Method for manufacturing single-crystal spherical silicon nanoparticles

Abstract

The present invention is a manufacturing method for single crystal spherical silicon nanoparticles that are single crystals, are spherical, and have an average particle diameter of 1 nm to 20 nm. The manufacturing method includes a step for mixing and reacting the following: a raw material solution containing halogenated silicon; and a reducing solution containing anions of a condensed aromatic compound generated from the condensed aromatic compound and lithium, sodium, or potassium. The anions of the condensed aromatic compound are prepared by mixing the lithium, sodium, or potassium with the condensed aromatic compound at a temperature below 0°C. The single crystal spherical silicon nanoparticles manufactured by using the manufacturing method of the present invention make it possible to generate red fluorescence from blue fluorescence due to excitation by using wide wavelength light that ranges from deep ultraviolet light of 200 nm to 300 nm to visible light, and make it possible to increase the fluorescence quantum efficiency of previously known silicon nanoparticles from around 1% to at least 10%.

Description

[Technical Field]

[0001] This invention relates to a method for producing single-crystal spherical silicon nanoparticles. [Background technology]

[0002] Silicon is a semiconductor that has supported the development of electronics in recent years. Since the confirmation of visible light emission in porous silicon in 1990, research and development in the field of silicon photonics has been progressing for its application in light-emitting devices. Although silicon is a semiconductor, when considering the emission and absorption of visible light, it is classified into two types of semiconductors: direct bandgap semiconductors and indirect bandgap semiconductors. In direct bandgap semiconductors, in the energy space with respect to momentum, the peak of the valence band energy and the bottom of the conduction band energy are located at the same momentum, so the momentum can be satisfied with the energy of visible light alone, resulting in high emission (fluorescence) efficiency. However, in indirect bandgap semiconductors, which include ordinary semiconductor silicon, the peak of the valence band energy and the bottom of the conduction band energy do not coincide, so in emission, the momentum is the sum of the momentum of visible light and the momentum of the lattice vibrations of the semiconductor silicon, resulting in lower emission (fluorescence) efficiency compared to direct bandgap semiconductors. Conventional silicon produces near-infrared fluorescence with a wavelength of approximately 1 μm, which corresponds to an energy of 1.2 eV in its band gap. However, by reducing the silicon nanoparticle diameter to less than 10 nm, fluorescence equivalent to visible light emission can be obtained. This is attributed to the shift from an indirect to a direct transition type fluorescence emission when silicon is nanoscaled. Furthermore, if silicon nanoparticles are oxidized from the surface, the effective silicon nanoparticle diameter contributing to visible light emission decreases, meaning that silicon particle diameters down to 20 nm are actually acceptable.

[0003] Regarding silicon nanoparticles that emit fluorescence in visible light, Patent Document 1 discloses a method for producing silicon nanoparticles using commercially available silicon particles (particle size 100 nm, silicon purity 98% or higher). This method involves treating crystalline silicon powder with hydrofluoric acid to remove the surface oxide film, then re-oxidizing the surface with nitric acid to generate an oxide film, and finally removing this with hydrofluoric acid. However, because commercially available silicon particles are used, the produced silicon nanoparticles are not single crystals, and the particle size distribution of the particles in Experimental Example 2 was approximately 2000 nm and 10-20 nm, with two peaks. Furthermore, this manufacturing method uses acidic substances, hydrofluoric acid and nitric acid, requiring extremely careful handling, making it difficult to manufacture easily on an industrial scale.

[0004] Patent Document 2 discloses a method for producing silicon nanoparticles by irradiating silicon powder with a pulsed laser and depositing the evaporated silicon onto a desired substrate. However, the particle size of the produced silicon nanoparticles was only about 50 to 100 nm. Furthermore, this manufacturing method requires a pulsed laser, making it impossible to produce semiconductor silicon nanoparticles inexpensively.

[0005] Patent Document 3 discloses a method for producing silicon nanoparticles by reducing an inverse micelle structure, which is a mixture of a silicon compound and an alcohol, with a reducing substance. However, the silicon nanoparticles obtained in Experiment No. 9 were reported to fluoresce in the ultraviolet wavelength region of 300 nm to 350 nm, which is not in the visible light wavelength region. Therefore, its range of industrial applications is narrow and it cannot be applied to the fields of lighting or displays.

[0006] Patent Document 4 discloses a method for producing silicon nanoparticles in an organic solvent using a reducing agent at a reaction temperature of 0°C or lower. Sections

[0065] to

[0067] state that the reaction temperature is limited to 0°C or lower to suppress side reactions. However, it is not stated whether the produced silicon nanoparticles are single crystals and spherical. Furthermore, since the production method is carried out under closed conditions in a flask, and the silicon nanoparticles are generated in an atmosphere where silicon nanoparticles and reactants coexist, there are concerns about side reactions between the silicon nanoparticles and reactants. In Example 1, a tetrahydrofuran (THF) solution of DBB (4,4'-di-tert-butylbiphenyl) is added to metallic lithium, and a reducing solution is prepared by stirring at room temperature for 2 to 4 hours. Silicon tetrachloride is then added all at once at -60°C and reacted to produce chlorine-terminated silicon nanoparticles, and the surface is stabilized with magnesium hexyl bromide to produce alkyl-terminated silicon nanoparticles. However, as described in Comparative Example 1 of this specification, the alkyl-terminated silicon nanoparticles in Example 1 of Patent Document 4 are polycrystalline and not single crystals or spherical.

[0007] Patent Document 5, relating to the applicant of this application, discloses a method for producing silicon nanoparticles using a fluid processing apparatus equipped with a relatively rotating processing surface that can move toward and away from each other. It also states that the produced silicon nanoparticles can emit fluorescence from blue to near-infrared depending on the manufacturing temperature. However, it does not disclose that the silicon nanoparticles are single crystals and spherical. In Examples 6 to 9, alkyl (hexyl group) terminated silicon nanoparticles are produced by reacting them with magnesium hexyl bromide. It is disclosed that the silicon nanoparticles are of such purity that no chlorine or oxygen is detected. Furthermore, as described in Comparative Example 1 of this specification, the alkyl-terminated silicon nanoparticles of Example 6 in Patent Document 5 are polycrystalline, not single crystals and spherical. In Examples 10 to 13, it is disclosed that silicon nanoparticles can be produced by a reverse micelle method using a surfactant, but a problem was the large loss of silicon nanoparticle recovery due to the washing and removal of the surfactant. Furthermore, in Examples 14 to 17, since both the first and second fluids supplied to the fluid processing apparatus are aqueous solutions, a problem was the very low yield of silicon nanoparticles.

[0008] Patent document 6 discloses a method for producing semiconductor nanoparticles having a core-shell structure by carrying out a reaction in a channel less than 1 mm wide, called a microchemical process. Specifically, it is said that by carrying out the reaction in a microchannel within a microreactor, the mixing rate and efficiency are improved, the uniformity of concentration and temperature in the reaction conditions within the channel is improved, and side reactions are suppressed, thereby effectively and efficiently achieving uniform particle size and single reaction products. However, there is a high possibility of the microchannel becoming blocked due to the accumulation of silicon nanoparticles and by-products generated by reduction reactions, and since the reaction basically proceeds only by molecular diffusion, it was not applicable to all reactions. Furthermore, the microchemical process uses a scale-up method called numbering up, which involves arranging small reactors in parallel, but there were problems such as the small production capacity of a single reactor making large-scale scaling unrealistic, and the difficulty in matching the performance of each reactor, which prevented obtaining uniform products. Furthermore, in reactions involving highly viscous reaction liquids or those that increase viscosity, extremely high pressure is required to circulate the liquid through minute channels. This limits the types of pumps that can be used, and the high pressure makes it difficult to resolve leaks from the equipment. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2014-172766 [Patent Document 2] Japanese Patent Publication No. 2017-081770 [Patent Document 3] Japanese Patent Publication No. 2010-205686 [Patent Document 4] Japanese Patent Publication No. 2007-012702 [Patent Document 5] Patent No. 4458202 [Patent Document 6] Japanese Patent Publication No. 2007-197382 [Overview of the project] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide a method for producing silicon nanoparticles that can generate blue to orange fluorescence with high fluorescence quantum efficiency by excitation with light of a wide wavelength range from deep ultraviolet light of 200 nm to 300 nm to visible light, and that can densely pack electrode materials for solar cells and secondary ion batteries. [Means for solving the problem]

[0011] In order to solve the aforementioned problems, the present inventors conducted diligent research and found that single-crystal spherical silicon nanoparticles, which are single crystals, spherical in shape, and have an average particle diameter of 1 nm to 20 nm, are single crystals that do not have grain boundaries that reduce fluorescence efficiency. Therefore, they can generate fluorescence with high fluorescence quantum efficiency when excited by light of a wide wavelength range from deep ultraviolet light of 200 nm to 300 nm to visible light, and can be densely packed as electrode materials for solar cells and secondary ion batteries, thus completing the present invention. In other words, the present invention is as follows:

[0012] [1] A method for producing single-crystal spherical silicon nanoparticles that are single crystals, spherical in shape, and have an average particle diameter of 1 nm to 20 nm, The process includes a step of mixing a raw material liquid containing a silicon halide with a reducing solution containing an anion of the condensed aromatic compound, which is produced from lithium, sodium, or potassium and the condensed aromatic compound, and reacting them together. A method for producing the anion of the condensed aromatic compound, wherein the condensed aromatic compound is prepared by mixing lithium, sodium, or potassium with the condensed aromatic compound at a temperature below 0°C. [2] The manufacturing method according to [1], wherein the raw material liquid and the reducing liquid are mixed and reacted in a thin film fluid formed between processing surfaces arranged facing each other so as to be able to approach and separate from each other, and at least one of which rotates relative to the other.

[0013] [3] A device comprising a fluid pressure application mechanism for applying pressure to a fluid to be processed, at least two processing parts, a first processing part and a second processing part that can move relatively closer to and away from the first processing part, and a rotational drive mechanism for rotating the first processing part and the second processing part relative to each other, In each of the above processing sections, at least two processing surfaces, a first processing surface and a second processing surface, are provided at positions facing each other. Each of these processing surfaces constitutes part of a sealed flow path through which the fluid to be processed at the above pressure flows. Between the two processing surfaces, two or more fluids to be processed, each containing a reactant, are mixed and reacted. Of the first and second processing sections described above, at least the second processing section is equipped with a pressure-receiving surface, and at least a part of this pressure-receiving surface is composed of the second processing surface, and this pressure-receiving surface receives the pressure applied to the fluid to be processed by the fluid pressure application mechanism described above and generates a force that moves the second processing surface away from the first processing surface, and the fluid to be processed under the above pressure is passed between the first processing surface and the second processing surface, which are able to approach and separate from each other and rotate relative to each other, thereby forming a thin film fluid, and further the fluid to be processed under the above pressure flows through The manufacturing method according to [2], comprising a separate introduction passage independent of the flow path between each processing surface, at least one of the first processing surface and the second processing surface having at least one opening leading to the separate introduction passage, and by introducing at least one fluid to be processed sent from the separate introduction passage between the two processing surfaces, the reactants contained in at least one of the fluids to be processed and a fluid to be processed different from the fluid to be processed are mixed in the thin film fluid, and the raw material liquid and the reducing solution are mixed and reacted using such a device.

[0014] [4] The manufacturing method according to [3], wherein the opening is located downstream of the point at which the flow of the fluid to be processed, passed between the two processing surfaces, becomes laminar. [5] A manufacturing method according to any one of [1] to [4], wherein the reducing solution is cooled to 5°C or below, and the raw material solution and the reducing solution are mixed and reacted. [6] The manufacturing method according to any one of [1] to [5], wherein the molar ratio of lithium, sodium, or potassium to silicon halide is 7:1 to 4:1.

[0015] [7] The method for producing an aromatic compound according to any one of [1] to [6], wherein the condensed aromatic compound is at least one selected from the group consisting of biphenyl, naphthalene, 1,2-dihydronaphthalene, anthracene, phenanthrene, and pyrene. [8] The manufacturing method according to any one of [1] to [7], wherein the solvent contained in the reducing solution is tetrahydrofuran and / or dimethoxyethane having a residual water content of 10 ppm or less. [9] The manufacturing method according to any one of [1] to [7], wherein the solvent contained in the reducing solution contains a phenolic polymerization inhibitor, has a residual water content of 10 ppm or less, and a residual oxygen concentration of less than 0.1 ppm, and the solvent contains a tetrahydrofuran.

[10] The manufacturing method according to any one of [1] to [9], wherein the solvent contained in the raw material liquid is a tetrahydrofuran having a residual water content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm.

[11] The manufacturing method according to any one of [1] to

[10] , wherein the halogenated silicon is silicon tetrachloride, silicon tetrabromide, or silicon tetraiodide.

[0016]

[12] The single-crystal spherical silicon nanoparticles are obtained using the perimeter (Z) and area (S) of the projection image of the single-crystal spherical silicon nanoparticles observed by a transmission electron microscope, using the formula: 4πS / Z 2 A manufacturing method according to any one of [1] to

[11] , wherein the average value of the circularity calculated is 0.9 or higher.

[13] The single-crystal spherical silicon nanoparticles exhibit an IR absorption spectrum of 1950 cm⁻¹. -1 ~2150cm -1 A manufacturing method according to any one of [1] to

[12] , which exhibits absorption attributed to the Si-H bond in the wavenumber region.

[14] The single-crystal spherical silicon nanoparticles have an IR absorption spectrum of 1000 cm². -1 ~1200cm -1Let the peak intensity of the maximum peak in the wavenumber range be A, and 400 cm -1 ~500 cm -1 Let the peak intensity of the maximum peak in the wavenumber range be B, and the calculated ratio: B / A is less than 0.2. The production method according to any one of [1] to

[13] .

[0017]

[15] The single-crystalline spherical silicon nanoparticles, in the IR absorption spectrum, let the peak intensity of the maximum peak in the wavenumber range of 1000 cm -1 ~1200 cm -1 be A, and 530 cm -1 ~630 cm -1 Let the peak intensity of the maximum peak in the wavenumber range be C, and the calculated ratio: C / A is less than 0.2. The production method according to any one of [1] to

[14] .

[16] The single-crystalline spherical silicon nanoparticles produce a fluorescence maximum in the wavelength range of 400 nm to 600 nm. The production method according to any one of [1] to

[15] .

[17] The single-crystalline spherical silicon nanoparticles produce a fluorescence maximum in the wavelength range of 400 nm to 600 nm by deep ultraviolet light with an excitation light wavelength of 300 nm or less. The production method according to any one of [1] to

[16] . [Advantages of the Invention]

[0018] The single-crystal spherical silicon nanoparticles produced by the manufacturing method of the present invention are single crystals without grain boundaries that reduce fluorescence efficiency. Therefore, they can generate fluorescence with high fluorescence quantum efficiency when excited by light of a wide wavelength range from deep ultraviolet light of 200 nm to 300 nm to visible light, making it possible to increase the fluorescence quantum efficiency of conventionally known silicon nanoparticles from around 1% to over 10%. Furthermore, the single-crystal spherical silicon nanoparticles produced by the manufacturing method of the present invention do not have the biotoxicity of compound semiconductors formed from cadmium, selenium, and tellurium. Moreover, because the single-crystal spherical silicon nanoparticles produced by the manufacturing method of the present invention are spherical, they can be densely packed as electrode materials for solar cells and secondary ion batteries, and can be used as negative electrodes for lithium-ion batteries, electrode materials for solar cells, and bonding materials to substrates for semiconductor devices. [Brief explanation of the drawing]

[0019] [Figure 1] The TEM image of the single-crystal spherical silicon nanoparticles from Example 1-1 is shown. [Figure 2] STEM images of the single-crystal spherical silicon nanoparticles from Examples 1-4 are shown. [Figure 3] These are the electron diffraction patterns of the single-crystal spherical silicon nanoparticles of Examples 1-4. [Figure 4] The IR spectra of the single-crystal spherical silicon nanoparticles of Examples 1-2 at wavenumbers 1800 cm⁻¹ to 2300 cm⁻¹ are shown. [Figure 5a] The IR spectra of single-crystal spherical silicon nanoparticles from Examples 1-4 at wavenumbers 900 cm⁻¹ to 1300 cm⁻¹ are shown. The vertical axis represents absorbance normalized to 1.0, where the peak intensity of the maximum peak in the wavenumber range of 900 cm⁻¹ to 1300 cm⁻¹ is set to 1.0. [Figure 5b] The IR spectra of the single-crystal spherical silicon nanoparticles of Examples 1-4 at wavenumbers 400 cm⁻¹ to 550 cm⁻¹ are shown. [Figure 5c] The IR spectra of the single-crystal spherical silicon nanoparticles of Examples 1-4 at wavenumbers 450 cm⁻¹ to 650 cm⁻¹ are shown. [Figure 5d] The IR spectra of the single-crystal spherical silicon nanoparticles of Examples 1-4 at wavenumbers 550 cm⁻¹ to 700 cm⁻¹ are shown. [Figure 6] The normalized fluorescence spectra of single-crystal spherical silicon nanoparticles from Examples 1-3 are shown, with the maximum intensity set to 1.0, and the excitation wavelength varied in 40 nm increments from 340 nm to 500 nm. [Figure 7] The excitation wavelength dependence of the fluorescence peak wavelength of the single-crystal spherical silicon nanoparticles of Examples 1-4 is shown. [Figure 8] The measurement results for particle size and fluorescence peak wavelength as a function of disk rotation speed for single-crystal spherical silicon nanoparticles in Examples 1-1 to 1-4 are shown. [Figure 9] The fluorescence spectra of single-crystal spherical silicon nanoparticles from Examples 1-2, induced by deep ultraviolet excitation, are shown. [Figure 10] The STEM image of the polycrystalline silicon nanoparticles of Comparative Example 1-1 is shown. [Figure 11] The IR spectra of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at wavenumbers 900 cm⁻¹ to 1300 cm⁻¹ are shown. [Figure 12a] The IR spectra of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at wavenumbers 900 cm⁻¹ to 1300 cm⁻¹ are shown. The vertical axis represents the absorbance normalized to 1.0, with the peak intensity of the maximum peak in the wavenumber range of 900 cm⁻¹ to 1300 cm⁻¹. [Figure 12b] The IR spectra of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at wavenumbers 400 cm⁻¹ to 550 cm⁻¹ are shown. [Figure 12c] The IR spectra of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at wavenumbers 450 cm⁻¹ to 650 cm⁻¹ are shown. [Figure 12d] The IR spectra of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at wavenumbers 550 cm⁻¹ to 700 cm⁻¹ are shown. [Figure 13a] The fluorescence spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at a deep ultraviolet excitation wavelength of 220 nm is shown. [Figure 13b]The fluorescence spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at a deep ultraviolet excitation wavelength of 260 nm is shown. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described below. However, the present invention is not limited to the embodiments described below. Furthermore, while examples of application to fluorescence-emitting materials will be described, the applications of the single-crystal spherical silicon nanoparticles of the present invention are not limited to these.

[0021] 1. Single-crystal spherical silicon nanoparticles The single-crystal spherical silicon nanoparticles obtained by the manufacturing method of the present invention are single crystals, spherical in shape, and have an average particle diameter of 1 nm to 20 nm. The single-crystal spherical silicon nanoparticles are preferably expressed using the formula: 4πS / Z, where the perimeter (Z) and area (S) of the projection image of the single-crystal spherical silicon nanoparticles observed by a transmission electron microscope are used. 2 The average value of the circularity calculated is 0.9 or higher, more preferably 0.92 or higher, and even more preferably 0.95 or higher. The average particle diameter is preferably 1.2 nm to 10 nm, more preferably 1.5 nm to 7 nm, and even more preferably 2 nm to 5 nm.

[0022] It is preferable that single-crystal spherical silicon nanoparticles have Si-H bonds on their surface. If there are sites on the surface of single-crystal spherical silicon nanoparticles where the bonds between silicon atoms are broken, they become unstable and can generate new energy levels in the band gap, affecting the fluorescence wavelength. Therefore, the presence of Si-H bonds, where the broken silicon atoms are bonded to hydrogen atoms, stabilizes them and reduces the influence on the fluorescence wavelength. Accordingly, it is preferable that single-crystal spherical silicon nanoparticles have a 1950 cm⁻¹ value in the IR absorption spectrum that is attributed to the stretching vibration of the Si-H bond. -1 ~2150cm -1Absorption exists in the wavenumber region. The single-crystal spherical silicon nanoparticles of Examples 1-2, as shown in Figure 4, exhibit absorption at 2105 cm⁻¹. -1 An absorption peak exists at this point.

[0023] Single-crystal spherical silicon nanoparticles are preferably low in dissolved oxygen. Specifically, for example, in the IR absorption spectrum, 1000 cm⁻¹ is preferable. -1 ~1200cm -1 Let A be the peak intensity of the maximum peak in the wavenumber range, and 400cm -1 ~500cm -1 Let B be the peak intensity of the maximum peak in the wavenumber range, and the calculated ratio B / A is less than 0.2. For example, the single-crystal spherical silicon nanoparticles of Examples 1-1 to 1-4, as shown in Figures 5a and 5b, have a peak intensity of 1095 cm². -1 Let A be the peak intensity of the maximum peak, and 460cm -1 Let B be the peak intensity of the maximum peak. As shown in Table 3, the ratio B / A is between 0.08 and 0.10, and is less than 0.2.

[0024] Single-crystal spherical silicon nanoparticles are preferably characterized by a low number of Si-Cl bonds. Specifically, for example, in the IR absorption spectrum, a low number of Si-Cl bonds is preferable. -1 ~1200cm -1 Let A be the peak intensity of the maximum peak in the wavenumber range, and 530 cm -1 ~630cm -1 Let C be the peak intensity of the maximum peak in the wavenumber range, and the calculated ratio C / A is less than 0.2. For example, the single-crystal spherical silicon nanoparticles of Examples 1-1 to 1-4, as shown in Figures 5a and 5c, have a frequency of 1095 cm⁻¹. -1 Let A be the peak intensity of the maximum peak, and let 612 cm be the peak intensity of the maximum peak. -1 Assuming C is the peak intensity of the maximum peak, the ratio C / A is between 0.06 and 0.08, as shown in Table 3, and is less than 0.2.

[0025] The fluorescence of silicon nanoparticles is known to occur through the following three different mechanisms. (A) Control of fluorescence color by controlling a physical factor that changes the band gap of electron energy according to the particle size of silicon nanoparticles (known as a quantum effect). (B) Surface modification by treating the surface of silicon nanoparticles with various chemical substances to chemically bond various substituents such as alkyl groups and amino groups with different molecular chain lengths to the surface of silicon nanoparticles, thereby controlling the fluorescence color via surface substituents. (C) Control of fluorescence color by chemical factors by utilizing compositional changes mediated by oxygen and nitrogen contained in silicon nanoparticles.

[0026] The single-crystal spherical silicon nanoparticles obtained by the manufacturing method of the present invention produce fluorescence through the synergistic action of (A) the quantum effect mechanism and (C) the oxygen-mediated mechanism, among the three mechanisms (A) to (C) described above. This mechanism differs from the alkyl-terminated silicon nanoparticles described in Patent Documents 4 and 5, which use (A) the quantum effect mechanism and (B) the surface modification mechanism. The single-crystal spherical silicon nanoparticles obtained by the manufacturing method of the present invention preferably exhibit a fluorescence maximum in the wavelength range of 400 nm to 600 nm. More preferably, a fluorescence maximum in the wavelength range of 400 nm to 600 nm is generated by deep ultraviolet light with an excitation light wavelength of 300 nm or less.

[0027] 2. Method for producing single-crystal spherical silicon nanoparticles The present invention relates to a method for producing single-crystal spherical silicon nanoparticles that are single crystals, spherical in shape, and have an average particle diameter of 1 nm to 20 nm. The method includes a step of mixing and reacting a raw material solution containing silicon halide with a reducing solution containing anions of a condensed aromatic compound produced from lithium, sodium, or potassium and the condensed aromatic compound, wherein the anions of the condensed aromatic compound are prepared by mixing lithium, sodium, or potassium and the condensed aromatic compound at a temperature below 0°C.

[0028] (Liquid raw material for single-crystal spherical silicon nanoparticles) Examples of silicon halides contained in the raw material liquid for single-crystal spherical silicon nanoparticles include silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide, with silicon tetrachloride and silicon tetrabromide being preferred.

[0029] The solvent included in the single-crystal spherical silicon nanoparticle raw material liquid is not particularly limited as long as it can reduce silicon halides to precipitate single-crystal spherical silicon nanoparticles and is inert without affecting the reduction reaction. Preferred solvents include ethers, more preferably tetrahydrofuran (THF), dioxane, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl ether, polyethylene glycol dimethyl ether, or mixtures thereof, and even more preferably THF, DME, etc. Preferred solvents include tetrahydrofuran, etc., having a residual water content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm.

[0030] When THF is used as a solvent, ring-opening polymerization of THF is initiated by Lewis acids, which are electrophilic reagents. Therefore, polymers of THF may form during storage of the THF solution of silicon halogens. However, THF polymerization can be suppressed by adding 2,6-di-tert-4-methylphenol (BHT), which inhibits the formation of peroxides by THF, to the starting material solution. For this reason, it is preferable to add BHT to the THF solvent.

[0031] The concentration of silicon halide in the single-crystal spherical silicon nanoparticle raw material liquid is not particularly limited, but for example, it can be 0.01 to 1 mol / L, preferably 0.02 to 0.5 mol / L, and more preferably 0.05 to 0.2 mol / L.

[0032] (Reducing solution for single-crystal spherical silicon nanoparticles) The reducing solution for single-crystal spherical silicon nanoparticles used in the present invention contains anions of condensed aromatic compounds generated from lithium, sodium, or potassium with the condensed aromatic compound, and the anions of the condensed aromatic compound are a reducing solution prepared by mixing lithium, sodium, or potassium with the condensed aromatic compound at a temperature below 0°C. Since the electrochemical equilibrium potentials of lithium, sodium, and potassium are very low and have a noble potential, theoretically, silicon halides can be reduced by using any of these metals alone or in mixtures. However, lithium, sodium, or potassium cannot be dissolved in organic solvents such as ether. In order to dissolve lithium, sodium, or potassium in organic solvents such as ether, it is necessary to have a condensed aromatic compound in the presence of the condensed aromatic compound, and to move the one electron generated when lithium, sodium, or potassium becomes an alkali metal ion to the lowest unoccupied orbital (LUMO) of the condensed aromatic compound, thereby generating anions (radical anions) of the condensed aromatic compound.

[0033] The condensed aromatic compounds used in the present invention include those that can transfer one electron from lithium, sodium, or potassium to the condensed aromatic compound to generate an alkali metal ion and a condensed aromatic compound anion (radical anion). In order to reduce silicon halides to silicon, the potential of the anion of the condensed aromatic compound must be lower than -2.0V. Here, the potential is the value relative to silver (Ag) / silver chloride (AgCl) as the reference electrode. Examples of condensed aromatic compounds with a potential lower than -2.0V include naphthalene (-2.53V), DBB (-2.87V), biphenyl (-2.68V), 1,2-dihydronaphthalene (-2.57V), phenanthrene (-2.49V), anthracene (-2.04V), pyrene (-2.13V), or mixtures thereof, with naphthalene, biphenyl, etc. being preferred. On the other hand, tetracene (-1.55V) and azulene (-1.62V) are not suitable for the reduction of silicon halides.

[0034] The solvent included in the reducing solution for single-crystal spherical silicon nanoparticles is not particularly limited as long as it can reduce silicon halides to precipitate single-crystal spherical silicon nanoparticles and is inert without affecting the reduction reaction. Preferred solvents include ethers, more preferably tetrahydrofuran (THF), dioxane, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl ether, polyethylene glycol dimethyl ether, or mixtures thereof, and even more preferably THF, DME, etc. Preferably, tetrahydrofuran and dimethoxyethane have a residual moisture content of 10 ppm or less, and more preferably tetrahydrofuran contains a phenolic polymerization inhibitor, has a residual moisture content of 10 ppm or less, and a residual oxygen concentration of less than 0.1 ppm.

[0035] The concentrations of lithium, sodium, or potassium in the reducing solution for single-crystal spherical silicon nanoparticles are not particularly limited, but are determined according to the molar ratio of lithium, sodium, or potassium to silicon halide. The molar ratio of lithium, sodium, or potassium to the condensed aromatic compound is, for example, 1:1 to 1.5:1, preferably 1:1 to 1.2:1, and more preferably 1:1 to 1.1:1.

[0036] The molar ratio of lithium, sodium, or potassium to silicon halide is, for example, 7:1 to 4:1, preferably 6:1 to 4:1, and more preferably 5:1 to 4:1. It is preferable to use lithium, sodium, or potassium in excess of the raw materials for single-crystal spherical silicon nanoparticles. By using an excess, it is possible to produce single-crystal spherical silicon nanoparticles with fewer residual halogen elements. If a smaller amount of lithium, sodium, or potassium is used than the raw materials for single-crystal spherical silicon nanoparticles, for example, if 3 / 4 the amount is used as shown in Comparative Example 1, the reduction is not complete, and halogen atoms derived from silicon halide remain in the single-crystal spherical silicon nanoparticles, resulting in polycrystalline and non-spherical nanoparticles.

[0037] (Cold-temperature preparation of reducing solution) In this invention, a reducing solution for single-crystal spherical silicon nanoparticles is prepared by mixing lithium, sodium, or potassium with a condensed aromatic compound at a temperature below 0°C. The preparation temperature can be, for example, -50°C to less than 0°C, preferably -40°C to -10°C, and more preferably -30°C to -15°C. In Example 1, the solution was prepared at -20°C. In contrast, if the dissolution temperature is above 0°C, the condensed aromatic compound anion becomes unstable, and a chemical reaction occurs between the condensed aromatic compound and the alkali metal atom, impairing the effectiveness of the reducing solution. For example, if the condensed aromatic compound is naphthalene (molecular formula: C 10 H8), when potassium (K) is used, C 10 A problem arises when compounds like H7K are formed, which tends to alter the concentration of naphthalene anions that act as reducing agents. In Example 1 of Patent Document 4 and Examples 6-9 of Patent Document 5, the reducing solution was prepared at room temperature. In Comparative Example 1 of this specification, Example 6 of Patent Document 5 was replicated, and when the solution was prepared at 15-16°C (room temperature), the reducing agent became unstable, by-products were formed, and the single-crystal spherical silicon nanoparticles became polycrystalline and lost their spherical shape.

[0038] (Solvent molecule-mediated alkali metal cation and condensed aromatic compound anion) The condensed aromatic compound anions (radical anions) generated by electron transfer of lithium, sodium, or potassium to the condensed aromatic compound can bond to the lithium, sodium, or potassium cations generated by the electron transfer via Coulomb forces. In this case, there is concern about changes in reducing power due to reverse electron transfer from the generated condensed aromatic compound anions to the lithium, sodium, or potassium cations. Since fluctuations in reducing power lead to the particle size distribution of the resulting single-crystal spherical silicon nanoparticles, suppressing fluctuations in reducing power due to reverse electron transfer requires that the lithium, sodium, or potassium cations and the condensed aromatic compound anions have a bond state via Coulomb forces through solvent molecules. It is known that the state of anions and cations in such solutions can be confirmed by measuring ultraviolet-visible absorption spectra. According to this, for example, in a combination of lithium and naphthalene dissolved in THF, the state with THF present accounts for 60% to 80% at 25°C. In a combination of metallic sodium and naphthalene dissolved in THF, the sodium cation and naphthalene anion are directly bonded by Coulomb forces with almost no THF intervening. However, it is known that by cooling to -50°C, THF can become almost 100% intervening.

[0039] (Solvation in low-temperature preparations) To introduce a solvent, the solvent temperature must be low. Introducing a solvent means that the lithium, sodium, or potassium cation and the condensed aromatic compound anion are each surrounded by solvent molecules, resulting in a state where solvated cations and anions exist, and these solvated ions are bonded together by Coulomb forces. Because this solvent-mediated state of cation and anion contact can be created in the solution, the condensed aromatic compound anion can exist stably, and reverse electron transfer from the condensed aromatic compound anion to the alkali metal cation can be suppressed. If a reducing solution prepared at temperatures above 0°C does not allow sufficient solvation, or if there is a distribution in the solvation state, is cooled to low temperatures during silicon nanoparticle production, complete solvation will not occur, leading to variations in reducing power and causing a distribution in the particle size of silicon nanoparticles within the solution. In a state where ions are directly bonded by Coulomb forces and in equilibrium, even when cooled to low temperatures during silicon nanoparticle production, solvent molecules are less likely to overcome the Coulomb forces and penetrate between the cation and anion. Therefore, the temperature during solution preparation is more important than the temperature during silicon nanoparticle production.

[0040] As described above from the standpoint of solvation, the need to prepare the reducing solution at low temperatures is important. In addition, it is necessary to keep the storage temperature after preparation low. This is because if the storage temperature of the reducing solution is high, when THF is used as the solvent, a reduction polymerization reaction of THF will occur due to condensed aromatic compound anions. Since the polymers generated by such THF polymerization are mixed with the single-crystal spherical silicon nanoparticles produced by the reduction of silicon halides, it is necessary to suppress the polymerization reaction. As an inhibitor of the THF polymerization reaction, BHT (2,6-di-tert-butyl-4-methylphenol), which is added to suppress the formation of THF peroxides, can be used.

[0041] (Manufacturing method for single-crystal spherical silicon nanoparticles: apparatus) In the manufacturing method of the present invention, for example, an apparatus described in Japanese Patent Publication No. 2009-112892, proposed by the applicant of this application, is used. The apparatus has a stirring tank having an inner surface with a circular cross-sectional shape, and a stirring tool attached to the inner surface of the stirring tank with a small gap between them. The stirring tank is equipped with at least two fluid inlets and at least one fluid outlet. From one of the fluid inlets, a first fluid to be treated, containing one of the reactants from the fluid to be treated, is introduced into the stirring tank, and from the other fluid inlet, a second fluid to be treated, containing one reactant different from the reactant mentioned above, is introduced into the stirring tank from a different flow path than that of the first fluid to be treated. At least one of the stirring tank and the stirring tool rotates at high speed relative to the other, causing the fluid to be treated to become a thin film, and reactants contained in at least the first fluid to be treated and the second fluid to be treated react with each other in this thin film. Another example is an apparatus with a principle similar to the fluid treatment apparatus described in Patent Document 5.

[0042] (Manufacturing method for single-crystal spherical silicon nanoparticles: Method overview) In the manufacturing method of the present invention, single-crystal spherical silicon nanoparticles are produced by mixing a solution of the reducing solution for single-crystal spherical silicon nanoparticles, which is kept at a temperature of 5°C or below, with the raw material solution for single-crystal spherical silicon nanoparticles. Single-crystal spherical silicon nanoparticles are produced in two steps: first, nuclei of single-crystal spherical silicon nanoparticles are formed, and then the single-crystal spherical silicon nanoparticles grow. Even when the raw material solution comes into contact with the reducing solution, which is kept at a temperature of 5°C or below, and the reaction begins, the frequency of nuclei formation of single-crystal spherical silicon nanoparticles is low, and therefore the frequency of contact between the nuclei of single-crystal spherical silicon nanoparticles is also reduced. As a result, in the growth of single-crystal spherical silicon nanoparticles, the influence of changes in the raw material solution concentration due to the growth of surrounding single-crystal spherical silicon nanoparticles is reduced, and the supply of silicon halide, the raw material necessary for the growth of single-crystal spherical silicon nanoparticles, becomes uniform.

[0043] (Suppression of the formation of polycrystalline silicon nanoparticles) By using a flow reactor that can quickly discharge the product from the reaction solution, the halogen atoms, which are the reduction intermediates of silicon halides (a reaction intermediate), do not leave the reactor, preventing the formation of polyvalent silicon radicals in which silicon atoms are in a radical state. This provides one of the factors that can suppress the formation of polycrystalline silicon nanoparticles.

[0044] (Inorganic by-products in the reduction reaction of single-crystal spherical silicon nanoparticles) The reduction reaction byproducts generated during the production of single-crystal spherical silicon nanoparticles are lithium, sodium, or potassium halides, which consist of halogen ions desorbed from silicon halide and lithium, sodium, or potassium cations. In ether-based organic solvents, each of these dissolves as an ion. However, when separating them as single-crystal spherical silicon nanoparticles, for example, when lithium is used, the solubility of lithium chloride in ether-based organic solvents is greater than that of sodium chloride and potassium chloride, and it dissociates into lithium ions and chloride ions. This has the advantage of facilitating separation from the single-crystal spherical silicon nanoparticles by centrifugal separation. In other words, while it is possible to use alkali metal elements other than lithium in the production of single-crystal spherical silicon nanoparticles, the solubility of the salts, which are compounds of alkali metal element halides that are reaction byproducts, in ether-based organic solvents is lower than that of lithium chloride. As a result, these salts become mixed with the single-crystal spherical silicon nanoparticles, making separation by centrifugal separation difficult. Therefore, from the viewpoint of separating such reduction reaction byproducts from single-crystal spherical silicon nanoparticles, it is preferable to use lithium.

[0045] (Organic by-products in the reduction reaction of single-crystal spherical silicon nanoparticles) In the reduction reaction of silicon halides by condensed aromatic compound anions, for example, the silicon atom that has had a chlorine atom removed from silicon tetrachloride becomes a radical, making it highly reactive. This allows for the production of single-crystal spherical silicon nanoparticles through bonding with the radical states of adjacent silicon atoms. Simultaneously, compounds in which silicon is bonded to the condensed aromatic compound are also produced. Once the condensed aromatic compound is bonded to the silicon atom, it is not easily reduced by the condensed aromatic compound anion, resulting in by-products other than single-crystal spherical silicon nanoparticles. Specifically, alkyl silicon halides, which have become stable due to the bonding of a portion of the silicon halide with the condensed aromatic compound, are produced. In this compound, the silicon atoms bonded to halogen atoms that are not bonded to alkyl groups can become silicon radicals in the reducing solution. Therefore, the halogens in these alkyl silicon halides are continuously removed by the reducing agent, producing alkylpolysilanes where silicon radicals bond to each other. The formation of polysilanes results in losses because they precipitate as heavier particles than silicon nanoparticles. To prevent the reaction temperature from reaching a level that would lead to loss reactions due to organic by-products, the temperature of the reducing solution must be controlled to 5°C or below.

[0046] Therefore, by having a narrow particle size distribution and supplying isotropic raw materials, spherical single-crystal silicon nanoparticles (referred to as single-crystal spherical silicon nanoparticles in this invention) can be produced. When the reaction temperature is high, the frequency of single-crystal spherical silicon nanoparticle nuclei increases, but because many other single-crystal spherical silicon nanoparticle nuclei exist around the nuclei of the single-crystal spherical silicon nanoparticles, it becomes difficult to uniformly supply the silicon halide necessary for growth, and the single-crystal spherical silicon nanoparticles are produced with a distributed shape. Accordingly, in the production method of this invention, by setting the temperature of the reducing solution to 5°C or lower, the frequency of single-crystal spherical silicon nanoparticle nuclei is suppressed, and the supply of the raw material solution to the nuclei of the single-crystal spherical silicon nanoparticles is controlled to ensure uniform supply, thereby enabling the production of single-crystal spherical silicon nanoparticles with a narrow particle size distribution.

[0047] Preferably, single-crystal spherical silicon nanoparticles are produced by mixing the raw material solution and the reducing solution at 5°C or below in the thin film fluid. Single-crystal spherical silicon nanoparticles are produced in a two-step process: first, nuclei of single-crystal spherical silicon nanoparticles are formed, and then the single-crystal spherical silicon nanoparticles grow. Even when the raw material solution comes into contact with the reducing solution at 5°C or below and the reaction begins, the frequency of nuclei formation of single-crystal spherical silicon nanoparticles is low, and therefore the frequency of contact between the nuclei of single-crystal spherical silicon nanoparticles is also reduced. As a result, in the growth of single-crystal spherical silicon nanoparticles, the influence of changes in the raw material solution concentration due to the growth of surrounding single-crystal spherical silicon nanoparticles is reduced, and the supply of raw materials necessary for the growth of single-crystal spherical silicon nanoparticles becomes uniform.

[0048] The temperature of the reducing solution introduced into the thin film fluid formed between two processing surfaces arranged opposite each other, which are movable and can move away from one another, and at least one of which rotates relative to the other, can be, for example, -30°C to 5°C, preferably -10°C to 5°C, and more preferably 0°C to 5°C. In Examples 1 and 2, when the raw material solution temperature was set to 5°C, single-crystal spherical silicon nanoparticles that were spherical and produced fluorescence with high fluorescence quantum efficiency were successfully manufactured. In Comparative Example 4, when the raw material solution temperature was set to 25°C, the fluorescence quantum efficiency decreased. In Patent Document 4, sections

[0065] to

[0067] emphasize that the reaction temperature should be limited to 0°C or below in order to suppress side reactions, and in the examples, the reaction was carried out at a much lower temperature of -60°C. In Examples 6 to 9 of Patent Document 5, the reaction was also carried out at a much lower temperature of -50°C to -90°C. In contrast, the present invention has the remarkable effect of being able to obtain extremely satisfactory single-crystal spherical silicon nanoparticles even at a reaction temperature of 5°C, which is above 0°C, the temperature that was inhibited in Patent Document 4. This remarkable effect could not have been predicted by those skilled in the art based on Patent Documents 4 and 5.

[0049] The temperature of the raw material solution introduced into the thin film fluid formed between two processing surfaces arranged opposite each other, which are movable and can move away from one another, and at least one of which rotates relative to the other, can be, for example, -10°C to 25°C, preferably 0°C to 20°C, and more preferably 10°C to 18°C. In Examples 1 and 2, when the raw material solution temperature was set to 15°C, it was possible to produce single-crystal spherical silicon nanoparticles that are spherical, single-crystal, and exhibit high fluorescence quantum efficiency.

[0050] (Fluorescence of silicon nanoparticles and manufacturing methods) It is known that fluorescence from silicon nanoparticles can be obtained in two ranges depending on the manufacturing method: (1) ultraviolet to green fluorescence, and (2) green to near-infrared fluorescence. (1) is obtained by the fabrication of silicon nanoparticles by laser irradiation in a liquid (laser ablation) and by reduction in a solution (electron reduction of silicon halide). (2) is obtained by methods such as electrochemical etching, thermal decomposition of silicon precursors, laser ablation in a vacuum or inert gas, and etching of Si / SiO2 nanostructures with hydrofluoric acid (HF).

[0051] (Presence of hydrogen in silicon nanoparticles) During the manufacturing of silicon nanoparticles, the silicon nanoparticles can be stabilized by Si-H bonds formed when silicon atoms are bonded to hydrogen atoms at sites where silicon atom bonds have been broken. In the single-crystal spherical silicon nanoparticles according to the present invention, sites where silicon atom bonds have been broken, which may be randomly generated during manufacturing, create new energy levels in the band gap and affect the fluorescence wavelength, but this effect can be reduced by Si-H bonds.

[0052] The single-crystal spherical silicon nanoparticles can be isolated from the reaction solution containing the manufactured single-crystal spherical silicon nanoparticles by conventional methods. For example, ultracentrifugation can be performed.

[0053] 3. Applications of single-crystal spherical silicon nanoparticles The single-crystal spherical silicon nanoparticles produced by the manufacturing method of the present invention can be used, for example, as light-emitting elements, light-emitting materials that produce fluorescence, negative electrodes for lithium-ion batteries, electrode materials for solar cells, and bonding materials for semiconductor devices to substrates. [Examples]

[0054] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0055] (Transmission electron microscope (TEM): Preparation of samples for TEM observation) The single-crystal spherical silicon nanoparticles obtained in the examples and comparative examples were dispersed in THF at a concentration of approximately 0.001% in a container. The container containing the obtained dispersion was placed in a glove box under an argon atmosphere, and the dispersion was dropped onto a carbon support film and dried to prepare a sample for TEM observation.

[0056] (TEM observation) A transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.) was used for TEM observation of single-crystal spherical silicon nanoparticles. The above-mentioned TEM observation sample was used as the sample. The observation conditions were an acceleration voltage of 200kV and an observation magnification of 10,000x or more. The particle diameter was calculated from the distance between the maximum outer circumferences of the single-crystal spherical silicon nanoparticles observed by TEM, and the average value (average particle diameter) of the single-crystal spherical silicon nanoparticle diameters measured for 50 particles was calculated.

[0057] (Scanning transmission electron microscope (STEM)) For STEM observation of single-crystal spherical silicon nanoparticles, an atomic-resolution analytical electron microscope JEM-ARM200F (manufactured by JEOL Ltd.) was used. The above-mentioned TEM observation sample was used as the sample. The observation conditions were an acceleration voltage of 80 kV, an observation magnification of 50,000x or more, and analysis was performed using a beam diameter of 0.2 nm.

[0058] (Infrared (IR) absorption spectrum) The IR absorption spectra of single-crystal spherical silicon nanoparticles were measured using the Total Reflectance Attenuation (ATR) method with a Fourier transform infrared spectrophotometer FT / IR-6600 (manufactured by JASCO Corporation). The measurement conditions were a resolution of 4.0 cm. -1 For a total of 128 approximations, a diamond prism (PKS-D1F) (wide-range): refractive index 2.4) was incorporated into the ATRPRO ONE accessory of the FT / IR-6600, and the incident angle was set to 45°. The infrared (IR) absorption spectra measured for the single-crystal spherical silicon nanoparticles produced in the example and the polycrystalline silicon nanoparticles produced in the comparative example are denoted as IR spectra.

[0059] (Fluorescence spectrum) The fluorescence spectra of single-crystal spherical silicon nanoparticles were measured using a spectrofluorometer FT-6500 (manufactured by JASCO Corporation). As a sample, a sample solution dispersed in THF or DME was placed in a quartz cell (optical path length: 1 cm) in a glove box under an argon atmosphere, sealed at the top, and then removed from the glove box for measurement. The measurement conditions were: excitation bandwidth 3 nm, fluorescence bandwidth 3 nm, response time 0.1 seconds, scanning speed 100 nm / min, and data acquisition interval 0.5 nm. Similarly, the fluorescence spectrum of 9,10-diphenylanthracene, used as a reference material for relative fluorescence quantum efficiency, was measured under the same conditions.

[0060] (Waveform separation of fluorescence spectra) The fluorescence spectra of the measured single-crystal spherical silicon nanoparticles were subjected to waveform separation to calculate the relative fluorescence quantum efficiency with respect to the fluorescence quantum efficiency of 9,10-diphenylanthracene. The area % of the fluorescence spectrum showing a peak at 430 nm was then calculated. Waveform separation was performed using the waveform separation software built into the FT / IR-6600, which was used for IR absorption spectrum measurement.

[0061] (Relative fluorescence quantum efficiency) The fluorescence quantum efficiency of a fluorescent material can be evaluated by the efficiency of fluorescence produced in response to excitation light. In this invention, the fluorescence quantum efficiency of single-crystal spherical silicon nanoparticles was calculated as a relative value to 9,10-diphenylanthracene, which was set as a reference material with a fluorescence quantum efficiency of 1.0. The relative fluorescence quantum efficiency was calculated by the following equation (1). Φ x =Φ s (F x / F s )(A s / A x )(I s / I x )(n x 2 / n s 2 )···(1) [In the formula, x represents single-crystal spherical silicon nanoparticles. s represents 9,10-diphenylanthracene. Φ] x Φ is the relative fluorescence quantum efficiency of single-crystal spherical silicon nanoparticles. s is the quantum efficiency of 9,10-diphenylanthracene. F is the area of ​​the fluorescence spectrum. A is the absorbance at the excitation wavelength. I is the intensity of the excitation light. n is the refractive index of the solvent used. In this invention, the measurement conditions of the spectrofluorometer used to measure fluorescence—the excitation light bandpass width, fluorescence bandpass width, scanning speed, data acquisition interval, and measurement sensitivity—are all kept constant for the reference material 9,10-diphenylanthracene and single-crystal spherical silicon nanoparticles, and the same solvent THF is used, so in equation (1), (I s / I x )(n x 2 / n s 2 The value of ) is 1.0. Therefore, it was calculated from the area of ​​the fluorescence spectra of the THF dispersion of single-crystal spherical silicon nanoparticles and the THF solution of 9,10-diphenylanthracene, respectively, and the absorbance value at the time of measurement.

[0062] (ICP-OES measurement) The concentrations of silicon and lithium in single-crystal spherical silicon nanoparticles were measured using ICP-OES (Inductively Coupled Plasma Atomic Emission Spectrometer ICPS-8100, Shimadzu Corporation). The measurement conditions involved weighing 4 mg of single-crystal spherical silicon nanoparticles, dissolving them in hydrofluoric acid and nitric acid, then dissolving them in a 25 mL volumetric flask to determine the lithium content. The sample solution was then diluted with pure water to determine the silicon content. Calibration curves were prepared using silicon standard solutions for atomic absorption spectrometry (Kanto Chemical Co., Ltd.) and lithium standard solutions for atomic absorption spectrometry (Kanto Chemical Co., Ltd.). The emission line at 670.784 nm was used for lithium identification and quantification, and the emission line at 251.611 nm was used for silicon identification and quantification.

[0063] (UV-visible absorption spectroscopy measurement) The UV-vis (ultraviolet-visible) absorption spectra of single-crystal spherical silicon nanoparticles were measured using an ultraviolet-visible near-infrared spectrophotometer (product name: V-770, manufactured by JASCO). The measurement range was 200 nm to 900 nm, with a sampling rate of 0.2 nm and a slow measurement speed. A 10 mm thick liquid quartz cell was used for the measurements. To calculate the relative fluorescence quantum efficiency of the single-crystal spherical silicon nanoparticles, the nanoparticles were diluted with THF so that the absorbance in the wavelength range of 300 nm to 400 nm was 0.05 or less, and then measured. The absorbance of a THF solution of 9,10-diphenylanthracene was measured under similar measurement conditions.

[0064] (Circularity) The circularity of single-crystal spherical silicon nanoparticles was calculated as an index to evaluate their sphericity, as follows: The circularity of single-crystal spherical silicon nanoparticles was approximated as an ellipse using the TEM image software iTEM (Olympus Soft Imaging Solutions GmbH) based on images obtained by TEM observation. Next, the major axis (D), perimeter (Z), and area (S) of the ellipse, which is the projected image of the single-crystal spherical silicon nanoparticles, were determined from the analysis results of the TEM image analysis software. The perimeter (Z) and area (S) values ​​were used to calculate 4πS / Z 2The value of circularity was calculated and defined as the degree of circularity. The closer the degree of circularity is to 1, the closer the particle is to a sphere, and if the particle shape is a perfect sphere, the degree of circularity can be as high as 1. Furthermore, the average value of the major axis (D) of the ellipse was calculated and used as the average particle diameter. The measurement was performed on 50 independent single-crystal spherical silicon nanoparticles.

[0065] Example 1 In Example 1, a THF solution of silicon tetrachloride (SiCl4), which is the raw material (single-crystal spherical silicon nanoparticle raw material solution), was reduced using a THF solution of lithium metal dissolved in naphthalene (single-crystal spherical silicon nanoparticle reducing solution) to produce single-crystal spherical silicon nanoparticles. Table 1 shows the formulations for Examples 1-1 to 1-4. The solvent used in Example 1 was ultra-dehydrated tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with a residual water content of 10 ppm or less, and contained 2,6-di-tert-butyl-4-methylphenol (BHT) as a polymerization inhibitor. Single-crystal spherical silicon nanoparticle reducing solution (Solution A) and single-crystal spherical silicon nanoparticle raw material solution (Solution B) were prepared in a glove box under an argon atmosphere. Specifically, Solution A, the single-crystal spherical silicon nanoparticle reducing solution, was prepared by dissolving metallic lithium to a concentration of 0.4 mol / L in a THF solution in which naphthalene was dissolved at a preparation temperature of -20°C using a glass-coated magnetic stirrer. Similarly, after dissolving silicon tetrachloride, the raw material for single-crystal spherical silicon nanoparticles in Solution B, in THF, the mixture was stirred for at least 60 minutes using a glass-coated magnetic stirrer. For the substances indicated by the chemical formulas and abbreviations listed in Table 1, SiCl4 is silicon tetrachloride (manufactured by Tokyo Chemical Industry Co., Ltd.), Li is metallic lithium (manufactured by Kishida Chemical Co., Ltd.), and C 10 H8 is naphthalene (manufactured by Kanto Chemical Co., Ltd.).

[0066] [Table 1]

[0067] Next, the prepared single-crystal spherical silicon nanoparticle reducing solution (Solution A) and single-crystal spherical silicon nanoparticle raw material solution (Solution B) were mixed using a fluid processing apparatus described in Patent Document 5 by the applicant of the present application. Here, the fluid processing apparatus described in Patent Document 5 is the apparatus shown in Figure 1(A) of the said publication, in which the opening d2 of the second introduction section is a concentric ring shape surrounding the central opening of the processing surface 2, which is a disc formed in the shape of a ring. Specifically, Solution A was introduced from the first introduction section d1 between the processing surfaces 1 and 2, and while operating the processing section 10 at a rotation speed of 700 rpm to 5000 rpm, Solution B was introduced from the second introduction section d2 between the processing surfaces 1 and 2 to mix the single-crystal spherical silicon nanoparticle raw material solution and the single-crystal spherical silicon nanoparticle reducing solution in a thin film fluid, thereby precipitating single-crystal spherical silicon nanoparticles between the processing surfaces 1 and 2. The discharge liquid containing single-crystal spherical silicon nanoparticles was discharged from between the processing surfaces 1 and 2 of the fluid processing apparatus. The discharged dispersion of single-crystal spherical silicon nanoparticles was collected in a beaker via a vessel.

[0068] Table 2 shows the operating conditions of the fluid processing apparatus of Example 1. The introduction temperature (delivery temperature) and introduction pressure (delivery pressure) of liquids A and B shown in Table 2 were measured using a thermometer and a pressure gauge installed in a sealed introduction passage (first introduction section d1 and second introduction section d2) connecting processing surfaces 1 and 2. The introduction temperature of liquid A shown in Table 2 is the actual temperature of liquid A under the introduction pressure in the first introduction section d1, and similarly, the introduction temperature of liquid B is the actual temperature of liquid B under the introduction pressure in the second introduction section d2.

[0069] [Table 2]

[0070] A wet cake sample was prepared from a dispersion of single-crystal spherical silicon nanoparticles discharged from a fluid processing device and collected in a beaker. The preparation method followed a conventional procedure: the discharged dispersion of single-crystal spherical silicon nanoparticles was collected, and the single-crystal spherical silicon nanoparticles were settled from this collected liquid by ultracentrifugation (1,000,000 G for 4 hours), and the supernatant was separated. Subsequently, ultrasonic washing and settling were repeatedly performed using THF to obtain the final wet cake of single-crystal spherical silicon nanoparticles. A portion of the wet cake was dried at -0.10 MPaG at 25°C for 20 hours to obtain a dry powder.

[0071] Figure 1 shows a TEM image of the single-crystal spherical silicon nanoparticles of Example 1-1. Similar results were confirmed for the single-crystal spherical silicon nanoparticles of Examples 1-2 to 1-4.

[0072] Figure 2 shows STEM images of the single-crystal spherical silicon nanoparticles of Examples 1-4, and Figure 3 shows the Fourier-transformed electron diffraction patterns of the STEM images. Similar interference patterns of electron beams within the particles due to the silicon crystal lattice planes, as well as electron diffraction patterns with dot patterns typical of single crystals, were observed for the single-crystal spherical silicon nanoparticles of Examples 1-1 to 1-3. Therefore, it was confirmed that the spherical silicon nanoparticles produced in Example 1 were single crystals. The lattice plane spacing calculated from the obtained electron diffraction patterns was 0.162 nm, confirming that the diffraction pattern originated from the (311) plane of crystalline silicon.

[0073] (Si-H bond) Figure 4 shows the IR spectral measurement results for wavenumber 1800 cm⁻¹ of single-crystal spherical silicon nanoparticles in Examples 1-2. -1 ~2300cm -1 The results of measurements taken in the following area are shown: 2105 cm². -1The absorption was attributed to the stretching vibration of the Si-H bond, confirming that the surface of the single-crystal spherical silicon nanoparticles was hydrogenated. Similar confirmation was made for Examples 1-1, 1-3, and 1-4. Since the Si-H bond can hydrophobize the surface of the single-crystal spherical silicon nanoparticles, it was confirmed that the single-crystal spherical silicon nanoparticles can be well dispersed in organic solvents. As shown in Figure 1, it was observed that the single-crystal spherical silicon nanoparticles of the present invention were dispersed even at extremely small distances of around 5 nm.

[0074] (Si-O bond) Figure 5a shows 900 cm -1 ~1300cm -1 The IR spectrum in the wavenumber region is shown. The single-crystal spherical silicon nanoparticles of Examples 1-4 have a wavelength of 1095 cm⁻¹. -1 An absorption maximum was observed, and the absorption peak wavenumber of this peak was 10⁹⁵ cm⁻¹, which is the same as the absorption peak wavenumber of the reagent amorphous silica (SiO₂). -1 This matches. For comparison, the IR spectrum of a single-crystal silicon wafer is shown. The wavenumber of this absorption maximum is 1105 cm⁻¹. -1 This has been confirmed and represents absorption in a state where oxygen is solidly dissolved between the silicon crystal lattice. Figure 5b shows 400cm -1 ~550cm -1 The IR spectrum in the wavenumber region is shown. In the single-crystal spherical silicon nanoparticles of Examples 1-4, no clear absorption peaks showing a maximum were observed, but in the reagent amorphous silica (SiO2), a peak of 460 cm² was observed. -1 A maximum absorption peak is observed at 1100 cm². This suggests that the commonly known Si-O bond is responsible for this peak. -1 The nearby peak and the 460 cm⁻¹ point indicated by amorphous silica (SiO₂) -1 When the peaks are observed simultaneously, it means that the substance is considered to be oxidized SiO2.

[0075] (Solid dissolved oxygen in silicon crystals) According to the IR spectra shown in Figures 5a and 5b, the IR spectra of the single-crystal spherical silicon nanoparticles of Examples 1-4 do not simultaneously show the two absorption points that are considered to be SiO2. Therefore, 1095 cm⁻¹ -1 The absorption is affected by various states in which oxygen is dissolved in the silicon crystal, with the absorption peak wavenumber due to dissolved oxygen being 1105 cm⁻¹. -1 10cm -1 Unlike the previous example, the spectral width was broadened during measurement. The single-crystal spherical silicon nanoparticles of Examples 1-4 exhibit fluorescence spectra, confirming that they are silicon crystals. Furthermore, it is desirable to minimize the presence of oxygen capable of bonding with silicon atoms in the silicon crystal. IR spectrum at wavenumber 1000 cm⁻¹ -1 ~1200cm -1 Let A be the peak intensity of the maximum peak observed in the region, with a wavenumber of 400 cm. -1 ~500cm -1 Let B be the peak intensity of the maximum peak observed in the given region. It is desirable that the ratio B / A is less than 0.2. In Examples 1-4, the ratio B / A is 0.1, which is less than 0.2. In contrast, the reagent amorphous silica (SiO2) has a peak wavenumber of 460 cm⁻¹. -1 It shows a maximum peak, with a ratio of 0.4 (B / A), which is greater than 0.2.

[0076] (Si-Cl bond) Figure 5c shows the results of an investigation into the Si-Cl bond between a silicon atom and a chlorine atom. When a Si-Cl bond is present, the IR spectrum at 530 cm⁻¹ is... -1 ~630cm -1 In the wavenumber region, absorption is observed where the absorbed wavenumber changes depending on the number of chlorine atoms bonded to the silicon atom. Si-Cl bonds are highly likely to hydrolyze with moisture in the atmosphere, leading to the formation of silicon oxides and hydroxides, so it is desirable to reduce them as much as possible. The proportion of Si-Cl bonds is 1000 cm⁻¹. -1 ~1200cm -1 Let A be the peak intensity of the maximum peak observed at 530 cm. -1 ~630cm -1It is desirable that the ratio C / A is less than 0.2, where C is the peak intensity of the maximum Si-Cl bond observed in the wavenumber region. When the ratio C / A is less than 0.2, single-crystal spherical silicon nanoparticles did not immediately change color and transform into silicon oxide or silicon hydroxide when exposed to air. In Example 1-4, the ratio C / A was 0.06, which is less than 0.2. Similar results were obtained in Examples 1-1 to 1-3.

[0077] (Substituting carbon in silicon crystals) Figure 5d shows 550cm -1 ~700cm -1 The IR spectrum in the wavenumber region is shown. It is known that absorption exists in this region due to the substitution of silicon atoms with carbon atoms in the silicon crystal. Therefore, the wavenumber region of the absorption due to the Si-C bond is 530 cm⁻¹ compared to the absorption due to the Si-Cl bond described in the previous paragraph. -1 ~630cm -1 This overlaps with the example. In Examples 1-4, the wavenumber is 612 cm. -1 Although the absorption was attributed to the Si-Cl bond, even at wavenumber 612 cm⁻¹ -1 Even if the absorption is due to Si-C bonding by dissolved carbon atoms, the wavenumber 610 cm² observed in silicon wafers... -1 Compared to a ratio of 0.5 for C / A, the ratio in Examples 1-4 is 0.06, which means the carbon concentration is lower than that of a silicon wafer. In the present invention, since the single-crystal spherical silicon nanoparticles are produced by reducing silicon halide with an aromatic compound, it was expected that carbon would be mixed in as an impurity in the single-crystal spherical silicon nanoparticles. However, the single-crystal spherical silicon particles of the present invention contain almost no carbon atoms, resulting in high-purity single-crystal spherical silicon nanoparticles. Because the absorption wavenumber due to Si-C bonding and the absorption wavenumber due to Si-Cl bonding overlap, the 612 cm⁻¹ observed in Examples 1-4 is obtained. -1 Although it is not possible to definitively determine which type of absorption is being observed, the single-crystal spherical silicon nanoparticles in Examples 1-4 are single-crystal spherical silicon nanoparticles with low concentrations of carbon and chlorine.

[0078] Figure 6 shows the fluorescence spectra of the single-crystal spherical silicon nanoparticles of Examples 1-3. The fluorescence spectra are normalized by setting the maximum intensity of the fluorescence spectrum obtained for each excitation wavelength to 1.0, and the results are obtained by changing the excitation wavelength in 40 nm increments from 340 nm to 600 nm. From the results in Figure 6, it was confirmed that the fluorescence of the single-crystal spherical silicon nanoparticles of Examples 1-3 shows a maximum peak between 400 nm and 610 nm. Figure 7, created based on the results in Figure 6, shows the excitation wavelength dependence of the fluorescence peak wavelength of the single-crystal spherical silicon nanoparticles in Examples 1-3. Since it is known that the fluorescence peak wavelength shifts to longer wavelengths as the particle size of silicon nanoparticles increases, it was confirmed that fluorescence reflecting the particle size distribution of the single-crystal spherical silicon nanoparticles was obtained.

[0079] Figure 8 shows the measurement results of particle size and fluorescence peak wavelength as disk rotation speed for single-crystal spherical silicon nanoparticles in Examples 1-1 to 1-4. It was confirmed that the particle size of the single-crystal spherical silicon nanoparticles decreased as the disk rotation speed increased. Therefore, it was confirmed that the particle size of the single-crystal spherical silicon nanoparticles can be controlled by the disk rotation speed. Furthermore, it was confirmed that the fluorescence peak wavelength shifted to the shorter wavelength side as the disk rotation speed increased, that is, as the silicon nanoparticle diameter decreased. This change in fluorescence peak wavelength due to particle size is explained by the quantum effect (A) among the three mechanisms (A) to (C) described above. That is, the fluorescence peak wavelength of silicon nanoparticles is thought to have shifted to the shorter wavelength side because the band gap of the silicon nanoparticles increases as the particle size of the silicon nanoparticles decreases, and this is a result of the quantum effect mechanism (A). Furthermore, since the silicon nanoparticles of the present invention do not undergo surface modification such as alkyl groups or amino groups, and the (B) surface modification mechanism among the three mechanisms described above is absent, it is thought that the (C) oxygen-mediated mechanism, resulting from the solid solution of oxygen in the silicon crystal, acts synergistically with the (A) quantum effect mechanism.

[0080] Figure 9 shows the visible light fluorescence spectrum of the single-crystal spherical silicon nanoparticles of Example 1-2 at deep ultraviolet wavelengths. Deep ultraviolet refers to light in the wavelength range of 200 nm to 300 nm. In addition to the fluorescence spectrum excited by visible light shown in Figure 6, it was confirmed that visible light fluorescence in the wavelength range of 400 nm to 600 nm, showing fluorescence peaks at 470 nm and 550 nm, can also be obtained by using even shorter wavelength deep ultraviolet light. Similar results were obtained in Examples 1-1, 1-3, and 1-4. Thus, since visible light fluorescence can be obtained with excitation light of a wide wavelength range from deep ultraviolet to visible light, it was confirmed that the single-crystal spherical silicon nanoparticles of the present invention have a broader range of applications where fluorescence can be utilized.

[0081] The lithium concentration of the single-crystal spherical silicon nanoparticles in Examples 1-1 to 1-4, as measured by ICP-OES, was confirmed to be less than 1 ppm. This confirms that the single-crystal spherical silicon nanoparticles of the present invention do not incorporate metallic lithium contained in the single-crystal spherical silicon nanoparticle reducing solution and have high purity.

[0082] Table 3 shows the average particle size, circularity, relative fluorescence quantum efficiency, and the ratios B / A and C / A obtained from the IR spectra of single-crystal spherical silicon nanoparticles for Examples 1-1 to 1-4. For the single-crystal spherical silicon nanoparticles of Examples 1-1 to 1-4, the ratios B / A were 0.08 to 0.10 and the ratios C / A were 0.06 to 0.08, both of which are less than 0.2.

[0083] [Table 3]

[0084] Example 2 In Example 2, silicon tetrabromide (SiBr4) was used instead of silicon tetrachloride (SiCl4) as used in Example 1. Single-crystal spherical silicon nanoparticles were produced by reducing a THF solution of silicon tetrabromide (single-crystal spherical silicon nanoparticle raw material solution) with a naphthalene-dissolved THF solution of metallic lithium (single-crystal spherical silicon nanoparticle reducing solution). Table 4 shows the formulations for Examples 2-1 to 2-4. The solvent used in Example 2 was ultra-dehydrated tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with a residual water content of 10 ppm or less, and contained BHT as a polymerization inhibitor. In the same manner as in Example 1, a single-crystal spherical silicon nanoparticle reducing solution (Solution A) and a single-crystal spherical silicon nanoparticle raw material solution (Solution B) were prepared in a glove box under an argon atmosphere.

[0085] [Table 4]

[0086] Next, in the same manner as in Example 1, the prepared single-crystal spherical silicon nanoparticle reducing solution (Solution A) and the single-crystal spherical silicon nanoparticle raw material solution (Solution B) were mixed using the fluid processing apparatus described in Patent Document 5 by the applicant of the present application. Table 5 shows the operating conditions of the fluid processing apparatus.

[0087] [Table 5]

[0088] Dry powder and wet cake samples were prepared from a dispersion of single-crystal spherical silicon nanoparticles discharged from a fluid processing device and collected in a beaker. The preparation method followed a conventional procedure: the discharged dispersion of single-crystal spherical silicon nanoparticles was collected, and the single-crystal spherical silicon nanoparticles were settled from the collected liquid by ultracentrifugation (1,000,000 G for 4 hours), and the supernatant was separated. Subsequently, ultrasonic washing and settling were repeatedly performed using THF, and finally, a portion of the wet cake of single-crystal spherical silicon nanoparticles was dried at -0.10 MPaG at 25°C for 20 hours to obtain dry powder. The remainder was used as the wet cake sample.

[0089] Table 6 shows the average particle size, circularity, relative fluorescence quantum efficiency, and ratios B / A and C / A obtained from the IR spectra of single-crystal spherical silicon nanoparticles for Examples 2-1 to 2-4. The single-crystal spherical silicon nanoparticles for Examples 2-1 to 2-4 have a B / A ratio of 0.09 or 0.10 and a C / A ratio of 0.06 to 0.08, both of which are less than 0.2.

[0090] [Table 6]

[0091] Comparative Example 1 In Comparative Example 1, silicon nanoparticles were produced by reducing a silicon tetrachloride THF solution (silicon nanoparticle raw material solution) with a metallic lithium DBB (4,4'-di-tert-butylbiphenyl) dissolved THF solution (silicon nanoparticle reducing solution) according to Example 6 of Patent Document 5. Table 7 shows the formulations for Comparative Examples 1-1 to 1-3. The THF used in Comparative Example 1 was ultra-dehydrated tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with a residual moisture content of 10 ppm or less, and contained BHT as a polymerization inhibitor. The silicon nanoparticle reducing solution (Solution A) and the silicon nanoparticle raw material solution (Solution B) were prepared in a glove box under an argon atmosphere. Specifically, for Solution A, the silicon nanoparticle reducing solution, 30 mmol of metallic lithium was measured out in advance into a flask at room temperature (16°C to 17°C), and 200 mL of THF solution in which 40 mmol of DBB was dissolved was poured in and dissolved using a glass-coated magnetic stirrer. Similarly, after dissolving silicon tetrachloride, the raw material for the silicon nanoparticles in Solution B, in THF, the mixture was stirred for at least 60 minutes using a glass-coated magnetic stirrer. For the substances indicated by the chemical formulas or abbreviations listed in Table 7, SiCl4 is silicon tetrachloride (manufactured by Tokyo Chemical Industry Co., Ltd.), Li is metallic lithium (manufactured by Kishida Chemical Co., Ltd.), and DBB is 4,4'-di-tert-butylbiphenyl (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0092] [Table 7]

[0093] Next, in the same manner as in Example 1, the prepared silicon nanoparticle reducing solution (Solution A) and silicon nanoparticle raw material solution (Solution B) were mixed using the fluid processing apparatus described in Patent Document 5 by the applicant of the present application. Table 8 shows the operating conditions of the fluid processing apparatus in Comparative Examples 1-1 to 1-3.

[0094] [Table 8]

[0095] (Preparation of hexyl-terminated silicon nanoparticles) Next, the silicon nanoparticle dispersion discharged and recovered from the fluid processing device was subjected to the surface stabilization treatment described in Example 6 of Patent Document 5. Specifically, 10 mL of the silicon nanoparticle dispersion was placed in a 100 mL three-necked flask in a glove box under an argon atmosphere, and kept in a cooling tank maintained at -3°C with IPA as the refrigerant. After connecting a three-way stopcock to the three-necked flask to allow argon aeration, a solution of magnesium hexyl bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) prepared to four times the molar concentration of silicon in the silicon nanoparticle dispersion was added dropwise to the discharged liquid using a glass syringe with a metal needle inserted through the rubber septum of the three-necked flask. After addition, the cooling tank was removed, and the temperature was gradually raised to room temperature (16°C to 17°C) and stirred under an argon atmosphere for 24 hours. As a result, the surface of the chlorinated silicon nanoparticles dispersed in the discharged liquid was stabilized to obtain silicon nanoparticles with hexyl groups terminated. To purify the hexyl-terminated silicon nanoparticles, hexane was added to a flask, and the hexyl-terminated silicon nanoparticles dispersed in the THF solution were extracted into the hexane layer. After separating the hexane layer, pure water was added to dissolve and wash away residues caused by reaction products such as lithium chloride and magnesium hexyl bromide.

[0096] Figure 10 shows a STEM image of the hexyl-terminated silicon nanoparticles prepared in Comparative Example 1-1. The STEM image revealed that although the hexyl-terminated silicon nanoparticles are crystalline, the lattice planes within the silicon nanoparticles are not aligned in a consistent direction, and it was confirmed that they are polycrystalline with intersecting lattice planes. Furthermore, unlike in Example 1, it was confirmed that the silicon nanoparticles were not spherical but exhibited an irregular particle shape. As shown in Table 9, the circularity of the hexyl-terminated silicon nanoparticles in Comparative Examples 1-1 to 1-3 was 0.83 or 0.84, and was not 0.9 or higher.

[0097] The following reasons are possible for the formation of polycrystalline material. In Example 1 of the present invention, the reduction solution for single-crystal spherical silicon nanoparticles was prepared at a temperature of -20°C, but in Comparative Example 1, it was prepared at room temperature of 16°C to 17°C. This was to match the preparation of the reduction solution from metallic lithium and DBB at room temperature in Example 1 of Patent Document 4 and Example 6 of Patent Document 5. By preparing the reduction solution at room temperature, the DBB anion (radical anion) generated when metallic lithium releases electrons and dissolves in THF, and one electron is transferred from metallic lithium to the DBB molecule, undergoes a disproportionation reaction, resulting in an equilibrium reaction in which DBB dianions and uncharged DBB molecules are produced, thus lowering the concentration of DBB anions. It is thought that the presence of various molecular species in the THF solution inhibits the spheroidization through uniform crystal growth from silicon tetrachloride to silicon nanoparticles, and that the distribution of reaction rates causes polycrystalline silicon particles.

[0098] (Temperature of reducing solution delivery) DBB anions are generated when electrons produced when metallic lithium dissolves as lithium ions in THF transfer to DBB. In THF, DBB anions and lithium ions can coexist via THF, but if the temperature during solution preparation is above 0°C, DBB anions can directly form ionic bonds with lithium ions without the need for THF. Therefore, once ionic bonds are formed between DBB anions and lithium ions, it becomes difficult for THF to intervene between the DBB anions and lithium ions, even if the liquid transfer temperature during silicon nanoparticle production is kept low. When lithium ions and DBB anions are directly ionically bonded, reverse electron transfer from DBB anions to lithium ions is likely to occur. This is thought to lead to variations in the reducing power of silicon nanoparticles, resulting in non-uniform crystal growth rates of silicon particles, and causing the resulting silicon particle shape to deviate significantly from spherical, resulting in polycrystalline particles instead of single crystals.

[0099] Furthermore, in Comparative Example 1, chlorine atoms were bonded to the surface of the silicon nanoparticles in order to subsequently perform surface stabilization treatment with hexyl groups. Therefore, the number of moles of metallic lithium, which is the reducing agent, was set to 3 / 4 times the number of moles of silicon tetrachloride. This was done to match the molar ratio of metallic lithium in Example 1 of Patent Document 4 and Example 6 of Patent Document 5. The silicon nanoparticles before surface stabilization treatment differ from the single-crystal spherical silicon nanoparticles of the present invention in that the surface is intentionally chlorinated. In addition, since chlorine atoms that remain on the surface of the silicon nanoparticles after surface stabilization treatment without being replaced by hexyl groups are present, it is presumed that these chlorine atoms undergo hydrolysis during pure water washing after hexane extraction, changing the shape of the silicon nanoparticles. Similar results were confirmed for the silicon nanoparticles of Comparative Examples 1-2 and 1-3.

[0100] (Si-H bond in polycrystalline silicon nanoparticles of Comparative Example 1) Figure 11 shows the 1800 cm² of polycrystalline silicon nanoparticles of Comparative Example 1-1. -1 ~2300cm -1shows the IR spectrum in the wavenumber range. In Comparative Example 1-1, the absorption peak due to the Si-H bond near 2100 cm -1 was not observed. This is thought to be because the metal lithium mole number of the reducing solution was set to 3 / 4 of the metal lithium raw material concentration of the silicon nanoparticle raw material solution so that chlorine could remain on the surface of the polycrystalline silicon nanoparticles in Comparative Examples 1-1 to 1-3, preparing chlorinated polycrystalline silicon nanoparticles, and then substituting the chlorine atoms with hexyl groups using hexylmagnesium bromide.

[0101] (Si-O bond of polycrystalline silicon nanoparticles in Comparative Example 1) Figures 12a and 12b show the IR spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1. In Example 1-4, an absorption peak with a wide spectral width is observed at 1095 cm -1 , but in Comparative Example 1-1, an absorption peak with a narrow spectral width was confirmed at 1084 cm -1 . Also, in Comparative Example 1-1, an absorption peak was confirmed at 450 cm -1 on the low wavenumber side. Regarding the IR spectrum, taking the peak intensity of the maximum peak confirmed in the region of 1000 cm -1 to 1200 cm -1 as A, and the peak intensity of the maximum peak confirmed at 400 cm -1 to 500 cm -1 as B, the ratio: B / A was 0.38 and was not less than 0.2. From this result, it was confirmed that the Si-O bond state of the polycrystalline silicon nanoparticles of Comparative Example 1-1 is different from that of the single-crystalline spherical silicon nanoparticles of Example 1-4. Similar results to those of Comparative Example 1-1 were obtained for Comparative Examples 1-2 and 1-3.

[0102] (Si-Cl bond of polycrystalline silicon nanoparticles in Comparative Example 1) Figure 12c shows the IR spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1 at a wavenumber of 450 cm -1 to 650 cm -1 . Different from the single-crystalline spherical silicon nanoparticles of Example 1-4, at 620 cm -1A clear maximum absorption peak was observed, confirming the presence of a Si-Cl bond. In the IR spectrum, at 1000 cm⁻¹ -1 ~1200cm -1 Let A be the peak intensity of the maximum peak observed in the region, and 530 cm. -1 ~630cm -1 Taking C as the peak intensity of the maximum peak observed in the sample, the ratio C / A is 0.25, which is not less than 0.2. Similar results were obtained for Comparative Examples 1-2 and 1-3 as for Comparative Example 1-1. From this, it can be inferred that there are chlorine atoms on the surface of the chlorinated polycrystalline silicon nanoparticles that cannot be completely replaced by hexyl groups even after surface stabilization treatment with magnesium hexyl bromide.

[0103] (Substituting carbon in polycrystalline silicon nanoparticles of Comparative Example 1) Figure 12d shows the wavenumber of 550 cm for the polycrystalline silicon nanoparticles of Comparative Example 1-1. -1 ~700cm -1 The IR spectrum at 620 cm⁻¹ is shown. Unlike the single-crystal spherical silicon nanoparticles of Examples 1-4, the IR spectrum at 620 cm⁻¹ is shown. -1 An absorption peak with an absorbance of 0.25 was observed. This wavenumber region is 530 cm, where absorption occurs even when silicon atoms and chlorine atoms are bonded, as described in

[0101] . -1 ~630cm -1 This also overlaps. As mentioned above, the ratio C / A is 0.25, which is not less than 0.2. This result indicates that Si-Cl bonds or substituted carbons are present in the polycrystalline silicon nanoparticles of Comparative Example 1-1, and it was confirmed that they have a different composition from the single-crystal spherical silicon nanoparticles of Example 1-4.

[0104] (Fluorescence spectrum of polycrystalline silicon nanoparticles in Comparative Example 1) Comparative Example 1-1's polycrystalline silicon nanoparticles were confirmed to exhibit a fluorescence maximum in the wavelength range of 400 nm to 600 nm. However, as shown in Figures 13a and 13b, the fluorescence peak wavelength of the polycrystalline silicon nanoparticles of Comparative Example 1-1, when excited by deep ultraviolet light below 300 nm, was confirmed to be below 400 nm. Similarly, the fluorescence spectra of the polycrystalline silicon nanoparticles of Comparative Examples 1-2 and 1-3, when excited by deep ultraviolet light, also showed peaks below 400 nm. These results differ from those of Example 1-4, which showed a fluorescence peak wavelength of 547 nm at an excitation wavelength of 220 nm and a fluorescence peak at 568 nm at an excitation wavelength of 260 nm. Since the fluorescence peak wavelengths of the polycrystalline silicon nanoparticles of Comparative Examples 1-1 to 1-3, when excited by deep ultraviolet light, were all below 400 nm, it was confirmed that they have a different electronic energy structure than single-crystal spherical silicon nanoparticles that show fluorescence peaks in the visible light region of 400 nm to 600 nm. This can be explained by the fact that the silicon nanoparticles in Comparative Example 1 are polycrystalline, being an aggregate of single crystals with different crystallite sizes, and therefore the electron energy levels at which they absorb excitation light and emit fluorescence are different from those of single-crystal spherical silicon nanoparticles. In particular, since the silicon particle size prepared in the Examples and Comparative Examples is around 5 nm, even a slight change in crystallite size has a significant effect on the size of the silicon band gap. Furthermore, in polycrystalline materials, the presence of grain boundaries where each crystallite of the single crystals touches suggests the existence of electron energy levels due to the presence of these grain boundaries.

[0105] Table 9 shows the average particle size, circularity, relative fluorescence quantum efficiency, and ratios B / A and C / A obtained from the IR spectra of the polycrystalline silicon nanoparticles of Comparative Examples 1-1 to 1-3. The silicon nanoparticles of Comparative Example 1 are polycrystalline silicon nanoparticles, and the ratios B / A and C / A are 0.2 or higher. These values ​​were found to be different from the ratios B / A and C / A of the single-crystal spherical silicon nanoparticles of Examples 1 and 2.

[0106] [Table 9]

[0107] Example 3 Table 10 shows the formulations for Examples 3-1 and 3-2. Table 11 shows the operating conditions of the fluid processing apparatus for Examples 3-1 and 3-2. Table 12 shows the average particle size, circularity, relative fluorescence quantum efficiency, and the ratios B / A and C / A obtained from the IR spectra of the single-crystal spherical silicon nanoparticles for Examples 3-1 and 3-2. When the alkali metal in the reducing solution was sodium, the relative fluorescence quantum efficiency ranged from 11 to 13%. The ratios of silicon nanoparticles B / A and C / A in Example 3 were 0.1 or less. These values ​​were confirmed to be equivalent to the ratios of single-crystal spherical silicon nanoparticles B / A and C / A in Examples 1 and 2.

[0108] [Table 10]

[0109] [Table 11]

[0110] [Table 12]

[0111] Example 4 Table 13 shows the formulations for Examples 4-1 and 4-2. Table 14 shows the operating conditions of the fluid processing apparatus for Comparative Example 4-1 and Example 4-2. Table 15 shows the average particle size, circularity, relative fluorescence quantum efficiency, and the ratios B / A and C / A obtained from the IR spectra of the single-crystal spherical silicon nanoparticles for Examples 4-1 and 4-2. When the reducing solution metal was potassium, the relative fluorescence quantum efficiency ranged from 11% to 13%. The ratios B: / A and C / A were confirmed to be equivalent to those of the single-crystal spherical silicon nanoparticles in Examples 1 to 3.

[0112] [Table 13]

[0113] [Table 14]

[0114] [Table 15]

[0115] Comparative Example 2 Table 16 shows the formulations of Comparative Example 2-1 and Comparative Example 2-2. Table 17 shows the operating conditions of the fluid processing apparatus for Comparative Example 2-1 and Comparative Example 2-2. The alkali metal in the reducing solution was metallic lithium, and the temperature of the reducing solution A was set to 25°C. The disk rotation speeds were set to 3500 rpm and 5000 rpm. Table 18 shows the average particle size, circularity, relative fluorescence quantum efficiency, and the ratios B / A and C / A obtained from the IR spectra of single-crystal spherical silicon nanoparticles for Comparative Example 2-1 and Comparative Example 2-2. Due to the high temperature of the reducing agent in solution A, the average particle size remained large at over 4 nm even with increased disk rotation speed, and the relative fluorescence quantum efficiency decreased to less than 5%. The ratios B / A and C / A were found to be larger and different from those of the single-crystal spherical silicon nanoparticles in Examples 1 to 4.

[0116] [Table 16]

[0117] [Table 17]

[0118] [Table 18]

[0119] Comparative Example 3 Table 19 shows the formulations of Comparative Examples 3-1 and 3-2. Table 20 shows the operating conditions of the fluid processing apparatus for Comparative Examples 3-1 and 3-2. The alkali metal in the reducing solution A was lithium metal, and the temperature of the reducing solution was maintained at 5°C. Table 21 shows the average particle size, circularity, relative fluorescence quantum efficiency, and the ratios B / A and C / A obtained from the IR spectra of single-crystal spherical silicon nanoparticles for Comparative Examples 3-1 and 3-2. Although the temperature of the reducing solution was maintained at a low temperature of 5°C, the average particle size increased when the disk rotation speed was set to 350 rpm and 500 rpm, and the relative fluorescence quantum efficiency decreased to less than 5%. The ratios B / A and C / A were found to be larger and different from those of the single-crystal spherical silicon nanoparticles in Examples 1 to 4.

[0120] [Table 19]

[0121] [Table 20]

[0122] [Table 21] [Industrial applicability]

[0123] The single-crystal spherical silicon nanoparticles produced by the manufacturing method of the present invention are single crystals without grain boundaries that reduce fluorescence efficiency. Therefore, they can generate fluorescence with high fluorescence quantum efficiency when excited by light of a wide wavelength range from deep ultraviolet light of 200 nm to 300 nm to visible light, making it possible to increase the fluorescence quantum efficiency of conventionally known silicon nanoparticles from around 1% to over 10%.

Claims

1. A method for producing single-crystal spherical silicon nanoparticles that are single crystals, spherical in shape, and have an average particle diameter of 1 nm to 20 nm, The process includes a step of mixing and reacting a raw material liquid containing silicon halide with a reducing solution at 5°C or below containing anions of condensed aromatic compounds generated from lithium, sodium, or potassium, in a thin film fluid formed between processing surfaces arranged facing each other so as to be able to approach and separate from one another, with at least one of them rotating relative to the other. The rotation speed of the processing surface is 700 rpm or more. A method for producing the aforementioned condensed aromatic compound anion, wherein the anion is prepared by mixing lithium, sodium, or potassium with the condensed aromatic compound at a temperature below 0°C.

2. An apparatus comprising a fluid pressure application mechanism for applying pressure to a fluid to be processed, at least two processing parts, a first processing part and a second processing part that can move relatively closer to and further away from the first processing part, and a rotational drive mechanism for rotating the first processing part and the second processing part relative to each other, In each of the above processing sections, at least two processing surfaces, a first processing surface and a second processing surface, are provided at positions facing each other. Each of these processing surfaces constitutes part of a sealed flow path through which the fluid to be processed at the above pressure flows. Between the two processing surfaces, two or more fluids to be processed, each containing a reactant, are mixed and reacted. Of the first and second processing sections described above, at least the second processing section is equipped with a pressure-receiving surface, and at least a portion of this pressure-receiving surface is composed of the second processing surface. This pressure-receiving surface receives the pressure applied to the fluid to be processed by the fluid pressure application mechanism described above and generates a force that moves the second processing surface away from the first processing surface. As the fluid to be processed under the above pressure passes between the first and second processing surfaces, which are able to approach and separate from each other and rotate relative to each other, the fluid to be processed forms a thin film fluid, and further fluid to be processed under the above pressure flows through it. The manufacturing method according to claim 1, comprising: a separate introduction passage independent of the flow path between each processing surface; at least one of the first processing surface and the second processing surface having at least one opening leading to the separate introduction passage; and by introducing at least one fluid to be processed sent from the separate introduction passage between the two processing surfaces, the raw material liquid and the reducing solution are mixed and reacted in the thin film fluid using an apparatus.

3. The manufacturing method according to claim 2, wherein the opening is located downstream of the point at which the flow of the fluid to be processed, passed between the two processing surfaces, becomes laminar.

4. The manufacturing method according to any one of claims 1 to 3, wherein the molar ratio of lithium, sodium, or potassium to silicon halide is 7:1 to 4:

1.

5. The method for producing an aromatic compound according to any one of claims 1 to 3, wherein the condensed aromatic compound is at least one selected from the group consisting of biphenyl, naphthalene, 1,2-dihydronaphthalene, anthracene, phenanthrene, and pyrene.

6. The manufacturing method according to any one of claims 1 to 3, wherein the solvent contained in the reducing solution is tetrahydrofuran and / or dimethoxyethane having a residual water content of 10 ppm or less.

7. The manufacturing method according to any one of claims 1 to 3, wherein the solvent contained in the reducing solution is a tetrahydrofuran containing a phenolic polymerization inhibitor, having a residual water content of 10 ppm or less, and a residual oxygen concentration of less than 0.1 ppm.

8. The manufacturing method according to any one of claims 1 to 3, wherein the solvent contained in the raw material liquid is tetrahydrofuran having a residual water content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm.

9. The manufacturing method according to any one of claims 1 to 3, wherein the halogenated silicon is silicon tetrachloride, silicon tetrabromide, or silicon tetraiodide.

10. The single-crystal spherical silicon nanoparticles are measured using the perimeter (Z) and area (S) of the projection image of the single-crystal spherical silicon nanoparticles observed by a transmission electron microscope, using the formula: 4πS / Z 2 The manufacturing method according to any one of claims 1 to 3, wherein the average value of the circularity calculated is 0.9 or higher.

11. The aforementioned single-crystal spherical silicon nanoparticles exhibit an IR absorption spectrum of 1950 cm⁻¹. -1 ~2150cm -1 A manufacturing method according to any one of claims 1 to 3, which exhibits absorption attributed to the Si-H bond in the wavenumber region.

12. The aforementioned single-crystal spherical silicon nanoparticles exhibit an IR absorption spectrum of 1000 cm⁻¹. -1 ~1200cm -1 Let A be the peak intensity of the maximum peak in the wavenumber range, and 400 cm -1 ~500cm -1 A manufacturing method according to any one of claims 1 to 3, wherein the calculated ratio B / A is less than 0.2, with B being the peak intensity of the maximum peak in the wavenumber range.

13. The single-crystalline spherical silicon nanoparticles have a peak intensity of a maximum peak in a wave number range of 1000 cm -1 to 1200 cm -1 designated as A, and a peak intensity of a maximum peak in a wave number range of 530 cm -1 to 630 cm -1 designated as C, and the calculated ratio: C / A is less than 0.

2. The manufacturing method according to any one of claims 1 to 3.

14. The manufacturing method according to any one of claims 1 to 3, wherein the single-crystal spherical silicon nanoparticles produce a fluorescence maximum in the wavelength range of 400 nm to 600 nm.

15. The manufacturing method according to any one of claims 1 to 3, wherein the single-crystal spherical silicon nanoparticles produce a fluorescence maximum in the wavelength range of 400 nm to 600 nm when excited by deep ultraviolet light with an excitation wavelength of 300 nm or less.

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