CN111180293A - A flexible ZnO@TiN core-shell structure array cathode and its preparation method - Google Patents
A flexible ZnO@TiN core-shell structure array cathode and its preparation method Download PDFInfo
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- 239000011258 core-shell material Substances 0.000 title claims abstract description 62
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 64
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 63
- 239000004744 fabric Substances 0.000 claims abstract description 63
- 239000002073 nanorod Substances 0.000 claims abstract description 62
- 238000003491 array Methods 0.000 claims abstract description 20
- 238000000034 method Methods 0.000 claims abstract description 20
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000007791 liquid phase Substances 0.000 claims abstract description 7
- 238000003980 solgel method Methods 0.000 claims abstract description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 45
- 239000000243 solution Substances 0.000 claims description 19
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 18
- 239000008367 deionised water Substances 0.000 claims description 18
- 229910021641 deionized water Inorganic materials 0.000 claims description 18
- 238000001035 drying Methods 0.000 claims description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 18
- 238000010438 heat treatment Methods 0.000 claims description 15
- 238000003756 stirring Methods 0.000 claims description 14
- HZAXFHJVJLSVMW-UHFFFAOYSA-N 2-Aminoethan-1-ol Chemical compound NCCO HZAXFHJVJLSVMW-UHFFFAOYSA-N 0.000 claims description 12
- 239000011259 mixed solution Substances 0.000 claims description 12
- 239000000758 substrate Substances 0.000 claims description 10
- 239000010936 titanium Substances 0.000 claims description 8
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 238000000137 annealing Methods 0.000 claims description 6
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- 238000004544 sputter deposition Methods 0.000 abstract description 2
- NRTOMJZYCJJWKI-UHFFFAOYSA-N Titanium nitride Chemical compound [Ti]#N NRTOMJZYCJJWKI-UHFFFAOYSA-N 0.000 description 32
- 239000000523 sample Substances 0.000 description 30
- 239000007789 gas Substances 0.000 description 13
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- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/30—Cold cathodes, e.g. field-emissive cathode
- H01J1/304—Field-emissive cathodes
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- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
- H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2201/00—Electrodes common to discharge tubes
- H01J2201/30—Cold cathodes
- H01J2201/304—Field emission cathodes
- H01J2201/30446—Field emission cathodes characterised by the emitter material
- H01J2201/30488—Nitrides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2201/00—Electrodes common to discharge tubes
- H01J2201/30—Cold cathodes
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Abstract
本发明涉及一种柔性ZnO@TiN核壳结构阵列阴极及其制备方法，ZnO@TiN核壳结构阵列阴极包括碳布，碳布两侧面均涂覆有ZnO种子层，两侧面的ZnO种子层上均设有ZnO纳米棒阵列，其中一侧面的ZnO纳米棒阵列上沉积有TiN，以形成核壳结构阵列。其制备方法包括：（1）采用溶胶凝胶法在碳布两侧面上制备ZnO种子层；（2）采用液相法在两侧面的ZnO种子层上制备ZnO纳米棒阵列；（3）采用磁控溅射法在一侧面的ZnO纳米棒阵列上沉积TiN，从而制备得到ZnO@TiN核壳结构阵列阴极。该ZnO@TiN核壳结构阵列阴极开启和阈值电场低，发射电流密度大，电子输运和传导性好，可应用于真空场发射电子源器件。
The invention relates to a flexible ZnO@TiN core-shell structure array cathode and a preparation method thereof. The ZnO@TiN core-shell structure array cathode comprises carbon cloth. Both sides of the carbon cloth are coated with ZnO seed layers, and the ZnO seed layers on both sides are on the ZnO seed layers. Both are provided with ZnO nanorod arrays, and TiN is deposited on one side of the ZnO nanorod array to form a core-shell structure array. The preparation method includes: (1) using a sol-gel method to prepare ZnO seed layers on both sides of the carbon cloth; (2) using a liquid phase method to prepare ZnO nanorod arrays on the ZnO seed layers on both sides; (3) using magnetic The ZnO@TiN core-shell structure array cathode was prepared by the controlled sputtering method to deposit TiN on the ZnO nanorod array on one side. The ZnO@TiN core-shell structure array has low cathode opening and low threshold electric field, high emission current density, good electron transport and conductivity, and can be applied to vacuum field emission electron source devices.
Description
Technical Field
The invention belongs to the field of cold cathode electron emission materials, and particularly relates to a flexible ZnO @ TiN core-shell structure array cathode and a preparation method thereof.
Background
The field emission, i.e. cold cathode electron emission, is a phenomenon that the height and width of a potential barrier on the surface of a material are reduced and the electrons penetrate or cross the surface potential barrier to enter vacuum through the tunneling effect of quantum mechanics. The cold cathode electron field emission material is widely applied to vacuum microelectronic devices (such as X-ray tubes, electron sources, microwave tubes and the like). Cold cathode materials meeting these device requirements generally have low work functionsφ) And high field enhancement factor: (β). One-dimensional oxide nanostructure arrays, such as: ZnO nanowires, nanorods, nanobelts, and the like exhibit better field electron emission performance due to a larger aspect ratio and a small tip radius of curvature. In practical application, the problems of low electron transport capacity, high threshold voltage, small field emission current density and the like caused by the intrinsic semiconductor characteristics of the materials need to be solved. According to the vacuum field emission theory, the work function is a physical quantity related to the material, and the field enhancement factor mainly depends on the appearance of an emitter, so that the improvement of the field emission performance can be realized by designing the structure and the appearance of the material. On the other hand, transition metal nitrides such as TiN (M.K.Faruque, K.M.Darkwa, Z.G.xu, D.Kumar, appl. surf. Sci.260 (2012) 36-41), LaB6(J.Q.Xu, G.H.Hou, H.Q.Li, T.Y.ZHai, et al, NPG Asia Materials, 5(2013) 1-5) have the characteristics of low work function and excellent electron transport performance, but the preparation of the one-dimensional nanostructure of the nano-structure needs a high-temperature process, and the substrate selection and the scale preparation of the nano-structure are restricted. The existing one-dimensional ZnO nanometer cold cathode electron emitter has the main problems that: 1. the opening and threshold electric fields caused by the high work function of the material are high; 2. the saturation emission current density is small; 3. the electron transport and thermal conductivity are poor, and the emitter tip is easily burned under the action of joule heat.
Disclosure of Invention
The invention aims to provide a flexible ZnO @ TiN core-shell structure array cathode which is low in opening and threshold electric field, large in emission current density and good in electron transportation and conductivity and a preparation method thereof.
In order to achieve the purpose, the technical scheme of the invention is as follows: the flexible ZnO @ TiN core-shell structure array cathode comprises carbon cloth, ZnO seed layers are coated on two side faces of the carbon cloth, ZnO nanorod arrays are arranged on the ZnO seed layers on the two side faces, TiN is deposited on the ZnO nanorod arrays on one side face, and therefore a core-shell structure array is formed.
Furthermore, the flexible ZnO @ TiN core-shell structure array cathode is applied to a vacuum field emission electron source device.
The invention also provides a preparation method of the flexible ZnO @ TiN core-shell structure array cathode, which comprises the following steps:
(1) preparing ZnO seed layers on two side surfaces of the carbon cloth by a sol-gel method;
(2) preparing ZnO nanorod arrays on the ZnO seed layers on the two side faces by a liquid phase method;
(3) and depositing TiN on the ZnO nanorod array on one side surface by adopting a magnetron sputtering method, thereby preparing the ZnO @ TiN core-shell structure array cathode.
Further, the step (1) includes the steps of:
(101) 1.4-2.8 g of Zn (CH)3COOH)2Dissolving in 35-80 mL of absolute ethyl alcohol, stirring at room temperature for 20-40 min, and slowly dripping 0.8-1.5 mL of ethanolamine; putting the obtained solution into a drying oven, and aging for 6-14 h at 50-80 ℃ to form sol;
(102) soaking the carbon cloth in the sol for 8-20 s, then taking out, and putting the carbon cloth subjected to dip coating into a drying oven at 70-90 ℃ for heat treatment for 10-20 min;
(103) and (4) repeating the step (102) for a plurality of times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 400-480 ℃, and preserving the heat for 40-70 min, thereby preparing ZnO seed layers on two sides of the carbon cloth.
Further, the step (2) comprises the steps of:
(201) 0.8 to 1.8 g of Zn (CH)3COOH)2Adding the mixture into 30-60 ml of deionized water, and fully stirring to form Zn (CH)3COOH)2A solution of 3.2 to 5.3Adding g of NaOH into 25-50 mL of deionized water, fully stirring to form a NaOH solution, mixing the two solutions to form a mixed solution, and putting the mixed solution into a reaction kettle;
(202) vertically inserting the carbon cloth coated with the ZnO seed layer obtained in the step (1) into a reaction kettle filled with the mixed solution, performing hydrothermal reaction at 80-100 ℃ for 4-12 h, taking out the carbon cloth, and repeatedly washing the carbon cloth with deionized water until the pH value is 7;
(203) and drying the ZnO nano-rod arrays in a constant temperature box body at 50-70 ℃ for 8-12 h, thereby preparing the ZnO nano-rod arrays on the ZnO seed layers on the two side surfaces.
Further, the step (3) includes the steps of:
(301) fixing the sample prepared in the step (2) on a carrier of a coating chamber, wherein the distance from the target to the substrate is 7-10 cm;
(302) starting the mechanical pump and the molecular pump to vacuumize so that the background vacuum degree of the cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 300-400 ℃, starting a carrier to rotate at a rotating speed of 2-8 r/min, introducing Ar gas into the cavity chamber, controlling the flow to be 28-40 SCCM, adjusting the pressure intensity of the vacuum chamber to be 0.3-0.6 Pa, applying 30-90V negative bias to the sample, starting a titanium target power supply, adjusting the power to be 60-150W, and performing glow discharge cleaning on the target for 10-20 min;
(303) introducing N into the cavity chamber2And (3) controlling the flow of gas to be 1-6 SCCM, opening the sample baffle after the work is stable, and depositing TiN on the ZnO nanorod array on one side surface for 30-300 s, thereby preparing the ZnO @ TiN core-shell structure array cathode.
Compared with the prior art, the invention has the following beneficial effects:
1. the ZnO @ TiN core-shell nanorod array has the characteristics of low opening and threshold electric field, high emission current density and high field enhancement factor.
2. The ZnO @ TiN core-shell nanorod array has the characteristics of small work function, excellent electron transporting and conducting capacity and stable large-current work, and can be used in the field of vacuum field emission electron sources.
3. The ZnO @ TiN structure has the characteristics of core-shell interface matched oriented growth and excellent core-shell bonding strength.
4. The preparation process of the ZnO @ TiN cathode array is low in temperature, simple in procedure and convenient for large-scale industrial production.
Drawings
FIG. 1 is a flow chart of a preparation method of a ZnO @ TiN core-shell structure array cathode in an embodiment of the invention.
FIG. 2 is an XRD spectrum of a ZnO @ TiN core-shell nanorod sample in example two of the invention.
FIG. 3 is a SEM image of a ZnO @ TiN core-shell nanorod sample in accordance with a second embodiment of the present invention.
FIG. 4 is the EDS spectrum of the ZnO/TiN core-shell nanorod sample in example two of the present invention.
FIG. 5 is a TEM image of a ZnO/TiN core-shell nanorod sample in example two of the present invention.
FIG. 6 is a comparison graph of field emission characteristics of pure ZnO nanorods and ZnO @ TiN core-shell nanorod arrays in the examples of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
The invention provides a flexible ZnO @ TiN core-shell structure array cathode which comprises carbon cloth, wherein ZnO seed layers are coated on two side faces of the carbon cloth, ZnO nanorod arrays are arranged on the ZnO seed layers on the two side faces, the ZnO seed layers and ZnO nanorods have the same shape and structure when growing on the two side faces, TiN is deposited on the ZnO nanorod arrays on one side face, and therefore a core-shell structure array is formed. The flexible ZnO @ TiN core-shell structure array cathode is applied to a vacuum field emission electron source device.
The invention also provides a preparation method of the flexible ZnO @ TiN core-shell structure array cathode, which comprises the following steps of:
(1) and preparing ZnO seed layers on two sides of the carbon cloth by a sol-gel method. The method specifically comprises the following steps:
(101) 1.4-2.8 g of Zn (CH)3COOH)2Dissolving the mixture in 35-80 mL of absolute ethyl alcohol, stirring at room temperature for 20-40 min, and then slowly addingSlowly dripping 0.8-1.5 mL of ethanolamine; putting the obtained solution into a drying oven, and aging for 6-14 h at 50-80 ℃ to form sol;
(102) soaking the carbon cloth in the sol for 8-20 s, then taking out, and putting the carbon cloth subjected to dip coating into a drying oven at 70-90 ℃ for heat treatment for 10-20 min;
(103) and (4) repeating the step (102) for a plurality of times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 400-480 ℃, and preserving the heat for 40-70 min, thereby preparing ZnO seed layers on two sides of the carbon cloth.
(2) And preparing ZnO nanorod arrays on the ZnO seed layers on the two side faces by adopting a liquid phase method. The method specifically comprises the following steps:
(201) 0.8 to 1.8 g of Zn (CH)3COOH)2Adding the mixture into 30-60 ml of deionized water, and fully stirring to form Zn (CH)3COOH)2Adding 3.2-5.3 g of NaOH into 25-50 mL of deionized water, fully stirring to form a NaOH solution, mixing the two solutions to form a mixed solution, and putting the mixed solution into a reaction kettle;
(202) vertically inserting the carbon cloth coated with the ZnO seed layer obtained in the step (1) into a reaction kettle filled with the mixed solution, performing hydrothermal reaction at 80-100 ℃ for 4-12 h, taking out the carbon cloth, and repeatedly washing the carbon cloth with deionized water until the pH value is 7;
(203) and drying the ZnO nano-rod arrays in a constant temperature box body at 50-70 ℃ for 8-12 h, thereby preparing the ZnO nano-rod arrays on the ZnO seed layers on the two side surfaces.
(3) And depositing TiN on the ZnO nanorod array on one side surface by adopting a magnetron sputtering method, thereby preparing the ZnO @ TiN core-shell structure array cathode. The method specifically comprises the following steps:
(301) fixing the sample prepared in the step (2) on a carrier of a coating chamber, wherein the distance from the target to the substrate is 7-10 cm;
(302) starting the mechanical pump and the molecular pump to vacuumize so that the background vacuum degree of the cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 300-400 ℃, starting the carrier to rotate at the rotating speed of 2-8 r/min, introducing Ar gas into the cavity chamber, controlling the flow to be 28-40 SCCM, and adjusting the pressure of the vacuum chamber to be 0Applying negative bias voltage of 30-90V to the sample at 3-0.6 Pa, starting a titanium target power supply, adjusting the power to 60-150W, and performing glow discharge cleaning on the target for 10-20 min;
(303) introducing N into the cavity chamber2And (3) controlling the flow of gas to be 1-6 SCCM, opening the sample baffle after the work is stable, and depositing TiN on the ZnO nanorod array on one side surface for 30-300 s, thereby preparing the ZnO @ TiN core-shell structure array cathode.
The following examples further illustrate the preparation method of the ZnO @ TiN core-shell structure array cathode of the present invention.
Example 1
(1) Preparation of ZnO seed layer by sol-gel method
2.6 g of Zn (CH)3COOH)2Dissolved in 80 mL of ethanol, stirred at room temperature for 30 min, and then slowly dropped with 1.4 mL of ethanolamine, and then the resulting solution was put into a drying oven and aged at 70 ℃ for 14 h to form a sol. Then, a carbon cloth (3 cm. times.6 cm) was immersed in the sol for 15 seconds and taken out, and the carbon cloth after dip coating was heat-treated in a drying oven at 80 ℃ for 20 min. Repeating the above process for four times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 480 ℃, and preserving heat for 50 min.
(2) Liquid phase method for preparing ZnO nano-rod array
1.3 g of Zn (CH)3COOH)2Adding into 45 ml deionized water, stirring thoroughly to form Zn (CH)3COOH)2Solution 5.1 g of NaOH was added to 35 mL of deionized water and stirred well to form a NaOH solution. Then vertically inserting the carbon cloth coated with the seed layer in the step (1) into a furnace containing Zn (CH)3COOH)2And carrying out hydrothermal reaction on the carbon cloth and NaOH mixed solution in a reaction kettle (100 ml) at 85 ℃ for 10 h, taking out the carbon cloth, repeatedly washing the carbon cloth by using deionized water until the pH value is 7, and then drying the carbon cloth in a constant temperature box at 60 ℃ for 12 h.
(3) Preparation of ZnO @ TiN core-shell nanostructure by magnetron sputtering
Fixing the prepared sample on a carrier of a film coating chamber, wherein the distance from the target to the substrate is 8 cm, starting a mechanical pump and a molecular pump to vacuumize so that the background vacuum degree of the cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 330 ℃, starting a carrier to rotate at a rotating speed of 5 r/min, introducing Ar gas into the cavity chamber at a flow rate of 34.5 SCCM, adjusting the pressure of the vacuum chamber to 0.5 Pa, adding 60V negative bias to the sample, starting a power supply of a titanium target (with the purity of 99.99%), adjusting the power to 110W, and performing glow discharge cleaning on the target for 15 min; then introducing N into the cavity2Gas, nitrogen and nitrogen2The flow rate of the gas was controlled to 1.5 SCCM, and after the operation was stabilized, the sample shutter was opened to deposit TiN for about 120 seconds. The opening electric field of the obtained sample is 0.73V/mum, the threshold electric field is 0.95V/mum, the field enhancement factor is 11979, and the maximum emission current density is 6.10 mA/cm2。
Example 2
(1) Preparation of ZnO seed layer by sol-gel method
2.2 g of Zn (CH)3COOH)2Dissolved in 50 mL of ethanol, stirred at room temperature for 30 min, and then 1.2 mL of ethanolamine was added slowly dropwise, followed by putting the resulting solution in a drying oven and aging at 60 ℃ for 8 h to form a sol. Then, a carbon cloth (3 cm. times.6 cm) was immersed in the sol for 10 seconds, taken out, and the carbon cloth after dip coating was heat-treated in a drying oven at 90 ℃ for 10 min. Repeating the above process for four times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 450 ℃, and preserving heat for 60 min.
(2) Liquid phase method for preparing ZnO nano-rod array
1.2 g of Zn (CH)3COOH)2Adding into 40 ml deionized water, stirring thoroughly to form Zn (CH)3COOH)2Adding 4.6 g of NaOH into 30 mL of deionized water, and fully stirring to form a NaOH solution; then vertically inserting the carbon cloth coated with the seed layer in the step (1) into a furnace containing Zn (CH)3COOH)2And carrying out hydrothermal reaction on the carbon cloth and NaOH mixed solution in a reaction kettle (100 ml) at 95 ℃ for 6 h, taking out the carbon cloth, repeatedly washing the carbon cloth by using deionized water until the pH value is 7, and then drying the carbon cloth in a constant temperature box at 60 ℃ for 8 h.
(3) Preparation of ZnO @ TiN core-shell nanostructure by magnetron sputtering
Fixing the prepared sample on a carrier of a film coating chamber, wherein the distance between the target and the substrate is about 8cm, starting a mechanical pump and a molecular pump to vacuumize so that the background vacuum degree of the cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 350 ℃, starting a carrier to rotate at a rotating speed of 5 r/min, introducing Ar gas into the cavity chamber at the flow rate of 35 SCCM, adjusting the pressure intensity of the vacuum chamber to be 0.5 Pa, adding 60V negative bias to the sample, starting a power supply of a titanium target (the purity is 99.99 percent), adjusting the power to be 100W, and performing glow discharge cleaning on the target for 15 min; then introducing N into the cavity2Gas, nitrogen and nitrogen2The flow rate of the gas is controlled to be 1 SCCM, and after the operation is stable, a sample baffle is opened, and TiN is deposited for about 180 s. The opening electric field of the obtained sample is 0.59V/mum, the threshold electric field is 0.72V/mum, the field enhancement factor is 14752, and the maximum emission current density is 16.41 mA/cm2。
Example 3
(1) Preparation of ZnO seed layer by sol-gel method
1.6 g of Zn (CH)3COOH)2Dissolved in 40 mL of ethanol, stirred at room temperature for 30 min, and then 1.3 mL of ethanolamine was added slowly dropwise, followed by putting the resulting solution in a drying oven and aging at 70 ℃ for 12 hours to form a sol. Then, a carbon cloth (3 cm. times.6 cm) was immersed in the sol for 20 seconds and taken out, and the carbon cloth after dip coating was heat-treated in a drying oven at 80 ℃ for 15 min. Repeating the above process for four times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 400 ℃, and preserving heat for 70 min.
(2) Liquid phase method for preparing ZnO nano-rod array
1.1 g of Zn (CH)3COOH)2Adding into 40 ml deionized water, stirring thoroughly to form Zn (CH)3COOH)2Adding 4.7 g of NaOH into 35 mL of deionized water, and fully stirring to form a NaOH solution; then vertically inserting the carbon cloth coated with the seed layer in the step (1) into a furnace containing Zn (CH)3COOH)2And carrying out hydrothermal reaction on the carbon cloth and NaOH mixed solution in a reaction kettle (100 ml) at 90 ℃ for 8 h, taking out the carbon cloth, repeatedly washing the carbon cloth by using deionized water until the pH value is 7, and then drying the carbon cloth in a constant temperature box at 70 ℃ for 10 h.
(3) Preparation of ZnO @ TiN core-shell nanostructure by magnetron sputtering
The above steps are preparedThe sample is fixed on a carrier of a film coating chamber, the distance between a target material and a substrate is about 8 cm, a mechanical pump and a molecular pump are started to pump vacuum so that the background vacuum degree of a cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 380 ℃, starting a carrier to rotate at a rotating speed of 5 r/min, introducing Ar gas into the cavity chamber at a flow rate of 34 SCCM, adjusting the pressure of the vacuum chamber to 0.5 Pa, adding 60V negative bias to the sample, starting a power supply of a titanium target (with the purity of 99.99 percent), adjusting the power to 100W, and performing glow discharge cleaning on the target for 15 min; then introducing N into the cavity2Gas, nitrogen and nitrogen2The flow rate of the gas is controlled to be 2 SCCM, and after the operation is stable, a sample baffle is opened, and TiN is deposited for about 300 s. The opening electric field of the obtained sample is 0.64V/mum, the threshold electric field is 0.93V/mum, the field enhancement factor is 13215, and the maximum emission current density is 6.08 mA/cm2。
FIG. 2 is an XRD spectrum of a ZnO @ TiN core-shell nanorod sample in example two of the invention. As can be seen from fig. 2, all diffraction peaks correspond to ZnO of wurtzite structure except that the peak position is from the carbon cloth substrate, and no TiN peak occurs probably because the peak position of the core-shell structure cannot be changed due to the small amount of TiN.
FIG. 3 is a SEM image of a ZnO @ TiN core-shell nanorod sample in accordance with a second embodiment of the present invention. FIGS. 3(a) and 3(b) are pure ZnO nanorods; 3(c) and 3(d) are ZnO @ TiN core-shell nanorods. As can be seen from FIGS. 3(a) and 3(b), the prepared ZnO nanorod has the length of 3.5-5 μm, the diameter of 25-35 nm, the height-diameter ratio is large, the needle-shaped tip is obvious, and the nanorod grows radially in three dimensions on the carbon cloth substrate, so that the shielding effect of an electric field is effectively reduced; FIGS. 3(c) and 3(d) show the ZnO @ TiN core-shell structure with TiN shell layer, and it can be seen from the figure that the arrangement structure of the ZnO @ TiN core-shell structure on the carbon cloth is not obviously changed except for the slightly increased diameter of the nano-rod after TiN is sputtered.
FIG. 4 is the EDS spectrum of the ZnO/TiN core-shell nanorod sample in example two of the present invention. As can be seen from the EDS spectrum, the ZnO/TiN elements are composed of C, Zn, O, Ti and N, the C peak comes from the carbon cloth substrate, the Zn and O elements come from the ZnO nano-rod grown hydrothermally, and the Ti and N elements are TiN shell layers formed by sputtering; no other impurity elements exist in EDS peaks, which shows that the synthesized ZnO/TiN material has higher purity.
FIG. 5 is a TEM image of the ZnO/TiN core-shell nanorod sample measured after the ZnO/TiN core-shell nanorod sample is ultrasonically dispersed in an ethanol solution with power of 350W for more than 2h and dropped on a copper mesh in example II of the present invention: the 5(a) picture is a low-magnification picture, and the inset picture is a high-magnification picture of the ZnO nanorod. And the picture 5(b) is a single ZnO/TiN core-shell nanorod TEM picture, and the inset picture is a selected area diffraction picture of a TiN shell layer. As can be seen from FIG. 5(a), TiN nanorods are vertically epitaxially grown on the surface of the ZnO nanorods and are uniformly distributed; besides, the TiN nanorods do not obviously fall off after high-power and long-time ultrasound, which shows that the core-shell binding force is better. The inset is a high-power TEM photograph of the ZnO rod, and the clear stripe structure indicates that the synthesized ZnO nanorod is single-crystalline. As can be seen from FIG. 5(b), the TiN nanorods with fine tips are uniformly distributed on the surface of ZnO, and the unique morphology and structure advantages can fully exert the advantages of synergistic enhancement as the cathode. The inset is a selected area diffraction photo of the shell TiN, and the clear annular structure shows that the synthesized TiN is a polycrystalline structure.
And (3) field emission testing:
the field emission test of the sample is to measure the vacuum degree of the cavity at 6 multiplied by 10-5Pa, room temperature, the space between the anode and the cathode is fixed to 1080 mu m in the test, the vacuumizing process of the field emission test system is completed through a mechanical pump and a molecular pump, the cathode is a one-dimensional ZnO @ TiN core-shell nanorod array grown on carbon cloth, the corresponding anode is a copper probe coated with low-pressure fluorescent powder, and the electronic emission of the sample is measured by utilizing a Gishley high-pressure source test system (model: 2290E-6485) to obtain an I-V characteristic curve. Turning on the electric field (E to) The current density which is specified to be emitted is 10 muA/cm2The required electric field strength; and threshold electric field: (E th) The current density for emission reaches 1mA/cm2The required electric field strength; the field enhancement factor is based on the F-N theory:
and (4) calculating. For maximum emission current densityJ maxAnd (4) showing. FIG. 6 and Table 1 compare the field emission characteristics of pure ZnO nanorods and ZnO @ TiN core-shell nanorod arrays。
Titanium nitride (TiN) is a metalloid material with low work function (2.8 eV), high melting point (2980 ℃), excellent heat conduction and stable performance. The ZnO nanorod has the characteristics of easy shape control and large height-diameter ratio, ZnO with large height-diameter ratio is used as a core, TiN with low work function is used as a shell, the advantages of the ZnO and the TiN are fully combined, and the synergistic effect of the ZnO and the TiN is utilized to prepare the ZnO @ TiN core-shell array cathode with excellent performance.
The TiN nanorod prepared by the method grows on the surface of the ZnO nanorod in a vertical epitaxial mode to form a unique ZnO @ TiN core-shell nanorod structure. Meanwhile, the ZnO @ TiN core-shell array cathode combines the advantages of small curvature radius, low work function, good electron and heat conduction of the TiN nanorods and three-dimensional radial growth of the ZnO nanorods on carbon cloth with larger height-diameter ratio. The synergistic effect of the two not only reduces the shielding effect of an electric field, but also effectively increases electron emission points of a ZnO @ TiN core-shell structure. In addition, because the interface matching between the ZnO core and the TiN shell is good, the ZnO @ TiN core-shell structure grown by vertical epitaxy has excellent binding force (experiments show that the ZnO @ TiN nanorod rods do not obviously fall off in the case of ultrasonic processing for more than 2 hours at 350W in an ethanol solution).
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.
Claims (6)
1. The flexible ZnO @ TiN core-shell structure array cathode is characterized by comprising carbon cloth, ZnO seed layers are coated on two side faces of the carbon cloth, ZnO nanorod arrays are arranged on the ZnO seed layers on the two side faces, TiN is deposited on the ZnO nanorod arrays on one side face, and a core-shell structure array is formed.
2. The flexible ZnO @ TiN core-shell structure array cathode according to claim 1, which is applied to a vacuum field emission electron source device.
3. The preparation method of the flexible ZnO @ TiN core-shell structure array cathode according to claim 1 or 2, characterized by comprising the following steps:
(1) preparing ZnO seed layers on two side surfaces of the carbon cloth by a sol-gel method;
(2) preparing ZnO nanorod arrays on the ZnO seed layers on the two side faces by a liquid phase method;
(3) and depositing TiN on the ZnO nanorod array on one side surface by adopting a magnetron sputtering method, thereby preparing the ZnO @ TiN core-shell structure array cathode.
4. The preparation method of the flexible ZnO @ TiN core-shell structure array cathode according to claim 3, wherein the step (1) comprises the following steps:
(101) 1.4-2.8 g of Zn (CH)3COOH)2Dissolving in 35-80 mL of absolute ethyl alcohol, stirring at room temperature for 20-40 min, and slowly dripping 0.8-1.5 mL of ethanolamine; putting the obtained solution into a drying oven, and aging for 6-14 h at 50-80 ℃ to form sol;
(102) soaking the carbon cloth in the sol for 8-20 s, then taking out, and putting the carbon cloth subjected to dip coating into a drying oven at 70-90 ℃ for heat treatment for 10-20 min;
(103) and (4) repeating the step (102) for a plurality of times, putting the carbon cloth coated with the gel into a muffle furnace, annealing to 400-480 ℃, and preserving the heat for 40-70 min, thereby preparing ZnO seed layers on two sides of the carbon cloth.
5. The preparation method of the flexible ZnO @ TiN core-shell structure array cathode according to claim 3, wherein the step (2) comprises the following steps:
(201) 0.8 to 1.8 g of Zn (CH)3COOH)2Adding the mixture into 30-60 ml of deionized water, and fully stirring to form Zn (CH)3COOH)2Adding 3.2-5.3 g of NaOH into 25-50 mL of deionized water, fully stirring to form a NaOH solution, mixing the two solutions to form a mixed solution, and putting the mixed solution into a reaction kettlePerforming the following steps;
(202) vertically inserting the carbon cloth coated with the ZnO seed layer obtained in the step (1) into a reaction kettle filled with the mixed solution, performing hydrothermal reaction at 80-100 ℃ for 4-12 h, taking out the carbon cloth, and repeatedly washing the carbon cloth with deionized water until the pH value is 7;
(203) and drying the ZnO nano-rod arrays in a constant temperature box body at 50-70 ℃ for 8-12 h, thereby preparing the ZnO nano-rod arrays on the ZnO seed layers on the two side surfaces.
6. The preparation method of the flexible ZnO @ TiN core-shell structure array cathode according to claim 3, wherein the step (3) comprises the following steps:
(301) fixing the sample prepared in the step (2) on a carrier of a coating chamber, wherein the distance from the target to the substrate is 7-10 cm;
(302) starting the mechanical pump and the molecular pump to vacuumize so that the background vacuum degree of the cavity is lower than 3 multiplied by 10-4Pa, opening a heating system, heating to 300-400 ℃, starting a carrier to rotate at a rotating speed of 2-8 r/min, introducing Ar gas into the cavity chamber, controlling the flow to be 28-40 SCCM, adjusting the pressure intensity of the vacuum chamber to be 0.3-0.6 Pa, applying 30-90V negative bias to the sample, starting a titanium target power supply, adjusting the power to be 60-150W, and performing glow discharge cleaning on the target for 10-20 min;
(303) introducing N into the cavity chamber2And (3) controlling the flow of gas to be 1-6 SCCM, opening the sample baffle after the work is stable, and depositing TiN on the ZnO nanorod array on one side surface for 30-300 s, thereby preparing the ZnO @ TiN core-shell structure array cathode.
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