KR100918293B1 - Synthesis of SiC nanowires - Google Patents

Abstract

The present invention relates to a method for producing silicon carbide nanowires, and more particularly, as a single precursor for simultaneously providing silicon (Si) and carbon (C), in particular dichloromethylvinylsilane (CH ₂ CHSiC (CH ₃ ) Cl ₂ ). ) And injected into the reactor in a reducing atmosphere maintained at high temperature with a controlled carrier gas and deposited on a substrate, thereby reproducibly producing silicon carbide nanowires having a very small diameter and having excellent single crystallinity. Therefore, the present invention relates to a method for producing silicon carbide nanowires, which enables the production of field emission devices exhibiting excellent field emission characteristics.

Nanowires, Silicon Carbide, Field Emission Devices

Description

Method for producing silicon carbide nanowires {Synthesis of SiC nanowires}

1 is a schematic cross-sectional view of an apparatus for manufacturing silicon carbide nanowires according to the present invention.

2 is a scanning electron micrograph of silicon carbide nanowires [Sample 3] grown on a silicon substrate according to Example 1 of the present invention.

3 is an X-ray diffraction graph of silicon carbide nanowires [Sample 3] prepared according to Example 1 of the present invention.

Figure 4 is a transmission electron micrograph and electron diffraction photograph of the silicon carbide nanowires [Sample 3] prepared according to Example 1 of the present invention.

5 is a structural diagram of a field emission device using silicon carbide nanowires prepared according to the present invention.

6 is a graph showing a current density according to an applied voltage of a silicon carbide nanowire [Sample 11] prepared according to Example 2 of the present invention and a Fowler-Nordheim graph.

[Description of Major Symbols in Drawing]

10: heating element

20: reaction tube 21: dilution gas inlet 22: gas outlet

30: reaction material and carrier gas inlet

40 substrate 50 reactant material 60 cooling tank

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

Cathode is a key part of the field emission display technology. Much research is being conducted on cathode technology that can be driven at low voltage and can be manufactured in large areas at low process costs.

The field emission cathode must have a high electric field or have a low work function value for the cathode material to obtain a high emission current. In particular, the tip of the field emission cathode material is destroyed and deteriorated at high temperatures due to the heat generated when electrons are released. Should be considered.

Currently, Mo, Si, W, etc. are widely used as the field emission cathode material, but there is a big problem in the lifespan and stability of the cathode material due to long time operation, and because of the poor electron emission efficiency, high conductivity and sharp tip shape Attention has been paid to the use of carbon nanotubes as the field emission cathode emitter tips. [C. A. Spindt, J. Appl. Phys. 39, 3504-3505 ((1968), Nai Gui Shang, et al. Adv. Mat. 14, 1308-1311 (2002))

As an alternative material for overcoming the above problems of cathode materials, recent researches incorporating nanotechnology based on high aspect ratio 1D nanomaterials such as carbon nanotubes (CNT) into cathodes have been actively conducted. However, there are disadvantages in that durability and thermal stability are weak.

On the other hand, the optimal field emission cathode material should have a low work function value, excellent durability and thermal stability, and excellent field emission characteristics. For this purpose, the diameter of the tip of the field emission cathode material should be as small as possible and sharp to have good field emission characteristics.

Accordingly, the present invention is a field emission cathode replacement material such as Mo, Si, and carbon nanotubes, based on the above-mentioned problems and needs of the prior art, has a low work function value, has excellent durability and thermal stability, and has a high aspect ratio. The silicon carbide compound is selected as a field emission cathode material and injected into an environment where high temperature reducing conditions are maintained by limiting carrier gas and flow rate, and deposited on a substrate on which a catalyst layer is formed. Silicon carbide nanowires can be produced in a reproducible manner, and it is possible to manufacture a large area, thereby finding a low cost process design, thereby completing the present invention.

In addition, the manufactured silicon carbide nanowires can be used to fabricate fabricated field emission devices that exhibit excellent field emission characteristics with low turn-on voltage and high field enhancement factor (β). have.

Accordingly, an object of the present invention is to provide a method for reproducibly producing silicon carbide nanowires having a small diameter and excellent single crystallinity, and a field emission device using the same.

The present invention provides a process for forming a catalyst layer in which a catalyst selected from gold, nickel, iron, cobalt, palladium, or an alloy thereof is deposited on a substrate, and dichloromethylvinylsilane in a reducing atmosphere maintained at 900 to 1200 ° C. And a method for producing silicon carbide nanowires comprising the step of injecting a carrier gas together with a carrier gas at a flow rate of 1 to 20 sccm and a flow rate of 100 to 1000 sccm for 10 to 120 minutes. .

Hereinafter, the present invention will be described in detail.

The present invention uses dichloromethylvinylsilane (CH ₂ CHSiC (CH ₃ ) Cl ₂ ) as a single precursor that provides silicon (Si) and carbon (C) at the same time. Since the silicon carbide nanowires having a very small diameter and having excellent single crystallinity can be reproducibly produced by injecting into a reactor of a reducing atmosphere maintained in the reactor, manufacturing of a field emission device exhibiting excellent field emission characteristics is possible. It is related with the manufacturing method of the silicon carbide nanowire made possible.

The present invention is characterized by using dichloromethylvinylsilane as a feedstock for silicon and carbon. The dichloromethyl vinylsilane contains a larger amount of carbon than silicon, unlike MTS (methyltrichlorosilane), TMS (tetramethylsilane), and HMDS (hexamethyldisilane), which are known as single precursors that can simultaneously supply silicon and carbon. The production of the gland is easy, and thus may have good single crystallinity.

In addition, the volatility is much stronger than the single precursor, there is a feature that can lower the manufacturing temperature of the nanowires, due to this feature the silicon carbide nanowires of the present invention will have a small diameter and excellent single crystallinity.

In addition, according to the present invention, in preparing the silicon carbide nanowires, the diameter of the dichloromethylvinylsilane is 200 through thermal decomposition of the dichloromethylvinylsilane gas by injecting the dichloromethylvinylsilane into the high temperature reaction tube through the injection port at a constant flow rate together with the carrier gas. Silicon carbide nanowires of less than or equal to nm, preferably in the range of 20 to 200 nm, can be produced.

A schematic diagram of the apparatus used for the production of the silicon carbide nanowires of the present invention is shown in FIG. 1. The apparatus includes a heating element 10 for controlling the internal temperature of the reaction tube, a reaction tube 20 designed to introduce and discharge a carrier gas, and an injection port 30 for dichloromethyl vinylsilane and a carrier gas and an injection port 21 for dilution gas. , The outlet 22, the substrate 40 located inside the reaction tube, the cooling tank 60 for cooling the dichloromethyl vinylsilane raw material 50, and the like.

The heating element 10 serves to control the internal temperature of the reaction tube 20 to between 1300 ℃ at room temperature, the reaction tube 20 is located inside the horizontal while penetrating the inside of the heating element 10 horizontally. At the end, the carrier gas and the dilution gas outlet 22, the dichloromethyl vinylsilane 50, the carrier gas 21 and diluent gas injection port 21 of the dichloromethyl vinylsilane and the substrate 40 inside the reaction tube This is located.

The method for producing the silicon carbide nanowires according to the present invention is as follows.

First, a catalyst layer on which a catalyst selected from gold, nickel, iron, cobalt, palladium, or an alloy thereof is deposited is formed on a substrate. The introduction of this method to selectively fabricate silicon carbide nanowires at specific locations is well known, known as the Vapor-Liquid-Solid process. The principle is that the catalytic materials such as and the like react with each other to form a eutectic alloy.

As the substrate, particularly, silicon and sapphire are more preferable for the purpose of the present invention. In addition, when using the E-beam evaporation (E-beam evaporation) process in the formation of the catalyst layer, the thickness of the catalyst layer can be adjusted thinly and accurately, and more preferable for the purpose of the present invention in terms of forming a homogeneous catalyst layer.

Silicon carbide nanowires are grown after depositing the catalyst layer on the substrate in the range of 10 to 100 GPa.

That is, a substrate is mounted in the reaction tube as shown in FIG. 1, and the temperature inside the reactor is raised to a range of 900 to 1200 ° C., and maintained for about 10 to 20 minutes. At this time, the inside of the reactor continuously flows the diluted gas (diluted gas) of 100 to 1000 sccm from the time of starting the temperature to make the inside of the reaction tube into a reducing atmosphere.

Here, when the temperature inside the reaction tube is less than 900 ℃, an amorphous phase such as SiOx is generated, and as the temperature inside the reactor increases, the ratio of the silicon carbide single crystal produced on the substrate increases, the temperature inside the reactor is 1200 ℃ If too high, a Si crystal phase is formed, or a silicon substrate used as a substrate causes a chemical reaction with dichloromethylvinylsilane, which is a reaction gas, thereby making it difficult to manufacture nanowires.

As the diluent gas, an inert gas or a reducing gas may be used, and specifically, for example, argon gas (Ar), nitrogen gas (N ₂ ), hydrogen gas (H ₂ ), methane gas (CH ₄ ), or the like. The gas selected can be used.

Subsequently, dichloromethylvinylsilane gas is injected into the reactor together with a carrier gas at a temperature in the reactor at a temperature in the range of 900 to 1200 ° C, wherein the dichloromethylvinylsilane and the carrier gas are in the range of 1 to 20 sccm, respectively. The silicon carbide nanowires are grown by injecting together at a flow rate of 100 and 1000 sccm and maintaining them for 10 to 120 minutes. In this case, when the dichloromethyl vinylsilane flow rate is less than the above range, it is difficult to manufacture silicon carbide nanowires due to a decrease in the source of silicon and carbon, and when the dichloromethyl vinylsilane flow rate is exceeded, the diameter of the manufactured nanowires increases or inhibits crystallinity. If the flow rate of the carrier gas is less than the above range, the flow rate decreases, so that the source does not reach the substrate inside the reaction tube, so that the production of silicon carbide nanowires is not easy. The time for silicon to participate in the growth of a silicon substrate is limited, making the silicon carbide nanowires difficult.

In particular, it is advantageous for the production of silicon carbide nanowires having a small diameter and excellent single crystal properties desired in the present invention only when the flow rates of dichloromethylvinylsilane and a carrier gas satisfy the above ranges at the same time.

As the carrier gas, an inert gas or a reducing gas that is commonly used is used, and specifically, hydrogen gas, argon gas (Ar), nitrogen gas (N ₂ ), hydrogen gas (H ₂ ), methane gas (CH ₄ ), and the like. One kind or a mixture of two or more kinds selected from can be used.

In addition, the dichloromethyl vinylsilane and the carrier gas injected in the above range of flow rates induce the growth of the silicon carbide nanowires while maintaining for 10 to 120 minutes, preferably 30 to 60 minutes, inside the reactor in a high temperature and reducing atmosphere. At this time, if the retention time is less than the above range, the density and crystallinity of the manufactured silicon carbide nanowires are inferior, and if the above range is exceeded, the diameter of the manufactured silicon carbide nanowires is increased or the thickness of the amorphous layer on the surface of the nanowires is increased, thereby increasing the crystallinity. Can be inhibited.

As suggested above, silicon carbide nanowires having a very small diameter in the range of about 20 to 200 nm, a length in the range of about 10 to 100 mm, and having excellent single crystallinity can be produced in large quantities with reproducibility.

In addition, the manufactured silicon carbide nanowires have a driving voltage required to flow 10 mA / cm 2 or more and ˜1.6 V / cm, and drive voltages required to flow 1 mA / cm 2 or more appear to ˜2.5 V / cm or less, resulting in low driving. It exhibits excellent field emission characteristics even at voltage.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the following Examples.

Example  1. Silicon and Carbon source  Comparison by type

A metal catalyst layer having a thickness of 20 to 100 GPa was formed on the silicon substrate by using the E-beam evaporation method.

The environment of the reactor equipped with the substrate on which the catalyst layer was formed was controlled as follows, wherein hydrogen gas was used as the diluent gas and its flow rate was 300 to 600 sccm, and the nanowire growth temperature (temperature inside the reactor) was 900 to Silicon carbide nanowires were prepared by adjusting the temperature to 1100 ° C., the flow rate of silicon and carbon source 1 to 10 sccm, the holding time of the reactor to 30 to 90 minutes, and the temperature of the cooling bath at 0 ° C. under the same conditions. The types of, silicon and carbon sources were different as shown in the following Table 1.

The single crystallinity of the prepared silicon carbide nanowires was measured by calculating the half width using an X-ray diffraction pattern, and the diameter was measured using a high magnification electron microscope, and the field emission characteristic was " Flat screen "method was used to measure the constant between the nanowire and the anode at a high vacuum of 10 ⁶ Torr or more, the results are shown in Table 1 below.

As shown in Table 1, it can be seen that the half width and diameter are smaller than those of methyl triclosilane and hexamethylvinylsilane using dichloromethylvinylsilane as the silicon and carbon source, and thus the field emission characteristics are excellent. Can be.

Example 2 Comparison with Nanowire Growth Temperature

The silicon carbide nanowires were prepared under the same conditions as in Example 1, but dichloromethylvinylsilane was used as the silicon and carbon source, and the results obtained by varying the growth temperature of the nanowires are shown in Table 2 below.

As shown in Table 2, when the dichloromethyl vinyl silane is used as the silicon and carbon source, the growth temperature of the nanowire is in the range of 900 ~ 1200 ℃ it can be seen that the diameter is small and excellent in single crystal and field emission characteristics. In particular, when the growth temperature of the nanowires is less than 900 ℃, amorphous SiOx is formed, when the growth temperature is above 1200 ℃ Si crystal phase is formed, or the silicon substrate used as a substrate is a chemical reaction with dichloromethyl vinyl silane, a reaction gas of the nanowires It can be seen that manufacturing is difficult.

Example 3 Comparison with Flow

The silicon carbide nanowires were prepared under the same conditions as in Example 1, using dichloromethylvinylsilane as the silicon and carbon source, the growth temperature of the nanowires to 1100 ° C., and the flow rates of the dichloromethylvinylsilane and the carrier gas were varied. The results obtained are shown in Table 3 below.

As shown in Table 3 above, when the flow rates of dichloromethylvinylsilane and carrier gas were adjusted in the range of 1 to 20 sccm and 100 to 1000 sccm, respectively, silicon carbide nanowires having a small diameter and excellent single crystal and field emission characteristics were prepared. It can be seen that.

In addition, when the flow rate of dichloromethyl vinylsilane is low, the production of silicon carbide nanowires is difficult due to the reduction of the source of silicon and carbon, and in many cases, the diameter of the manufactured nanowires may increase or may inhibit crystallinity. Even when the flow rate of dichloromethylvinylsilane is in the range of 1 to 20 sccm, when the flow rate of the carrier gas is small, the production of silicon carbide nanowires is not easy because the supply source does not reach the substrate inside the reaction tube due to the decrease in the flow rate. Due to the increased flow rate, the time required for silicon carbide to participate in the growth of the silicon substrate appears to be difficult to manufacture silicon carbide nanowires, so the flow rate range of the dichloromethylvinylsilane and the carrier gas of the present invention can be applied. In this case, it can be seen that an optimal effect can be obtained.

On the other hand, Figure 2 shows a scanning electron micrograph of the silicon carbide nanowires of Sample 3 prepared by Example 1, Figure 3 is an X-ray diffraction graph, Figure 4 is a transmission electron micrograph and electrons of the prepared nanowires Diffraction photographs are shown. As shown in each figure, the diameters of the prepared silicon carbide nanowires ranged from about 20 to 200 nm, the lengths ranged from about 10 to 100 μm, and it was confirmed that the silicon carbide nanowires grew in the [111] crystal direction. .

In addition, the field emission device in which the silicon carbide nanowires of the sample 11 prepared in Example 2 is introduced shows excellent field emission characteristics in terms of excellent single crystallinity and small diameter, and FIG. 5 shows an example of such a field emission device. It is shown as a structural diagram. The field emission characteristics were measured under a high vacuum of 10 ^-6 torr or less using the "Flat screen" method. The silicon carbide produced had a driving voltage of -1.8 V / cm for flowing 10 ㎂ / ㎠ or more and 1 mA / ㎠ The driving voltage required for the abnormal flow was ˜2.5 V / cm or less, showing excellent field emission characteristics even at a low driving voltage. The field enhancement factor (β) showed a high field enhancement factor of 10,000 or more. In addition, the distance of an anode and a cathode material (silicon carbide nanowire) was measured using the spacer of 160 micrometers.

The resulting current-voltage curve and Fowler-Nordheim graph are shown in FIG. 6, where the slope of the Fowler-Nordheim graph is shown in a straight line, which is according to the field emission theory. It means that the silicon carbide produced in the invention has a uniform diameter, a certain length shape.

As described above, the silicon carbide nanowires prepared in the present invention have low turn-on voltage and high field enhancement factor (β) values of 10000 or more due to the advantages of excellent physical properties and shapes of the materials themselves. It was confirmed that the present invention can be used for the field emission device in the future.

As described above, the silicon carbide nanowires prepared according to the present invention have low power and high efficiency due to the excellent physical properties of the material itself such as low work function value, excellent durability, and excellent thermal stability and the shape of the one-dimensional nanowires. Its excellent field emission characteristics, low cost manufacturing process, large area, and selective patterning on the substrate enable it to occupy a very advantageous position when manufacturing semiconductor nanostructure field emission devices including nanowires and nanorods in the future. It is expected.

Claims (4)

Forming a metal catalyst layer by depositing a catalyst selected from a metal selected from gold, nickel and cobalt or an alloy containing two or more of these metals in a thickness of 10 to 100 GPa on a substrate; In a reducing atmosphere maintained at 900 to 1200 ° C., the reaction raw material and carrier gas of dichloromethylvinylsilane were injected together at a flow rate of 1 to 20 sccm and a flow rate of 100 to 1000 sccm, respectively for 10 to 120 minutes. Maintaining and reacting and depositing a reaction raw material in the catalyst layer to grow into silicon carbide nanowires having a diameter of 20 to 200 nm and a length of 10 to 100 μm, Method of producing a silicon carbide (silicon carbide) nanowires comprising a. delete The method of claim 1, The substrate is a method of manufacturing silicon carbide nanowires, characterized in that the silicon or sapphire. delete

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