A high-density SiC dendrite array field emission cathode material and a preparation method thereof

Abstract

The application discloses a high-density SiC dendrite array field emission cathode material and a preparation method thereof. A carbon fiber cloth with grown triclinic SiC nanowires is covered above a quartz boat with CoCl2 powder, a catalyst CoO is deposited on the surface of the triclinic SiC nanowires of the substrate by using a chemical vapor deposition method in a tube furnace, and then the obtained carbon fiber cloth substrate is subjected to a second high-temperature pyrolysis treatment, so that the carbon fiber cloth with grown SiC dendrite arrays is obtained and used as a field emitter cathode material. The high-density SiC dendrite array with directional growth is used as the field emission cathode material for the first time, stable emission current can be obtained while reducing the opening electric field of electron emission, and excellent field emission performance is shown.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology and relates to a high-density SiC dendrite array field emission cathode material and its preparation method. Background Technology

[0002] Field emitters are widely used in fields such as miniature X-ray tubes and electronic displays. Low-dimensional nanomaterials, due to their excellent physical properties and reduced size, offer significant advantages in the miniaturization, lightweighting, and integration of field emitters. To improve the main performance characteristics of field emitters (low turn-on electric field and high stability), increasing the number of electron emission sites in the cathode material is the most direct and effective method. For example, Huang et al. (ACS Appl. Mater. Interface, 14, (2022) 4389-4398) prepared a diamond-modified C nanosheet field emission cathode with a turn-on electric field of 1.8 V / μm. -1 The turn-on electric field of a pure C nanosheet field emission cathode is 3.0 V / μm. -1 .

[0003] SiC nanomaterials, due to their excellent physical properties (high thermal stability, high electron mobility, high thermal conductivity, etc.), are considered one of the best candidates for developing high-performance field emission cathode materials. Currently, SiC field emission cathode nanomaterials mainly include: SiC nanowires, SiC nanoribbons, SiC nanoneedles, and serrated SiC nanowires. However, the simple one-dimensional SiC nanostructure limits the number of electron emission sites. Depositing nanoparticles on the surface of one-dimensional SiC nanowires is one effective method to increase the number of field emission sites in cathode materials. For example, Cui et al. (Phys. Chem. Chem. Phys., 13, (2011) 985-990) prepared an Al2O3 nanoparticle-modified SiC nanotube field emitter with an on-state electric field of 2.4 V / μm. -1 Zhang et al. (J. Mater. Chem. C, 3, (2015) 658) prepared an amorphous carbon-modified SiC nanowire field emitter with an on-state electric field of 2.1 V / μm. -1 Chen et al. (J. Mater. Chem. C, 4, (2016) 1363) prepared a gold nanoparticle-modified SiC nanowire field emitter with an on-state electric field of 1.14 V / μm. -1 However, the interface between the modified heterogeneous nanoparticles and the SiC host nanowires is unfavorable for electron transport and heat diffusion during field emission, making it prone to electron emission site detachment and resulting in unstable emission current. Constructing an integrated SiC field emission cathode material with multiple electron emission sites is crucial for developing advanced high-performance field emitters.

[0004] Compared to simple one-dimensional nanostructures, dendritic structures possess more electron emission sites. Currently, only Lan et al. (Journal of Physics and Chemistry of Solid, 2020, 136, 109124) have conducted exploratory research on the preparation of SiC dendritic nanomaterials. However, due to the use of chemical plating to deposit the catalyst for dendrite growth, the catalyst particle density, uniformity, and size controllability are poor, making it impossible to achieve the localized growth of dendrites, resulting in a very low SiC dendrite density.

[0005] Currently, there are no research reports on how to prepare directionally grown high-density SiC dendrite array field emission cathode materials. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing a high-density SiC dendrite array field emission cathode material.

[0007] The second objective of this invention is to provide a high-density SiC dendrite array field emission cathode material prepared by the above-mentioned method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] On one hand, the present invention provides a method for preparing a high-density SiC dendrite array field emission cathode material, comprising the following steps:

[0010] A carbon fiber cloth with triangular prism-shaped SiC nanowires was placed on top of a quartz boat containing CoCl2 powder. CoO catalyst particles were deposited on the surface of the triangular prism-shaped SiC nanowires in a tube furnace using chemical vapor deposition. The carbon fiber cloth substrate was then subjected to a second high-temperature pyrolysis treatment to obtain a carbon fiber cloth with a SiC dendrite array, which was used as a cathode material for a field emitter.

[0011] Preferably, the chemical vapor deposition is performed at a pressure of 140 Pa, with an atmosphere of oxygen:nitrogen = 5:95. The vapor deposition parameters for the catalyst particles used in the secondary growth are: heating to 540 °C at a rate of 10 °C / min, holding at that temperature for 15 min, and then cooling to room temperature.

[0012] Preferably, the second high-temperature pyrolysis process is as follows: under inert gas protection, the temperature is raised to 1400°C at a rate of 29°C / min, then raised to 1500°C at a rate of 25°C / min, and then the temperature is lowered from 1500°C to 1300°C within 8-24 minutes. Finally, the temperature is cooled to room temperature with the furnace to obtain pure SiC dendritic nanoarray material.

[0013] Further optimization resulted in a temperature reduction time of 24 minutes from 1500℃ to 1300℃. This secondary sintering temperature profile yielded a higher dendrite array density and a lower electron emission turn-on electric field.

[0014] Preferably, the method for preparing the carbon fiber cloth with grown triangular prism-shaped SiC nanowires includes the following steps:

[0015] (1) The organic precursor containing Si and C elements was thermally crosslinked and cured at 250℃ for 30 min under an inert atmosphere and then ball-milled into an ultrafine powder.

[0016] (2) The carbon fiber cloth substrate was immersed in Co(NO3)2 6H2O aqueous solution for a period of time, and then taken out and dried as a substrate for nanomaterial growth;

[0017] (3) Place the organic precursor powder from step (1) and the carbon fiber cloth substrate soaked in step (2) into a high-purity graphite crucible and place it into a high-temperature atmosphere sintering furnace. The atmosphere furnace is first evacuated to 10°C. -4 Pa, then fill with inert gas until atmospheric pressure is reached, and heat to 1500℃ at a rate of 28℃ / min under inert atmosphere, then heat to 1600℃ at a rate of 5℃ / min, and finally cool to room temperature with the furnace to obtain triangular prism-shaped SiC backbone nanowires with carbon fiber cloth as substrate.

[0018] Preferably, the organic precursor in step (1) is polysilazane.

[0019] On the other hand, the present invention also provides a high-density SiC dendrite array field emission cathode material, wherein the field emission cathode material is a carbon fiber cloth with SiC dendrite array grown on it, prepared by the above-mentioned preparation method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention uses carbon fiber cloth with a high density of SiC dendrite array as field emission cathode. By utilizing the high electron emission site density of SiC dendrite array, the electron emission sites can be effectively increased and the field emission start-up electric field can be reduced.

[0022] (2) The SiC dendrites of the present invention are obtained by epitaxial growth of SiC backbone nanowires. There is no obvious interface between the dendrites and the backbone nanowires, which is conducive to electron transport and heat diffusion and helps to maintain a stable emission current.

[0023] (3) The present invention controls the cooling rate of the secondary sintering to reduce the temperature from 1500℃ to 1300℃ within 24 minutes, resulting in SiC dendrites with higher density and more electron emission sites.

[0024] (4) The present invention uses chemical vapor deposition to deposit catalyst particles on the surface of the backbone nanowire, which is beneficial to the control of catalyst particle size, density and uniformity. Attached Figure Description

[0025] Figure 1 (a1-a3) are scanning electron microscope (SEM) images of the triangular prism-shaped SiC backbone nanowires prepared by the first pyrolysis of the organic precursors in Examples 1-3 at different magnifications;

[0026] Figure 1 (b1-b3) are scanning electron microscope (SEM) images of the SiC dendritic nanomaterials prepared in Example 1 at different magnifications;

[0027] Figure 1 (c1-c3) are scanning electron microscope (SEM) images of the SiC dendritic nanomaterials prepared in Case 2 at different magnifications;

[0028] Figure 1 (d1-d3) are scanning electron microscope (SEM) images of the SiC dendritic nanomaterials prepared in Case 3 at different magnifications;

[0029] Figure 2 (a) Transmission electron microscope (TEM) image of the SiC dendritic nanomaterials prepared in Example 3;

[0030] Figure 2 (b) is a high-magnification transmission electron microscope (HTEM) image of the SiC dendritic nanomaterials prepared in Example 3;

[0031] Figure 2 (c) is the selected area electron diffraction (SAED) pattern of the SiC dendritic nanomaterials prepared in Example 3;

[0032] Figure 3 X-ray diffraction (XRD) spectra of SiC backbone nanowires, SiC and surface catalysts, and SiC dendritic nanomaterials.

[0033] Figure 4 The graph shows the relationship between electric field strength and current density for the SiC nanomaterial field emission cathodes prepared in Case 1-3.

[0034] Figure 5 To implement the electron emission turn-on electric field and threshold electric field corresponding to the SiC nanomaterial field emission cathodes prepared in Cases 1-3, respectively;

[0035] Figure 6 To demonstrate the Fowler-Nordheim curves corresponding to the SiC nanomaterial field emission cathodes prepared in Cases 1-3;

[0036] Figure 7 The field enhancement factors are respectively for the SiC nanomaterial field emission cathodes prepared in Examples 1-3;

[0037] Figure 8 The emission current stability curve of the SiC dendrite array field emission cathode prepared in Case 3 is shown. Detailed Implementation

[0038] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0039] Example 1

[0040] Polysilazane was selected as the organic precursor and thermally crosslinked and cured at 250℃ for 25 min under Ar atmosphere protection. The cured solid was then placed in a nylon resin ball mill jar and ball-milled into powder. 300 mg of polysilazane was weighed and placed at the bottom of a graphite crucible. A 7×7 cm piece of carbon fiber cloth was cut. 2 Immerse in a 0.05 mol / L cobalt nitrate solution for 20 min, remove and air dry. Place carbon fiber cloth as a substrate on top of the graphite crucible, and place the graphite crucible in a graphite resistance heating atmosphere sintering furnace. The atmosphere furnace is first evacuated to 10... -4 Pa was added, followed by Ar gas (99.99% purity) until the pressure reached one atmosphere, which was then kept constant. Under inert gas protection, the temperature was increased to 1500℃ at a rate of 28℃ / min, then increased to 1600℃ at a rate of 5℃ / min, and finally cooled to room temperature with the furnace to obtain triangular prism-shaped SiC backbone nanowires with carbon fiber cloth as the substrate.

[0041] 100 mg of CoCl2 powder was then placed inside a quartz boat, and carbon fiber cloth with grown matrix nanowires was placed over the boat. The tube furnace was evacuated to 0.01 Pa, then a mixture of O2:N2 in a ratio of 5:95 was introduced while maintaining the pressure inside the tube at 140 Pa. Subsequently, the furnace chamber was heated to 540 °C at a rate of 10 °C / min, held at that temperature for 15 min, and then cooled to room temperature with the furnace to deposit CoO catalyst particles for dendrite growth on the surface of the triangular prism-shaped SiC backbone nanowires.

[0042] Finally, the carbon fiber cloth obtained above was used as a substrate for a second high-temperature pyrolysis treatment of the organic precursor. The raw material was still 300 mg of polysilazane. The pyrolysis temperature parameters were: heating to 1400℃ at a rate of 29℃ / min under inert gas protection, then heating to 1500℃ at a rate of 25℃ / min, then cooling the temperature from 1500℃ to 1300℃ in 8 min, and finally cooling to room temperature in the furnace to obtain carbon fiber cloth with SiC dendrite arrays.

[0043] Example 2

[0044] The difference between Example 2 and Example 1 is that in Example 2, the temperature was lowered from 1500°C to 1300°C in 16 minutes during the second high-temperature pyrolysis treatment of the organic precursor. Otherwise, it was the same as Example 1.

[0045] Example 3

[0046] The difference between Example 3 and Example 1 is that in Example 3, the temperature was lowered from 1500°C to 1300°C in 24 minutes during the second high-temperature pyrolysis treatment of the organic precursor. Otherwise, it is the same as Example 1.

[0047] Figure 1 (a1-a3) are SEM images of the triangular prism-shaped SiC backbone nanowires prepared by the first pyrolysis of the organic precursor in Example 1 at different magnifications. They show that the SiC backbone nanowires are triangular prism-shaped, and their surface structure is more stable than that of cylindrical nanowires, which is conducive to the uniform distribution of catalyst particles for secondary growth. Figure 1 (b1-b3) are SEM images of the SiC nanomaterials prepared in Case 1 at different magnifications, showing that after the secondary high-temperature pyrolysis of the organic precursor, the surface of the SiC backbone nanowires is wrapped with a layer of SiC nanoparticles, forming primary SiC dendritic nanomaterials. Figure 1 (c1-c3) are SEM images of the SiC dendritic nanomaterials prepared in Case 2 at different magnifications, showing that SiC dendrites were successfully grown on the surface of the SiC backbone nanowires. Figure 1 (d1-d3) are SEM images of the SiC dendritic nanomaterials prepared in Case 3 at different magnifications. They show that as the temperature drops from 1500℃ to 1300℃ during the secondary high-temperature pyrolysis of the organic precursor, the SiC dendrite density gradually increases, and finally a high-density SiC dendrite array is successfully grown on the surface of the trunk nanowire.

[0048] Figure 2 (a) is a transmission electron microscope (TEM) image of the SiC dendritic nanomaterial prepared in Example 3, showing that SiC dendrites are grown on the surface of the SiC backbone nanowires; Figure 2(b) is a high-magnification transmission electron microscope (HRTEM) image of the SiC dendritic nanomaterial prepared in Example 3. The upper right and lower left and lower right insets are magnified views of regions A, B and C marked in the upper left inset, respectively. It shows that the lattice spacing between adjacent crystals in the three regions is 0.25 nm. No obvious change in lattice spacing was found between the dendrites and the trunk nanowires. This indicates that the SiC dendrites were obtained by the continued epitaxial growth of the trunk nanowires at the catalyst site. Figure 2 (c) is the selected region electron diffraction (SAED) pattern of the SiC dendritic nanomaterial prepared in Example 3, which shows that the prepared SiC dendritic material has a single crystal structure.

[0049] Figure 3 The X-ray diffraction (XRD) spectra of the SiC backbone nanowires, SiC and surface catalysts, and SiC dendritic nanomaterials described in Example 3 show that the secondary growth catalyst deposited on the surface of the SiC backbone nanowires is CoO, and the final SiC dendritic nanoarray material is a 3C-SiC material.

[0050] Under room temperature conditions, the field emission performance of the SiC nanomaterial field emission cathodes in Examples 1-3 was tested: S0 (triangular prism-shaped SiC backbone nanowire), S8 (SiC dendritic nanomaterial obtained in Example 1), S16 (SiC dendritic array obtained in Example 2), and S24 (high-density SiC dendritic array obtained in Example 3).

[0051] A metal plate with a radius of 1 cm was used as the anode of the field emitter. Carbon fiber cloth with a high-density SiC dendrite array was cut into 0.4 × 0.4 cm pieces. 2 A small positive-direction plate is used as the cathode of the field emitter. The cathode and anode are placed in a vacuum chamber, and the chamber pressure is evacuated to 1.5 × 10⁻⁶. -7 Pa, where the distance between the cathode and anode is 700 micrometers.

[0052] Figure 4 The diagram shows the relationship between electric field strength and current density of the SiC nanomaterial field emission cathodes prepared in Examples 1-3. The SiC field emitter built on the surface can emit a stable current, and the emission current density increases with the increase of dendrite density. Sample S24 prepared in Example 3 shows the highest emission current.

[0053] Figure 5 The electron emission turn-on electric field and threshold electric field of the SiC nanomaterial field emission cathodes prepared in Examples 1-3 were compared to demonstrate that as the temperature decreased from 1500℃ to 1300℃ during the secondary high-temperature pyrolysis of the organic precursor, the turn-on electric field and threshold electric field gradually decreased. Sample S24 prepared in Example 3 exhibited the lowest turn-on electric field (0.61 V / μm). -1) and threshold electric field (1.18Vμm) -1 ).

[0054] Figure 6 The Fowler-Nordheim curves corresponding to the field emission cathodes of SiC nanomaterials prepared in Case 1-3 show an approximately linear trend, indicating that the electrons emitted from the SiC nanomaterials follow the traditional field emission theory, that is, electrons in the material tunnel through the quantum barrier and are emitted from the material under the action of an external electric field.

[0055] Figure 7 To determine the field enhancement factor of the SiC nanomaterial field emission cathodes prepared in Examples 1-3, sample S24 prepared in Example 3 exhibits the highest field enhancement factor, reaching 9530. This is mainly attributed to the increased number of electron emission sites due to the high-density SiC dendrite array structure.

[0056] Figure 8 To demonstrate the emission current stability curve of the SiC dendrite array field emission cathode prepared in Case 3, sample S24 prepared in Case 3 was tested at a current density of 1.15 mA / cm². 2 When working continuously for 10 hours, the current density fluctuation was only 3.5%, indicating that the S24 sample has excellent current emission stability as a field emission cathode material.

[0057] The specific embodiments described herein are merely illustrative of the spirit of the invention and do not limit the scope of protection of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a high-density SiC dendrite array field emission cathode material, characterized in that, Includes the following steps: A carbon fiber cloth with triangular prism-shaped SiC nanowires was placed on top of a quartz boat containing CoCl2 powder. CoO catalyst particles were deposited on the surface of the triangular prism-shaped SiC nanowires in a tube furnace using chemical vapor deposition. The carbon fiber cloth substrate was then subjected to a second high-temperature pyrolysis treatment to obtain a carbon fiber cloth with a SiC dendrite array, which was used as a cathode material for a field emitter.

2. The method for preparing a high-density SiC dendrite array field emission cathode material according to claim 1, characterized in that, The chemical vapor deposition was performed at a pressure of 140 Pa, with an atmosphere of oxygen:nitrogen = 5:

95. The vapor deposition parameters for the catalyst particles used in the secondary growth were: heating to 540 °C at a rate of 10 °C / min, holding at that temperature for 15 min, and then cooling to room temperature.

3. The method for preparing a high-density SiC dendrite array field emission cathode material according to claim 1, characterized in that, The second high-temperature pyrolysis process is as follows: under inert gas protection, the temperature is raised to 1400℃ at a rate of 29℃ / min, then raised to 1500℃ at a rate of 25℃ / min, and then the temperature is lowered from 1500℃ to 1300℃ within 8-24 minutes. Finally, the temperature is cooled to room temperature with the furnace to obtain pure SiC dendritic nanoarray material.

4. The method for preparing a high-density SiC dendrite array field emission cathode material according to claim 3, characterized in that, The time taken to cool the temperature from 1500℃ to 1300℃ is 24 minutes.

5. The method for preparing a high-density SiC dendrite array field emission cathode material according to claim 1, characterized in that, The method for preparing the carbon fiber cloth with triangular prism-shaped SiC nanowires includes the following steps: (1) The organic precursor containing Si and C elements was thermally crosslinked and cured at 250℃ for 30 min under an inert atmosphere and then ball-milled into an ultrafine powder. (2) The carbon fiber cloth substrate was immersed in Co(NO3)2 6H2O aqueous solution for a period of time, and then taken out and dried as a substrate for nanomaterial growth; (3) Place the organic precursor powder from step (1) and the carbon fiber cloth substrate soaked in step (2) into a high-purity graphite crucible and place it into a high-temperature atmosphere sintering furnace. The atmosphere furnace is first evacuated to 10°C. -4 Pa, then fill with inert gas until atmospheric pressure is reached, and heat to 1500℃ at a rate of 28℃ / min under inert atmosphere, then heat to 1600℃ at a rate of 5℃ / min, and finally cool to room temperature with the furnace to obtain triangular prism-shaped SiC backbone nanowires with carbon fiber cloth as substrate.

6. The method for preparing a high-density SiC dendrite array field emission cathode material according to claim 5, characterized in that, The organic precursor mentioned in step (1) is polysilazane.

7. A high-density SiC dendrite array field emission cathode material, characterized in that, The field emission cathode material is carbon fiber cloth with SiC dendrite array grown on it, prepared by the method described in any one of claims 1 to 6.

Images