JP2020189761A - Carbon nitride dispersion and method for forming carbon nitride film using the same - Google Patents

Abstract

To provide a carbon nitride dispersion excellent in dispersibility of nano-amorphous layered carbon nitride for forming a film by a coating method, and to provide a method for forming a carbon nitride film using the carbon nitride dispersion.SOLUTION: A carbon nitride dispersion of the present invention comprises nano-amorphous layered carbon nitride dispersed in a dispersion medium. The dispersion medium is a strongly acidic oxo acid or a strong base. In the carbon nitride dispersion of the present invention, the nano-amorphous layered carbon nitride is dispersed in a dispersion medium, and the difference between a surface free energy of the nano-amorphous layered carbon nitride and a surface free energy of the dispersion medium is 15 mJ/m2 or less. A method for forming a carbon nitride film of the present invention is a method of electrostatically spraying the carbon nitride dispersion of the present invention.SELECTED DRAWING: None

Description

The present invention relates to a carbon nitride dispersion liquid in which carbon nitride is dispersed in a dispersion medium and a method for forming a carbon nitride film using the same.

The phenomenon of emitting light by applying a voltage is called electroluminescence (EL).
A light emitting diode (Light-Emitting Diode: LED) is known as a light emitting element utilizing this phenomenon. In particular, light emitting diodes made of organic substances are referred to as organic light-emitting diodes (OLEDs).

Since OLEDs have a response speed, high color rendering properties, flexibility, and self-luminous light, thin and inexpensive devices can be realized, and are currently being researched as new displays and lighting. However, there is a problem that the life is shortened due to the deterioration of organic substances, and research on sealing to prevent the deterioration is currently being actively conducted.

Further, the InGaN blue LED, which is a general light emitting diode, uses indium, which is a rare metal. However, crystal growth by MOCVD requires toxic gas, and the sapphire substrate needs to be heated to more than 1000 ° C., which causes a problem of environmental load and also a problem of being expensive.

Nano-amorphous layered carbon nitride (na-g-C ₃ N ₄ ) has the potential to solve these problems. This material is a non-metal semiconductor having an energy bandgap of about 2.7 eV, and is nanoparticles of about 50 nm. And, like graphite, it is a layered substance in which each layer is stacked by Van der Waals force. This substance has an interesting molecular structure, and is attracting much attention because of its high thermal stability, chemical stability, biocompatibility, variable bandgap, and its ability to be synthesized only from nitrogen and carbon, which are abundant on the earth. It is a substance that exists. Therefore, various possibilities such as light emitting elements, photocatalysts, solar cells, fuel cells, and fluorescence sensing have been reported (see, for example, Non-Patent Document 1).

H. Tabuchi et al., Jpn. J. Appl. Phys., 46, 1596 (2007)

In order to produce a light emitting diode, it is necessary to repeat film formation on the electrode to form a laminated structure.
Currently, when producing OLEDs, film formation by the vacuum vapor deposition method is the mainstream. This is because the laminated structure can be easily incorporated, the functions are separated in each layer, and high efficiency and long life are achieved.
However, this film forming process requires a high vacuum and has a large size dependence, so that it is difficult to increase the area. Also, when it comes to making the na-g-C ₃ N ₄ thin film by a vacuum deposition method, defects that are likely birth problematic broken structure.
Therefore, the present invention is premised on the study of film formation using a coating method for forming a thin film from a solution or a dispersion. The film formation by the coating method has the advantages of not requiring a high vacuum, an inexpensive film forming apparatus, a short film forming time, and a large area, so that the productivity is higher and the manufacturing cost can be suppressed. However, since na-g-C ₃ N ₄ has high chemical stability, it exhibits poor solubility and poor dispersion in various solvents and dispersion media.
Therefore, the present invention provides a carbon nitride dispersion having excellent dispersibility of nano-amorphous layered carbon nitride in order to form a film by a coating method, and also provides a method for forming a carbon nitride film using this carbon nitride dispersion. The challenge is to provide.

In order to solve the above problems, the present invention has the following configuration.
That is, in the carbon nitride dispersion liquid according to the present invention, nanoamorphous layered carbon nitride is dispersed in a dispersion medium, and the dispersion medium is a strongly acidic oxo acid or a strong base, or nanoamorphous layered carbon nitride is used. Is dispersed in a dispersion medium, and the difference between the surface free energy of the nanoamorphous layered carbon nitride and the surface free energy of the dispersion medium is 15 mJ / m ² or less.
The method for forming a carbon nitride film according to the present invention is a method for electrostatically spraying the carbon nitride dispersion liquid according to the present invention.

The carbon nitride dispersion liquid according to the present invention is useful for producing a thin film of carbon nitride because nanoamorphous layered carbon nitride is well dispersed.
Further, since the carbon nitride dispersion liquid according to the present invention can be electrostatically sprayed like the method for forming a carbon nitride film according to the present invention, high vacuum is not required, the film forming apparatus is inexpensive, and the film forming time is short. Because of the advantages of being short and capable of increasing the area, productivity is high and manufacturing costs can be suppressed.
Carbon nitride has the characteristics of high thermal stability, chemical stability, biocompatibility, variable band gap, and can be synthesized only from nitrogen and carbon, which are abundant on the earth, and emits blue light. It is valuable as an excellent light emitting material to replace OLEDs and InGaN blue LEDs. Therefore, the industrial value of the present invention, which is useful for producing a thin film of carbon nitride, is high.

It is a figure which shows the molecular structure of the s-heptazine ring core (s-heptazine ring core). It is a figure which shows the crystal model of na-g-C ₃ N ₄ . It is a figure which shows the laminated structure of na-g-C ₃ N ₄ . It is a figure which shows the outline of the atmospheric pressure nitrogen plasma method. It is a figure which shows the outline of the electrostatic spraying apparatus. It is a photograph of na-g-C ₃ N ₄ prepared in the example. In the evaluation of dispersibility of the embodiment is a schematic diagram showing the process of dispersion of the na-g-C ₃ N ₄ with a strong acid. In the evaluation of the dispersion of Example is a graph showing a PL spectrum measurement results of the na-g-C ₃ N ₄ film formed form a film from the dispersion. In the evaluation of the dispersion of Example is a graph showing the absorption spectra measurement results of the na-g-C ₃ N ₄ film formed form a film from the dispersion. In the evaluation of the dispersion of Example is a graph showing a result of IR measurement na-g-C ₃ N ₄ film formed form a film from the dispersion. is a diagram illustrating a specific number of infrared absorption vibration to _{na-g-C 3 N 4} . In the evaluation of the dispersion of Example is a graph showing XPS measurement results (C1s) of na-g-C ₃ N ₄ film formed form a film from the dispersion. In the evaluation of the dispersion of Example is a graph showing XPS measurement results (N1s) of na-g-C ₃ N ₄ film formed form a film from the dispersion. In the evaluation of the dispersion of Example is a graph showing XPS measurement results (O1s) of the na-g-C ₃ N ₄ film formed form a film from the dispersion. It is a schematic view showing an electrostatic spraying device used in the film formation na-g-C ₃ N ₄ film in the Examples. In na-g-C ₃ N ₄ film deposited in Example, to secure the working distance to 10 mm, nozzle diameter Φ of 25μm or 40 [mu] m, when formed by changing the voltage to 6,8 or 10kV It is an SEM photograph which shows the change of the surface. In na-g-C ₃ N ₄ film deposited in Example, to secure the working distance to 12.5 mm, 25 [mu] m or 40μm nozzle diameter [Phi, were formed by changing the voltage to 6,8 or 10kV It is an SEM photograph which shows the change of the surface with time. In na-g-C ₃ N ₄ film deposited in Example, to secure the working distance to 15 mm, nozzle diameter Φ of 25μm or 40 [mu] m, when formed by changing the voltage to 6,8 or 10kV It is an SEM photograph which shows the change of the surface. In na-g-C ₃ N ₄ film deposited in Example is an SEM photograph showing an example of a mountain range structure found in the formed na-g-C ₃ N ₄ film.

Hereinafter, preferred embodiments of the carbon nitride dispersion liquid according to the present invention and the method for forming a carbon nitride film using the same will be described in detail, but the scope of the present invention is not limited to these explanations. Other than the above examples, modifications can be made as appropriate without impairing the gist of the present invention.

[Carbon nitride dispersion]
In the carbon nitride dispersion liquid according to the present invention, nano-amorphous layered carbon nitride is dispersed in a dispersion medium.

<Nanoamorphous layered carbon nitride>
The nano-amorphous layered carbon nitride can be produced, for example, by the atmospheric pressure nitrogen plasma method.
This nano-amorphous layered carbon nitride is considered to be composed as follows.
That is, it is considered that this nanoamorphous layered carbon nitride crystal is composed of an s-heptazine ring core (C ₆ N ₇ ). The s-heptazine ring nucleus is shown in FIG.

s- Heputajin cyclic nucleus bidentate having 3 carbon C (sp ² -C) coordination, sp ² hybrid orbital with sp ² hybrid orbital is formed from 3-coordinate nitrogen N (sp ² -N) ing.
The s-heptazine cyclic nucleus is linked by the linking group X that binds to carbon C1 at the s-heptazine cyclic nucleus edge. The linking group X may be tricoordinated nitrogen, imide group> NH, or the like.
The s-heptazine cyclic nucleus has three bond point carbons C1, and if all the linking groups are nitrogen N, a two-dimensional plane formed by connecting three s-heptazine cyclic nuclei to each s-heptazine cyclic nucleus is formed. Will be done. This crystal model is shown in FIG. The crystal model was first proposed by Bojdys et al. (See Non-Patent Document 1 above). Further, the two-dimensionally spread surfaces are stacked by Van der Waals force to form a layered shape as shown in FIG.

In addition to the imide group and the amino group, various terminal groups are considered to exist in the terminal group, and it is considered that there are further variations in the chemical bond of the layered carbon nitride. In the production of nano-amorphous layered carbon nitride by the atmospheric nitrogen plasma method, it is considered that there are few NH ₂ terminal groups because the heat treatment is performed in vacuum.

FIG. 4 shows a schematic view of the atmospheric pressure nitrogen plasma apparatus.
As a manufacturing mechanism, when nitrogen gas is flowed from a plasma head to a quartz tube and microwave power is concentrated on the tip of a carbon rod inside the quartz tube, the nitrogen gas is excited and nitrogen plasma is generated. The plasma heat sublimates the carbon rod, and the generated active nitrogen and activated carbon form carbon nitride (CN) molecules.
When the CN molecule flows downstream, it is water-cooled through a quartz tube, and nano-amorphous layered carbon nitride is deposited on the molybdenum (Mo) plate.
In the gas phase, three CN molecules gather to form a triazine ring, three triazine rings gather to form a heptadin, three heptazines are tricoordinated with N, and the nanoamorphous layered carbon nitride shown in FIG. 3 is synthesized. It is thought that it will be done.
The processing conditions are not particularly limited, and may be appropriately determined based on the conditions generally adopted in the past.

<Dispersion medium>
As the dispersion medium, either (1) or (2) below is used.
(1) Strongly acidic oxo acid or strong base (2) Difference in surface free energy from nano-amorphous layered carbon nitride is 15 mJ / m ² or less

Specific examples of the strongly acidic oxo acid preferably include sulfuric acid, nitric acid, methanesulfonic acid, and trifluoroacetic acid.

As the strong base, for example, hydroxides, particularly sodium hydroxide, calcium hydroxide and the like are preferably mentioned.

Examples of those having a surface free energy difference of 15 mJ / m ² or less from the nano-amorphous layered carbon nitride include dimethyl sulfoxide and γ-butyrolactone.

[Dispersion]
The concentration of the carbon nitride dispersion may be appropriately determined in consideration of dispersibility, film forming property and the like.

[Method for forming a carbon nitride film]
In the method for forming a carbon nitride film according to the present invention, the carbon nitride dispersion liquid described above is electrostatically sprayed.
Electrostatic spraying utilizes the principle of electrospray for film formation. Electrospray refers to a phenomenon in which a liquid is ejected from a capillary nozzle maintained at a high potential, and charged droplets are finely dispersed to form a spray.

The electrostatic spray device has a configuration as shown in FIG.
As a specific principle, first, a droplet positively charged by applying a high voltage spreads in space while repeating miniaturization due to Coulomb repulsion between the droplets. Droplets that have been miniaturized to a certain size or less are attracted to the substrate by Coulomb force. Then, the solvent or dispersion medium reaches the substrate in a state of evaporation, or the atomized liquid reaches the substrate, and then the solvent or dispersion medium evaporates to form a thin film.
Since the droplets are positively charged, there is an advantage that there is less unevenness when the droplets reach the substrate as compared with the general mist method.
Here, in the wet process, a film is often formed by a spin coating method or the like, but since a solvent is used in this method, there is a possibility that the underlying layer will be melted when forming a laminated structure. On the other hand, with the electrostatic coating method, there is no need to worry about melting the substrate. Further, in the spin coating method, the liquid agent efficiency is not good because the substrate rotates and the liquid agent is formed while splashing the liquid agent around. On the other hand, in the electrostatic coating method, since the spray can be concentrated on the substrate, there is an advantage in using an expensive material with high liquid agent efficiency, and the cost of production can be expected to be reduced.
Due to these characteristics, electrostatic spray can be formed not only with a solution but also with a dispersion liquid, and the formation of quantum dots is also expected.

Since the nano-amorphous layered carbon nitride has high stability, it exhibits poor solubility and poor dispersibility in various solvents and dispersion media. However, in the carbon nitride dispersion liquid according to the present invention, the nano-amorphous layered carbon nitride is dispersed. Since of its high property, it is possible to apply the above-mentioned electrostatic spray.

As the electrode in the electrostatic spray device, for example, a known electrode such as an ITO (indium tin oxide) electrode or a zinc oxide electrode can be used.

Further, the conditions for electrostatic spraying may be appropriately determined according to the type of dispersion liquid, the area and thickness of the thin film to be obtained, and the like.
From the results of the examples described later, for example, the conditions can be determined based on the following viewpoints.
First, from the viewpoint of obtaining a flat thin film, if the work distance is too large, the spray spreads too much. Therefore, for example, a work distance of 12.5 mm or less is preferable.
Further, the larger the voltage, the larger the Coulomb force, the larger the deposition amount per unit time, and the formation of a flat thin film. Therefore, although it depends on the type of dispersion medium, for example, the voltage is preferably 10 kV or more.
Furthermore, regarding the nozzle diameter, the type of dispersion medium is that the nanoamorphous layered carbon nitride gathers in a wet state without volatilizing immediately when the droplet reaches the substrate, which leads to the formation of a flat thin film. Although it depends on the temperature of the substrate and the temperature of the substrate, for example, Φ = 12.5 mm or more is preferable.

The carbon nitride dispersion according to the present invention can be suitably used for the above electrostatic coating, but in addition to this, spin coating, roll coating, spin casting, doctor braiding, dip coating, spray coating, screen printing, etc. The film can be formed by using various film forming methods such as gravure printing, inkjet printing, and die coating method.

Hereinafter, more specific examples of the carbon nitride dispersion liquid according to the present invention and the method for forming a carbon nitride film using the same will be shown, but the present invention is not limited to the following examples.

[Example of dispersion]
<Example 1>
A nano-amorphous layered carbon nitride was produced using the atmospheric pressure nitrogen plasma apparatus shown in FIG.
Plasma was generated for 60 minutes at an input power of 700 W for microwave output and samples were deposited. Then, the sample deposited on the Mo substrate inserted in the quartz tube was heat-treated in vacuum at 400 ° C. for 5 hours. The nano-amorphous layered carbon nitride (na-g-C ₃ N ₄ ) deposited on the Mo substrate is shown in FIG. The portion used in this embodiment is the region indicated by A (yellow). The region indicated by C (black) contains a large amount of carbon.
The prepared na-g-C ₃ N ₄ was added to nitric acid at a ratio of 0.1% by weight (999 mg of nitric acid to 1 mg of na-g-C ₃ N ₄ ), and ultrasonic waves were used for 6 hours. Dispersion was performed. Then, using a centrifuge (FB-4000 manufactured by Kurabo Industries), centrifugation was performed at a rotation speed of 12000 rpm for 15 minutes to try to remove unnecessary precipitates. After that, only the supernatant was collected.

<Examples 2 to 8 and Comparative Examples 1 to 20>
The supernatants of Examples 2 to 8 and Comparative Examples 1 to 20 were prepared in the same manner as in Example 1 except that the nitric acid was changed as shown in the table below. In addition, "DMSO" of Example 2 is an abbreviation of dimethylsulfoxide.

<Evaluation and consideration of dispersibility>
The dispersibility of na-g-C ₃ N ₄ was confirmed for the supernatants of the above-mentioned Examples and Comparative Examples.
Specifically, first, irradiated with 365nm of UV light was confirmed fluorescence na-g-C ₃ N ₄ in the liquid.
In addition, the presence or absence of the Tyndall phenomenon was confirmed by irradiating a laser, and the dispersibility as a colloidal solution was evaluated.
As a result, fluorescence was confirmed in each of the supernatants of Examples 1 to 8, and most of the dispersions became pale yellow liquids, with the exception of dark brown liquids only when sulfuric acid was used.
It is considered that all of these dispersions are dispersed as colloidal solutions because the optical path was visible when the laser was irradiated. Therefore, the particle size is also considered to be particles with a diameter of about 10 ^-9 to 10 ^-7 m. In addition, even if any of the dispersions was left for 3 months, no precipitate was formed and the dispersions were stably dispersed.
On the other hand, in each of the supernatants of Comparative Examples 1 to 20, no fluorescence or Tyndall phenomenon was observed, and the desired dispersibility was not observed.

From the above results, in order to improve the dispersibility of the na-g-C ₃ N ₄ It has been found that there are two ways.

The first is a method of dispersing in a strong acid or a strong base.
When the examples are classified, Example 1 (nitric acid, pKa = -1.4), Example 3 (trifluoroacetic acid, pKa = -0.3), Example 5 (methanesulfonic acid, pKa = -2.6). ), Example 6 (sulfuric acid, pKa = -3.0) is classified as a strong acid, and Example 7 (sodium hydroxide) and Example 8 (calcium hydroxide) are classified as strong bases.
With weak acids such as Comparative Example 13 (acetic acid), Comparative Example 14 (acetic anhydride), Comparative Example 15 (formic acid), and weak bases such as Comparative Example 19 (ammonium hydroxide), na-g-C ₃ N ₄ is stable. Could not be dispersed in.
Further, even in a strong acid, as in Comparative Example 20 (hydrochloride), if not oxo acid, a na-g-C ₃ N ₄ could not be stably dispersed.

The process of dispersion with a strong acid is presumed as follows (see also FIG. 7).
That is, the ionized protons (H ⁺ ) in the liquid are transferred to na-g-C ₃ N ₄ , and the protons enter between the layers by applying ultrasonic waves to give energy, and the layers are stacked by van der Waals force. Peel each other. Since the separated layers are provided with protons, they retain an electric charge, and it is considered that they repel each other by Coulomb force and disperse in the liquid. Therefore, the particles are considered to be similar to nanosheets in which one to several layers are stacked. This dispersion mechanism is the same for sodium hydroxide, and it is considered that the ionized hydroxide ions enter the layers by the energy of ultrasonic waves, are separated, and are dispersed. In the IR spectrum measurement described later for the evaluation of the dispersion, it is considered that the increase of the peak around 3400 cm ^-1 indicates the addition of protons.

Another method for increasing the dispersibility is to disperse the na-g-C ₃ N ₄ in a material having a surface free energy close to that of the na-g-C 3N ₄ .
In the examples, Example 2 (DMSO) and Example 4 (γ-butyrolactone) are classified into this.
The dispersion in these examples is different from the dispersion of a strong acid or a strong base, and the surface free energy of the dispersion medium and the dispersoid is close to each other, so that the van der Waals force acting between the layers is separated by irradiation with ultrasonic waves to disperse. It is speculated that it can be done. The surface free energy of DMSO and γ-butyrolactone is about 60 mJm- ² . On the other hand, na-g-C ₃ N ₄ is about 70 mJm ^-2 . In this way, it is considered that the values could be dispersed because the values of the surface free energy were close.

<Evaluation of dispersion>
For each dispersion of Example 1 (nitric acid) and Example 2 (DMSO), was cast into the synthetic quartz substrate was deposited na-g-C ₃ N ₄ film, as follows, PL (photo-luminescence) spectrum , Absorption spectrum and IR absorption spectrum were measured. Further, XPS (X-ray photoelectron spectroscopy) measurement was performed.
In the following, the na-g-C ₃ N ₄ membrane obtained by using the dispersion liquid of Example 1 (nitric acid) is referred to as "SA-na-g-C ₃ N ₄ membrane", and is referred to as Example 2 ( the na-g-C ₃ N ₄ film obtained using the dispersion of the DMSO) may be referred to as _{"DMSO-na-g-C 3} N 4 film."

(PL spectrum)
Spectrofluorometer (FP-8500 type, manufactured by Nippon Spectroscopy) was measured using a PL spectrum of na-g-C ₃ N ₄ film. The excitation wavelength was 325 nm.

(Measurement of absorption spectrum)
Ultraviolet-visible spectrophotometer (UV 2450, Shimadzu) was used to measure the absorption spectrum of the na-g-C ₃ N ₄ film.

(IR measurement)
Fourier transform infrared spectrophotometer (FT / IR-4100, manufactured by Nippon spectroscopy) was used to measure the IR absorption spectrum of the na-g-C ₃ N ₄ film.

(XPS measurement)
X-ray photoelectron spectrometer (PHI5000 VersaProbe2, manufactured by ULVAC-PHI, Inc.) was used to the na-g-C ₃ N ₄ film was subjected to XPS measurement.

<Results and discussion>
FIG. 8 shows the change in the PL spectrum, FIG. 9 shows the change in the absorption spectrum, and FIG. 10 shows the change in the FT-IR spectrum.
From the results of the PL spectrum of FIG. 8, it was found that the PL spectrum when nitric acid and DMSO were used were both blue-shifted as compared with those before dispersion. It was also found that the absorption spectrum was also blue-shifted for both nitric acid and DMSO.
The emission brightness of the PL of SA-na-g-C ₃ N ₄ was larger than that of na-g-C ₃ N ₄ .
Taking into account that the color of SA-na-g-C ₃ N ₄ itself changed from the original brown to yellow, the above results show that the absorption spectrum is blue-shifted, resulting in less absorption on the long wavelength side. It is considered that this is because the inhibition of luminescence due to self-absorption no longer occurs.

Moreover, when the spectrum of FT-IR in FIG. 9 was confirmed, the spectrum around about 1400 cm ^-1 changed significantly when nitric acid was used. Also, when DMSO was used, there was a large change around the same wavenumber.
Since the ratios of the three main peaks (see FIG. 11) are all observed, it is considered that the structure is changed. However, since the vibration of the triazine skeleton peculiar to carbon nitride of about 811 cm ^-1 is observed, it is considered that the structure derived from carbon nitride remains to some extent.
In addition, the increase in the broad absorption band of about 3400 cm ^-1 of SA-na-g-C ₃ N ₄ is considered to be a change derived from -OH and -NH. From this result, it can be seen that the proton of nitric acid was adsorbed on na-g-C ₃ N ₄ and the carbon nitride was protonated.

It can be predicted that the above-mentioned changes in the spectrum before and after the dispersion are caused by the following two factors due to the ultrasonic dispersion.
Hypothesis (1): na-g- C 3 N 4 by the chemical structure is broken, increase the band gap caused by the conjugation length of the bond is shortened.
Hypothesis (2): Ultrasonic dispersion caused the layers to peel off to form nanosheets or nanoparticles with several layers. Therefore, the quantum size effect is generated and the band gap is increased.

Therefore, in order to investigate the change in structure, XPS measurement of SA-na-g-C ₃ N ₄ and DMSO-na-g-C ₃ N ₄ was performed as described above. FIG. 12 shows the C1s spectrum. Next, FIG. 13 shows the N1s spectrum, and finally, FIG. 14 shows the O1s spectrum.

First, looking at the C1s spectrum shown in FIG. 12, both SA-na-g-C ₃ N ₄ and DMSO-na-g-C ₃ N ₄ are compared with the original spectrum of na-g-C ₃ N _4. It can be seen that the sizes of the left and right mountains are changing. The mountain near 288.2 eV, which is the center of the mountain on the left side, is a peak showing a bond related to carbon corresponding to C1 and C2 in FIG. 1, and is a peak originally existing in na-g-C ₃ N ₄ . The peak of 284.6 eV, which is the peak of high binding energy on the right side, is a peak derived from hydrocarbons.
From this result, it was confirmed that both SA-na-g-C ₃ N ₄ and DMSO-na-g-C ₃ N ₄ have the original carbon nitride structure.
Further, SA-na-g-C ₃ N ₄ and DMSO-na-g-C ₃ N ₄ had similar spectra. Regarding the increase in hydrocarbon-derived peaks, one is that the dispersion medium breaks the double bond of the s-heptazine cyclic nucleus of carbon nitride, and both dispersion media act as oxidants, so they are given from the dispersion medium side. It is possible that the amount of hydrogen produced has increased due to the binding. Secondly, it is possible that the dispersion medium removal is overheated.

Next, the N1s spectra shown in FIG. 13 are compared.
The 398.6 eV spectrum is a peak showing the bond around nitrogen in N1 in FIG. The spectrum of 400.3 eV is a spectrum showing the bonds around N2 in FIG. 1 and the tricoordinated nitrogen that crosslinks the s-heptazine cyclic nuclei. Therefore, the spectrum of na-g-C ₃ N _{4 is} a spectrum in which the base of the left shoulder portion is widened as shown in FIG. 13 (a). On the other hand, in the N1s spectrum of SA-na-g-C ₃ N ₄ , the spectrum around 398.6 eV on the right side of FIG. 13 (b) has a small peak of 400.3 eV. This indicates that SA-na-g-C ₃ N ₄ has a structure with a small amount of tricoordinated nitrogen. That is, it is expected that the s-heptazine cyclic nuclei are not continuously arranged with each other and are approaching the structure of heptazine (FIG. 1). Thus expected, also illustrating the change in color of the _{SA-na-g-C 3} N 4, the structure of Heputajin so thin color because it is the middle stage of the polymerization, it results overall color as is thinned It is thought that it turned yellow. In addition, a new peak of 405.5 eV was generated in SA-na-g-C ₃ N ₄ . Since this peak is around 407 eV, it is a spectrum of nitrate. It is considered that this is a spectrum due to the addition of nitric acid to the nitrogen of N1 in FIG.

No significant change was observed in the O1s spectrum shown in FIG.

From the above results, it was confirmed that the above hypothesis (1), that is, the blue shift was caused by the broken structure. In this way, it was found that the structure of na-g-C ₃ N ₄ was changed by dispersion. This suggests that the emission characteristics can be changed and adjusted by selecting the dispersion medium.
The effect of heat on the chemical structure of the above hypothesis (2) has not been clarified in this experiment and needs to be investigated in the future.

[Example of a method for forming a carbon nitride film]
<Examples 9 to 26>
A carbon nitride dispersion was electrostatically sprayed to form a film using an electrostatic spraying device having the configuration shown in FIG.
The substrate used was an ITO substrate, and the dispersion was the dispersion of Example 2 (DMSO). Insulating polyimide was used for the stage so that droplets would not be attracted to the stage side around the substrate.
In addition, since the droplets have an electric charge, when the substrate is charged up, it repels the mist that flies later and the spread of the spray becomes large, which makes it difficult to deposit on the substrate. When it was actually formed on a glass substrate, it hardly accumulated. Therefore, the stage was set so that the ITO was grounded to the ground and the charge was released.
The voltage is changed at V = 6, 8, 10 kV, the work distance is changed at d = 10, 12.5, 15 mm, and the outer diameter of the nozzle tip is changed at Φ = 25, 40 μm, and the thin film is formed in a total of 18 patterns. Made. The temperature of the substrate during spraying was set to 160 ° C., and no back pressure was applied.
The table below summarizes the conditions for each example.

<Evaluation and consideration of thin films>
The 18 types of thin films obtained as described above were surface-observed with a scanning electron microscope, and how they were deposited was observed.
As shown in Table 2, FIGS. 16 (a) to 16 (f) represent surface photographs of Examples 9 to 14, respectively, and FIGS. 17 (a) to 17 (f) show the surfaces of Examples 15 to 20, respectively. Photographs are represented, and FIGS. 18 (a) to 18 (f) represent surface photographs of Examples 21 to 26, respectively.

First, when the work distance of FIG. 18 was 15 mm, the film was particularly sparse, and as shown in FIGS. 18 (d) and 18 (c), the substrate was deposited in a partially visible form. It is considered that this is because the amount of spray on the substrate was small as a result of the spread of the spray due to the large work distance. It is considered that a relatively uniform thin film can be produced by increasing the coating amount. However, it is considered that the conditions are not preferable in terms of liquid agent efficiency and film formation time.

Comparing the one with a nozzle diameter of 25 μm and the one with a nozzle diameter of 40 μm, the overall tendency is that the thin film formed with a nozzle diameter of 25 μm is smaller on the thin film than the thin film formed with a nozzle diameter of 40 μm. Many grains are seen. In this regard, the nozzle of 25 μm has a smaller droplet size at the time of ejection than the nozzle of 40 μm, and the size of the droplet at the time of reaching the substrate is smaller. Therefore, it is considered that the dispersion medium volatilized immediately after reaching the substrate, resulting in the appearance of small particles.

Among those formed with a 40 μm nozzle, those having a work distance of 10 mm and 12.5 mm (FIGS. 16 (d) to (f) and 17 (d) to (f)) have a rounded thin film shape. It turned out that it was easy to take a mountain-like shape. The size of this mountain varied from small to large depending on the conditions. Further, this shape could be similarly observed in FIGS. 16A to 16C. This peak was only observed with a 25 μm nozzle when the work distance was close to 10 mm. From this result, it was found that all the conditions for forming peaks were expressed only under the condition that the amount deposited on the substrate per unit time was relatively large. This droplets rather than become grains na-g-C ₃ N ₄ and simultaneously volatilize the substrate reaches, attached to the substrate in a state that some of the liquid droplets at the same time wet by reaching the substrate After that, it is probable that a mountain was formed because the dispersion medium flew away due to heat and became one large mass of na-g-C ₃ N ₄ . As evidence, it can be seen from the image that each mountain has one nucleus. The nuclei occurs agglomeration around the na-g-C ₃ N ₄ particles deposited simultaneously with the volatilization of the dispersion medium to be attached to the substrate, gathered in the nucleus to form the mountain. Therefore, it is considered that the formation of ridges is affected by whether or not the droplets can volatilize when reaching the substrate.

Further, it can be seen that the diameter of the mountain increases as the voltage increases in each of FIGS. 16 (d) to (f) and FIGS. 17 (d) to 17 (f). In this case as well, the Coulomb force increases as the voltage increases, so it is considered that the increase in the amount of deposition per unit time is involved.
For example, looking at FIG. 17 (f), it is considered that a large mountain was formed as a result of overlapping several mountains. Also, looking at the part with three mountains on the left side of FIG. 16 (d), it can be seen that the mountains are growing and continuing. In other words, if the amount of sedimentation per unit time is large, many nuclei forming mountains are formed. Therefore, it is considered that the mountains that have aggregated and grown from the nucleus easily overlap each other, forming a large mountain and forming a flat shape. Further, it is considered that the mountain ranges existing on the surface of the mountains in FIGS. 16A, 16B, and 16D are also formed in the process of forming the mountains. It is thought that when these mountains grow and grow larger, they become large mountains and become thin films. FIG. 19 shows an example of the mountain range structure (work distance d = 10 mm, Φ = 25 μm, voltage 8 kV).
From these results, it is considered that the conditions of Φ = 40 μm, voltage 10 kV, and d = 12.5 mm in FIG. 17 (f) have flatness and are most suitable when attempting to make a device. In particular, since it is a uniform and flat thin film, it is highly applicable to light emitting diodes and the like.

Claims (5)

A carbon nitride dispersion in which nano-amorphous layered carbon nitride is dispersed in a dispersion medium, and the dispersion medium is a strongly acidic oxo acid or a strong base. The carbon nitride dispersion according to claim 1, wherein the strongly acidic oxo acid is selected from sulfuric acid, nitric acid, methanesulfonic acid and trifluoroacetic acid, and the strong base is sodium hydroxide or calcium hydroxide. A carbon nitride dispersion in which nano-amorphous layered carbon nitride is dispersed in a dispersion medium, and the difference between the surface free energy of the nano-amorphous layered carbon nitride and the surface free energy of the dispersion medium is 15 mJ / m ² or less. The carbon nitride dispersion according to claim 3, wherein the dispersion medium is dimethyl sulfoxide or γ-butyrolactone. A method for forming a carbon nitride film, which comprises electrostatically spraying the carbon nitride dispersion according to any one of claims 1 to 4.