A pyramid-shaped CoO composite SiC nanowire composite material and its preparation method and application

Abstract

The present invention belongs to the technical field of field emission cathode nanomaterials and relates to a pyramid-shaped CoO-SiC nanowire composite material, its preparation method, and application. The present invention discloses a pyramid-shaped CoO-SiC nanowire composite material, comprising N-doped SiC quasi-array nanowires and pyramid-shaped CoO particles deposited on the surface of the nanowires. The present invention also discloses a method for preparing the pyramid-shaped CoO-SiC nanowire composite material, comprising: using N-doped SiC quasi-array nanowires as a template and CoCl2 as a metal substitution source, heating in a tubular furnace to perform a substitution reaction, and cooling to obtain the pyramid-shaped CoO-SiC nanowire composite material. The present invention also discloses the application of the pyramid-shaped CoO-SiC nanowire composite material in cold cathode field emission testing.

Description

Technical Field

[0001] The invention belongs to the technical field of field emission cathode nanomaterials and relates to a pyramid-shaped CoO composite SiC nanowire composite material and a preparation method and application thereof. Background Art

[0002] Field emission is the emission of electrons from a material's surface via quantum mechanical tunneling in response to an external electric field. Field emission-based electron sources offer numerous advantages, including room-temperature operation, rapid response to external electric fields, uniform and brighter fluorescent displays, and lower power consumption. These exceptional properties hold promise for a variety of vacuum microelectronic applications, including flat-panel displays, X-ray sources, microwave power devices, and sensors. As the "heart" of vacuum electronics, cathode emitters, with their exceptional field emission properties, including low turn-on field, long operating lifetime, and high emission stability, play a key role in vacuum electronics. Among field emission materials, one-dimensional SiC nanostructures are considered a prominent candidate due to their versatility. Their exceptional mechanical properties, high thermal conductivity, excellent heat resistance, and strong chemical stability support their use in harsh operating environments, such as high temperature, high power, and high voltage. To date, three main approaches have been developed to improve the field emission behavior of nanostructured SiC emitters, based on the Fowder-Nordheim (FN) theory. The first is to increase the field enhancement factor (β) by reducing the radius of curvature and / or adjusting the geometry of emitters with high aspect ratios. The second is to reduce the work function (Φ) of the emitter by doping or building a heterojunction. The third is to increase the density of electron emission points on the emitter surface. Summary of the Invention

[0003] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose a pyramid-shaped CoO composite SiC nanowire composite material with ultra-low turn-on electric field, high current density and high emission stability, which increases the density of electron emission points on the emitter surface.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A pyramid-shaped CoO-SiC nanowire composite material comprises N-doped SiC quasi-array nanowires and pyramid-shaped CoO particles deposited on the surface of the nanowires.

[0006] The present invention loads pointed pyramid-shaped CoO particles on the surface of smooth N-doped SiC quasi-array nanowires to increase robust electron emission points.

[0007] Preferably, the size of the CoO particles is 50-200 nm, and the diameter of the N-doped SiC quasi-array nanowires is 600-800 nm.

[0008] The present invention also discloses a method for preparing a pyramid-shaped CoO composite SiC nanowire composite material. The preparation method comprises: using N-doped SiC quasi-array nanowires as a template, CoCl2 as a metal replacement source, heating in a tubular furnace to perform a replacement reaction, and obtaining the pyramid-shaped CoO composite SiC nanowire composite material after cooling.

[0009] The present invention uses N-doped SiC quasi-array nanowires as a template and CoCl2 as a metal replacement source. At a certain temperature, a cation exchange method is used to replace the oxide layer on the surface of the SiC material with a CoCl2 atmosphere to obtain a CoO layer. When heating is continued, cobalt chloride vapor reacts with O2 in the tubular furnace cavity and is deposited on the SiC surface, uniformly distributing pyramid-shaped CoO particles on the surface of the SiC nanowires.

[0010] Preferably, the temperature in the tube furnace is 500-600° C., the heating rate is 8-12° C. / min, and the holding time is 20-60 min.

[0011] Preferably, the vacuum degree in the tube furnace is 80-140 Pa.

[0012] Preferably, the CoCl2 is anhydrous cobalt chloride powder.

[0013] More preferably, the ratio of the area of the substrate loaded with N-doped SiC quasi-array nanowires to the mass of CoCl2 is (0.1-0.5) cm 2 :(0.12~0.5)g.

[0014] The present invention can ensure the reaction rate and particle growth density by controlling the addition amount of cobalt chloride; a higher vacuum degree can ensure a certain O2 infiltration and ensure the continuous growth of CoO particles.

[0015] Preferably, the inert gas in the tube furnace is one of nitrogen and argon, and the gas flow rate is 30 to 100 sccm.

[0016] The present invention also discloses an application of a pyramid-shaped CoO composite SiC nanowire composite material in a cold cathode field emission test. The cold cathode field emission test process of the pyramid-shaped CoO composite SiC nanowire composite material includes: cutting a substrate loaded with the pyramid-shaped CoO composite SiC nanowire composite material and attaching it to a cathode platform; transferring it to a measuring device, evacuating it, adjusting the distance from the cathode surface to the anode surface, and conducting a test.

[0017] Preferably, the test area of the pyramid-shaped CoO composite SiC nanowire composite material is 0.1 to 0.5 cm 2 .

[0018] Preferably, the cold cathode field emission test includes a high vacuum chamber, a high voltage platform, a spacing control device and a voltage and current detection system, the test anode is a metal plate, and the cathode is a pyramid-shaped CoO composite SiC nanowire composite material prepared by the above preparation method.

[0019] Further preferably, the vacuum degree of the field emission test is 5×10 -7 ~5×10 -8 Pa.

[0020] More preferably, the distance (d) from the cathode surface to the anode surface is adjusted to 750-900 μm and is precisely controlled by a micrometer caliper.

[0021] The greater the distance from the field emission cathode surface to the anode surface, the greater the field emission start-up electric field, but its current density will also increase. Further increasing the field electrode spacing will reduce the field emission current, resulting in performance degradation; therefore, it is necessary to control the distance from the cathode surface to the anode surface.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The pyramid-shaped CoO composite SiC nanowire composite material of the present invention deposits tiny and sharp pyramid-shaped CoO particles on the surface of N-doped SiC quasi-array nanowires to increase the density of electron emission points on the emitter surface, thereby improving the field emission behavior of the nanostructured SiC emitter.

[0024] 2. The pyramid-shaped CoO-SiC nanowire composite material of the present invention has a strong connection between the CoO nanoparticles and the SiC nanowires, which can prevent structural damage during long-term field emission operation.

[0025] 3. The pyramid-shaped CoO particles on the surface of the pyramid-shaped CoO composite SiC nanowire composite material prepared by the preparation method of the present invention are evenly distributed, and the preparation process is controllable.

[0026] 4. The pyramid-shaped CoO-SiC nanowire composite material of the present invention is a heterojunction material that increases the density of electron emission points on the emitter surface, and can exhibit ultra-low turn-on electric field, high current density and high emission stability.

[0027] 5. The current fluctuation of the pyramid-shaped CoO-SiC nanowire composite material of the present invention is only ±2% during a 10-hour test. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope (SEM) image of the pyramid-shaped CoO composite SiC nanowire composite material prepared in Example 1.

[0029] Figure 2 This is a scanning electron microscope (SEM) image of the N-doped SiC quasi-array nanowires in Example 1.

[0030] Figure 3 This is a low-magnification TEM image of the N-doped SiC quasi-array nanowire and pyramid-shaped CoO composite SiC nanowire composite material in Example 1.

[0031] Figure 4 (a) is a low-magnification TEM image of the N-doped SiC quasi-array nanowires in Example 1; (b) is a high-resolution transmission electron microscope HRTEM image.

[0032] Figure 5 The low-magnification TEM image (a) of the pyramid-shaped CoO-SiC nanowire composite material in Example 1, the TEM image of the extreme end of the CoO particle (b), the HRTEM image of the CoO tip (c), and the HRTEM image of the CoO and SiC interface (d).

[0033] Figure 6 This is the XRD pattern of the SiC nanowires and the pyramid-shaped CoO-SiC nanowire composite material in Example 1.

[0034] Figure 7 This is the full XPS spectrum of the pyramid-shaped CoO-SiC nanowire composite material in Example 1.

[0035] Figure 8 These are the Si 2p high-resolution spectrum (a), C 1s high-resolution spectrum (b), Co 2p high-resolution spectrum (c), and O 1s high-resolution spectrum (d) of the pyramid-shaped CoO-SiC nanowire composite material of Example 1.

[0036] Figure 9 Field emission voltage-current curve (a) of the SiC nanowire and pyramid-shaped CoO composite SiC nanowire composite material in Example 1; FN (Fowder-Nordheim) curve (b).

[0037] Figure 10 This is a long-term field emission current-time curve of the pyramid-shaped CoO composite SiC nanowire composite material in Example 1.

[0038] Figure 11 2 is the field emission voltage-current curve of the pyramid-shaped CoO composite SiC nanowire composite material in Example 1 at different electrode spacings. DETAILED DESCRIPTION

[0039] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0040] Pyramid-shaped CoO composite SiC nanowire composite material was used as cathode for field emission test in a high vacuum chamber:

[0041] The pyramid-shaped CoO composite SiC nanowire composite was cut into pieces with a size of 0.25 × 0.25 cm. 2 The small piece was attached to the cathode platform as a standard sample for field emission measurement; after the sample was transferred to the measurement device, the vacuum chamber was evacuated for more than 24 hours to a temperature of 5×10 -7 ~5×10 -8 The high vacuum level of 1.5 Pa was maintained. The distance (d) from the cathode surface to the anode surface was adjusted to 750–900 μm and precisely controlled using a microcaliper. The voltage-current curves and current emission stability of the selected emitter samples were recorded using a Keithley 248 instrument with a detection resolution of 0.1 fA.

[0042] Test methods include:

[0043] (1) Set the voltage from 0 to high voltage and detect the field emission current and voltage values;

[0044] (2) Set a constant bias voltage and detect the current change curve over time.

[0045] Example 1

[0046] N-doped SiC quasi-array nanowires:

[0047] The organic precursor powder (polysilazane) and nitrogen source powder (melamine) with a mass ratio of 3:1 were mixed and placed at the bottom of a graphite crucible. A carbon fiber cloth substrate soaked with a catalyst (cobalt nitrate) was placed on the top of the graphite crucible. The graphite crucible was then placed in a sintering furnace and evacuated to 10 -4 Pa, then heated to 1500℃ at a rate of 54℃ / min under inert gas protection, then heated to 1600℃ at a rate of 5℃ / min, and finally cooled to room temperature with the furnace to obtain N-doped SiC nanowires with flexible carbon fiber cloth (CC) as the substrate.

[0048] Pyramid-shaped CoO-SiC nanowire composite material (abbreviated as CoO / SiC in the accompanying figure):

[0049] Flexible carbon fibers (1*0.3cm) loaded with N-doped SiC quasi-array nanowires 2) was placed in Ark 1, and 0.2g of CoCl2 was placed in Ark 2. Both Arks were placed in a tube furnace, with Ark 2 positioned 4cm from the center of the tube furnace, in the direction of the upper airflow. The argon gas valve was opened to a flow rate of 50 sccm, and the mechanical vacuum pump was turned on to maintain a constant vacuum (120 Pa) during the experiment. The temperature was increased at a rate of 10°C / min to 540°C and held for 30 minutes. The temperature was then cooled in the furnace, and the sample was removed, cleaned, and used for later use.

[0050] according to Figures 1 to 5 It can be seen that the N-doped SiC quasi-array nanowires present a quasi-nanoarray structure, specifically a one-dimensional nanostructure with a smooth surface, a length of micron-level, and a diameter of about 700nm; the CoO particles on the surface of the pyramid-shaped CoO composite SiC nanowire composite material present a pyramid-shaped structure, and the CoO particles can show sharp tips at the nanoscale, and CoO is evenly distributed on the SiC surface; Figure 5 The dark area in (a) is CoO, which has uniform brightness and darkness, indicating that the CoO is evenly distributed. 5(b) is the extreme of CoO, showing that the CoO nanoparticles still appear as sharp tips at an extremely small scale. 5(c) is the HRTEM image of the CoO tip, and its lattice spacing corresponds to the CoO crystal phase. 5(d) is the HRTEM image of the interface between CoO and SiC, showing good interfacial contact between CoO and SiC surfaces.

[0051] Figure 6 The XRD patterns of N-doped SiC quasi-array nanowires and pyramid-shaped CoO composite SiC nanowire composite materials show that the characteristic peaks corresponding to the nanoparticles added on the surface are CoO crystal types.

[0052] Figure 7 This is the full XPS spectrum of the pyramid-shaped CoO composite SiC nanowire composite material, indicating that the prepared material has obvious Co element introduction; Figure 8 The XPS graphs of each element show that CoO and SiC have good bond energy.

[0053] Perform cold cathode field emission testing:

[0054] The distance (d) from the cathode surface to the anode surface was adjusted to 800 μm, and the vacuum chamber was set to 1.5×10 -7 Pa high vacuum degree.

[0055] According to the test results and Figure 9 It can be seen that the pyramid-shaped CoO composite SiC nanowire composite material generates 10μA / cm 2 The J value corresponds to a bias voltage E value of 0.40 V / μm; it generates 1 mA / cm 2The J value of N-doped SiC quasi-array nanowires generates 10μA / cm 2 The J value of E corresponds to a bias voltage E value of 0.53V / μm; it generates 1mA / cm 2 The J value corresponds to a bias voltage E value of 2.37V / μm.

[0056] Figure 10 The long-term field emission current time curve is shown in the figure. It can be seen from the figure that the pyramid-shaped CoO composite SiC nanowire composite material has good stability at ~0.87mA / cm 2 After working continuously for 10 hours at a current density of 1.5 GHz, the current fluctuation is only ±2%, and there is no obvious current attenuation.

[0057] Example 2

[0058] Compared with Example 1, the difference is that the temperature in the tube furnace is 520°C.

[0059] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.42 V / μm.

[0060] Example 3

[0061] Compared with Example 1, the difference is that the temperature in the tube furnace is 580°C.

[0062] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.45 V / μm.

[0063] Example 4

[0064] Compared with Example 1, the difference is that the temperature in the tube furnace is 480°C.

[0065] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.63 V / μm.

[0066] Example 5

[0067] Compared with Example 1, the difference is that the temperature in the tube furnace is 610°C.

[0068] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. toThe measured value (corresponding to E value) is 0.65 V / μm.

[0069] Example 6

[0070] Compared with Example 1, the difference is that the holding time in the tube furnace is 20 minutes.

[0071] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.47 V / μm.

[0072] Example 7

[0073] Compared with Example 1, the difference is that the holding time in the tube furnace is 40 minutes.

[0074] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.46 V / μm.

[0075] Example 8

[0076] Compared with Example 1, the difference is that the holding time in the tube furnace is 70 minutes.

[0077] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.62 V / μm.

[0078] Example 9

[0079] Compared with Example 1, the difference is that the holding time in the tube furnace is 15 minutes.

[0080] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.66 V / μm.

[0081] Example 10

[0082] Compared with Example 1, the difference is that the vacuum degree in the tube furnace is 90 Pa.

[0083] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.51 V / μm.

[0084] Example 11

[0085] Compared with Example 1, the difference is that the vacuum degree in the tube furnace is 60 Pa.

[0086] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.79 V / μm.

[0087] Example 12

[0088] Compared with Example 1, the difference is that the added amount of CoCl2 is 0.15g.

[0089] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.47 V / μm.

[0090] Example 13

[0091] Compared with Example 1, the difference is that the added amount of CoCl2 is 0.4g.

[0092] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.46 V / μm.

[0093] Example 14

[0094] Compared with Example 1, the difference is that the added amount of CoCl2 is 0.1 g.

[0095] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.76 V / μm.

[0096] Example 15

[0097] Compared with Example 1, the difference is that the added amount of CoCl2 is 0.6g.

[0098] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test according to the method described in Example 1. to The measured value (corresponding E value) is 0.61 V / μm.

[0099] Example 16

[0100] Compared with Example 1, the difference is that the distance (d) from the cathode surface to the anode surface is adjusted to 600 μm.

[0101] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test. to The measured value (corresponding E value) is 0.74 V / μm.

[0102] Example 17

[0103] Compared with Example 1, the difference is that the distance (d) from the cathode surface to the anode surface is adjusted to 750 μm.

[0104] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test. to The measured value (corresponding to E value) is 0.50 V / μm.

[0105] Example 18

[0106] Compared with Example 1, the difference is that the distance (d) from the cathode surface to the anode surface is adjusted to 900 μm.

[0107] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test. to The measured value (corresponding E value) is 0.47 V / μm.

[0108] Example 19

[0109] Compared with Example 1, the difference is that the distance (d) from the cathode surface to the anode surface is adjusted to 1000 μm.

[0110] The prepared pyramid-shaped CoO composite SiC nanowire composite material was subjected to cold cathode field emission test. to The measured value (corresponding E value) is 0.56 V / μm.

[0111] Comparative Example 1

[0112] Compared with Example 1, the difference is that the holding time in the tube furnace is 5 minutes.

[0113] The surface of SiC nanowires is only a CoO layer, and pyramid-shaped CoO particles have not yet formed.

[0114] The prepared composite material was subjected to cold cathode field emission test, E to The measured value (corresponding E value) is 1.05 V / μm.

[0115] According to the above data, combined with Figure 9It can be seen that the field emission voltage-current curve (a) shows the dependence of the test emission current density (J) on the functional applied electric field (E). The voltage-current curve is obtained after multiple voltage sweeps to remove residual gases and pollutants. The consistent and relatively smooth curve reveals stable electron emission; the curve in (a) shows that the decoration-induced field emission behavior of CoO nanoparticles is significantly improved; and by precisely adjusting the size, spacing and density of CoO nanoparticles optimized by the cation exchange process, the field electron emission performance of the nanowire can be further improved. In addition, the pyramid-shaped CoO composite SiC nanowire composite material of the present invention has an ultra-low E detected in the test. to This demonstrates that the composite material may be the most advanced SiC nanostructure emitter reported to date, and further proves that the composite nanowires obtained by the present invention have excellent comprehensive field emission performance.

[0116] Combine Figure 11 It can be seen that E to With the increase of spacing (600, 800, 1000 μm), it first decreases and then increases, indicating that the d value has a significant influence on the field emission behavior of pyramidal CoO composite SiC nanowire composites; in the current case, the spacing-dependent field emission characteristics are largely attributed to the different electric fields between the emitter surface and the anode plate caused by the varying spacing values; under a constant area of the anode, different spacings will result in different abilities of the anode to capture electrons escaping from the cathode emission sites, ultimately leading to the spacing-dependent field emission performance of the composite material.

[0117] In summary, the pyramid-shaped CoO composite SiC nanowire composite material of the present invention deposits tiny and sharp pyramid-shaped CoO particles on the surface of N-doped SiC quasi-array nanowires to increase the density of electron emission points on the emitter surface, thereby improving the field emission behavior of the nanostructured SiC emitter.

[0118] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A pyramid-shaped CoO composite SiC nanowire composite material, characterized in that: The composite material comprises N-doped SiC quasi-array nanowires and pyramid-shaped CoO particles deposited on the surface of the nanowires.

2. The pyramid-shaped CoO-SiC nanowire composite material according to claim 1, characterized in that: The size of the CoO particles is 50-200 nm, and the diameter of the N-doped SiC quasi-array nanowires is 600-800 nm.

3. A method for preparing the pyramid-shaped CoO-SiC nanowire composite material according to claim 1, characterized in that: The preparation method comprises: using N-doped SiC quasi-array nanowires as a template, CoCl2 as a metal replacement source, heating in a tube furnace to perform a replacement reaction, and obtaining a pyramid-shaped CoO-SiC nanowire composite material after cooling; The temperature in the tube furnace is 500-600°C, the heating rate is 8-12°C / min, and the holding time is 20-60min; The vacuum degree in the tube furnace is 80-140 Pa.

4. The method for preparing the pyramid-shaped CoO-SiC nanowire composite material according to claim 3, wherein: The CoCl2 is anhydrous cobalt chloride powder.

5. The use of the pyramid-shaped CoO-SiC nanowire composite material in cold cathode field emission testing according to claim 1, characterized in that: The cold cathode field emission test process of the pyramid-shaped CoO composite SiC nanowire composite material includes: cutting a substrate loaded with the pyramid-shaped CoO composite SiC nanowire composite material and attaching it to a cathode platform; transferring it to a measuring device, evacuating it, adjusting the distance between the cathode surface and the anode surface, and conducting the test.

6. The use according to claim 5, characterized in that The test area of the pyramid-shaped CoO composite SiC nanowire composite material is 0.1~0.5cm 2 .

7. The use according to claim 5, characterized in that The vacuum degree of the field emission test is 5×10 -7 ~5×10 -8 Pa; the distance from the cathode surface to the anode surface is 750~900μm.

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