KR20110069560A - Zno nanorod - graphene thin film hybrid architectures and fabricating methods thereof - Google Patents

Abstract

PURPOSE: A manufacturing method of a hybrid structure of ZnO nanorod-graphene thin film is provided to obtain a device combining graphene and features of ZnO nanorods by allowing graphene and nanorods to be integrated in a low temperature with a simple and cheap method. CONSTITUTION: The hybrid structure(100) includes a graphene thin film(30); and a ZnOnanorod(50) grown up on the graphene thin film.The graphene thin film is a sheet shape obtained by a graphene evaporation using a vapor carbon source. The manufacturing method of the hybird structure includes following steps.(a) The sheet shaped graphene thin film is manufactured.(b) The ZnO nanorods on the graphene thin film are grown up by a hydrothermal process. The step(b) includes following steps.(i) A photoresist layer is spread on the graphene thin film and a hole is patterned.(ii) A ZnO seed layer is exposed with etching through the hole.(iii) The ZnO nanorods are selectively grown up from the ZnO seed layer by dipping a substrate for the device into an aqueous solution capable of growing ZnO.

Description

ZnO nanorod-graphene thin film hybrid architectures and fabricating methods

The present invention relates to a hybrid structure in which a two-dimensional thin film and a one-dimensional nanostructure are integrated and a method of manufacturing the same.

As the development of new devices having various functions in electronic and optoelectronic systems is required, the synthesis of new materials and integration into devices are being actively studied.

A representative example is the one-dimensional structure of ceramic materials such as nanowires or carbon nanotubes. The ceramic material of one-dimensional structure has good mechanical flexibility and optical transmittance and can guarantee excellent device performance due to the single crystal structure.

In order to use such a one-dimensional structure as a three-dimensional device structure, not only the synthesis of the material itself but also an intermediate structure structure for integrating the device and a manufacturing method thereof are particularly required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hybrid structure in which a one-dimensional structure having excellent characteristics is integrated in a two-dimensional structure.

Another object of the present invention is to provide a method for manufacturing such a hybrid structure in a simple and inexpensive manner.

Hybrid structure according to the present invention for solving the above problems includes a graphene thin film, and zinc oxide (ZnO) nanorods grown on the graphene thin film.

The graphene thin film is preferably in the form of a sheet obtained through graphene deposition using a gaseous carbon source.

In the hybrid structure manufacturing method according to the present invention for solving the above-mentioned other problems, after manufacturing a sheet-like graphene thin film, ZnO nanorods are grown on the graphene thin film by a hydrothermal process.

In a preferred embodiment, the manufacturing of the sheet-like graphene thin film may include depositing a graphene thin film on the SiO ₂ substrate through graphene deposition using a vapor carbon source; Separating the graphene thin film from the SiO ₂ substrate; And attaching the graphene thin film separated from the SiO ₂ substrate to a device substrate, wherein the device substrate has a ZnO seed layer formed thereon to grow ZnO nanorods on the graphene film by a hydrothermal process. The method may include: patterning holes after applying a photoresist layer on the graphene thin film; Etching the graphene thin film through the hole to expose the ZnO seed layer; And immersing the device substrate in an aqueous solution of a composition capable of growing ZnO to selectively grow ZnO nanorods from the exposed ZnO seed layer.

In another preferred embodiment, the manufacturing of the sheet-like graphene thin film may include: depositing the graphene thin film through graphene deposition using a vapor carbon source on a SiO ₂ substrate; Separating the graphene thin film from the SiO ₂ substrate; And attaching the graphene thin film separated from the SiO ₂ substrate to a device substrate.

In the step (b), the step of growing the ZnO nanorods on the graphene thin film by a hydrothermal process may include: patterning holes after applying a photoresist layer on the graphene thin film; Forming a ZnO layer on the photoresist layer and then applying a lift-off process to leave a ZnO seed pattern on the graphene thin film; And immersing the device substrate in an aqueous solution having a composition capable of growing ZnO to selectively grow ZnO nanorods from the ZnO seed pattern.

In the hybrid structure manufacturing method according to the present invention, in order to manufacture the graphene thin film, a substrate on which a graphitized metal film is formed is charged into a chamber, and then a current is applied to at least one of the graphitized metal film and the substrate in the chamber. After heating the graphitized metal film by the heat transfer effect at that time, supplying a gaseous carbon source into the chamber while the graphitized metal film is heated to solidify a carbon component in the graphitized metal film, and the current By controlling the amount of and cooling the graphitized metal film at a controlled rate, graphene is deposited on the surface of the graphitized metal film from the solid solution carbon, and then the graphitized metal film is removed by acid treatment, thereby depositing the precipitated metal film. Graphene from the substrate It is preferable to.

The hybrid structure according to the present invention has the electrical superiority of the graphene itself by including the graphene thin film having a high electrical conductivity, and also has the superiority of the ZnO nanorods itself by including the ZnO nanorods. In particular, by integrating the two-dimensional graphene thin film with the one-dimensional ZnO nanorods, it is possible to manufacture a three-dimensional structure for device utilization and impart versatility.

The hybrid structure according to the present invention maintains the characteristics of the flexible graphene thin film and integrates with ZnO nanorods to be used in new devices as transparent and flexible electric conductive layers, or as active elements in flexible electronic, optical, and photovoltaic systems. It can be applied to a wide range of new applications up to.

In the production method of the present invention, ZnO nanorods are grown by hydrothermal methods. The ZnO nanorods thus formed show excellent electrical and optical properties compared to the nanorods manufactured by the existing expensive equipment and expensive methods. Therefore, the use of the hybrid structure formed by the present invention is a simple and inexpensive manufacturing method with a wide range of usable values, such as high density next-generation storage devices, medical lasers, industrial lasers, optical communication and holographic.

In addition, according to the present invention, it is possible to integrate graphene-ZnO nanorods at a low temperature without using a complicated device, thereby manufacturing a new device that combines the characteristics of graphene and ZnO nanorods, which are most promising due to excellent electrical properties. Do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments make the disclosure of the present invention complete, and the scope of the invention to those skilled in the art. It is provided for complete information.

In the hybrid structure proposed in the present invention, one-dimensional ZnO nanorods are integrated on a two-dimensional graphene thin film, and FIG. 1 is a schematic perspective view of such a hybrid structure.

Referring to FIG. 1, in the hybrid structure 100 according to the present invention, ZnO nanorods 50 are integrated on the graphene thin film 30. The ZnO nanorods 50 may be in the form of an array with a constant arrangement. The ZnO nanorod 50 may have a composition containing ZnO as a main component and further including a dopant such as a small amount of magnesium (Mg), manganese (Mn), cadmium (Cd), selenium (Se), and the like.

The hybrid structure 100 may be integrated in a device substrate (not shown) and used as various devices. Device substrates are generally used for semiconductor devices, such as transparent inorganic substrates such as glass, quartz, Al ₂ O ₃ , SiC, PET (polyethylene terephthalate), PS (polystyrene), PI Transparent organic substrates such as (polyimide), PVC (polyvinyl chloride), PVP (poly vinyl pyrrolidone), PE (polyethylene) or Si, GaAs, InP, InSb, AlAs, AlSb, CdTe, ZnTe, ZnS, CdSe, CdSb , GaP or the like can be used. When the transparent substrate is used as the device substrate, incident light may be incident on both the upper and lower ends of the hybrid structure 100, and thus the incident light may be manufactured as a solar cell or a photodetector device having increased photovoltaic efficiency. If a plastic substrate such as PET is used, the hybrid structure 100 may be included and manufactured as a flexible device.

The graphene thin film 30 is a sheet shape obtained through graphene deposition using a gaseous carbon source, and can be attached to a substrate for an element by physically conveying the form of a continuous film according to the manufacturing method described below. .

As the hybrid structure 100 of the present invention includes the graphene thin film 30 having high electrical conductivity, the graphene itself has electrical superiority, and the ZnO nanorods themselves also have the superiority of the ZnO nanorods themselves. . In particular, by integrating the two-dimensional graphene thin film with the one-dimensional ZnO, it is possible to manufacture a three-dimensional structure for device utilization and impart versatility.

Graphene is a material composed of carbon atoms bonded in two dimensions like graphite, and unlike graphite, it is formed as a single layer or a very thin layer of 2-3 layers. These graphenes are flexible, have very high electrical and thermal conductivity, and are transparent. In the past, research is limited to using such graphene as an electrode material, but in the present invention, the graphene is integrated with ZnO nanorods, thereby enabling application to new devices and applications.

ZnO is attracting attention as a new material to replace the III-V nitride compound semiconductor, which is currently the most widely used UV-laser and LED, as room temperature UV laser emission is observed. 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. ZnO has a direct transition band structure and a high exciton bonding energy of 60 meV, so that a high efficiency light emitting device can be manufactured using recombination of these excitons even at room temperature. In addition, when the nanorod is manufactured, high efficiency light emitting devices and nano light emitting devices having lower threshold currents may be developed using the nanorods.

In the hybrid structure according to the present invention, electrical conductivity, optical transmittance, and mechanical flexibility are comparable to those of pure graphene. In addition, new optical functions derived from ZnO nanorods are conferred on one- and two-dimensional structure-coupled hybrid structures, presenting a broad spectrum of applications ranging from transparent conductive electrodes to active elements in flexible electronic, optical, and photovoltaic systems. do.

2 is a flowchart illustrating a process of performing a hybrid structure manufacturing method according to the present invention.

Referring to Figure 2, first to prepare a large-area graphene thin film (step S1), then transfer the graphene film to a suitable substrate (step S2), and optionally growing ZnO nanorods at low temperature on the graphene film ( The hybrid structure is manufactured through step S3). Step S3 is preferably performed by a hydrothermal process in an aqueous solution. In order to grow into an array of regularly arranged ZnO nanorods, holes are formed in the graphene thin film and used as a growth mask, and a seed pattern on the graphene thin film is used. The method is described in detail with the following examples.

3 is a flowchart of a first embodiment in which a hole is formed in the graphene thin film and used as a growth mask, and FIG. 4 is a process perspective view thereof. With reference to Figures 3 and 4 will be described in detail a method of manufacturing a hybrid structure according to the present invention.

First, according to step S11 of FIG. 3 and (a) of FIG. 4, first, the graphene thin film 30 is deposited on the SiO ₂ substrate 10. To this end, the SiO ₂ substrate 10 on which Ni 20 is deposited is placed in a chemical vapor deposition (CVD) chamber and filled with hydrogen and argon gas in an appropriate ratio, such as 1: 4. The gaseous carbon source CH ₄ gas and the hydrogen-argon mixed gas were flowed for a predetermined time, for example, 30 seconds while maintaining a constant atmospheric pressure, and then slowly cooled to room temperature. In this process, the graphene thin film 30 is grown on the Ni 20.

Conventionally, the graphene thin film production method is divided into a method of preparing graphite thin film by using a catalyst and a wet method using graphene oxide. The method for preparing a graphene thin film by refining graphite was to apply a catalyst on the graphite attached on the substrate, then cover the polymer and heat treatment to obtain graphene from the graphite, and then remove the substrate to obtain a graphene thin film.

The method using graphite and catalyst can obtain high quality graphene thin film, but the process is rather complicated. The method of using oxidized graphene has the advantage of being simpler than the method of purifying graphite. However, since the oxidized graphene is used, the electrical properties are inferior to those of pure graphene, and since they are formed into small pieces rather than a single thin film, the characteristics as transparent electrodes are inferior to those of conventional ITO.

However, according to the manufacturing method of the present invention, a graphene thin film is manufactured by depositing graphene using a gaseous carbon source, and the graphene can be obtained through a simple vapor deposition process such as CVD. The quality of the thin film is also excellent.

Next, the graphene thin film 30 is separated from the SiO ₂ substrate 10 (step S12 of FIG. 3). At this time, in order to protect the graphene thin film 30 as shown in (b) of FIG. 4, after the protective film 35 such as PMMA is first coated, the graphene thin film 30 is separated from the SiO ₂ substrate 10. desirable. While the protective film 35 is coated, the SiO ₂ substrate 10 is sequentially added to the HF solution and the Ni etchant respectively to etch SiO ₂ and Ni to completely separate the graphene thin film 30. As the Ni etchant, TFB or TFG solution may be used.

Next, the graphene thin film 30 obtained in step S12 is transferred to a suitable substrate, for example, an element substrate 40 such as glass or PET (step S13 of FIG. 3, FIG. 4 (c)). After attaching the graphene thin film 30, the protective film 35, which has been coated to protect the graphene thin film 30, is removed by a chemical or physical method.

In this embodiment, the element substrate 40 uses a glass or plastic substrate, on which a ZnO seed layer 45 is formed. The ZnO seed layer 45 may be formed by CVD or PVD. When describing a growth method using organometallic chemical vapor deposition (MOCVD) among CVD, first, the device substrate 40 is loaded into a reactor, and then, as a reaction precursor. Diethyl zinc (DEZn), dimethyl zinc (DMZn) and the like are used, and the oxide source gas is oxygen (O ₂ ) to form the ZnO seed layer 45. In the case of PVD, after loading the element substrate 40 into the reactor, the ZnO seed layer 45 is formed from the target by a method selected from a pulsed laser, an electron beam, and a chemical beam.

After attaching the graphene thin film 30 to the device substrate 40 on which the ZnO seed layer 45 is formed, the process according to steps S14 and 4 (d) of FIG. 3 is performed. First, the photoresist layer PR is coated on the graphene thin film 30, and then the hole H is patterned by using a photolithography process. The graphene thin film 30 is etched using the patterned photoresist layer PR as an etch mask to expose the ZnO seed layer 45 under the graphene thin film 30.

Thereafter, ZnO nanorods 50 are selectively grown (step S15 of FIG. 3, FIG. 4E). The substrate 40 for the device is immersed in an aqueous solution capable of growing ZnO, and nucleation and growth are induced from the ZnO seed layer 45 exposed in the hole H by a hydrothermal method, thereby increasing ZnO from the inside of the hole H. The nanorods 50 are selectively grown. Preferably a nutrient solution comprising Zn nitrate, Zn acetate or derivatives thereof and hexamethylenetetraamine can be used. By adjusting the concentration and composition ratio of the nutrient solution, the size and shape of the nanorods can be arbitrarily adjusted. Next, the photoresist PR is removed.

5 is a flowchart of a second embodiment using a seed pattern on a graphene thin film, and FIG. 6 is a process perspective view accordingly. 5 and 6 will be described in detail with respect to the manufacturing method of the hybrid structure according to the present invention.

Referring to steps S21 and S22 of FIG. 5 and FIGS. 6A and 6B, the graphene thin film 30 is obtained. At this time, the process may proceed in the same manner as in the steps S11 and S12 of FIG. 3 and in FIGS. 4A and 4B.

Next, the graphene thin film 30 obtained in step S22 is transferred to a suitable device substrate 40 'such as a device substrate, glass or PET (step S23 of FIG. 5, FIG. 6 (c)). After attaching the graphene thin film 30, the protective film 35 that has been coated to protect the graphene thin film 30 is removed. In the present embodiment, the element substrate 40 'uses a glass or plastic substrate, and no seed layer is formed on the element substrate 40'.

Next, the process according to step S24 of FIG. 4 and FIG. 6 (d) is performed. First, after applying a photoresist layer (not shown) on the graphene thin film 30, the hole is patterned by using a photolithography process. After forming a ZnO layer on the patterned photoresist, a lift-off process is applied to remove the ZnO layer formed on the photoresist side and the photoresist layer, and as shown in FIG. 6 (d), on the graphene thin film 30. The ZnO seed pattern 46 is left.

Next, the ZnO nanorods 50 ′ are selectively grown by the hydrothermal method using the ZnO seed pattern 46 (step S25 of FIG. 5 and FIG. 6E). At this time, nanorod growth in the nutrient solution of the method described with reference to step S15 of FIG. 3 and FIG. 4E can be used in the same manner.

In the production method of the present invention, ZnO nanorods are grown by hydrothermal methods. The ZnO nanorods thus formed show excellent electrical and optical properties compared to the nanorods manufactured by the existing expensive equipment and expensive methods. Therefore, the use of the hybrid structure formed by the present invention has a wide range of useful values, such as high density next-generation storage devices, medical lasers, industrial lasers, optical communications, and holographics. In addition, according to the present invention, it is possible to integrate graphene-ZnO nanorods at a low temperature without using a complicated device, thereby manufacturing a new device that combines the characteristics of graphene and ZnO nanorods, which are most promising due to excellent electrical properties. Do.

Meanwhile, in the above embodiments, the graphene thin film is formed by growing graphene on the SiO ₂ substrate on which Ni is deposited. The substrate, which is a substrate means for forming the graphene thin film, is not limited to the SiO ₂ substrate. no. In addition, the growth of graphene may be performed by general CVD, but in the following method, a higher quality graphene thin film may be obtained, and thus the quality of a device adopting the electrode may be improved. Let's do it.

7 is a flowchart of a preferred embodiment for obtaining a graphene thin film for use in the hybrid structure of the present invention, and FIGS. 8 to 10 are schematic implementation views accordingly.

First, as shown in FIG. 8, the graphitized metal film 220 is formed on the substrate 210 and prepared in the chamber 230 as shown in FIG. 9 (step I1 of FIG. 7).

The chamber 230 here is basically provided with a gas supply mechanism 235 capable of supplying various gases to the substrate 210 side so as to perform CVD. Although the gas supply mechanism 235 can be comprised by the showerhead normally used as a gas supply mechanism of this kind of apparatus, for example, it is not limited to this. After charging the substrate 210 on which the graphitized metal film 220 is formed into the chamber 230, air in the chamber 230 is removed using a pump or the like not shown. Thereafter, while maintaining the vacuum in the chamber 230, an appropriate atmospheric gas such as hydrogen and argon gas is flowed through the gas supply mechanism 235 at a ratio of 1: 1 to 1: 6 to maintain the atmospheric pressure.

The substrate 210 is an auxiliary means for forming a graphene thin film, but the material of the substrate 210 does not matter much, but it must be able to withstand heating to around 1000 ° C. in a subsequent process, and the sheet separated from the substrate 210. In order to obtain a graphene thin film of the shape is preferably selected as a material that can be easily removed by acid treatment and the like. In this embodiment, a doped or undoped silicon substrate is adopted as the material of the substrate 210 that satisfies these properties and is not expensive and easily available, and after forming the silicon oxide film 215 thereon, the graphitized metal film 220 ).

The graphitized metal film 220 is a film including a graphitized metal catalyst, the graphitized metal catalyst serves to help the carbon components are bonded to each other to form a hexagonal plate-like structure, for example, to synthesize graphite or , A catalyst used to induce a carbonization reaction or to prepare carbon nanotubes can be used. More specifically, at least one metal selected from the group consisting of Ni, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V and Zr Or alloys can be used.

The graphitized metal film 220 may be formed by dissolving such a metal complex or an alkoxide of a metal in a solvent such as alcohol, and then applying the same to the substrate 210 to dry it. Or it may be formed by depositing on the substrate 210 by a metal deposition method such as thermal deposition.

In particular, the inside of the chamber 230 used in the present embodiment is that the electrode 240 is installed in the vicinity of both ends of the substrate 210, this electrode 240 is a power source (250, DC or AC power source) outside the chamber When the electrode 240 is in contact with the substrate 210 on which the graphitized metal film 220 is formed, as shown in FIG. 8, the substrate 210 is graphitized when the substrate 210 is insulated like an undoped silicon substrate. The current may flow through the metal film 220, and if the substrate 210 is a conductive substrate such as a doped silicon substrate, the current may flow through at least one of the graphitized metal film 220 and the substrate 210. Can be. The electrode 240 illustrated in FIG. 9 is two pairs of electrodes extending along two opposite sides of the substrate 210 at upper and lower ends of the substrate 210, but the shape of the electrode 240 is illustrated. Any structure may be used as long as it is not limited to one and can be configured to evenly conduct the graphitized metal film 220 and / or the substrate 210.

Next, the graphitized metal film is caused by a heat transfer effect by flowing a current to at least one of the graphitized metal film 220 and the substrate 210 in the chamber 230 while maintaining the atmospheric pressure of H ₂ and Ar. Heat 220 (step I2 of FIG. 7). That is, the temperature of the graphitized metal film 220 is raised by using a heat resistance heating method. Preferably it raises the temperature to 600-1000 degreeC, More preferably, it is 850-1000 degreeC. Due to the heating effect at this time, as the particle size of the graphitized metal film 220 increases, the surface of the graphitized metal film 220 becomes flat. This temperature increase process is performed for about 10 minutes.

As mentioned above, the electrode 240 in the chamber 230 is brought into contact with the substrate 210 so that the graphitized metal film 220 and / or the substrate 210 can be fed to the graphite 210 and the graphite is caused by the heat transfer effect at this time. The metallization film 220 is heated. When the substrate 210 is insulative, the temperature is increased by direct heating of the graphitized metal film 220 while the graphitized metal film 220 is energized. Since the metal catalyst is formed in the form of a film and the electrode 240 is in contact with both ends of the substrate 210, the current can flow almost uniformly over the entire surface of the graphitized metal film 220. As described above, only the current is flowed through the graphitized metal film 220, and the whole of the graphitized metal film 220 is heated almost uniformly by the heat transfer effect, without performing complicated control. When the substrate 210 is conductive, when the substrate 210 is energized, the substrate 210 generates heat and the graphitized metal film 220 formed thereon is easily heated.

In this step, the graphitized metal film 220 has a large particle size constituting the graphitized metal film 220 due to not only a heating effect but also an additional effect by an electric field formed by a flowing current. The surface of the metal film 220 becomes very flat. In a subsequent process, the graphene is formed on the graphitized metal film 220 thus flattened, so that the quality thereof is excellent.

Next, a gaseous carbon source is supplied into the chamber 230 through the gas supply mechanism 235 while the graphitized metal film 220 is heated to solidify a carbon component in the graphitized metal film 220 (FIG. 7). Step I3).

The gaseous carbon source may use a hydrocarbon gas family such as ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, hexanes, and in particular may include CH ₄ gas, You can supply more. In other words, CH ₄ gas, which is a gaseous carbon source, may be supplied at this stage while continuously supplying a mixed gas of hydrogen-argon gas for maintaining the atmospheric pressure in the chamber 230. It is possible to control the amount of carbon component dissolved in the graphitized metal film 220 by adjusting the heating temperature, the time, the supply amount of the gaseous carbon source, and the like in this step. Increasing the amount of carbon component dissolved by increasing the time and amount of supply can result in increasing the thickness of the graphene thin film. Conversely, reducing the amount of carbon component by reducing the time and supply amount can reduce the thickness of the graphene thin film. Can be made small. If the supply is small, lengthening the time allows for the desired amount of carbon content to be dissolved. In the experiment, 50 sccm of CH ₄ was supplied for 10 minutes.

In the processing of the substrate which normally requires heating, a method of heating the substrate indirectly by radiant heat of a resistance heater or a lamp is mainly used. In recent years, the graphene thin film for transparent electrodes is also required to be enlarged due to the increase in the size of the thin film display, the increase in the demand for inexpensive solar panels, and the like. In order to obtain such a large graphene thin film, the substrate 210 as a substrate on which the graphene thin film is formed should be large. In the method of indirectly heating by radiation using a conventional resistance heater or a lamp, the size of a heater or the like is used. There is also a concern that an increase in manufacturing cost is necessary because of the need to increase the size.

However, in this case, since the substrate 210 and / or the graphitized metal film 220 are directly energized and heated by using a heat resistance heating method, the substrate 210 can be efficiently heated by a simple configuration and there is no increase in manufacturing cost. It is possible to heat the graphitized metal film 220 even in the case of insulating as well as conductive.

Next, the supply of the gaseous carbon source is stopped and the amount of current flowing in the heat resistance heating method is reduced, thereby cooling the graphitized metal film 220 at a controlled rate (step I4 in FIG. 7), whereby the graphitized metal film ( The graphene thin film 260 is formed by depositing graphene on the surface of the graphitized metal film 220 from the carbon component in the solid solution 220 as shown in FIG. 10.

This cooling process is an important step to obtain high quality by uniformly depositing graphene. Rapid cooling can lead to graphene films that fall short of the desired thickness or cause cracks in the resulting graphene film. It is desirable to cool at a controlled constant rate as much as possible because the thickness of is too thick or inhibits productivity. The ideal cooling rate is 1 to 50 ° C per second, and the ideal case is 10 ° C per second. At the time of cooling, the atmosphere can be Ar.

Cooling after normal film formation is mainly performed by flowing inert gas or natural cooling. However, in this embodiment, since the calorific value can be controlled by controlling the amount of current, by changing the amount of current, the cooling rate of the graphitized metal film 220 can be accurately controlled to grow high quality graphene.

Next, the graphene thin film 260 is separated from the substrate 210 by removing the graphitized metal film 220 by acid treatment. In the exemplary embodiment, when the substrate 210 on which the graphene thin film 260 is formed is sequentially immersed in an HF and TFG solution, the silicon oxide film 215 and the graphitized metal film 220 are sequentially removed to form a sheet-like graphene thin film 260. ) Can be extracted completely from the substrate 210. The graphene thin film 260 separated from the substrate 210 is the graphene thin film 30 in the first embodiment described with reference to FIGS. 3 and 4 or the second embodiment described with reference to FIGS. 5 and 6. It is used as.

Experimental Example

According to two embodiments of the manufacturing method, a hybrid structure in which a two-dimensional graphene thin film-one-dimensional ZnO nanorod was integrated was manufactured.

First, a graphene thin film is manufactured by forming a silicon oxide film 200 nm on a doped or undoped silicon substrate and then depositing about 200 nm of Ni with a graphitized metal film, as described with reference to FIGS. 7 to 10. The graphene thin film was deposited by the method. Ni was heated at 850 to 1000 ° C. for about 10 minutes while maintaining H ₂ and Ar atmosphere at atmospheric pressure, and then 50 sccm of CH ₄ was supplied for 10 minutes. Then, the supply of CH ₄ was stopped and the amount of current flowing in the heat resistance heating method was reduced to cool by 10 占 폚 per second.

In the first experimental example, the graphene thin film was manufactured and then transferred to a glass substrate according to the first embodiment to grow ZnO nanorods on the graphene thin film.

First, in order to protect the graphene thin film, the PMMA was coated at about 200 nm, and then sequentially added to the HF solution and the Ni etchant to etch SiO ₂ and Ni to completely separate the graphene thin film. After supplying 50 sccm Ar, 20 sccm O _2, and 3 sccm DEZn for 20 minutes on a glass substrate at a temperature of 170 to 180 ° C. to form a ZnO seed layer with a polycrystalline ZnO layer having a thickness of about 200 nm, the graphene thin film was formed. Transferred on it and attached. PMMA was then removed using acetone. After the photoresist layer (AZ1512) having a thickness of about 3 μm was coated on the graphene thin film, a 5 μm square hole was patterned by using a photolithography process. Using a patterned photoresist as an etch mask, an oxygen plasma using 150 sccm O ₂ at 300 W (2.45 GHz microwave) power was cut for 80 seconds to etch the graphene thin film to expose the ZnO seed layer under the graphene thin film. Then, the glass substrate was immersed in an aqueous 80 ° C. solution containing zinc nitrate and hexamethylenediamine for 12 hours to selectively grow the ZnO nanorods from the hole up from the hole by hydrothermal method.

In the second experimental example, ZnO nanorods were grown on the graphene thin film by moving the graphene thin film prepared as described above to the PET substrate according to the second embodiment.

First, in order to protect the graphene thin film, the PMMA was coated at about 200 nm, and then sequentially added to the HF solution and the Ni etchant to etch SiO ₂ and Ni to completely separate the graphene thin film. PET was used as the device substrate, and the graphene thin film was attached onto the PET, and PMMA was removed with acetone. After the photoresist layer (AZ1512) was applied on the graphene thin film, a 5 μm square hole was patterned by using a photolithography process. A ZnO layer having a thickness of 100 to 200 nm was formed on the patterned photoresist, and then a lift off process was applied to form a ZnO seed pattern. Next, the ZnO nanorods were selectively grown by immersing the PET substrate in an 80 ° C aqueous solution containing zinc nitrate and hexamethylenediamine for 12 hours.

11 (a) is an optical micrograph of the hybrid structure according to the first experimental example. Referring to FIG. 11A, a large graphene thin film (~ 1 cm cm 1 cm) is formed on a glass substrate, and a regular array of ZnO nanocrystals (shown as black dots) is formed thereon. .

Figure 11 (b) is a scanning electron microscope (Scanning Electron Microscopy, SEM) photograph of the hybrid structure according to the first experimental example. Referring to FIG. 11 (b), it can be seen that the black dots of FIG. 11 (a) correspond to high density ZnO nanorods having an average diameter of 100 nm and an average length of 7 μm grown through holes in the graphene thin film. In particular, the ZnO nanorods are radially oriented and dense to form a bundle of ZnO nanorods, such as flower shapes, the diameter of which is about 15 μm. Since the shape and crystallographic orientation of the ZnO nanorods are influenced by the ZnO seed layer, the growth of the nanorods was investigated using the ZnO epilayer grown on the sapphire substrate.

As shown in FIG. 11 (c), ZnO rods in which hexagonal facets having a diameter of 5-10 μm are developed in the graphene thin film holes are grown. Meanwhile, small diameter ZnO nanorods are grown along the edges of the ZnO rods and are oriented radially. This suggests that the size and shape of the holes in graphene, as well as the seed layer, play an important role in ZnO growth behavior.

Although ZnO nanorods have been grown, the underlying graphene thin film is still flat, free of visible deformation, and no significant defects or damage has been formed. Only a slight contrast change was observed on the optical microscope (box photo in Fig. 11 (a)), which is due to the change in thickness of the graphene film.

Raman spectroscopy was used to further investigate the structural properties and quality of graphene films in hybrid structures. Figure 11 (d) shows the Raman spectrum of the graphene thin film (Comparative Example 1) transferred to the glass substrate and the hybrid structure (Experimental Example 1) according to the first experimental example. Both samples showed Raman peaks at 1580 to 1584 cm ^-1 and 2711 to 2713 cm ^-1 , corresponding to graphite (G, ~ 1582 cm ^-1 ) and 2D bands (2D, 2726 cm ^-1 in graphite), respectively. It can be seen that 3 to 5 layers of graphene thin films were formed from the G and 2D band intensity ratios (~ 1.5 to 2) and the positions of the 2D band peaks, which is consistent with the transmission electron micrographs of FIG. 11 (e). do.

In addition, since the relative intensity of the irregular D band (D, ˜1355 cm ⁻¹ ) is low and similar in both samples, it can be seen that there was no degradation of the graphene thin film after a series of processes. A wide background signal gradually increasing with increasing Raman shift was observed in Experimental Example 1, which may be due to a textured ZnO seed layer or ZnO nanorods.

As such, the high quality of the graphene thin film in the hybrid structure was confirmed by SEM and Raman measurement, and thus, the hybrid structure may be expected to have excellent characteristics derived from the graphene thin film.

First, the current capability of the graphene thin film in the hybrid structure was confirmed by two-terminal I-V measurement. Silver electrodes were formed on both surfaces of the graphene thin film to measure I-V characteristics. As shown in Figure 12 (a), the I-V curve of Experimental Example 1 showed a high current flow of ~ 1.1mA when the applied voltage is 1V. This is 100 times greater than flowing through the ZnO layer even though the graphene thickness is about 100 times smaller than the ZnO layer. For comparison, the graphene film was transferred to an insulated substrate, and the resistance was measured in a similar range (R = ~ 1-5㏀). Therefore, even after the growth of the ZnO nanorods it can be seen that no significant deterioration in the electrical properties of the graphene thin film. Ignoring the contact resistance, the sheet resistance of the sample is calculated to be 1000 mA / square. Although two-terminal measurements do not rule out contact resistance, these values are considerably lower than the sheet resistances of the assembled graphene and are comparable to sheet resistance (300-1000 Ω / □) in continuous graphene films measured by the 4-probe method. Do.

Second, we evaluated the tendency of the resistance to increase in tensile stress due to bending, because one of the useful advantages of graphene is its mechanical strength and elasticity. The hybrid structure made in the PET substrate (Experimental Example 2) did not break even at a bending radius of 0.38 cm (corresponding to a tensile stress of 9.2%), and a small resistance change of 25% or less as shown in the box in Fig. 12 (a). It showed stable performance with. The reduced resistance was restored to its original value through recovery from the bent state, and the response remained stable for several cycles even after repeated bending and unfolding.

In addition to excellent electrical properties, arrays of ZnO nanorods provide new optical functions such as luminescence and optical coupling. The luminisense properties of the hybrid structure were investigated using cathode luminisense (CL) and photo luminisense (PL). Light emission from the ZnO nanorods can be confirmed from the CL image of FIG. 12 (b). And as shown in Figure 12 (c), the PL spectrum of the hybrid structure showed an ultraviolet band in the 450-800nm range. The UV emission peak corresponds to near band edge emission, which relates to the free excitons of ZnO and the wide visible band reflects deep level defects in ZnO.

The optical transmittance of the sample prepared on the transparent substrate was also investigated. 12 (d) shows optical transmittance spectra of Comparative Examples and Experimental Examples 1 and 2. FIG. In the comparative example, graphene was transferred onto a ZnO-coated glass substrate. All three samples showed high optical transmittance in the visible region, 80% for Comparative Example 1, 70% for Experimental Example 1, and 75% for Experimental Example 2. Optical scattering by radially oriented ZnO nanorods reduces the transmission in the hybrid structure. However, optical interactions through ZnO nanostructures can increase the coupling of light into and out of the active region when implemented in optoelectronic devices. Thus, through a suitable design, the hybrid structure according to the present invention can be effectively integrated into various optoelectronic systems as a transparent conductive layer with excellent optical injection / extraction and / or antireflection functions.

Scattering of incident light by an array of regular ZnO nanorods on transparent graphene results in optical diffraction. In this experiment, a hybrid structure with ZnO nanorods of 70um spacing array was placed perpendicular to incident light from a laser diode of 660nm wavelength as shown in FIG. 13 (a). The diffracted beam formed a rectangular array of diffraction spots having a unit length of 4.9 cm on the screen 560 cm apart as shown in FIG. 13 (b). The corresponding diffraction angle of 0.5 degrees was in good agreement with the prediction based on Bragg's law of diffraction.

The contact area between the individual ZnO nanorods and the graphene film is very small, and the ZnO nanorods are less affected by the lateral stresses. According to this particular geometric shape, the regularity of the ZnO nanorods can be maintained for axial (tensile-compression) or flexible (bending) deformation. These characteristics were evaluated through the bending test of the hybrid structure (Experimental Example 2) prepared on the PET substrate. When the substrate was bent, as shown in Figs. 13 (c) and (d), each diffraction spot was enlarged upwards and downwards, and the width gradually increased as the bending radius decreased. The divergence of the spot is due to the sample deflection due to the bending as well as the light refraction at the bent side. Note that, as shown in FIG. 13 (d), when the bending radius is bent to 4 mm (corresponding to 8.9% of tensile stress) and the bending force is removed, the diffraction pattern is completely restored to its original shape. In addition, the sample showed a stable response even after repeated bending and unfolding in 10 cycles, indicating that the one- and two-dimensional hybrid structures have flexibility comparable to two-dimensional graphene films.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific preferred embodiments described above, and the technology to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

1 is a schematic perspective view of a hybrid structure according to the present invention.

2 is a flowchart illustrating a process of performing a hybrid structure manufacturing method according to the present invention.

3 is a flowchart of a first embodiment of a method for manufacturing a hybrid structure according to the present invention, and FIG. 4 is a process perspective view accordingly.

5 is a flowchart of a second embodiment of a method for manufacturing a hybrid structure according to the present invention, and FIG. 6 is a process perspective view accordingly.

7 is a flow chart of a preferred embodiment for obtaining a graphene thin film for use in the hybrid structure of the present invention, Figures 8 to 10 are schematic implementation views accordingly.

11 (a) is an optical micrograph of the hybrid structure (Experimental Example 1) according to the first experimental example, Figure 11 (b) is a scanning electron microscope (Scanning Electron Microscopy, SEM) photograph, Figure 11 (c) is SEM image of the nanorods grown using the ZnO epitaxial layer grown on the sapphire substrate, Figure 11 (d) is a graphene thin film (Comparative Example 1) and the Raman spectrum of Experimental Example 1 transferred to the glass substrate, Figure 11 (e ) Is a transmission electron micrograph of a graphene thin film.

12 (a) is an IV measurement curve of the graphene thin film in Experimental Example 1, FIG. 12 (b) is a cathode minisense (CL) image in Experimental Example 1, and FIG. 12 (c) is Experimental Example 1 The photoluminescence sense (PL) spectrum of Fig. 12 (d) is an optical transmittance spectrum of the hybrid structure (Experimental Example 2) according to Comparative Example, Experimental Example 1 and the second Experimental Example.

Figure 13 (a) is a layout photograph for viewing the diffraction characteristics of Experimental Example 2, Figure 13 (b) is a diffraction spot of Experimental Example 2, Figure 13 (c) and (d) shows the deformation of the diffraction spot according to the bending Shows.

<Description of the symbols for the main parts of the drawings>

10 ... SiO ₂ substrate 20 ... Ni 30 ... graphene thin film

35 ... 40, 40 '... substrate for devices

45 ... ZnO seed layer 46 ... ZnO seed pattern PR ... photoresist layer

H ... hole 50, 50 '... ZnO nanorod

100 ... hybrid structure

Claims (8)

Graphene thin film; And Hybrid structure comprising zinc oxide (ZnO) -based nanorods grown on the graphene thin film. The hybrid structure of claim 1, wherein the graphene thin film has a sheet shape obtained through graphene deposition using a gaseous carbon source. (a) preparing a sheet-like graphene thin film; And (b) growing a ZnO nanorod on the graphene thin film by a hydrothermal process. The method of claim 3, wherein step (a) comprises: Depositing a graphene thin film through graphene deposition using a vapor carbon source on a SiO ₂ substrate; Separating the graphene thin film from the SiO ₂ substrate; And Attaching the graphene thin film separated from the SiO ₂ substrate to a device substrate, The device substrate is formed with a ZnO seed layer, In step (b), Patterning a hole after applying a photoresist layer on the graphene thin film; Etching the graphene thin film through the hole to expose the ZnO seed layer; And And immersing the device substrate in an aqueous solution of a composition capable of growing ZnO, and selectively growing ZnO nanorods from the exposed ZnO seed layer. The method of claim 3, wherein step (a) comprises: Depositing a graphene thin film through graphene deposition using a vapor carbon source on a SiO ₂ substrate; Separating the graphene thin film from the SiO ₂ substrate; And Attaching the graphene thin film separated from the SiO ₂ substrate to a device substrate, In step (b), Patterning a hole after applying a photoresist layer on the graphene thin film; Forming a ZnO layer on the photoresist layer and then applying a lift-off process to leave a ZnO seed pattern on the graphene thin film; And And immersing the device substrate in an aqueous solution of a composition capable of growing ZnO, and selectively growing ZnO nanorods from the ZnO seed pattern. The method of claim 3, wherein the manufacturing of the graphene thin film, Charging a substrate in which a graphitized metal film is formed into a chamber; Heating the graphitized metal film by a heat transfer effect by flowing a current to at least one of the graphitized metal film and the substrate in the chamber; Supplying a gaseous carbon source into the chamber while the graphitized metal film is heated to solidify a carbon component in the graphitized metal film; Controlling the amount of current to cool the graphitized metal film at a controlled rate, thereby depositing graphene on the graphitized metal film surface from the solid solution carbon component; And And removing the graphitized metal film by an acid treatment, thereby separating the precipitated graphene from the substrate. 7. The method of claim 4, wherein the gaseous carbon source comprises a CH ₄ gas. The method of claim 6, wherein the cooling rate of the graphitized metal film is 1 to 50 ° C. per second while depositing the graphene.

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