CN113436946A - Metal carbide needle tip, preparation method and application thereof, and electron gun - Google Patents
Metal carbide needle tip, preparation method and application thereof, and electron gun Download PDFInfo
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- CN113436946A CN113436946A CN202110712011.2A CN202110712011A CN113436946A CN 113436946 A CN113436946 A CN 113436946A CN 202110712011 A CN202110712011 A CN 202110712011A CN 113436946 A CN113436946 A CN 113436946A
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Abstract
The application belongs to the technical field of metal material functionalization, and particularly relates to a metal carbide needle tip, a preparation method and application thereof, and an electron gun. The application provides a preparation method of a metal carbide needle tip, which comprises the following steps: injecting the metal wire with the processed sharp top end into the hollow area of the carbon nanocone to enable the sharp top end of the metal wire to be in contact with the carbon nanocone; applying voltage to the metal wire and the carbon nanocones, and enabling the carbon nanocones and the metal wire to perform melting reaction at a junction until the temperature reaches the covalent bond reaction temperature of the metal carbide, so that the carbon nanocones completely react with the metal wire to generate the metal carbide; controlling the current of the metal carbide and applying a preset voltage to the metal carbide to obtain the metal carbide needle point with the diameter of 10nm-300 nm. The application provides a method for preparing a single crystal superfine metal carbide needle point with high strength, high hardness, high melting point and low work function.
Description
Technical Field
The application belongs to the technical field of metal material functionalization, and particularly relates to a metal carbide needle tip, a preparation method and application thereof, and an electron gun.
Background
The metal carbide belongs to hard alloy and metal ceramic materials, and has the characteristics of high strength, high hardness, high melting point and the like. In recent years, metal carbide tips have been found to have a relatively low electron emission work function, can stably work in a high-temperature environment, and have a unique application value in the fields of scanning probe tips, field emission electron sources and the like.
The metal carbide is prepared by mixing transition metals (elements in IIIB group to VIII group of the periodic table) and carbon elements and then heating at high temperature. The carbon atoms have a radius of 77pm and easily enter the metal to form interstitial carbides. For metals with atomic radii less than 130pm, such as Cr, Mn, Fe, Co, Ni, etc. The carbides of these metals have properties between ionic and interstitial types; for metals with atomic radii larger than 130pm, such as W, Hf, Ti, Zr, Nb, Ta, etc., carbon atoms do not deform the metal lattice, but make the lattice more compact and solid, both are almost completely solid-dissolved and form a continuous solid solution, such as tantalum carbide and tungsten carbide, etc., have extremely high melting point and hardness and exhibit good metal properties such as electrical conductivity.
The metal carbide has excellent performance, but the shape of a needle point is difficult to obtain, and at present, three main obstacles exist: 1. the carbide material has the characteristics of high hardness, high temperature resistance, wear resistance, corrosion resistance and the like, and the traditional block material is very difficult to process into a nanometer-diameter needle point shape; 2. the field emission cathode is related to the crystal orientation and curvature diameter of the tip of the material, the emitting work functions of the needle points of different crystal orientations are different, the needle point curvature determines the resolution of the probe, the probe with smaller radius can effectively improve the imaging resolution, and the growth of the needle point of the single crystal metal carbide and the control of the curvature diameter are very difficult at present. 3. The metal carbide processing method has defects, for example, although the metal carbide needle tip can be prepared by using the focused ion beam method, the surface of the needle tip has serious Ga ion pollution, and the processing cost of the method is expensive.
Heretofore, no method has been found that can produce a metal carbide tip having a single crystal structure, controllable diameter and curvature, perfect surface atomic structure arrangement, no breakage and impurity adsorption, and strong mechanical bonding.
Disclosure of Invention
Aiming at the defects and the blank of the prior art, the application provides a method for preparing the single crystal superfine metal carbide needle point with high strength, high hardness, high melting point and low work function.
In a first aspect, the present application provides a method for preparing a metal carbide tip, comprising:
wherein the range of the preset voltage is: the metal melting critical voltage of the metal wire is-5V to + 5V.
Specifically, the preset voltage unit is V. When a certain voltage is reached, the metal wire begins to appear liquid from solid, and the voltage is the metal melting critical voltage.
Specifically, the pointed tip of the metal wire is arranged in the hollow area of the carbon nanocone. After the metal wire is contacted with the carbon nanocone, voltage is applied to the outside, and joule heat is generated by the voltage and the current so that the metal wire and the carbon nanocone are subjected to melting reaction.
Specifically, if the metal melting critical voltage of the metal wire is 30V, the preset voltage range is 25-35V.
Specifically, the top end of the metal wire tip in the step 1 is made of pure metal, and the metal carbide tip in the step 3 is made of metal carbide; the diameter of the top end of the metal wire tip in the step 1 is larger than that of the metal carbide tip in the step 3.
In another embodiment, step 2 specifically includes: two metal wires are adopted, the sharp top end of one metal wire is subjected to melting treatment to form a metal ball, the sharp top end of the other metal wire is inserted into the hollow area of the carbon nanocone and is contacted with the hollow area, the metal ball is contacted with the metal wire, the metal wire is conducted with the metal ball after being contacted, electric pulse is applied to the position of the metal ball and is uniformly discharged, the electric pulse generates enough joule heat to reach the melting temperature of the metal wire, at the moment, the sharp top end of the metal wire is melted and enters the hollow area of the carbon nanocone, the carbon nanocone and the metal wire are subjected to melting reaction at the junction until the temperature reaches the covalent bond reaction temperature of metal carbide, and the carbon nanocone completely reacts with the metal wire to generate the metal carbide.
In another embodiment, the metal wire is made of one or more of W, Ta, Hf, Ti, Zr, Co and Ni, and the diameter of the metal wire is 0.1mm-0.5 mm.
In another embodiment, the processing treatment is selected from one of an electrochemical corrosion method, a mechanical shearing method or a focused ion beam method, the diameter of the top end of the metal wire tip is 30 nm-3 μm, and the vertex angle is 10-70 degrees.
Specifically, the diameter of the tip end of the wire tip is preferably 300nm to 500 nm.
Specifically, the electrochemical etching method comprises the following steps: the tungsten wire is used as an anode and is connected with the positive pole of a direct current power supply meter, and the platinum sheet (Pt) is used as a cathode and is connected with the negative pole of the direct current power supply meter. A1 mol/L sodium hydroxide solution (NaOH) was prepared as an electrolyte. The metal wire is immersed into the electrolyte solution through the lifting platform, and the tungsten wire is easy to penetrate into the solution 1 mm. The etching voltage was set to 2V, and after the electrochemical reaction started to occur after the power was turned on. The number of the ammeter will be slowly reduced, about 15 minutes, the number of the ammeter will be suddenly 0, and at the moment, the tungsten filament corrosion preparation is completed, and the pointed tips with different diameters are obtained, namely, the pointed tip of the tungsten filament with 0.1mm is corroded into the pointed tip with the diameter of 300nm-500 nm.
Specifically, the focused ion beam method includes: the wires were placed in a focused Ion beam fib (focus Ion beam) apparatus and wire tip tips of different diameters were obtained using Ga Ion beam machining.
In another embodiment, in step 2, the pointed end of the metal wire is heated by one of an electric pulse heating method, a microwave heating method or a laser heating method, so that the pointed end of the metal wire is partially melted. The melting of the sharp tip portion of the wire facilitates the application of a voltage across the wire and the carbon nanocone.
In another embodiment, in step 1, the carbon nanocone is selected from a normal temperature carbon cone and/or a high temperature carbon cone; the taper angle of the carbon nanocone is one of 112.9 °, 83.6 °, 60 °, 38.9 ° or 19.2 °.
Wherein, the normal temperature carbon cone is a commercial product, the high temperature carbon cone is the carbon cone processed by keeping the normal temperature carbon cone at 2400 ℃ for 1 hour, the processed graphite has obvious crystal lattice and high graphitization degree.
In another embodiment, in the step 2, the current introduced into the metal wire is a fixed value within 0.01mA-0.5 mA.
In another embodiment, in step 3,
the range of the preset voltage: the metal melting critical voltage of the metal wire is-5V to-1V, and a metal carbide needle tip with the diameter less than or equal to 30nm is obtained;
the range of the preset voltage: the metal melting critical voltage of the metal wire is + 1V-the metal melting critical voltage of the metal wire is +5V, and the metal carbide needle tip with the diameter larger than 100nm is obtained.
In a second aspect, the present application provides a metal carbide tip comprising the metal carbide tip made by the method of making.
The third aspect of the application provides the metal carbide needle tip prepared by the preparation method or the application of the metal carbide needle tip in an electron gun.
The present application in a fourth aspect provides an electron gun comprising: a base and the metal carbide needle tip or the metal carbide needle tip prepared by the preparation method;
the metal carbide needle point is fixed on the electrode hair fork of the base.
According to the method, the sharp top end of a metal wire is arranged in a hollow area of a carbon nanocone through a micro-nano operation method, and the carbon nanocone completely reacts with the metal wire to generate the metal carbide through an electric pulse method high-temperature reaction; finally, the voltage is simply adjusted to reshape the molten metal, and the superfine metal carbide needle points with different diameters and different curvature radiuses are prepared. The metal carbide needle tip has the advantages of excellent performance, good metalloid conductivity, reliable chemical stability, high-temperature environment thermal stability, low electron work function and the like.
Compared with the prior art, the method has the following advantages:
firstly, selecting a carbon nanocone material and a transition group metal, and preparing the superfine metal carbide functional needle tip through a high-temperature reaction by a micro-nano operation method and an electric pulse method.
Secondly, the voltage of the electric pulse is adjusted, and the superfine metal carbide needle points with different diameters and different curvature radiuses can be prepared.
Thirdly, the method is simple and easy to operate, the preparation process can be observed in real time, and the technological parameters are accurate and controllable; the surface atomic structure of the single crystal metal carbide needle point is perfect, and the single crystal metal carbide needle point is free from damage and impurity adsorption; has the excellent characteristics of high strength, high hardness, high melting point, low work function and the like.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
Fig. 1 is a schematic view of the shapes of different carbon nanocones provided in the embodiments of the present application;
FIG. 2 is a flow chart of the preparation of a metal carbide tip provided in the examples of the present application;
FIG. 3 is a micrograph of a metal carbide tip and interplanar spacing results provided in example 1 of the present application;
FIG. 4 is a micrograph of a metal carbide tip at different magnifications provided in example 2 of the present application;
FIG. 5 is a micrograph of a metal carbide tip at different magnifications provided in example 3 of the present application;
FIG. 6 is a micrograph of a metal carbide tip at different magnifications provided in example 4 of the present application;
FIG. 7 is a micrograph of a metal carbide tip at different magnifications provided in example 5 of the present application;
FIG. 8 is a micrograph of a metal carbide tip at different magnifications provided in example 6 of the present application;
fig. 9 is an external view of an electron gun according to embodiment 7 of the present application.
Detailed Description
The application provides a metal carbide needle tip and a preparation method and application thereof, and fills the vacancy that the prior art can not prepare the metal carbide needle tip with a single crystal structure, controllable diameter and curvature, perfect surface atomic structure arrangement, no damage and impurity adsorption and firm mechanical combination.
The technical solutions in the embodiments of the present application will be described clearly and completely below, and it should be understood that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The raw materials and reagents used in the following examples are commercially available or self-made.
The following examples do not specify particular techniques or conditions, according to the techniques or conditions described in the literature in the field, or according to the product specifications. The reagents or instruments used are conventional products available from regular distributors, not indicated by the manufacturer.
KW-4A type film throwing instrument produced by the institute of electronics of Chinese academy of sciences;
the micromanipulation arms for the micro-nano manipulations used in the following examples were purchased from: kleindi Nanotechnik Inc.;
the carbon nanopyramids used in the following examples were purchased from: n-Tec corporation; the carbon nanocones adopted in the following examples are carbon nanocones prepared at high temperature, and the graphite lattice fringes are clear, and the graphitization degree is good;
tungsten wires used in the following examples were obtained from: nilaco corporation, diameter 0.1mm to 0.5 mm;
the environmental scanning microscope used in the following examples was Quanta 200 FEG.
Referring to fig. 1, fig. 1 is a schematic view illustrating shapes of different carbon nanocones according to an embodiment of the present disclosure; a is the carbon nanocones with cone angles of 19.2 degrees, 38.9 degrees, 60 degrees, 83.6 degrees and 112.9 degrees, b is a carbon nanocone micrograph with cone angles of 60 degrees, and c is a high-resolution image of a carbon nanocone wall dozen layers of graphite sheet structures with cone angles of 60 degrees. As can be seen from fig. 1, the carbon nanocones of the present application have a hollow region inside.
Referring to FIG. 2, FIG. 2 is a flow chart illustrating the fabrication of a metal carbide tip according to an embodiment of the present disclosure; a is a schematic diagram of micro-nano operation adopted in the embodiment of the application, #1 is a partially melted metal ball, and #2 is a metal wire; b is a schematic diagram of a hollow area of the metal wire injected carbon nanocone; c is a simple preparation diagram of the metal carbide needle point, c-1 is a schematic diagram of a hollow area of the metal wire with the sharp top end injected with the carbon nanocone, c-2 is a schematic diagram of a hollow area of the metal wire with electric pulse applied to enable the metal to be melted and filled with the carbon nanocone, and c-3 is a schematic diagram of the metal wire with electric pulse applied to enable the carbon nanocone to completely react with the metal wire to generate the metal carbide when the temperature of the metal wire reaches the covalent bond reaction temperature of the metal carbide.
Referring to fig. 9, fig. 9 is an external view of an electron gun according to an embodiment of the present disclosure; a is a tungsten carbide needle point micrograph used on an electron gun, b is a field emission current result of a tungsten carbide needle point under the voltage of 145V, c is a structure diagram of the electron gun, 1 is a ceramic base, 2 is a tungsten electrode fork, 3 is a tungsten carbide needle point (the diameter is 19nm), the electrode fork 2 is welded and fixed on the ceramic base 1, the tungsten carbide needle point 3 is welded and fixed on the tungsten electrode fork 2, the tungsten carbide needle point 3 faces to an emission direction, the diameter of the ceramic base 1 is 12.69mm, a metal suppressor is arranged according to the conventional means, a field emission electron gun is assembled, and the field emission current of the field emission electron gun under the voltage of 145V is measured to be 60 nA.
The following examples, which take tungsten wire and carbon nanocone as an example, propose a method for preparing a single crystal metal tungsten carbide tip, comprising:
step (1): a tungsten wire (W) with the diameter of 0.2mm is used as an anode and is connected with the positive electrode of a direct current power supply meter, and a platinum sheet (Pt) is used as a cathode and is connected with the negative electrode of the direct current power supply meter. A1 mol/L sodium hydroxide solution (NaOH) was prepared as an electrolyte. The tungsten wire is immersed in the electrolyte solution by means of a lifting table, preferably with the metal extending 1mm deep into the solution. The etching voltage was set to 2V, and after the electrochemical reaction started to occur after the power was turned on. The amperometric number will slowly decrease for about 15 minutes and suddenly become 0, at this time, the tungsten wire corrosion preparation is completed, and the diameter of the sharp top end of the tungsten wire is 300nm-500nm as the best.
Step (2): selecting two tungsten metal wires in the two steps (1), wherein a No. 1 tungsten metal wire is applied with 70V voltage to form a tungsten ball at the tip end of the No. 1 tungsten metal wire, a No. 2 tungsten metal wire extends into the carbon nanocone on the silicon wafer substrate, and the carbon nanocone is lifted up through physical adsorption;
and (3): the current pulse joule heating is the product of current and voltage: setting different voltage parameters and current parameters to obtain metal carbide needles with different diameters, applying a small voltage of 3V-6V after the carbon nanocone on the #2 tungsten wire in the step (2) is contacted with the #1 tungsten ball, reacting the carbon nanocone with the #2 tungsten wire to form tungsten carbide covalent bond combination, and controlling the current flowing through the metal wire to be 0.01mA-0.1 mA;
and (4): the method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from a tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, wherein the electric pulse generates enough joule heat to reach the tungsten melting temperature when the voltage is about 20V to 40V under the normal condition, melting tungsten at the tip end of the No. 2 tungsten metal wire into the hollow interior of a carbon nanocone, and enabling the current flowing through a needle body to be 0.01mA-0.5 mA;
and (5): continuously increasing the voltage by 0.5V step length, observing the reaction condition of the carbon nanocone on the No. 2 tungsten wire, increasing the temperature of the carbon nanocone and the tungsten wire tip along with the increase of the voltage, and when reaching the reaction temperature of the tungsten carbide covalent bond, the carbon nanocone starts to react with the tungsten wire at the junction to generate tungsten carbide, and at the moment, observing the melting phenomenon of the No. 2 tungsten wire, wherein the carbon atoms start to permeate into the tungsten atoms, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for multiple times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone, and the carbon nanocone is sleeved on the surface of the tungsten wire, and the structure of the carbon nanocone on the outer surface and the tungsten carbide on the inner wall is obtained in the step;
and (6): observing the reaction consumption condition of the carbon nanocone in the step (5), when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the tungsten metal wire and the side surface of the carbon nanocone is completely consumed, applying voltage, enabling the carbon nanocone to completely react to generate a tungsten carbide needle, and at the moment, changing the voltage can influence the shape of the finally obtained tungsten carbide needle tip. Firstly, setting a certain fixed value in the range of 0.01mA-0.5mA, wherein the joule heat generated by current pulse is only related to voltage, and when the voltage is increased to a certain value, such as the metal melting critical voltage is 30V, applying 25-30V pulse voltage (0-5V lower than the metal melting critical voltage), and obtaining a tungsten carbide needle tip (less than 30nm) with a very thin diameter; and (3) applying a voltage of 31-35V (1-5V higher than the metal melting critical voltage), obtaining a tungsten carbide needle tip (more than 100nm) with a thicker diameter, or reducing the voltage and then increasing the voltage, and controlling the relative positions of the electric pulse and the #2 tungsten wire, wherein the tungsten carbide needle tip can be accurately controlled to obtain various different shapes.
The following examples, which take the reaction of tantalum wire and carbon nanocone as an example, propose a method for preparing a single crystal metallic tantalum carbide single crystal tip, comprising:
step (1): two tantalum metal wires (Ta) with the diameter of 0.1mm are placed in focused Ion beam FIB (focused Ion beam) equipment, and the two tantalum metal wire sharp tops with the diameter of 200nm are obtained by Ga Ion beam processing.
Step (2): two tantalum wires, one tantalum wire, were selected, and a tantalum ball, called a #3 tantalum ball, was formed at the tip by applying 60V. The other #4 tantalum metal wire extends into the carbon nanocone on the silicon chip substrate, and the carbon nanocone is lifted up through physical adsorption;
and (3): after the carbon nanocone on the #4 tantalum metal wire in the step (2) is contacted with the #3 tantalum ball, applying a voltage of 6V, wherein the current flowing through the metal wire is 0.01mA-0.1mA, and the #4 tantalum metal wire and the carbon nanocone react to form tantalum carbide covalent bond;
and (4): the method comprises the following steps of (1) enabling a #3 tantalum ball to be close to a position, about 2 mu m away from a tip, of a #4 tantalum metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step of 1V, wherein the electric pulse generates enough Joule heat to reach the melting temperature of the tantalum metal when the voltage is about 20V to 40V under the normal condition, melting the tantalum metal at the tip of the #4 tantalum metal wire into the hollow interior of a carbon nano cone, and enabling the current flowing through the metal wire to be 0.01mA-0.5 mA;
and (5): continuously increasing the voltage by 0.5V step length, observing the reaction condition of the carbon nanocone on the No. 4 tantalum wire, increasing the temperature of the carbon nanocone and the tip of the tantalum wire along with the increase of the voltage, and when the reaction temperature of the tantalum carbide covalent bond is reached, the carbon nanocone and the tantalum metal are subjected to melting reaction at the junction to generate tantalum carbide, and then observing the melting phenomenon of the No. 4 tantalum wire, wherein the carbon atoms start to permeate into the tantalum atoms, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react with the carbon nanocone, and the carbon nanocone is sleeved on the surface of the tantalum needle, and the carbon nanocone obtained in the step is of a structure with the carbon nanocone on the outer surface and the tantalum carbide on the inner wall;
and (6): observing the reaction consumption condition of the carbon nanocones in the step (5), when only the foremost end (about hundreds of nanometers) of the carbon nanocones is remained on the tantalum metal wire and the side surfaces of the carbon nanocones are completely consumed, applying voltage, enabling the carbon nanocones to completely react to generate tantalum carbide needles, and at the moment, changing the voltage can influence the shape of the finally obtained tantalum carbide needle tips. Firstly, setting a certain fixed value in the range of 0.01mA-0.5mA, wherein the joule heat generated by current pulse is only related to voltage, and when the voltage is increased to a certain value, such as the metal melting critical voltage is 30V, applying 25-30V pulse voltage (0-5V lower than the metal melting critical voltage), and obtaining a tantalum carbide needle tip (less than 30nm) with a very thin diameter; applying a voltage of 31-35V (1-5V higher than the metal melting critical voltage), and obtaining a tantalum carbide needle tip (more than 100nm) with a thicker diameter; or the voltage can be reduced and then increased, and the relative position of the electric pulse and the #4 tantalum wire can be controlled, so that the tip of the tantalum carbide needle can be accurately controlled to obtain various shapes.
Example 1
The embodiment of the application provides a preparation method of a tungsten carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with the cone angle of 83.6 degrees and the cone tail size of 600 nm.
Referring to fig. 2a, two tungsten wires are selected, wherein a #1 tungsten wire is applied with a voltage of 70V to melt the tip thereof into a #1 tungsten ball, a #2 tungsten wire with a tip diameter of 300nm is inserted into a hollow area of a carbon nanocone, the carbon nanocone is lifted up by physical adsorption, the carbon nanocone on the #2 tungsten wire is contacted with the #1 tungsten ball, then a small voltage of 6V is applied, the carbon nanocone reacts with the #2 tungsten wire to form a tungsten carbide covalent bond, and a current flowing through the #2 tungsten wire is 0.05 mA.
The method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from the tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, generating enough Joule heat by the electric pulse when the voltage is about 30V, reaching the melting temperature of the No. 2 tungsten metal wire, melting tungsten at the tip end of the No. 2 tungsten metal wire into a hollow area of a carbon nanocone, and enabling the current flowing through the metal wire to be 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 2 tungsten metal wire is observed, the temperature of the carbon nanocone and the top end of the No. 2 tungsten metal wire is increased along with the increase of the voltage, when the reaction temperature of the tungsten carbide covalent bond is reached, the carbon nanocone and the metal tungsten react at the junction to generate tungsten carbide, the melting phenomenon of the No. 2 tungsten metal wire is observed, the carbon atom starts to permeate to the tungsten atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 2 tungsten wire, the side surface of the carbon nanocone is completely consumed; then, the current was set to a fixed value of 0.01mA, and then a melting pulse voltage was applied to a position 1 μm from the carbon nanocone, with an initial voltage of 10V, and the voltage was increased in steps of 1V, and when the voltage was increased to 26V, the metal tungsten and the carbon nanocone reacted substantially completely. At this time, the voltage was lowered by 2V, that is, a 24V pulse voltage was applied again, and after 10ms of treatment, an ultrafine tungsten carbide tip having a diameter of 17nm was obtained.
The result of microscopic examination of the ultrafine tungsten carbide tip according to the present embodiment is shown in fig. 3, the left graph in fig. 3 shows that the diameter of the tungsten carbide tip according to the present embodiment is 17nm, and the right graph in fig. 3 shows that the tungsten carbide tip according to the present embodiment is alpha-type tungsten carbide (α -WC), and the interplanar spacing (100) thereof is 0.253 nm. The stable crystal form of tungsten metal adopted in the embodiment is body-centered cubic, and the lattice constant is 0.316 nm. The carbon nanocone of the embodiment has a graphene-like structure, and the interlayer spacing is 0.34nm, so that the tungsten carbide tip of the embodiment has an obvious difference from the lattice spacing of a pure carbon nanocone and a pure tungsten metal, and the tungsten carbide tip is successfully prepared in the embodiment.
Example 2
The embodiment of the application provides a preparation method of a tungsten carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with the cone angle of 83.6 degrees and the cone tail size of 600 nm.
Referring to fig. 2a, two tungsten wires are selected, wherein a #1 tungsten wire is applied with a voltage of 70V to melt the tip thereof into a #1 tungsten ball, a #2 tungsten wire with a tip diameter of 300nm is inserted into a hollow area of a carbon nanocone, the carbon nanocone is lifted up by physical adsorption, the carbon nanocone on the #2 tungsten wire is contacted with the #1 tungsten ball, then a small voltage of 6V is applied, the carbon nanocone reacts with the #2 tungsten wire to form a tungsten carbide covalent bond, and a current flowing through the #2 tungsten wire is 0.05 mA.
The method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from the tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, generating enough Joule heat by the electric pulse when the voltage is about 30V, reaching the melting temperature of the No. 2 tungsten metal wire, melting tungsten at the tip end of the No. 2 tungsten metal wire into a hollow area of a carbon nanocone, and enabling the current flowing through the metal wire to be 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 2 tungsten metal wire is observed, the temperature of the carbon nanocone and the top end of the No. 2 tungsten metal wire is increased along with the increase of the voltage, when the reaction temperature of the tungsten carbide covalent bond is reached, the carbon nanocone and the metal tungsten react at the junction to generate tungsten carbide, the melting phenomenon of the No. 2 tungsten metal wire is observed, the carbon atom starts to permeate to the tungsten atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 2 tungsten wire, the side surface of the carbon nanocone is completely consumed; then, the current was set to a fixed value of 0.01mA, and then a melting pulse voltage was applied to a position 1 μm from the carbon nanocone, with an initial voltage of 10V, and the voltage was increased in steps of 1V, and when the voltage was increased to 26V, the metal tungsten and the carbon nanocone reacted substantially completely. At this time, the voltage was lowered by 1V, that is, a pulse voltage of 25V was applied again, and after 10ms, an ultrafine tungsten carbide tip having a diameter of 19nm was obtained.
The result of microscopic examination of the ultrafine tungsten carbide tip according to the embodiment of the present invention is shown in fig. 4, and fig. 4b shows a single crystal structure, with orderly atomic arrangement, no defects such as dislocation and stacking fault, and no special structures such as interstitial phase and twin crystal.
Example 3
The embodiment of the application provides a preparation method of a tungsten carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with cone angle of 60 degrees and cone tail size of 500 nm.
Referring to fig. 2a, two tungsten wires are selected, wherein a #1 tungsten wire is applied with a voltage of 70V to melt the tip thereof into a #1 tungsten ball, a #2 tungsten wire with a tip diameter of 400nm is inserted into a hollow area of a carbon nanocone, the carbon nanocone is lifted up by physical adsorption, the carbon nanocone on the #2 tungsten wire is contacted with the #1 tungsten ball, then a small voltage of 6V is applied, the carbon nanocone reacts with the #2 tungsten wire to form a tungsten carbide covalent bond, and a current flowing through the #2 tungsten wire is 0.05 mA.
The method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from the tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, generating enough Joule heat by the electric pulse when the voltage is about 30V, reaching the melting temperature of the No. 2 tungsten metal wire, melting tungsten at the tip end of the No. 2 tungsten metal wire into a hollow area of a carbon nanocone, and enabling the current flowing through the metal wire to be 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 2 tungsten metal wire is observed, the temperature of the carbon nanocone and the top end of the No. 2 tungsten metal wire is increased along with the increase of the voltage, when the reaction temperature of the tungsten carbide covalent bond is reached, the carbon nanocone and the metal tungsten react at the junction to generate tungsten carbide, the melting phenomenon of the No. 2 tungsten metal wire is observed, the carbon atom starts to permeate to the tungsten atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 2 tungsten wire, the side surface of the carbon nanocone is completely consumed; then, the current is set to be a fixed value of 0.3mA, then the melting pulse voltage is applied at the position 500nm away from the carbon nanocone, the initial voltage is 10V, the voltage is increased by taking 1V as the step length, and when the voltage is 30V, the metal tungsten and the carbon nanocone are basically and completely reacted. When the voltage is increased by 2V, namely 32V pulse voltage is applied again, the single crystal carbide tip with the diameter of 122nm and the uniform and symmetrical shape of two sides is obtained after 10 ms.
The result of microscopic examination of the ultrafine tungsten carbide tip according to the embodiment of the present invention is shown in fig. 5, and fig. 5b shows that the single crystal structure is also seen, the atoms are arranged orderly, and the ultrafine tungsten carbide tip has no defects such as dislocation and stacking fault, and has no special structures such as interstitial phase and twin crystal.
Example 4
The embodiment of the application provides a preparation method of a tungsten carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with the cone angle of 112.9 degrees and the cone tail size of 1.2 mu m.
Referring to fig. 2a, two tungsten wires are selected, wherein a #1 tungsten wire is applied with a voltage of 70V to melt the tip thereof into a #1 tungsten ball, a #2 tungsten wire with a tip diameter of 300nm is inserted into a hollow area of a carbon nanocone, the carbon nanocone is lifted up by physical adsorption, the carbon nanocone on the #2 tungsten wire is contacted with the #1 tungsten ball, then a small voltage of 6V is applied, the carbon nanocone reacts with the #2 tungsten wire to form a tungsten carbide covalent bond, and a current flowing through the #2 tungsten wire is 0.05 mA.
The method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from the tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, generating enough Joule heat by the electric pulse when the voltage is about 30V, reaching the melting temperature of the No. 2 tungsten metal wire, melting tungsten at the tip end of the No. 2 tungsten metal wire into a hollow area of a carbon nanocone, and enabling the current flowing through the metal wire to be 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 2 tungsten metal wire is observed, the temperature of the carbon nanocone and the top end of the No. 2 tungsten metal wire is increased along with the increase of the voltage, when the reaction temperature of the tungsten carbide covalent bond is reached, the carbon nanocone and the metal tungsten react at the junction to generate tungsten carbide, the melting phenomenon of the No. 2 tungsten metal wire is observed, the carbon atom starts to permeate to the tungsten atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 2 tungsten wire, the side surface of the carbon nanocone is completely consumed; then, the current is set to a fixed value of 0.2mA, then a melting pulse voltage is applied at a position 500nm away from the carbon nanocone, the initial voltage is 10V, the voltage is increased by taking 1V as a step, and when the voltage is increased to 35V, the metal and the carbon nanocone are almost completely reacted. At the moment, 2V voltage is increased, namely 37V pulse voltage is applied again, and after 10ms, the single crystal tungsten carbide needle point with the middle trapezoidal bulge and the uniform and symmetrical shapes at two sides is obtained.
The results of microscopic examination of the ultrafine tungsten carbide tips according to the examples of the present application are shown in fig. 6, and fig. 6b shows that the tungsten carbide tip according to the present example has a diameter of 100nm at the forefront and a diameter of 270nm at the rear end.
Example 5
The embodiment of the application provides a preparation method of a tungsten carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with cone angle of 60 degrees and cone tail size of 600 nm.
Referring to fig. 2a, two tungsten wires are selected, wherein a #1 tungsten wire is applied with a voltage of 70V to melt the tip thereof into a #1 tungsten ball, a #2 tungsten wire with a tip diameter of 400nm is inserted into a hollow area of a carbon nanocone, the carbon nanocone is lifted up by physical adsorption, the carbon nanocone on the #2 tungsten wire is contacted with the #1 tungsten ball, then a small voltage of 6V is applied, the carbon nanocone reacts with the #2 tungsten wire to form a tungsten carbide covalent bond, and a current flowing through the #2 tungsten wire is 0.05 mA.
The method comprises the following steps of (1) enabling a tungsten ball to be close to a position, about 2 mu m away from the tip end, of a No. 2 tungsten metal wire, applying an electric pulse, setting the initial voltage to be 10V, increasing the voltage slowly by a step length of 1V, generating enough Joule heat by the electric pulse when the voltage is about 30V, reaching the melting temperature of the No. 2 tungsten metal wire, melting tungsten at the tip end of the No. 2 tungsten metal wire into a hollow area of a carbon nanocone, and enabling the current flowing through the metal wire to be 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 2 tungsten metal wire is observed, the temperature of the carbon nanocone and the top end of the No. 2 tungsten metal wire is increased along with the increase of the voltage, when the reaction temperature of the tungsten carbide covalent bond is reached, the carbon nanocone and the metal tungsten react at the junction to generate tungsten carbide, the melting phenomenon of the No. 2 tungsten metal wire is observed, the carbon atom starts to permeate to the tungsten atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 2 tungsten wire, the side surface of the carbon nanocone is completely consumed; then, the current was set to a fixed value of 0.01mA, and then a melting pulse voltage was applied to a position 1 μm from the carbon nanocone, with an initial voltage of 10V, and the voltage was increased in steps of 1V, and when the voltage was 28V, the metal and the carbon nanocone reacted substantially completely. At this time, the voltage is reduced by 1V, namely, the pulse voltage of 27V is applied again, the voltage is increased by 3V after 10ms, namely, the pulse voltage of 30V is applied again, and after 10ms, the single crystal carbide needle tip with the superfine front end, the diameter of the foremost end of 32nm, the thicker rear end and the diameter of the rear end of 150nm and the uniform and symmetrical shapes at both sides is obtained.
Example 6
The embodiment of the application provides a preparation method of a tantalum carbide needle tip, which specifically comprises the following steps:
selecting the carbon nano cone with the cone angle of 83.6 degrees and the cone tail size of 500 nm.
Selecting two tantalum metal wires, wherein the #3 tantalum metal wire is melted into a tantalum ball by applying 60V, inserting the #4 tantalum metal wire with the diameter of 200nm at the pointed top end into a hollow area of a carbon nanocone, picking up the carbon nanocone through physical adsorption, contacting the carbon nanocone on the #4 tantalum metal wire with the #3 tantalum ball, applying a small voltage of 6V, reacting the carbon nanocone with the #4 tantalum metal wire to form tungsten carbide covalent bond combination, and then, the current flowing through the #4 tantalum metal wire is 0.05 mA.
And (3) enabling the #3 tantalum ball to be close to the position of the #4 tantalum metal wire, which is about 2 micrometers away from the tip end, applying an electric pulse, setting the initial voltage to be 10V, slowly increasing the voltage by 1V step length, wherein when the voltage is about 30V, the electric pulse generates enough Joule heat to reach the melting temperature of the #4 tantalum metal wire, at the moment, the tungsten at the tip end of the #4 tantalum metal wire is melted to enter a hollow area of the carbon nanocone, and at the moment, the current flowing through the metal wire is 0.3 mA.
The voltage is continuously increased by 0.5V step length, the reaction condition of the carbon nanocone on the No. 4 tantalum metal wire is observed, along with the increase of the voltage, the temperature of the carbon nanocone and the top end of the No. 4 tantalum metal wire is increased, when the reaction temperature of the tantalum carbide covalent bond is reached, the carbon nanocone starts to react with the tantalum metal at the junction to generate tantalum carbide, the melting phenomenon of the No. 4 tantalum metal wire is observed at the moment, the carbon atom starts to permeate to the tantalum atom, the permeation speed of the carbon nanocone is in direct proportion to the voltage, and the carbon nanocone needs to be subjected to voltage melting reaction for many times due to the thickness of the carbon nanocone, so that the carbon nanocone can completely react the carbon nanocone.
Observing the reaction consumption condition of the carbon nanocone, and when only the foremost end (about hundreds of nanometers) of the carbon nanocone is remained on the No. 4 tantalum metal wire, the side surface of the carbon nanocone is completely consumed; then, the current was set to a fixed value of 0.01mA, and then a melting pulse voltage was applied to a position 1 μm from the carbon nanocone, with an initial voltage of 10V, and the voltage was increased in steps of 1V, and when the voltage was 26V, the metal tantalum and the carbon nanocone reacted substantially completely. At this time, the voltage was lowered by 1V, that is, a pulse voltage of 25V was applied again, and after 10ms, an ultra-fine single-crystal tantalum carbide tip having a diameter of 22nm was obtained.
Example 7
The embodiment of the application provides a field emission electron gun, and the specific method comprises the following steps:
the ultra-fine tungsten carbide tip (19nm diameter) of example 1 was first welded to a tungsten hairpin, and the tungsten hairpin was then welded to a ceramic base electrode of 12.69mm diameter. Then, the ceramic base and the metal suppressor were assembled to obtain a practical field emission electron gun, and the external view of the field emission electron gun of this example is shown in fig. 9 c.
The field emission current of the field emission electron gun of this example was actually measured at a voltage of 145V, and as a result, as shown in FIG. 9b, the field emission current of the field emission electron gun was 60nA at a voltage of 145V.
In summary, in the embodiment of the present application, the metal wire with the partially melted top end is placed in the hollow region of the nanocarbon nanocone, and the graphite carbon atoms in the nanocarbon nanocone gradually penetrate into the metal under the action of the electric pulse, and simultaneously, the molten metal can be reshaped, so that the metal carbide tip with excellent performance and perfect structure is obtained. The needle tip has the advantages of good metalloid conductivity, reliable chemical stability, high-temperature environment thermal stability, low electron work function and the like. In addition, the metal carbide needle tip provided by the application can be assembled with a ceramic base and a metal suppression pole to obtain a metal carbide needle tip electron gun product.
The foregoing is only a preferred embodiment of the present application and it should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.
Claims (10)
1. A method of making a metal carbide tip, comprising:
step 1, placing a metal wire with a processed sharp top end in a hollow area of a carbon nanocone to enable the sharp top end of the metal wire to be in contact with the carbon nanocone;
step 2, applying voltage to the metal wire and the carbon nanocones, wherein the carbon nanocones and the metal wire are subjected to melting reaction at a junction until the temperature reaches the covalent bond reaction temperature of the metal carbide, so that the carbon nanocones completely react with the metal wire to generate the metal carbide;
step 3, controlling the current of the metal carbide, and applying a preset voltage to the metal carbide to obtain a metal carbide needle point with the diameter of 10nm-300 nm;
wherein the range of the preset voltage is: the metal melting critical voltage of the metal wire is-5V to + 5V.
2. The method according to claim 1, wherein the wire is made of one or more of W, Ta, Hf, Ti, Zr, Co and Ni, and the diameter of the wire is 0.1mm-0.5 mm.
3. The method according to claim 1, wherein the machining process is selected from electrochemical etching, mechanical shearing, and focused ion beam, and the diameter of the tip end of the wire is 30nm to 3 μm, and the apex angle is 10 to 70 °.
4. The method of claim 1, wherein in step 2, the sharp tip of the wire is heated by one of an electric pulse heating method, a microwave heating method, or a laser heating method, so that the sharp tip of the wire is partially melted.
5. The preparation method according to claim 1, wherein in step 1, the carbon nanocone is selected from a normal temperature carbon cone and/or a high temperature carbon cone; the taper angle of the carbon nanocone is one of 112.9 °, 83.6 °, 60 °, 38.9 ° or 19.2 °.
6. The method according to claim 1, wherein the current applied to the wire in step 2 is a constant value within a range of 0.01 to 0.5 mA.
7. The production method according to claim 1, wherein, in step 3,
the range of the preset voltage: the metal melting critical voltage of the metal wire is-5V to-1V, and a metal carbide needle tip with the diameter less than or equal to 30nm is obtained;
the range of the preset voltage: the metal melting critical voltage of the metal wire is + 1V-the metal melting critical voltage of the metal wire is +5V, and the metal carbide needle tip with the diameter larger than 100nm is obtained.
8. A metal carbide tip comprising the metal carbide tip made by the method of any one of claims 1 to 7.
9. Use of a metal carbide tip made by the method of any one of claims 1 to 7 or the metal carbide tip of claim 8 in an electron gun.
10. An electron gun, comprising: a base and a metal carbide tip made by the method of any one of claims 1 to 7 or the metal carbide tip of claim 9;
the metal carbide needle point is fixed on the electrode hair fork of the base.
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