JP2014227304A - Method for producing graphene thin film, electronic element equipped with graphene thin film, sensor, array device and sensing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a graphene thin film by using graphene oxide, which is capable of producing a graphene thin film having a high carrier mobility without deteriorating excellent electric characteristics such as original high mobility and high electrical conductivity of graphene.SOLUTION: The method for producing a graphene thin film includes a step of preparing a graphene oxide thin film in which a plurality of graphene oxide flakes are partially overlapped with one another and a step of reducing the graphene oxide thin film by bringing a carbon-containing gas into contact with the graphene oxide thin film.

Description

  The present invention relates to a method for producing a graphene thin film, and an electronic device, a sensor, an array device, and a sensing method provided with the graphene thin film.

  Graphene is a sheet-like substance that forms a graphite layer, and has a structure in which π electrons spread throughout the sheet. Due to the above structure, graphene is excellent in electrical characteristics such as electrical conductivity and mobility, and is applied to biosensors and the like.

  Graphene is extracted, for example, by mechanically peeling from a graphite crystal. However, the size of the graphene pieces thus obtained, that is, the graphene flakes, is very small. For this reason, it is difficult to increase the area of the graphene thin film, which is a major issue for practical application to biosensors.

  On the other hand, a method of using graphene oxide (GO), which is the same graphene material, is actively used for manufacturing a graphene thin film. Graphene oxide can be synthesized in a large amount at a relatively low cost, and it is possible to easily form a large area of graphene by thinning it. Therefore, application to electronic device materials and the like is being studied worldwide.

  For example, Non-Patent Document 1 discloses a method for producing graphene by performing a reduction treatment with hydrazine on a graphene oxide (GO) thin film. However, the rGO (reduced GO) thin film obtained by the reduction treatment has electrical characteristics such as mobility and electrical conductivity due to carrier scattering between flakes and defect structure in graphene flakes generated in the process of chemical peeling. It is pointed out that it will decline.

  On the other hand, Non-Patent Document 2 discloses a method for producing graphene flakes by reducing a single graphene oxide (GO) flake by a heat treatment (thermal CVD method) in an alcohol gas phase. According to this method, not only the reduction of the graphene oxide flakes, but also the structural repair of the six-membered ring (π electrons) constituting the graphene effectively proceeds to reduce defects in the graphene oxide flakes. It has been reported that transistor characteristics can be dramatically improved when used as a channel material. However, Non-Patent Document 2 merely discloses a method for producing graphene oxide (rGO) obtained by reducing a single graphene oxide (GO) flake.

Toshiyuki Kobayashi et al., “Channel-Length-Depedent-Field-Effect Mobility and Carrier Concentration of Reduced Graphene Oxide ThinSol. 6, pp. 1210-1215, May 2010 Ching-Yuan Su et al., “Highly Efficient Restoration of Graphic Structure in Graphite Oxide Alcohol Vapors”, ACS NANO, Vol. 4, pp. 5285-5292, August 2010

  In recent years, there has been a demand for providing an array element for a biosensor that can detect a plurality of types of proteins deeply involved in biological phenomena such as antigens, antibodies, DNA, etc. on a single substrate with high sensitivity and at low cost. . The surface plasmon (SPR) biosensor currently in practical use can detect the adsorption of host molecules and guest molecules immobilized on a metal surface with excellent sensitivity, but it is a light source and prism for generating resonance. It has problems such as complexity of systems such as angle detectors, high cost. Moreover, it is difficult for the SPR biosensor to detect a plurality of types of proteins simultaneously with high sensitivity.

  On the other hand, as described in Non-Patent Documents 1 and 2, a method for producing graphene by reducing graphene oxide that can be formed at a low cost and with a large area has been proposed. However, Non-Patent Document 1 reports that the electrical characteristics of a graphene thin film having a size of several μm deteriorate when reduced with hydrazine. Non-Patent Document 2 merely discloses a method of reducing using a single graphene oxide flake, and does not provide a design guideline for a graphene thin film for a large area application.

  The present invention has been made in view of the above circumstances, and an object of the present invention is a method for producing a graphene thin film by reducing graphene oxide, without degrading the original excellent electrical characteristics of graphene, and carrier transfer An object of the present invention is to provide a manufacturing method capable of manufacturing a graphene thin film having a high degree.

  Another object of the present invention is to provide an electronic device such as a field effect transistor capable of detecting a target protein or the like with high sensitivity, simply and inexpensively; a pH sensor or a biosensor equipped with the device. An array element having a plurality of such elements on the same substrate; and a sensing method capable of simultaneously detecting a plurality of test substances of the same or different types using the array elements.

  The graphene thin film manufacturing method (first manufacturing method) according to the present invention that has solved the above problems includes a step of preparing a graphene oxide thin film in which a plurality of graphene oxide flakes partially overlap each other, and the graphene oxide thin film And a step of reducing the graphene oxide thin film by bringing a carbon-containing gas into contact therewith.

  In a preferred embodiment of the present invention, the carbon-containing gas includes alcohol and / or hydrocarbon.

  In a preferred embodiment of the present invention, the carbon-containing gas further contains water vapor.

  In a preferred embodiment of the present invention, the alcohol is ethanol and the hydrocarbon is acetylene.

  In a preferred embodiment of the present invention, the graphene oxide thin film used in the step of preparing the graphene oxide thin film is obtained by applying a dispersion of graphene oxide flakes on a substrate by a spin coating method.

  Another method (second manufacturing method) for producing a graphene thin film according to the present invention that has solved the above-described problems includes a step of preparing a graphene oxide thin film, a hydrocarbon containing carbon as a carbon-containing gas in the graphene oxide thin film, And a step of reducing the graphene oxide thin film by bringing a mixture of hydrocarbon and water, a mixture of alcohol and water, or a mixture of hydrocarbon, alcohol and water into contact with each other.

  The present invention also includes an electronic device having a graphene thin film obtained by any of the manufacturing methods described above in a channel layer.

  In a preferred embodiment of the present invention, the electronic device is a field effect transistor.

In a preferred embodiment of the present invention, the carrier mobility of the electronic element is 5 cm ² / V · s or more.

  The present invention also includes a sensor including any of the electronic elements described above.

  According to the present invention, a graphene thin film having at least a first region and a second region obtained by any one of the manufacturing methods described above on the same substrate; a first graphene thin film having the first region A first field effect transistor having a channel layer, a first source electrode and a first drain electrode provided on both sides of the first channel layer, and a first gate electrode; and the second region A second electric field having a second channel layer having the graphene thin film, a second source electrode and a second drain electrode provided on both sides of the second channel layer, and a second gate electrode. An effect transistor having a first functional group bonded to a first test substance on the surface of the graphene thin film in the first region, and on the surface of the graphene thin film in the second region A second functional group that binds to a second test substance, and the first test substance and the second test substance, and the first functional group and the second functional group are the same. Or, array elements that are different are included.

  The present invention provides a sensing method for detecting a test substance in a detection solution using the array element described above, which includes the first detection solution containing the first test substance and the second test substance. Bringing the second detection solution into contact with the first channel layer and the second channel layer, respectively, and each of the first test substance and the second test substance being the first functional group Detecting the first test substance and the second test substance by detecting potential changes in the first channel layer and the second channel layer caused by binding to the second functional group. And a sensing method including:

  Since the method for producing a graphene thin film according to the present invention is configured as described above, it is possible to easily and inexpensively produce a graphene thin film having excellent electrical characteristics inherent in graphene such as high mobility and high electrical conductivity. can do.

The carrier mobility of the FET including the graphene thin film obtained by the above manufacturing method is very high, for example, 5 cm ² / V · s or more, and a uniform large-area thin film can be obtained on a single substrate. Therefore, the graphene thin film can be applied to an electronic element such as an FET, a sensor typified by a biosensor, an array element having a plurality of electronic elements such as an FET, a sensing method using the array element, and the like. As a result, a plurality of test substances of the same type or different types can be simultaneously detected with high sensitivity. For example, a desired functional group (for example, an aptamer molecule such as a nucleic acid aptamer or a peptide aptamer) that selectively binds to a target test substance is disposed on the surface of the graphene thin film obtained by the production method of the present invention. Can be selectively detected. Therefore, if the technology of the present invention is used, it can be expected to be applied and developed in a wide range of fields such as a pharmaceutical field and a diagnostic medical field such as a tumor marker and an immune reaction test.

FIG. 1 is a diagram illustrating the relationship between the channel length (Lc; μm) and the mobility (cm ² / V · s) of the rGO-FET when each reduction process is performed in Experimental Example 1. FIG. 2 is a diagram illustrating a result when each reduction treatment is performed on a graphene oxide partially overlapping each other in Experimental Example 2. FIG. 3 is a diagram schematically showing the junction state and the behavior of the π-electron system when each reduction treatment is performed on the graphene oxide partially overlapping in Experimental Example 2. FIG. 4 shows the relationship between the Raman spectrum from the graphene oxide thin film after CVD treatment using ethanol as a carbon source and the treatment temperature, and the comparison of the Raman spectrum from the graphene oxide thin film after ethanol and normal Ar / H ₂ reduction treatment. FIG. FIG. 5 is a diagram for explaining a sensing principle by an FET having a graphene thin film obtained by the manufacturing method of the present invention in a channel layer. FIG. 6 is a diagram showing an embodiment of an array element having a graphene thin film obtained by the manufacturing method of the present invention in a channel layer. FIG. 7 is a diagram showing the results of pH sensing when an array element in which a plurality of FETs are arranged in parallel on one chip is used. FIG. 8 is a diagram showing the results of a protein detection experiment in a test solution when an array element in which a plurality of the FETs are arranged in parallel on one chip is used.

  The present inventors have intensively studied to solve the above problems. As a result, when producing graphene thin films by reducing graphene oxide, graphene oxide thin films in which multiple graphene oxide flakes partially overlap each other are used as starting materials, and carbon-containing gas is brought into contact therewith to reduce graphene oxide It was found that the above problems can be solved.

  Conventionally, when graphene oxide thin films, in which multiple graphene oxide flakes partially overlap, are reduced with hydrazine, device properties such as mobility are greatly reduced compared to single flakes due to carrier scattering between the flakes. Is reported in Non-Patent Document 1 described above. Therefore, until now, it has not been considered at all to use such a graphene oxide thin film as a starting material. However, according to the results of experiments conducted by the present inventors, when a carbon-containing gas is brought into contact with a graphene oxide thin film in which a plurality of graphene oxide flakes partially overlap with each other and reduced, unexpectedly, high mobility and high electrical conductivity are obtained. It was found that a graphene thin film capable of effectively exhibiting the excellent electrical properties of graphene inherent such as the degree was obtained (see Experimental Examples 1 and 2 described later).

  Furthermore, according to the experimental results of the present inventors, in producing graphene thin film by reducing graphene oxide, not only alcohol such as ethanol as a carbon-containing gas, but also hydrocarbon, a mixture of hydrocarbon and water, alcohol and The present invention has been completed by finding that the above problem can be solved even by using a mixture of water or a mixture of hydrocarbon, alcohol and water.

  In this specification, “reducing the graphene oxide thin film” means that in addition to the desorption of oxygen from the graphene oxide thin film, the recovery of the π electron system of the graphene oxide is promoted, and the graphene structure is formed. To do.

  In the following description, graphene oxide is abbreviated as GO. In some cases, graphene oxide obtained by reducing graphene oxide is particularly abbreviated as rGO.

  First, using Example 1 and Example 2 below, an rGO thin film obtained by bringing a carbon-containing gas into contact with a GO thin film in which a plurality of GO flakes partially overlap each other has high mobility and low electrical resistance. It is explained that it has excellent electrical characteristics.

(Experimental example 1)
First, a Si substrate (film thickness 380 μm) having a SiO ₂ film (film thickness 280 nm) formed on the surface was prepared. Next, GO (obtained from Graphene Laboratories Inc.) was diluted in water to prepare a 100-500 mg / L GO aqueous solution. The GO aqueous solution thus obtained was applied onto the Si substrate by a spin coating method to produce a GO thin film in which one or two GO layers partially overlap each other. The application conditions of the spin coating method are as follows.
Hold for 60 seconds at 1000 rpm → Increase speed from 1000 rpm to 3000 rpm over 10 seconds → Hold for 60 seconds at 3000 rpm

Next, the GO thin film was reduced by the following treatment (I) or (II).
(I) CVD treatment using ethanol as a carbon source (example of the present invention)
Ethanol flow rate: 0.5 sccm
Carrier gas (dilution gas): Ar gas mixed with H ₂ at a rate of 3% Carrier gas flow rate: 100 sccm
Processing temperature: 900 ° C
Processing time: 60 minutes Processing pressure: 200 Pa
(II) Reduction treatment by Ar / H ₂ atmosphere (conventional example)
Mixing H ₂ at a rate of 3% in Ar gas Heating temperature: 900 ° C

  Next, the rGO thin film thus reduced was used as a channel layer, and a source electrode and a drain electrode connected to the channel layer were formed by sputtering, respectively, to produce a field effect transistor (rGO-FET). . Note that a laminate material of Au (40 nm) and Ni (5 nm) was used for each material of the source electrode and the drain electrode.

  Next, the mobility of the rGO-FET was calculated based on the following equation.

In the formula, C _g is a gate capacitance, L _c is a channel length, W _ch is a channel width, V _sd is a source / drain voltage, V _g is a gate voltage, and I _sd is a source / drain current.

FIG. 1 shows the relationship between the channel length (L _c ; μm) and the mobility (cm ² / V · s) of the rGO-FET when each reduction treatment is performed.

  Here, the average GO flake size is 1 μm or less. Therefore, in FIG. 1, the section having a channel length of 1 μm or less reflects the mobility of an FET having rGO flakes as a channel layer, while the section having a channel length of 1 μm or more reflects an rGO thin film comprising a plurality of GO flakes as a channel layer. This reflects the mobility of the FET as shown in FIG.

First, focusing on the single flake region in FIG. 1, the mobility of the FET when reduced by the alcohol CVD process as in the present invention is about 6.5 cm ² / V · s, and the conventional Ar / H ₂ process is performed. Compared with the mobility of the FET (about 0.4 cm ² / V · s) when performing the above, a remarkable improvement of one digit or more was recognized. This is presumably because the carbon in the alcohol used as the carbon source promoted the structural repair of GO and the mobility was improved by the recovery of the π-electron system.

  In FIG. 1, the point to be particularly noted is the result of the thin film region. As described in detail below, when the reduction treatment according to the example of the present invention was performed, high mobility in the single flake region was maintained even in the thin film region and hardly changed.

First, the mobility of rGO, which is a channel layer when it is reduced by a conventional reduction treatment (Ar / H ₂ ) without containing a carbon source, is significantly lower than that of a single flake. This experimental result is consistent with the result of Non-Patent Document 1 described above, and it is considered that the mobility of the graphene thin film is lowered due to the influence of scattering between flakes.

  On the other hand, when the reduction by the alcohol CVD treatment was performed as in the present invention example, the mobility of rGO as the channel layer hardly changed from the single flake region to the thin film region. This result is presumed to be because carrier scattering between GO flakes was suppressed as a result of the recovery and formation of the π-electron system being promoted by the carbon source in the alcohol. That is, the π-π stack interaction between the flakes is strengthened by the recovery of the π electron system of each GO flake; or the flake edge dangling bond is combined with the other dangling bond, It is considered that the mobility of the same degree as that of the single flake region was observed.

(Experimental example 2)
Here, the following experiment was performed using a sample in which two GO flakes A and B partially overlap each other.

First, the reduction treatment (I) or (II) described in Experimental Example 1 was performed on the sample. However, the treatment temperature by the vapor phase treatment of alcohol (I) was 850 ° C., and the treatment temperature by Ar / H ₂ of (II) was 1000 ° C. FIG. 2A shows the state of the rGO flakes after the reduction treatment.

Next, in the rGO flakes obtained by the above reduction treatments, between 1 and 2 shown in FIG. 2 (a), between 3 and 4 (hereinafter referred to as a single layer region), between 1 and 4, 2 The sheet resistance between 1 and 3, between 2 and 4, and between 1 and 3 (the region where flakes overlap each other) was calculated as follows. First, the sheet resistance ρ _A (single layer) in the single layer region of rGO flake A is measured by measuring the resistance R (single layer) (for example, between electrodes 1 and 2), and ρ ₁₂ (single layer) = R ₁₂ (single layer). was calculated based on the _{layer) / (L a / W a} ). Here, W _A and L _A are the average of the width and length of the rGO flake A. Further, the sheet resistance ρ _A (overlap) of the overlapping region where the flakes A and B overlap each other is measured by measuring individual ρ (single layer) and resistance R (overlap) (for example, between the electrodes 1 and 4). (Overlapping) = (W _A / L _A ) ρ _A (single layer) + (W _B / L _B ) ρ _B (single layer) + (W overlapping / L overlapping) ρ (overlapping) Here, W overlap and L overlap are the average of the width and length of the overlap region where the rGO flakes A and B overlap.

The results thus obtained are shown in FIG. FIG. 2 (b) shows the results when the alcohol vapor phase treatment (example of the present invention) is performed, and FIG. 2 (c) shows the results when the treatment with Ar / H ₂ (conventional example) is performed. .

As shown in FIG. 2 (c), in the conventional reduction treatment with Ar / H ₂ , the sheet resistance in the single layer region is very high, 80 to 128 MΩ, and the sheet resistance in the overlapping region where the flakes overlap is equivalent. Or further increased to about 150 MΩ. This experimental result is consistent with the report of Non-Patent Document 1 described above.

  On the other hand, when the reduction by the alcohol vapor phase treatment was performed as in the present invention, the sheet resistance was remarkably reduced to the KΩ level (see FIG. 2B). More surprisingly, the sheet resistance in the overlapping region where the flakes overlap each other tends to be lower than the sheet resistance in the single layer region (about 100 to 250 KΩ), which is reduced to at least 80 KΩ (2 and Between 3). The above experimental results greatly reversed the conventional recognition that carrier scattering is unavoidable between GO flakes and GO flakes, and the mobility is greatly reduced.

  As described above, when the production method of the present invention is used, the reason why a graphene thin film having excellent electrical characteristics can be obtained even when a GO thin film in which GO flakes partially overlap is reduced is that the carbon source species in alcohol is GO. It is presumed that the structural repair of the flakes was promoted, and the recovery of the π-electron system occurred, so that the bonding of the region where the flakes overlapped became very strong.

FIG. 3 is a schematic diagram for explaining the above phenomenon. As shown in FIG. 3B, when the conventional reduction process using Ar / H ₂ is performed, the junction of the region where the flakes overlap is very weak, and the π electron system is localized and does not spread over the whole. Therefore, it is considered that the sheet resistance increases. On the other hand, if reduction by alcohol vapor phase treatment is performed as in the present invention, the π electron system spreads as a whole as shown in FIG. Become. As a result, even when flakes are partially overlapped, it is considered that only a low sheet resistance like a single sheet is exhibited.

  From the results of Experimental Example 1 and Experimental Example 2, it is possible to produce a graphene thin film having excellent electrical characteristics using a graphene oxide thin film in which GO flakes partially overlap each other by performing reduction by alcohol vapor phase treatment. confirmed.

Next, the manufacturing method of the graphene thin film which concerns on this invention is demonstrated. The production method of the present invention comprises the following first and second production methods.
(1) First manufacturing method A method of preparing a GO thin film in which a plurality of GO flakes partially overlap each other and bringing the carbon-containing gas into contact therewith to reduce the GO thin film; Alcohol and / or hydrocarbon, or the alcohol and / or hydrocarbon further containing water vapor; more preferably, the alcohol is ethanol and the hydrocarbon is acetylene.
(2) Second production method A method of using a hydrocarbon, a mixture of hydrocarbon and water, a mixture of alcohol and water, or a mixture of hydrocarbon, alcohol and water as the carbon-containing gas for the GO thin film.

  First, the first manufacturing method will be described.

(1) First Manufacturing Method Among the graphene thin film manufacturing methods according to the present invention, a first manufacturing method includes a step of preparing a graphene oxide thin film in which a plurality of GO flakes partially overlap each other, and the GO thin film And a step of reducing the GO thin film by bringing a carbon-containing gas into contact therewith. Here, as a method for reducing the GO thin film by bringing a carbon-containing gas into contact with the GO thin film, a vapor phase chemical growth method (CVD method) is typically mentioned.

  Comparing the first invention with the method described in Non-Patent Document 2 described above, both are common in that reduction is performed by CVD using ethanol as a carbon-containing gas (carbon source). Patent Document 2 is different in that a single (single layer) GO flake is used instead of a GO thin film in which a plurality of GO flakes partially overlap each other as a starting material as in the present invention. In detail, the reduction conditions by the CVD method in both are also different (details will be described later). Further, Non-Patent Document 2 does not intend to produce a graphene thin film, but merely discloses a technique for producing graphene flakes obtained by reducing single (single layer) GO flakes.

  First, GO flakes are prepared. Here, the GO flakes used in the present invention each have an average size (maximum width; maximum length) of 500 nm to 2000 nm (preferably 1 μm or more, the larger the better). Single layer). The GO flakes can be produced, for example, by known chemical exfoliation of bulk graphite. Or a commercial item can also be used as said GO flakes.

  Next, using the above GO flakes, a GO thin film in which the GO flakes partially overlap each other is produced. The GO thin film can be obtained, for example, by applying a dispersion of GO flakes on a substrate by a known method. At this time, the number and concentration of the GO thin film can be appropriately adjusted by controlling the concentration of the GO flake dispersion and the spin coating conditions.

The substrate used in the above method is not particularly limited as long as it is usually used in the technical field of the present invention, and examples thereof include a Si substrate. As the substrate, a substrate on which SiO ₂ or the like is formed may be used.

The substrate is preferably modified from a hydrophobic surface to a hydrophilic surface by a known surface modification treatment, whereby a uniform large-area graphene thin film can be obtained. The surface modification treatment is not particularly limited, and examples thereof include a cleaning method using UV ozone, and a UV ozone cleaning method is preferable. The preferable conditions of the UV ozone cleaning method used in the present invention are, for example, as follows.
Inflow of oxygen gas at 3 L / min for 5 minutes → UV irradiation for 60 minutes after stopping the inflow of oxygen gas

  The dispersion used in the above method is not particularly limited as long as it can disperse GO flakes. For example, water, dimethylformamide (DMF), ethanol, acetone, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetonitrile, dimethyl ether, toluene; or a mixture containing at least two of these. A preferred concentration of the GO flake dispersion is, for example, in the range of 100 to 500 mg / L.

The method for applying the GO flake dispersion on the substrate is not particularly limited, and examples thereof include a spin coating method, a casting method, a transfer method, and various printing methods. Among these, the spin coating method is preferably used because a thin film with high uniformity can be easily generated and the film thickness can be controlled. For example, when preparing a GO dispersion having a concentration of 100 to 500 mg / L, preferred application conditions for spin coating are as follows. Moreover, the film thickness of the GO thin film can be controlled by changing the number of times of dropping.
Hold for 30 to 180 seconds at 500 to 2000 rpm → Increase to the target rotational speed over 1 to 10 seconds → Hold for 30 to 180 seconds at 3000 to 6000 rpm

  Next, a carbon-containing gas is brought into contact with the GO thin film obtained as described above.

  The carbon-containing gas used in the present invention is not particularly limited as long as it has carbon, and examples thereof include alcohols or hydrocarbons, or mixtures of alcohols and hydrocarbons. As said alcohol, C1-C2 alcohol is mentioned, for example. Ethanol is preferable. Moreover, as said hydrocarbon, a C1-C2 hydrocarbon is mentioned, for example. Acetylene is preferred.

  The carbon-containing gas may further contain water vapor, thereby further promoting the high quality effect of graphene by removing the amorphous carbon structure by etching. A preferable partial pressure of water vapor is, for example, in the range of 0.01 to 1 Pa.

  A typical method for reducing the GO thin film by bringing a carbon-containing gas into contact with the GO thin film is a vapor phase chemical growth method (CVD method). The type of the CVD method is not particularly limited, and a thermal CVD method or a plasma CVD method can be used.

  In performing the reduction by the CVD method using the carbon-containing gas, it is preferable to control as follows.

First, the higher the treatment temperature (reduction temperature), the better, thereby increasing the Raman spectrum ratio [intensity ratio between 2D band and G band = I (2D) / I (G)] indicating the improvement in graphene crystallinity. To do. FIG. 4 shows a comparison between a Raman spectrum from a GO thin film after a CVD process using ethanol as a carbon source and a normal Ar / H ₂ reduction process. As shown in FIG. 4, the ethanol CVD process clearly improves the crystallinity of the graphene thin film as compared with the normal Ar / H ₂ process. Furthermore, when a graphene thin film is produced at a processing temperature of 1100 ° C., the above-mentioned ratio of Raman spectrum is increased to 0.7 or more. The above ratio of the Raman spectrum is closely related to the progress of GO reduction and structural repair. Therefore, the progress of these processes is further promoted by increasing the treatment temperature. However, if the processing temperature is too high, amorphous carbon is generated from the carbon source gas due to the association reaction between the carbon-based molecules generated by the spontaneous pyrolysis reaction in the gas phase during the CVD process, and these are deposited on the GO thin film. This will cause significant deterioration of crystallinity and electronic properties. A preferable processing temperature is, for example, in the range of 600 to 2000 ° C. However, treatment at 3000 ° C., for example, is possible by optimizing the gas phase conditions.

  For the same reason as described above, the longer the processing time (reduction time), the better. A preferable processing time is, for example, in the range of 60 to 300 minutes.

  Furthermore, it is preferable to appropriately control the flow rate and processing pressure of the carbon-containing gas. Thereby, the quality of the graphene thin film after CVD processing is improved. Specifically, the preferable flow rate of the carbon-containing gas is 0.1 to 2.0 sccm. If the flow rate of the carbon-containing gas is too large, the supply will be excessive and amorphous carbon will be generated, resulting in deterioration of electrical characteristics. On the other hand, if the flow rate of the carbon-containing gas is too small, the effect of the gas addition is not exhibited effectively, and the structure repair effect of the graphene thin film is insufficient. For the same reason, a preferable processing pressure is 100 to 200 Pa.

(Second manufacturing method)
Of the graphene thin film manufacturing methods according to the present invention, the second manufacturing method includes a step of preparing a GO thin film, and a mixture of alcohol and water or a hydrocarbon, alcohol and water as a carbon-containing gas in the GO thin film. And a step of reducing the GO thin film by bringing the mixture into contact with each other.

  Since the second manufacturing method is different from the first manufacturing method described above only in the following points, and is otherwise the same as the first manufacturing method, description of overlapping portions is omitted, and only the differences are described. To do.

  In contrast, the second manufacturing method may use a GO thin film as a starting material, and is not limited to the use of a GO thin film in which GO flakes partially overlap each other as in the first manufacturing method. This is different from the first manufacturing method. Therefore, a single GO thin film can also be used in the second manufacturing method. The single GO thin film can be produced by, for example, a chemical peeling method.

  Furthermore, the second production method is different from the first production method described above in that no alcohol single gas is used as the carbon-containing gas. The carbon-containing gas used in the second production method is not disclosed in Non-Patent Document 2 described above and is novel. For the upper limit of the type of carbon-containing gas and the CVD method, the first manufacturing method described above may be referred to.

  The method for manufacturing the GO thin film according to the present invention has been described above.

  Next, an electronic element, a sensor, an array element, and a sensing method using the array element of the present invention will be described.

The electronic device of the present invention has a graphene thin film obtained by the above manufacturing method in a channel layer. Examples of the electronic element include a field effect transistor (FET), a diode, and a solar cell. According to the present invention, even when a graphene thin film is formed in a large area, an electronic device having high mobility similar to a single flake and a very high carrier density of 5 cm ² / V · s or more can be obtained. Therefore, the electronic device of the present invention is suitably used as a sensor such as a pH sensor or a biosensor.

  Hereinafter, with reference to FIG. 5, the sensing principle by the FET having the graphene thin film obtained by the manufacturing method of the present invention in the channel layer will be described.

FIG. 5A is a diagram illustrating a potentiostat including an FET having the graphene thin film as a channel layer. The FET includes an insulating substrate (for example, a Si substrate on which SiO ₂ is formed), a graphene thin film as a channel layer, and a source electrode and a drain electrode formed on both sides of the graphene thin film. In the potentiostat, a reference electrode RE (top gate electrode), a counter electrode CE, and a working electrode WE are arranged, and the current and voltage of the FET are measured. A top gate electrode is formed so as to be in contact with an electrolytic solution containing a substance to be detected (such as ions or a protein having a charge), and a gate voltage is applied to the graphene thin film channel serving as a sensing site via the electrolytic solution.

  As shown in FIG. 5B, the FET is a detection substance utilizing a change in the potential of the channel caused by the electric double layer formed at the interface between the graphene thin film (channel) and the electrolyte containing the substance to be detected. Acts as a sensor to detect For example, if the electrolyte contains proteins with ions or charges, the ions approach the surface of the graphene thin film so that the ions and proteins act as capacitors and adsorb on the surface of the graphene thin film. The potential is modulated. As a result, the reference potential of the gate voltage changes (shifts to the right) as shown in FIG. 5C, and the source / drain current of the FET changes. This is equivalent to the gate voltage being effectively applied to the graphene thin film. Therefore, by measuring the change in the source / drain current, adsorption of ions and proteins can be detected.

  The electronic device of the present invention is useful as a pH sensor, for example, and can detect a change in pH with high sensitivity. For example, when the pH in the buffer solution is changed stepwise, when the change in the source / drain current of the FET is measured using the FET having the graphene thin film obtained by the manufacturing method of the present invention in the channel layer, the source -The drain current clearly shows a stepwise change corresponding to the change in pH.

  According to the present invention, since electronic elements can be integrated, the present invention can be applied to an array element having a plurality of electronic elements such as field effect transistors. The stepwise change in pH can be clearly detected by the sensing method using the array element. Alternatively, a specific test substance can be selectively detected from a plurality of test substances with high sensitivity.

  Hereinafter, the sensing method of the present invention will be described using the array element of FIG. However, FIG. 6 is a diagram showing an embodiment of the array element according to the present invention, and the array element of the present invention is not limited to this.

  As shown in FIG. 6, the array element 10 includes a graphene thin film 2 obtained by the above manufacturing method, at least a first field effect transistor 7 a and a second field effect transistor 7 b on a substrate 1. The graphene thin film 2 has at least a graphene thin film 2a in the first region and a graphene thin film 2b in the second region. The first field effect transistor 7a includes a first channel layer having a graphene thin film 2a in a first region, a first source electrode 3a and a first drain electrode 4a disposed on both sides of the first channel layer. And a first gate electrode 5a. Similarly, the second field effect transistor 7b includes a second channel layer having the graphene thin film 2b in the second region, and a second source electrode 3b and a second drain electrode provided on both sides of the second channel layer. 4b and a second gate electrode 5b.

  On the surfaces of the graphene thin film 2a in the first region and the graphene thin film 2b in the second region, a first functional group and a second functional group that selectively bind to the first test substance and the second test substance, respectively. Are combined.

  The target first test substance and second test substance may be the same or different. The kind of said test substance is not specifically limited, For example, DNA, an antibody, protein etc. are mentioned.

  The kind of the 1st and 2nd functional group can be suitably selected according to the kind of test substance. Examples thereof include an antigen that selectively binds to a specific antibody, and an aptamer molecule such as a DNA aptamer or a peptide aptamer that selectively binds to a specific DNA or peptide.

  The sensing method for detecting the test substance in the detection solution using the array element described above includes the first detection solution 6a containing the first test substance and the second detection solution 6b containing the second test substance, respectively. , Contacting the first channel layer and the second channel layer, and binding the first test substance and the second test substance to the first functional group and the second functional group, respectively. Detecting potential changes in the first channel layer and the second channel layer to detect the first test substance and the second test substance.

  According to the above sensing method, the same kind or plural kinds of test substances can be simultaneously detected with high sensitivity by the sensing principle shown in FIG. For example, when the first test substance and the second test substance are the same in the sensing method, it is possible to detect variations between the test substances. Further, when the first test substance and the second test substance are different in the sensing method, it is possible to simultaneously detect different types of test substances with high sensitivity.

  Hereinafter, the usefulness of the array element and the sensing method according to the present invention will be described in more detail with reference to FIGS.

FIG. 7 is a diagram showing the results of pH sensing when an array element in which a plurality of field effect transistors (FETs) are arranged in parallel on one chip is used. In any FET, a clear change in source / drain current is obtained for each pH value (pH = 4.0, 5.1, 8.2), and there is almost no variation in sensitivity of each element. It was. In the figure in particular, [Delta] I _SD for each of the FET, but shows a change in the source-drain current I _SD to changes in pH (pH 4.0 from pH 8.2), in any of the FET, [Delta] I _SD Was approximately the same (about 0.14 μA ± 10%). This result means that a uniform large area graphene thin film can be obtained with high sensitivity.

  FIG. 8 is a diagram showing the results of a protein detection experiment in a test solution when an array element in which a plurality of the FETs are arranged in parallel on one chip is used. The test solution contains both the target protein human immunoglobulin E (IgE: 50 nM) and the non-target protein bovine serum albumin (BSA: 50 nM). In addition, an IgE aptamer is arranged in advance on the surface of the graphene thin film obtained by the production method of the present invention as an aptamer molecule that selectively binds only to the target protein IgE.

  As shown in FIG. 8, no change in the source / drain current of the FET was observed even when the non-target protein (BSA) was injected, but when the target protein (IgE) was injected, the change in the source / drain current of the FET was observed. Was clearly observed. That is, it was found that a specific protein can be selectively detected with high sensitivity (nM level) similar to that of the existing surface plasmon (SPR) by using the array element of the present invention.

  Although the said protein was selectively detected using the adapter molecule | numerator selectively couple | bonded with one type of target protein in the above, this invention is not limited to this. When it is desired to detect a large number of target proteins at the same time, as shown in FIG. 6 described above, each target protein specifically binds to the surface of the graphene thin film in the first region and the graphene thin film in the second region. A functional group may be arranged. Moreover, the target substance is not limited to protein.

  As described above, by using the technique of the present invention, a specific protein can be selectively detected with high sensitivity. Thus, for example, to a wide range of fields such as a pharmaceutical field and a diagnostic medical field such as a simple tumor marker and an immune reaction test. Can be expected to be applied and expanded.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Graphene thin film 2a Graphene thin film 2a of 1st area | region 2b Graphene thin film of 2nd area | region 3a 1st source electrode 3b 2nd source electrode 4a 1st drain electrode 4b 2nd drain electrode 5a 1st gate electrode 5b Second gate electrode 6a First detection solution containing first test substance 6b Second detection solution containing second test substance 7a First field effect transistor 7b Second field effect transistor 10 Array element

Claims (12)

Preparing a graphene oxide thin film in which a plurality of graphene oxide flakes partially overlap each other;
Reducing the graphene oxide thin film by bringing a carbon-containing gas into contact with the graphene oxide thin film;
A method for producing a graphene thin film, comprising:   The method for producing a graphene thin film according to claim 1, wherein the carbon-containing gas contains alcohol and / or hydrocarbon.   The method for producing a graphene thin film according to claim 2, wherein the carbon-containing gas further contains water vapor.   The method for producing a graphene thin film according to claim 2 or 3, wherein the alcohol is ethanol and the hydrocarbon is acetylene.   The graphene oxide thin film used in the step of preparing the graphene oxide thin film is obtained by applying a dispersion of graphene oxide flakes on a substrate by a spin coating method. Thin film manufacturing method. Preparing a graphene oxide thin film;
The graphene oxide thin film is reduced by bringing the graphene oxide thin film into contact with a hydrocarbon, a mixture of hydrocarbon and water, a mixture of alcohol and water, or a mixture of hydrocarbon, alcohol and water as a carbon-containing gas. Process,
A method for producing a graphene thin film, comprising:   The electronic device which has the graphene thin film obtained by the manufacturing method in any one of Claims 1-6 in a channel layer.   The electronic device according to claim 7, which is a field effect transistor. The electronic device according to claim 7, wherein the carrier mobility is 5 cm ² / V · s or more.   The sensor provided with the electronic device in any one of Claims 7-9. On the same substrate
A graphene thin film having at least a first region and a second region obtained by the production method according to claim 1;
A first channel layer having a graphene thin film in the first region; a first source electrode and a first drain electrode provided on both sides of the first channel layer; and a first gate electrode. A first field effect transistor;
A second channel layer having a graphene thin film in the second region; a second source electrode and a second drain electrode provided on both sides of the second channel layer; and a second gate electrode. A second field effect transistor;
An array element comprising:
On the surface of the graphene thin film in the first region, the first functional group that binds to the first test substance,
A second functional group that binds to a second test substance on the surface of the graphene thin film in the second region;
The array element, wherein the first test substance and the second test substance, and the first functional group and the second functional group are the same or different, respectively. A sensing method for detecting a test substance in a detection solution using the array element according to claim 11,
Contacting the first detection solution containing the first test substance and the second detection solution containing the second test substance with the first channel layer and the second channel layer, respectively. ,
The potentials of the first channel layer and the second channel layer generated when the first test substance and the second test substance are bonded to the first functional group and the second functional group, respectively. Detecting a change to detect the first test substance and the second test substance;
A sensing method comprising: