JP2021195272A - Single-layer graphene sheet, chemical sensor using the same, and method for treating single-layer graphene sheet - Google Patents

Abstract

To provide a graphene sheet having many defects and retaining excellent conductivity, and to provide a chemical sensor using the same.SOLUTION: A single-layer graphene sheet has a carbon-deficient defect and/or a reconstructed structure defect and an enolate-bonded structure, an epoxy-bonded structure and/or an ether-bonded structure formed in the defect, has a sheet resistance of 700 Ω/sq or less., and a ratio ID/IG of an intensity of D band to an intensity of G band in the Raman spectrum of 0.2 or greater.SELECTED DRAWING: Figure 5

Description

The present invention relates to a single-layer graphene sheet, a chemical sensor using the same, and a method for treating the single-layer graphene sheet.

Graphene, which is a monatomic layer formed by sp2 bonds of carbon atoms, has exceptional conductivity, mechanical strength, and chemical stability, and can be applied to various fields by utilizing these properties. Has been done. Further, in recent years, application to seawater desalination separation membranes and gas separation membranes has been studied by introducing depleted sites into graphene to enable the permeation of molecules and ions. Furthermore, by inducing depleted sites in graphene and introducing other elements to the graphene surface, the graphene surface is locally activated to form gas adsorption / reaction sites, thereby achieving gas adsorption performance and catalytic reaction. It is also known that it can be a chemical sensor with improved reactivity and dramatically improved gas detection capability.

As a graphene suitable for a chemical sensor, for example, graphene synthesized by a chemical vapor deposition (CVD) method ^{is collided with Si +} ions to form an atomic level defect, and then an Ar—H ₂ mixed gas is used. It has been reported that the etching was performed in (Non-Patent Document 1).

Further, it has been reported that defects are formed by performing reactive ion etching (RIE) using oxygen plasma on graphene synthesized by the CVD method (Non-Patent Document 2). Non-Patent Document 2 also reports that an epoxy group, a carbonyl group and an ether group are adsorbed on the defect.

Furthermore, by treating graphene synthesized by the CVD method with ozone generated by irradiation with an ultraviolet lamp in the atmosphere, functional groups containing oxygen such as ether, epoxy and carbonyl are placed on the surface. Those introduced have also been reported (Non-Patent Document 3).

MA et al., “Gas sensor based on defective graphene / priority graphene hybrid towards high sensitivity detection of NO2”, AIP Advances, 2019, 9, 075207 LEE et al., “Defect-engineered graphene chemical sensors with ultrahigh sensitivity”, Phys. Chem. Chem. Phys., 2016, 18, p.14198-14204 CHUNG et al, “Highly sensitive NO2 gas sensor based on ozone treated graphene”, Sensors and Actuators B, 2012, 166-167, p.172-176

Reactive ion etching by ion impact using heavy elements such as silicon, which is reported in Non-Patent Document 1, has a large destructive element to graphene, and an unnecessarily large-scale defect is formed. There was something. For this reason, it was difficult to form carbon-depleted sites at the single atomic level.

Also, regardless of the method, the introduction of defects into graphene caused a decrease in conductivity. For example, Non-Patent Document 2 reports that the mobility of holes in graphene decreases as the amount of defects increases, and Non-Patent Document 3 reports that the mobility of holes in graphene decreases as the ozone treatment time increases. It has been reported that the sheet resistance of graphene increases.

If the decrease in conductivity when a defect is formed in graphene can be suppressed, it is expected that the chemical sensor using this will further increase the sensitivity and the response speed. Therefore, it is an object of the present invention to provide a graphene sheet having a large number of defects and maintaining excellent conductivity and a chemical sensor using the graphene sheet.

As a result of various studies to solve the above-mentioned problems, the present inventor irradiates the single-layer graphene sheet with ultraviolet rays in an atmosphere containing oxygen to cause carbon deficiency defects and / or reconstructed structural defects. And, it was found that the problem can be solved by forming an enolate bond structure, an epoxy bond structure and / or an ether bond structure formed in the defect, and the present invention has been completed.

One aspect of the present invention for solving the above-mentioned problems includes a carbon deficiency defect and / or a reconstructed structure defect, and an enolate bond structure, an epoxy bond structure and / or an ether bond structure formed in the defect. However, the sheet resistance is 700Ω / sq. Or less, the ratio _I D / _{I G} of the intensity of D-band to the intensity of the G band in Raman spectra _{(I G) (I D)} is 0.2 or more, a single-layer graphene sheet.

Further, another aspect of the present invention is a chemical sensor using the above-mentioned single-layer graphene sheet.

Further, another aspect of the present invention is to prepare a single-layer graphene sheet, which is irradiated with ultraviolet rays in an oxygen-containing atmosphere to cause carbon deficiency defects and / or reconstructed structural defects. A method for treating a single-layer graphene sheet, which comprises forming an enolate bond structure, an epoxy bond structure and / or an ether bond structure formed in the defect.

According to the present invention, it is possible to provide a single-layer graphene sheet having a large number of defects and maintaining excellent conductivity and a chemical sensor using the same layer graphene sheet.

Schematic diagram of an ultraviolet light irradiation reaction furnace that can be used in the method for treating a single-layer graphene sheet according to one aspect of the present invention. Raman spectra of single-layer graphene sheets according to Examples 1 to 4 and Comparative Examples 1 to 2. Scanning transmission electron microscope (STEM) image of the single-layer graphene sheet according to Example 1 and Comparative Example 1 ((a): Example 1, (b) Comparative Example 1) Scanning transmission electron microscope (STEM) image showing defects due to carbon reconstruction in the single-layer graphene sheet according to Example 1. Scanning transmission electron microscope (STEM) image showing oxygen forming a bonded structure with carbon in the single-layer graphene sheet according to Example 1. Scanning transmission electron microscope (STEM) image of the single-layer graphene sheet according to Comparative Example 2. In the Raman spectrum of single-layer graphene sheet, the ratio I _{D /} I _G peak intensity of D-band to the peak intensity of G-band _{(I G) (I D)} , the relationship between the oxygen concentration in the atmosphere during UV irradiation Graph shown Emission spectrum when ultraviolet irradiation is performed using a mercury lamp in an atmosphere with oxygen concentration of 0% and 100%. Graph showing the relationship between the intensity ratio of the emission line of a mercury lamp and the oxygen concentration in the atmosphere A graph showing the relationship between the oxygen concentration in the atmosphere and the rate of change in sheet resistance during ultraviolet irradiation in the single-layer graphene sheets according to Examples 5 to 11 and Comparative Examples 3 to 4.

Hereinafter, each aspect of the present invention will be described with reference to the drawings in terms of configuration and operation / effect. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. In addition, when "~" is described between two numerical values to represent a numerical range, these numerical values are also included in the range.

[Single-layer graphene sheet]
The single-layer graphene sheet according to one aspect of the present invention (hereinafter, may be simply referred to as “first aspect”) has a carbon deficiency defect and / or a reconstructed structural defect and an enolate bond formed in the defect. It has a structure, an epoxy bond structure and / or an ether bond structure. And the sheet resistance is 700Ω / sq. Or less, the ratio _I D / _{I G} of the intensity of D-band to the intensity of the G band in Raman spectrum is 0.2 or more.

The single-layer graphene sheet, which is the basic structure, has a structure in which carbon atoms are arranged at the vertices of hexagons arranged on a plane without gaps. The carbon atoms are sp2 bonded to each other, which exhibits excellent conductivity, mechanical strength and chemical stability.

The single-layer graphene sheet can be obtained by a known method. As an example, a method of forming a graphene film on a copper foil by a plasma CVD method and then removing the copper foil by etching can be mentioned.

The single layer graphene sheet according to the first aspect has a carbon deficiency defect and / or a reconstructed structural defect in the structure. Here, the carbon deficiency defect means a defect in which a carbon atom does not exist at the apex position of the hexagon in which carbon should be arranged and the position is a void. Further, the carbon reconstructed structural defect refers to a defect that is a polygon having various angles and distances between the bonds due to the rotation of the carbon-carbon bond and the uptake of new carbon atoms. These defects act as gas adsorption / reaction sites, imparting the function of a single-layer graphene sheet as a chemical sensor.

The fact that the single-layer graphene sheet has a carbon deficiency defect and / or a reconstructed structural defect means that a D-band peak is detected in the Raman spectrum described later, and / or a scanning transmission electron microscope (STEM) or the like. This can be confirmed by observing the disorder of the atomic arrangement with a high-resolution electron microscope.

Oxygen atoms are bonded to each of the above-mentioned defects to form an enolate bond structure, an epoxy bond structure and / or an ether bond structure. As a result, the decrease in conductivity of the single-layer graphene sheet is suppressed. This is considered to be due to the following reasons. _{The sheet resistance R s} of the film-like substance is represented by the following formula (1) by the film thickness t, the carrier charge q, the carrier density n and the carrier mobility μ.

As described above, when a defect is formed in the single-layer graphene sheet, the carrier mobility μ decreases, so that the sheet resistance R _s increases and the conductivity decreases. On the other hand, during the formation of each of the above-mentioned bonds, electrons are supplied from the π orbitals of graphene to oxygen in the atomic or molecular state, so that the graphene is doped with holes and the carrier density n increases. This increase in carrier density n compensates for the decrease in carrier mobility μ due to the above-mentioned defects, so that _{the increase in sheet resistance R s} and the resulting decrease in conductivity are suppressed.

The specific value of the sheet resistance at this time is 700Ω / sq. It shall be as follows. The sheet resistance of the single-layer graphene sheet with no defects introduced is 500Ω / sq. Therefore, if the sheet resistance is within this range, the decrease in conductivity is suppressed, and it is expected that the sensitivity and the response speed will be improved when the chemical sensor is used. The value of the sheet resistance is 650Ω / sq. It is preferably 600Ω / sq. The following is more preferable. Further, as a single-layer graphene sheet before defect formation, a high-quality and low-resistance sheet, for example, a sheet resistance of 400 Ω / sq. If the following are used, 500Ω / sq. Even after defect formation. The following sheet resistance can be achieved. In this case, if favorable conditions are met, 450Ω / sq. It is also possible to obtain the sheet resistance of.

The formation of each of the above-mentioned bonding structures can be confirmed by observation with a scanning transmission electron microscope (STEM). In the STEM image, the oxygen atom (atomic number 8) is observed brighter than the carbon atom (atomic number 6) because each atom is observed with a brightness substantially proportional to the square of the atomic number. Therefore, it can be said that the above-mentioned bond structure is formed if a portion that looks brighter than the surroundings is confirmed at the position of the carbon deficiency defect or the reconstructed structure defect.

Further, the above-mentioned sheet resistance value can be measured by a contact type measuring method such as a four-probe method or a non-contact type measuring method such as an eddy current method. Above all, the measurement by the eddy current method is preferable in that the thin single-layer graphene sheet can be prevented from being damaged.

Of the above-mentioned bond structures, oxygen forming the enolate bond structure and the epoxy bond structure is chemically active and easily bonds with other elements such as hydrogen. Therefore, the single-layer graphene sheet having these bonded structures is expected to improve the adsorption and reactivity of gas and become a more sensitive chemical sensor.

Monolayer graphene sheet according to the first aspect, the ratio _I D / _{I G} of the intensity of D-band to the intensity of the G band in Raman spectra _{(I G) (I D)} is 0.2 or more. In the Raman spectrum, the G-band peak is due to a normal six-membered ring and the D-band peak is due to a defect. Therefore, the value of the intensity ratio I _{D /} I _G is large, it means that the amount of defects in the monolayer graphene sheet is large. As described above, the defect of the single-layer graphene sheet acts as a gas adsorption / reaction site. Therefore, by increasing the amount of the defect, high sensitivity can be obtained when it is used as a chemical sensor. The value of the said intensity ratio _I D / _{I G} is preferably 0.3 or more, and more preferably 0.4 or more. The upper limit of the intensity ratio I _{D /} I _G, if within the scope of the expected conductivity is retained is not particularly limited.

The method for measuring the Raman spectrum is not particularly limited, and known devices and methods can be used. However, since the peak position of each band in the obtained spectrum depends on the number of graphene layers and the laser wavelength used for excitation, care must be taken when identifying the peak. For example, when measured monolayer graphene with an excitation wavelength of 514.5 nm, a peak of the 2D band, G band and D band, respectively ^{2700 cm -1,} 1582cm -1, it has been reported that appears in the vicinity of 1350 cm ^-1 ( AC Ferrari et al., “Raman Spectrum of Graphene and Graphene Layers”, Phys. Rev. Lett., 2006, 97, 187401). It is generally known that as the number of graphene layers increases, the peak of the 2D band shifts to the higher wavelength side and the half width of the peak increases. At this time, the peak of the 2D band in which the full width at half maximum is increased can be fitted at one Lorentzian peak in the single-layer graphene, four in the two-layer graphene, and six in the three-layer graphene. It is also known that when the excitation wavelength becomes shorter, the peak of the 2D band shifts to the higher wavelength side. If both the G band and the 2D band are observed in the Raman spectrum, the membrane is identified as graphene.

[Chemical sensor using single-layer graphene sheet]
The chemical sensor according to the other aspect of the present invention (hereinafter, may be simply referred to as “second aspect”) includes the single-layer graphene sheet according to the first aspect described above.

The chemical sensor detects a potential difference or current generated by adsorption / reaction of a molecule or ion to be detected to a defect of the single-layer graphene sheet according to the first aspect described above by a circuit connected to the graphene sheet. -By measuring, the molecule or ion is detected or quantified.

The configuration of the circuit connected to the single-layer graphene sheet, and the material and shape of the electrode for connecting the circuit are not particularly limited, and anything that can be conceived by those skilled in the art can be used.

[Processing method for single-layer graphene sheet]
The method for treating a single-layer graphene sheet according to another aspect of the present invention (hereinafter, may be simply referred to as “third aspect”) is to prepare a single-layer graphene sheet, and to the single-layer graphene sheet, Irradiation with ultraviolet light in an oxygen gas or an argon-oxygen mixed gas causes a carbon deficiency defect and / or a reconstructed structure defect to form an enolate bond structure, an epoxy bond structure and / or an ether bond structure formed in the defect. Including to generate.

The single-layer graphene sheet to be treated may be prepared by the method described in the first aspect.

Irradiation of a single-layer graphene sheet with an oxygen gas or an argon-oxygen mixed gas with a carbon deficiency defect and / or a reconstructed structure defect and an enolate bond structure, an epoxy bond structure and / formed in the defect Alternatively, it is performed under the condition that an ether bond structure is formed. It is considered that the excited atomic oxygen (O ( ¹ D)) generated when oxygen is irradiated with ultraviolet rays contributes to the formation of these defects and bonded structures. This atomic oxygen is generated as follows. First, as represented by the following formula (2), oxygen molecules absorb ultraviolet rays having a wavelength of 175 to 200 nm by the Schumann-Runge band, and atomic oxygen in the ground state (O ( ³ P)). )) Disassemble into. Next, as represented by the following formula (3), after the generated atomic oxygen (O ( ³ P)) in the ground state repeatedly collides with the inner wall of the reactor and other molecules (M). Combines with oxygen molecules to produce ozone. Finally, as represented by the following formula (4), the generated ozone absorbs ultraviolet rays having a wavelength of 220 to 300 nm by the Hartley bands, and the excited atomic oxygen (O ( ¹ D)). To generate.

From this, the ultraviolet irradiation in oxygen gas or argon-oxygen mixed gas has the wavelength of the ultraviolet rays to be irradiated so that the ultraviolet rays are sufficiently absorbed by each of the Schumann-Lunge band of oxygen molecules and the Hartley band of ozone. It is performed by selecting the intensity, irradiation time, and the like. As an ultraviolet source, a mercury lamp is used because it can irradiate two types of ultraviolet rays, one with a wavelength of 184.9 nm absorbed by the Schumann-Lunge band of oxygen molecules and the other with a wavelength of 253.7 nm absorbed by the Hartley band of ozone. It is preferable to use it. The irradiation time is determined according to the oxygen concentration in the atmosphere and the wavelength and intensity of ultraviolet rays, and an example thereof is 1 to 30 minutes.

When an argon-oxygen mixed gas is used as the atmosphere gas when irradiated with ultraviolet rays, the oxygen concentration is not particularly limited, but defects and bond structures generated by activating the reactions represented by the above formulas (2) to (4). From the viewpoint of increasing the amount of oxygen, the oxygen concentration is preferably 20% or more, and more preferably 25% or more. On the other hand, even if the oxygen concentration is made too high, the amount of defects and bonded structures produced will reach a plateau. This is a reaction represented by the formula (4) in which ozone generated by the reactions represented by the formulas (2) to (3) forms an ozone layer between the ultraviolet source and the single-layer graphene sheet. It is understood that the amount ^{of O (1} D) generated in the vicinity of the single-layer graphene sheet reaches a plateau by absorbing the ultraviolet rays required for this. Therefore, the oxygen concentration in the argon-oxygen mixed gas is preferably 60% or less, more preferably 55% or less.

Ultraviolet irradiation in an oxygen gas or an argon-oxygen mixed gas is performed using, for example, the ultraviolet light irradiation reaction furnace 1 shown in FIG. The ultraviolet light irradiation reaction furnace 1 includes an ultraviolet source 2 provided in the furnace and a gas supply means 3 for introducing a gas containing oxygen into the furnace. Further, in the furnace, a sample support 4 for installing a single-layer graphene sheet is installed facing the ultraviolet source 2.

A mercury lamp is used as the ultraviolet source 2. In addition to the above-mentioned two types of ultraviolet rays, the mercury lamp also irradiates light in the ultraviolet-visible light region called i-line (365 nm), h-line (405 nm) and g-line (436 nm). However, the energy of these lights is 327.7 kJ / mol (i-line) at the maximum, which is smaller than the dissociation energy of the CC single bond of 348 kJ / mol, and does not contribute to the formation of defects. Therefore, there is no problem even if such light is irradiated.

As the gas supply means 3, a gas cylinder 31 and a mass flow controller 32 arranged outside the furnace and a pipe 33 connected to the gas cylinder 31 are used. An oxygen cylinder and an argon cylinder are used as the gas cylinder 31, and the oxygen concentration in the atmosphere in the furnace can be adjusted by controlling the amount of gas supplied from both cylinders. When the gas supply means 3 having such a configuration is used, it is preferable to supply gas into the furnace prior to irradiation with ultraviolet rays to replace the gas in the furnace. The time for gas replacement is determined according to the volume of the furnace and the amount of gas supplied, and an example thereof is 1 to 30 minutes.

As the sample support 4, a stainless steel one is used. This makes it possible to prevent the single-layer graphene sheet from reacting with the sample support 4 during ultraviolet irradiation.

Further, the reaction furnace door 5 provided at the inlet of the ultraviolet light irradiation reaction furnace 1 is provided with an optical fiber feed-through 51, and the optical fiber 61 can be inserted into the furnace. In the optical fiber 61, the inner end of the furnace is arranged in the vicinity of the sample support 4, and the optical fiber 61 is connected to the spectroscope 62 and the light emission measuring device 63 outside the furnace, and the ultraviolet rays generated in the vicinity of the single-layer graphene sheet during ultraviolet irradiation. -It is possible to detect the emission of visible light.

According to the method for treating a single-layer graphene sheet according to the third aspect described above, defects at the single atom level can be efficiently formed while suppressing a decrease in conductivity.

Hereinafter, each aspect of the present invention will be described in more detail with reference to examples, but it goes without saying that the present invention is not limited thereto.

[Example 1]
In this example, and in Examples 2 to 4 and Comparative Examples 1 to 2 described later, it was confirmed that the single-layer graphene sheet was irradiated with ultraviolet rays in an oxygen atmosphere to form a bond structure containing defects and oxygen. did.

(Making a single-layer graphene sheet)
First, a copper foil having a thickness of about 18 μm was set in the chamber of an inductively coupled plasma CVD apparatus, and the temperature of the copper foil was raised to about 900 ° C. by energization heating. Next, with 500 sccm of hydrogen and 5 sccm of methane introduced into the chamber as raw material gas, plasma was irradiated for 120 seconds to form a single-layer graphene sheet on the copper foil. Next, the graphene on the copper foil was coated with polymethylmethacrylate (PMMA) by a spin coating method to form a protective film layer. Next, the obtained PMMA / graphene / copper foil composite film was immersed in a 0.5 mol / L ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) aqueous solution, and the copper foil was removed by chemical etching. .. After washing the removed composite film with pure water several times, the graphene side was laminated on a silicon substrate with a silicon oxide film and sufficiently dried. Finally, PMMA was removed with acetone and isopropyl alcohol and washed to obtain a single-layer graphene sheet / silicon substrate laminate.

(Irradiation of single-layer graphene sheet with ultraviolet rays)
Each of the above-mentioned single-layer graphene sheets was irradiated with ultraviolet rays using the ultraviolet light irradiation reaction furnace shown in FIG. This ultraviolet light irradiation reactor is equipped with three ^{5.2 W / cm-2 mercury lamps as an ultraviolet source.} Prior to irradiation with ultraviolet rays, a single-layer graphene sheet was placed on a sample support, the reactor door was closed, an argon-oxygen mixed gas having an oxygen concentration of 50% was introduced, and gas replacement inside the reactor was performed for 10 minutes. rice field. Then, while continuing the introduction of the argon-oxygen mixed gas, ultraviolet rays were irradiated from the mercury lamp for 10 minutes.

(Raman spectrum measurement)
The Raman spectrum of the single-layer graphene sheet after ultraviolet irradiation was measured using a Raman spectrum measuring device (XploRA, manufactured by HORIBA, Ltd.). A semiconductor laser was used as the excitation laser, the excitation wavelength was 532 nm, the laser beam spot was 1 μm in diameter, the spectroscope had 1200 gratings, the aperture was 300 μm, the slit was 100 μm, and the output of the laser source was 9.8 mW. The Raman spectrum was acquired by integrating 5 measurements with an exposure time of 5 seconds. In the obtained Raman spectrum, the wave number showing the maximum intensity in the range of ^{1320 to 1370 cm -1} is the peak position of the D band, and the wave number showing the maximum intensity in the range of ^{1580 to 1630 cm -1 is the peak position of the G band.} The intensities at the positions were defined as the peak intensity of the D band ( _ID ) and the peak intensity of the G band ( _IG ), respectively. Then, from the peak intensity obtained it was calculated the ratio _I D / _{I G} to the peak intensity of G-band peak intensity of D-band _{(I D) (I G)} . The obtained Raman spectrum is shown in FIG. 2 as (d). The resulting value is calculated from the intensity ratio _I D / _{I G} was 0.68.

(Observation by STEM)
Regarding the single-layer graphene after irradiation with ultraviolet rays, the presence or absence of defects and bonded structures was confirmed using a scanning transmission electron microscope (STEM) (manufactured by JEOL Ltd., JEM-2100F) equipped with a DELTA aberration correction device. The acceleration voltage was 60 kV, the current value was 20 pA, the zero loss energy resolution of the cold cathode field emission gun was 0.4 eV, and the electron probe diameter was about 0.1 nm. In addition, an imaging filer detector GIF Quantum manufactured by Gatan was used to acquire the STEM image. Further, the observation was carried out while heating the sample to about 500 ° C. using a heating holder manufactured by JEOL Ltd. in order to prevent contamination of the sample by organic substances in the electron microscope. The STEM image obtained by observation is shown in FIG. 3 as (a). In FIG. 3, for comparison, the STEM image of the single-layer graphene before ultraviolet irradiation prepared in Comparative Example 1 described later is also shown as (b). From FIG. 3, it can be seen that a large number of carbon deficiency defects, defects due to reconstruction, and defect structures due to the uptake of foreign element atoms were formed by irradiation with ultraviolet rays in an atmosphere containing oxygen. The observed carbon deficiency defects consisted of at most several deficiencies and no major deficiencies were observed. In addition, among the defects due to carbon reconstruction, those having the structure shown in FIG. 4 were observed, and a Stone-walles type defect (a) consisting of two 5-membered rings and two 7-membered rings was observed particularly frequently. , A defect structure (b) containing an 8-membered ring and a 4-membered ring, and a structure (c) stabilized by an 8-membered ring and a 5-membered ring were also confirmed. Further, in the STEM image, as shown in FIG. 5, an oxygen atom (a) forming an ether bond structure with two carbon atoms and an oxygen atom (b) forming an enolate bond structure by substituting with a 6-membered ring structure of graphene. ), And an oxygen atom (c) that bridges between carbon-carbon atoms to form an epoxy structure were also observed.

[Examples 2 to 4]
When the single-layer graphene sheet is irradiated with ultraviolet rays, the oxygen concentration in the argon-oxygen mixed gas introduced into the furnace is 25% (Example 2), 75% (Example 3) and 100% (Example 4). The single-layer graphene sheet according to Examples 2 to 4 was prepared by the same method as in Example 1 except for the above, and its structure and characteristics were confirmed.

The obtained Raman spectra are shown in FIG. 2 as (c) (Example 2), (e) (Example 3) and (f) (Example 4), respectively. Each value of these calculated results the intensity ratio _I D / _{I G} is 0.46 (Example 2), was 0.51 (Example 3) and 0.48 (Example 4). Further, the obtained STEM image showed the same structure as that of Example 1, although there was a slight difference in the number of defects.

[Comparative Example 1]
A single-layer graphene sheet according to Comparative Example 1 was prepared by the same method as in Example 1 except that the single-layer graphene sheet was not irradiated with ultraviolet rays, and its structure and characteristics were confirmed.

The obtained Raman spectrum is shown in FIG. 2 as (a). The value of the calculated from the measurement result the intensity ratio _I D / _{I G} was 0.05. The obtained STEM image is shown in FIG. 3 as (b).

[Comparative Example 2]
When the single-layer graphene sheet was irradiated with ultraviolet rays, the single-layer graphene sheet according to Comparative Example 2 was prepared in the same manner as in Example 1 except that the gas introduced into the furnace was argon gas (oxygen concentration 0%). It was prepared and its structure and characteristics were confirmed.

The obtained Raman spectrum is shown in FIG. 2 as (b). The value of the calculated from the measurement result the intensity ratio _I D / _{I G} was 0.05. The obtained STEM image is shown in FIG.

In the Raman spectrum shown in Figure 2, in all instances, the peak of G-band near 1590 cm ^-1 is a peak of the 2D band around 2680cm ^-1 were observed respectively. Further, in each example, the half width of the peak of the 2D band was ^{about 32 cm -1} , and in the peak fitting using Lorentzian, it was possible to fit with a single peak. Furthermore, in each of the examples, the ratio _I 2D / _{I G} peak intensity of a peak intensity _{(I G)} and 2D band G band _{(I 2D)} was in the range of 1.3 to 2. From these results, it can be said that the obtained graphene sheet is a single-layer graphene. On the other hand, in FIG. 2, the peak of the D band was confirmed in the spectra of (c) to (f), but the peak could not be confirmed in the spectra of (a) and (b). From this, it can be said that defects were introduced into the single-layer graphene sheet by irradiation with ultraviolet rays in an atmosphere containing oxygen.

Figure 7 shows the relationship between the oxygen concentration at the time of the peak intensity ratio I _{D /} I _G and the ultraviolet irradiation of the Raman spectrum. From Figure 7, the peak intensity ratio I _{D /} I _G, the oxygen concentration in the atmosphere is increased to 50% with an increase in oxygen concentration, or the excess of it is constant, it can be seen that slightly decreased.

Since the peak intensity ratio I _{D /} I _G with increasing oxygen concentration to investigate the reason for saturation, luminescence measurement for degradation of the ozone in the formation and samples near the ozone by ultraviolet irradiation in an oxygen atmosphere Was carried out. In the apparatus shown in FIG. 1, the fiber vacuum feedthrough (manufactured by Ocean Insight) was used for the feedthrough 51 for optical fiber, the optical fiber with a core diameter of 450 μm was used for the optical fiber 61, and the spectroscope 62 was manufactured by Ocean Insight. HR2000 + was used respectively. The measurement wavelength region was 200 to 890 nm, and the measurement time was 20000 μs per spectrum. FIG. 8 shows the results at oxygen concentrations of 0% and 100%.

In FIG. 8, a typical peak due to a mercury lamp was observed around 254,365,404,435,546,578 nm. Of these, the emission lines found at 365, 404 and 435 nm are called i-line, h-line and g-line, respectively, as described above. Comparing the emission spectra at 0% and 100% oxygen concentration, strong attenuation is seen in the intensity of the emission line observed at 254 nm. From the emission spectra obtained at each oxygen concentration, the ratio of the emission intensity at 254 nm to each intensity of i-line and h-line was calculated, and a graph plotted against the oxygen concentration is shown in FIG. As shown in FIG. 9, the emission intensity ratio tends to decrease as the oxygen concentration increases. From this decreasing tendency, it can be seen that the amount of ozone produced by the photochemical reactions represented by the above-mentioned formulas (2) and (3) increases with the increase in oxygen concentration. That is, the increase in the amount of ozone generated in the vicinity of the mercury lamp with high reaction efficiency to form the ozone layer causes an increase in the amount of ultraviolet rays of 254 nm absorbed by the Hartley zone at that location, which extends to the vicinity of the surface of graphene. It is presumed that this will lead to a decrease in the amount of ultraviolet rays that reach. Then, saturation phenomenon of the peak intensity ratio I _{D /} I _G to increasing oxygen concentration in the graphene surface vicinity, atomic oxygen (O ⁽¹ D in the excited state produced by a photochemical reaction represented by above-mentioned formula (4) )) Is understood to be due to a decrease in the formation probability.

[Examples 5 to 11, Comparative Examples 3 to 4]
In Examples 5 to 11 and Comparative Examples 3 to 4, a single-layer graphene sheet was formed on the PET film, and the sheet resistance was measured by irradiating the single-layer graphene sheet with ultraviolet rays in an atmosphere of various oxygen concentrations.

(Making a single-layer graphene sheet)
First, a single-layer graphene sheet was formed on the copper foil by the same method as in Example 1. Next, a heat release sheet was attached to the graphene on the copper foil. Next, the obtained heat release sheet / graphene / copper foil composite film was immersed in a 0.5 mol / L ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) aqueous solution, and the copper foil was chemically etched. Removed. After washing the removed composite film with ultrapure water several times, the graphene side was laminated on the PET film. Finally, the heat release sheet was peeled off by heat treatment at 80 ° C. in the atmosphere to obtain a graphene / PET film laminate.

(Irradiation of single-layer graphene sheet with ultraviolet rays)
With respect to the single-layer graphene sheet on the obtained laminate, the oxygen concentration in the argon-oxygen mixed gas introduced into the reaction furnace was 0% (Comparative Example 4), 5% (Example 5), and 10% (Implementation). Example 1 except for Examples 6), 20% (Example 7), 40% (Example 8), 60% (Example 9), 80% (Example 10) and 100% (Example 11). The single-layer graphene sheets according to Examples 5 to 11 and Comparative Example 4 were prepared by irradiating with ultraviolet rays in the same manner as in the above. The single-layer graphene sheet according to Comparative Example 3 was produced by the same method as in Example 11 except that it was not irradiated with ultraviolet rays.

(Sheet resistance measurement)
For the single-layer graphene sheets according to each Example / Comparative Example, the sheet resistance before and after the above-mentioned treatment was measured using a non-contact resistance measuring device (manufactured by Napson Corporation, EC-80). The measurement was carried out 5 times for a sample of a graphene / PET film laminate of 4.0 cm × 4.0 cm, and the average value was taken as the sheet resistance. The obtained sheet resistances are summarized in Table 1.

FIG. 10 summarizes the relationship between the sheet resistance after the treatment obtained in Examples 5 to 11 and Comparative Examples 3 to 4 and the oxygen concentration in the atmosphere at the time of ultraviolet irradiation. The figure shows the rate of change in sheet resistance from Comparative Example 3 not irradiated with ultraviolet rays. From FIG. 10, it can be seen that when ultraviolet rays are irradiated in an atmosphere having an oxygen concentration of 0% (Comparative Example 4), the sheet resistance increases by at least 20% or more as compared with the case where no irradiation is performed (Comparative Example 3). .. It is considered that this is because the carbon-carbon σ bond is excited and weakened by the irradiation with ultraviolet rays, and defects are introduced and the electron mobility is impaired. As shown in FIG. 2 (b), in the single-layer graphene sheet irradiated with ultraviolet rays in an oxygen-free atmosphere, the peak of the D band due to the defect was not confirmed in the Raman spectrum, so that it was slight. Defects are thought to significantly limit carrier transport. On the other hand, from FIG. 10, it can be seen that the increase in sheet resistance is suppressed in each embodiment irradiated with ultraviolet rays in an atmosphere containing oxygen. In particular, it can be seen that irradiation with ultraviolet rays in an atmosphere having an oxygen concentration of 20% or more hardly causes an increase in sheet resistance. It is considered that this is because, as described above, the formation of a bond structure containing oxygen in the defect compensated for the increase in carrier density and the decrease in carrier mobility.

As described above, the single-layer graphene sheet according to one aspect of the present invention is in a state where the surface is activated as compared with the non-defect graphene due to carbon deficiency defects and / or structural defects due to reconstruction. This activated state is further promoted by adsorbing oxygen atoms to the above-mentioned defects to form an enolate-bonded structure and / or an epoxy-bonded structure. Further, in the single-layer graphene sheet, oxygen atoms are adsorbed on the above-mentioned defects to form an enolate bond structure, an epoxy bond structure and / or an ether bond structure, so that the conductivity is deteriorated due to the defects, which has been a conventional problem. Can be improved. Therefore, the single-layer graphene sheet according to one aspect of the present invention has both high surface activity and conductivity, and is expected to be applied to new devices such as chemical sensors by utilizing this. In addition, it can be said that it may be applicable to hydrogen stores by taking advantage of its high surface activity and high surface area characteristics.

1 Ultraviolet light irradiation reactor 2 Ultraviolet source 3 Gas supply means 31 Gas bomb 32 Mass flow controller 33 Piping 4 Sample support 5 Reaction furnace door 51 Feed-through for optical fiber 61 Optical fiber 62 Spectrometer 63 Luminescence measuring device

Claims (5)

Carbon deficiency defects and / or reconstructed structural defects,
It has an enolate bond structure, an epoxy bond structure and / or an ether bond structure formed in the defect, and has an enolate bond structure, an epoxy bond structure and / or an ether bond structure.
Sheet resistance is 700Ω / sq. Is below
The ratio of the intensity of the D band to the intensity of the G band in the Raman spectrum _ID / _IG is 0.2 or more.
Single layer graphene sheet. A chemical sensor comprising the single-layer graphene sheet according to claim 1. Preparing a single-layer graphene sheet,
The single-layer graphene sheet is irradiated with ultraviolet rays in oxygen gas or an argon-oxygen mixed gas to form a carbon deficiency defect and / or a reconstructed structure defect, and an enolate bond structure, an epoxy bond structure and an epoxy bond structure formed in the defect. / Or to generate an ether bond structure,
How to treat a single layer graphene sheet, including. The method for treating a single-layer graphene sheet according to claim 3, wherein the irradiation with ultraviolet rays is performed in a gas having an oxygen concentration of 20% or more. The method for treating a single-layer graphene sheet according to claim 3 or 4, wherein the irradiation with ultraviolet rays is performed in a gas having an oxygen concentration of 60% or less.

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