Method for producing monocrystalline spherical silicon nanoparticles

Abstract

The present invention relates to a method for producing monocrystal, spherical, monocrystal spherical silicon nanoparticles having an average particle diameter of 1 nm to 20 nm, the method comprising a step of mixing and reacting a raw material solution containing silicon halide with a reducing solution containing an anion of a condensed aromatic compound produced from lithium, sodium or potassium and the condensed aromatic compound, the anion of the condensed aromatic compound being prepared by mixing lithium, sodium or potassium with the condensed aromatic compound at below 0°C. The monocrystal spherical silicon nanoparticles produced by the method of the present invention can produce blue to red fluorescence by excitation of light of a wide wavelength from deep ultraviolet light of 200 nm to 300 nm to visible light, and can increase the fluorescence quantum efficiency of the currently known silicon nanoparticles from about 1% to more than 10%.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing a single crystal spherical silicon nanoparticle. BACKGROUND

[0002] Silicon is a semiconductor that has supported the development of electronics in recent years. Since it was confirmed in 1990 that visible light emission was possible in porous silicon, research and development in the field of silicon photonics is being promoted in order to apply it to light emitting elements. Silicon is a semiconductor, but when considering the emission and absorption of visible light, it is investigated as two types of semiconductors, direct transition type and indirect transition type. In a semiconductor of the direct transition type, the top of the valence band (valence band top) and the bottom of the conduction band (conduction band bottom) are located at the same momentum in the energy space with respect to momentum, so only the energy of visible light is sufficient for the momentum, and thus the emission (fluorescence) efficiency is high. However, in an indirect transition type semiconductor containing ordinary semiconductor silicon, the valence band top and the conduction band bottom are not consistent, so when emitting light, it becomes a momentum in which the momentum of the crystal lattice vibration of the semiconductor silicon is added to the momentum of the visible light, so the emission (fluorescence) efficiency is lower than that of the direct transition type semiconductor. In ordinary silicon, fluorescence of near-infrared light of about 1 μm wavelength, which is equivalent to the energy of the band gap, 1.2 eV, is obtained, but by setting the silicon nanoparticle diameter to be less than 10 nm, fluorescence equivalent to visible light emission can be obtained. The reason is believed to be that by making the silicon nano-sized, a transition from the indirect transition type to the direct transition type is induced. Note that in the case where the silicon nanoparticle is oxidized from the surface, the actual silicon nanoparticle diameter that contributes to visible light emission decreases, so a silicon particle diameter as large as 20 nm can actually be allowed.

[0003] Regarding a silicon nanoparticle that emits visible light fluorescence, Patent Literature 1 discloses a method for producing a silicon nanoparticle in which commercially available silicon particles (particle diameter 100 nm, silicon purity 98% or more) are used, a hydrogen fluoride acid treatment is performed on the crystalline silicon powder to remove the surface oxide film, the surface is oxidized again with nitric acid to generate an oxide film, and the oxide film is removed with hydrogen fluoride acid. However, since commercially available silicon particles are used, the produced silicon nanoparticle is not a single crystal, and the particle diameter of the particles of Experimental Example 2 is a particle size distribution of two peaks of about 2000 nm and 10 to 20 nm. In addition, in this production method, since an acidic substance of hydrogen fluoride acid and nitric acid is used, the operation needs to be paid much attention to, and it is difficult to easily produce in industry.

[0004] Patent Literature 2 discloses a method for producing a silicon nanoparticle in which a pulsed laser is irradiated to a silicon powder, and the evaporated silicon is deposited on a desired substrate. However, the particle diameter of the produced silicon nanoparticle is about 50 to 100 nm. In addition, in this production method, a laser capable of pulsed oscillation is required, and it is not possible to inexpensively produce semiconductor silicon fine particles.

[0005] Patent Document 3 discloses a method of producing silicon nanoparticles by reducing a reverse micelle structure of a silicon compound mixed with a compound as a silicon raw material and an alcohol with a reducing material. However, the silicon nanoparticles obtained in Experiment No. 9 emit fluorescence in the ultraviolet wavelength region of 300 nm to 350 nm, not in the visible light wavelength region. Therefore, the range of industrial application thereof is narrow, and it cannot be applied to the fields of illumination and displays.

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

[0065] to

[0067] describe that the reaction temperature is limited to 0°C or lower in order to suppress side reactions and the like. However, it is not described whether the produced silicon nanoparticles are single crystals and spherical. In addition, since it is a production method under a closed condition in a flask, the production of silicon nanoparticles is performed in an atmosphere in which the silicon nanoparticles produced by the reaction coexist with the reaction materials, and thus there is a possibility of side reactions of the silicon nanoparticles with the reaction materials. In Example 1, a reducing solution is prepared by adding a tetrahydrofuran (THF) solution of DBB (4,4'-di-tert-butylbiphenyl) to metallic lithium, stirring at room temperature for 2 to 4 hours, adding silicon tetrachloride at -60°C at once to make it react, producing silicon nanoparticles capped with chlorine, and performing surface stabilization treatment with hexylmagnesium bromide to produce silicon nanoparticles capped with an alkyl group. However, as described in Comparative Example 1 of the present application, the silicon nanoparticles capped with an alkyl group of Example 1 of Patent Document 4 are polycrystals, not single crystals and spherical.

[0007] Patent Document 5 proposed by the applicant of the present application discloses a method of producing silicon nanoparticles by using a fluid processing device having a processing surface capable of approaching / separating and relatively rotating. In addition, it is described that the produced silicon nanoparticles can produce fluorescence from blue to near infrared depending on the production temperature. However, it is not disclosed that the silicon nanoparticles are single crystals and spherical. The silicon nanoparticles produced in Examples 6 to 9 are produced by reacting with hexylmagnesium bromide to produce silicon nanoparticles capped with an alkyl (hexyl) group. It is disclosed that the purity of chlorine and oxygen is not detected in the silicon nanoparticles. In addition, as described in Comparative Example 1 of the present application, the silicon nanoparticles capped with an alkyl group of Example 6 of Patent Document 5 are polycrystals, not single crystals and spherical. It is disclosed in Examples 10 to 13 that the silicon nanoparticles can be produced by a reverse micelle method using a surfactant, but the loss of the recovery amount of the silicon nanoparticles becomes a problem as the surfactant is removed by washing. Furthermore, in Examples 14 to 17, since both of the first fluid and the second fluid supplied to the fluid processing device use aqueous solutions, the production rate of the silicon nanoparticles becomes a problem.

[0008] In Patent Literature 6, a method of producing semiconductor fine particles having a core-shell structure by performing a reaction in a flow path of 1 mm or less in width called micro-chemical process is disclosed. Specifically, by performing a reaction in a micro-flow path in a micro-reactor, the mixing speed, efficiency, concentration and temperature uniformity under the reaction conditions in the flow path, and the like are improved, and the uniformization of particle size and the singling of reaction products can be performed effectively and efficiently. However, since there is a high possibility that the flow path is closed due to clogging of the flow path by silicon nanoparticles or by-products generated by a reduction reaction, or since the reaction is performed by molecular diffusion alone, it cannot be adapted to all reactions. In addition, for the micro-chemical process, there are problems that although a scale-up method using numbering-up of small reactors arranged in parallel is used, the production capacity of one reactor is small, large scale-up is not realistic, it is difficult to make the performance of each reactor uniform, and uniform products cannot be obtained. Furthermore, for a reaction liquid having a high viscosity or a reaction accompanied by an increase in viscosity, there are problems that a very high pressure is required to circulate a small flow path, the usable pumps are limited, or leakage from the device cannot be solved due to exposure to high pressure.

[0009] Prior Art Documents

[0010] Patent Literature

[0011] Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2014-172766

[0012] Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 2017-081770

[0013] Patent Literature 3: Japanese Patent Application Laid-Open (JP-A) No. 2010-205686

[0014] Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 2007-012702

[0015] Patent Literature 5: Japanese Patent No. 4458202

[0016] Patent Literature 6: Japanese Patent Application Laid-Open (JP-A) No. 2007-197382 SUMMARY

[0017] PROBLEMS TO BE SOLVED BY THE INVENTION

[0018] The present application relates to a method of producing silicon nanoparticles that can produce fluorescence from blue to orange with high fluorescence quantum efficiency by excitation with light of a wide wavelength from deep ultraviolet light of 200 nm to 300 nm to visible light, and can be densely filled as electrode materials for solar cells and secondary ion batteries.

[0019] Means for solving the problem

[0020] The present inventors have conducted intensive studies to solve the above problem, and as a result, have found that single-crystal, spherical, single-crystal spherical silicon nanoparticles having an average particle diameter of 1 nm to 20 nm can produce fluorescence with high fluorescence quantum efficiency by excitation from deep ultraviolet light to visible light of a wide wavelength range, and can be densely filled in electrode materials for solar cells and secondary ion batteries, and the like, because they are single crystals that do not have grain boundaries that reduce fluorescence efficiency, thereby completing the present invention.

[0021] That is, the present invention is as follows.

[0022] [1] A method for producing single-crystal, spherical silicon nanoparticles, wherein the single-crystal, spherical silicon nanoparticles have an average particle diameter of 1 nm to 20 nm,

[0023] The production method includes a step of mixing and reacting a raw material liquid and a reducing liquid, wherein the raw material liquid contains silicon halide, and the reducing liquid contains an anion of a condensed aromatic compound generated from lithium, sodium, or potassium and the condensed aromatic compound.

[0024] The anion of the condensed aromatic compound is prepared by mixing lithium, sodium, or potassium and a condensed aromatic compound at lower than 0°C.

[0025] [2] The production method according to [1], wherein the raw material liquid and the reducing liquid are mixed and reacted in a thin film fluid formed between treatment surfaces that are disposed to be able to approach and depart from each other and that are relatively rotated at least one of which with respect to the other.

[0026] [3] The production method according to [2], wherein the raw material liquid and the reducing liquid are mixed and reacted using a device,

[0027] The device has a fluid pressure application mechanism that applies pressure to a treated fluid, at least two treatment sections of a first treatment section and a second treatment section that is able to approach and depart from the first treatment section in a relative manner, and a rotation drive mechanism that relatively rotates the first treatment section and the second treatment section,

[0028] The device is configured as follows:

[0029] At least two treatment surfaces of a first treatment surface and a second treatment surface are disposed at positions that face each other in the respective treatment sections, the respective treatment surfaces constitute a part of a sealed flow path through which the treated fluid flows at the pressure, at least one of the two treatment surfaces is caused to mix and react two or more treated fluids that contain reactants therebetween, and

[0030] In the first processing portion and the second processing portion, at least the second processing portion has a pressure receiving surface, at least a part of which is constituted by the second processing surface, and the pressure receiving surface receives the pressure of the fluid pressure imparting mechanism imparting the pressure of the processing fluid to generate a force that moves the second processing surface in a direction away from the first processing surface, so that the processing fluid of the pressure passes between the first processing surface and the second processing surface that can approach / away and relatively rotate, thereby the processing fluid forms a thin film fluid, and further has another introduction path independent of a flow path between the processing surfaces through which the processing fluid of the pressure flows, and at least one opening portion on at least one of the first processing surface and the second processing surface communicates with the other introduction path, and at least one processing fluid introduced from the other introduction path is introduced between the two processing surfaces, and at least one of the reactants included in the processing fluid and a processing fluid different from the processing fluid are mixed in the thin film fluid.

[0031] [4] The production method according to [3], wherein the opening portion is provided at a position on a downstream side of a point at which the flow of the processing fluid between the two processing surfaces becomes laminar flow.

[0032] [5] The production method according to any one of [1] to [4], wherein the reducing liquid is set to 5°C or lower, and the raw material liquid is mixed and reacted with the reducing liquid.

[0033] [6] The production method according to any one of [1] to [5], wherein the molar ratio of the lithium, sodium or potassium to the silicon halide is 7:1 to 4:1.

[0034] [7] The production method 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.

[0035] [8] The production method according to any one of [1] to [7], wherein the solvent contained in the reducing liquid is tetrahydrofuran and / or dimethoxyethane in which the residual moisture is 10 ppm or less.

[0036] [9] The production method according to any one of [1] to [7], wherein the solvent contained in the reducing liquid is tetrahydrofuran containing a phenol-based polymerization inhibitor, and in which the residual moisture is 10 ppm or less and the residual oxygen concentration is less than 0.1 ppm.

[0037]

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

[0038]

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

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

[0039]

[12] The production method according to any one of [1] to

[11] , wherein the single-crystal spherical silicon nanoparticles are such that, using the perimeter Z and the area S of a projection image of the single-crystal spherical silicon nanoparticles observed by transmission electron microscopy, the circularity is calculated from the formula: 4πS / Z 2 The average of the calculated circularity is 0.9 or more.

[0040]

[13] The production method according to any one of [1] to

[12] , wherein the single-crystal spherical silicon nanoparticles exhibit, in an IR absorption spectrum, an absorption attributed to Si-H bond in a wave number region of 1950 cm -1 to 2150 cm -1 .

[0041]

[14] The production method according to any one of [1] to

[13] , wherein the single-crystal spherical silicon nanoparticles are such that, in an IR absorption spectrum, the peak intensity of a maximum peak in a wave number range of 1000 cm -1 to 1200 cm -1 is set as A, the peak intensity of a maximum peak in a wave number range of 400 cm -1 to 500 cm -1 is set as B, and the calculated ratio: B / A is less than 0.2.

[0042]

[15] The production method according to any one of [1] to

[14] , wherein the single-crystal spherical silicon nanoparticles are such that, in an IR absorption spectrum, the peak intensity of a maximum peak in a wave number range of 1000 cm -1 to 1200 cm -1 is set as A, the peak intensity of a maximum peak in a wave number range of 530 cm -1 to 630 cm -1 is set as C, and the calculated ratio: C / A is less than 0.2.

[0043]

[16] The production method according to any one of [1] to

[15] , wherein the single-crystal spherical silicon nanoparticles exhibit a fluorescence maximum in a wavelength range of 400 nm to 600 nm.

[0044]

[17] The production method according to any one of [1] to

[16] , wherein the single-crystal spherical silicon nanoparticles exhibit a fluorescence maximum in a wavelength range of 400 nm to 600 nm by excitation with deep ultraviolet light having a wavelength of 300 nm or less.

[0045] Effects of the Invention

[0046] The single-crystal spherical silicon nanoparticles manufactured by the 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 by being excited by a wide range of wavelengths of light, from deep ultraviolet light (200 nm to 300 nm) to visible light, increasing the fluorescence quantum efficiency of known silicon nanoparticles from about 1% to over 10%. Furthermore, the single-crystal spherical silicon nanoparticles manufactured by the method of the present invention are non-toxic to biological materials, unlike compound semiconductors formed from cadmium, selenium, or tellurium. Moreover, because the single-crystal spherical silicon nanoparticles manufactured by the method of the present invention are spherical, they can be densely packed into 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 (adhesive materials) for semiconductor devices to substrates. Attached Figure Description

[0047] Figure 1 TEM images showing the single-crystal spherical silicon nanoparticles of Example 1-1.

[0048] Figure 2 STEM images showing the single-crystal spherical silicon nanoparticles of Examples 1-4.

[0049] Figure 3 These are the electron diffraction patterns of the single-crystal spherical silicon nanoparticles from Examples 1-4.

[0050] Figure 4 The wavenumber of the single-crystal spherical silicon nanoparticles in Examples 1-2 is 1800 cm⁻¹. -1 ~2300cm -1 The IR spectrum.

[0051] Figure 5a The wavenumber of the single-crystal spherical silicon nanoparticles in Examples 1-4 is 900 cm⁻¹. -1 ~1300cm -1 The IR spectrum. The vertical axis represents the 900cm... -1 ~1300cm -1 The peak intensity of the maximum peak within the wavenumber range is set to 1.0, and the normalized absorbance is set to 1.0.

[0052] Figure 5b The wavenumber of the single-crystal spherical silicon nanoparticles in Examples 1-4 is 400 cm⁻¹. -1 ~550cm -1 The IR spectrum.

[0053] Figure 5c The wavenumber of the single-crystal spherical silicon nanoparticles in Examples 1-4 is 450 cm⁻¹. -1 ~650cm -1 The IR spectrum.

[0054] Figure 5d The wave number of 550 cm -1 ~ 700 cm -1 of the IR spectrum of the single crystal spherical silicon nanoparticles of Example 1-4.

[0055] Figure 6 The results of setting the maximum intensity to 1.0 in the normalized fluorescence spectrum of the single crystal spherical silicon nanoparticles of Example 1-3 and changing the excitation wavelength every 40 nm from 340 nm to 500 nm are shown.

[0056] Figure 7 The excitation wavelength dependence of the fluorescence peak wavelength of the single crystal spherical silicon nanoparticles of Example 1-4 is shown.

[0057] Figure 8 The results of measuring the particle diameter and fluorescence peak wavelength of the single crystal spherical silicon nanoparticles of Example 1-1 to Example 1-4 with respect to the rotation speed of the disk are shown.

[0058] Figure 9 The fluorescence spectrum of the excitation light of deep ultraviolet rays of the single crystal spherical silicon nanoparticles of Example 1-2 is shown.

[0059] Figure 10 The STEM observation image of the polycrystal silicon nanoparticles of Comparative Example 1-1 is shown.

[0060] Figure 11 The IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 at a wave number of 900 cm -1 ~ 1300 cm -1 .

[0061] Figure 12a The IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 at a wave number of 900 cm -1 ~ 1300 cm -1 . The vertical axis shows the absorbance normalized by setting the peak intensity of the maximum peak in the wave number range of 900 cm -1 ~ 1300 cm -1 to 1.0.

[0062] Figure 12b The IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 at a wave number of 400 cm -1 ~ 550 cm -1 .

[0063] Figure 12c The IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 at a wave number of 450 cm -1 ~ 650 cm -1 .

[0064] Figure 12d This indicates that the wavenumber of the polycrystalline silicon nanoparticles in Comparative Example 1-1 is 550 cm⁻¹. -1 ~700cm -1 The IR spectrum.

[0065] Figure 13a The fluorescence spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1 with a deep ultraviolet excitation wavelength of 220 nm is shown.

[0066] Figure 13b The fluorescence spectrum of the polycrystalline silicon nanoparticles of Comparative Example 1-1 with a deep ultraviolet excitation wavelength of 260 nm is shown. Detailed Implementation

[0067] The following describes embodiments of the present invention. However, the present invention is not limited to the embodiments described below. Furthermore, although examples of applications to fluorescent materials have been exemplified, the uses of the single-crystal spherical silicon nanoparticles of the present invention are not limited thereto.

[0068] 1. Single-crystal spherical silicon nanoparticles

[0069] The single-crystal spherical silicon nanoparticles of the present invention are single crystals, spherical, and have an average particle size of 1 nm to 20 nm.

[0070] For single-crystal spherical silicon nanoparticles, it is preferable to use the perimeter (Z) and area (S) of the projected image of the single-crystal spherical silicon nanoparticles observed by transmission electron microscopy, expressed as: 4πS / Z 2 The calculated average value of roundness is 0.9 or higher, more preferably 0.92 or higher, and even more preferably 0.95 or higher.

[0071] The average particle size 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.

[0072] Single-crystal spherical silicon nanoparticles preferably have Si-H bonds on their surface. If there are sites on the surface of single-crystal spherical silicon nanoparticles where silicon atomic bonds are broken, the nanoparticles are unstable and may sometimes generate new energy levels in the band gap, affecting the fluorescence wavelength. Therefore, by having Si-H bonds formed by the bonded silicon atoms and hydrogen atoms, the nanoparticles are stabilized, reducing the impact on the fluorescence wavelength. Therefore, single-crystal spherical silicon nanoparticles are preferably characterized by a 1950 cm⁻¹ band at which the stretching vibrations attributable to Si-H bonds are present in the IR absorption spectrum. -1 ~2150cm -1 Absorption exists in the wavenumber region. The single-crystal spherical silicon nanoparticles of Examples 1-2, such as... Figure 4 As shown, at 2105cm -1 An absorption peak is present at this location.

[0073] Single-crystal spherical silicon nanoparticles are preferably those with low dissolved oxygen content. Specifically, for example, in the IR absorption spectrum, 1000 cm⁻¹... -1 ~1200cm -1 Let A be the peak intensity of the maxima within the wavenumber range, and let 400 cm⁻¹ be the peak intensity. -1 ~500cm -1 The peak intensity of the maximum peak within the wavenumber range is defined as B, 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... Figure 5a and 5b As shown, 1095cm -1 Let the peak intensity at the maximum point be A, and let 460cm be the maximum peak intensity. -1 The peak intensity of the maximum peak at the location is set as B, as shown in Table 3. The ratio B / A is 0.08 to 0.10, which is less than 0.2.

[0074] Single-crystal spherical silicon nanoparticles are preferably those with fewer Si-Cl bonds. Specifically, for example, in the IR absorption spectrum, 1000 cm⁻¹... -1 ~1200cm -1 Let A be the peak intensity of the maxima within the wavenumber range, and let 530 cm⁻¹ be the peak intensity. -1 ~630cm -1 The peak intensity of the maximum peak within the wavenumber range is set as C, 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, such as... Figure 5a and 5c As shown, 1095cm -1 Let the peak intensity at the maximum peak be A, and let 612 cm⁻¹ be the value of the peak. -1 The peak intensity of the maximum peak at the location is set as C, as shown in Table 3. The ratio C / A is 0.06 to 0.08, which is less than 0.2.

[0075] The fluorescence of silicon nanoparticles is known to be generated by the following three different mechanisms.

[0076] (A) Fluorescence color can be controlled by adjusting physical factors such as the band gap that causes changes in electron energy, based on the particle size of silicon nanoparticles (as a quantum effect is known).

[0077] (B) By treating the surface of silicon nanoparticles with various chemicals, the fluorescence color mediated by surface substituents can be controlled in a state in which the surface of silicon nanoparticles is chemically bonded to various substituents such as alkyl or amino with different molecular chain lengths.

[0078] (C) Fluorescence color is controlled by utilizing the compositional changes caused by oxygen and nitrogen contained in silicon nanoparticles, i.e., by using chemical factors.

[0079] The single crystal spherical silicon nano-particles obtained by the production method of the present application generate fluorescence in the wavelength range of 400 nm to 600 nm by the synergistic effect of the (A) quantum effect mechanism and the (C) oxygen-mediated mechanism among the above-mentioned three mechanisms of (A) to (C). This is different from the mechanism of the alkyl-terminated silicon nano-particles of Patent Literature 4 and Patent Literature 5 which adopt the (A) quantum effect mechanism and the (B) surface modification mechanism.

[0080] The single crystal spherical silicon nano-particles obtained by the production method of the present application preferably generate fluorescence extremely in the wavelength range of 400 nm to 600 nm. More preferably, fluorescence extremely in the wavelength range of 400 nm to 600 nm is generated by deep ultraviolet light having a wavelength of 300 nm or less as excitation light.

[0081] 2. Method for producing single-crystal spherical silicon nanoparticles

[0082] The production method of the present application is a production method of single crystal, spherical, single crystal spherical silicon nano-particles having an average particle diameter of 1 nm to 20 nm, the production method comprising a step of mixing and reacting a raw material liquid and a reducing liquid, wherein the raw material liquid contains halogenated silicon, the reducing liquid contains an anion of a condensed aromatic compound generated from lithium, sodium or potassium and the condensed aromatic compound, and the anion of the condensed aromatic compound is prepared by mixing lithium, sodium or potassium and the condensed aromatic compound at lower than 0°C.

[0083] (Raw material liquid of single crystal spherical silicon nano-particles)

[0084] The halogenated silicon contained in the raw material liquid of the single crystal spherical silicon nano-particles can be, for example, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide or the like, and preferably can be silicon tetrachloride, silicon tetrabromide or the like.

[0085] As the solvent contained in the raw material liquid of the single crystal spherical silicon nano-particles, there is no particular limitation as long as it is a non-reactive substance which does not affect the reduction reaction and enables the precipitation of the single crystal spherical silicon nano-particles by the reduction of the halogenated silicon. As the solvent, preferably can be ethers and the like, and more preferably can be tetrahydrofuran (THF), diethyl ether, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, polyethylene glycol dimethyl ether, or a mixture thereof or the like, and more preferably can be THF, DME or the like. As the preferred solvent, can be tetrahydrofuran or the like having a residual moisture content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm. The halogenated silicon contained in the raw material liquid of the single crystal spherical silicon nano-particles can be, for example, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide or the like, and preferably can be silicon tetrachloride, silicon tetrabromide or the like.

[0086] When THF is used as the solvent, since the ring-opening polymerization of THF is initiated by a Lewis acid as an electrophilic reagent, there is a possibility that a polymer of THF is generated during the storage of the THF solution of the halogenated silicon. However, by adding 2,6-di-tert-butyl-4-methylphenol (BHT) which suppresses the generation of peroxide of THF in the raw material solution, the polymerization of THF can be suppressed. Therefore, it is preferable to add BHT in the THF solvent.

[0087] The concentration of the halogenated silicon in the single crystal spherical silicon nanoparticle raw material solution is not particularly limited, and for example, 0.01 to 1 mol / L can be mentioned, preferably 0.02 to 0.5 mol / L can be mentioned, and more preferably 0.05 to 0.2 mol / L can be mentioned.

[0088] (Reduction solution of single crystal spherical silicon nanoparticles)

[0089] The reduction solution of single crystal spherical silicon nanoparticles used in the present application is a reduction solution containing an anion of a fused aromatic compound generated from lithium, sodium or potassium and the fused aromatic compound, which is prepared by mixing lithium, sodium or potassium and a fused aromatic compound at lower than 0°C. The electrochemical equilibrium potential of lithium, sodium and potassium is very low because of the very low low potential, and therefore, theoretically, it is possible to reduce halogenated silicon by using any one of these metals alone or using a mixture of these metals. However, lithium, sodium or potassium cannot be dissolved in an organic solvent such as an ether. In order to dissolve lithium, sodium or potassium in an organic solvent such as an ether, it is necessary to coexist with a fused aromatic compound, and to move one electron generated while lithium, sodium or potassium becomes an alkali metal ion to the lowest unoccupied orbital (LUMO) of the fused aromatic compound to generate an anion (radical anion) of the fused aromatic compound.

[0090] As the fused aromatic compound used in the present application, a fused aromatic compound which can move one electron from lithium, sodium or potassium to generate an alkali metal ion and a fused aromatic compound anion (radical anion) can be mentioned. In order to reduce halogenated silicon to silicon, the potential of the anion of the fused aromatic compound must be a low potential of lower than -2.0 V. Here, the potential refers to the value with respect to silver (Ag) / silver chloride (AgCl) as a reference electrode (reference electrode). As the fused aromatic compound having a potential of lower than -2.0 V, for example, naphthalene (-2.53 V), DBB (-2.87 V), diphenyl (-2.68 V), 1,2-dihydronaphthalene (-2.57 V), phenanthrene (-2.49 V), anthracene (-2.04 V), pyrene (-2.13 V), or a mixture thereof, etc. can be mentioned, and preferably naphthalene, diphenyl, etc. can be mentioned. On the other hand, naphthacene (-1.55 V), azulene (-1.62 V) are not suitable for the reduction of halogenated silicon.

[0091] The solvent contained in the reducing solution for single-crystal spherical silicon nanoparticles is not particularly limited, as long as it is an inactive substance capable of reducing silicon halide to precipitate single-crystal spherical silicon nanoparticles without affecting the reduction reaction. Examples of preferred solvents include ethers, and more preferably tetrahydrofuran (THF), dihydrofuran, etc. Alkane, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl ether, polyethylene glycol dimethyl ether, or mixtures thereof, and more preferably, THF, DME, etc. Tetrahydrofuran and dimethoxyethane with a residual moisture content of 10 ppm or less are preferred examples, and tetrahydrofuran containing a phenolic polymerization inhibitor, with a residual moisture content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm are more preferred examples.

[0092] The concentration of lithium, sodium, or potassium in the reducing solution for single-crystal spherical silicon nanoparticles is not particularly limited, but is determined based on the molar ratio of lithium, sodium, or potassium to silicon halide.

[0093] The molar ratio of lithium, sodium or potassium to the fused aromatic compound can be, for example, 1:1 to 1.5:1, preferably 1:1 to 1.2:1, and more preferably 1:1 to 1.1:1.

[0094] The molar ratio of lithium, sodium, or potassium to silicon halide can be, 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 an excess of lithium, sodium, or potassium compared to the raw material for monocrystalline spherical silicon nanoparticles. By using an excess, monocrystalline spherical silicon nanoparticles with less residual halogen can be produced. When using a smaller amount of lithium, sodium, or potassium than the raw material for monocrystalline spherical silicon nanoparticles, for example, using 3 / 4 of the amount as shown in Comparative Example 1, halogen atoms from silicon halide remain in the monocrystalline spherical silicon nanoparticles because they are not completely reduced, resulting in polycrystalline structures that are not spherical.

[0095] (Low-temperature conditioning of the reducing solution)

[0096] In this invention, lithium, sodium, or potassium is mixed with a fused aromatic compound at a temperature below 0°C to prepare a reducing solution for single-crystal spherical silicon nanoparticles. Examples of suitable solutions temperature include -50°C to below 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, when the dissolution temperature is above 0°C, the following problem arises: the anions of the fused aromatic compound become unstable, leading to a chemical reaction between the fused aromatic compound and alkali metal atoms, resulting in impaired reducing effectiveness. For example, when naphthalene (molecular formula: C...) is used as the fused aromatic compound... 10 When H8 and potassium (K) are produced, C is generated. 10The concentration of the naphthalene anion, which functions as a reducing agent, tends to change in the case of a compound such as H7K, and this becomes a problem. In Example 1 of Patent Literature 4 and Examples 6 to 9 of Patent Literature 5, a reducing solution is prepared at room temperature. In Comparative Example 1 of the present application specification, Example 6 of Patent Literature 5 was additionally tested, and a reducing agent became unstable and a by-product was generated when prepared at 15 to 16°C (room temperature), and the single-crystal spherical silicon nanoparticles became polycrystalline and were not spherical.

[0097] (Solvent molecule-mediated alkali metal cation and fused aromatic compound anion)

[0098] The fused aromatic compound anion (radical anion) generated by the transfer of an electron from lithium, sodium or potassium to a fused aromatic compound can be combined with the cation of lithium, sodium or potassium generated by the transfer of an electron by Coulomb force. At this time, the electron can also move in reverse from the temporarily generated fused aromatic compound anion to the cation of lithium, sodium or potassium to cause a change in the reducing power. The change in the reducing power affects the particle size distribution of the obtained single-crystal spherical silicon nanoparticles, and therefore in order to suppress the change in the reducing power caused by reverse electron movement, the cation of lithium, sodium or potassium and the fused aromatic compound anion can be combined in a state produced by solvent molecule-mediated Coulomb force. The state of the anion and the cation in such a solution is known to be able to be confirmed by measurement of ultraviolet-visible absorption spectroscopy. According to this, for example, in the combination of lithium and naphthalene dissolved in THF, the THF-mediated state is 60 to 80% at 25°C. It is known that in the combination of metallic sodium and naphthalene dissolved in THF, there is almost no direct sodium cation and naphthalene anion of THF, and the state in which the sodium cation and the naphthalene anion are directly combined by Coulomb force, but by cooling to -50°C, THF can almost completely mediate.

[0099] (Solvation in low-temperature adjustment of solution)

[0100] In order to allow the solvent to intervene, this can be achieved by setting the temperature of the solvent to a low temperature. By the so-called intervention of the solvent, it means that the solvated cation in which the cation of lithium, sodium or potassium and the anion of the condensed aromatic compound are each surrounded by solvent molecules, and the solvated anion in which the cation and the anion that are solvated with each other are combined with each other by a coulomb force. Due to such intervention of the solvent, a state in which the cation and the anion are in contact within the solution is generated, and thus the anion of the condensed aromatic compound can be stably present, and the reverse electron movement from the anion of the condensed aromatic compound to the alkali metal cation can be suppressed. For a reduced solution prepared in a state in which the solvation does not sufficiently proceed at a temperature of 0°C or higher or in a state in which the distribution is generated in the solvated state, even if the temperature is low at the time of manufacturing the silicon nanoparticles, the solvation cannot be completely performed, and thus a fluctuation in the reduction force is generated, resulting in the generation of a particle size distribution of the silicon nanoparticles within the solution. For a state in which the ions are directly combined by the coulomb force to become an equilibrium state, even if the temperature is cooled to a low temperature at the time of manufacturing the silicon nanoparticles, the solvent molecules are difficult to intrude between the cation and the anion by overcoming the coulomb force. Therefore, the temperature at the time of preparing the solution is more important than the temperature at the time of manufacturing the silicon nanoparticles.

[0101] In addition to the necessity of preparing the reduced solution at a low temperature as described from the viewpoint of the solvation, the storage temperature after the preparation of the solution must also be set to a low temperature. This is because, when the storage temperature of the reduced solution becomes high, in the case where the solvent is THF, a reduction polymerization reaction of THF is generated by the anion of the condensed aromatic compound. Such a polymer generated by the polymerization of THF is mixed in the single crystal spherical silicon nanoparticles generated by the reduction of the halogenated silicon, and thus it is necessary to suppress the polymerization reaction. As a polymerization reaction inhibitor of THF, BHT (2,6-di-tert-butyl-4-methylphenol) added in order to suppress the generation of peroxide of THF can be used.

[0102] (Method for manufacturing single crystal spherical silicon nanoparticles: apparatus)

[0103] In the production method of the present application, for example, the device described in Japanese Patent Application Publication No. 2009-112892 by the applicant of the present application can be used. The device has a stirring tank having an inner peripheral surface with a circular cross-sectional shape and an agitator attached with a slight gap to the inner peripheral surface of the stirring tank, at least two fluid inlets and at least one fluid outlet in the stirring tank, a first treated fluid containing one of the reactants among the treated fluids is introduced into the stirring tank from one of the fluid inlets, and a second treated fluid containing one of the reactants different from the above-mentioned reactant is introduced into the stirring tank from a flow path different from the above-mentioned first treated fluid from the other of the fluid inlets. By high-speed rotation of at least one of the stirring tank and the agitator relative to the other, the treated fluids become in a thin film state, and at least the reactants contained in the above-mentioned first treated fluid and the second treated fluid react with each other in the thin film. In addition, a device of the same principle as the fluid treatment device described in Patent Document 5 can be cited.

[0104] (Method for producing single crystal spherical silicon nanoparticles: outline of the method)

[0105] In the production method of the present application, single crystal spherical silicon nanoparticles are produced by mixing a solution state of a reducing solution of single crystal spherical silicon nanoparticles at 5°C or lower with a raw material solution of single crystal spherical silicon nanoparticles. Single crystal spherical silicon nanoparticles can be produced by the steps of first generating a core of single crystal spherical silicon nanoparticles and then growing the single crystal spherical silicon nanoparticles. Even if the raw material solution is brought into contact with the reducing solution at 5°C or lower to start the reaction, since the frequency of generation of the core of single crystal spherical silicon nanoparticles that grows is low, the frequency of contact of the cores of single crystal spherical silicon nanoparticles with each other is also low. Therefore, in the growth of single crystal spherical silicon nanoparticles, the influence of the change in the concentration of the raw material solution caused by the growth of the surrounding single crystal spherical silicon nanoparticles is less likely to be received, and the supply of the raw material silicon halide required for the growth of single crystal spherical silicon nanoparticles becomes uniform.

[0106] (Inhibition of generation of polycrystal silicon nanoparticles)

[0107] By using a flow reactor that can rapidly discharge the product from the reaction solution, a polyvalent silicon radical in which a silicon atom becomes in a radical state by the halogen atom, which is an intermediate in the reduction of the silicon halide, detaching, is not generated, and thus one of the factors that can inhibit the generation of polycrystal silicon nanoparticles can be provided.

[0108] (Inorganic by-products in the reduction reaction of single crystal spherical silicon nanoparticles)

[0109] The reduction reaction by-product generated in the production of the single crystal spherical silicon nano-particles is a lithium, sodium or potassium halide composed of a halogen ion separated from the silicon halide and a lithium, sodium or potassium cation. In an ether-based organic solvent, they are dissolved as ions, respectively, but in the case of separation of the single crystal spherical silicon nano-particles, for example, in the case of using lithium, the solubility of lithium chloride in the ether-based organic solvent is greater than that of sodium chloride and potassium chloride, ionizes into lithium ions and chloride ions, and thus has the advantage of being easily separated from the single crystal spherical silicon nano-particles by centrifugal separation. That is, although an alkali metal element other than lithium can be used for the production of the single crystal spherical silicon nano-particles, the solubility of the halide of the alkali metal element as a reaction by-product, that is, the salt, in the ether-based organic solvent is lower than that of lithium chloride and is mixed into the single crystal spherical silicon nano-particles, and thus it is difficult to separate by centrifugal separation. Therefore, from the viewpoint of separation of such a reduction reaction by-product from the single crystal spherical silicon nano-particles, it is preferable to use lithium.

[0110] (Organic by-product in reduction reaction of single crystal spherical silicon nano-particles)

[0111] In the reduction reaction of silicon halide using the fused aromatic compound anion, for example, the silicon atom from which the chlorine atom of silicon tetrachloride has been separated becomes a radical state, and thus the reactivity is very high, and by bonding in the radical state with an adjacent silicon atom, single crystal spherical silicon nano-particles can be produced. At the same time, by the reaction with the fused aromatic compound, a compound in which silicon is bonded to the fused aromatic compound is also generated. Once the fused aromatic compound is bonded to the silicon atom, it is not easily reduced for the fused aromatic compound anion, and a by-product other than the single crystal spherical silicon nano-particles is generated. That is, a part of the silicon halide is bonded to the fused aromatic compound to generate a stable halogenated alkyl silicon. In this compound, the site of silicon bonded to the halogen atom not bonded to the alkyl group can become a silicon radical in the reduction liquid, and thus the halogen of this halogenated alkyl silicon is continuously separated by the reducing agent to generate an alkyl polysilane in which silicon radicals are bonded to each other. The generation of the polysilane results in a loss because it is heavier than the silicon nano-particles and precipitates. It is necessary to control the temperature of the reduction liquid to be 5°C or lower so that the reaction temperature does not reach a temperature at which a loss reaction caused by such an organic by-product occurs.

[0112] Accordingly, by performing the supply of the raw material having a narrow particle size distribution and isotropy, it is possible to produce spherical single crystal silicon nanoparticles (hereinafter referred to as single crystal spherical silicon nanoparticles). In the case where the reaction temperature is high, the frequency of generation of the core of the single crystal spherical silicon nanoparticles becomes high, but since a plurality of other cores of the single crystal spherical silicon nanoparticles exist around the core of the single crystal spherical silicon nanoparticles, it is difficult to uniformly supply the silicon halide required for growth, and it is only possible to produce in a state where the shape of the single crystal spherical silicon nanoparticles has a distribution. Therefore, in the production method of the present application, by setting the temperature of the reducing liquid to 5°C or lower, the frequency of generation of the core of the single crystal spherical silicon nanoparticles is suppressed, and by controlling so that the raw material liquid is uniformly supplied to the core of the single crystal spherical silicon nanoparticles, it is possible to produce single crystal spherical silicon nanoparticles having a narrow particle size distribution.

[0113] It is preferable to produce the single crystal spherical silicon nanoparticles by mixing the raw material liquid with the reducing liquid having a temperature of 5°C or lower in the thin film liquid. The single crystal spherical silicon nanoparticles can be produced by the steps of first generating the core of the single crystal spherical silicon nanoparticles and then growing the single crystal spherical silicon nanoparticles. Even if the raw material liquid is brought into contact with the reducing liquid having a temperature of 5°C or lower to start the reaction, since the frequency of generation of the core of the single crystal spherical silicon nanoparticles becomes low, the frequency of contact of the cores of the single crystal spherical silicon nanoparticles with each other also decreases. Therefore, in the growth of the single crystal spherical silicon nanoparticles, it is less likely to be affected by the change in the concentration of the raw material liquid caused by the growth of the surrounding single crystal spherical silicon nanoparticles, and the supply of the raw material required for the growth of the single crystal spherical silicon nanoparticles becomes uniform.

[0114] As the temperature of the raw material liquid introduced in the thin film liquid formed between the oppositely disposed approachable / avoidable, two processing surfaces which relatively rotate with respect to each other, for example, -30°C to 5°C can be cited, preferably -10°C to 5°C can be cited, and more preferably 0°C to 5°C can be cited. In Examples 1 and 2, as a result of production in which the temperature of the raw material liquid was set to 5°C, it was possible to produce single crystal, spherical, single crystal spherical silicon nanoparticles which emit fluorescence with a high fluorescence quantum efficiency. In Comparative Example 4, as a result of production in which the temperature of the raw material liquid was set to 25°C, the fluorescence quantum efficiency was low.

[0115] In the paragraphs

[0065] to

[0067] of Patent Literature 4, in order to suppress side reactions and the like, the reaction temperature is emphasized to be limited to 0°C or lower, and in the examples, the reaction is performed at a very low temperature of -60°C. In Examples 6 to 9 of Patent Literature 5, the reaction is also performed at a very low temperature of -50°C to -90°C. In contrast, in the present application, even at a reaction temperature of 5°C or higher, which is hindered by Patent Literature 4, very satisfactory single-crystal spherical silicon nanoparticles, i.e., having a remarkable effect, can be obtained. This remarkable effect is an effect that cannot be anticipated by those skilled in the art based on Patent Literature 4 and Patent Literature 5.

[0116] As the temperature of the raw material liquid introduced in the thin film fluid formed between the two processing surfaces that are relatively disposed to be approachable / remote from each other and relatively rotate with respect to each other, for example, -10°C to 25°C can be cited, preferably 0°C to 20°C can be cited, and more preferably 10°C to 18°C can be cited. In Examples 1 and 2, the temperature of the raw material liquid was set to 15°C, and as a result of the production, single-crystal, spherical, single-crystal spherical silicon nanoparticles that emit fluorescence with a high fluorescence quantum yield can be produced.

[0117] (Fluorescence of silicon nanoparticles and production method)

[0118] As for the fluorescence from silicon nanoparticles, it is known that depending on the production method, (1) green fluorescence is obtained from ultraviolet light, and (2) green fluorescence is obtained from near-infrared light. (1) is obtained by producing silicon nanoparticles by laser irradiation in a liquid (laser ablation) and by producing silicon nanoparticles by reduction in a solution (by reduction of an electron of a silicon halide). (2) is obtained by methods such as electrochemical etching, pyrolysis of a silicon precursor, laser ablation in a vacuum or non-reactive gas, etching of Si / SiO2 nanostructure with hydrofluoric acid (HF), and the like.

[0119] (Presence of hydrogen in silicon nanoparticles)

[0120] In the production of silicon nanoparticles, the site at which the bond of a silicon atom is cut can be stabilized by Si-H bond in which a silicon atom and a hydrogen atom are bonded. In the production of single-crystal spherical silicon nanoparticles of the present application, it is also possible that the site at which the bond of a silicon atom is cut at random generates a new energy level in the band gap and affects the fluorescence wavelength, but by the Si-H bond, the influence thereof can be reduced.

[0121] According to a conventional method, single-crystal spherical silicon nanoparticles can be separated from the reaction liquid containing the produced single-crystal spherical silicon nanoparticles. For example, ultracentrifugal separation or the like can be performed.

[0122] 3. Use of single-crystal spherical silicon nanoparticles

[0123] The single crystal spherical silicon nanoparticles produced by the production method of the present application can be used, for example, as a light emitting element, a luminescent material that generates fluorescence, a negative electrode for a lithium ion battery, an electrode material for a solar cell, a bonding material (adhesive material) for a semiconductor device to a substrate, and the like.

[0124] Examples

[0125] The present application is further described below by way of examples, but the present application is not limited to these examples.

[0126] (Transmission Electron Microscope (TEM): Preparation of TEM observation sample)

[0127] The single crystal spherical silicon nanoparticles obtained in the examples and comparative examples were dispersed in THF at a concentration of about 0.001% in a container. The container containing the obtained dispersion liquid was introduced into a glove box in an argon atmosphere, and the dispersion liquid was dropped onto a carbon support film and dried to prepare a TEM observation sample.

[0128] (TEM observation)

[0129] The TEM observation of the single crystal spherical silicon nanoparticles was performed using a transmission electron microscope JEM-2100 (manufactured by JEOL Ltd.). As the sample, the TEM observation sample described above was used. The observation conditions were an acceleration voltage of 200 kV and an observation magnification of 10,000x or more. The particle diameter was calculated from the distance between the largest outer peripheries of the single crystal spherical silicon nanoparticles observed by TEM, and the average value (average particle diameter) of the single crystal spherical silicon nanoparticle diameter measurement results of 50 particles was calculated.

[0130] (Scanning Transmission Electron Microscope (STEM))

[0131] The STEM observation of the single crystal spherical silicon nanoparticles was performed using an atomic resolution analysis type electron microscope JEM-ARM200F (manufactured by JEOL Ltd.). As the sample, the TEM observation sample described above was used. The observation conditions were an acceleration voltage of 80 kV and an observation magnification of 50,000x or more, and analysis was performed using a beam diameter of 0.2 nm in diameter.

[0132] (Infrared (IR) absorption spectrum)

[0133] The IR absorption spectrum of the single crystal spherical silicon nanoparticles was measured using a Fourier transform infrared spectrophotometer FT / IR-6600 (manufactured by JASCO Corporation) by an attenuated total reflection (ATR) method. The measurement conditions were a resolution of 4.0 cm -1The total number of measurements was 128. A diamond prism (PKS-D1F) (wide area: refractive index 2.4) was assembled in the ATRPRO ONE accessory of the FT / IR-6600, with an incident angle of 45°. The infrared (IR) absorption spectra measured for the single-crystal spherical silicon nanoparticles fabricated in the examples and the polycrystalline silicon nanoparticles fabricated in the comparative examples are referred to as IR spectra.

[0134] (fluorescence spectrum)

[0135] The fluorescence spectra of single-crystal spherical silicon nanoparticles were measured using a spectrophotometer FT-6500 (manufactured by Nippon Spectrophotometer Co., Ltd.). As samples, the sample solution dispersed in THF or DME was placed in a quartz cell (optical path length: 1 cm) within an argon-atmospheric glove box. After sealing the top, the sample was removed from the glove box for measurement. The measurement conditions were: excitation bandwidth 3 nm, fluorescence bandwidth 3 nm, response 0.1 sec, scan 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.

[0136] (Waveform separation of fluorescence spectra)

[0137] In order to calculate the relative fluorescence quantum efficiency relative to 9,10-diphenylanthracene in the fluorescence spectra of the measured single-crystal spherical silicon nanoparticles, waveform separation was performed, and the area % of the fluorescence spectrum showing a peak at 430 nm was calculated. Waveform separation was performed using the waveform separation software built into the FT / IR-6600 used in IR absorption spectroscopy measurements.

[0138] (Relative fluorescence quantum efficiency)

[0139] The fluorescence quantum efficiency of a fluorescent material can be evaluated by the efficiency of fluorescence generated by excitation light. In this invention, the fluorescence quantum efficiency of single-crystal spherical silicon nanoparticles is calculated as a relative value to the fluorescence quantum efficiency of 9,10-diphenylanthracene, which is used as a reference material, and is set to 1.0. The relative fluorescence quantum efficiency is calculated using the following formula (1).

[0140] φ x =φ s (F x / F s (A) s / A x (I) s / I x )(n x 2 / n s 2 )……(1)

[0141] [In the formula, x indicates a single crystal spherical silicon nanoparticle. s indicates 9,10-diphenylanthracene. φ x is the relative fluorescence quantum efficiency of a single crystal spherical silicon nanoparticle. φ s is the quantum efficiency of 9,10-diphenylanthracene. F is the area of a fluorescence spectrum. A is the absorbance at the excitation wavelength. I is the intensity of excitation light.

[0142] n is the refractive index of the solvent used.

[0143] In the present application, for 9,10-diphenylanthracene and a single crystal spherical silicon nanoparticle as reference substances, the passband width of excitation light, the fluorescence passband width, the scanning speed, the data taking interval, and the measurement sensitivity as the measurement conditions of a spectrofluorophotometer for measuring fluorescence are all constant, and in addition, since the same solvent THF is used, the value of (I s / I x )(n x 2 / n s 2 ) is 1.0. Therefore, it is calculated from the area of the respective fluorescence spectra of the THF dispersion of a single crystal spherical silicon nanoparticle and the THF solution of 9,10-diphenylanthracene and the value of the absorbance at the time of measurement.

[0144] (ICP-OES measurement)

[0145] The concentrations of silicon and lithium in a single crystal spherical silicon nanoparticle were measured using ICP-OES (high-frequency inductively coupled plasma emission spectrometer ICPS-8100, manufactured by Shimadzu Corporation). The measurement conditions were that 4 mg of a single crystal spherical silicon nanoparticle was weighed, dissolved in hydrofluoric acid and nitric acid, and then made up to 25 mL in a volumetric flask, and lithium was quantified, and then the sample solution was diluted with pure water, and silicon was quantified. An atomic absorption analysis silicon standard solution (manufactured by Kanto Chemical Co., Inc.) and an atomic absorption analysis lithium standard solution (manufactured by Kanto Chemical Co., Inc.) were used to prepare a standard curve. The identification and quantification of lithium used a luminescence line of 670.784 nm, and the identification and quantification of silicon used a luminescence line of 251.611 nm.

[0146] (Ultraviolet-visible light: UV-vis absorption spectrum measurement)

[0147] The UV-vis (ultraviolet-visible) absorption spectrum of the single crystal spherical silicon nanoparticles was measured using an ultraviolet-visible near-infrared spectrophotometer (product name: V-770, manufactured by Shimadzu Corporation). The measurement conditions were as follows: the measurement range was 200 nm to 900 nm, the sampling rate was 0.2 nm, and the measurement speed was low. A liquid quartz cell having a thickness of 10 mm was used for the measurement. In order to calculate the relative fluorescence quantum efficiency of the single crystal spherical silicon nanoparticles, the absorbance at a wavelength of 300 nm to 400 nm was diluted with THF so as to be 0.05 or less, and the absorbance was measured. The absorbance of a THF solution of 9, 10-diphenylanthracene was measured under the same measurement conditions.

[0148] (roundness)

[0149] As an index for evaluating the sphericity of the single crystal spherical silicon nanoparticles, the roundness was calculated as follows. The roundness of the single crystal spherical silicon nanoparticles was calculated using TEM image software iTEM (manufactured by Olympus Soft Imaging Solutions GmbH) to approximate the image obtained by TEM observation to an ellipse. Next, based on the analysis results of the TEM image analysis software, the major axis (D), the circumference (Z), and the area (S) of the ellipse as the projected image of the single crystal spherical silicon nanoparticles were calculated. The value of the roundness was calculated using the values of the circumference (Z) and the area (S) as follows: 2 The value of the roundness is closer to 1, the closer the particle is to a spherical shape, and in the case where the particle shape is a perfect sphere, the roundness is maximized to 1.

[0150] In addition, the average value of the major axis (D) of the ellipse was calculated as the average particle diameter. The measurement was performed by calculating the values of 50 independent single crystal spherical silicon nanoparticles.

[0151] Example 1

[0152] In Example 1, a THF solution of silicon tetrachloride (SiCl4) (single crystal spherical silicon nanoparticle raw material solution) used as a raw material was reduced using a THF solution of naphthalene dissolved with lithium metal (single crystal spherical silicon nanoparticle reducing solution) to produce single crystal spherical silicon nanoparticles.

[0153] Table 1 shows the formulations for Examples 1-1 to 1-4. The solvent used in Example 1 was a super-dehydrated tetrahydrofuran (manufactured by Fujifilm and Koichi Chemical Co., Ltd.) with a residual water content of less than 10 ppm, containing 2,6-di-tert-butyl-4-methylphenol (BHT) as a polymerization inhibitor. 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. Specifically, the single-crystal spherical silicon nanoparticle reducing solution A was prepared by dissolving metallic lithium to a concentration of 0.4 mol / L in a THF solution where naphthalene was dissolved at a solution preparation temperature of -20°C using a glass-coated magnetic stirrer. Similarly, silicon tetrachloride, which served as the single-crystal spherical silicon nanoparticle raw material for solution B, was dissolved in THF and stirred for at least 60 minutes using a glass-coated magnetic stirrer. Regarding the substances represented by chemical formulas and abbreviations listed in Table 1, SiCl4 is silicon tetrachloride (manufactured by Tokyo Chemical Industry Co., Ltd.), Li is lithium metal (manufactured by Kishida Chemical Co., Ltd.), and C... 10 H8 is naphthalene (manufactured by Kanto Chemical Co., Ltd.).

[0154] [Table 1]

[0155]

[0156] Next, using the fluid processing apparatus described in the applicant's Patent Document 5, the manufactured single-crystal spherical silicon nanoparticle reducing solution (liquid A) and single-crystal spherical silicon nanoparticle raw material solution (liquid B) are mixed. Here, the fluid processing apparatus described in Patent Document 5 is the one disclosed in that publication. Figure 1 (A) The apparatus described herein is a concentric annular device surrounding the opening d2 of the second inlet section, which is formed as a ring-shaped disk (i.e., the central opening of the processing surface 2). Specifically, liquid A is introduced from the first inlet section d1 between processing surfaces 1 and 2. While the processing section 10 is rotated at a speed of 700 rpm to 5000 rpm, liquid B is introduced from the second inlet section d2 between processing surfaces 1 and 2. The single-crystal spherical silicon nanoparticle raw material liquid and the single-crystal spherical silicon nanoparticle reducing liquid are mixed in a thin-film fluid, and single-crystal spherical silicon nanoparticles are precipitated between processing surfaces 1 and 2. The sprayed liquid containing single-crystal spherical silicon nanoparticles is sprayed out from between processing surfaces 1 and 2 of the fluid processing apparatus. The sprayed single-crystal spherical silicon nanoparticle dispersion is recovered into a beaker via a container.

[0157] Table 2 shows the operating conditions of the fluid treatment device of Example 1. The introduction temperature (feed temperature) and the introduction pressure (feed pressure) of the A liquid and the B liquid shown in Table 2 were measured using a thermometer and a pressure gauge provided in the closed introduction path (first introduction portion dl and second introduction portion d2) between the treatment faces 1 and 2, and the introduction temperature of the A liquid shown in Table 2 is the actual temperature of the A liquid under the introduction pressure in the first introduction portion dl, and similarly, the introduction temperature of the B liquid is the actual temperature of the B liquid under the introduction pressure in the second introduction portion d2.

[0158] [Table 2]

[0159]

[0160] A wet cake sample was prepared from the monocrystalline spherical silicon nanoparticle dispersion ejected from the fluid treatment device and recovered into a beaker. As the preparation method, a conventional method was performed, the ejected monocrystalline spherical silicon nanoparticle dispersion was recovered, and the monocrystalline spherical silicon nanoparticles were precipitated from the recovered liquid using ultracentrifugal separation (1,000,000 G, 4 hours), and the supernatant was separated. Then, ultrasonic washing with THF and precipitation were repeated, and a wet cake of the finally obtained monocrystalline spherical silicon nanoparticles was prepared. In addition, a part was dried at -0.10 MPa G, 25°C for 20 hours, and a dried powder was obtained.

[0161] Figure 1 A TEM observation image of the monocrystalline spherical silicon nanoparticles of Example 1-1 is shown. The same results were confirmed for the monocrystalline spherical silicon nanoparticles of Example 1-2 to Example 1-4.

[0162] Figure 2 A STEM observation image of the monocrystalline spherical silicon nanoparticles of Example 1-4 is shown, Figure 3 An electron diffraction pattern of the Fourier transform of the STEM observation image is shown. The same interference image of the silicon lattice plane using an electron beam and the spot-like electron diffraction pattern that can be observed in the case of a single crystal were confirmed for the monocrystalline spherical silicon nanoparticles of Example 1-1 to Example 1-3. Thus, it was confirmed that the spherical silicon nanoparticles produced in Example 1 were single crystals. The interplanar spacing calculated from the obtained electron diffraction pattern was 0.162 nm, and it was confirmed to be an electron beam diffraction pattern from the (311) plane of crystalline silicon.

[0163] (Si-H bond)

[0164] Figure 4 A measurement result in the region of wave number 1800 cm -1 ~ 2300 cm -1 of the IR spectrum measurement result of the monocrystalline spherical silicon nanoparticles of Example 1-2 is shown. The measurement result at 2105 cm -1The absorption is attributed to the stretching vibrations of the Si-H bonds, thus confirming that the surface of the single-crystal spherical silicon nanoparticles is hydrogenated. Examples 1-1, 1-3, and 1-4 also showed the same confirmation. Since the Si-H bonds can hydrophobize the surface of the single-crystal spherical silicon nanoparticles, it is confirmed that the single-crystal spherical silicon nanoparticles can be well dispersed in organic solvents. Figure 1 As shown, it was observed that even at an extremely small distance of about 5 nm, the single-crystal spherical silicon nanoparticles of the present invention were dispersed.

[0165] (Si-O bond)

[0166] Figure 5a Indicates at 900cm -1 ~1300cm -1 The IR spectrum in the wavenumber region. For the single-crystal spherical silicon nanoparticles of Examples 1-4, the IR spectrum at 1095 cm⁻¹. -1 The absorption peak was confirmed to be at a certain point, and its wavenumber was similar to that of the amorphous silica (SiO2) absorption peak at 1095 cm⁻¹. -1 Consistent. For comparison, the IR spectrum of a single-crystal silicon wafer is shown. The wavenumber of the absorption peak is confirmed to be 1105 cm⁻¹. -1 It is the absorption of oxygen in the state of solid dissolved in the silicon lattice.

[0167] Figure 5b This indicates that at 400cm -1 ~550cm -1 The IR spectrum in the wavenumber region. For the single-crystal spherical silicon nanoparticles of Examples 1-4, no significantly large absorption peaks were observed, but for the amorphous (non-crystalline) silica (SiO2) reagent, a peak was observed at 460 cm⁻¹. -1 A very large absorption peak was observed at 1100 cm⁻¹. This means that when the generally known Si-O bond-based 1100 cm⁻¹ absorption peak is simultaneously confirmed, this is significant. -1 The nearby peaks and the 460 cm⁻¹ peaks of amorphous (non-crystalline) silica (SiO₂) are shown. -1 When the peak value is reached, the substance is considered to be oxidized SiO2.

[0168] (Solid dissolved oxygen in silicon crystals)

[0169] according to Figure 5a and Figure 5b The IR spectra shown, for the single-crystal spherical silicon nanoparticles of Examples 1-4, cannot simultaneously confirm the absorption at both of the aforementioned locations that are considered to be SiO2. Therefore, it is believed that the 1095 cm⁻¹... -1 The absorption is based on the various states of oxygen dissolved in silicon crystals, and the absorption peak wavenumber of dissolved oxygen is 1105 cm⁻¹. -1 10cm difference -1, is the spectral width expansion and measured. Single crystal spherical silicon nanoparticles of Examples 1-4 show fluorescence spectrum, so it is confirmed that it is a silicon crystal. In addition, it is desirable that the presence of oxygen that can bond to silicon atoms in the silicon crystal is as little as possible. In the IR spectrum, the peak value intensity of the extremely large peak confirmed in the region of wave number 1000 cm -1 ~ 1200 cm -1 is set to A, and the peak value intensity of the extremely large peak confirmed in the region of wave number 400 cm -1 ~ 500 cm -1 is set to B, and the ratio: B / A is desired to be less than 0.2. In Examples 1-4, the ratio: B / A is 0.1, which is less than 0.2. In contrast, in the reagent amorphous silica (SiO2), an extremely large peak is shown at a peak wave number of 460 cm -1 , and the ratio: B / A is 0.4, which exceeds 0.2.

[0170] (Si-Cl bond)

[0171] Figure 5c represents the results of the study of Si-Cl bonds in which silicon atoms are bonded to chlorine atoms. In the case where Si-Cl bonds exist, in the wave number region of 530 cm -1 ~ 630 cm -1 of the IR spectrum, an absorption in which the wave number of the absorption varies depending on the number of chlorine atoms bonded to silicon atoms is observed. The Si-Cl bond is highly likely to be hydrolyzed by moisture in the atmosphere to generate an oxide or a hydroxide of silicon, and thus it is desirable that the Si-Cl bond is as little as possible. Regarding the proportion of the Si-Cl bond, the peak value intensity of the extremely large peak confirmed in the wave number region of 1000 cm -1 ~ 1200 cm -1 is set to A, and the peak value intensity of the extremely large peak of the Si-Cl bond confirmed in the wave number region of 530 cm -1 ~ 630 cm -1 is set to C, and the ratio: C / A is desired to be less than 0.2. When the ratio: C / A is less than 0.2, even if the single crystal spherical silicon nanoparticles are taken out to the atmosphere, immediate discoloration to become a silicon oxide or a silicon hydroxide is not observed. In Examples 1-4, the ratio: C / A is 0.06, which is less than 0.2. The same results are obtained in Examples 1-1 to 1-3.

[0172] (substituted carbon in silicon crystal)

[0173] Figure 5d represents the study of substituted carbon in the silicon crystal in the region of 550 cm -1 ~ 700 cm -1region of the IR spectrum. It is known that absorption due to substitution of silicon atoms and carbon atoms in the silicon crystal exists in this region. Therefore, the wave number region of the absorption of the Si-C bond overlaps with the wave number region of the absorption of the Si-Cl bond described in the above paragraph 530 cm -1 ~ 630 cm -1 . In Examples 1 to 4, the absorption at a wave number of 612 cm -1 was assumed to be based on the Si-Cl bond, but even if the absorption at a wave number of 612 cm -1 is based on the Si-C bond of the solid-solved carbon atom, when compared with the ratio: C / A of 0.5 based on the wave number of 610 cm -1 confirmed from the silicon wafer, the ratio C / A in Examples 1 to 4 is 0.06, and thus the carbon concentration is lower than that of the silicon wafer. For the single crystal spherical silicon nanoparticles of the present application, although it is expected that carbon will be mixed into the single crystal spherical silicon nanoparticles as an impurity due to the production of the halogenated silicon using a reducing solution containing an aromatic compound, the single crystal spherical silicon nanoparticles of the present application contain almost no carbon atoms, and are single crystal spherical silicon nanoparticles with high purity. Since the absorption wave number of the Si-C bond overlaps with the absorption wave number of the Si-Cl bond, it cannot be determined unambiguously which absorption at 612 cm -1 confirmed in Examples 1 to 4 is, but it can be confirmed that the single crystal spherical silicon nanoparticles of Examples 1 to 4 are single crystal spherical silicon nanoparticles with low concentrations of both carbon and chlorine.

[0174] Figure 6 is a fluorescence spectrum of the single crystal spherical silicon nanoparticles of Example 1-3. The fluorescence spectrum normalized so that the maximum intensity of the fluorescence spectrum obtained for each excitation wavelength is 1.0 is a result of changing the excitation wavelength every 40 nm from 340 nm to 600 nm. From the result, it can be confirmed that the fluorescence of the single crystal spherical silicon nanoparticles of Example 1-3 shows a very large peak at 400 nm to 610 nm. Figure 6

[0175] Figure 7 is a result based on the result of Figure 6 is a result based on the result of

[0176] Figure 8 ​The results of measurement of the particle diameter and the fluorescence peak wavelength of the single crystal spherical silicon nanoparticles of Examples 1-1 to 1-4 with respect to the rotation speed of the disk are shown. It was confirmed that the particle diameter of the single crystal spherical silicon nanoparticles decreased as the rotation speed of the disk increased. It was thus confirmed that the particle diameter of the single crystal spherical silicon nanoparticles could be controlled by the rotation speed of the disk. It was also confirmed that the fluorescence peak wavelength shifted to the short wavelength side as the rotation speed of the disk increased, that is, as the particle diameter of the silicon nanoparticles decreased. The change in the fluorescence peak wavelength due to the particle diameter was explained by the (A) quantum effect among the three mechanisms of (A) to (C) described above. That is, with respect to the fluorescence peak wavelength of the silicon nanoparticles, it was considered that as the particle diameter of the silicon nanoparticles decreased, the band gap of the silicon nanoparticles increased, and thus the fluorescence peak wavelength shifted to the short wavelength side, which was a result of the mechanism of the (A) quantum effect. Further, since the silicon nanoparticles of the present application were not surface-modified with an alkyl group or an amino group, and the like, the (B) surface modification mechanism among the three mechanisms described above was not present, and thus it was considered that the (C) presence of oxygen mechanism due to the solid solution of oxygen in the silicon crystal cooperated with the mechanism of the (A) quantum effect.

[0177] Figure 9 The visible light fluorescence spectrum of the single crystal spherical silicon nanoparticles of Example 1-2 at the wavelength of deep ultraviolet light is shown. Deep ultraviolet light refers to light in the wavelength range of 200 nm to 300 nm. In addition to the fluorescence spectrum excited by the light of visible light shown in Figure 6 It was confirmed that by the light of deep ultraviolet light with a shorter wavelength, the fluorescence of visible light in the wavelength range of 400 nm to 600 nm showing fluorescence peaks at 470 nm and 550 nm was obtained. The same results were obtained in Examples 1-1, 1-3, and 1-4. In this way, by the excitation light of a wide wavelength from deep ultraviolet light to visible light, the fluorescence of visible light could be obtained, and thus it was confirmed that the single crystal spherical silicon nanoparticles of the present application could be used in a wider range of applications using fluorescence.

[0178] It was confirmed that the lithium concentration of the single crystal spherical silicon nanoparticles of Examples 1-1 to 1-4 measured by ICP-OES was less than 1 ppm. It was thus confirmed that the single crystal spherical silicon nanoparticles of the present application did not incorporate the metallic lithium contained in the single crystal spherical silicon nanoparticle reducing solution, and were high in purity.

[0179] Table 3 shows the values of the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A, and the ratio: C / A obtained from the IR spectrum of the single crystal spherical silicon nanoparticles of Examples 1-1 to 1-4. The ratio: B / A of the single crystal spherical silicon nanoparticles of Examples 1-1 to 1-4 was 0.08 to 0.10, and the ratio: C / A was 0.06 to 0.08, both of which were less than 0.2.

[0180] [Table 3]

[0181] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Example 1-1 3.1 0.93 11 0.10 0.06 Example 1-2 2.7 0.95 13 0.09 0.07 Example 1-3 2.5 0.95 13 0.08 0.08 Example 1-4 2.5 0.95 13 0.10 0.06

[0182] Example 2

[0183] In Example 2, instead of silicon tetrachloride (SiCl4) used in Example 1, silicon tetrabromide (SiBr4) was used, and a THF solution of silicon tetrabromide (monocrystalline spherical silicon nanoparticle raw liquid) was reduced using a naphthalene-dissolved THF solution of metallic lithium (monocrystalline spherical silicon nanoparticle reduction liquid) to produce monocrystalline spherical silicon nanoparticles.

[0184] Table 4 shows the formulations of Example 2-1 to Example 2-4. The solvent used in Example 2 was super-dehydrated tetrahydrofuran (manufactured by FUJIFILM and LIGHT PURE CO., LTD.) having a residual moisture content of 10 ppm or less, which contained BHT as a polymerization inhibitor. Monocrystalline spherical silicon nanoparticle reduction liquid (A liquid) and monocrystalline spherical silicon nanoparticle raw liquid (B liquid) were produced in the same manner as in Example 1 in an argon atmosphere glove box.

[0185] [Table 4]

[0186]

[0187] Next, in the same manner as in Example 1, the produced monocrystalline spherical silicon nanoparticle reduction liquid (A liquid) and monocrystalline spherical silicon nanoparticle raw liquid (B liquid) were mixed using the fluid treatment device described in Patent Literature 5 by the applicant of the present application. Table 5 shows the operating conditions of the fluid treatment device.

[0188] [Table 5]

[0189]

[0190] From the monocrystalline spherical silicon nanoparticle dispersion liquid ejected from the fluid treatment device and recovered into a beaker, a dry powder and a wet cake sample were produced. As the production method, the ejected monocrystalline spherical silicon nanoparticle dispersion liquid was recovered, and the monocrystalline spherical silicon nanoparticles were precipitated from the recovered liquid by ultracentrifugation (1,000,000 G, 4 hours) to separate the supernatant. Then, ultrasonic washing with THF and precipitation were repeated, and a part of the wet cake of the finally obtained monocrystalline spherical silicon nanoparticles was dried at -0.10 MPa G and 25°C for 20 hours to obtain a dry powder. The remainder was used as a wet cake sample.

[0191] Table 6 shows the values of the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A and the ratio: C / A from the IR spectrum of the single crystal spherical silicon nanoparticles of Example 2-1 to Example 2-4. The ratio: B / A of the single crystal spherical silicon nanoparticles of Example 2-1 to Example 2-4 was 0.09 or 0.10, and the ratio: C / A was 0.06 to 0.08, both of which were less than 0.2.

[0192] [Table 6]

[0193] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Example 2-1 3.2 0.93 11 0.09 0.06 Example 2-2 2.8 0.94 12 0.10 0.08 Example 2-3 2.8 0.94 12 0.10 0.08 Example 2-4 2.7 0.95 12 0.09 0.07

[0194] Comparative Example 1

[0195] In Comparative Example 1, the THF solution of silicon tetrachloride (silicon nanoparticle raw material solution) according to Example 6 of Patent Document 5 was reduced using a DBB (4,4'-di-tert-butylbiphenyl) solution of metallic lithium (silicon nanoparticle reducing solution) to produce silicon nanoparticles.

[0196] Table 7 shows the formulations of Comparative Example 1-1 to Comparative Example 1-3. The THF used in Comparative Example 1 was super dehydrated tetrahydrofuran (manufactured by FUJIFILM and LIGHT PURE CO., LTD.) having a residual moisture of 10 ppm or less, and contained BHT as a polymerization inhibitor. In an argon atmosphere glove box, a silicon nanoparticle reducing solution (A solution) and a silicon nanoparticle raw material solution (B solution) were produced. Specifically, the silicon nanoparticle reducing solution of the A solution was produced by weighing 30 mmol of metallic lithium in a flask at a solution temperature of 16°C to 17°C, pouring 200 mL of a THF solution in which 40 mmol of DBB was dissolved into the flask, and dissolving with a glass-coated magnetic stirrer. Similarly, after dissolving silicon tetrachloride as the silicon nanoparticle raw material of the B solution in THF, the solution was stirred for at least 60 minutes with a glass-coated magnetic stirrer. As for the chemical formula and the abbreviated symbol of the substance described 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.).

[0197] [Table 7]

[0198]

[0199] Next, the prepared silicon nanoparticle reducing solution (A solution) and the silicon nanoparticle raw material solution (B solution) were mixed using the fluid processing device described in Patent Document 5 proposed by the applicant of the present application, as in Example 1. Table 8 shows the operation conditions of the fluid processing device in Comparative Example 1-1 to Comparative Example 1-3.

[0200] [Table 8]

[0201]

[0202] (Preparation of hexyl-terminated silicon nanoparticles)

[0203] Next, the silicon nanoparticle dispersion liquid recovered by spouting from the fluid treatment device was subjected to the surface stabilization treatment described in Example 6 of Patent Document 5. Specifically, 10 mL of the silicon nanoparticle dispersion liquid was put in a 100 mL three-necked flask in an argon atmosphere glove box, and IPA was kept in a cooling tank maintained at -3°C as a refrigerant. A three-way cock was attached to the three-necked flask to enable argon to be bubbled, and then hexylmagnesium bromide (manufactured by Tokyo Chemical Industry) was adjusted to a solution having a concentration four times the silicon molar concentration in the silicon nanoparticle dispersion liquid, and was added dropwise to the spouting liquid using a glass syringe with a through metal needle through the rubber septum of the three-necked flask. After the dropwise addition, the cooling tank was removed, and the temperature was gradually increased to 16 to 17°C, which is room temperature, and stirring was performed under an argon atmosphere for 24 hours. In this way, silicon nanoparticles whose surfaces were terminated with hexyl groups were obtained, which were dispersed in the spouting liquid. In order to purify the hexyl-terminated silicon nanoparticles, hexane was added to the flask, and the hexyl-terminated silicon nanoparticles dispersed in the THF solution were extracted into the hexane layer. After the hexane layer was separated, pure water was added to the hexane layer, and residues and the like caused by lithium chloride or hexylmagnesium bromide, which are reaction products, were dissolved and washed.

[0204] Figure 10 An STEM observation image of the hexyl-terminated silicon nanoparticles prepared in Comparative Example 1-1 is shown. From the STEM observation image, it was confirmed that the silicon nanoparticles with hexyl terminals were crystals, but it was observed that the crystal planes within the silicon nanoparticles were not consistent in a certain direction, and became polycrystals in which the crystal planes intersected.

[0205] In addition, unlike Example 1, it was confirmed that the silicon nanoparticles were not spherical, but were in a deformed particle shape. As shown in Table 9, the circularity of the hexyl-terminated silicon nanoparticles of Comparative Examples 1-1 to 1-3 was 0.83 or 0.84, and was not 0.9 or more.

[0206] As a reason for the formation of polycrystals, the following reason was considered.

[0207] The preparation of the single crystal spherical silicon nanoparticle reducing solution was performed at a temperature of -20°C in Example 1 of the present application and at room temperature of 16°C to 17°C in Comparative Example 1. This is because in Example 1 of Patent Literature 4 and Example 6 of Patent Literature 5, the reducing solution was prepared from metallic lithium and DBB at room temperature. By preparing the reducing solution at room temperature, in the reaction in which the metallic lithium releases electrons in THF to dissolve, the DBB anion (radical anion) generated by the movement of one electron from the metallic lithium to the DBB molecule is reduced in concentration by disproportionation reaction, because of the equilibrium reaction between the DBB dianion and the uncharged DBB molecule. Thus, it is considered that various molecular species exist mixed in the THF solution, which hinders the uniform crystallization growth of the silicon nanoparticles from the silicon tetrachloride to the spherical shape, and the distribution of the reaction rate becomes a cause of the polycrystallization of the silicon particles.

[0208] (Pumping temperature of the reducing solution)

[0209] The DBB anion is generated by the movement of the electron generated when the metallic lithium dissolves in THF as lithium ion. In THF, the DBB anion and the lithium ion can exist apart by THF, but when the temperature at the time of preparation is 0°C or higher, the DBB anion can directly form an ionic bond with the lithium ion without passing through THF. Therefore, once the DBB anion forms an ionic bond with the lithium ion, even if the pumping temperature at the time of preparation of the silicon nanoparticles is set to a low temperature, it is difficult for THF to intervene between the DBB anion and the lithium ion. In the state in which the lithium ion and the DBB anion are directly ionic-bonded, the reverse electron transfer from the DBB anion to the lithium ion is easily generated. Thereby, the variation in the reducing power of the silicon nanoparticles is generated, the crystallization growth rate of the silicon particles becomes uneven, the deviation of the shape of the obtained silicon particles from the spherical shape becomes large, and this becomes a cause of the change from the single crystal to the polycrystal.

[0210] In addition, in Comparative Example 1, since the surface stabilization treatment using hexyl was performed subsequently, a state in which a chlorine atom is bonded to the surface of the silicon nanoparticle was formed. Therefore, the number of moles of the metallic lithium as the reducing agent was set to 3 / 4 times the number of moles of the silicon tetrachloride. This is because the molar ratio of the metallic lithium coincides with that in Example 1 of Patent Literature 4 and Example 6 of Patent Literature 5. The silicon nanoparticle before the surface stabilization treatment is different from the single crystal spherical silicon nanoparticle of the present application in that the surface is intentionally chlorinated. In addition, since the chlorine atom that is not substituted with hexyl remains on the surface of the silicon nanoparticle after the surface stabilization treatment, it is presumed that this chlorine atom is hydrolyzed at the time of the pure water washing after the hexane extraction and changes the shape of the silicon nanoparticle. The same result was confirmed for the silicon nanoparticles of Comparative Example 1-2 and Comparative Example 1-3.

[0211] (Si-H bond of the polycrystal silicon nanoparticle of Comparative Example 1)

[0212] Figure 11 IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 in the wave number range of 1800 cm -1 ~ 2300 cm -1 . In Comparative Example 1-1, the absorption peak due to Si-H bond around 2100 cm -1 confirmed in Example 1-2 was not observed. It is considered that this is because, for the polycrystal silicon nanoparticles of Comparative Examples 1-1 to 1-3, the number of moles of metal lithium of the reducing solution was set to 3 / 4 of the metal lithium raw material concentration of the silicon nanoparticle raw material solution, whereby the chlorinated polycrystal silicon nanoparticles were prepared, and then the chlorine atoms were substituted with hexyl groups using hexylmagnesium bromide.

[0213] (Si-O bond of the polycrystal silicon nanoparticles of Comparative Example 1)

[0214] Figure 12a and Figure 12b IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1. In Example 1-4, an absorption peak with a wide spectrum width was observed at 1095 cm -1 , but in Comparative Example 1-1, an absorption peak with a narrow spectrum width was observed at 1084 cm -1 . In addition, in Comparative Example 1-1, an absorption peak was observed at 450 cm -1 on the low wave number side. In the IR spectrum, the peak value intensity of the extremely large peak confirmed in the region of 1000 cm -1 ~ 1200 cm -1 was set to A, and the peak value intensity of the extremely large peak confirmed in the region of 400 cm -1 ~ 500 cm -1 was set to B, and the ratio: B / A was 0.38, which was not less than 0.2. From this result, it was confirmed that the Si-O bond state of the polycrystal silicon nanoparticles of Comparative Example 1-1 was different from that of the single crystal spherical silicon nanoparticles of Example 1-4. The same results were obtained for Comparative Examples 1-2 and 1-3 as for Comparative Example 1-1.

[0215] (Si-Cl bond of the polycrystal silicon nanoparticles of Comparative Example 1)

[0216] Figure 12c IR spectrum of the polycrystal silicon nanoparticles of Comparative Example 1-1 in the wave number range of 450 cm -1 ~ 650 cm -1 . Unlike the single crystal spherical silicon nanoparticles of Example 1-4, a clear extremely large absorption peak was observed at 620 cm -1 , confirming the presence of Si-Cl bond. In the IR spectrum, the peak value intensity of the extremely large peak confirmed in the region of 1000 cm -1~ 1200 cm -1 The peak intensity of the peak of the maximum peak confirmed in the region of 530 cm -1 ~ 630 cm -1 was set to C, and the ratio: C / A was 0.25, not less than 0.2. The same results as Comparative Example 1-1 were also obtained for Comparative Examples 1-2 and 1-3. It was thus presumed that on the surface of the chlorinated polysilicon nanoparticle, there were chlorine atoms that could not be completely substituted with hexyl groups even by the surface stabilization treatment with hexylmagnesium bromide.

[0217] (Substituted carbon in polysilicon nanoparticle of Comparative Example 1)

[0218] Figure 12d indicates the IR spectrum of the polysilicon nanoparticle of Comparative Example 1-1 at a wave number of 550 cm -1 ~ 700 cm -1 . Unlike the single-crystal spherical silicon nanoparticle of Example 1-4, an absorption peak with an absorbance of 0.25 was observed at 620 cm -1 . This wave number region overlaps with 530 cm -1 ~ 630 cm -1 as described in paragraph

[0101] when an absorption is also generated when a silicon atom is bonded to a chlorine atom. As described above, the ratio: C / A was 0.25, not less than 0.2. This result indicates that in the polysilicon nanoparticle of Comparative Example 1-1, there is a Si-Cl bond or a substituted carbon, confirming that it has a different composition from the single-crystal spherical silicon nanoparticle of Example 1-4.

[0219] (Fluorescence spectrum of polysilicon nanoparticle of Comparative Example 1)

[0220] It was confirmed from the polysilicon nanoparticle of Comparative Example 1-1 that fluorescence maximum was exhibited in the wavelength range of 400 nm ~ 600 nm. However, as Figure 13a and Figure 13bIn the fluorescence spectrum of the polycrystal silicon nanoparticle of Comparative Example 1-1 under the excitation of the deep ultraviolet light of 300 nm or less, it was confirmed that the fluorescence peak wavelength was 400 nm or less, and it was observed that the fluorescence spectrum of the polycrystal silicon nanoparticle of Comparative Example 1-2 and Comparative Example 1-3 under the excitation of the deep ultraviolet light also showed a peak at 400 nm or less. These results were different from the results of Example 1-4 in which the excitation wavelength was 220 nm and the fluorescence peak wavelength was 547 nm, and the excitation wavelength was 260 nm and the fluorescence peak was shown at 568 nm. Since the fluorescence peak wavelength under the excitation of the deep ultraviolet light of the polycrystal silicon nanoparticle of Comparative Example 1-1 to Comparative Example 1-3 was 400 nm or less, it was confirmed that the polycrystal silicon nanoparticle had a different electronic energy level structure from the single crystal spherical silicon nanoparticle which showed a fluorescence peak in the visible light region of 400 nm to 600 nm. This indicates that since the silicon nanoparticle of Comparative Example 1 is a polycrystal which is a collection of single crystals having different crystal diameters, the electronic energy level of the excitation light and the emitted fluorescence is different from that of the single crystal spherical silicon nanoparticle. In particular, this is because the silicon particle diameter prepared in the examples and comparative examples was about 5 nm, and therefore a slight change in the diameter of the microcrystal has a large effect on the size of the band gap of silicon, and the polycrystal is considered to have an electronic energy level due to the presence of the grain boundary at which the respective microcrystals of the single crystal meet.

[0221] Table 9 shows the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A and the ratio: C / A values from the IR spectrum of the polycrystal silicon nanoparticle of Comparative Example 1-1 to Comparative Example 1-3. The silicon nanoparticle of Comparative Example 1 was a polycrystal silicon nanoparticle, and the ratio: B / A and the ratio: C / A values were 0.2 or more. These values were confirmed to be different from the ratio: B / A and the ratio: C / A of the single crystal spherical silicon nanoparticle of Example 1 and Example 2.

[0222] [Table 9]

[0223] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Comparative Example 1-1 3.2 0.84 10 0.38 0.25 Comparative Example 1-2 2.8 0.88 8 0.42 0.30 Comparative Example 1-3 2.8 0.83 8 0.40 0.29

[0224] Example 3

[0225] Table 10 shows the prescription of Example 3-1 and Example 3-2. Table 11 shows the operating conditions of the fluid treatment device of Example 3-1 and Example 3-2. Table 12 shows the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A and the ratio: C / A values from the IR spectrum of the single crystal spherical silicon nanoparticle of Example 3-1 and Example 3-2.

[0226] When the alkali metal of the reducing solution is sodium, the relative fluorescence quantum efficiency is 11 to 13%. The values of the ratio: B / A and the ratio: C / A of the silicon nanoparticles of Example 3 are 0.1 or less. These values are confirmed to be equivalent to the ratio: B / A and the ratio: C / A of the single crystal spherical silicon nanoparticles of Example 1 and Example 2.

[0227] [Table 10]

[0228]

[0229] [Table 11]

[0230]

[0231] [Table 12]

[0232] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Example 3-1 2.2 0.94 11 0.10 0.08 Example 3-2 2.0 0.95 13 0.09 0.08

[0233] Example 4

[0234] Table 13 shows the formulations of Example 4-1 and Example 4-2. Table 14 shows the operating conditions of the fluid treatment apparatus of Comparative Example 4-1 and Example 4-2. Table 15 shows the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the values of the ratio: B / A and the ratio: C / A from the IR spectrum of the single crystal spherical silicon nanoparticles of Example 4-1 and Example 4-2.

[0235] When the metal of the reducing solution is potassium, the relative fluorescence quantum efficiency is 11 to 13%. The values of the ratio: B / A and the ratio: C / A are confirmed to be equivalent to the ratio: B / A and the ratio: C / A of the single crystal spherical silicon nanoparticles of Example 1 to Example 3.

[0236] [Table 13]

[0237]

[0238] [Table 14]

[0239]

[0240] [Table 15]

[0241] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Example 4-1 2.2 0.94 11 0.10 0.08 Example 4-2 2.0 0.95 13 0.09 0.08

[0242] Comparative Example 2

[0243] 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 of Comparative Example 2-1 and Comparative Example 2-2. The alkali metal of the reducing solution was metallic lithium, and the temperature of the reducing solution of the A liquid was 25°C. The disc rotation speed was 3500 rpm and 5000 rpm. Table 18 shows the values of the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A, and the ratio: C / A from the IR spectrum of the single crystal spherical silicon nanoparticles of Comparative Example 2-1 and Comparative Example 2-2.

[0244] Since the temperature of the reducing agent of the A liquid was high, even if the disc rotation speed was increased, the average particle diameter was as large as 4 nm or more, and the relative fluorescence quantum efficiency was as low as less than 5%. The values of the ratio: B / A and the ratio: C / A were greater than those of the single crystal spherical silicon nanoparticles of Examples 1 to 4, and were confirmed to be different.

[0245] [Table 16]

[0246]

[0247] [Table 17]

[0248]

[0249] [Table 18]

[0250] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Comparative Example 2-1 4.5 0.92 3 0.45 0.32 Comparative Example 2-2 4.2 0.94 4 0.35 0.30

[0251] Comparative Example 3

[0252] Table 19 shows the formulations of Comparative Example 3-1 and Comparative Example 3-2. Table 20 shows the operating conditions of the fluid processing apparatus of Comparative Example 3-1 and Comparative Example 3-2. The alkali metal of the reducing solution of the A liquid was metallic lithium, and the temperature of the reducing solution was maintained at 5°C. Table 21 shows the values of the average particle diameter, the circularity, the relative fluorescence quantum efficiency, the ratio: B / A, and the ratio: C / A from the IR spectrum of the single crystal spherical silicon nanoparticles of Comparative Example 3-1 and Comparative Example 3-2.

[0253] Although the temperature of the reducing solution was maintained at a low temperature of 5°C, by setting the disc rotation speed to 350 rpm and 500 rpm, the average particle diameter increased, and the relative fluorescence quantum efficiency was as low as less than 5%. The values of the ratio: B / A and the ratio: C / A were greater than those of the single crystal spherical silicon nanoparticles of Examples 1 to 4, and were confirmed to be different.

[0254] [Table 19]

[0255]

[0256] [Table 20]

[0257]

[0258] [Table 21]

[0259] Average particle diameter [nm] Circularity Relative fluorescence quantum efficiency [%] B / A C / A Comparative Example 3-1 4.5 0.94 3 0.35 0.30 Comparative Example 3-2 4.2 0.94 3 0.48 0.34

[0260] Industrial applicability

[0261] The single crystal spherical silicon nano-particles manufactured according to the manufacturing method of the present application, being single crystals without grain boundaries that reduce fluorescence efficiency, can produce fluorescence with high fluorescence quantum efficiency through excitation of light from deep ultraviolet light of 200 nm to 300 nm to wide wavelength light of visible light, and can increase the fluorescence quantum efficiency of the currently known silicon nano-particles from about 1% to more than 10%.

Claims

1. A method for producing monocrystalline spherical silicon nanoparticles, wherein, The single-crystal spherical silicon nanoparticles are single-crystal, spherical, and have an average particle diameter of 1 nm to 20 nm, The manufacturing method includes a step of mixing and reacting a raw material liquid and a reducing liquid of 5°C or lower in a thin film fluid formed between processing surfaces that are disposed to be able to approach and separate from each other and that are relatively rotated with respect to each other, wherein the raw material liquid contains silicon halide, and the reducing liquid contains an anion of a condensed aromatic compound generated from lithium, sodium, or potassium and a condensed aromatic compound, The rotational speed of the processing surfaces is 700 rpm to 5,000 rpm, The anion of the condensed aromatic compound is prepared by mixing lithium, sodium, or potassium and a condensed aromatic compound at 0°C or lower.

2. The manufacturing method of claim 1, wherein, The raw material liquid is mixed and reacted with the reducing liquid using a device, The device includes a fluid pressure application mechanism that applies pressure to a fluid to be processed, at least two processing units including a first processing unit and a second processing unit that is able to approach and separate from the first processing unit, and a rotational drive mechanism that relatively rotates the first and second processing units, The device is configured as follows: At least two processing surfaces including a first processing surface and a second processing surface are provided at positions that face each other in each processing unit, each processing surface forms a part of a sealed flow path through which the fluid to be processed flows, at least one of the two processing surfaces is mixed and reacted with two or more fluids to be processed that contain a reactant, and In the first and second processing units, at least the second processing unit includes a pressure receiving surface, at least a part of the pressure receiving surface is formed by the second processing surface, the pressure receiving surface receives pressure applied to the fluid to be processed by the fluid pressure application mechanism to generate a force that moves the second processing surface in a direction away from the first processing surface, the fluid to be processed under pressure passes between the first and second processing surfaces that are able to approach and separate from each other and relatively rotate, and the fluid to be processed forms a thin film fluid, the device further includes a separate introduction path that is independent of the flow path between the processing surfaces through which the fluid to be processed flows, at least one opening is provided in at least one of the first and second processing surfaces, and the opening communicates with the separate introduction path, at least one of the fluids to be processed is introduced from the separate introduction path between the two processing surfaces, and at least one of the reactants contained in at least one of the fluids to be processed and a fluid to be processed that is different from the fluids to be processed are mixed in the thin film fluid.

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

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

1.

5. The production method according to any one of claims 1 to 4, 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 production method according to any one of claims 1 to 5, wherein The solvent contained in the reducing liquid is tetrahydrofuran and / or dimethoxyethane in which the residual moisture is 10 ppm or less.

7. The production method as claimed in any one of claims 1 to 5, wherein The solvent contained in the reducing solution is tetrahydrofuran containing a phenol-based polymerization inhibitor, and having a residual moisture content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm.

8. The production method according to any one of claims 1 to 7, wherein The solvent contained in the raw material solution is tetrahydrofuran having a residual moisture content of 10 ppm or less and a residual oxygen concentration of less than 0.1 ppm.

9. The production method according to any one of claims 1 to 8, wherein The halogenated silicon is silicon tetrachloride, silicon tetrabromide or silicon tetraiodide.

10. The production method according to any one of claims 1 to 9, wherein The single crystal spherical silicon nanoparticle uses the circumference Z and the area S of the projection image of the single crystal spherical silicon nanoparticle observed by a transmission electron microscope, in the formula: 4πS / Z 2 The average of the calculated circularity is 0.9 or more.

11. The production method according to any one of claims 1 to 10, wherein The single crystal spherical silicon nanoparticles show absorption attributed to Si-H bond in the wave number region of 1950 cm -1 ~ 2150 cm -1 in the IR absorption spectrum.

12. The production method according to any one of claims 1 to 11, wherein The single crystal spherical silicon nanoparticle has a peak intensity A of an extreme maximum peak in the wave number range of 1000 cm -1 ~ 1200 cm -1 -1, and a peak intensity B of an extreme maximum peak in the wave number range of 400 cm -1 ~ 500 cm -1 -1, and a calculated ratio: B / A is less than 0.

2.

13. The production method according to any one of claims 1 to 12, wherein The single crystal spherical silicon nanoparticle has a peak intensity A of a maximum peak in a wave number range of 1000 cm -1 ~ 1200 cm -1 -1, and a peak intensity C of a maximum peak in a wave number range of 530 cm -1 ~ 630 cm -1 -1, and a calculated ratio: C / A is less than 0.

2.

14. The production method according to any one of claims 1 to 13, wherein The single-crystal spherical silicon nano-particles have a fluorescence maximum in a wavelength range of 400 nm to 600 nm.

15. The production method according to any one of claims 1 to 14, wherein The single-crystal spherical silicon nano-particles have a fluorescence maximum in a wavelength range of 400 nm to 600 nm by excitation with deep ultraviolet light having a wavelength of 300 nm or less.

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