KR100460332B1 - Production method of silicon carbide nanowires - Google Patents

Abstract

The present invention relates to a novel method for producing silicon carbide nanowires, which uses gallium, gallium nitride, and iron as catalysts, and reacts a silicon substrate with a methane and hydrogen mixed gas at a temperature in the region of 1000 to 1200 ° C. for high purity and high density. It relates to a method for producing the silicon carbide nanowires. The method for producing silicon carbide according to the present invention comprises the steps of dissolving an iron salt in a polar solvent, thereby coating a silicon substrate; Placing the coated silicon substrate in a reactor, placing the gallium metal and gallium nitride in a quartz boat, placing the coated silicon substrate close to the substrate, and then heating the reactor; And after reaching a temperature in the region of 1000 to 1200 ° C., injecting methane gas and hydrogen gas into the reactor, and cooling to room temperature. The silicon carbide nanowires prepared according to the present invention are impurities It grows to high purity, high density of about 10 ¹⁰ / cm ² and has excellent crystallinity and is oriented perpendicular to the substrate. In addition, the diameter ranges from 10 to 60 nm and grows to a length of 300 to 500 μm, and has a long diameter ratio of about 10 ⁴ .

Description

Production Method of Silicon Carbide Nanowires {PRODUCTION METHOD OF SILICON CARBIDE NANOWIRES}

The present invention relates to a method for producing silicon carbide nanowires.

Since the structure of carbon nanotubes was reported in 1991 (S. Iijima, Nature 354, 56 (1991)), methods of using carbon nanotubes in the synthesis of nanotubes and nanowires have been studied. The surface or empty interior of the carbon nanotubes is highly likely to be replaced or filled with other elements. In fact, using a carbon nanotube as a template, GaN, Si ₃ is reacted with a volatile metal oxide or a metal halide. Nanotubes and nanowires of nitrides such as N ₄ , BN, carbides such as TiC and SiC have been synthesized (J. Zhu, S. Fan, J. Mat. Res. 14, 1175 (1999); HAn, S. Fan, Q. Li, B. Gu, Appl. Phys. Lett. 71, 2271 (1997); W. Han, P. Redlich, F. Ernst, M. Ruhle, Appl. Phys. Lett. 75, 1875 (1999); H. Dai, EW Wong, YZ Lu, SS Fan, CM Lieber, Nature 375, 769 (1995)). This method is called the carbon nanotube confinement reaction, which was first reported in 1995 for the synthesis of silicon carbide nanowires (H. Dai, EW Wong, YZ Lu, SS Fan, CM Lieber, Nature 375, 769). 1995) and then vertically oriented silicon carbide nanowires were synthesized by reacting well-oriented carbon nanotubes with silicon oxide powder at 1400 ° C. in argon atmosphere (Z. Pan, HL Lai, FCK). Au, X. Duan, W. Zhou, W. Shi, N. Wang, CS Lee, NB Wong, ST Lee, S. Xie, Adv. Mater. 12, 1186 (2000)).

Several methods for the synthesis of silicon carbide nanowires have been reported, some of which have been studied over the past 40 years and have been modified from the well known method of synthesis of silicon carbide whiskers. First of all, there is a thermal carbon reduction method of silica, which is synthesized at 1650 ° C. in a porous dry gel state containing nano-sized carbon particles (GW Meng, Z. Cui, LD Zhang, F. Phillipp, J. Crystal). Growth 209, 801 (2000)). In addition, there is a method of synthesizing silicon chloride and carbon tetrachloride by using a catalyst metal sodium as a reducing agent for a long time at 400 ° C. under high pressure (JQ Hu, QY Lu, KB Tang, B. Deng, RR Jiang, YT Qian, WC). Yu, GE Zhou, XM Liu, JX Wu, J. Phys. Chem. B 104, 5251 (2000)). Electric discharge method (T. Seeger, P. Kohler-Redlich, M. Ruhle, Adv. Mater. 12, 279 (2000)) generally used for the synthesis of nanotubes and nanowires, laser vaporization (W. Shi, Y. Zheng, H. Peng, N. Wang, CS Lee, ST Lee, J. Am. Ceram. Soc. 83, 3228 (2000)), thermal filament chemical vapor deposition (XT Zhou, N. Wang, HL Lai, HY) Peng, I. Bello, NB Wong, CS Lee, ST Lee, Appl. Phys. Lett. 74, 3942 (1999)), chemical vapor deposition (XT Zhou, HL Lai, HY Peng, FCK Au, LS Liao, N.). Wang, I. Bello, CS Lee, ST Lee, Chem. Phys. Lett. 318, 58 (2000)). Except for thermal carbon reduction, the above described methods use metal catalysts and the silicon carbide nanowires can be deposited using the VLS (Vapor-Liquid-Solod) mechanism (RS Wagner, WC Ellis, Appl. Phys. Lett. 4, 89 (1964)). They have something in common. That is, when the reactants are vaporized at the synthesis temperature, the gaseous raw materials are adsorbed onto the substrate on which the metal catalyst is deposited, become a liquid molten state together with the catalyst, and the raw materials continuously supplied thereto are saturated. Through the process of becoming.

A method that does not go through the VLS mechanism has been reported, which was successfully synthesized by coating a 40 nm thick nickel and carbon layer on a silicon substrate. Here, solid silicon melts at the synthesis temperature, becomes a liquid molten state containing nickel and carbon, and then becomes supersaturated to form solid silicon carbide nanowires (YJ Xing, QL Hang, HF Yan, HY Pan, J. Xu, DP Yu, ZH Xi, ZQ Xue, SQ Feng, Chem. Phys. Lett. 345, 29 (2001)). However, there is a disadvantage in that yield and density are low as in the above methods.

An object of the present invention is to provide a new method for producing a high purity, high density silicon carbide nanowires that can solve the problems appearing in the conventional method for manufacturing nanowires as described above.

1 is a schematic diagram of an apparatus used in an embodiment of the manufacturing method according to the present invention.

2 is a scanning electron micrograph of a silicon substrate coated with iron chloride.

Figure 3 is a scanning electron micrograph of the metal particles produced by the reduction of iron chloride.

Figure 4 is a scanning electron micrograph of the silicon carbide nanowires prepared according to the present invention.

5 is a graph showing the results of X-ray trace analysis of silicon carbide nanowires prepared according to the present invention.

Figure 6 is a transmission electron micrograph of the silicon carbide nanowires prepared according to the present invention.

Figure 7 (a) is a high magnification transmission electron micrograph of the silicon carbide nanowires prepared according to the present invention, (b) is an enlarged photograph of (a).

8 is an electron diffraction photo of silicon carbide nanowires prepared according to the present invention.

9 is an X-ray diffraction graph of silicon carbide nanowires according to the present invention

Explanation of symbols of the main parts of the drawings

101: tubular electric furnace (furnace) 102: quartz tube

103: quartz boat 104: silicon substrate

105: gas injection direction 106: gas discharge direction

In order to achieve the object as described above, the present inventors have made intensive studies, and have found that silicon carbide nanowires of high purity and high density can be manufactured.

The present invention provides a novel method for producing silicon carbide nanowires, and particularly, using high purity and high density silicon carbide using gallium, gallium nitride and iron as catalysts, and reacting a silicon substrate with a mixture of methane and hydrogen gas. It relates to a method of manufacturing a route.

The present invention comprises the steps of dissolving iron chloride hydrate in a polar solvent thereby coating a silicon substrate; Placing the coated silicon substrate in a reactor, placing the gallium metal and gallium nitride in a quartz boat, placing the coated silicon substrate close to the substrate, and then heating the reactor; After reaching a temperature in the region of 1000 ~ 1200 ℃, it provides a method for producing silicon carbide nanowires comprising the step of injecting methane gas and hydrogen gas into the reactor and cooling to room temperature.

In the present invention, a conventional silicon substrate is used as a raw material of silicon. At this time, any kind of silicon wafer can be used, regardless of polishing, having a crystal plane such as (100) or (111). In the present invention, coating the mixed solution of the iron salt and the polar solvent on the silicon substrate is a step for producing nanoparticles on the silicon substrate. The resulting nanoparticles act as a catalyst for nanowire synthesis, and hydrogen gas was used to serve as an etching gas that makes the metal nanoscale. Iron nitrate may be used instead of the iron chloride hydrate used in the present invention. In addition, other metal salts such as nickel and cobalt may be used instead, but these salts are difficult to adsorb on the surface of the silicon substrate and are not uniform, so that high-density nanoparticles are not produced. Not used in the present invention. As the iron chloride hydrate or nitrate, one selected from iron chloride tetrahydrate, iron chloride hexahydrate, and iron nitrate hydrate can be used.

As the solvent used for dissolving the metal salt, alcohols and the like, which are solvents that evaporate well, can be used as the polar solvent which dissolves the metal salt well, and water can also be used. However, since water has a problem that evaporation is difficult compared to ethanol or methanol, it is more preferable to use alcohols such as ethanol or methanol.

The amount of methane gas and hydrogen gas used in the present invention is controlled in units of standard cubic centimeter per minute (sccm), and the optimum relative flow rate for the synthesis of nanowires is 10 to 40 sccm for methane gas and 300 to 500 sccm for hydrogen. . In the case of methane, if the flow rate is less than 10 sccm, there is not enough carbon to decrease the density during the synthesis of the nanowires, and if it exceeds 40 sccm, the amount of carbon supplied increases so that more carbon particles are formed than the nanowires. Covering may occur. In case of hydrogen, less than 500 sccm, the amount of nanowires could not be reduced enough to help the decomposition of methane, and if it exceeds 700 sccm, hydrogen would be excessively supplied, preventing the decomposition of methane and causing severe etching of the substrate. This makes the nanowire synthesis difficult.

Methane gas and hydrogen gas are injected and mixed at the same time to maintain the same flow rate for about 20-30 minutes. In this case, the silicon carbide nanowires are synthesized in about 5 to 10 minutes, but only after 20 minutes or more, the density increases and grows vertically. In the case of injection for 30 minutes or more, even if injected up to 1 hour, the result of injection for 30 minutes in the diameter, length, density, etc. of the nanowires is almost no difference, so it is not necessary to inject more than 1 hour. For this reason, carbon generated in the gaseous phase must be supplied to the catalyst particles deposited on the silicon substrate, but if the density of the silicon nanowires is increased to several hundred microns at a density of 10 ¹⁰ / cm 2, the growth of carbon is prevented from reaching the substrate. It seems to stop.

In the method of manufacturing the nanowire according to the present invention, when coating the silicon with the iron salt, the thickness of the iron salt on the substrate should be in the range of 100nm ~ 1㎛, in particular it is effective to uniformly coated in 200 ~ 400nm. If the coated metal film is too thick, micro-size particles larger than nano size may be produced when etched with hydrogen gas, and if the thickness is too thin, the metal may not remain on the substrate by hydrogen gas etching, which may lead to nanowire synthesis. It can be difficult. In addition, nanowires grow on both sides when coated with iron salt, regardless of the polished or unpolished surface of the silicon substrate or the crystal orientation.

The reaction temperature should be in the range of 1000 to 1200 ° C., and the temperature is raised to the reaction temperature while injecting argon gas which is an inert gas. When the temperature of the reactor rises above 900 ° C., gallium is deposited from gallium and gallium nitride onto a silicon-coated silicon substrate in a vapor state. At this time, since argon gas is injected, gallium vapor can be effectively deposited on the silicon substrate. If only gallium is used without using gallium and gallium nitride at the same time, the synthesized nanowires have a lower density, which is believed to increase the vapor pressure of gallium by forming an eutectic melting point. Gallium is deposited in the liquid phase on the iron coated on the silicon substrate, and when the reaction temperature is reached to inject methane gas and hydrogen gas, the hydrogen gas etches these gallium and the deposited iron to form nano-sized particles. Silicon is dissolved in gallium to form nanoparticles of gallium-iron-silicon component, and carbon generated by decomposition of methane gas is adsorbed to the particles to form nanoparticles of gallium-iron-silicon-carbon component. When supersaturated by continuously melting silicon and carbon, solid silicon carbide nanowires grow. According to the literature, it is known that silicon is dissolved in gallium at an atomic ratio of 14 to 51% at 1000 to 1200 ° C. The role of gallium can be interpreted as helping to synthesize nanowires by increasing the reaction rate with carbon by making silicon better melt and increasing the concentration of reactants. The amount of gallium is about 0.01 g is sufficient for the silicon substrate area of about 10 cm ² , gallium nitride can be used in the same amount.

Injecting an inert gas in the present invention serves to block the intake of air to prevent oxidation. If no inert gas is injected at the step of raising the temperature, the iron salt is oxidized, which lowers its role as a catalyst and cannot effectively deposit gallium vapor on the substrate. In addition, the silicon carbide nanowires may be oxidized if the inert gas is not injected in the step of lowering the temperature. For this purpose, in the present invention, argon gas is used. , Nitrogen gas and the like can also be used. In an embodiment of the present invention, argon gas was maintained at about 500 sccm to inject to increase the yield of silicon carbide nanowires.

Most nanowire manufacturing methods use the VLS mechanism. That is, the synthetic raw material is supplied in a gaseous state, and these are melted with a metal catalyst to undergo a process of synthesizing a solid product through a liquid state. It is also reported that the reactants are fed into the solid phase and dissolved in the catalyst to make a solid product (SLS), and the reaction method is produced via a mechanism (VS) in which the reactant is converted directly into a solid product without forming a catalyst and a liquid phase (Y. Zhang, N. Wang, R. He, J. Liu, X. Zhang, J. Zhu, J. Crystal Growth 233, 803 (2001)), but the manufacturing method according to the present invention is a mixture of VLS and SLS mechanisms. Silicon carbide nanowires are synthesized by supplying solid silicon and gaseous carbon at the same time.

In particular, since a conventional silicon substrate can be used as a source of silicon, an additional gaseous or solid silicon raw material is not required, and since methane is used as a carbon raw material, it can be a relatively simple method.

In addition, by using gallium and gallium nitride as a catalyst and coating iron salt on the substrate, nanowires can grow at a high density because highly reactive nano-sized catalyst is evenly covered on a large-area substrate. To grow. It was also confirmed that the crystallinity of the grown crystals was also very good.

Hereinafter, a method of manufacturing a nanowire according to the present invention will be described in more detail with reference to Examples. The scope of the present invention is not limited by the following examples.

Example

After inserting the quartz tube 102 in the tubular electric furnace 101 and installing it as shown in FIG. 1, a piece of gallium having a weight equal to 0.01 g of gallium nitride powder is placed in the quartz boat 103 and the quartz tube 102. Located in the middle of the. Iron chloride tetrahydrate was dissolved in ethanol to make a 0.01 M ethanol solution. The polished side of the silicon substrate of size 1 × 10 cm ² required for synthesis was coated with a few drops of the solution and then dried at room temperature for 10 minutes. A scanning electron microscope (SEM) photograph of the iron chloride coated substrate is shown in FIG. 2. The thickness of iron chloride was about 300 nm.

The substrate coated on the quartz boat 104 was placed horizontally and placed near the quartz boat 103 containing gallium, and then the temperature of the electric furnace was increased to 1100 ° C. while argon gas was injected at 500 sccm. Argon gas is to prevent the oxidation of iron chloride, iron chloride was reduced to iron, the scanning electron micrograph of the metal particles produced by reducing the iron chloride is shown in FIG. The particles had a micrometer size.

After it became 1100 degreeC, methane gas and hydrogen gas were made to react by flowing for 30 minutes by the constant flow rates of 40 sccm and 500 sccm, respectively. After 30 minutes, the mixture was cooled to room temperature while flowing argon gas at 500 sccm into the quartz tube.

The cooled silicon substrate was taken out to confirm that the iron salt coated side turned blue or gray. Scanning electron micrographs of the synthesized silicon carbide nanowires are shown in FIG. 4. The length of the nanowire was 500 μm and the diameter was 10-60 nm, and it was confirmed that high-purity, high-density nanowires were vertically oriented and synthesized on the substrate.

Analysis of the components with an EDS (Enegy Dispersive x-ray Spectrometer) revealed that the synthesized nanowires were composed of a 1: 1 ratio of Si: C and contained trace amounts of gallium. The oxygen content due to the silicon oxide surrounding the surface of the nanowires was also measured. The result graph is shown in FIG.

Analysis of the nanowires by TEM (Transmission Electron Microscopy) revealed that they have a 10-60 nm distribution with an average diameter of 40 nm and do not contain catalyst particles at the ends or surfaces of the nanowires. . It can be confirmed by transmission electron micrograph shown in Figure 6 that the smooth and straight nanowires were synthesized.

As a result of analysis using a high resolution transmission electron microscope, it was confirmed that the synthesized nanowires had a cube single crystal structure coated with silicon oxide. Figure 7 (a) shows a high magnification transmission electron micrograph showing that the long axis (growth direction) of the silicon carbide nanowire is parallel to the (111) direction. In (b), which is an enlarged photograph of (a) of FIG. 7, the streaks perpendicular to the axial direction represent the (111) plane of silicon, and the distance therebetween is measured to be 2.53 m 3, indicating that the silicon carbide of the cube. It can be seen that the silicon oxide layer covers the surface of the nanowires with a thickness of about 2 nm.

In addition, it can be confirmed that the synthesized nanowire is a single crystal of a cube even through a SAED (Selected Area Electron Diffraction) shape. The photo is shown in FIG.

The nanowires were analyzed by XRD (X-ray diffractometer, X-ray diffractometer) and the graphs are shown in FIG. 9. It can be seen that only silicon carbide single crystals are produced without other components, and that they are in good agreement with the international standard line (shown as straight lines in the graph) of the cubic silicon carbide single crystals. No spectra were shown for other compounds including gallium, iron, silicon.

In the present invention, since the silicon substrate can be used as a source of silicon, no additional gaseous or solid silicon raw materials are required, and since methane is used as a carbon raw material, high purity and high density nanowires can be obtained through a relatively simple method. It can manufacture.

In addition, use of gallium and gallium nitride as a catalyst, and because it can uniformly cover the nano-sized high reactivity on a substrate having a large area catalyst in a manner that coats the iron salt to the substrate at a constant size, the silicon carbide nanowires 10 ¹⁰ / It grows in the vertical direction at a high density of about cm ² . In addition, silicon carbide nanowires are very crystalline and grow in high purity with almost no impurities such as particles of other compounds.

The manufactured silicon carbide nanowires are single crystals having the same growth direction and have a long diameter ratio of 1 to 60 nm in diameter and 300 to 500 µm in length and a large diameter to length ratio of 10 ⁴ dimensions. Have excellent strength, toughness, passion. Therefore, not only can be used in nano-electric materials and electronic devices, but also can be used as a high functional polymer or ceramic reinforcing material to replace the conventional gilicon whiskers.

Claims (7)

Dissolving the iron salt in a polar solvent, thereby coating the silicon substrate; Placing the coated silicon substrate into a reactor, placing the gallium metal and gallium nitride in a quartz boat and placing the substrate close to the substrate, and then heating the reactor; And After the reactor reaches a temperature in the region of 1000 to 1200 ° C., injecting methane gas and hydrogen gas into the reactor, and then cooling to room temperature; Silicon carbide nanowires manufacturing method comprising a. According to claim 1, The iron salt is selected from iron chloride tetrahydrate, iron chloride hexahydrate and iron nitrate hemihydrate Way. According to claim 1, Coating thickness in the step of coating the silicon is to be 100 nm ~ 1 ㎛ Way. According to claim 1, The silicon substrate is used as a raw material of silicon Way. According to claim 1, Characterized by using gallium metal and gallium nitride as catalysts together with iron Way. According to claim 1, Injecting the methane gas and hydrogen gas at the same time characterized in that the use of carbon raw material Way. Under the temperature of 1000 ~ 1200 ℃ Using gallium, gallium nitride and iron as catalysts, It is characterized by using a reaction of methane gas and hydrogen gas on the silicon substrate Method for producing silicon carbide nanowires.