WO2022151349A1 - 碳纳米锥功能化针尖及其制备方法 - Google Patents

碳纳米锥功能化针尖及其制备方法 Download PDF

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WO2022151349A1
WO2022151349A1 PCT/CN2021/072144 CN2021072144W WO2022151349A1 WO 2022151349 A1 WO2022151349 A1 WO 2022151349A1 CN 2021072144 W CN2021072144 W CN 2021072144W WO 2022151349 A1 WO2022151349 A1 WO 2022151349A1
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Prior art keywords
tip
carbon
needle
needle tip
carbon nanocone
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PCT/CN2021/072144
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English (en)
French (fr)
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徐建勋
赵宇亮
葛逸飞
卢明明
王嘉豪
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国家纳米科学中心
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Priority to JP2022577165A priority Critical patent/JP2023529233A/ja
Priority to PCT/CN2021/072144 priority patent/WO2022151349A1/zh
Priority to EP21918556.8A priority patent/EP4159670A4/en
Publication of WO2022151349A1 publication Critical patent/WO2022151349A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
    • B81C1/00023—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems without movable or flexible elements
    • B81C1/00111—Tips, pillars, i.e. raised structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01J1/3042—Field-emissive cathodes microengineered, e.g. Spindt-type
    • H01J1/3044—Point emitters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2203/00—Basic microelectromechanical structures
    • B81B2203/03—Static structures
    • B81B2203/0361—Tips, pillars
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • H01J2201/30403—Field emission cathodes characterised by the emitter shape
    • H01J2201/30407—Microengineered point emitters
    • H01J2201/30415—Microengineered point emitters needle shaped
    • 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
    • H01J2201/30403—Field emission cathodes characterised by the emitter shape
    • H01J2201/30426—Coatings on the emitter surface, e.g. with low work function materials
    • 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
    • H01J2201/30453—Carbon types
    • H01J2201/30461—Graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2235/00—X-ray tubes
    • H01J2235/06—Cathode assembly
    • H01J2235/062—Cold cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/063—Electron sources
    • H01J2237/06325—Cold-cathode sources
    • H01J2237/06341—Field emission

Definitions

  • the present application relates to the technical field of functionalization of metal materials, in particular to a carbon nanocone functionalized needle tip and a preparation method thereof.
  • Electron emission sources are the core components of vacuum electronic equipment, and are widely used in X-ray sources, microwave sources, mass spectrometer ionization chambers, field emission displays and other fields. Among them, the electron source with high brightness and large beam current can be used as the light source of electron microscope, electron beam exposure equipment, etc.
  • nanomaterials provide a wealth of materials for the development of electron guns.
  • the preparation methods of nanomaterial-functionalized tips are mainly divided into two categories, namely direct growth method and micro-nano assembly method.
  • the direct growth method is to directly synthesize and grow nanomaterials on the needle tip substrate. At present, this method cannot control the length, diameter, orientation and other parameters of nanomaterials.
  • the micro-nano assembly method is to operate a high-precision three-dimensional manipulation device under a microscope to control the precise movement of the probe, and realize the assembly of specific nanomaterials and needle tip substrates. This method has high controllability and is more conducive to controlling the structure and orientation of nanomaterials.
  • the tip of the electron gun needle must also keep its surface free of contaminants and structural defects. Both contamination and structural defects can cause problems such as uncontrollable emission of electron beams, poor stability and even failure of the electron gun.
  • the existence of surface contaminants mainly amorphous carbon, hydrocarbons, etc.
  • purification of the carbon nanocone tip is necessary for its application in electron sources.
  • the above-disclosed patent documents do not include the purification method of the carbon nanocone tip, and the usual purification treatment methods, such as air oxidation method, wet hydrogen treatment method, etc., will produce a large number of structures while removing the pollutants on the surface of the carbon nanocone. Defect [7] . So far, there is no report on the method of obtaining clean and complete tip structures of carbon nanocone tips.
  • the present application aims to solve at least one of the technical problems existing in the prior art.
  • the present application provides a carbon nanocone functionalized needle tip, wherein the front end of the needle tip base is decorated with carbon nanocone;
  • the carbon nanocone is a cone-shaped nanocarbon material composed of a layered graphite structure
  • the material of the needle tip base is metal, selected from one or more of tungsten, iron, cobalt, nickel, and titanium
  • the tail end of the carbon nanocone is connected with the needle tip base to form a covalent bond interface, and the orientation of the tip is consistent with the orientation of the central axis of the needle tip.
  • the surface of the tip of the carbon nanocone is clean and the structure of the graphite layer is complete.
  • the present application provides a method for preparing a carbon nanocone functionalized needle tip, comprising the following steps:
  • the needle body is brought into contact with another metal body, and an instantaneous current is applied between the needle body and the metal body, so that the outer graphite layer of the carbon nanocone and the contaminants are removed.
  • step S101 specifically includes: using a micro-nano operating arm to control the front end of the needle tip base to extend into the interior of the carbon nanocone to adhere the carbon nanocone to the front end of the needle tip base,
  • the needle tip base is brought into contact with another metal body, a voltage is applied between the metal body and the needle tip base, a current is passed through the needle tip base, and the front end portion of the needle tip base is heated and adhered to the The carbon nanocones are combined.
  • both the needle body and the other metal body are fixed on a micro-nano operating arm, and the operating arm is used to control their movement under microscope observation.
  • step S102 it further includes: controlling the carbon nanocone tip of the needle body to contact the other metal body to form an electrical path, and the magnitude of the instantaneous current is 0.01-10 mA.
  • step S102 it further includes: controlling the side surface of the needle body to contact the other metal body to form an electrical path, and the position where the metal body contacts the needle body is away from the tip of the needle tip
  • the distance is 0.01-1 ⁇ m, and the magnitude of the instantaneous current is 1-100 mA.
  • the present application provides another method for preparing a carbon nanocone functionalized needle tip, comprising the following steps:
  • the weak oxidant is carbon dioxide or water.
  • step S201 specifically includes: using a micro-nano operating arm to control the front end of the needle tip base to extend into the interior of the carbon nanocone to adhere the carbon nanocone to the front end of the needle tip base,
  • the needle tip base is brought into contact with another metal body, a voltage is applied between the metal body and the needle tip base, a current is passed through the needle tip base, and the front end portion of the needle tip base is heated and adhered to the The carbon nanocones are combined.
  • step S202 the needle body and the other metal body are both fixed on the micro-nano operating arm, and the operating arm is used to control their movement under microscope observation.
  • step S202 it further includes: contacting the side surface of the needle body with the other metal body, and applying a continuous current between the needle body and the metal body, so that the tip of the needle tip is A localized high temperature is reached and reacts with the active species.
  • the method further includes: installing the needle tip on a needle tip holding device, placing it in a vacuum tube furnace, feeding carbon dioxide or water vapor, and raising the temperature to a target temperature to remove the needle tip. Contamination on the tip surface.
  • the carbon nanocone-functionalized needle tips obtained by the preparation methods of the embodiments of the present application can provide stable, large-beam controllable electron emission, Realize the application of electron emission source; realize the covalent bond interface connection between the carbon nanocone and the metal tip substrate, and its excellent mechanical strength and electrical conductivity ensure the stability of the carbon nanocone tip in the electron emission process; carbon nanocone The orientation of the tip coincides with the orientation of the overall central axis of the needle tip, which ensures the controllability of the active emission site of the carbon nanocone needle tip during electron emission; and the carbon nanocone functionalized needle tip prepared in the examples of this application has clean,
  • the carbon nanocone tip with a complete graphite layered structure avoids the damage or even failure of the tip structure caused by the electron emission noise caused by the contaminants on the tip surface and the uncontrollable emission current.
  • Fig. 1 (a) is the overall structure diagram of the carbon nanocone provided by the embodiment of the present application.
  • Figure 1(b) is a high-resolution transmission electron microscope photo of the carbon nanocone tip provided in the embodiment of the present application, showing the layered graphite structure of the carbon nanocone, and the arrows in the figure indicate the pollutants on the surface of the carbon nanocone;
  • Figure 2(a) is a side view of a metal needle tip mounted on a micro-nano manipulator in a scanning electron microscope, and the arrows indicate three micro-nano manipulators;
  • Figure 2(b) is a top view of a metal needle tip mounted on a micro-nano manipulator in a scanning electron microscope;
  • Figure 3(a) is a scanning electron microscope photograph of the tip of the carbon nanocone functionalized needle tip (#1) in contact with another metal body (#2) provided in the embodiment of the present application;
  • Figure 3(b) is a TEM photo of the clean carbon nanocone tip after transient current treatment
  • Figure 4(a) is a scanning electron microscope photograph of the side surface of the carbon nanocone functionalized needle tip (#1) in contact with another metal body (#2) provided in the embodiment of the present application;
  • Figure 4(b) is a TEM photo of the clean carbon nanocone tip after transient current treatment
  • Figure 4(c) is a field emission curve diagram of the prepared carbon nanocone functionalized tip
  • Fig. 4(d) is the electron microscope photograph of field emission test with a certain electric field applied between the carbon nanocone functionalized tip (#1) and the anode (#3);
  • Fig. 5 (a) is the scanning electron microscope photograph of the carbon nanocone functionalized needle tip provided in the embodiment of the present application;
  • FIG. 5( b ) is a structural diagram of a clean and complete graphite layer of the carbon nanocone provided by the embodiment of the present application.
  • Fig. 6 (a) is the scanning electron microscope photograph of the carbon nanocone functionalized needle tip provided in the embodiment of the present application;
  • FIG. 6( b ) is a structural diagram of a clean and complete graphite layer of the carbon nanocone provided by the embodiment of the present application.
  • FIG. 1( a ) is an overall structural diagram of the carbon nanocone provided by the embodiment of the present application
  • FIG. 1( b ) is a high-resolution transmission electron microscope photograph of the tip of the carbon nanocone provided by the embodiment of the present application.
  • the present application provides a carbon nanocone functionalized needle tip, wherein the front end of the needle tip base is modified by carbon nanocone;
  • the carbon nanocone is a cone-shaped nano-carbon material composed of a layered graphite structure
  • the material of the needle tip base is metal, selected from one or more of tungsten, iron, cobalt, nickel, and titanium
  • the tail end forms a covalent interface with the tip base and the tip is oriented in the same direction as the central axis of the tip.
  • the surface of the carbon nanocone tip is clean and the graphite layer structure is complete, free of contamination and damage.
  • the present application provides a method for preparing and purifying carbon nanocone functionalized needle tips.
  • the assembly of carbon nanocones and metal tip bases adopts the method described in the published patent ZL201610091160.0.
  • the front end of the metal needle tip base is controlled by the micro-nano manipulator arm to protrude into the interior of the carbon nanocone, the carbon nanocone is adhered to the front end of the needle tip base, and then the needle tip base is contacted with another metal body.
  • a voltage is applied between the tip bases, causing an electric current to pass through the tip bases, and the tip of the needle is heated and combined with the adhered carbon nanocones.
  • the distance between the position where the metal body contacts the base of the needle tip and the tip of the needle tip is 0.2-100 ⁇ m, and the current passing through the needle body is 0.01-5A.
  • the purification method proposed in this application refers to the removal of pollutants such as amorphous carbon and hydrocarbons on the surface of carbon nanocones by instantaneous current ablation method or selective chemical reaction method.
  • the preparation of carbon nanocone functionalized tip by instantaneous current ablation includes the following steps:
  • the needle body is brought into contact with another metal body, and an instantaneous current is applied between the needle body and the metal body, so that the outer graphite layer of the carbon nanocone is removed together with the contaminants.
  • step S102 both the needle body and the other metal body are fixed on the micro-nano manipulator arm, and the manipulator arm is used to control their movement under microscope observation, as shown in Figure 2(a) and Figure 2(b).
  • step S102 it also includes: controlling the carbon nanocone tip of the needle body to contact another metal body to form an electrical path, and the magnitude of the instantaneous current is 0.01-10 mA.
  • step S102 it also includes: controlling the side surface of the needle body to contact another metal body to form an electrical path, the distance between the position where the metal body contacts the needle body and the tip of the needle tip is 0.01-1 ⁇ m, and the magnitude of the instantaneous current is 1 ⁇ 100mA.
  • the possible mechanism for removing the outer graphite layer of the carbon nanocone with instantaneous current is as follows: Since the carbon nanocone has a multi-layer graphite structure, the interlayer resistivity (10 - 3 ⁇ m) of graphite is 1000 times the resistivity (10 -6 ⁇ m). Therefore, the instantaneous current will preferentially pass through the outer graphite layer to cause the rupture of the carbon-carbon bond in the layer, and combined with the Joule heat generated by the instantaneous current, the outer graphite layer and the surface pollutants will crack and volatilize into the vacuum, and finally a clean inner graphite will be obtained. layer structure. Furthermore, in this embodiment, step S102 can be repeated many times to controllably remove a certain number of outer graphite layers to obtain a clean carbon nanocone functionalized needle tip with a sharper tip.
  • the preparation of carbon nanocone functionalized tip by selective chemical reaction method includes the following steps:
  • step S202 both the needle body and the other metal body are fixed on the micro-nano manipulator arm, and the manipulator arm is used to control their movement under microscope observation, as shown in Figure 2(a) and Figure 2(b).
  • step S202 it also includes: contacting the side surface of the needle body with another metal body, applying a continuous current between the needle body and the metal body, so that the tip of the needle tip reaches a local high temperature and reacts with the active material.
  • the distance between the position where the metal body contacts the needle body and the tip of the needle tip is 0.2-100 ⁇ m, and the current passing through the needle body is 0.01-5A.
  • Carbon dioxide or water vapor is introduced into the SEM sample chamber by using the gas circuit control valve of the environmental SEM, and the pressure range of the active gas in the SEM sample chamber is 10-2000Pa.
  • step S202 it also includes: installing the needle tip on the needle tip holding device, placing it in a vacuum tube furnace, feeding carbon dioxide or water vapor and raising the temperature to a target temperature to remove contaminants on the surface of the needle tip.
  • the flow rate of carbon dioxide or water vapor is 100-1000 sccm
  • the heating rate is 1-10°C/min
  • the target temperature is 450°C-750°C
  • the holding time is 30-600min.
  • the amorphous carbon and hydrocarbon pollutants on the surface of the carbon nanocone have higher chemical reactivity than the graphite structure of the carbon nanocone, and will preferentially react with various oxidants and convert into gaseous products to purify the surface. the goal of.
  • mild oxidizing agents such as carbon dioxide or water vapor are used in the solution proposed in this application.
  • Carbon dioxide reacts with amorphous carbon and hydrocarbon pollutants to generate carbon monoxide
  • water vapor reacts with amorphous carbon and hydrocarbon pollutants to generate carbon monoxide and hydrogen
  • a clean carbon nanocone tip with a complete graphite structure is obtained.
  • the micro-nano operating arm selects the product of Kleindiek Nanotechnik company
  • the scanning electron microscope selects the Quanta 200 type scanning electron microscope of Thermo Fisher company
  • the transmission electron microscope selects the F20 type transmission electron microscope of Thermo Fisher company.
  • two tungsten needles are fixed on two micro-nano operating arms; both the micro-nano operating arms and the carbon nanocone samples are placed in the scanning electron microscope.
  • a tungsten needle (#2) was approached to its side wall from a distance of 50 ⁇ m from the top of the #1 metal tungsten needle tip, and a voltage of 60V was applied between #1 and #2 to generate an arc. The arc caused the tip of the #2 tungsten needle to melt into a spherical shape.
  • the tip of needle #1 was extended into the apex of the selected carbon nanocone and was in contact with the carbon nanocone and adhered to the apex of the needle tip.
  • the ball at the tip of the #2 tungsten needle was brought into contact with the side surface of the above-mentioned tungsten needle tip (#1), and the contact position was 2 ⁇ m from the topmost tip of the needle tip #1.
  • the duration of the power-on is 0.1ms.
  • the top of the metal tungsten tip (#1) is melted, and the molten metal tungsten automatically enters and fills the inner space of the carbon nanocone, as shown in Figure 3
  • two tungsten needles are fixed on two micro-nano operating arms; both the micro-nano operating arms and the carbon nanocone samples are placed in the scanning electron microscope.
  • a tungsten needle (#2) was approached to its side wall from a distance of 50 ⁇ m from the top of the #1 metal tungsten needle tip, and a voltage of 60V was applied between #1 and #2 to generate an arc. The arc caused the tip of the #2 tungsten needle to melt into a spherical shape.
  • the tip of needle #1 was extended into the apex of the selected carbon nanocone and was in contact with the carbon nanocone and adhered to the apex of the needle tip. After that, the ball at the tip of the #2 tungsten needle was brought into contact with the side surface of the above-mentioned tungsten needle tip (#1), and the contact position was 3 ⁇ m from the topmost tip of the needle tip #1. Apply a voltage to the two tungsten tips to generate a current of 3A for 0.1ms, the top of the metal tungsten tip (#1) melts, and the molten metal tungsten automatically enters and fills the inner space of the carbon nanocone, as shown in Figure 4 The #1 functionalized tip shown in (a).
  • two tungsten needles are fixed on two micro-nano operating arms; both the micro-nano operating arms and the carbon nanocone samples are placed in the scanning electron microscope.
  • a tungsten needle (#2) was approached to its side wall from a distance of 50 ⁇ m from the top of the #1 metal tungsten needle tip, and a voltage of 60V was applied between #1 and #2 to generate an arc. The arc caused the tip of the #2 tungsten needle to melt into a spherical shape.
  • the tip of needle #1 was extended into the apex of the selected carbon nanocone and was in contact with the carbon nanocone and adhered to the apex of the needle tip. After that, the ball at the tip of the #2 tungsten needle was brought into contact with the side surface of the above-mentioned tungsten needle tip (#1), and the contact position was 3 ⁇ m from the topmost tip of the needle tip #1.
  • the electron microscope was switched to the environmental scanning electron microscope mode, and a carbon dioxide atmosphere was introduced, and the carbon dioxide pressure in the sample chamber was controlled to 1000 Pa through the air pressure regulating valve of the electron microscope.
  • the contact position between the ball of the #2 tungsten needle and the side of the #1 carbon nanocone tip remained unchanged, and a current of 0.6A was applied to the two needles for 10 minutes.
  • the carbon nanocone functionalized tip was quickly withdrawn to avoid electron beam irradiation.
  • nitrogen was put in, and the carbon nanocone tip was taken out.
  • the high-resolution morphology of the carbon nanocone tip was observed by transmission electron microscopy, as shown in Figure 5(b), it can be seen that the carbon nanocone has a clean and complete graphite layer structure.
  • the preparation method of the carbon nanocone functionalized needle tip (as shown in FIG. 6( a )) is the same as that in Example 3.
  • the carbon nanocone functionalized needle tip is fixed on a needle tip holding device made of ceramic material, with the needle tip part facing upward, and placed in the heating area of the vacuum tube furnace.
  • the target temperature of the tube furnace was set to 500 °C, the heating rate was 1 °C/min, and the holding time was 60 min.
  • carbon dioxide was introduced into the tube furnace, and the flow rate of carbon dioxide was adjusted to 500 sccm. After the heating was completed, the temperature was naturally cooled to room temperature, nitrogen was introduced, and the carbon nanocone tip was taken out to observe its structural characteristics under a transmission electron microscope, as shown in Figure 6(b).

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Abstract

本申请提供一种碳纳米锥功能化针尖，针尖基底的前端被碳纳米锥修饰；其中，所述碳纳米锥是由层状石墨结构构成的锥形的纳米碳材料；所述针尖基底的材料为金属，选自钨、铁、钴、镍、钛中的一种或多种；所述碳纳米锥的尾端与所述针尖基底形成共价键的界面连接且尖端取向与针尖整体的中心轴取向一致。本申请还提供一种碳纳米锥功能化针尖的制备方法。本申请提供的碳纳米锥尖端取向与针尖整体中心轴的取向重合，保证了碳纳米锥针尖在电子发射时活性发射位点的可控性；所制备的碳纳米锥功能化针尖具有洁净的、完整石墨层状结构的碳纳米锥尖端，该针尖结构特征避免了尖端表面污染物造成的电子发射噪音及不可控发射电流所引发的针尖结构破坏甚至失效。

Description

碳纳米锥功能化针尖及其制备方法 技术领域
本申请涉及金属材料功能化技术领域，尤其涉及一种碳纳米锥功能化针尖及其制备方法。
背景技术
电子发射源是真空电子类设备的核心部件，在X射线源、微波源、质谱仪电离腔、场发射显示器等领域有广泛的应用。其中高亮度、大束流的电子源可作为电子显微镜、电子束曝光设备等的光源。
近年来，材料科学和纳米技术的蓬勃发展大力促进了新型电子发射源的研究 [1-3]。碳纳米管因其特殊的结构和性质曾被广泛寄希望于场发射电子源方面的应用。以De Jonge等人的工作为代表的初期研究结果显示了碳纳米管针尖在较低的析出电压下即可获得高亮度、单色性好的电子束 [4,5]。然而，碳纳米管针尖的制备方法可控性低，无法保证碳纳米管尖端(有效电子发射位点)的结构和取向，同时碳纳米管和金属W针尖本体的物理粘附连接不牢固。这些问题导致了碳纳米管针尖无法作为实用化的电子枪。2016年，日本国立物质材料研究所的Zhang等人制备并表征了LaB 6单晶纳米线的场发射性能，显示了优异的电子束单色性和发射稳定性 [2]。然而，和碳纳米管类似，一维纳米线在组装至金属针尖本体的制备过程中很难保证纳米线尖端的取向以及纳米线与针尖本体之间界面结构的机械和电学性能。2018年，新加坡国立大学的Khursheed课题组在Ni针尖表面利用化学气相沉积法生长石墨烯并展示了该功能化针尖极低的表面功函数和较高的电子束亮度 [6]。然而，由于在Ni针尖尖端表面(非单一晶面)生长的石墨烯无法避免大量结构缺陷的存在，该功能化针尖的电子发射束流稳定性差、噪音很大(约30％)。综上而言，纳米材料为电子枪的研制提供了丰富的材料，然而为了实现纳米材料功能化电子枪的应用，就必须实现针尖制备方法的精准控制，保证界面结构的性能、针尖尖端的取向、尖端晶体结构的完整性和洁净。
纳米材料功能化针尖的制备方法主要分为两类，即直接生长法和微纳组装法。直接生长法即在针尖基底上直接进行纳米材料的合成生长，这种 方法目前无法控制纳米材料的长度、直径、取向等参数。微纳组装法是在显微镜下操作高精度的三维操纵设备控制探针的精密移动，实现特定纳米材料与针尖基底的组装，该方法可控性高，更利于控制纳米材料的结构和取向。本发明人利用微纳操作结合原位电流加热的方法制备得到一种锥形纳米碳材料功能化针尖(中国专利ZL201610091160.0、美国专利US10823758B2)。与之前的纳米材料功能化针尖相比，这种锥形纳米碳材料功能化针尖能保证纳米材料针尖尖端取向与针尖基底的轴向完全一致，并且纳米材料和针尖基底之间的界面具有优异的机械强度以及导电性能。
如上所述，电子枪针尖尖端必须同时保证其表面没有污染物和结构缺陷的存在。污染物和结构缺陷均会造成发射电子束的不可控、稳定性差甚至电子枪失效等问题。碳纳米锥的合成、保存及微纳组装过程中无法避免表面污染物(主要为无定型碳、碳氢化合物等)的存在(见图1)。因此，碳纳米锥针尖的净化对于其在电子源的应用是必需的。上述公开的专利文献中未包含碳纳米锥尖端的净化方法，而通常的净化处理方法，如空气氧化法、湿氢处理法等，在去除碳纳米锥表面污染物的同时，会产生大量的结构缺陷 [7]。目前为止，尚未有可获得洁净且尖端结构完整的碳纳米锥针尖方法的报道。
参考文献
1.De Jonge,N.；Lamy,Y.；Schoots,K.；Oosterkamp,T.H.:High brightness electron beam from a multi-walled carbon nanotube.Nature 2002,420,393-395.
2.Zhang,H.；Tang,J.；Yuan,J.；Yamauchi,Y.；Suzuki,T.T.；Shiya,N.；Nakajima,K.；Qin,L.-C.:An ultrabright and monochromatic electron point source made of a LaB6 nanowire.Nature Nanotechnology 2015.
3.Narasimha,K.T.；Ge,C.；Fabbri,J.D.；Clay,W.；Tkachenko,B.A.；Fokin,A.A.；Schreiner,P.R.；Dahl,J.E.；Carlson,R.M.K.；Shen,Z.；Melosh,N.A.:Ultralow effective work function surfaces using diamondoid monolayers.Nature Nanotechnology 2015.
4.De Jonge,N.:Carbon Nanotube Electron Sources for Electron Microscopes.Adv Imag Elect Phys 2009,156,203-233.
5.De Jonge,N.；Bonard,J.M.:Carbon nanotube electron sources and applications.Philos T R Soc A 2004,362,2239-2266.
6.Shao,X.Y.；Srinivasan,A.；Ang,W.K.；Khursheed,A.:A high-brightness large-diameter graphene coated point cathode field emission electron source.Nature Communications 2018,9,1288.
7.Huang,W.；Xu,J.X.；Lu,X.:Tapered carbon nanocone tips obtained by dynamic oxidation in air.RSC Adv.2016,6,25541.
发明内容
本申请旨在至少解决现有技术中存在的技术问题之一。
为此，一方面，本申请提供一种碳纳米锥功能化针尖，其中，针尖基底的前端被碳纳米锥修饰；
其中，所述碳纳米锥是由层状石墨结构构成的锥形的纳米碳材料；所述针尖基底的材料为金属，选自钨、铁、钴、镍、钛中的一种或多种；所述碳纳米锥的尾端与所述针尖基底形成共价键的界面连接，尖端取向与针尖的中心轴取向一致。
根据本申请的一个实施例，所述碳纳米锥的尖端的表面洁净且石墨层结构完整。
另一方面，本申请提供一种碳纳米锥功能化针尖的制备方法，包括如下步骤：
S101，将碳纳米锥组装在针尖基底的前端；
S102，将针体与另一个金属体接触，在所述针体和所述金属体之间施加瞬间电流，使所述碳纳米锥的外部石墨层连同污染物被去除。
根据本申请的一个实施例，步骤S101具体包括：利用微纳操作臂控制所述针尖基底的前端伸入所述碳纳米锥的内部将所述碳纳米锥粘附在所述针尖基底的前端，将所述针尖基底与另一个金属体接触，在所述金属体和所述针尖基底之间施加电压，使电流通过所述针尖基底，使所述针尖基底的前端部位受热并与粘附的所述碳纳米锥结合。
根据本申请的一个实施例，在步骤S102中，所述针体和所述另一个金属体均固定在微纳操作臂上，在显微镜观察下利用所述操作臂控制其移动。
根据本申请的一个实施例，在步骤S102中，还包括：控制所述针体的碳纳米锥尖端与所述另一个金属体接触形成电学通路，所述瞬间电流的大小为0.01～10mA。
根据本申请的一个实施例，在步骤S102中，还包括：控制所述针体的侧面与所述另一个金属体接触形成电学通路，所述金属体与所述针体接触的位置距离针尖顶端的距离为0.01～1μm，所述瞬间电流的大小为1～100mA。
又一方面，本申请提供另一种碳纳米锥功能化针尖的制备方法，包括如下步骤：
S201，将碳纳米锥组装在针尖基底的前端；
S202，将所述针尖加热至目标温度，通入活性物质，使其选择性地与所述针尖表面的污染物反应以净化所述碳纳米锥功能化针尖；其中，所述活性物质为弱氧化剂。
根据本申请的一个实施例，所述弱氧化剂为二氧化碳或水。
根据本申请的一个实施例，步骤S201具体包括：利用微纳操作臂控制所述针尖基底的前端伸入所述碳纳米锥的内部将所述碳纳米锥粘附在所述针尖基底的前端，将所述针尖基底与另一个金属体接触，在所述金属体和所述针尖基底之间施加电压，使电流通过所述针尖基底，使所述针尖基底的前端部位受热并与粘附的所述碳纳米锥结合。
根据本申请的一个实施例，在步骤S202中，针体和另一个金属体均固定在微纳操作臂上，在显微镜观察下利用所述操作臂控制其移动。
根据本申请的一个实施例，在步骤S202中，还包括：将所述针体侧面与所述另一个金属体接触，在所述针体和所述金属体之间施加持续电流，使针尖尖端达到局域高温并与所述活性物质反应。
根据本申请的一个实施例，在步骤S202中，还包括：将所述针尖安装在针尖夹持装置上，放入真空管式炉中，通入二氧化碳或水汽并升温至目标温度，以去除所述针尖表面的污染物。
本申请实施例中的上述一个或多个技术方案，至少具有如下技术效果：利用本申请实施例的制备方法所获得的碳纳米锥功能化针尖可提供稳定的、大束流的可控电子发射，实现电子发射源的应用；实现碳纳米锥与金 属针尖基底之间的共价键界面连接，其优异的机械强度和导电性能保证了碳纳米锥针尖在电子发射过程中的稳定性；碳纳米锥尖端取向与针尖整体中心轴的取向重合，保证了碳纳米锥针尖在电子发射时活性发射位点的可控性；并且，本申请实施例中所制备的碳纳米锥功能化针尖具有洁净的、完整石墨层状结构的碳纳米锥尖端，该针尖结构特征避免了尖端表面污染物造成的电子发射噪音及不可控发射电流所引发的针尖结构破坏甚至失效。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1(a)是本申请实施例提供的碳纳米锥的整体结构图；
图1(b)是本申请实施例提供的碳纳米锥尖端的高分辨透射电镜照片，示出了碳纳米锥的层状石墨结构，图中箭头标出了碳纳米锥表面的污染物；
图2(a)是在扫描电镜中，安装在微纳操作臂上的金属针尖的侧视图，箭头标示为三个微纳操作臂；
图2(b)是在扫描电镜中，安装在微纳操作臂上的金属针尖的俯视图；
图3(a)是本申请实施例提供的碳纳米锥功能化针尖(#1)的尖端与另一个金属体(#2)接触的扫描电镜照片；
图3(b)是经过瞬间电流处理后的洁净的碳纳米锥尖端的透射电镜照片；
图4(a)是本申请实施例提供的碳纳米锥功能化针尖(#1)的侧面与另一个金属体(#2)接触的扫描电镜照片；
图4(b)是经过瞬间电流处理后的洁净的碳纳米锥尖端的透射电镜照片；
图4(c)是制备所得的碳纳米锥功能化针尖的场发射曲线图；
图4(d)是在碳纳米锥功能化针尖(#1)和阳极(#3)之间施加一定电场进行场发射测试的电镜照片；
图5(a)是本申请实施例提供的碳纳米锥功能化针尖的扫描电镜照片；
图5(b)是本申请实施例提供的碳纳米锥洁净且完整的石墨层结构图。
图6(a)是本申请实施例提供的碳纳米锥功能化针尖的扫描电镜照片；
图6(b)是本申请实施例提供的碳纳米锥洁净且完整的石墨层结构图。
具体实施方式
为使本申请实施例的目的、技术方案和优点更加清楚，下面将结合附图，对本申请实施例中的技术方案进行清楚、完整地描述。显然，所描述的实施例是本申请的一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
图1(a)是本申请实施例提供的碳纳米锥的整体结构图，图1(b)是本申请实施例提供的碳纳米锥尖端的高分辨透射电镜照片。如图1(a)、图1(b)所示，本申请提供一种碳纳米锥功能化针尖，其中，针尖基底的前端被碳纳米锥修饰；
其中，碳纳米锥是由层状石墨结构构成的锥形的纳米碳材料；针尖基底的材料为金属，选自钨、铁、钴、镍、钛中的一种或多种；碳纳米锥的尾端与针尖基底形成共价键的界面连接且尖端取向与针尖的中心轴取向一致。碳纳米锥尖端的表面洁净且石墨层结构完整，无污染物、无破损。
另一方面，本申请提供一种碳纳米锥功能化针尖的制备和净化方法。
碳纳米锥与金属针尖基底的组装采用已公开专利ZL201610091160.0中所描述的方法。在电子显微镜下，利用微纳操作臂控制金属针尖基底的前端伸入碳纳米锥的内部将碳纳米锥粘附在针尖基底的前端，之后将针尖基底与另一个金属体接触，在金属体和针尖基底之间施加电压，使电流通过针尖基底，针的前端部位受热并与粘附的碳纳米锥结合。其中，金属体与针尖基底接触的位置距离针尖顶端的距离为0.2～100μm，通过针体的电流为0.01～5A。
本申请所提出的净化方法是指利用瞬间电流烧蚀法或选择性化学反应法去除碳纳米锥表面的无定型碳和碳氢化合物等污染物。
利用瞬间电流烧蚀法制备碳纳米锥功能化针尖包括如下步骤：
S101，利用微纳操作法结合原位电流加热法，将碳纳米锥组装在针尖基底的前端；
S102，将针体与另一个金属体接触，在针体和金属体之间施加瞬间 电流，使碳纳米锥的外部石墨层连同污染物被去除。
进一步地，在步骤S102中，针体和另一个金属体均固定在微纳操作臂上，在显微镜观察下利用操作臂控制其移动，如图2(a)、图2(b)所示。
进一步地，在步骤S102中，还包括：控制针体的碳纳米锥尖端与另一个金属体接触形成电学通路，瞬间电流的大小为0.01～10mA。
进一步地，在步骤S102中，还包括：控制针体的侧面与另一个金属体接触形成电学通路，金属体与针体接触的位置距离针尖顶端的距离为0.01～1μm，瞬间电流的大小为1～100mA。
在一个优选的实施例中，利用瞬间电流去除碳纳米锥外部石墨层的可能机制如下：由于碳纳米锥具有多层石墨结构，石墨的层间电阻率(10 - 3Ω·m)是层内电阻率(10 -6Ω·m)的1000倍。因此，瞬间电流将优先通过外部石墨层引发层内碳-碳键的断裂，结合瞬间电流所产生的焦耳热，使得外部石墨层连同表面的污染物裂解并挥发进入真空，最终获得洁净的内部石墨层结构。更进一步，在本实施例中可多次重复步骤S102，可控地去除一定数目的外部石墨层，获得洁净的、具有更尖锐尖端的碳纳米锥功能化针尖。
利用选择性化学反应法制备碳纳米锥功能化针尖包括如下步骤：
S201，利用微纳操作法结合原位电流加热法，将碳纳米锥组装在针尖基底的前端；
S202，将针尖加热至目标温度，通入活性物质，使其选择性地与针尖表面的污染物反应以净化碳纳米锥功能化针尖；其中，活性物质为二氧化碳或水等弱氧化剂。
进一步地，在步骤S202中，针体和另一个金属体均固定在微纳操作臂上，在显微镜观察下利用操作臂控制其移动，如图2(a)、图2(b)所示。
进一步地，在步骤S202中，还包括：将针体侧面与另一个金属体接触，在针体和金属体之间施加持续电流，使针尖尖端达到局域高温并与活性物质反应。优选地，金属体与针体接触的位置距离针尖顶端的距离为0.2～100μm，通过针体的电流为0.01～5A。利用环境扫描电镜的气路控制阀往扫描电镜样品室内通入二氧化碳或水汽，活性气体在电镜样品室内的压力范围为10～2000Pa。
进一步地，在步骤S202中，还包括：将针尖安装在针尖夹持装置上，放入真空管式炉中，通入二氧化碳或水汽并升温至目标温度，以去除针尖表面的污染物。优选地，二氧化碳或水汽的流速为100～1000sccm，升温速率为1～10℃/min，目标温度为450℃～750℃，保温时间为30～600min。
具体地，碳纳米锥表面的无定形碳及碳氢化合物污染物相比较碳纳米锥的石墨结构而言具有更高的化学反应活性，会优先与各类氧化剂反应转化为气体产物而达到净化表面的目的。为了在去除表面污染物的同时，避免在碳纳米锥的石墨结构中引入缺陷，本申请提出的方案中使用二氧化碳或水蒸气这类柔和的氧化剂。二氧化碳与无定形碳及碳氢化合物污染物反应生成一氧化碳，水蒸气与无定形碳及碳氢化合物污染物反应生成一氧化碳和氢气，最终获得洁净的、具有完整石墨结构的碳纳米锥针尖。
现以以下具体实施例来说明本申请的技术方案。实施例中未注明具体技术或条件者，按照本领域内的文献所描述的技术或条件，或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可通过正规渠道商购买得到的常规产品。
以下具体实施例中，微纳操作臂选用Kleindiek Nanotechnik公司的产品，扫描电镜选用Thermo Fisher公司的Quanta 200型扫描电镜，透射电镜选用Thermo Fisher公司的F20型透射电镜。
实施例1
在本实施例中，将两根钨针固定在两个微纳操作臂上；微纳操作臂及碳纳米锥样品均放置于扫描电镜内。首先将一根钨针(#2)从距#1金属钨针尖基底顶端50μm处接近其侧壁，在#1和#2之间施加60V的电压产生电弧，电弧导致#2钨针顶端熔为圆球形。
将#1针的尖端伸入选中的碳纳米锥的锥顶内并与碳纳米锥接触并粘附在针尖顶端。之后，将#2钨针顶端的圆球与上述钨针尖(#1)侧面接触，接触位置距离针尖#1最顶端2μm。在两根钨针尖上施加电压产生2A的电流，通电持续时间为0.1ms，金属钨针尖(#1)顶端发生熔融，熔融的金属钨自动进入并填充碳纳米锥的内部空间，得到如图3(a)所示的#1功能化针尖。
移动#1碳纳米锥功能化针尖使其尖端与#2钨针顶端的圆球接触，施 加一个1mA的瞬间电流，电流持续时间为0.5μs。通电结束后，迅速退出碳纳米锥针尖并避免电子束照射针尖表面。对于取出的碳纳米锥针尖，在透射电镜下观察其形貌，得到图3(b)所示洁净且无破损石墨层的针尖尖端。
实施例2
在本实施例中，将两根钨针固定在两个微纳操作臂上；微纳操作臂及碳纳米锥样品均放置于扫描电镜内。首先将一根钨针(#2)从距#1金属钨针尖基底顶端50μm处接近其侧壁，在#1和#2之间施加60V的电压产生电弧，电弧导致#2钨针顶端熔为圆球形。
将#1针的尖端伸入选中的碳纳米锥的锥顶内并与碳纳米锥接触并粘附在针尖顶端。之后，将#2钨针顶端的圆球与上述钨针尖(#1)侧面接触，接触位置距离针尖#1最顶端3μm。在两根钨针尖上施加电压产生3A的电流，通电持续时间为0.1ms，金属钨针尖(#1)顶端发生熔融，熔融的金属钨自动进入并填充碳纳米锥的内部空间，得到如图4(a)所示的#1功能化针尖。
移动#1碳纳米锥功能化针尖使其碳纳米锥侧面与#2钨针顶端的圆球接触，施加一个20mA的瞬间电流，电流持续时间为0.5μs。通电结束后，迅速退出#1碳纳米锥针尖并避免电子束照射针尖表面。对于取出的碳纳米锥针尖，在透射电镜下观察其形貌，得到图4(b)所示洁净且无破损石墨层的针尖尖端。
利用原位透射电镜样品杆上的驱动装置，移动#1碳纳米锥功能化针尖接近#3Au电极表面约500nm，如图4(d)所示。在Au电极(阳极)和碳纳米锥功能化针尖(阴极)之间施加连续变化的电压(40～200V)并记录相应的电流，得到如图4(c)所示的场发射曲线。可见，利用本发明制备的碳纳米锥功能化针尖可提供100μA的大束流发射。
实施例3
在本实施例中，将两根钨针固定在两个微纳操作臂上；微纳操作臂及碳纳米锥样品均放置于扫描电镜内。首先将一根钨针(#2)从距#1金属钨针尖基底顶端50μm处接近其侧壁，在#1和#2之间施加60V的电压产生电弧，电弧导致#2钨针顶端熔为圆球形。
将#1针的尖端伸入选中的碳纳米锥的锥顶内并与碳纳米锥接触并粘 附在针尖顶端。之后，将#2钨针顶端的圆球与上述钨针尖(#1)侧面接触，接触位置距离针尖#1最顶端3μm。在两根钨针尖上施加电压产生3A的电流，通电持续时间为0.1ms，金属钨针尖(#1)顶端发生熔融，熔融的金属钨自动进入并填充碳纳米锥的内部空间，得到碳纳米锥功能化针尖如图5(a)所示。
将电镜切换至环境扫描电镜模式，并通入二氧化碳气氛，通过电镜的气压调节阀控制样品室内二氧化碳压力为1000Pa。#2钨针的圆球与#1碳纳米锥针尖的侧面仍保持接触位置不变，在两根针体上施加0.6A的电流，通电持续10min。加热结束后，迅速撤出碳纳米锥功能化针尖，避免电子束照射。电镜切换回高真空模式后放入氮气，取出碳纳米锥针尖。利用透射电镜观察碳纳米锥针尖的高分辨形貌，如图5(b)所示，可见碳纳米锥具有洁净完整的石墨层结构。
实施例4
在本实施例中，碳纳米锥功能化针尖(如图6(a)所示)的制备方法与实施例3相同。
将碳纳米锥功能化针尖固定在一个陶瓷材料制作的针尖夹持装置上，针尖部位朝上，并放置于真空管式炉的加热区域。设定管式炉的目标温度为500℃，升温速率为1℃/min，保温时间为60min。加热开始前，向管式炉中通入二氧化碳，调节二氧化碳的流速为500sccm。加热完成后自然降温至室温，通入氮气，取出碳纳米锥针尖在透射电子显微镜下观察其结构特征，如图6(b)所示。
以上实施方式仅用于说明本申请，而非对本申请的限制。尽管参照实施例对本申请进行了详细说明，本领域的普通技术人员应当理解，对本申请的技术方案进行各种组合、修改或者等同替换，都不脱离本申请技术方案的精神和范围，均应涵盖在本申请的权利要求范围中。

Claims (12)

  1. 一种碳纳米锥功能化针尖，其特征在于，针尖基底的前端被碳纳米锥修饰；
    其中，所述碳纳米锥是由层状石墨结构构成的锥形的纳米碳材料；所述针尖基底的材料为金属，选自钨、铁、钴、镍、钛中的一种或多种；所述碳纳米锥的尾端与所述针尖基底形成共价键的界面连接且尖端取向与针尖的中心轴取向一致。
  2. 根据权利要求1所述的碳纳米锥功能化针尖，其特征在于，所述碳纳米锥的尖端的表面洁净且石墨层结构完整。
  3. 一种碳纳米锥功能化针尖的制备方法，包括如下步骤：
    S101，将碳纳米锥组装在针尖基底的前端；
    S102，将针体与另一个金属体接触，在所述针体和所述金属体之间施加瞬间电流，使所述碳纳米锥的外部石墨层连同污染物被去除。
  4. 根据权利要求3所述的制备方法，其特征在于，在步骤S102中，所述针体和所述另一个金属体均固定在微纳操作臂上，在显微镜观察下利用所述操作臂控制其移动。
  5. 根据权利要求4所述的制备方法，其特征在于，在步骤S102中，还包括：
    控制所述针体的碳纳米锥尖端与所述另一个金属体接触形成电学通路，所述瞬间电流的大小为0.01～10mA。
  6. 根据权利要求4所述的制备方法，其特征在于，在步骤S102中，还包括：
    控制所述针体的侧面与所述另一个金属体接触形成电学通路，所述金属体与所述针体接触的位置距离针尖顶端的距离为0.01～1μm，所述瞬间电流的大小为1～100mA。
  7. 一种碳纳米锥功能化针尖的制备方法，包括如下步骤：
    S201，将碳纳米锥组装在针尖基底的前端；
    S202，将所述针尖加热至目标温度，通入活性物质，使其选择性地与所述针尖表面的污染物反应以净化所述碳纳米锥功能化针尖；其中，所述活性物质为弱氧化剂。
  8. 根据权利要求7所述的制备方法，其特征在于，所述弱氧化剂为二氧化碳或水。
  9. 根据权利要求7所述的制备方法，其特征在于，在步骤S202中，针体和另一个金属体均固定在微纳操作臂上，在显微镜观察下利用所述操作臂控制其移动。
  10. 根据权利要求9所述的制备方法，其特征在于，在步骤S202中，还包括：
    将所述针体侧面与所述另一个金属体接触，在所述针体和所述金属体之间施加持续电流，使针尖尖端达到局域高温并与所述活性物质反应。
  11. 根据权利要求7所述的制备方法，其特征在于，在步骤S202中，还包括：
    将所述针尖安装在针尖夹持装置上，放入真空管式炉中，通入二氧化碳或水汽并升温至目标温度，以去除所述针尖表面的污染物。
  12. 根据权利要求3或7所述的制备方法，其特征在于，所述将碳纳米锥组装在针尖的基底的前端包括：
    利用微纳操作臂控制所述针尖基底的前端伸入所述碳纳米锥的内部将所述碳纳米锥粘附在所述针尖基底的前端，将所述针尖基底与另一个金属体接触，在所述金属体和所述针尖基底之间施加电压，使电流通过所述针尖基底，使所述针尖基底的前端部位受热并与粘附的所述碳纳米锥结合。
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