CN101381887B - Single crystal boron nanotaper, method for preparing same and applications in electricity and field emission device - Google Patents

Abstract

The invention provides a single crystal boron nanocone, which is composed of pure boron and has a single crystal structure. The present invention also provides a method for preparing boron nano cones. The method uses a mixture of borides and boron powder as a source material, _a mixture of _Fe3O4 catalyst nanoparticles and a small amount of boron powder as a co-catalyst, and utilizes chemical vapor deposition CVD method Synthesis of boron nanocones. The boron nano cone prepared by the method of the invention has good electrical properties and field emission performance.

Description

Single crystal boron nanocone, its preparation method and application in electrical and field emission devices

technical field

The invention relates to a boron one-dimensional nanometer material, in particular to a single crystal boron nanocone, its preparation method and its application in electrical and field emission devices.

Background technique

Since Iijima discovered carbon nanotubes in 1992 (S. Jijima, Nature, 354(1991), 56), the preparation and application of metal, semiconductor, oxide and composite nano-one-dimensional materials have aroused great interest, especially It is their potential application in electronics, information, biomedicine, national defense, energy and other fields.

Boron is the only semiconductor element in group IIIA. Since boron has a unique electronic structure of "three centers and two electrons" and a unique icosahedral structure, boron one-dimensional nanomaterials (nanotubes, nanowires, nanobelts, and nanocones, etc.) can be formed with icosahedrons as structural units. ). Moreover, elemental boron is a solid with low density, high melting point, and low volatility. Its hardness is second only to that of diamond. It is one of the few elements that can be used in nuclear reactions, spacecraft reinforcement materials and protective layers, and high-temperature semiconductors. Meanwhile, theoretical calculations show that boron can form exotic quasi-planar, cage-like, and tubular structures. And compared with carbon nanotubes, boron nanotubes show a metallic density of states. Therefore, boron one-dimensional nanomaterials are a very good conductor. Therefore, boron one-dimensional nanostructure materials are capable of field emission, hydrogen storage, and lithium storage. And it has potential application value in high-temperature light materials and high-temperature electronic devices.

However, the current research on boron one-dimensional nanomaterials is still limited to boron nanowires and nanoribbons, and there are no literature and patent reports on boron nanocones that may have peculiar electrical and field emission properties.

Contents of the invention

The object of the present invention is to provide a single crystal boron nano cone, a simple preparation method of the single crystal boron nano cone, and the application of the single crystal boron nano cone in electrical and field emission devices.

A first aspect of the invention relates to a boron nanocone consisting of pure boron with a single crystal structure. The bottom diameter of the boron nano cone is 300-500 nanometers, the top diameter is 50-100 nanometers, and the length is 3-10 μm.

The second aspect of the present invention relates to a method for preparing boron nanocones, which uses a mixture of borides and boron powder as a source material, _a mixture of _Fe3O4 catalyst nanoparticles and a trace amount of boron powder as a co-catalyst, and utilizes chemical vapor deposition The boron nano cone is synthesized by CVD method, and the method comprises the following steps:

(a) the _{Fe3O4catalyst} nanoparticle solution of _surfactant coating is mixed with trace boron powder to form co-catalyst;

(b) depositing the cocatalyst obtained in step (a) on a silicon wafer substrate;

(c) under a protective gas atmosphere, heating the substrate at a temperature of 200-500° C. to remove the solvent and the surfactant in the co-catalyst;

(d) Under the atmosphere of protective gas, at the temperature of 1000-1300 ℃, the mixture of boride and boron powder as the source material is heated together with the substrate deposited with the co-catalyst from which the solvent has been removed, so that the source material evaporates and diffuses into The co-catalysts on the surface of the substrate are melted onto the droplets, thereby forming boron nanocones via a gas-liquid-solid growth mode.

In the above method, the surfactant in the step (a) includes oleylamine and oleic acid, the Fe in the co _- catalyst _O The particle diameter of the catalyst nanoparticles is 8-14nm, and the particle diameter of the boron powder is 500nm-20μm, And the weight _of the trace boron powder and _Fe3O4 catalyst nano particle solution is 0.0001-0.001. Among them, the role of doping a small amount of boron in Fe ₃ O ₄ nanoparticles is to form boron-iron alloy, which becomes a mixture of boride and boron powder. After the source material is evaporated, active points are deposited, which is beneficial to the formation of nanocones.

In the above method, the protective gas is a mixed gas of inert gas and 0-10% hydrogen, and the inert gas includes nitrogen and argon. Also, chemical vapor deposition CVD can be performed in vacuum or at one atmospheric pressure.

In the above method, the boride includes B ₂ O ₃ , and the weight ratio of boride to boron powder is 1:5˜5:1.

In the above method, the protective gas flow rate in step (d) is less than 100 sccm.

The third aspect of the present invention relates to the application of boron nanocones in field emission devices.

The fourth aspect of the present invention relates to the application of boron nanocones in electrical devices.

The present invention obtains high-quality single-crystal boron nanocone for the first time, which has good shape. And the method for preparing boron nanocone of the present invention is a kind of simple method, adopts this method to be able to prepare large-area, high-quality monocrystalline boron nanocone, prepared boron nanocone has good electrical property and field emission performance.

Description of drawings

Figure 1 is a TEM image of monodisperse Fe ₃ O ₄ nanoparticles.

Figure 2 is a SEM image of a single crystal boron nanocone; a) is a large-area image, and b) is a partially enlarged image.

Figure 3 is a TEM image and a selected area electron diffraction image (SAED) of a single crystal boron nanocone.

Fig. 4 is an electron energy loss spectrum (EELS) diagram of a single crystal boron nanocone.

Figure 5 is a graph showing the flow rate of carrier gas and the corresponding B nanocone topography.

Fig. 6 is an SEM image of boron nanocones under different growth times.

Figure 7 is the field emission curve of the B nanocone.

Fig. 8 is an SEM photo of three B nanocone device electrodes with different sizes.

Fig. 9 is a current curve of three B nanocone electrodes at an input voltage of -20 to 20V.

Detailed ways

Example 1. Preparation of Monodisperse Magnetic Nanoparticles Fe ₃ O ₄

Fe ₃ O ₄ nanoparticles were synthesized by the high-temperature liquid phase reduction method of Sun Shouheng et al. (Sun, SH et al., J.Am.Chem.Soc.2004, 126, 273), but the reaction conditions were improved to obtain 8-14 Nano Fe ₃ O ₄ particles. The specific preparation method is as follows:

0.5mmol iron acetylacetonate, 20ml phenyl ether, 2.5mmol 1,2-dodecanediol, 0.75mmol oleic acid and 0.75mmol oleylamine were sequentially added into the three-necked flask. Heat the mixed solution to 200°C at a heating rate of 5°C/min, react for half an hour, then continue heating to raise the temperature to 270°C, react at this temperature for one hour, remove the heat source, and let the reaction solution cool naturally to room temperature. Then add 40ml of absolute ethanol and stir for ten minutes, let it stand for 3-4 hours, centrifuge at 7000rpm, disperse the obtained sample in ethanol, micro-sonicate and centrifuge again, and finally the black product obtained is dispersed in heptane for preservation. If reacted at 270°C for 2 hours, 8nm Fe ₃ O ₄ particles can be obtained; if the concentration of iron acetylacetonate is increased, 14nm Fe ₃ O ₄ particles can be obtained.

The TEM (transmission electron microscope) image of 8 nm Fe ₃ O ₄ particles prepared by this method is shown in FIG. 1 .

Embodiment two: the preparation of single crystal boron nanocone:

First, mix 2ml of Fe ₃ O ₄ nanoparticle heptane solution with 0.1-1.0 mg of boron powder, then drop the mixed solution on the silicon substrate, and let it dry naturally.

Secondly, B ₂ O ₃ (99.99%) and B (99.9%) are mixed together at a mass ratio of 1:5, ground evenly, and put into an Al ₂ O ₃ reaction boat. The substrate silicon wafer is placed on the vertical upper end of the Al ₂ O ₃ reaction boat, and the reaction boat is placed in a horizontal quartz tube, and the reaction boat is placed outside the low-temperature reaction zone before heating.

Afterwards, chemical vapor deposition is carried out in two heating steps, as follows:

In the first step, under the protection of H ₂ /Ar mixed gas (5% H ₂ ), the reaction zone is first heated to 300-400°C at a rate of 5-50°C/min, and the reaction boat is quickly pushed into the high-temperature reaction zone. Insulated for 30 to 60 minutes, keeping the H ₂ /Ar mixed gas (5% H ₂ ) gas flow at 200 to 300 sccm (standard cubic centimeters per minute), to remove the organic molecules coated on the Fe ₃ O ₄ nanoparticles, and then Move the reaction boat out of the high temperature reaction area.

The second step is to quickly heat the reaction zone to 1000-1300℃ at a heating rate of 20-30℃/min, and then quickly push the reaction boat into the high-temperature reaction zone again, and react at this temperature for 1-4 hours. At this time, the H ₂ The flow rate of the /Ar mixed gas (5% H ₂ ) is 20-40 sccm (standard cubic centimeter per minute). After the reaction, the product was cooled to room temperature under the protection of H ₂ /Ar gas mixture (95% Ar and 5% H ₂ ). A layer of dark black or brown-black film can be observed on the surface of the silicon wafer. SEM images were obtained by direct scanning electron microscope observation of the silicon wafer. In addition, the silicon wafer was placed in absolute ethanol for ultrasonication, and the resulting solution was dropped on the microgrid for TEM testing.

Electron micrographs of boron nanocones are shown in Figure 2 (SEM, scanning electron microscope) and Figure 3 (TEM, transmission electron microscope). The bottom diameter of the nano cone is between 300-500 nanometers, the top diameter is between 50-100 nanometers, and the length is about 3-10 μm. The selected area electron diffraction pattern (SAED) shows that the boron nanocone has a single crystal structure. The electron energy loss spectrum (Electron Energy Loss Spectrum) test result of nanocone is shown in Fig. 4, and the K shell peak of B element appears in EELS spectrum at 188eV, and the characteristic peak of other elements is not found in EELS spectrum detection result, shows The composition of the prepared nanocones is pure boron.

Instance three, B ₂ O ₃ and the influence of B mass ratio

When the mass ratio of B ₂ O ₃ (99.99%) to B (99.9%) is 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1 and When the ratio is 5:1, the reaction temperature is 1000-1300° C., and the reaction time is 1-4 hours, and boron nanocones can be obtained. Boron nanocones with consistent morphology can be obtained under these ratios.

Example 4. Influence of shielding gas flow rate

When the reaction temperature is 1200°C, the reaction time is 1-4 hours, and the gas flow of Ar and H ₂ mixed gas (5% H ₂ ) is respectively 20, 30, 40, 50, 60, 70, 80 sccm, high-purity Boron nanocones whose shape and size are basically consistent with the surface. Electron micrographs of boron nanocones are shown in Figure 5. When the gas flow exceeds 100 sccm, no B nanocone formation is found.

Example 5. The Influence of Reaction Time

When the mass ratio of B ₂ O ₃ (99.99%) to B (99.9%) is 1:5, the reaction temperature is 1000-1300° C., and the reaction time is 1 hour, 2 hours, 3 hours and 4 hours, high purity can be obtained , high-density boron nanocone, and the electron micrograph of boron nanocone is shown in Figure 6. The reaction time has little effect on its morphology, but the diameter and length of the nanocones increase gradually when the reaction time increases.

Example six, the influence of temperature of reaction

Under the conditions that the mass ratio of _B2O3 ( _99.99 %) to B (99.9%) is 1:5, the reaction time is 2 hours, and the reaction temperature is 1000, 1100, 1200 and 1300°C, high purity and high Density of boron nanocones, as shown in Figure 2. Therefore, the reaction temperature has little effect on the surface morphology of boron nanocones.

Example seven, boron nano cone field emission performance test:

The boron nanocone grown on the silicon surface was used as the field emission cathode, the Mo needle tip was used as the anode, and the distance between the two electrodes was 200 μm. Slowly increase the voltage between the two electrodes while recording the emission current. Figure 7 is the field emission curve of the boron nanocone, when the voltage reaches 10μA/cm ² , the turn-on field strength is 3.5V/μm. When reaching the minimum emission current density required by flat panel display, ie 1mA/cm ² , the threshold field strength is 5.3V/μm. The field emission performance test shows that the single crystal boron nanocone has low turn-on field strength and threshold field strength, and is a very ideal field emission material.

Example eight, electrical property test of boron nanocone device:

Three boron nanocone electrodes were prepared by EBL (electron beam exposure) technique. Figure 8 shows the SEM pictures of three boron nanocone electrodes with different sizes. The dimensions of the three electrodes are: (a) electrode 1 (length: 3.1 μm, diameter: 110 nm and 90 nm), (b) electrode 2 (length: 3.8 μm, diameter: 240 nm and 280 nm), (c) electrode 3 (length: 2.5 μm, diameter: 450 nm).

KEITHLEY 4200-SCS semiconductor high-precision measuring instrument was used to test the electrical properties of the devices composed of three boron nanocones. Figure 9 shows the current curves of these three electrodes at an input voltage of -20 to 20V. Use the following formula to calculate its conductivity: σ=l/RS (σ is the conductivity, the unit is Ω cm ^-1 ; l is the length, the unit is cm; R is the resistance, the unit is Ω; S is the cross-sectional area, the unit is cm ² ). For device 1, the positive and negative saturation currents are 20pA and 40pA, respectively, and the calculated conductivities are 3.7×10 ^-5 (Ω·cm) ^-1 and 7.3×10 ^-5 (Ω·cm) ^-1 ; for device 2 , the positive and negative saturation currents are 32pA and 27pA respectively, and the calculated conductivities are 2.1×10 ^-5 (Ω·cm) ^-1 and 1.8×10 ^-5 (Ω·cm) ^-1 respectively; The negative saturation currents are 60pA and 60pA respectively, and the calculated conductivity is 1.0×10 ^-5 (Ω·cm) ^-1 . The measured IV data show that the electron transport of B nanocones does not change significantly compared with that of bulk boron.

Claims (11)

1. A boron nanocone is composed of pure boron and has a single crystal structure. The bottom diameter of the boron nanocone is 300-500 nanometers, the top diameter is 50-100 nanometers, and the length is 3-10 μm. 2. a method for preparing boron nano cone according to claim 1, the method _is with the mixture of boride and boron powder as source material, Fe _o The mixture of catalyst nanoparticles and trace boron powder is as co-catalyst, utilizes The chemical vapor deposition CVD method synthesizes the boron nano cone, and the method comprises the following steps: (a) the _{Fe3O4catalyst} nanoparticle solution of _surfactant coating is mixed with trace boron powder to form co-catalyst; (b) depositing the cocatalyst obtained in step (a) on a silicon wafer substrate; (c) under a protective gas atmosphere, heating the substrate at a temperature of 200-500° C. to remove the solvent and the surfactant in the co-catalyst; (d) Under the atmosphere of protective gas, at the temperature of 1000-1300 ℃, the mixture of boride and boron powder as the source material is heated together with the substrate deposited with the co-catalyst from which the solvent has been removed, so that the source material evaporates and diffuses to The co-catalyst on the surface of the substrate melts onto the droplets, thereby forming boron nanocones through the gas-liquid-solid growth mode, Wherein the surfactant is oleylamine and oleic acid, and the weight ratio of _a trace amount of boron powder to the _Fe3O4 catalyst nano particle solution is 0.0001-0.001. 3. The method according to claim 2, wherein in step (a), the particle diameter of _Fe3O4 catalyst nanoparticles is _8-14nm , and the particle diameter of boron powder is 500nm-20μm. 4. The method according to claim 2, wherein said protective gas is a mixed gas of inert gas and 0-10% hydrogen. 5. The method of claim 4, wherein said inert gas comprises nitrogen and argon. 6. The method according to claim 2, wherein chemical vapor deposition (CVD) can be performed under vacuum or one atmosphere. 7. _The method of claim 2, wherein the boride comprises _B2O3 . 8. The method according to claim 7, wherein the weight ratio of boride to boron powder is 1:5˜5:1. 9. The method of claim 2, wherein the shielding gas flow in step (d) is less than 100 sccm. 10. The application of the boron nanocone according to claim 1 in field emission devices. 11. The application of the boron nanocone according to claim 1 in electrical devices.

Images