JP7360690B2 - Composite and method of manufacturing the composite - Google Patents

Description

The present application relates to a composite comprising an N-type doped carbon-based thin film that can control the electron concentration over a wide range of concentrations and is stable for long periods in the atmosphere, and a method for manufacturing the composite.

In order to put into practical use high-sensitivity, high-speed sensors or high-frequency devices using graphene, it is necessary to freely control and stabilize carriers into P-type/N-type without causing defects in graphene. Although it is well known that graphene exhibits P-type, a method for stabilizing N-type doping (electron doping) of graphene in the atmosphere for a long period of time has not been established. N-type doping of graphene, which is stable for long periods in the atmosphere, is one of the technologies in particular demand.

Patent Document 1 describes a method of N-doping graphene by forming a film of an electron-donating organic molecule such as TTF on the graphene surface. According to this method, N-type doped graphene with an electron concentration of 10 ¹³ cm ^-2 or higher is obtained. However, it is unclear whether this N-type doped graphene is stable for long periods in the atmosphere. Further, in this N-type doped graphene, the electron concentration cannot be freely controlled in the electron concentration region of less than 10 ¹³ cm ⁻² .

International Publication No. 2014/030534

The object of the present application is to provide a composite comprising an N-type doped carbon-based thin film whose electron concentration can be controlled over a wide concentration range and which is stable for long periods in the atmosphere.

The composite of the present application includes an N-type doped carbon-based thin film, a base derivative derived from a photobase generator, which is provided on the carbon-based thin film, and a positively charged base derivative and the carbon-based thin film. and an acid derivative derived from a substance from which a base has been removed from a photobase generator.

The method for producing a composite of the present application involves forming a photobase generator layer on a carbon-based thin film of a laminate having a base material that transmits ultraviolet light and a carbon-based thin film provided on the base material. The method includes a generator layer forming step and an ultraviolet light irradiation step of irradiating the carbon-based thin film with ultraviolet light from the base material side of the laminate.

According to the present application, a composite including an N-type doped carbon-based thin film is obtained, in which the electron concentration can be controlled over a wide concentration range and is stable for a long time in the atmosphere.

A chemical formula and a chemical reaction formula showing the structure of a certain photobase generator, the structural change of this photobase generator due to photoreaction, and the interaction between this photobase generator and graphene. (a) Graph showing the change over time in the conductance of the bilayer graphene of the composite of the example. (b) A graph showing the thermoelectromotive force of the bilayer graphene of the composite of the example before and after irradiation with ultraviolet light. (a) Graph showing the change over time in the conductance of the single-layer graphene of the composite of the example. (b) A graph showing the change over time in the conductance of the bilayer graphene of the composite of the example. 2 is a graph showing changes over time in thermoelectromotive force of two-layer graphene of a composite of an example. 2 is a graph showing changes in sheet resistance, Hall coefficient, carrier concentration, and mobility of bilayer graphene of a laminate or composite of an example. 3 is a graph showing changes in sheet resistance, Hall coefficient, carrier concentration, and mobility of single-layer graphene of a laminate or composite of an example. Raman spectra of the 1.7-layer graphene of the laminate or composite of the example before and after treatment. Structural model of graphene coated with a photobase generator and irradiated with ultraviolet light.

The hole concentration in graphene is often as high as about 10 ¹³ cm ⁻² due to the influence of oxygen or water molecules adsorbed in the atmosphere and the base material. The inventors of this application believe that the process of applying a photobase generator to graphene and irradiating it with ultraviolet light can not only be used to suppress the hole concentration in graphene, but also that graphene can be doped with N-type by the progress of a photoreaction. We conducted an experiment. As a result, the sign change of the Seebeck coefficient and Hall coefficient confirmed that the graphene was N-type doped as conceived.

Furthermore, this N-type doped state of graphene is stable even after 2 months in the atmosphere, and the carrier mobility increases 2 to 4 times that before application of the photobase generator. They also discovered that graphene exhibits extremely high carrier mobility for graphene, and that no defects are formed by ultraviolet light irradiation. This long-term stability is due to the fact that the non-ionized (inactive) molecule that is the pair of the N-type dopant in the photobase generator is a protective agent that prevents oxygen or moisture in the air from entering the N-type doped graphene. I thought it was because I was playing a role. Furthermore, it was found that the carrier concentration of less than 10 ¹³ cm ⁻² from P type to N type can be arbitrarily controlled by adjusting the amount of light irradiation.

The composite of the embodiment of the present application includes a carbon-based thin film, a base derivative, and an acid derivative. The carbon-based thin film is a film whose main component is carbon and whose thickness is 0.24 nm or more and 0.66 nm or less. Examples of carbon-based thin films include single-layer graphene, double-layer graphene, and graphene in which a single-layer graphene region is partially mixed in double-layer graphene. The average value of the number of layers calculated by light transmittance measurement is 0.8 or more and 1.2 or less for single-layer graphene, 1.8 or more and 2.2 or less for bilayer graphene, and some monolayers in bilayer graphene. It is 0.8 or more and 2.2 or less for graphene in which graphene regions are mixed.

The carbon-based thin film of the embodiment of the present application is N-type doped. The base derived from the photobase generator is an N-type dopant for the carbon-based thin film. A base derivative is a derivative of a base derived from a photobase generator. In other words, the base derivative is a substance that is positively charged by the base generated by irradiating the photobase generator with ultraviolet light and donating electrons to the carbon-based thin film. A photobase generator generates a base when irradiated with ultraviolet light. Ultraviolet light is light with a wavelength of 10 nm to 400 nm.

As a photobase generator, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,2-dicyclohexyl-4 2-(9-oxoxanthen-2-yl)propionic acid , 4,5,5-tetramethylbiguanidium n-butyltriphenylborate, and 1,2-diisopropyl-3-[bis(dimethylamino)methylene]guanidium 2-(3-benzoylphenyl)propionate. Both are commercially available. The base and base derivative generated from the photobase generator are provided on the carbon-based thin film. The base and base derivative may be in contact with the carbon-based thin film or may be provided on the carbon-based thin film via an acid derivative or other substance, as long as the base can function as an N-type dopant for the carbon-based thin film.

The acid derivative is derived from a substance from which a base has been removed from a photobase generator. In other words, the acid derivative is the substance itself that remains when the photobase generator is irradiated with ultraviolet light to generate a base, and the generated base is _desorbed from the photobase generator. A substance with molecules missing, a simple chemical species such as H ⁺ added to this substance, or a substance whose chemical structure has changed as it is.

The acid derivative is provided on the carbon-based thin film. The acid derivative may be in contact with the carbon-based thin film, or may be provided on the carbon-based thin film via a base, a base derivative, or another substance. The composite of the embodiment may further include a base material that transmits ultraviolet light, and a carbon-based thin film may be provided on the base material. This is because the composite of the embodiment can be easily manufactured by irradiating ultraviolet rays from the base material side of a multilayer structure comprising a base material, a carbon-based thin film on the base material, and a photobase generator on the carbon-based thin film. be.

The method for producing a composite according to an embodiment of the present application includes a photobase generator layer forming step and an ultraviolet light irradiation step after the photobase generator layer forming step. In the photobase generator layer forming step, a photobase generator layer is formed on the surface of the laminate. The laminate includes a base material and a carbon-based thin film provided on the base material. The photobase generator layer is formed on the carbon-based thin film on the surface of the laminate. The substrate is transparent to ultraviolet light. "Transmits ultraviolet light" means that the photobase generator has ultraviolet light transmittance to such an extent that the photobase generator generates a base when the photobase generator is irradiated with ultraviolet light through the object. Note that "irradiating with ultraviolet light" means irradiating with light containing ultraviolet light, and includes irradiating with light that includes light other than ultraviolet light.

The photobase generator layer forming step preferably includes a process of transferring the photobase generator layer formed on the surface of an elastic body, such as dimethylpolysiloxane (PDMS) or polyimide film, to the surface of the laminate. Through this process, the photobase generator is uniformly and sufficiently applied to the surface of the carbon-based thin film. For this reason, the effect of N-type doping due to the photoreaction of the photobase generator is uniformly applied to the carbon-based thin film, and when there is insufficient photobase generator present on the surface of the carbon-based thin film, air or moisture may be absorbed into the carbon. It can be prevented from penetrating the system thin film and impairing the effect of N-type doping.

In the ultraviolet light irradiation step, ultraviolet light is irradiated from the base material side of the laminate. That is, the base material is irradiated with ultraviolet light so that the ultraviolet light that has passed through the base material is irradiated onto the carbon-based thin film. Since the carbon-based thin film is thin, the ultraviolet light irradiated onto the carbon-based thin film via the base material reaches the photobase generator formed on the carbon-based thin film. The photobase generator generates a base by the ultraviolet light that reaches the photobase generator. This base undergoes a structural change, donates electrons to the carbon-based thin film, and further becomes a base derivative. In other words, this base functions as an N-type dopant for the carbon-based thin film.

Furthermore, by irradiating ultraviolet light from the base material side of the laminate, a large amount of base is generated at the boundary between the carbon-based thin film and the photobase generator, promoting N-type doping of the carbon-based thin film. The base derivative is positively charged and exists in a stabilized state on the carbon-based thin film. Note that when a base is generated from the photobase generator, an acid derivative derived from a substance from which the base is removed from the photobase generator also exists on the carbon-based thin film.

Note that when the photobase generator formed on the surface of the carbon-based thin film is irradiated with ultraviolet light from the carbon-based thin film side, a region ( In some cases, there is a photoreactive region) and a region deposited on the photoreactive region that does not react with ultraviolet light (unreacted region) (see FIG. 8). In the photoreaction region, the photobase generator changes into a base that donates electrons to the carbon-based thin film and makes the carbon-based thin film an N-type conductor, and an inert acid derivative. Note that at least a portion of the base exists on the carbon-based thin film as a base derivative after the carbon-based thin film is made into an N-type conductor.

The base, base derivative, and acid derivative prevent oxygen or moisture in the air from entering the surface of the carbon-based thin film, thereby suppressing damage to the N-type state of the carbon-based thin film. In addition, if there is an unreacted region, the unreacted region also prevents oxygen or moisture in the air from entering the photoreactive region and the surface of the carbon-based thin film, thereby impairing the N-type state of the carbon-based thin film. suppress. Therefore, in a composite that further includes a photobase generator on top of a base, a base derivative, and an acid derivative, the N-type dope of the carbon-based thin film is stable for a long time in the atmosphere, for example, for about 2 months.

(Manufacture of graphene)
While heating the copper foil, the carbon components in the copper foil are activated by the energy of charged particles or electrons in the plasma, and the carbon components contained in the copper foil, trace amounts of carbon components adhering to the inside of the reaction vessel, and the processing gas are Single-layer graphene and double-layer graphene (hereinafter, single-layer graphene and double-layer graphene may be collectively referred to as graphene) were manufactured on copper foil using a trace amount of carbon component (Unexamined Japanese Patent Publication No. (See Publication No. 2015-13797).

(Transfer of graphene to PET base material and processing of laminate)
Graphene on copper foil was pasted on a thermal release sheet (manufactured by Nitto Denko Corporation, Riva Alpha). After etching the copper foil with 0.5 mol/L ammonium persulfate, it was washed with running water. The graphene portion of this thermal release sheet and graphene laminate was attached to an A4 size PET base material. The release sheet was peeled off by heating to obtain a laminate in which graphene was formed on a transparent PET base material. The A4 size laminate was cut to obtain a square laminate with a side of 10 mm or a rectangle with a width of 10 mm and a length of 20 to 20 mm.

(Transfer of graphene to quartz base material)
A 2% by mass anisole solution of polymethyl methacrylate resin (PMMA) was spin-coated on the surface of graphene on the copper foil at 3000 rpm for 30 seconds. After air drying, the copper foil was etched with 0.5 mol/L ammonium persulfate, and then washed with running water. The graphene portion of the PMMA layer and graphene laminate was attached to a square quartz substrate with sides of 10 mm. PMMA was removed by infiltration with acetone to obtain a laminate in which graphene was formed on a transparent quartz substrate.

(Measurement of the number of graphene layers)
The number of graphene layers was measured by light transmittance measurement using a haze meter (Nippon Denshoku Industries Co., Ltd., NDH5000SP). The light source is a white LED, and the observation area is approximately 10 mm x 10 mm. Using the fact that the light transmittance of graphene decreases by 2.3% per layer, the number of layers n can be calculated using the following formula.
n=LOG (sample transmittance/substrate transmittance)/LOG (0.977)
From this calculation result, in consideration of measurement errors and the like, 0.8≦n≦1.2 was set as a single layer, and 1.8≦n≦2.2 was set as a two-layer.

(Application of photobase generator)
As shown in Figure 1, the photobase generator (PBG) 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionic acid (manufactured by Tokyo Kasei Kogyo, O0396) is an anionized molecule A (2-(9-oxoxanthen-2-yl)propionic acid) and a cationized molecule A salt composed of B (1,5,7-triazabicyclo[4.4.0]dec-5-ene: 1,5,7-triazabicyclo[4.4.0]dec-5-ene) be.

A 10 to 20 mg/mL methanol solution of this photobase generator was dropped onto a PDMS (polydimethylsiloxane) sheet (Toray SILPOT 184) or a polyimide film (DuPont Toray Kapton 20EN, thickness 7 μm). The PDMS sheet or polyimide film was pressed against a portion other than both ends or four corners of the graphene in the laminate to transfer the photobase generator onto the surface of the graphene in the laminate. This laminate, the surface of which was provided with a photobase generator, was placed on a hot plate and dried in the air at 80° C. for 20 minutes to remove methanol as a solvent.

(Ultraviolet light irradiation)
Using a light source (manufactured by Spectrometer, high-intensity spectral light source: SM25 type Hyper Monolight), ultraviolet light (UV) with a wavelength of 340 nm and a maximum intensity of 1.3 mWcm ^-2 is emitted at a maximum of 460 nm from the quartz and PET substrate sides. After irradiation for seconds, a composite comprising a quartz substrate or a PET substrate, graphene, and a substance derived from a photobase generator was obtained.

(Measurement of conductance and thermoelectromotive force)
Both end portions of the graphene of the composite where the photobase generator is not provided are portions that are brought into contact with an electrode for conductance measurement and a thermocouple for temperature measurement. Ultraviolet light irradiation was performed while measuring the conductance and thermoelectromotive force of graphene in the composite, and the change over time of graphene carriers from P-type to N-type as the irradiation amount increased was measured. Probe electrodes of a conductance measuring device (2400 type source meter, manufactured by Keithley Instruments) were brought into contact with both ends of the graphene, and the conductance of the graphene was measured while applying a constant bias current of 1 mA between the two terminals.

The graphene composite was placed on two electrically insulated and separated metal plates. Thin K thermocouples for temperature measurement were fixed in contact with both ends of the graphene. These two kinds of metal plates are heated as a heat bath and controlled to different temperatures to create a temperature difference. The thermoelectromotive force between the wires was recorded with a measuring device (manufactured by Hioki Electric, LR8400 type Memory Hilogger).

(Measurement of sheet resistance and Hall coefficient)
Gold electrodes are brought into contact with the four corners of the graphene of the stack or composite where the photobase generator is not provided, and the distance between these four terminals is measured by the van der Pauw method using a Hall measurement system (Resitest 8300, manufactured by Toyo Technica). Sheet resistance and Hall coefficient were measured. In other words, a laminate consisting of a base material and graphene, a composite body consisting of a base material, graphene, and a photobase generator, and a composite body consisting of a base material, graphene, and a photobase generator, in which the photobase generator is exposed to ultraviolet light. The sheet resistance and Hall coefficient of graphene of three types of composite samples after irradiation were measured. The current applied to the sample was 0.2 to 0.5 mA, and the applied magnetic field was 0.55 T for both positive and negative magnetic fields.

(Calculation of carrier concentration and mobility)
The _carrier concentration n ^and mobility μ of _graphene are calculated as follows: n=t/(eR _H ) and μ= Calculated using the formula R _H /(tRs). Here, t is the thickness of graphene, and the thicknesses of single-layer, double-layer, and 1.7-layer graphene were 0.3 nm, 0.6 nm, and 0.51 nm, respectively. Based on the sign of R _H , it was determined whether the carriers in graphene were holes (P type) or electrons (N type).

(Raman spectrum measurement)
In order to investigate defect formation and structural changes in graphene due to application of a photobase generator and irradiation with ultraviolet light, we measured the Raman spectrum of graphene in a stack or composite using a laser Raman spectrophotometer (NRS-2100, manufactured by JASCO Corporation). was measured. In this experiment, in order to clearly measure the Raman spectrum of graphene, a synthetic quartz substrate with a square top surface of 10 mm on a side and a thickness of 1.0 mm was used as the base material. In addition, since there is a large overlap between the Raman spectrum of the photobase generator itself and the Raman spectrum of graphene, after measuring the Raman spectrum of graphene on a synthetic quartz substrate, we coated the graphene with a photobase generator and irradiated it with ultraviolet light. After washing and removing the photobase generator with methanol, the Raman spectrum of graphene was measured again.

(result)
Figure 2(a) shows the conductance of the two-layer graphene over time when the PET base material is irradiated with ultraviolet light after a photobase generator is applied onto the two-layer graphene in a laminate of a PET base material and two-layer graphene. It shows change. When UV light irradiation was started at a time of 50 seconds, the conductance of the bilayer graphene decreased, reaching the lowest value at about a time of 70 seconds (20 seconds after the start of UV light irradiation), and then started increasing again until a time of 300 seconds. It approached saturation (250 seconds after the start of ultraviolet light irradiation). This change is believed to be due to the base generated from the photobase generator by ultraviolet light.

As shown in Figure 1, 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionic acid can be molecule-treated by ultraviolet light irradiation. B releases one proton and becomes the base of molecule B'. By donating one electron per molecule of this base to graphene, the doping state of graphene is changed, that is, the Fermi level is moved, and graphene crosses the Dirac point, which is known as the electronic structure unique to graphene. It is presumed that the conductor changes from a type conductor to an N-type conductor.

Therefore, the results of measuring the thermoelectromotive force of the bilayer graphene before and after the ultraviolet light irradiation shown in FIG. 2(a) are shown in FIG. 2(b). Regardless of whether before or after irradiation with ultraviolet light, the thermoelectromotive force of bilayer graphene was proportional to the temperature change, and the Seebeck coefficient was determined. As a result, the Seebeck coefficient of the two-layer graphene before irradiation with ultraviolet light was +30 μV/K, and the two-layer graphene before irradiation with ultraviolet light was a P-type conductor. On the other hand, the Seebeck coefficient of the two-layer graphene after irradiation with ultraviolet light was −50 μV/K, and the two-layer graphene after irradiation with ultraviolet light became an N-type conductor. Therefore, as predicted above, it was confirmed that graphene, which was a P-type conductor, crossed the Dirac point due to the reaction of the photobase generator, and the bilayer graphene after irradiation with ultraviolet light changed to an N-type conductor. .

Figure 3(a) shows the conductance of single-layer graphene over time when the PET base material is irradiated with ultraviolet light after a photobase generator is applied onto the single-layer graphene in a laminate of a PET base material and single-layer graphene. It shows change. The change in conductance of the two-layer graphene shown in FIG. 2(a) was also observed in the single-layer graphene. Figure 3(b) shows the conductance of the two-layer graphene over time when the PET base material is irradiated with ultraviolet light after a photobase generator is applied onto the two-layer graphene in a laminate of a PET base material and two-layer graphene. It shows change. Note that the conductance of bilayer graphene was measured using a sample different from the sample shown in FIG. 2(a). As shown in FIGS. 2(a) and 3(b), the conductance change of the bilayer graphene was reproducible.

In the experiments shown in Figures 3(a) and 3(b), the irradiation density of ultraviolet light was 1.3 mW/ ^cm2 , but for both single-layer graphene and bilayer graphene, approximately The re-increase in conductance after ultraviolet light irradiation was saturated in about 300 seconds. It is considered that the N-type doping state of single-layer graphene and bilayer graphene becomes saturated depending on the amount of ultraviolet light irradiation.

Figure 4 shows the change over time in the thermoelectromotive force of the two-layer graphene when the PET base material was irradiated with ultraviolet light after a photobase generator was applied onto the two-layer graphene in a laminate of a PET base material and two-layer graphene. It shows. In this experiment, a constant temperature difference of 6K was applied to the bilayer graphene and the thermoelectromotive force was measured. As a result, as soon as ultraviolet light irradiation was started, the sign of the thermoelectromotive force reversed from positive to negative, and the bilayer graphene changed from a P-type conductor to an N-type conductor. Regarding the Hall coefficient, we also confirmed that the sign of both single-layer graphene and bilayer graphene was reversed (changed from P-type to N-type) by ultraviolet light irradiation.

Figure 5 shows the measurement results of the sheet resistance and Hall coefficient of two-layer graphene on a PET substrate, and the values of carrier concentration and mobility calculated from them, before application of a photobase generator to the two-layer graphene (treatment). (before), a state in which PBG was applied to two-layer graphene but not irradiated with ultraviolet light, and a state in which PBG was irradiated with ultraviolet light from the PET base material side. In this experiment, the irradiation density of ultraviolet light was 1.3 mW/cm ² and the irradiation time was 300 seconds.

As is well known, the two-layer graphene before treatment is P-type (Hall coefficient has a positive sign), has a carrier (hole) concentration of approximately 2.0×10 ¹³ cm ⁻² , and has a mobility was approximately 1200 cm ² /Vs. On the other hand, immediately after applying PBG to the bilayer graphene, the bilayer graphene turned to N-type (the sign of the Hall coefficient is negative), but if we continued to measure the Hall coefficient in the dark, 50 minutes after applying PBG, has returned to type P.

The absolute value of the carrier concentration of the two-layer graphene immediately after applying PBG is reduced to about 1/10 compared to the absolute value of the carrier concentration of the two-layer graphene before applying PBG, and the mobility is 1.5 to 2.0 times higher. increased to Even with PBG coating alone, the bilayer graphene changed to N-type. This is because the PBG coating process was performed in a laboratory with natural indoor light, so some PBG reacted and the bilayer graphene became N-type immediately after coating, but the amount of UV light irradiation was It is thought that the N-type doping state was unstable due to the small amount of N-type doping, and the bilayer graphene quickly returned to P-type.

Furthermore, graphene in the atmosphere is heavily doped with holes due to the influence of oxygen and water molecules adsorbed on its surface. It is thought that by applying a photobase generator to this graphene, these molecules adsorbed on the surface of graphene were removed to some extent, and the absolute value of the carrier concentration after PBG application was reduced to about 1/10. Subsequently, the sign of the Hall coefficient of bilayer graphene after UV irradiation turned negative again, and the N-type state of bilayer graphene was maintained even after 150 minutes and even 2 months after UV irradiation. Ta.

The carrier (electron) concentration was 2.1×10 ¹² cm ⁻² immediately after UV irradiation, and although it increased once after 150 minutes, the electron concentration remained almost the same as immediately after UV irradiation even after 2 months. Furthermore, the electron mobility of the two-layer graphene after UV irradiation was 2320 to 3560 cm ² /Vs, which was maintained for two months at a value more than twice the hole mobility before PBG application.

FIG. 6 shows the results of the same experiment as shown in FIG. 5 for single-layer graphene. Like the bilayer graphene, the single-layer graphene before treatment is P-type (the sign of the Hall coefficient is positive), has a carrier (hole) concentration of approximately 1.6 × 10 ¹³ cm ^-2 , and a mobility of approximately 1000 cm. ² /Vs. On the other hand, after applying PBG, the conductor changed to an N-type conductor (the sign of the Hall coefficient was negative). This is because the PBG coating process was performed in a laboratory with natural indoor light, so some of the PBG reacted and the single-layer graphene became an N-type conductor immediately after coating, but it was not exposed to ultraviolet light. The irradiation dose was small and the N-type doping state was low and unstable.

In addition, even after 150 minutes and even 2 months after UV irradiation, the monolayer graphene remains in the N-type state, and the carrier (electron) concentration is around 2.0 × 10 ¹² cm ^-2 ( 1.3 to 2.9×10 ¹² cm ⁻² ). The electron mobility is 3610 to 4240 cm ² /Vs after PBG application and before UV irradiation, and 2120 to 2750 cm ² /Vs after UV irradiation, which is more than twice the hole mobility before PBG application. Maintained for a month.

Figure 7 shows the Raman spectrum of 1.7-layer graphene on a quartz substrate. In the 1.7-layer graphene before treatment, three characteristic peaks, the D band around ¹³³⁰ cm, the G band around ¹⁵⁸⁰ cm, and the 2D band around 2700 ^cm , are affected by the spectrum of the quartz substrate. I was able to measure it without any problems. After PBG coating and UV irradiation (irradiation density 1.3 mW/cm ² , irradiation time 300 seconds), the photobase generator was removed and the Raman spectrum of the 1.7-layer graphene on the quartz substrate was measured as 1. .There was no significant change from the Raman spectrum of 7-layer graphene. In particular, the relative intensity of the D band, which is caused by defect formation in graphene, did not change. This indicates that no defects were observed in the 1.7-layer graphene due to PBG application and UV irradiation.

This also supports the results shown in Figures 5 and 6, in which double-layer graphene and single-layer graphene maintain carrier mobility that is approximately twice as high for two months compared to before application of the photobase generator. It is. From the experimental results shown in FIGS. 2 to 7, the following four points were confirmed.
(1) It was confirmed by the change in sign of thermoelectromotive force (Seebeck coefficient) and Hall coefficient that double-layer graphene and single-layer graphene changed from P-type to N-type by application of a photobase generator and irradiation with ultraviolet light. The state of the mold conductor could be maintained for two months.
(2) The electron concentration of double-layer graphene and single-layer graphene after changing to N-type is determined by ultraviolet light irradiation at an irradiation density of 1.3 mW/cm ² and an irradiation time of 300 seconds. The concentration was reduced to about 1/10.

(3) The carrier mobility after graphene changes to N-type is approximately 30% higher than that before application of the photobase generator by ultraviolet light irradiation at an irradiation density of 1.3 mW/cm ² and an irradiation time of 300 seconds. It has increased more than twice.
(4) Changes in the D-band intensity of the Raman spectrum due to defect formation in graphene were not observed even after application of a photobase generator and irradiation with ultraviolet light (PBG application & UV irradiation → after PBG removal). No defect formation was observed.

Here, we will discuss the mechanism by which the photobase generator changes the doping state of graphene from P-type to N-type by irradiation with ultraviolet light, and the reason why the N-type state was stably maintained for two months. When the photobase generator coated on graphene is irradiated with ultraviolet light, as shown in Figure 1, _CO2 separates from molecule A, which then changes to molecule A', which is bonded with the proton separated from molecule B. It becomes non-ionized and stabilized. On the other hand, molecule B', which releases one proton from molecule B, becomes a base, donates one electron per molecule to graphene, and becomes stable as molecule B'', which is a positively ionized base derivative.

PBG coating and UV irradiation were performed using the pigment phenol red instead of graphene. A phenol red film was formed on a PET base material, a photobase generator was coated on the phenol red film, and the phenol red film was irradiated with ultraviolet light for a maximum of 10 minutes from the PET base material side. It was confirmed by the light absorption spectrum of the phenol red film coated with the photobase generator that the longer the UV light irradiation time, the stronger the red color of the phenol red film. Phenol red takes on a red color when electrons are donated. In other words, the phenol red film coated with the photobase generator received electrons from molecule B' when irradiated with ultraviolet light. From this, when a photobase generator is coated on a film that can accept electrons and irradiated with ultraviolet light, the base generated from the photobase generator donates electrons to this film and becomes a base derivative that exists on the film. It is thought that then.

FIG. 8 shows a structural model of graphene coated with a photobase generator on the front surface and irradiated with ultraviolet light from the back surface. When ultraviolet light passes through the carbon-based thin film from the back surface and reaches the photobase generator layer, it changes into molecules B' and A' by the reaction shown in FIG. However, depending on the thickness of the photobase generator layer, there may be not only a region where the photoreaction has been completed near the graphene surface (photoreactive region), but also an unreacted region (unreacted region) deposited on top of it. There is also. In the photoreaction region, the holes in graphene, which is a P-type conductor, are erased by the electrons donated by the molecule B', and then the graphene becomes an electron-doped state (N-type conductor).

Although not shown in FIG. 8, the electron-donated molecule B' changes into a base derivative molecule B''. Molecule A' is inactive and does not contribute to doping. Molecule B', molecule B'', and molecule A' prevent oxygen or moisture in the air from entering the graphene surface and damaging the N-type state of graphene, and stabilize the N-type conductor in the atmosphere. It is thought that it gives sex. In addition, the unreacted region also prevents oxygen or moisture in the air from entering the photoreactive region or the graphene surface and damaging the N-type state, giving stability to the N-type conductor in the atmosphere. it is conceivable that.

Claims (8)

an N-type doped carbon-based thin film;
a positively charged base derivative that is provided on the carbon-based thin film and is derived from a photobase generator;
an acid derivative provided on the carbon-based thin film and derived from a substance from which the base has been removed from the photobase generator;
the photobase generator provided on the base derivative and the acid derivative;
A complex with. an N-type doped carbon-based thin film provided on a base material that transmits ultraviolet light;
a positively charged base derivative that is provided on the carbon-based thin film and is derived from a photobase generator;
an acid derivative provided on the carbon-based thin film and derived from a substance from which the base has been removed from the photobase generator;
A complex with . In claim 1 or 2 ,
The carbon-based thin film may include single-layer graphene with an average number of layers of 0.8 or more and 1.2 or less, bilayer graphene with an average number of layers of 1.8 or more and 2.2 or less, and A composite consisting of graphene in which a region of single-layer graphene is partially mixed in a double-layer graphene with an average value of 0.8 or more and 2.2 or less. In any one of claims 1 to 3 ,
A complex wherein the photobase generator is 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionic acid. A photobase generator layer forming step of forming a photobase generator layer on the carbon-based thin film of a laminate having a base material that transmits ultraviolet light and a carbon-based thin film provided on the base material;
After the photobase generator layer forming step, an ultraviolet light irradiation step of irradiating ultraviolet light from the base material side of the laminate;
A method for producing a composite having the following. In claim 5 ,
The method for producing a composite body, wherein the photobase generator layer forming step includes transferring the photobase generator layer formed on the surface of the elastic body onto the carbon-based thin film. In claim 5 or 6 ,
The carbon-based thin film may include single-layer graphene with an average number of layers of 0.8 or more and 1.2 or less, bilayer graphene with an average number of layers of 1.8 or more and 2.2 or less, and A method for producing a composite comprising graphene in which a region of single-layer graphene is partially mixed in a double-layer graphene having an average value of 0.8 or more and 2.2 or less. In any one of claims 5 to 7 ,
A method for producing a composite, wherein the photobase generator is 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionic acid.

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