KR20080017604A - Zno nanowalls and their synthesis method thereof - Google Patents

Abstract

A method for manufacturing zinc oxide nanowalls is provided to form zinc oxide nanowalls easily by proceeding the process under an atmospheric pressure condition, and have high reproducibility. A method for manufacturing zinc oxide nanowalls includes a step of producing a zinc gas by pyrolysis of a raw material powder and a graphite powder(50) used as a catalyst, and reacting the zinc gas with a metal catalyst deposited on a substrate(60) at a predetermined synthesis temperature under an atmospheric pressure condition through a chemical vapor deposition method by a chemical vapor deposition apparatus to prepare zinc oxide nanowalls. Further, the raw material powder is one of ZnO powder, Zn powder, Zn pellet, Zn metal, DEZn(diethylzine) and DMZn(dimethylzinc).

Description

ZnO Nanowalls And Their Synthesis Method Thereof}

1 is a schematic view showing an example of a chemical vapor deposition apparatus for synthesizing zinc oxide nanowall according to an embodiment of the present invention;

Figure 2 is an enlarged view 2000 times magnified using FE-SEM equipment after growing zinc oxide nanowall according to an embodiment of the present invention;

3 is a view showing that the Ar flow at the temperature of 940 ℃ in the synthesis of zinc oxide nanowall according to an embodiment of the present invention measured at an inclination angle of 30 ° with an FE-SEM image tested under the conditions of 800 sccm;

4 is a view showing that the Ar flow at a temperature of 920 ° C measured at an inclination angle of 30 ° with an FE-SEM image tested under conditions of 800 sccm;

5 is a view showing that the Ar flow at a temperature of 900 ° C measured at an inclination angle of 30 ° with an FE-SEM image tested under conditions of 800 sccm;

6 is a view showing that the Ar flow was measured at an inclination angle of 30 ° with an FE-SEM image tested at 800 sccm at a temperature of 880 ℃.

7 is a view showing a cross-section measured by the FE-SEM image experimented with Ar flow at 800 sccm at 900 ℃ temperature;

8a to 8c is an experimental view showing the results of the analysis divided into three parts through the EDS analysis in order to analyze the components of the present invention zinc oxide;

9 shows an analysis of a crystal structure using an emission accelerator beamline;

10 shows the results of performing HR-TEM measurements to analyze the crystallinity of the nanowall itself;

11 is a schematic view showing a growth mechanism of zinc oxide nanowalls according to an embodiment of the present invention; And

12 is a graph showing room temperature PL analysis.

※ Explanation of symbols for main parts of drawing

4: boat 10: reaction tube

24: resistance heating element 50: catalyst powder

60: substrate

The present invention relates to a method for producing zinc oxide nanowalls (ZnO nanowalls) at atmospheric pressure in the air, and to a zinc oxide nanowall synthesized thereby, more specifically using zinc oxide powder and graphite powder acting as a catalyst The present invention relates to a zinc oxide nanowall having a new crystal form and orientation of a nanowall among zinc oxide nanostructures through a chemical vapor deposition method in which a zinc gas reacts with gold as a catalyst on a substrate (GaN), and a method of manufacturing the same.

Recently, room temperature UV laser emission has been observed in zinc oxide (ZnO) semiconductors, attracting attention as a new material to replace III-V nitride based semiconductors, which are currently the most widely used UV-laser and LED. In the case of bulk ZnO, laser emission is only observed at cryogenic temperatures, while when the size of ZnO is reduced to nanometer levels, laser emission begins to manifest at room temperature. Accordingly, many studies have been conducted to increase the laser characteristics by reducing the size of ZnO.

In addition, zinc oxide (ZnO) -based materials have been widely used in the field of optical devices such as transparent electrodes, window materials of solar cells, varistors, etc. Recently, wide bandgap (3.37eV) has been used. It is attracting attention as a material for a light emitting device to replace a gallium nitride (GaN) compound semiconductor by utilizing the characteristic that has. Zinc oxide (ZnO) has a wide bandgap of 3.37 eV at room temperature, and has a 60 meV exciton binding energy greater than 24 meV, which is a thermal energy at room temperature (25 ° C.). It is an easy material. Therefore, zinc oxide (ZnO) is being studied as an optical device such as an ultraviolet light emitting diode or a laser diode due to such excellent optical properties.

In recent years, leading research groups abroad have used zinc oxide (ZnO) nanostructures to research advanced sources such as chemical-bio sensors, hydrogen storage devices, fuel-sensitized solar cells, organic / inorganic hybrid solar cells, and flexible transparent TFTs. Is very active.

Many methods for producing zinc oxide (ZnO) nanostructures include organometallic chemical vapor deposition, molecular beam deposition, sol-gel deposition, sputtering, reaction evaporation, spray pyrolysis, pulsed laser deposition, and electric discharge. There is this.

For example, Korean Patent Laid-Open Publication No. 2005-0043362 proposes a method for forming a ZnO nano-array for an ultraviolet laser and a method for forming a ZnO nanowall array on a silicon substrate, and the conventional invention is a method for synthesizing a conventional ZnO nanorod array. The present invention relates to a method for synthesizing a ZnO nano-array on a substrate at a low temperature by overcoming the shortcomings.

However, the manufacturing method uses a chemical solution synthesis method, there are various problems in performing such a method, such as controlling the ambient atmosphere such as vacuum, gas partial pressure, raw material selection, specimen pretreatment. In addition, this method also has a problem in that it is difficult to obtain a perfect nanowall because there is a limit to the synthesis of zinc oxide nanowall in the zinc oxide nanostructure.

The present invention has been made to solve the above problems, the present invention is the oxidation by proceeding the process at atmospheric pressure in the air, without the problem of controlling the ambient atmosphere such as vacuum and gas partial pressure for the conventional zinc oxide nanowall production An object of the present invention is to provide a method for preparing zinc oxide nanowalls which are easily formed and reproducible zinc nanowalls, and the zinc oxide nanowalls synthesized thereby.

Another object of the present invention is to provide a method for more easily and completely manufacturing zinc oxide nanowalls and structures using zinc oxide powder and graphite powder as catalysts at atmospheric pressure.

In addition, an object of the present invention is to provide a method for producing a zinc oxide nanowall having a relatively uniform thickness by using a gold catalyst on a substrate.

Zinc oxide nanowall production method of the present invention for achieving the above object is produced by the thermal decomposition reaction of the graphite powder acting as a catalyst and the raw material powder in the atmospheric pressure state in the air through the chemical vapor deposition method using a chemical vapor deposition apparatus A zinc oxide nanowall is prepared by reacting zinc gas with a metal reaction catalyst deposited on a substrate at a predetermined synthesis temperature.

Preferably, the raw material is prepared zinc oxide nanowall using any one of ZnO powder, Zn powder, Zn pellet, Zn metal, DEZn (diethylzine), and DMZn (dimethylzinc).

Also preferably, the substrate may be GaN, Si-wafer, sapphire (a-Al ₂ O ₃ , c-Al ₂ O ₃ , m-Al ₂ O ₃ , r-Al ₂ O ₃ ), ScAlMgO ₄ , LiNbO ₃ Zinc oxide nanowalls are prepared using any one of ZnO, SiO ₂ , and Si ₃ N ₄ .

Also preferably, the metal reaction catalyst deposited on the substrate may include derivatives of Au, Zn, Sn, In, Pd, Pd-Au, or Pt, with a catalyst having a thickness of 1-20 nm and a diameter of 1- 100 nm nanoparticles are used.

Also preferably, the synthesis temperature of the zinc oxide nanowall is 300 ° C-1200 ° C.

Also preferably, any one of air, argon gas, oxygen gas, nitrogen gas, and a mixed gas thereof in the reactor of the chemical vapor deposition apparatus during the synthesis process of the zinc oxide nanowall during the synthesis process of the zinc oxide nanowall And more preferably, the amount of gas introduced into the chemical vapor deposition reactor is 10-4000 sccm.

Also preferably, the chemical vapor deposition method may be any one of thermal CVD, organometallic chemical vapor deposition (MOCVD), and plasma chemical vapor deposition (PECVD).

The present invention also discloses a zinc oxide nanowall produced by the above method.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, a variable used in an embodiment of the present invention will be described.

The GaN substrate was deposited on sapphire (Al ₂ O ₃ ) to 4㎛ thickness, the gold thin film deposited on the GaN substrate as a catalyst was deposited to a thickness of 1 ~ 20nm in order to improve direct reactivity with zinc gas. In addition, zinc gas, which is a reactive gas, is transferred to the substrate through argon gas, and the zinc oxide nanostructure may be changed according to the distance between the powder and the substrate.

Raw material powder is used to generate the zinc oxide nanowall according to the present invention, but in one embodiment of the present invention, ZnO powder is used as the raw material, but preferably Zn powder, Zn pellet, Zn metal, DEZn ( diethylzine) and DMZn (dimethylzinc) may be used.

In addition, although gold was used as a material of the thin film deposited on the substrate as a metal reaction catalyst, a derivative of Zn, Sn, In, Pd, Pd-Au, or Pt may be preferably used. Thin films of 1-20 nm and nanoparticles of 1-100 nm in diameter are used.

Meanwhile, in one embodiment of the present invention, a GaN substrate is used, but the substrate is Si-wafer, sapphire (a-Al ₂ O ₃ , c-Al ₂ O ₃ , m-Al ₂ O ₃ , r-Al ₂ O ₃ ), ScAlMgO ₄ , LiNbO ₃ , ZnO, SiO _2, and Si ₃ N ₄ may be used.

In general, the synthesis of argon gas varies depending on the reaction tube, but in one embodiment of the present invention, a 50φ reaction tube is used, and the argon gas flow uses 10-4000 sccm (Standard Cubic Centimeter per Minute). It was. Preferably, in one embodiment of the present invention, the gas supplied into the reactor of the chemical vapor deposition apparatus during the synthesis of the zinc oxide nanowall is argon gas, but any one of air, oxygen gas, nitrogen gas, and a mixed gas thereof. Gas may be supplied.

On the other hand, in the change of temperature which is the biggest variable of this invention, it is preferable to carry out at the temperature of 300-1200 degreeC. The reason is that when the thermal CVD method, which is one of the chemical vapor deposition methods used in one embodiment of the present invention, the synthesis of zinc oxide nanostructures is performed at a temperature of less than 300 ° C, Zinc oxide nanostructures do not form on the substrate due to poor pyrolysis reaction on the graphite powder, and zinc oxide nanostructures are hardly generated since the melting point of gold is exceeded on the substrate when the temperature is exceeded 1200 ° C. Therefore, in one embodiment of the present invention, a temperature change of 940 ° C-880 ° C is considered as an appropriate temperature, and an experiment was performed to generate zinc oxide nanowalls with a temperature change between 940-880 ° C.

Preferably, in one embodiment of the present invention, the thermal CVD method, which is one of chemical vapor deposition methods, is used, but another example of chemical vapor deposition is an organic metal chemical vapor deposition (MOCVD) method or a plasma chemical vapor deposition method. Evaporation (PECVD) may be used.

Hereinafter, specific forms and structures of basic knowledge, chemical reaction formulas, and zinc oxide nanowalls required by the present invention will be described.

The catalyst gold deposited on the substrate contracts to reduce the surface energy by thermal energy and forms an island. In addition, zinc oxide powder and graphite powder generate zinc gas through a pyrolysis reaction, and zinc gas, which is a reactive gas, reacts with gold used as a catalyst on a substrate to form zinc oxide nanowalls.

This process is represented by the chemical equation as follows.

1) ZnO (p) + C (p) = Zn (v) + CO (g)

2) Zn (v) + Au (l) = ZnAu (s)

The zinc oxide nanowalls obtained in the above process are relatively uniform in thickness, and are generally plate-shaped materials composed of extremely fine network forms of several tens to hundreds of nm. In addition, the width between the wall and the wall of the nanowall is uneven, but the width can be freely adjusted by the gold catalyst.

The zinc oxide nanowall has one oxygen bonded to one zinc, forms a single crystal wurtzite structure, and the epitaxial relationship between gold, the substrate, and ZnO. Here, epitaxy means laminating a new layer on a single crystal substrate to form a single crystal layer.

1 is a schematic view showing an example of a chemical vapor deposition apparatus for synthesizing a zinc oxide nanowall according to an embodiment of the present invention. As shown in the figure, the chemical vapor deposition apparatus capable of synthesizing (manufacturing) zinc oxide nanowall according to an embodiment of the present invention is a reaction tube (10) made of alumina and the reaction tube (10) It includes a boat (4) located inside, and a resistance heating element (24) provided on the outside of the reaction tube (10).

The gas inlet 14 and the gas outlet 12 of the reaction tube 10 is provided with a gas inlet valve 32 and a gas outlet valve 11, respectively, the resistance heating element 24 is to be configured in the form of a coil Can be.

The chemical vapor deposition apparatus is used to mount the reactive powder 50 and the substrate 60 on the boat 4 in the reaction tube 10. In this case, the reactive powder 50 is positioned at the center of the resistance heating element 24, and the substrate 60 is positioned between the gas outlets 12 in the reactive powder 50. In addition, while heating the temperature, a certain amount of argon is flowed through the gas inlet 14, and then raised to a constant reaction temperature, maintained for a certain time, and then naturally cooled in the reactor of the chemical vapor deposition apparatus.

At this time, Zn, CO, CO _{2 ,} Ar, etc. are present as the gas in the reaction tube 10, Zn (v) reacts in the substrate 60, and CO, CO ₂ is used as the gas outlet 12. , Ar and the like are discharged.

In the accompanying drawings, FIG. 2 is an enlarged view 2000 times enlarged using FE-SEM equipment after growing zinc oxide nanowalls according to an embodiment of the present invention, whereby zinc oxide nanowalls are uniform in large area. You can see that.

In one embodiment of the present invention, a zinc oxide nanowall was produced in a large area at a growth temperature of 900 ° C., where Ar flow was 800 sccm and the growth time was 90 minutes.

As an example of the present invention, the growth temperatures of 940 ° C, 920 ° C, 900 ° C, and 880 ° C were experimented with all the conditions equal to the parameters of 20 ° C intervals.

This shows that there is a certain regular change according to the growth temperature of the nickname, the present invention is constantly changed by the conditions due to the regularity and was tested to increase the reliability of the present invention. In addition, this experiment was conducted to examine the growth mechanism of zinc oxide nanowalls more specifically with certain rules.

Experiments were conducted under the above temperature change conditions, and FIGS. 3 to 6 described below show analytical FE-SEM images accordingly.

In the accompanying drawings, Figure 3 shows that the Ar flow at the temperature of 940 ℃ in the synthesis of the zinc oxide nanowall according to an embodiment of the present invention was measured at an inclination angle of 30 ° with an FE-SEM image tested at 800 sccm Figure showing. As shown in the drawing, the wall of the zinc oxide nanowall cannot be clearly identified at 940 ° C., and the zinc oxide and the gold catalyst are completely mixed to obtain a thin zinc oxide film.

In the accompanying drawings, Figure 4 is a view showing that the Ar flow was measured at an inclination angle of 30 ° with an FE-SEM image experimented under the condition of 800 sccm at a temperature of 920 ℃. This can identify the wall of the nanowall more distinctly than the experiment at 940 ℃ previously, and can also check the thin wire from the gold catalyst particles that are not completely mixed.

In the accompanying drawings, Figure 5 is a view showing that the Ar flow was measured at an inclination angle of 30 ° with an FE-SEM image experimented under the condition of 800 sccm at a temperature of 900 ℃. This is an experiment of the nanowall of the present invention and it can be seen that a zinc oxide nanowall of a very constant thickness was formed.

In the accompanying drawings, Figure 6 is a view showing that the Ar flow was measured at an inclination angle of 30 ° with an FE-SEM image tested at 800 sccm at a temperature of 880 ℃. It can be seen that the nanowall and nanowires are distributed at the same time. At temperatures above 900 ° C, the gold catalyst is mixed with zinc oxide, but the mixing is not performed well as the temperature decreases, so that the nanowalls and nanowires are simultaneously distributed. do.

In the accompanying drawings, Figure 7 is a view showing the measurement of the cross section by the FE-SEM image experimented with Ar flow at 800 sccm condition at 900 ℃ temperature. In the present invention, it can be confirmed that a zinc oxide thin film is present as a measure to find a manufacturing mechanism of zinc oxide.

On the other hand, Figures 8a to 8c is an experimental view showing the results of the analysis divided into three parts through the EDS analysis in order to analyze the component of the zinc oxide of the present invention.

First, looking at Figure 8a, it can be confirmed that the zinc oxide nanowall as a result of the EDS analysis of the wall of the nanowall.

In addition, Figure 8b is measured by EDS analysis to investigate the components of the thin film formed on the zinc oxide nanowall, it can be confirmed that the zinc oxide.

In addition, Figure 8c is a measurement of the resulting substrate of the zinc oxide nanowall, it can be confirmed that the zinc oxide nanowall was produced on the GaN substrate.

9 is a view showing an analysis of the crystal structure using the radiation accelerator beamline, it can be seen that the GaN substrate, gold and zinc oxide have an epitaxy relationship.

In the accompanying drawings, FIG. 10 shows the results of performing HR-TEM measurements to analyze the crystallinity of the nanowall itself, whereby zinc oxide nanowalls have one oxygen bonded to one zinc, It can be seen that it has a single crystal wurtzite structure.

11A to 11F are schematic diagrams illustrating a growth mechanism of zinc oxide nanowalls according to an embodiment of the present invention. Hereinafter, specific examples of the zinc oxide nanowalls will be described with examples and analysis. I will explain the mechanism of nanowall.

First, as shown in FIG. 11A, a gold (3 nm) thin film is formed on a GaN substrate.

And, as shown in Figure 11b, by applying a temperature to the gold thin film on the substrate, the shrinkage is made to reduce the surface energy, wherein gold is present with an epitaxy structure on the substrate.

Also, as shown in FIG. 11C, when gold contracts through heat treatment, zinc gas flows in, and gold is lifted by a mechanism of a vapor-liquid-solid (VLS). However, zinc oxide has almost a 1.7% difference between the substrate and the crystal structure, so that zinc gas also grows epitaxially with the substrate.

In addition, as shown in FIG. 11D, in the case of zinc oxide nanowires, zinc oxide should lift gold through the growth mechanism of VLS, but the zinc oxide substrate is larger than the force to push up gold due to the small difference in crystal structure between zinc oxide and the substrate. Based on this, the force to spread and expand sideways will be greater.

In addition, as shown in FIG. 11E, the zinc oxide thin film expanded in the horizontal direction rather than vertically meets the zinc oxide thin film. However, even though the thin film has an epitaxial structure with the substrate, the initial nucleation of zinc oxide occurs on the gold island, and gold is present as an impurity in the zinc oxide thin film. As a result, a slight crystal structure shifts between the zinc oxide thin film and the thin film, and gold concentrates on the misaligned portion.

The concentration of gold in this misaligned portion is because the zinc oxide thin film pushes out gold, which is an impurity, in order to exist in a more stable state, so that gold exists in the outer shell.

As a result, as shown in FIG. 11F, nanowalls of zinc oxide are formed. Therefore, the zinc oxide thin film, which is the zinc oxide nanowall part and the bottom, has a U-shaped shape, which means that it grows at the interface, which is U-shaped between the walls by the interfacial energy.

In the accompanying drawings, FIG. 12 is a graph showing a room temperature PL analysis, whereby very strong free exciton and weak deep level emission can be confirmed, which is an excellent optical property of the zinc oxide nanowall fabricated through the embodiment of the present invention. Is showing.

As described above, the present invention clearly clarified the change of the structure according to the specific technology and growth conditions for the manufacturing method of the nanowall of the zinc oxide nanostructure through chemical vapor deposition method, and also by repeated experiments Reproducibility was ensured in the invention.

As described above, according to the zinc oxide nanowall according to the present invention and a method for manufacturing the same, oxidation of the zinc oxide nanowall according to the present invention is carried out at atmospheric pressure in the air without the problem of controlling the ambient atmosphere such as controlling the vacuum and gas partial pressure for manufacturing the existing zinc oxide nanowall. It is easier to produce zinc oxide nanowalls.

In addition, the present invention is easy and simple by the reaction of zinc gas with gold on the substrate using zinc oxide powder and graphite powder at atmospheric pressure in the air, there is an effect that can produce a zinc oxide nanowall having a relatively constant size.

Claims (9)

Through chemical vapor deposition by chemical vapor deposition, zinc gas generated by pyrolysis of raw powder and graphite powder acting as a catalyst under atmospheric pressure in air reacts with a metal reaction catalyst deposited on a substrate at a predetermined synthesis temperature. A method for producing zinc oxide nanowalls, the method comprising producing zinc oxide nanowalls. The method of claim 1, The raw material powder is ZnO powder, Zn powder, Zn pellet, Zn metal, DEZn (diethylzine), DMZn (dimethylzinc) using any one of the manufacturing method of the zinc oxide nanowall. The method of claim 1, The substrate is GaN, Si-wafer, sapphire (a-Al ₂ O ₃ , c-Al ₂ O ₃ , m-Al ₂ O ₃ , r-Al ₂ O ₃ ), ScAlMgO ₄ , LiNbO ₃ , ZnO, SiO ₂ , And Si ₃ N ₄ using any one of the zinc oxide nanowall production method. The method of claim 1, The metal reaction catalyst deposited on the substrate includes a derivative of Au, Zn, Sn, In, Pd, Pd-Au or Pt, wherein the catalyst is formed of a thin film having a thickness of 1-20 nm and a nanoparticle having a diameter of 1-100 nm. Method for producing a zinc oxide nanowall, characterized in that used. The method of claim 1, The synthesis temperature of the zinc oxide nanowall is a manufacturing method of the zinc oxide nanowall, characterized in that 300 ℃ -1200 ℃. The method of claim 1, Production of zinc oxide nanowalls comprising supplying any one of air, argon gas, oxygen gas, nitrogen gas, and a mixture of these gases into a reactor of a chemical vapor deposition apparatus during the synthesis of the zinc oxide nanowalls Way. The method of claim 6, The method for producing zinc oxide nanowalls, characterized in that the amount of gas flowing into the chemical vapor deposition apparatus reactor is 10-4000 sccm. The method of claim 1, The chemical vapor deposition method is any one of a thermal chemical vapor deposition (thermal CVD) method, organic metal chemical vapor deposition (MOCVD) method and plasma chemical vapor deposition (PECVD) method of producing a zinc oxide nanowall. Zinc oxide nanowall synthesized by the method according to any one of claims 1 to 8.

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