KR102072888B1 - Method for doping of graphene films by using graphene oxides - Google Patents

Abstract

The object of the present invention relates to simple and stable graphene doping, and more particularly, to a method of doping graphene and doped graphene thereof. The present invention as described above, in the doping method of graphene, it may be configured to include the step of doping the graphene using graphene oxide.

Description

Doping method of graphene with graphene oxide and its doped graphene {Method for doping of graphene films by using graphene oxides}

The present invention relates to a method of doping graphene with graphene oxide, and more particularly, to a method of doping graphene and doped graphene thereof.

Graphene is a large surface area material with a two-dimensional plate-like structure, which is a thin single-layered material in which hexagonal sp2 hybrid carbon atoms are arranged in a hexagonal shape, and its charge acts as a zero effective mass particle. As a result, various new and excellent physical properties are expressed and attract a lot of attention. Graphene is known to be the thinnest material ever known and has a very high electrical conductivity due to the faster electron transfer speed than silicon, and also has a high thermal conductivity, elasticity, and the like, and is strong enough to be diamond-like and flexible.

Such graphene is expected to be used as a new structural material or a new material that can replace an existing inorganic semiconductor electronic material based on its excellent properties. Graphene is used in energy industries such as ultra-capacitors, secondary batteries, hydrogen storage materials, solar cells, flexible displays such as transistors, sensors, transparent electrodes and organic light emitting diodes, as well as next-generation display fields such as touch panels and smart windows. In various electronic industries such as RFID and RFID, applications are expanding in terms of new materials.

Graphene may be produced by mechanical stripping, chemical stripping, chemical vapor deposition (CVD), or molecular beam epitaxy (MBE). Mechanical exfoliation and chemical exfoliation are processes that do not require transfer, and technology development has been made with electronic ink or additives, but there is a problem in obtaining graphene satisfying large area and high quality at the same time. The CVD method is a method for synthesizing graphene using a transition metal that adsorbs carbon well at a high temperature as a catalyst layer. The general growth method is to place nickel (Ni) or copper (Cu), etc. to be used as a catalyst layer in a chamber, to react with a mixture of methane and hydrogen at a high temperature of about 700-1000 ° C. to be adsorbed, and then rapidly cool to carry carbon. Crystallization is a method of growing graphene. General conditions for the CVD method can be found in the Nano Lett., 2009, 9 (1), pp 30-35 and ACS Nano, 2012, 6 (3), pp 2319-2325.

The graphene thus synthesized may be used to suit the intended purpose after separating the graphene from the catalytic metal substrate by removing the metal as a catalyst layer. The number of layers of graphene can be selectively grown by adjusting the type of catalyst, growth time, cooling rate and gas concentration. Graphene grown using the CVD method can grow graphene to a size of several square meters or more, and grow to be composed of pieces having a size of several micrometers by controlling growth conditions. Graphene grown on such metal flakes or metal thin films is required to be transferred to another target substrate for device application or quality inspection, so that a separate transfer technology is required.

Such graphene may improve electrical properties through doping. Graphene doping is primarily through chemical doping. As an example, in the doping of the graphene, n-type graphene is graphene doped with n-type impurities, n-type impurities mainly include one or more elements selected from the group consisting of N, F, Mn, ammonia, Benzyl viologen (BV) or mixtures thereof. On the other hand, p-type doped graphene is graphene doped with a p-type impurity, and the p-type impurity mainly includes one or more elements selected from the group consisting of O, Au, and Bi, and CH ₃ NO ₂ , HNO ₃ , HAuCl ₄ , H ₂ SO ₄ , HCl, AuCl ₃ , bis (trifluoromethanesulfonyl) amide (TFSA) and the like may be selected from at least one compound or a mixture thereof.

In the process of doping, the uniformity of doping may be a problem. In addition, the effect of chemical doping tends to decrease with time, and there is a need for improvement.

Thus, the inventors of the present invention while researching to improve the doping characteristics of graphene, using a graphene oxide, graphene doping method that can improve the uniformity and stability of graphene doping while improving or maintaining the doping characteristics Developed and completed the present invention.

Related patent publications include Korean Patent Publication No. 10-2014-0143756, Registration No. 10-1548537, and the like. In this document, graphene is doped with nitrogen, boron and nitrogen, respectively.

The problem to be solved by the present invention is to provide a doping method of graphene using the graphene oxide and doped graphene that can improve the uniformity and stability of doping in the doping of graphene.

As a viewpoint for solving the above technical problem, the present invention, in the doping method of graphene, may be configured to include the step of doping the graphene using graphene oxide.

Here, the graphene oxide is Hummers method [J. Am. Chem. Soc., 80, 1339 (1598)] may be a peeled graphene oxide having -OH, -COOH, epoxy group by a chemical method modified. However, the graphene oxide is not limited thereto. In addition, the graphene oxide may be formed as a thin film layer and then reduced and reduced graphene oxide (rGO). In this case, the reduction may be performed by a chemical method through heating or treatment with a reducing agent such as hydrazine (N ₂ H ₄ ), but the reduction is not limited thereto.

In addition, the graphene oxide may be an introduction of an organic compound, a metal introduction, or an introduction of an oxide. The energy level of the graphene oxide may be controlled by introducing the organic compound and introducing the metal or the oxide. At this time, the organic compound introduced into the graphene oxide as described above may be a primary amine, secondary amine or tertiary amine.

However, the introduction of the organic compound is not limited to the amine group, and an organic compound capable of controlling the energy level of graphene oxide in an appropriate range may be appropriately selected so as to be suitable for application by graphene doping.

In addition, the metal introduction may be performed by introducing at least one metal such as Al, Zn, Cu, Co, Ni, Mn, Sn, Fe, Pt, Ir, Ti, Zr, Hf,

The oxide introduction may be performed by introducing an oxide such as ITO, ZnO, ZTO, IZO, MoO ₃ , ZnO.

However, the introduction of the metal or oxide is not limited thereto, and the introduction may be performed by appropriately selecting a metal or oxide capable of controlling the energy level of graphene oxide to an appropriate range so as to be suitable for application by graphene doping. have.

In addition, the graphene oxide may be performed by introducing an oxide such as a Li compound such as LiF, Liq, LiCoO ₂ , LiBH ₄ , or a Cs compound such as CsF, Cs ₂ CO ₃ .

However, introduction of the Li compound or the Cs compound is not limited thereto, and the introduction may be performed by appropriately selecting a compound capable of controlling the energy level of graphene oxide in an appropriate range so as to be suitable for application by graphene doping. have.

 Here, the step of doping the graphene, it may be doped using a graphene oxide-graphene bond strength.

As another aspect for achieving the above technical problem, the present invention, in the doping method of graphene, preparing a graphene formed on a substrate; And preparing a solution in which the graphene oxide is dispersed. Adding the solution to the graphene; And it may be configured to include the step of drying the solution.

In this case, adding the solution to the graphene may be performed through a solution process. In this case, various coating techniques are introduced to coat the graphene oxide solution at a low cost in the solution process, and such techniques include dipping and dip coating, Physical Chemistry Chemical Physics, 2010, Vol. 12, pp. 2164 ~ 2169), Spin coating (ACS Nano, 2008, Vol. 2, No. 3, pp. 463 ~ 470), Spray coating, Carbon, 2010, Vol. 48, No. 7, pp 1945-1951), Electrophoresis (ACS Applied Materials & Interfaces, 2013, Vol. 5, No. 13, pp. 6369-6375) and Horizontal dip-coating, Journal of Materials Chemistry C, 2014 , Vol 2, pp 2622-2634).

However, the solution process for coating the graphene oxide is not limited thereto, and a solution process that is easy to form a graphene oxide thin film may be appropriately selected and used.

It is also possible to provide doped graphene obtained by the manufacturing method described above.

Further aspects of the present invention will become apparent from the following description, drawings, examples and claims.

According to embodiments of the present invention has at least the following effects.

Strong intermolecular bonds between graphene oxide and graphene can form a doped graphene film with improved stability.

The doping process using the bond between the graphene oxide and the graphene does not require a process such as deposition for doping, and the doping process can be greatly simplified since the doping can be performed by self-assembly in a solution where molecules are dispersed. have.

In addition, the uniformity of the doping can be greatly improved, which can further improve the reliability when using a large area of graphene.

Therefore, it is possible to provide doped graphene having doping characteristics with improved uniformity and stability, and thus it is expected that a high quality graphene device can be obtained, and various electronic devices (such as touch panels and next-generation display fields and solar cells) can be provided. It is expected to find widespread use in devices such as the energy industry such as batteries, smart windows, and RFID.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.

1 is a schematic diagram of a graphene FET (Graphene Field Effect Transistor, G-FET) manufacturing process according to a reference example of the present invention.
FIG. 2 is a graph of source-drain current characteristics data according to the back-gate applied voltage observed in a pure pristine (prior to graphene oxide coating) graphene active layer in a graphene FET fabricated according to an exemplary embodiment of the present invention. (a)) and a source-drain current characteristic data graph according to the liquid-gate applied voltage (FIG. 2 (b)).
3 is a graph illustrating the source-drain current characteristics data according to the back-gate applied voltage of the graphene FET observed after coating the graphene active layer of the graphene FET with graphene oxide according to Example 1 of the present invention (FIG. 3). (a)) and a source-drain current characteristic data graph according to the liquid-gate applied voltage (FIG. 3 (b)).
Figure 4 is a graph of the source-drain current characteristic data according to the back-gate applied voltage of the graphene FET observed after coating the graphene active layer of the graphene FET coating only the dispersion solvent of graphene oxide according to Comparative Example 1 of the present invention 4 (a) and a source-drain current characteristic data graph according to the liquid-gate applied voltage (FIG. 4 (b)).

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the present embodiments make the disclosure of the present invention complete, and those of ordinary skill in the art to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

Unless otherwise defined, all terms used in the present specification (including technical and scientific terms) may be used in a sense that can be commonly understood by those skilled in the art. In addition, terms that are defined in a commonly used dictionary are not ideally or excessively interpreted unless they are specifically defined clearly.

Graphene is a single atomic layer of carbon, and there are many ways to produce it. Although mechanical peeling can be produced in high quality, it is difficult to produce large area and large capacity, and chemical peeling is possible in mass production, but it is difficult to obtain high quality. Therefore, the production of graphene for commercial purposes is generally used chemical vapor deposition (CVD) method suitable for large-area and high-volume production. Catalytic metals that can be used include Cu, Ni, Co, Cr, Ag, Au, Al, Mg, Mn, Ir, Pt, Ru, Rh, Fe, W, Ta, Ti, U, V, Zr, or alloys thereof. It is a metal foil, a single crystal or a sputtered metal thin film, and high quality graphene is mainly obtained from flakes such as Cu and Ni. This method has the advantage that the graphene can be grown to the same size as the surface of the metal flakes, given only the metal flakes such as copper (Cu). The graphene transfer method in the present invention will be described using a sample grown by the CVD method. However, graphene samples may be samples of other growth methods. Metal flakes may be used a variety of metals but in the present invention will be described with a copper flake.

In one example, graphene growth is performed in a CVD system using copper flakes. Prior to insertion into the CVD system, the copper foil is washed with acetone, deionized water, isopropanol and then air dried under a stream of nitrogen. Copper flakes are placed in a quartz tube and reacted with a mixture of methane and hydrogen at a high temperature of 600-1100 ° C. to adsorb. In more detail, the copper foil is installed in the quartz tube and heats the heater while flowing a small amount of hydrogen after starting the vacuum pump. In the temperature increase period, the time is about 30-40 minutes to the growth temperature, and the vacuum degree is maintained at 30-50 mTorr. Anneal for 3 hours at 2.5 mbar under H ₂ (1000 sccm) / Ar (300 sccm) at 1050 ° C. before reaching the growth temperature. The next procedure is to raise the growth temperature and stabilize the temperature, followed by injection of methane precursor (1 sccm) for 10 minutes. Growth time is grown according to the method of literature. Journal of Physical Chemistry C. (2012), 116, 24068-24074; After growing, the methane supply must be stopped and cooled rapidly. At this time, hydrogen should be flowed in the whole process and can be replaced with nitrogen and argon gas. The growth parameters cited in the present invention may vary depending on the growth apparatus used and are not absolute. Methane can be used in place of acetylene, ethylene or the like.

Graphene (copper substrate-graphene) grown on copper foil or copper thin film is transferred to a silicon substrate with an oxide film, or a flexible substrate to produce a quality test of graphene or to manufacture electronic devices, biosensing devices, sensors, and the like. .

Graphene transfer is generally made by the following steps, using a metal (copper) substrate on which graphene is grown: (copper) substrate-graphene is coated with a precursor of a support layer and then optionally Preparing a (copper) substrate-graphene-support layer bonding layer to treat the support layer precursor. Here, treating the support layer precursor corresponds to curing the uncured polymer. UV curing, chemical curing, thermosetting, or a combination thereof may be used. In this way, a (copper) substrate-graphene-support layer bonding layer is formed.

The (copper) substrate-graphene-support layer bonding layer can be transferred to various substrates, and can be fabricated into a device after a photolithography process.

In some examples, the transfer support layer (layer) may be a polymer coating layer. In this case, the polymer supporting film for transfer may be formed by hardening after spin coating or drop coating a polymer solution on graphene. The transfer polymer support film may play a role of supporting the graphene to facilitate the process up to the process of transferring to the target substrate. Polymers include polymethylmethacrylate (PMMA), polyamide (PA), polybutylene terephthalate (poly (butylenes terephtalate): PBT), polycarbonate (PC), polyethylene (PE) ), Poly (oxymethylene: POM), polypropylene (PP), polyphenylether (poly (phenylenether): PPE), polystyrene (PS), polysulfone (PSU), liquid crystal Liquid crystal polymer (LCP), polyetheretherketone (PEEK), polyetherimide (PEI), polylactide (PLA), polydimethylsiloxane (poly ( dimethylsiloxane: PDMS), poly (lactic acid) (PLA), poly (phthaldehyde) (PPA), and cycloolefin copolymer (COC), Su8, photoresist (PR), poly (4-vinylpyridine) ( P4VP), fluoropolymer (Cytop, Asahi Glass Co.) or at least one of these may be used. For example, after the graphene is grown on a copper foil, a 2 μm thick PMMA layer (996k, 20% in anisole) is spin coated (1500 rpm, 60%) on the substrate. s), and then cured for 10 minutes at 80 ° C. and again for 10 minutes at 130 ° C. However, the transfer polymer support membrane is not limited thereto. In addition to the thermal release tape or the polymer coating layer, various films such as silicone and acrylic may be used as long as it is used for transferring to the target substrate to be transferred. For reference, one surface of the heat-peelable tape has adhesiveness at room temperature, but has a property of losing adhesiveness when heated above a predetermined peeling temperature, and a product having various peeling temperatures can be selected. In addition, a photolithography method may be applied in the transfer process. Photolithography includes a process of forming a thin photoresist having a photosensitive property on a surface of a substrate or a graphene, installing a desired mask pattern and applying light to develop and develop the pattern. In addition, the support film can be produced using various materials (Au, etc.). However, the present invention is not limited thereto, and the description will mainly be made with a PMMA polymer.

Next, the catalyst metal substrate (copper) is removed to form a graphene-support layer laminate. The metal substrate may be removed by a wet etching (etching) process. In some embodiments, the etchant used in the wet etching process is iron chloride (FeCl ₃ ), iron nitrate (Fe (NO ₃ ) ₃ ), copper chloride (CuCl ₂ ), ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) , At least one of sodium persulfate (Na ₂ S ₂ O ₈ ) solution and persulfate type solution can be used. For example, the specimen is allowed to float in the solution at 85 ° C. for 2 hours with the side without the supporting film facing the etching solution. The specimen is then transferred to a fresh etching solution and allowed to react for several hours at room temperature.

Next, the graphene-support layer laminated structure prepared by etching is cleaned and dried. By the cleaning and drying process, the etchant that may remain in the graphene may be removed. The cleaning process is D.I. This can be done by wiping off impurities with water.

In the next step, the separated graphene-support layer laminate sample may be applied to a target substrate for devices to be used in various other electrical applications, such as SiO ₂ (300 nm) / Si substrates for FETs, to be bonded, aligned and dried. As an example of the present invention, a graphene transfer device is manufactured by applying graphene transferred onto a SiO ₂ / Si target substrate, but is not limited thereto.

The target substrate on which graphene is to be transferred is a rigid substrate such as, for example, a silicon substrate, a silicon on insulator (SOI) substrate, a gallium arsenide substrate, a silicon germanium substrate, a ceramic substrate, a quartz substrate, or a glass substrate for display. Polyimide, Polyethylene Terephthalate (PET), PolyEthylene Naphthalate (PEN), Poly Methyl Meth Acrylate (PMMA), Polycarbonate (PC: PolyCarbonate), Polyethersulfone It may be a flexible plastic substrate such as (PES: PolyEtherSulfone) or polyester. In addition, the substrate may be, for example, a transparent substrate capable of transmitting light.

Next, the graphene transfer process is completed by removing the transfer polymer support layer from the target substrate-graphene-support layer laminate.

When the transfer polymer support layer is a heat peeling tape, a predetermined heat is applied to separate the graphene and the heat peeling tape. On the other hand, in the case where the transfer polymer support film is a polymer coating film such as PMMA, a silicone, or an acrylic carrier film, it is supported by a general method such as dissolving the support by an organic solvent such as acetone or chloroform or at a high temperature in a vacuum. Can be removed by evaporation.

Next, a doping process may be performed to improve electrical characteristics of the laminated structure. Graphene doping is primarily through chemical doping. However, as mentioned above, the doping uniformity may be a problem in the doping process. In addition, the effect of chemical doping tends to decrease with time, and there is a need for improvement.

In order to solve the above problems, the present invention includes the step of coating and doping the graphene oxide on the transferred graphene. That is, graphene oxide is applied and coated on the surface of the graphene, resulting in the graphene-graphene oxide interaction, resulting in the graphene being doped, and then, a high quality stable doped graphene can be obtained. have. Organizing doped graphene step by step as follows.

First, graphene formed on the substrate is prepared.

Such a substrate may be a catalytic metal substrate on which graphene is grown, and may be an intermediate support substrate or a final substrate on which graphene is transferred.

On the other hand, as described above, to prepare a dispersion solution in which graphene oxide is dispersed or dissolved.

Preparing the graphene and preparing a dispersion solution as described above may be made independently of each other.

Thereafter, a step of adding a dispersion solution in which such graphene oxide is dispersed is performed to graphene.

As such, by adding the dispersion solution to the graphene, the molecules described above have uniform crystallinity on the graphene and self-assemble to form a single layer doped layer.

In this case, the graphene used may be a single layer graphene or a multilayer graphene. More preferably, single layer graphene can be used.

Next, a step of drying the dispersion solution added to the graphene may be performed to complete the doping process.

By the doping process described above, it is possible to form doped graphene having improved stability through strong intermolecular bonds between the graphene oxide and graphene described above.

The doping process using such intermolecular bonds does not require a process such as deposition for doping, and the doping process may be greatly simplified since the doping may be performed by coating in a dispersion solution.

In addition, the uniformity of the doping can be greatly improved, which can further improve the reliability when using a large area of graphene.

Thus, as described above, it is possible to provide doped graphene having doping characteristics with improved uniformity and stability.

The process of adding the graphene oxide solution may be controlled to process within 1 to 60 minutes to perform doping on the graphene surface. More preferably, when the doping treatment is performed within 5 to 30 minutes, the doping treatment may be effectively performed without generating defects in the graphene.

The present invention is described with reference to several experimental examples depicted in the examples and drawings, but should not be construed as being limited thereto. Those skilled in the art can combine features as desired from aspects of the present invention as long as it is within the scope of the present invention. The full scope of the invention is as defined in the appended claims.

1. Reference Example 1: Fabrication and Characteristics of Graphene-Transferred FET Devices

As shown in FIG. 1, graphene was fabricated on a Cu substrate using a CVD method, and PMMA was coated on the graphene substrate by a spin coating method based on the above-mentioned process, and ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) to form a graphene-PMMA support film laminate by etching the solution, and then transferred onto a SiO ₂ / Si target substrate with a source and drain electrode formed in advance, and dissolved the PMMA support film with a chloroform organic solvent After removal, the graphene FET device was fabricated (channel width: 50 μm, length: 1.6 mm). According to an exemplary embodiment of the present invention, a graphene FET device is manufactured on a SiO ₂ / Si substrate as a graphene transfer device, but is not limited thereto.

2 (a) shows a current-voltage curve between source and drain according to the back gate voltage V _BG observed in the pure pristine graphene FET device of Reference Example 1 (at V _SD = 0.1 V). In general, in the case of an ideally pure pristine graphene-applied FET device, as a current-voltage characteristic, the gate's applied voltage (V _BG ) appears at the lowest point of the current (Dirac point voltage) near 0 V, and is V-shape type. The curve of is drawn. That is, the degree of pureness (or the degree of doping) of the graphene used as the presence or absence of the dirac point may be determined. As can be seen in Figure 2 (a), in the pure graphene device before the graphene oxide doping it can be seen that the lowest point of the current appears near about 13 V within the measurement range (V _BG = -40 V ~ +40 V) have. Accordingly, it can be seen that the intrinsic properties and properties of pure graphene are sufficiently expressed. When the dirac point voltage is not exactly 0 V but about 13 V, it means a weak p-type doping effect due to PMMA polymer or other SiO ₂ substrate adsorbed on the surface of graphene during the device fabrication process.

In general, a top liquid gate FET device has a higher capacitance than a bottom-back gate FET device, and thus exhibits better transfer characteristics. In order to examine in more detail, the current-voltage curve between the source and the drain according to the liquid gate voltage (V _LG ) of Reference Example 1 was measured, which is shown in FIG. 2 (b). . The liquid electrolyte solution used was acetonitrile (ACN): tetrabutylammonium hexafluorophosphate (TBAPF ₆ ) (0.1 M) and the current-voltage characteristics between the source and the drain were measured based on the potential of the Ag / AgCl reference electrode. (In this specification, the voltage applied to the working electrode is expressed relative to the Ag / AgCl reference electrode: vs. V _{Ag / AgCl} ) As can be seen, as a current-voltage characteristic of the graphene FET device, At +0.1 V _{Ag / AgCl} where the applied voltage (V _LG ) of the gate is close to 0 V _{Ag / AgCl} , the lowest point of the current (Dirac point voltage) appears, and the V-shape type curve is shown. Accordingly, it was verified that the intrinsic properties and properties of pure graphene are expressed.

In addition, with respect to the graphene active layer of the pure pristine graphene FET device of Reference Example 1, the work function of graphene was measured by the Kelvin Probe Microscope method. The measured work function is 4.71 eV, which is almost identical to the work function of the pure pristine graphene (4.6 ~ 4.7 eV).

2. Experimental Example 1: Characteristics of graphene FET device coated with graphene oxide

Hummers method [J. Am. Chem. Soc., 80, 1339 (1598)] was prepared from exfoliated graphene oxide having -OH, -COOH, epoxy group.

Looking at the graphene oxide manufacturing process in detail as follows. Graphite or graphite (1 g) is reacted with sulfuric acid (H ₂ SO ₄ , 50 mL) with potassium permanganate (KMnO ₄ , 5 g) in ice for 2 hours. After the ice was removed, the reaction was further reacted at 40 ° C. for 1 hour. Thereafter, distilled water (50 mL) is slowly added and further distilled water is added (150 mL), followed by further 1 hour of reaction. When hydrogen peroxide (H ₂ O ₂ , 10 mL) is added, the solution turns yellow and the reaction ends. After completion, residual acid components are removed from the synthesized graphene oxide by washing with HCl (5%) and distilled water and dried in an oven. The synthesized graphene oxide is subjected to repeated ultrasonic grinding and centrifugation to obtain the final graphene oxide. Graphene oxide dispersion was prepared by ultrasonically pulverizing the graphene oxide in ethanol, distilled water, or a solvent mixed with an appropriate ratio, depending on the concentration. In this experimental example, a graphene oxide solution in which graphene oxide was dispersed in distilled water was used.

As an embodiment of the present invention, a graphene oxide solution prepared on top of the graphene layer of the graphene FET device of Reference Example 1 was added and coated. In this embodiment, in order to precisely coat the graphene oxide solution with a uniform thickness, a graphene oxide film was prepared on the graphene by using a horizontal dip coating technique. During the horizontal dip coating, the graphene oxide solution was supplied at a rate of 1.5 ml / s and the coating speed was advanced at 0.25 cm / s. After coating, heat treatment was performed at 120 ° for 20 minutes in an N ₂ atmosphere for drying the graphene oxide. The final graphene oxide was about 4 nm thick (surface roughness 2.5 nm). The current-voltage characteristics between the source and the drain according to the applied back gate voltage (V _BG ) observed in the graphene FET device coated with graphene oxide were observed and shown in FIG. 3 (a).

As mentioned earlier, in the case of ideally pure pristine graphene, the Dirac point voltage is observed at 0 V of the gate applied voltage (V _BG ), and the V-shape curve is drawn. In the case of the graphene FET device coated with the present graphene oxide solution, as shown in FIG. 3 (a), the curve of the V-shape does not appear, and the lowest dirac point is the measured voltage range ( V _BG = +40 V ~ -40 V) was found out (> +40 V). This means that in the case of graphene coated with graphene oxide, the Dirac point voltage of graphene is changed by the excellent p-type doping effect.

In order to examine this in more detail, in the graphene oxide-coated graphene FET device of Example 1, the current-voltage curve between the source and the drain according to the liquid gate voltage (V _LG ) was observed. It is shown in Figure 3 (b). The electrolyte solution used was the same as ACN: TBAPF ₆ (0.1 M), and the current-voltage characteristics between the source and the drain were measured based on the potential of the Ag / AgCl reference electrode. As can be seen, as a current-voltage characteristic of the graphene FET device, the Dirac point voltage appears at about +0.4 V _{Ag / AgCl} instead of 0 V _{Ag / AgCl} and the gate applied voltage (V _LG ) is asymmetrical V. It can be seen that the shape of -shape is shown. Accordingly, it was demonstrated that graphene is doped with p-type by graphene oxide.

In addition, the graphene active layer coated with the graphene oxide of Example 1, the work function of the graphene was measured by the Kelvin Probe Microscope method. The measured work function was 5.3 eV, which is greatly increased compared to the work function of the pure pristine graphene (4.6 ~ 4.7 eV), and this increase of work function was proved to be an effect of doping.

4. Comparative Example 1: Characteristics of graphene FET device coated only with a solvent for dispersing graphene oxide

Comparative Example 1 was performed to clarify whether the doping effect of the graphene FET device of Example 1 is an effect of graphene oxide or a solvent in which graphene oxide is dispersed. First, the graphene oxide solution was centrifuged (10,000 rpm, 45 minutes), filtered (0.2 μm) to extract only graphene oxide, and then only a transparent dispersion solvent was taken, and added to the graphene FET device of the reference example to obtain a comparative example 1 device. Was produced. The manufacturing process is the same as in Example 1 except for removing the graphene oxide.

4 (a) shows the current-voltage characteristics between the source and the drain according to the back gate voltage observed in the graphene FET device after coating only the dispersion solvent according to Comparative Example 1 of the present invention. In the comparative example graphene FET device, as shown in FIG. 4 (a), it can be seen that the lowest point of the current, that is, the dirac point voltage, is observed at about V _BG = +30 V. Unlike the case of Example 1 device coated with graphene oxide, the graphene doping effect is very weak, and it can be seen that the graphene inherent characteristics are maintained.

In order to confirm this more accurately, the current-voltage curve between the source and the drain according to the liquid gate voltage (V _LG ) of the graphene FET device of Comparative Example 1 is observed and shown in FIG. 4 (b). It was. The electrolyte solution used was the same as ACN: TBAPF ₆ (0.1 M), and the current-voltage characteristics between the source and the drain were measured based on the potential of the Ag / AgCl reference electrode. As can be seen, as a current-voltage characteristic of the graphene FET device, similar to the current-voltage curve of the ideal pristine graphene, the applied voltage (V _LG ) of the gate shows a Dirac point voltage at 0 V _{Ag / AgCl} . , The symmetrical V-shape curve is shown. Accordingly, it was shown that the coating of only the graphene oxide dispersion solution could not explain the p-type doping phenomenon of Example 1, thereby demonstrating that the doping phenomenon of Example 1 was due to graphene oxide.

In addition, the graphene active layer coated only with the graphene oxide dispersion solution of Comparative Example 1, the work function of the graphene was measured by the Kelvin Probe Microscope method. The measured work function is 4.72 eV, which is not significantly changed compared to the work function of the conventional pure pristine graphene (4.6 ~ 4.7 eV), accordingly, the doping phenomenon of Example 1 was proved to be due to the graphene oxide Can be.

Therefore, it can be seen that applying the graphene oxide coating with graphene oxide coating conditions (concentration, etc.) to graphene, the doping degree of graphene can be easily adjusted.

In addition, the graphene oxide coating time is within about a few minutes, it was proved that the treatment time is very short. In addition, when doping the graphene oxide coating, the treatment temperature and thickness may be adjusted to various conditions as necessary.

Graphene doped with graphene oxide can be used in various applications such as flexible displays such as OLEDs, next-generation displays such as touch panels, energy industries such as polymer and inorganic solar cells, and various electronic industries such as smart windows and RFID. have.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

On the other hand, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. Therefore, the above-described embodiments are to be understood as illustrative in all respects and not as restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

No reference sign.

Claims (7)

In the doping method of graphene, doping the graphene with graphene oxide,
Doping the graphene,
Preparing a solution in which the graphene oxide is dispersed;
Adding the solution to the graphene; And
Doping method of the graphene comprising the step of drying the solution. The method of claim 1, wherein the graphene oxide is -OH, -COOH, exfoliated graphene oxide having an epoxy group, reduced and reduced graphene oxide, introduction of organic compounds, introduction of metals, or introduction of oxides is carried out. Method of doping the graphene, characterized in that at least one of the graphene oxide-based molecules in which the introduction of the graphene oxide, Li or Cs compound was performed. The method of claim 2, wherein the organic compound-based molecule comprises a secondary or tertiary amine. The method of claim 2, wherein the Li or Cs compound-based molecule comprises LiCO ₃ or Cs ₂ CO ₃ . The method of claim 1, wherein the doping the graphene is doped using an intermolecular bonding force. delete A doped graphene produced by the method of any one of claims 1 to 5.

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