Al-doped 4H-SiC nanowire field emission cathode and preparation method thereof

Abstract

The invention relates to the technical field of field emission cathodes, in particular to an Al-doped 4H-SiC nanowire field emission cathode and a preparation method thereof. The method comprises the following steps: performing electrochemical etching on a 4H-SiC wafer, and processing a bamboo-like 4H-SiC nanowire array on the surface of the 4H-SiC wafer; stripping off the bamboo-like 4H-SiC nanowire array, soaking the bamboo-like 4H-SiC nanowire array in an aluminum source solution containing an Al element, and then taking out and drying the bamboo-like 4H-SiC nanowire array; the obtained 4H-SiC nanowire array is sintered in an inert environment at the temperature of 800 DEG C to 900 DEG C, the Al-doped 4H-SiC nanowire array is obtained, and the Al-doped 4H-SiC nanowire array is the Al-doped 4H-SiC nanowire field emission cathode. According to the invention, the unique structure of the bamboo-like 4H-SiC nanowire is reserved, and Al doping is realized at a relatively low temperature; and the obtained field emission cathode is low in opening field intensity and high in electron emission stability.

Description

Technical Field

[0001] The invention relates to the technical field of field emission cathodes, and in particular to an Al-doped 4H-SiC nanowire field emission cathode and a preparation method thereof. Background Art

[0002] As the core component of vacuum electronic devices, the cathode has two main requirements: low turn-on electric field and high electron emission stability. Compared with carbon nanotube cathodes, SiC nanomaterial cathodes have attracted much attention for their excellent mechanical properties, low thermal expansion coefficient and stable chemical properties. The field emission cathode developed based on SiC nanomaterials has higher electron emission stability while maintaining a low turn-on electric field, and its electron emission has a low attenuation amplitude during long-term operation.

[0003] Al doping in the prior art is often achieved by an in-situ method, and the morphology of the nanowires is difficult to accurately control, and the temperature required for preparation is very high. For example, the preparation and application of an in-situ Al-doped SiC nanowire with a mesh surface layer disclosed in Chinese patent CN106298398B, the surface of the Al-doped SiC nanowire is a mesh nanostructure composed of SiO2 nanospheres connecting Al-doped SiC nanowires, polycarbosilane, silicon powder and aluminum nitrate are used as reaction raw materials, and nickel nitrate is used as a catalyst; the mixed and ground reaction raw materials and the graphite substrate with the catalyst are placed in a graphite reaction chamber and placed in a vacuum atmosphere furnace; Ar gas is passed, vacuumed to 50-80 Pa, and heated to 1350-1450°C at a heating rate of 15°C / min, and kept warm for 60-90 minutes. The obtained in-situ Al-doped SiC nanowire with a mesh surface layer is used as a field emission cathode material, the opening electric field is 0.5V / μm, and the current density fluctuation rate is 5.8%, and its current density fluctuation rate is 5.8%, which is relatively high. Another example is Chinese patent application CN118026731A which discloses a multifunctional Al-doped core-shell structure SiC nanowire and its preparation method and application. A mixed powder of SiO powder and Al powder is used as a precursor, and a substrate loaded with a catalyst is suspended above the precursor powder, which is then sealed and subjected to negative pressure heat treatment at 1250 to 1400°C to obtain a multifunctional Al-doped core-shell structure SiC nanowire, which is used in the field of optoelectronic materials. Summary of the invention

[0004] The purpose of the present invention is to provide an Al-doped 4H-SiC nanowire field emission cathode and a preparation method thereof, which can achieve Al doping at a lower temperature while retaining the unique structure of bamboo-shaped 4H-SiC nanowires. The obtained field emission cathode has a low turn-on field strength and high electron emission stability.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for preparing an Al-doped 4H-SiC nanowire field emission cathode comprises the following steps:

[0007] (1) electrochemically etching the 4H-SiC wafer to form a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and peeling the 4H-SiC nanowire array off the 4H-SiC wafer;

[0008] (2) immersing the 4H-SiC nanowire array obtained in step (1) in an aluminum source solution containing Al element, and then taking it out and drying it;

[0009] (3) Sintering the 4H-SiC nanowire array obtained in step (2) at 800-900° C. in an inert environment to obtain an Al-doped 4H-SiC nanowire array, wherein the Al-doped 4H-SiC nanowire array is an Al-doped 4H-SiC nanowire field emission cathode.

[0010] Furthermore, the Al doping amount in the Al-doped 4H-SiC nanowire array is 0.16 at % to 1.63 at %.

[0011] Furthermore, in the step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al element for 3 to 10 minutes, and then taken out and naturally dried or dried at a temperature below 60°C.

[0012] Furthermore, the aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate or aluminum sulfate; or the aluminum source solution is an acid solution of aluminum chloride, aluminum nitrate or aluminum sulfate.

[0013] Furthermore, in step (3), the 4H-SiC nanowire array obtained in step (2) is placed in a tubular furnace, the tubular furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the cycle is repeated multiple times;

[0014] The temperature was raised to 800-900°C at a heating rate of 5°C / min, kept at that temperature for 20-40min, then lowered to 400-500°C at a cooling rate of 5°C / min, and finally cooled to room temperature along with the furnace.

[0015] Furthermore, in the step (1), the 4H-SiC wafer is used as the anode, the Pt wafer is used as the cathode, the C surface of the 4H-SiC wafer is used as the etching surface facing the Pt electrode, and is placed in an etching solution for etching, the etching voltage is 20V, and the etching time is 27 to 30 minutes;

[0016] In the etching solution, the volume ratio of 99 vol% ethylene glycol, 45 wt% hydrofluoric acid and 30 wt% hydrogen peroxide is 6:3:1.

[0017] Furthermore, the etched 4H-SiC nanowire array was peeled off from the wafer, then immersed in an ethanol solution, washed and naturally air-dried;

[0018] Before etching, the 4H-SiC wafer was ultrasonically cleaned in acetone, ethanol and deionized water in sequence, and then naturally air-dried.

[0019] Furthermore, the 4H-SiC wafer is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1 cm×0.5 cm.

[0020] Furthermore, the nanowires of the bamboo-shaped 4H-SiC nanowire array have a length of 110 to 150 μm and a width of 15 to 38 nm.

[0021] An Al-doped 4H-SiC nanowire field emission cathode is prepared by the Al-doped 4H-SiC nanowire field emission cathode preparation method.

[0022] The technical solution provided by the present invention may include the following beneficial effects:

[0023] 1. Bamboo-shaped 4H-SiC nanowires are processed on the wafer by electrochemical etching, so that the growth process of the nanowires can be controlled, and the morphology of the nanowires can be controlled. Then, Al element is doped on this basis, and the unique structure of the nanowires is perfectly retained. The prepared Al-doped 4H-SiC nanowires have excellent field emission performance. The turn-on field strength of the Al-doped 4H-SiC nanowires is as low as 0.42V / μm, and the electron emission fluctuation after continuous operation for 3 hours is as low as 1.0%.

[0024] 2. In the sintering step of the present invention, a relatively low temperature of 800 to 900° C. is used to obtain Al-doped 4H-SiC nanowires;

[0025] 3. The Al-doped 4H-SiC nanowire field emission cathode preparation method of the present invention has a simple process, and the obtained field emission cathode exhibits a low turn-on electric field and extremely high electron emission stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a scanning electron microscope (SEM) image of 4H-SiC nanowire array;

[0027] Figure 2 is the energy spectrum (EDX) of Al-doped 4H-SiC nanowires;

[0028] Figure 3 It is a scan of the Al element in Al-doped 4H-SiC nanowires;

[0029] Figure 4This is the electron emission stability test result of the Al-doped 4H-SiC nanowire field emission cathode running continuously for 3 hours;

[0030] Figure 5 These are the start-up electric field test results of the emission cathodes obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0031] The invention discloses a method for preparing an Al-doped 4H-SiC nanowire field emission cathode. The Al-doping temperature is low and the nanowire array morphology is complete. The obtained field emission cathode has a low start-up field strength and high electron emission stability.

[0032] The preparation method of the present invention comprises the following steps:

[0033] (1) electrochemically etching a 4H-SiC wafer to form a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and then peeling the 4H-SiC nanowire array off the 4H-SiC wafer;

[0034] (2) immersing the 4H-SiC nanowire array obtained in step (1) in an aluminum source solution containing Al element, and then taking it out and drying it;

[0035] (3) Sintering the 4H-SiC nanowire array obtained in step (2) at 800-900° C. in an inert environment to obtain an Al-doped 4H-SiC nanowire array, wherein the Al-doped 4H-SiC nanowire array is an Al-doped 4H-SiC nanowire field emission cathode.

[0036] In the present invention, the bamboo-shaped 4H-SiC nanowires are firstly etched and processed on a wafer using an electrochemical etching technique, so that the growth process of the nanowires is controllable, and then the Al element is doped on this basis, and the unique structure of the nanowires is perfectly retained. The prepared Al-doped 4H-SiC nanowires have excellent field emission performance, and the turn-on field strength of the Al-doped 4H-SiC nanowires is as low as 0.42V / μm, and the electron emission fluctuation after continuous operation for 3 hours is as low as 1.0%. The Al-doped 4H-SiC nanowire field emission cathode preparation method of the present invention is simple in process, and the obtained field emission cathode exhibits a low turn-on electric field and extremely high electron emission stability.

[0037] The present invention further studies the Al doping amount, and the Al doping amount in the Al doped 4H-SiC nanowire array is 0.16at% to 1.63at%. Al doping can change the band structure of SiC and reduce the band gap. When the Al doping amount is within this range, it has a low turn-on electric field and high electron emission stability. Preferably, the Al doping amount in the Al doped 4H-SiC nanowire array is 0.36at%.

[0038] In order to achieve the desired Al doping amount, further, in the step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al element for 3 to 10 minutes, and then taken out and dried naturally or dried at a temperature below 60° C. After the 4H-SiC nanowire array is immersed in the aluminum source solution for a period of time, the Al element can penetrate into the nanowire array and adhere to it, and then taken out and dried naturally or dried at a temperature below 60° C. to prevent the nanowires from being oxidized.

[0039] Specifically, the aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate or aluminum sulfate; or the aluminum source solution is an acid solution of aluminum chloride, aluminum nitrate or aluminum sulfate. When aluminum chloride, aluminum nitrate or aluminum sulfate is dissolved in an acid solution or water, no interfering elements are introduced. Exemplarily, the acid solution is hydrochloric acid or sulfuric acid.

[0040] In order to ensure the doping effect and prevent the oxidation of the nanowires, further, in the step (3), the 4H-SiC nanowire array obtained in the step (2) is placed in a tubular furnace, the tubular furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the cycle is repeated multiple times;

[0041] The temperature was raised to 800-900°C at a heating rate of 5°C / min, kept at that temperature for 20-40min, then lowered to 400-500°C at a cooling rate of 5°C / min, and finally cooled to room temperature along with the furnace.

[0042] In this technical solution, the thermal kinetic energy of the dopant atoms is increased by controlling the heating rate, the maximum temperature and the cooling rate to promote the diffusion of the doping elements in the SiC lattice and ensure the doping amount. Preferably, the temperature is raised to 900°C at a heating rate of 5°C / min, kept at this temperature for 30 minutes, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature with the furnace, so that the Al doping amount can reach 0.16at% to 1.63at%.

[0043] Exemplarily, the 4H-SiC wafer obtained in step (2) is placed in a tubular furnace, the tubular furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the cycle is repeated three times to reduce the oxygen content in the furnace tube as much as possible, so that the internal environment of the tubular furnace tube is maintained in an inert environment, thereby preventing the bamboo-shaped 4H-SiC nanowire array from being oxidized by oxygen in the subsequent high-temperature annealing process.

[0044] In order to obtain a bamboo-shaped 4H-SiC nanowire array with excellent morphology, further, in the step (1), the 4H-SiC wafer is used as an anode, the Pt sheet is used as a cathode, the C surface of the 4H-SiC wafer is used as an etching surface facing the Pt electrode, and is placed in an etching solution for etching, the etching voltage is 20V, and the etching time is 27 to 30min;

[0045] In the etching solution, the volume ratio of 99 vol% ethylene glycol, 45 wt% hydrofluoric acid and 30 wt% hydrogen peroxide is 6:3:1.

[0046] In the present invention, by using a specific etching solution, limiting the etching voltage and etching time, a bamboo-shaped 4H-SiC nanowire array is obtained. During the etching process, a mesoporous structure will first be formed on the surface of the 4H-SiC wafer, and then the internal pore size of the mesoporous layer will increase, and the pore length will become deeper; then the pore walls between adjacent pores will be etched and disappear, and the pores will be connected. The connection of continuous pores will cause the unetched parts to be etched and divided into nanowires, thus forming a bamboo-shaped nanowire structure. The bamboo-shaped nanowires obtained by this method are independent, neatly arranged and straight, and are not connected into a strip shape. Concave and convex knots are periodically arranged on its surface. These protruding and sharp knots can act as electron emission sites during the field emission test, and can emit a large number of electrons under the same electric field strength, so that the turn-on electric field is low enough.

[0047] It should be noted that after etching, a nanowire array layer and a hole layer are formed on the surface of the 4H-SiC wafer, and the nanowire array layer is located between the hole layer and the unetched area of ​​the 4H-SiC wafer. The tape is tightly attached to the hole layer, and the hole layer carrying the nanoarray layer can be separated from the 4H-SiC wafer by tearing off the tape, thereby realizing the peeling of the 4H-SiC nanowire array from the 4H-SiC wafer.

[0048] Preferably, the 4H-SiC nanowire array obtained after etching is immersed in an ethanol solution, washed and naturally air-dried to prevent oxidation; before etching, the 4H-SiC wafer is ultrasonically cleaned in acetone, ethanol and deionized water in sequence, and then naturally air-dried to obtain a clean wafer, thereby etching to obtain bamboo-shaped nanowires with good morphology.

[0049] The 4H-SiC wafer in the embodiment of the present invention is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1 cm×0.5 cm.

[0050] Furthermore, the nanowire length of the bamboo-shaped 4H-SiC nanowire array is 110-150 μm and the width is 15-38 nm. The diameter width and overall length of the nanowire have a great influence on the field emission performance: the thinner and longer the nanowire, the lower the field emission turn-on electric field will be, but the stability will be worse. The length and width of the nanowire in this solution are reasonable, so that the field emission cathode has both low turn-on electric field and high stability.

[0051] Correspondingly, the present invention also provides an Al-doped 4H-SiC nanowire field emission cathode, which is prepared by the above-mentioned Al-doped 4H-SiC nanowire field emission cathode preparation method.

[0052] The present invention is further described below by way of examples and comparative examples.

[0053] Example 1

[0054] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode of this embodiment comprises the following steps:

[0055] S1. Take an N-doped 4H-SiC wafer with a length and width of 1 cm × 0.5 cm, and perform ultrasonic cleaning in acetone, ethanol, and deionized water in sequence, and then air-dry naturally;

[0056] S2, 4H-SiC wafer as anode, Pt wafer as cathode, the C surface of 4H-SiC wafer as etching surface facing Pt electrode, placed in etching solution for etching, etching voltage is 20V, etching time is 30min; in the etching solution, the volume ratio of 99vol% ethylene glycol, 45wt% hydrofluoric acid and 30wt% hydrogen peroxide is 6:3:1; the nanowires of the obtained bamboo-shaped 4H-SiC nanowire array are in the range of 110-150μm in length and 15-38nm in width ( Figure 1 ), peeling the obtained 4H-SiC nanowire array from the 4H-SiC wafer;

[0057] S3, soaking the obtained 4H-SiC nanowire array in an ethanol solution for 5 minutes, washing and air-drying naturally;

[0058] S4. Soak the 4H-SiC nanowire array in a 0.01 g / ml AlCl3 aqueous solution for 5 min, take it out and dry it naturally or dry it at a temperature below 60°C.

[0059] S5. The obtained 4H-SiC nanowire array is placed in a tubular furnace, and the tubular furnace is evacuated to -0.1Mpa, and then an inert gas is introduced to atmospheric pressure, and the cycle is repeated three times; the temperature is increased to 900°C at a heating rate of 5°C / min, and the temperature is kept at this temperature for 30 minutes, and then the temperature is decreased to 500°C at a cooling rate of 5°C / min, and finally the furnace is cooled to room temperature.

[0060] The Al-doped 4H-SiC nanowire array obtained in this embodiment has an Al-doping amount of 0.36 at% to 0.44 at% ( Figure 2 and Figure 3 ); the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.42 V / μm ( Figure 5 ), the electron emission fluctuation after 3 hours of continuous operation is 1.3% ( Figure 4 ).

[0061] Example 2

[0062] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Embodiment 1, except that: the 4H-SiC nanowire array in step S4 is immersed in a 0.03 g / ml AlCl3 aqueous solution for 5 minutes.

[0063] The Al doping amount in the Al doped 4H-SiC nanowire array obtained in this embodiment is 1.46at% to 1.63at%; the turn-on electric field of the Al doped 4H-SiC nanowire field emission cathode is 0.73V / μm ( Figure 5 ), the electron emission fluctuation after 3 hours of continuous operation was 1.6%.

[0064] Example 3

[0065] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Embodiment 1, except that: the 4H-SiC nanowire array in step S4 is immersed in a 0.005 g / ml AlCl3 aqueous solution for 5 minutes.

[0066] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.16at% to 0.23at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.55V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 2.1%.

[0067] Example 4

[0068] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is substantially the same as that in Embodiment 1, except that in step S4, the 4H-SiC nanowire array is immersed in a 0.01 g / ml aluminum nitrate aqueous solution for 5 minutes.

[0069] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.34at% to 0.48at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.44V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 1.5%.

[0070] Example 5

[0071] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Embodiment 1, except that: the 4H-SiC nanowire array in step S4 is immersed in a 0.01 g / ml AlCl3 aqueous solution for 3 minutes.

[0072] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.28at% to 0.32at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.51V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 1.5%.

[0073] Example 6

[0074] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Embodiment 1, except that:

[0075] The 4H-SiC nanowire array in step S4 was immersed in a 0.01 g / ml AlCl 3 aqueous solution for 10 min.

[0076] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.52at% to 0.63at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.64V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 1.8%.

[0077] Example 7

[0078] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Embodiment 1, except that the etching time in step S2 is 27 minutes.

[0079] The turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.70 V / μm, and the electron emission fluctuation after 3 hours of continuous operation is 1.0%.

[0080] Example 8

[0081] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that: in step S5, the temperature is raised to 800°C at a heating rate of 5°C / min, kept at this temperature for 30 minutes, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature in the furnace.

[0082] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.26at% to 0.32at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.48V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 2.3%.

[0083] Example 9

[0084] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this embodiment is basically the same as that in Example 1, except that: in step S5, the temperature is raised to 900°C at a heating rate of 5°C / min, kept at this temperature for 20 minutes, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature in the furnace.

[0085] The Al doping amount in the Al-doped 4H-SiC nanowire array obtained in this embodiment is 0.32at% to 0.38at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 0.46V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 1.5%.

[0086] Comparative Example 1

[0087] In this comparative example group, the 4H-SiC nanowire array obtained in step S3 of Example 1 was used as the field emission cathode, and the opening electric field was 0.81 V / μm ( Figure 5 ).

[0088] Comparative Example 2

[0089] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that: the 4H-SiC wafer in step S4 is immersed in a 0.05 g / ml AlCl3 aqueous solution for 5 minutes.

[0090] The Al-doped 4H-SiC nanowire array obtained in this embodiment has an Al-doping amount of 5.27 at% to 8.93 at%; the turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode is 1.50 V / μm ( Figure 5 ).

[0091] Comparative Example 3

[0092] The preparation method of the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that: in step S5, the temperature is raised to 600°C at a heating rate of 5°C / min, kept at this temperature for 30 minutes, then cooled to 500°C at a cooling rate of 5°C / min, and finally cooled to room temperature with the furnace.

[0093] The Al doping amount in the Al doped 4H-SiC nanowire array obtained in this comparative example is 0.18 at% to 0.24 at%; the turn-on electric field of the Al doped 4H-SiC nanowire field emission cathode is 0.58 V / μm.

[0094] Comparative Example 4

[0095] The method for preparing the Al-doped 4H-SiC nanowire field emission cathode in this comparative example is basically the same as that in Example 1, except that the etching time in step S2 is 32 minutes.

[0096] The turn-on electric field of the Al-doped 4H-SiC nanowire field emission cathode obtained in this embodiment is 0.36 V / μm, and the electron emission fluctuation after continuous operation for 3 hours is 3.4%.

[0097] Other structures and operations of an Al-doped 4H-SiC nanowire field emission cathode and a preparation method thereof according to an embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0098] In the description of this specification, the description with reference to the terms "embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0099] Although the 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 claims and their equivalents.

Claims

1. A method for preparing an Al-doped 4H-SiC nanowire field emission cathode, characterized in that: The following steps are involved: (1) electrochemically etching the 4H-SiC wafer to form a bamboo-shaped 4H-SiC nanowire array on the surface of the 4H-SiC wafer, and peeling the 4H-SiC nanowire array off the 4H-SiC wafer; (2) immersing the 4H-SiC nanowire array obtained in step (1) in an aluminum source solution containing Al element, and then taking it out and drying it; (3) Sintering the 4H-SiC nanowire array obtained in step (2) at 800-900° C. in an inert environment to obtain an Al-doped 4H-SiC nanowire array, wherein the Al-doped 4H-SiC nanowire array is an Al-doped 4H-SiC nanowire field emission cathode.

2. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that: The Al doping amount in the Al doped 4H-SiC nanowire array is 0.16 at % to 1.63 at %.

3. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 2, characterized in that: In the step (2), the 4H-SiC nanowire array is immersed in an aluminum source solution containing Al element for 3 to 10 minutes, and then taken out and naturally dried or dried at a temperature below 60°C.

4. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 3, characterized in that: The aluminum source solution is an aqueous solution of aluminum chloride, aluminum nitrate or aluminum sulfate; or the aluminum source solution is an acid solution of aluminum chloride, aluminum nitrate or aluminum sulfate.

5. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that: In the step (3), the 4H-SiC nanowire array obtained in the step (2) is placed in a tubular furnace, the tubular furnace is evacuated to -0.1 MPa, and then an inert gas is introduced to atmospheric pressure, and the cycle is repeated multiple times; The temperature was raised to 800-900°C at a heating rate of 5°C / min, kept at that temperature for 20-40min, then lowered to 400-500°C at a cooling rate of 5°C / min, and finally cooled to room temperature along with the furnace.

6. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 1, characterized in that: In the step (1), the 4H-SiC wafer is used as the anode and the Pt wafer is used as the cathode. The C surface of the 4H-SiC wafer is used as the etching surface facing the Pt electrode and placed in an etching solution for etching. The etching voltage is 20 V and the etching time is 27 to 30 minutes. In the etching solution, the volume ratio of 99 vol% ethylene glycol, 45 wt% hydrofluoric acid and 30 wt% hydrogen peroxide is 6:3:

1.

7. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 6, characterized in that: The 4H-SiC nanowire array on the etched 4H-SiC wafer was peeled off, and then immersed in an ethanol solution, washed and naturally air-dried; Before etching, the 4H-SiC wafer was ultrasonically cleaned in acetone, ethanol and deionized water in sequence, and then naturally air-dried.

8. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 6, characterized in that: The 4H-SiC wafer is an N-doped 4H-SiC wafer, and the length and width of the 4H-SiC wafer are 1 cm×0.5 cm.

9. The method for preparing an Al-doped 4H-SiC nanowire field emission cathode according to claim 8, characterized in that: The nanowires of the bamboo-shaped 4H-SiC nanowire array have a length of 110 to 150 μm and a width of 15 to 38 nm.

10. An Al-doped 4H-SiC nanowire field emission cathode, characterized in that: The 4H-SiC nanowire field emission cathode is prepared by the method for preparing the Al-doped 4H-SiC nanowire field emission cathode according to any one of claims 1 to 9.

Images