 2 of this application; Figure 10 This is the JE curve of the 100μm diameter cathode in Embodiment 2 of this application; Figure 11 This is the IV curve of the 75μm diameter cathode in Example 2 of this application; Figure 12 This is the JE curve of the 75μm diameter cathode in Embodiment 2 of this application; Figure 13 This is the JE curve of the 100μm diameter cathode test sample ① prepared in the same batch as in Example 1 of this application; Figure 14 This is the JE curve of the 100μm diameter cathode test sample ② prepared in the same batch as in Example 1 of this application. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the present application.

[0026] In one embodiment, a field emission cathode slurry is provided, the slurry comprising a dispersant, a cold cathode emitting material, conductive particles, and a thickener; Dispersants include terpineol, ethylene glycol, and glycerol.

[0027] In the above scheme, the formulation of the dispersant in the field emission cathode paste is improved by combining terpineol, ethylene glycol and glycerol. Terpineol ensures the printing leveling of the paste; ethylene glycol enhances the wetting and dispersing ability of carbon nanotubes and inhibits agglomeration; and glycerol moderately increases the viscosity of the system to prevent the paste from flowing after printing. The three substances work together to balance the viscosity, dispersibility and thermal decomposition characteristics of the organic carrier, reduce the turn-on electric field of the field emission cathode and improve the emission current and current output stability.

[0028] The slurry provided in this embodiment uses an alcohol dispersant that is easy to decompose and has low residue, and does not add functional additives such as PVP (polyvinylpyrrolidone). This simplifies the slurry formulation components and avoids the presence of other additives, thus preventing the decomposition of gas and the residue of amorphous carbon during vacuum heat treatment. This reduces the difficulty of the cathode degassing process and simultaneously improves emission stability.

[0029] In some optional embodiments of this application, based on the total volume of the dispersant, the volume fraction of terpineol is 50%~65%, the volume fraction of ethylene glycol is 20%~25%, and the volume fraction of glycerol is 10%~30%.

[0030] In the above technical solution, by limiting the volume fraction of terpineol to 50%~65%, the volume fraction of ethylene glycol to 20%~25%, and the volume fraction of glycerol to 10%~30%, the slurry viscosity is moderate, the cold cathode emission material is evenly dispersed, and the coating uniformity and film quality are guaranteed, thereby achieving the performance of low turn-on electric field and high emission current density of the field emission cathode.

[0031] Specifically, the volume fraction of terpineol can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, or a range selected from any two of the above values.

[0032] The volume fraction of ethylene glycol can be 20%, 21%, 22%, 23%, 24%, 25%, or a range selected from any two of the above values.

[0033] The volume fraction of glycerol can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range selected from any two of the above values.

[0034] In some optional embodiments of this application, based on the total volume of the dispersant, the volume fraction of terpineol is 60%, the volume fraction of ethylene glycol is 20%, and the volume fraction of glycerol is 20%. This configuration results in a field emission cathode with superior performance of low turn-on electric field and high emission current density.

[0035] In some optional embodiments of this application, the thickener is ethyl cellulose.

[0036] In some optional embodiments of this application, the mass ratio of cold cathode emitting material to dispersant is 1:(150~300), the mass ratio of conductive particles to dispersant is 1:(20~40), and the mass ratio of thickener to dispersant is 1:(80~120).

[0037] Specifically, the mass ratio of the cold cathode emitting material to the dispersant can be 1:150, 1:160, 1:170, 1:180, 1:190, 1:200, 1:210, 1:220, 1:230, 1:240, 1:250, 1:260, 1:270, 1:280, 1:290, 1:300, or a range selected from any two of the above values.

[0038] The mass ratio of conductive particles to dispersant can be 1:20, 1:22, 1:24, 1:26, 1:28, 1:30, 1:32, 1:34, 1:36, 1:38, 1:40, or a range selected from any two of the above values.

[0039] The mass ratio of thickener to dispersant can be 1:80, 1:85, 1:90, 1:95, 1:100, 1:105, 1:110, 1:115, 1:120, or a range selected from any two of the above values.

[0040] In some optional embodiments of this application, the cold cathode emitting material includes carbon nanotubes and graphene.

[0041] In some optional embodiments of this application, the length of the carbon nanotube is 50 μm to 100 μm, and the diameter of the carbon nanotube is 10 nm to 30 nm.

[0042] Specifically, the length of the carbon nanotubes can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or a range selected from any two of the above values. The diameter of the carbon nanotubes can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or a range selected from any two of the above values.

[0043] In some optional embodiments of this application, the cold cathode emitting material includes at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0044] In some optional embodiments of this application, the graphene monolayer thickness is 0.55nm~1.2nm, the graphene diameter is 0.5μm~3μm, and the number of graphene layers is 1~5.

[0045] Specifically, the thickness of a graphene monolayer can be 0.55 nm, 0.65 nm, 0.75 nm, 0.85 nm, 0.95 nm, 1.05 nm, 1.15 nm, 1.20 nm, or a range selected from any two of the above values. The diameter of the graphene can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or a range selected from any two of the above values. The number of graphene layers can be 1, 2, 3, 4 or 5.

[0046] In some optional embodiments of this application, the conductive particles are selected from at least one of copper, titanium, cobalt, molybdenum, iron, nickel and silver.

[0047] In some optional embodiments of this application, the conductive particles are selected from at least one of nickel-copper alloy, nickel-silver alloy, copper-silver alloy, copper-molybdenum alloy, copper-silver-titanium alloy, and iron-cobalt alloy.

[0048] In some optional embodiments of this application, the particle size of the conductive particles is 50nm~100nm.

[0049] Specifically, the size of the conductive particles is 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or a range selected from any two of the above values.

[0050] In another aspect, a method for preparing a field emission cathode is provided, using the field emission cathode paste as described above, the method comprising the following steps: The field emission cathode paste is coated onto the conductive electrode and then degassed and activated to obtain the field emission cathode.

[0051] In this embodiment, the field emission cathode paste is applied to the conductive electrode by screen printing.

[0052] In some optional embodiments of this application, the preparation steps of the field emission cathode paste include: The conductive particles are mixed with a dispersant to form a first slurry; The cold cathode emission material is mixed with the first slurry to form the second slurry; The thickener is mixed with the second slurry to form a field emission cathode slurry.

[0053] In some optional embodiments of this application, mixing conductive particles with a dispersant to form a first slurry includes: The conductive particles and dispersant are mixed and then ball-milled for 60 to 80 minutes at a ball mill speed of 300 to 500 r / min and a ball mill power of 250 W to 350 W to form the first slurry.

[0054] In this embodiment, before mixing the conductive particles with the dispersant, the conductive particles are added to a ball mill jar and ball-milled under dry milling conditions to form alloy particles, which are then mixed with the dispersant. This setup utilizes the mechanical alloying cold welding effect to construct multi-element alloy conductive particles, addressing the defects of poor slurry conductivity, high contact resistance at the carbon nanotube-substrate interface, and rapid emission current decay. The grinding balls continuously impact and compress the nano-metal particles at high speed, tearing the oxide film on the particle surface and exposing a highly active fresh metal surface. In a room temperature environment without high-temperature melting, the fresh metal interface undergoes plastic deformation and close bonding. Through a cycle of cold welding-crushing-re-welding, solid-state interdiffusion of dissimilar metal atoms is achieved, forming nanoscale multi-element composite alloy particles, rather than simple physical mixtures of elemental metal powders.

[0055] The cold-welded multi-element alloy particles have an atomically integrated structure, eliminating the high-resistance defects of point contact in single-element metals. After annealing, a continuous three-dimensional conductive network is built, significantly reducing electron transport loss. In the cold cathode emission material, graphene-coated alloy particles and carbon nanotubes embedded in the alloy substrate eliminate interfacial barriers. The synergistic effect of multiple metals ensures both high conductivity and high temperature resistance, reducing the overall resistivity of the slurry.

[0056] The alloy particles formed by ball milling and cold welding may include at least one of the following: nickel-copper alloy, nickel-silver alloy, copper-silver alloy, copper-molybdenum alloy, iron-cobalt alloy, titanium-copper alloy, copper-silver-titanium alloy, and molybdenum-nickel alloy; or at least one of copper-nickel-silver and alloy iron-cobalt-molybdenum alloy. The particle size of the alloy particles is 50 nm to 100 nm.

[0057] In some optional embodiments of this application, mixing the cold cathode emitting material with the first slurry to form the second slurry includes: The cold cathode emitting material is mixed with the first slurry and ball-milled for 180 min to 240 min at a ball milling speed of 400 r / min to 500 r / min and a ball milling power of 300 W to 400 W to form the second slurry.

[0058] In some optional embodiments of this application, the thickener is mixed with a second slurry to form a field emission cathode slurry, including: The thickener is mixed with the second slurry and ball-milled for 120 to 180 minutes at a ball mill speed of 500 to 600 r / min and a ball mill power of 350 W to 450 W to form a field emission cathode slurry.

[0059] In some optional embodiments of this application, the degassing activation process includes: degassing a conductive electrode coated with a field emission cathode paste under vacuum heat treatment, and then distributing the cold cathode emission material in a vertically upward direction.

[0060] The process of making the cold cathode emitting material present a vertically upward distribution includes: using low-viscosity tape to remove loose and particulate structures from the surface of the conductive electrode and making the cold cathode emitting material present a vertically upward distribution to achieve activation and obtain a field emission cathode.

[0061] With this setup, the low-viscosity tape only adsorbs loose carbon nanotubes on the surface, without dragging carbon nanotubes embedded in the metal layer at the root. This avoids squeezing the carbon nanotubes and prevents wear on the tips of the carbon nanotubes and the introduction of new impurities.

[0062] In the above scheme, after thorough ball milling and mixing, carbon nanotubes and graphene will wrap around the conductive metal particles. After conventional vacuum degassing and annealing, the conductive metal particles will form a conductive and thermally conductive layer on the surface of the electrode sheet, while the roots of cold cathode emitting materials such as carbon nanotubes will be implanted into the conductive and thermally conductive layer, forming a strong bond and providing good thermal and electrical conductivity.

[0063] In another aspect, a field emission cathode is provided, which is prepared by the field emission cathode preparation method described above.

[0064] The present application is further illustrated below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials, reagents, materials and equipment used in this application are all commercially available products conventionally used in the art.

[0065]

Example 1

[0066] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 65% terpineol, 25% ethylene glycol, and 10% glycerol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0067] S3. Mix the cold cathode emitting material with the first slurry and ball mill for 240 minutes at a ball milling speed of 500 r / min and a ball milling power of 350 W to form the second slurry. The cold cathode emitting material includes multi-walled carbon nanotubes with a length of 70 μm and a diameter of 20 nm and 3 layers of graphene. The mass ratio of the cold cathode emitting material to the dispersant is 1:200.

[0068] S4. The thickener ethyl cellulose is mixed with the second slurry and ball-milled for 180 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form a field emission cathode slurry; wherein the mass ratio of thickener to dispersant is 1:100.

[0069] S5. Apply the field emission cathode paste to the conductive electrode, then perform vacuum heat treatment at 700℃ to remove gas. After degassing, use low-viscosity tape to remove the loose and particulate structure on the surface of the conductive electrode and make the cold cathode emission material present in a vertically upward direction to achieve activation and obtain the field emission cathode.

[0070]

Example 2

[0071] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 60% terpineol, 20% ethylene glycol, and 20% glycerol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0072] S3, Same as Example 1.

[0073] S4, Same as in Example 1.

[0074] S5, Same as in Example 1.

[0075]

Example 3

[0076] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 50% terpineol, 20% ethylene glycol, and 30% glycerol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0077] S3, Same as Example 1.

[0078] S4, Same as in Example 1.

[0079] S5, Same as in Example 1.

[0080] Comparative Example 1 The difference between this comparative example and Example 1 is that only terpineol is used as the dispersant. The specific preparation method is as follows: S1 is the same as in Example 1.

[0081] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 100% terpineol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0082] S3, Same as Example 1.

[0083] S4, Same as in Example 1.

[0084] S5, Same as in Example 1.

[0085] Comparative Example 2 This comparative example differs from Example 1 in that only terpineol and ethylene glycol are used as the dispersant. The specific preparation method is as follows: S1 is the same as in Example 1.

[0086] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 70% terpineol by volume and 30% ethylene glycol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0087] S3, Same as Example 1.

[0088] S4, Same as in Example 1.

[0089] S5, Same as in Example 1.

[0090] Comparative Example 3 This comparative example differs from Example 1 in that only terpineol and glycerol are used as the dispersant. The specific preparation method is as follows: S1 is the same as in Example 1.

[0091] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 70% terpineol by volume and 30% glycerol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0092] S3, Same as Example 1.

[0093] S4, Same as in Example 1.

[0094] S5, Same as in Example 1.

[0095] Comparative Example 4 This comparative example differs from Example 1 in that only ethylene glycol and glycerol are used as the dispersant. The specific preparation method is as follows: S1 is the same as in Example 1.

[0096] S2. After mixing the nickel-copper alloy particles and the dispersant, the mixture is ball-milled for 80 minutes at a ball mill speed of 500 r / min and a ball mill power of 350 W to form the first slurry. The dispersant includes 50% ethylene glycol and 50% glycerol by volume. The mass ratio of conductive particles to dispersant is 1:30.

[0097] S3, Same as Example 1.

[0098] S4, Same as in Example 1.

[0099] S5, Same as in Example 1.

[0100] Table 1 summarizes some parameters from each embodiment and comparative example.

[0101]

[0102] The physical properties and microstructure of the field emission cathode paste and cathode body obtained in each embodiment and comparative example were observed. The test results are shown in Table 2. Figures 1 to 8 As shown.

[0103] The performance of the field emission cathodes obtained in each embodiment and comparative example was tested, and the test results are shown in Table 3. Figures 9 to 14 As shown. The test method is as follows: Field emission performance testing employed a standard planar diode test structure. Under high vacuum conditions, a field emission cathode with a pointed emission structure was placed parallel to a planar molybdenum anode, with a distance d between the two electrodes set to 200 μm. The molybdenum anode was connected to a 0–20 kV high-voltage power supply, the field emission cathode was grounded, and a source meter (SMU) was used to perform current-voltage (IV) curve scanning measurements on the field emission cathode.

[0104] Current density and turn-on electric field were acquired via IV scanning. Using a source meter (e.g., Keithley 2400), the anode voltage was gradually increased in steps. The initial anode voltage was set to 800V, the step value to 25V, and the final voltage value to 2300V. The sampling time for each voltage value was set to 1 second. The emission current was recorded simultaneously, and IV and JE curves were plotted. The turn-on electric field was defined as a current density reaching 1 μA / cm². 2 The corresponding applied electric field value at that time, the threshold electric field is defined as the value that produces 1 mA / cm 2 The applied electric field value corresponding to the current density was determined, and the data was converted into an FN diagram to verify the field emission mechanism.

[0105] Current fluctuation tests were conducted under a constant anode voltage, and the emission current was continuously recorded over time. Multiple test cycles of varying durations were designed, with each test duration selected from any value within the range of 0.5 hours to 2 hours. For each set of data, the maximum current I within that time period was used for testing. max With minimum current I min According to formula (I) max -I min ) / (I max +I min The current fluctuation rate is calculated by multiplying the result by 100%. Finally, the calculation results of all test groups are summarized to obtain the current fluctuation rate range.

[0106] Table 2

[0107] like Figures 1 to 3 As shown in the figure, the white spherical particles are conductive metal particles, the thin layer covering the particles is graphene, the thin filaments are carbon nanotubes, the graphene coats the metal nanoparticles, and the carbon nanotubes are interspersed and anchored on the surface of the graphene coating layer.

[0108] Table 3

[0109] As shown in Table 3, the saturated current densities of the 100μm samples measured in Examples 1 to 3 are all higher than those in Comparative Examples 1 to 4. The turn-on electric field and threshold electric field measured in Examples 1 to 3 are all lower than those in Comparative Examples 1 to 4. The current fluctuation range measured in Examples 1 to 3 is also smaller than that in Comparative Examples 1 to 4. This indicates that the dispersion effect of the single or dual-component dispersants in Comparative Examples 1 to 4 is limited, resulting in poor performance of the field emission cathode.

[0110] In Examples 1 to 3, the combination of the three dispersants produced a synergistic effect, which improved the dispersion stability of the slurry, reduced carbon nanotube agglomeration and carbon nanotube honeycomb bending and collapsing, thereby increasing the saturation current density of the field emission cathode, reducing the turn-on electric field and threshold electric field, and reducing current fluctuations.

[0111] In addition, in the compound system of Example 2, the dispersant includes 60% terpineol, 20% ethylene glycol, and 20% glycerol by volume, which further improves the performance of the field emission cathode.

[0112] Depend on Figure 1 As can be seen, carbon nanotubes are wrapped around metal particles and are evenly distributed on the substrate; Depend on Figure 2 As can be seen, carbon nanotubes are wrapped around the metal particles and are arranged in a clear, uniform, and vertically upward pattern, while the metal particles are relatively evenly dispersed. Depend on Figure 3 As can be seen, only a small number of collapsed carbon nanotubes are visible on the substrate, while most metal particles and carbon nanotubes are intercepted by the sieve. Depend on Figure 4 It is evident that carbon nanotubes exhibit aggregation and entanglement in localized areas; Depend on Figure 5 It is evident that the cathode film is uneven, with clear separation between carbon nanotubes and metal particles; Depend on Figure 6 As can be seen, at high magnification, metal particles agglomerate into large metal clusters; Depend on Figure 7 It is evident that a large number of carbon nanotubes aggregate and encapsulate a small amount of metal particles; Depend on Figure 8 As can be seen, the image shown is of the cathode after it has been damaged by arcing, revealing severely aggregated metal particles and molten pits. Figure 9 This is the IV curve of the 100μm diameter cathode in Embodiment 2 of this application; Figure 9 Two rounds of data were tested (i.e., the graph includes two curves), by Figure 9 It can be seen that current emission begins at a voltage of approximately 1500V, and the maximum current of 1.7mA is achieved at a voltage of approximately 2200V. Figure 10 This is the JE curve of the 100μm diameter cathode in Embodiment 2 of this application; Figure 10 Two rounds of data were tested, by Figure 10 It can be seen that the maximum current density is approximately 22 A / cm². 2 This was achieved at an electric field strength of approximately 11 V / μm. Figure 10 In the upper left figure, the FN curve is approximately a straight line with a downward slope, which is consistent with the field emission characteristics; Figure 11This is the IV curve of the 75μm diameter cathode in Example 2 of this application; Figure 11 Two rounds of data were tested, by Figure 11 It can be seen that current emission begins at a voltage of approximately 1600V, and the maximum current of 1.3mA is achieved at a voltage of approximately 2400V. Figure 12 This is the JE curve of the 75μm diameter cathode in Embodiment 2 of this application; by Figure 12 It can be seen that the maximum current density is approximately 30 A / cm². 2 This is achieved at an electric field strength of approximately 12 V / μm; Figure 12 In the upper left figure, the FN curve is approximately a straight line with a downward slope, which is consistent with the field emission characteristics; Figure 13 This is a JE curve of the 100μm diameter cathode test sample ① prepared in the same batch as in Example 1 of this application; by Figure 13 It can be seen that the maximum current density of test sample ① is approximately 14 A / cm². 2 This was achieved at an electric field strength of approximately 8.5 V / μm. Figure 13 In the upper left figure, the FN curve is an approximately downward-sloping straight line, which is consistent with the field emission characteristics; Figure 14 This is a JE curve of the 100μm diameter cathode test sample ② prepared in the same batch as in Example 1 of this application; by Figure 14 It can be seen that the maximum current density of test sample ② is approximately 12 A / cm². 2 This is achieved at an electric field strength of approximately 8.5 V / μm; Figure 14 In the upper left figure, the FN curve is an approximately downward-sloping straight line, which is consistent with the field emission characteristics.

[0113] Figure 9 This reflects the cathode's turn-on voltage and maximum current. Figure 10 This reflects the maximum current density of the cathode. Figure 9 and Figure 10 These are expressions of the same set of experimental data under different physical dimensions, and there is a linear conversion relationship between them. That is, the electric field strength E is obtained by dividing the voltage V by the electrode spacing d, and the current density J is obtained by dividing the current I by the effective emission area S. Since the electrode spacing d and the emission area S are constant values, the coordinate transformation is only a linear scaling, so the curve shape remains consistent.

[0114] Similarly, Figure 11 and Figure 12 These are also expressions of the same set of experimental data under different physical dimensions. The electric field strength E is also obtained by dividing the voltage V by the electrode spacing d, and the current density J is also obtained by dividing the current I by the effective emitting area S. Since both the electrode spacing d and the emitting area S are constant values, this coordinate transformation is only a linear scaling. Figure 11 and Figure 12The curve shape remains consistent.

[0115] Figures 9 to 12 This data represents two independent, repeated tests conducted on each cathode sample under identical testing conditions. In precision electron emission performance testing, the introduction of repeated test data aims to eliminate interference from random errors such as fluctuations in ambient temperature and humidity, slight changes in vacuum, or unstable contact resistance. The high degree of overlap between the two curves demonstrates the excellent performance stability of the emission site cathode, the reliability of the test results, and the consistency of the sample preparation process.

[0116] Figure 10 and Figure 12 The insets in the upper left corner show the Fowler-Nordheim (FN) characteristic curves obtained by mathematically transforming the two sets of current density-electric field strength (JE) data in the main graph. By converting any coordinate in the main graph, the corresponding coordinate point in the inset can be obtained, thus distinguishing the correspondence between the two curves in the inset and the two curves in the main graph.

[0117] It should be noted that, in this document, "comprising," "including," or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0118] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0119] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A field emission cathode paste, characterized in that, The slurry includes a dispersant, a cold cathode emitting material, conductive particles, and a thickener; The dispersant includes terpineol, ethylene glycol, and glycerol.

2. The field emission cathode paste as described in claim 1, characterized in that, Based on the total volume of the dispersant, the volume fraction of terpineol is 50%~65%, the volume fraction of ethylene glycol is 20%~25%, and the volume fraction of glycerol is 10%~30%.

3. The field emission cathode paste as described in claim 1 or 2, characterized in that, The mass ratio of the cold cathode emitting material to the dispersant is 1:(150~300), the mass ratio of the conductive particles to the dispersant is 1:(20~40), and the mass ratio of the thickener to the dispersant is 1:(80~120).

4. The field emission cathode paste as described in claim 1, characterized in that, The cold cathode emitting material includes carbon nanotubes and graphene; The length of the carbon nanotube is 50μm~100μm, and the diameter of the carbon nanotube is 10nm~30nm; The cold cathode emitting material includes at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. The graphene has a single-layer thickness of 0.55nm to 1.2nm, a diameter of 0.5μm to 3μm, and 1 to 5 layers.

5. The field emission cathode paste as described in claim 1, characterized in that, The conductive particles are selected from at least one of copper, titanium, cobalt, molybdenum, iron, nickel and silver; The particle size of the conductive particles is 50nm~100nm.

6. A method for preparing a field emission cathode, characterized in that, Using the field emission cathode paste as described in any one of claims 1 to 5, the preparation method comprises the following steps: The field emission cathode slurry is coated onto a conductive electrode and then degassed and activated to obtain a field emission cathode.

7. The method for preparing a field emission cathode as described in claim 6, characterized in that, The preparation steps of the field emission cathode paste include: The conductive particles are mixed with a dispersant to form a first slurry; The cold cathode emission material is mixed with the first slurry to form a second slurry; The thickener is mixed with the second slurry to form the field emission cathode slurry; The step of mixing conductive particles with a dispersant to form a first slurry includes: mixing the conductive particles and the dispersant, and then ball milling them for 60 min to 80 min at a ball milling speed of 300 r / min to 550 r / min and a ball milling power of 250 W to 350 W to form the first slurry. The step of mixing the cold cathode emitting material with the first slurry to form the second slurry includes: The cold cathode emitting material is mixed with the first slurry and ball-milled for 180 min to 240 min at a ball milling speed of 400 r / min to 500 r / min and a ball milling power of 300 W to 400 W to form the second slurry. The step of mixing the thickener with the second slurry to form a field emission cathode slurry includes: The thickener is mixed with the second slurry and ball-milled for 120 to 180 minutes at a ball milling speed of 500 to 600 r / min and a ball milling power of 350 W to 450 W to form the field emission cathode slurry.

8. The method for preparing a field emission cathode as described in claim 6, characterized in that, The degassing activation process includes: The conductive electrode coated with the field emission cathode paste is subjected to vacuum heat treatment to remove gas, and then the cold cathode emission material is distributed in a vertically upward direction.

9. The method for preparing a field emission cathode as described in claim 6, characterized in that, The method of applying the field emission cathode paste to the conductive electrode is screen printing.

10. A field emission cathode, characterized in that, It is prepared by the method for preparing a field emission cathode as described in any one of claims 6 to 9.

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