KR100836890B1 - Method for vertical growth of zno nanowires on ito substrate - Google Patents

Abstract

A method for manufacturing zinc oxide nanowires is provided to produce single crystal zinc oxide nanowires having uniform size, shape, and density vertically grown on an ITO substrate using a chemical vapor deposition method. A method for manufacturing zinc oxide nanowires on an ITO substrate includes the steps of: physically covering the ITO substrate with a metal foil having a macro hole; mixing ZnO and Zn powders; and manufacturing the zinc oxide nanowires by heat-treating the ITO glass covered with the metal foil and a crucial containing the ZnO/Zn mixture powder in an atmosphere of inert gas and oxygen gas. The ZnO and Zn powders are mixed in a weight ratio of ZnO : Zn ranging from 1:0.2 to 1:5.

Description

Method for Vertical Growth of ZnO Nanowires on ITO Substrate}

1 is an embodiment of wrapping an ITO substrate with a metal foil,

2 is an embodiment showing a heat treatment method according to the present invention,

3A is a scanning electron microscope (SEM) photograph of zinc oxide nanowires formed on an ITO substrate through Example 1,

FIG. 3B is a scanning electron micrograph of zinc oxide nanowires formed on the inside, outside and ITO substrate of an aluminum foil formed through Example 1,

4 is an X-ray diffraction pattern of zinc oxide nanowires formed on an ITO substrate through Example 1,

FIG. 5A is a transmission electron microscope (TEM) photograph of a zinc oxide nanowire formed on an ITO substrate through Example 1, and a photograph attached to the upper right of FIG. 5A shows a limited field electron diffraction (SAED; selected) of a zinc oxide nanowire. Area Electron Diffraction) pattern,

5b is a high resolution transmission electron microscope (HRTEM) photograph of a zinc oxide nanowire formed on an ITO substrate according to Example 1, and a photograph attached to the upper right of FIG. 5b is a fast Fourier transform of the zinc oxide nanowire of FIG. 5b. Pattern,

6 is an energy dispersive analysis result measured using an energy dispersive spectroscope (EDS) attached to an electron microscope for zinc oxide nanowires formed on an ITO substrate according to Example 1,

FIG. 7 is a graph measuring field emission characteristics of zinc oxide nanowires formed on an ITO substrate through Example 1. FIG.

The CRT, which has led the display market, is being replaced by flat panel displays in various areas, and new markets are being formed mainly on flat panel displays. Flat panel displays following the CRT include liquid crystal displays (LCDs), light emitting diodes (LEDs), plasma display panels (PDPs), and field emission displays (FEDs). Emission Display, etc. Among them, field emission display (FED), which has high quality, high efficiency, and low power consumption, is drawing attention as the next generation information display device. A field emission display is driven on the principle of emitting and entraining a myriad of electrons from an emitter, and is composed of a cathode panel and a cathode panel. Basically, electrons emitted from the cathode plate are designed to display the image by hitting the phosphor of the anode plate. The negative electrode panel of the field emission display is composed of a micro tip (FEA) that emits electrons, and the positive electrode panel is a part where the phosphor is applied to represent an image that can be viewed by a human. Field-emitting displays are expected to be widely used in small color TVs, industrial products and computers, with the advantages of ultra-thin, low power consumption, low process cost, excellent temperature characteristics and high speed operation.

Important technical elements of the field emission display include the processing technology of the emitter, which is the electron emission source, and the stability of the material.Silicone silicon (Si tip) or molybdenum tip (Mo tip) is still used mainly, but the stability is large. There is a need to develop new materials that are easy to process and have high stability due to problems. The core technology of the field emission display must first be able to synthesize the electron emission emitter with a large aspect ratio, and should not deteriorate with time when applied voltage is applied to the manufactured emitter. It can be said that the emitter of is produced reproducibly. In addition, since the field emission display uses glass as a substrate, low temperature growth technology is essential, and a technique for growing the emitter vertically or vertically is required for high efficiency electron emission.

Until now, carbon nanotubes (CNTs) have received great attention as a material for new field emission displays, but light emission is uneven and flickering or carbon nanotube destruction occurs, which can solve such problems. The need for new materials is emerging.

Zinc oxide nanowires not only possess the excellent properties of carbon nanotubes such as low driving voltage and large aspect ratio, but also solve the problems of carbon nanotubes due to their excellent mechanical, chemical and thermal durability. Is attracting attention as a new field emission display material.

Until now, when glass substrates such as ITO (Indium Tin Oxide) substrates were used, the low temperature growth method of synthesizing zinc oxide nanowires using liquid phase was mainly used. When synthesizing the route, a large amount of impurities are included or the crystals are not perfect, which causes a problem of inefficient efficiency.

On the other hand, when synthesizing zinc oxide nanowires using conventional chemical vapor deposition, it was possible to synthesize large amounts of vertically grown single crystal nanowires, but it was difficult to synthesize nanowires on low-melting ITO substrates due to high temperature experimental conditions. There were limitations to using metal catalysts such as gold, morphology of zinc oxide nanowires, vertical growth on ITO substrates, and uniform growth of zinc oxide nanowires.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide a method for producing single crystal zinc oxide nanowires having a uniform size, shape, and density on an ITO substrate and oriented perpendicular to the ITO substrate without using a catalyst by using chemical vapor deposition. Is in.

Another object of the present invention is to measure the field emission effect of vertically oriented zinc oxide nanowires grown vertically on an ITO substrate prepared by using the proposed method, and propose to use the field emission display as an emitter. It is.

The method for producing a zinc oxide nanowire of the present invention for achieving the above object is to form a zinc oxide nanowire (nanowire) on an ITO substrate, the metal foil (macro) hole is formed of the ITO (Indium) Tin Oxide) physically surrounding the substrate, and mixed with ZnO and Zn powder, the crucible containing the ITO substrate and the ZnO / Zn mixed powder wrapped in the metal foil is prepared by heat treatment in an atmosphere of flowing inert gas and oxygen gas do.

The macro hole has an area of 1 mm 2 to 40 mm 2 and forms at least one macro hole in the metal foil to surround the ITO substrate.

When wrapping the metal foil in which the macro holes exist on the ITO substrate, it is preferable to cover both the upper and lower surfaces of the ITO substrate using a single metal foil, and most preferably, to cover all the surfaces of the ITO substrate. It is also preferable to enclose the macro holes so that they are in a position to grow the zinc oxide nanowires on the ITO substrate.

The metal foil has a feature of using a metal foil having a linear thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. to 40 × 10 ⁻⁶ / ° C. at 500 ° C., which is used when heat-treating an ITO substrate wrapped in a metal foil, This is to cause thermal plastic deformation around the macro holes of the metal foil due to the difference in the coefficient of thermal expansion between the metal foils, causing the macro foils of the metal foils to swell to form an empty space separated from the ITO substrate.

The void space created by the difference in coefficient of thermal expansion provides a stable space in the synthesis of zinc oxide nanowires, and enables the formation of optimal conditions for vertical growth of the zinc oxide nanowires.

Specifically, when a crucible containing an ITO substrate wrapped in a metal foil and a ZnO / Zn mixed powder, which is a precursor for forming zinc oxide nanowires, is heat-treated in an atmosphere of inert gas and oxygen gas, the precursor vaporized is inert gas and As the oxygen gas flows, it moves to an ITO substrate wrapped in a metal foil, and maintains a quasi-equilibrium in the empty space that is not directly affected by the flow of the gas. Routes can be created and grown.

Therefore, if the coefficient of thermal expansion of the metal foil is 10 x 10 ^-6 / ℃ or less, the thermal plastic deformation sufficient to form the empty space at the heat treatment temperature of the manufacturing method proposed by the present invention cannot be obtained, and the coefficient of linear thermal expansion is 40 If x 10 ⁻⁶ / ° C. or more, a large plastic deformation occurs at the heat treatment temperature of the present invention, so that the empty space becomes too large to obtain a zinc oxide nanowire having a uniform and controlled shape.

If the area of the macro hole is also similar to the coefficient of thermal expansion of the metal foil, if the area of the macro hole is 1 mm 2 or less, the void space near the macro hole cannot be sufficiently formed. If the area of the macro hole is 40 mm 2 or more, too large empty space is formed, and the flow rate of the atmosphere gas. Will be directly affected.

Therefore, in order to maintain the quasi-equilibrium state of the precursor vaporized in the empty space and to efficiently grow zinc oxide nanowires, the macro holes present in the metal foil have a rectangular shape, and the long axis of the rectangle is perpendicular to the flow of the atmosphere gas. It is preferred to be located in the direction.

At this time, the metal foil is most preferable to use aluminum foil because it must be minimal vaporization at the heat treatment temperature of the present invention and should not be contained as impurities in the zinc oxide nanowires produced without reacting with the ITO substrate.

1 shows an embodiment in which an ITO substrate is wrapped with a metal foil and an empty space formed by heat treatment. In the above example, the rectangular single macro hole of the metal foil is wrapped around the ITO substrate so as to be located at the center of the ITO substrate, and the lower circle in FIG. 1 shows a cross-sectional view of the empty space around the macro hole formed by heat treatment. .

A mixture of ZnO and Zn powder, which are precursors of zinc oxide nanowires, is characterized in that the mass ratio of ZnO: Zn is 1: 0.2 to 1: 5. Maintaining a low level of supersaturation is essential for optimal nanowire synthesis. Since Zn has a higher vapor pressure at lower temperatures than ZnO, it is an important factor in supplying precursor vapor in the initial stage of the reaction. For this reason, if the mass of Zn is provided in the synthesis at less than 20% (ZnO: Zn = 1: 0.2) compared to ZnO, the amount of precursor vapor at the beginning of the synthesis is insufficient to maintain optimal conditions for the production of nanowires. it's difficult. On the other hand, when the mass of Zn is more than five times higher than that of ZnO (ZnO: Zn = 1: 5), the amount of precursor vapor in the initial stage of synthesis is excessively generated and supplied, making it difficult to manufacture nanowires. Occurs.

In addition, in order to control the bandgap energy of the zinc oxide nanowires when the ZnO and the Zn powder are mixed, a bandgap control material selected from a transition metal, tin, indium or sulfur, or a combination thereof may be further included. The transition metal used to control the bandgap energy is preferably a material selected from magnesium, cadmium, manganese, chromium or cobalt, or a combination thereof.

Figure 2 is an embodiment showing a heat treatment method according to the present invention, will be described in detail the heat treatment method of the present invention based on FIG.

As shown in FIG. 2, an ITO substrate in which a predetermined amount of inert gas and oxygen gas flows during heat treatment and is wrapped in a metal foil is physically separated from a crucible containing the ZnO / Zn mixed powder, and based on the crucible containing the ZnO / Zn mixed powder Inert gas and oxygen gas flow in the direction of flow. In addition, the crucible containing the ZnO / Zn mixed powder is preferably located at the hottest part of the quartz tube in the heat treatment apparatus, and the ITO substrate is controlled at a distance away from the crucible for optimum temperature conditions. Can be formulated. It is also possible to control the temperature individually, regardless of where the crucible is placed, using another heating element and a controller where the ITO substrate is placed.

When heat treating a crucible (alumina crucible) containing a mixture of ZnO / Zn powder, which is a precursor of zinc oxide nanowires, and an ITO substrate wrapped in the metal film, the vaporized precursor moves in accordance with the flow of an inert gas, thus containing argon. By flowing the inert gas to 10 sccm or more to induce a smooth movement of the vaporized precursor and to 300 sccm or less to make the vaporized precursor in the empty space to maintain a quasi-equilibrium state. In addition, it is preferable to flow oxygen gas at 0.1 sccm to 5 sccm together with the inert gas, which is for oxidizing Zn vaporized Zn. If it is 0.1 sccm or less, the vaporized Zn powder can be sufficiently oxidized to induce growth of zinc oxide nanowires. And the oxidation of evaporated Zn no longer helps the growth of zinc oxide nanowires even if it flows over 5sccm.

When heat-treating the atmosphere gas under the above conditions, the crucible containing the ZnO / Zn mixed powder is maintained at 700 ° C. to 850 ° C. to induce vaporization of the zinc oxide nanowire precursor and the ITO substrate wrapped in the metal foil. Zinc oxide is deposited by maintaining at a temperature of 450 ° C. to 600 ° C., which is lower than that of the crucible. The heating temperature of the crucible and the heating temperature of the ITO substrate affect the nucleation driving force and the growth rate of the zinc oxide nanowires growing on the ITO substrate. It does not induce vaporization of the material, and heat treatment above 850 ℃ no longer helps the growth of zinc oxide nanowires. In addition, if the temperature of the ITO substrate is lower than 450 ° C, the nucleation driving force is increased, but the growth is slow and if the temperature is higher than 600 ° C, the growth rate is fast while the driving force of the nucleation is small. It is difficult to obtain an array of vertical zinc oxide nanowires having a density and grown in a specific direction on an ITO substrate.

The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention is not limited to the embodiments described below and may be embodied in other forms.

(Example 1)

Make a 5 mm x 2 mm macro hole in aluminum foil and wrap the ITO substrate so that the macro hole is located in the center of the ITO substrate, and in the alumina crucible, ZnO powder (99.99%, Aldrich) and Zn powder (99.998%, Aldrich) was mixed in a mass ratio of 1: 1 and contained.

An ITO substrate is placed in a 1-inch diameter quartz tube of a heating furnace to flow 140 sccm of argon gas and 3 sccm of oxygen, and the ITO substrate is positioned in a direction in which argon gas and oxygen flow based on the alumina crucible. And alumina crucibles are placed in a furnace, which is divided into two heating zones.

The heating region in which the alumina crucible was placed was heated to 770 ° C., and the heating region in which the substrate was placed was heated to 500 ° C. for 10 minutes.

After the reaction was completed, the heating furnace was cooled, and the aluminum foil that completely wrapped the ITO substrate was removed. After the synthesis was completed, it was confirmed that light gray zinc oxide was synthesized on the substrate.

Measurement example

FIG. 3A is a scanning electron microscope (SEM) photograph of zinc oxide nanowires formed on an ITO substrate through Example 1 above. FIG. As can be seen in Figure 3, the diameter of the nanowires was about 80 nm to 100 nm, it was confirmed that the zinc oxide nanowires of uniform density having a length of several micrometers (㎛) was formed in a constant shape and size.

Figure 3b is a view of the zinc oxide nanowires formed on the outer surface of the aluminum foil and the inner surface of the aluminum foil and the ITO substrate forming an empty space in the empty space formed around a macro hole having a size of 5 mm x 2 mm of the aluminum foil Scanning electron micrograph. As can be seen in Figure 3b, the outer surface of the aluminum foil directly affected by the atmosphere gas during the heat treatment, the zinc oxide nanowires are made in the form of disordered nanowire cluster (cluster), inside the empty space maintaining the quasi-equilibrium state It can be seen that a uniform nanowire is formed.

FIG. 4 is an X-ray diffraction pattern of zinc oxide nanowires formed on the ITO substrate through Example 1, and only zinc oxide and ITO components were observed as can be seen from the results of FIG. 4. In addition, it can be seen that the (002) peak is very large, indicating that the growth direction of the zinc oxide nanowires analyzed by the transmission electron microscope is the [001] direction, and the nanowires synthesized throughout the ITO substrate are vertical. I could reaffirm my growth.

FIG. 5A is a transmission electron microscope (TEM) photograph of a zinc oxide nanowire formed on an ITO substrate through Example 1, and a photograph attached to the upper right of FIG. 5A shows a limited field electron diffraction (SAED; selected) of a zinc oxide nanowire. Area Electron Diffraction) pattern. As can be seen in FIG. 5A, the zinc oxide nanowires are composed of a single crystal and have a c-axis ([001]) growth direction.

5b is a high resolution transmission electron microscope (HRTEM) photograph of a zinc oxide nanowire formed on an ITO substrate according to Example 1, and a photograph attached to the upper right of FIG. 5b is a fast Fourier transform of the zinc oxide nanowire of FIG. 5b. Pattern. As can be seen in FIG. 5B and the attached fast Fourier transform pattern, it can be seen that it is a defect-free single crystal in which no stacking fault or dislocation defect is present in the resulting zinc oxide nanowire single crystal. Can be.

In addition, it can be seen that the zinc oxide nanowires have a wurtzite structure through the X-ray diffraction pattern of FIG. 4 and the electron diffraction pattern of FIG. 5A or 5B.

FIG. 6 is an energy dispersion analysis result using an energy dispersive spectroscope (EDS) attached to an electron microscope of zinc oxide nanowires formed on an ITO substrate through Example 1, whereby no aluminum component is observed. I could confirm that. Therefore, it can be seen that aluminum did not participate as a catalyst or other role in the synthesis of zinc oxide nanowires.

7 is a result of measuring the field emission characteristics using the zinc oxide nanowires formed on the ITO substrate in Example 1 above. To measure the field emission characteristics, two devices, the negative electrode plate and the positive electrode plate, were put together. Another ITO substrate was used as the positive electrode plate. Experiments for field emission characterization were performed in a chamber made at room temperature in a vacuum of 2 x 10 ^-6 Torr. The distance between the anode plate and the zinc oxide nanowire emitter tip is 570 μm and the measurement area is 26 mm ² . The current released at the tip of the emitter tip was recorded at 0.2 second intervals and measured with voltage from 100 V to 1200 V.

The turn-on electric field of the synthesized zinc oxide nanowires measured under the above conditions was measured at 3.3 V / µm, and the current density was found to be 3.8 mA / cm 2. The threshold electric field was 5.1 V / µm, and the current density was measured at 90 mA / cm 2. The above field emission characteristics show improved results compared to zinc oxide nanowires grown vertically on silicon substrates, and compared with the previous reports, it is found that the field emission characteristics are sufficient to be used as emitters in field emission displays. Can be.

By using the new synthesis method, single crystal zinc oxide nanowires having a uniform size, shape and density on the ITO substrate without having a catalyst and oriented vertically with respect to the ITO substrate were prepared. The synthesized nanowires had a diameter of about 80 nm to 100 nm and a length of several micrometers (μm). As a result of measuring field emission characteristics, the current density was measured as 3.8 mA / cm 2 at a turn-on electric field of 3.3 V / µm, and the maximum current density was measured as 90 mA / cm 2 at 5.1 V / µm. These field emission characteristics indicate that the synthesized nanowires have sufficient potential to be applied as emitters for field emission displays.

Claims (10)

In the method for producing zinc oxide nanowires on an ITO substrate, Physically surrounding the ITO substrate with a metal foil having macro holes By mixing ZnO and Zn powder, A crucible containing an ITO substrate and the ZnO / Zn mixed powder wrapped in the metal foil A method for producing zinc oxide nanowires, characterized in that the heat treatment is carried out in an atmosphere where an inert gas and oxygen gas flow. The method of claim 1, A method for producing zinc oxide nanowires, characterized in that at least one of the macro holes having an area of 1 mm 2 to 40 mm 2 is formed in the metal foil. The method of claim 1, The metal foil has a linear thermal expansion coefficient of 10 x 10 ^-6 / ℃ to 40 x 10 ^-6 / ℃ at 500 ℃ manufacturing method of zinc oxide nanowires. The method of claim 3, wherein The metal foil is a method for producing zinc oxide nanowires, characterized in that the aluminum foil. The method of claim 1, The method for producing zinc oxide nanowires, characterized in that the mass ratio of ZnO: Zn is 1: 0.2 to 1: 5 when the ZnO and Zn powder are mixed. The method of claim 1, The method for producing zinc oxide nanowires, characterized in that flowing the inert gas containing argon 10 sccm to 300 sccm and the oxygen gas at 0.1 sccm to 5 sccm. The method of claim 1, Maintaining the crucible containing the ZnO / Zn mixed powder at 700 ° C. to 850 ° C. during the heat treatment and maintaining the ITO substrate wrapped in the metal foil at 450 ° C. to 600 ° C. The method of claim 7, wherein The zinc oxide nano oxides are characterized in that the ITO substrate wrapped in the metal foil is physically separated from the crucible containing the ZnO / Zn mixed powder and placed in a direction in which the inert gas and the oxygen gas flow based on the crucible containing the ZnO / Zn mixed powder. Method of making the line. The method of claim 1, Zinc oxide nano, characterized in that the mixture further comprises a bandgap control material selected from transition metals, tin, indium, sulfur, and combinations thereof to control the bandgap energy of the zinc oxide nanowires when the ZnO and Zn powders are mixed. Method of making the line. delete

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