JP2000126681A - Manufacture of nanoparticle thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture a nanoparticle thin film without wasting nanoparticles by coating the top of a solid substrate by ink jet coating with a dispersion prepared by dispersing nanoparticles in an emulsion having an aqueous phase as a continuous phase and an oil phase as a dispersed phase. SOLUTION: Nanoparticles such as semiconductor crystals of a group I-VII compound semiconductor such as CuCl, a group II-VI compound semiconductor such as CdS or CdSe, a group III-V compound semiconductor such as InAs or a group IV semiconductor are dispersed in an emulsion having an aqueous phase prepared by adding a water-soluble organic solvent such as ethylene glycol, propylene glycol or butylene glycol to water as a continuous phase and an oil phase as a dispersed phase. The top of a solid substrate is coated with the resultant dispersion by ink jet coating to manufacture the objective nanoparticle thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a nanoparticle thin film. Specifically, the photoluminescence intensity increases when irradiated with excitation light, and the photoluminescence intensity before storage is indicated by storing light for a long time in a dark place without light irradiation and then re-irradiating light, that is, it is stored. Functions (also referred to as “TDLM” (Time Dependent Lumin
(hereinafter referred to as luminescence and memory).

[0002]

2. Description of the Related Art In recent years, various devices such as light-emitting devices / mediums and optical processing devices / mediums using nanometer-sized ultrafine particles have been studied. For application of such ultrafine particles to devices, high-density integration obtained by depositing a film or layer of ultrafine particles on a solid substrate is important. The thin film in which the ultrafine particles are integrated at a high density is, specifically, a light emitting device (LED) (Alivisatos et al.) And a photoelectric conversion device (Greenham, NC, et al., Phys. Rev. B, 54,
17628 (1996)), ultrafast detector (Bhargava),
Applications to electroluminescent displays and panels (Bhargava, Alivisatos et al.), Nanostructured memory elements (Chen et al.), Multicolor devices composed of nanoparticle arrays (Dushkin et al.) Have been reported.

On the other hand, as a method of forming an inorganic compound thin film having excellent orientation, molecular beam epitaxy (MBE), cluster ion beam method, ion beam irradiation vacuum deposition method,
Chemical vapor deposition (CVD), physical vapor deposition (PV
D), liquid phase epitaxy (LPE) and the like are known. As a method for forming an organic compound thin film, a Langmuir-Blodgett method (LB method) and the like are known. What is generally called a quantum dot can be manufactured by utilizing a process in which a raw material sublimated in a high vacuum using a vacuum apparatus such as the MBE method described above forms dots in a self-organizing manner on a solid substrate. it can.

[0004]

However, in the above-described method, it is difficult to control the distance between dots and the size distribution, and there is a problem that it takes a lot of cost to control the structure to a desired structure. . The present invention has been made in view of the above circumstances, and synthesizes nanometer-sized ultrafine particles (hereinafter, referred to as “nanoparticles”) by a colloid chemistry technique, and provides an emulsion containing the synthesized nanoparticles. By inkjet coating on a solid substrate, size distribution control and particle domain size can be easily controlled without the need for vacuum (for example, there are methods such as changing the concentration of surfactant in the emulsion), It is another object of the present invention to provide a method capable of efficiently producing a nanoparticle thin film without wasting particles to be applied.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, by coating an emulsion containing nanoparticles on a solid substrate by a specific method, The present inventors have found that a nanoparticle thin film capable of easily controlling the structure of the particle thin film and exhibiting the TDLM function can be manufactured, and arrived at the present invention.

That is, the gist of the present invention is to provide an ultrafine particle (hereinafter, referred to as an ultrafine particle) having a function of increasing or increasing and memorizing photoluminescence intensity (hereinafter referred to as “emission intensity”) as a function of irradiation time or irradiation amount of excitation light. A method of forming a thin film comprising an aggregate of “nanoparticles” on a solid substrate, comprising: dispersing a nanoparticle in an emulsion in which a continuous phase is an aqueous phase and a dispersed phase is an oil phase. A method for producing a nanoparticle thin film, which is characterized by performing inkjet coating thereon.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The TDLM function of the present invention is characterized in that, when a thin film having an aggregate of nanoparticles is used, photoluminescence from a region of the nanoparticle thin film irradiated with excitation light is exposed at room temperature and in contact with air. The (fluorescence) intensity increases several times over the initial intensity as a function of the irradiation time (irradiation dose). Thus, an arbitrary image (image) can be formed on the nanoparticle thin film from the difference (contrast) in the photoluminescence intensity between the excitation light irradiation region and the non-irradiation region on the nanoparticle thin film. Such an optical memory effect is an essential physical property of a multi-particle system in which nanoparticles are close to each other in a nano-particle thin film formed on a solid substrate by various coating methods. The thickness of the nanoparticle thin film,
The photoluminescence (fluorescence) intensity from the nanoparticle thin film can be controlled by changing the material of the solid substrate, the excitation light intensity, the irradiation method (continuous or intermittent), and the like.

In the present invention, the time for increasing the emission intensity is usually 3 hours or less, preferably 1 × 10 ⁻¹² seconds to 1 hour.
It is about time, and the rate of increase of the emission intensity is usually 1.1 times or more, preferably about 2 to 100 times the initial emission intensity. The storage time of the light emission intensity is 1 second or more, preferably 1 hour or more at a temperature of 77 K or more.

The nanoparticles to be used in the present invention include fine particles having a particle size of usually 0.5 to 100 nm, preferably 0.5 to 50 nm, and more preferably 1 to 10 nm. If the particle size is too large, it becomes bulky, and if it is too small, it becomes atoms or molecules themselves. The type of the nanoparticles is not particularly limited, and may be fine particles of a predetermined size.
Group I-VII compound semiconductors such as CuCl, CdS, CdS
semiconductor crystals such as II-VI compound semiconductors such as e, III-V compound semiconductors such as InAs, and group IV semiconductors;
Examples include metal oxides such as iO ₂ , SiO, and SiO ₂ , phosphors, inorganic compounds such as fullerenes and dendrimers, organic compounds such as phthalocyanines and azo compounds, and composite materials thereof.

It should be noted that, within a range not to impair the object of the present invention,
The surface of these nanoparticles may be chemically or physically modified, and additives such as a surfactant, a dispersion stabilizer and an antioxidant may be added. Such nanoparticles can be obtained by colloidal chemistry, such as the reverse micelle method (Lianos, P. et a).
l., Chem. Phys. Lett., 125, 299 (1986)) and the hot soap method (Peng, X. et al., J. Am. Chem. Soc., 119, 7).
019 (1997)).

According to the present invention, a nanoparticle thin film is prepared by inkjet-coating a dispersion of the above-mentioned nanoparticles in an emulsion (O / W emulsion) in which the continuous phase is an aqueous phase and the dispersed phase is an oil phase on a solid substrate. Is prepared.
By this method, the thickness of the nanoparticle thin film can be controlled by changing the concentration of the nanoparticles and the concentration of the surfactant in the dispersion.

The aqueous phase is mainly composed of water, but may be used by adding a water-soluble organic solvent to water. Examples of the water-soluble organic solvent include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol (# 200, # 4).
00), glycerin, alkyl ethers of the above glycols, N-methylpyrrolidone, 1,3-dimethylimidazolinone, thiodiglycol, 2-pyrrolidone, sulfolane, dimethylsulfoxide, diethanolamine,
Triethanolamine, ethanol, isopropanol and the like. The amount of the water-soluble organic solvent used in the aqueous dispersion medium is usually preferably 30% by weight or less, and more preferably 20% by weight or less.
More preferably, it is set to be% by weight.

The content of the nanoparticles in the dispersion varies depending on the desired film (layer) structure or particle arrangement structure and the film (layer) thickness, but is usually 0.01 to 10% by weight based on the total weight of the dispersion. , But more preferably in the range of 0.05 to 1% by weight. If the content of the nanoparticles is too small, the TDLM function may not be able to be sufficiently exhibited, and if too large, the ejection stability during inkjet coating is impaired.

In the method of the present invention, it is preferable that a surfactant and a solvent for dispersing the nanoparticles coexist in the dispersion used for ink-jet coating. Examples of the surfactant include known surfactants such as anionic surfactants (sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium laurate, ammonium salts of polyoxyethylene alkyl ether sulfate, etc.), nonionic surfactants Activators (polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, etc.), and these may be used alone or Two or more kinds can be used as a mixture. The amount of the surfactant is usually 0.1 to 30 with respect to the total weight of the ink.
Although it is used in the range of 5% by weight, it is more preferably in the range of 5 to 20% by weight. When the amount of the surfactant is less than this range, oil-water separation occurs in the aqueous dispersion, and a uniform coating may not be obtained. Conversely, if it is more than this range, the viscosity of the aqueous dispersion medium tends to be too high.

The solvent for dispersing the nanoparticles is usually a liquid such as toluene, hexane, pyridine or chloroform, and is preferably volatile. The amount of the dispersing solvent is usually used in the range of about 0.1 to 20% by weight, but is more preferably in the range of 1 to 10% by weight. If the amount of the dispersing solvent is less than this range, the amount of ultrafine particles that can be contained in the aqueous medium becomes small. Conversely, if it is more than this range, oil-water separation may occur in the aqueous dispersion medium.

Further, an organic compound can be dissolved in the dispersion. Such organic compounds include:
Trioctyl phosphine oxide (TOPO), thiophenol, photochromic compounds (such as spiropyran and fulgide), charge-transfer complexes, electron-accepting compounds, and the like are preferable, and those that are solid at room temperature are preferable. in this case,
The amount of the organic compound in the dispersion is 1/10000 or more, preferably 1/1000 to 1%, based on the weight of the nanoparticles.
It is about 0 times.

As long as the object of the present invention is not impaired, additives such as a surfactant, a dispersion stabilizer and an antioxidant, or a polymer or a binder such as a material which gels in a coating and drying process are added to the suspension. May be added. The solid substrate used in the present invention is usually an organic solid such as a polymer or paper, or an inorganic solid material such as a glass, a metal, a metal oxide, silicon, or a compound semiconductor. TDL
For the purpose of maintaining the intrinsic luminescence of the nanoparticle thin film having the M function, it is preferable that the material be a material that does not exhibit significant emission in or near the emission wavelength band of the nanoparticles. Note that the surface of the solid substrate can be modified to be hydrophobic or hydrophilic as long as the object of the present invention is not impaired.

After completion of the ink-jet coating, drying is usually performed by a conventional method. In the present invention, for example, first, at atmospheric pressure, air drying at -20 to 200 ° C., preferably at about 0 to 100 ° C. for 1 hour or more, preferably 3 hours or more, and then drying under reduced pressure if necessary. good. The degree of pressure reduction at this time may be 1 × 10 ⁵ Pa or less, but is preferably about 1 × 10 ⁴ Pa or less, and the temperature is usually −20 to 200 ° C., preferably 0 to 100 ° C. The decompression time is about 1 to 24 hours.

Although the thickness of the nanoparticle thin film obtained by the above method is not particularly limited, it is usually from the diameter of the nanoparticle to 1 mm, preferably from the diameter of the nanoparticle to 100 μm.
m. Further, it is preferable that the nanoparticles exist at a certain density or higher in the nanoparticle thin film. In that sense, the average interparticle distance between the individual nanoparticles in the aggregate of nanoparticles is usually within the range of 10 times the particle diameter, and more preferably within the range of 2 times the particle diameter. If this average interparticle distance is too large, the nanoparticles will not exhibit collective function.

In the present invention, it is possible to arbitrarily control the geometrical shape of the above-mentioned nanoparticle thin film by patterning (for example, a pattern with a hydrophilic / hydrophobic surface) on the solid substrate in advance. is there. The patterned or non-uniform (uniform) nanoparticle thin film obtained by the manufacturing method of the present invention exhibits a remarkable TDLM effect as described above. By exciting the nanoparticle thin film (continuously or intermittently) with light of a suitable wavelength, the photoluminescence intensity from the film increases as a function of the excitation light irradiation time. The increased photoluminescence intensity of the excitation light irradiation area on the film without any special treatment is maintained at room temperature for at least several hours. It is also possible to reduce (eliminate) the increased photoluminescence intensity by applying light, thermal, electrical, chemical, magnetic or mechanical external fields. Further, the photoluminescence intensity from the nanoparticle film can be controlled by changing the film thickness, the material of the solid substrate, the intensity of the excitation light, the irradiation method (continuous or intermittent), and the like. Such a nanoparticle thin film can be applied to various devices, specifically, an information recording medium, a display, an imaging device, an image processing device, a memory-based copy, an integrating optical sensor, a multi-channel processor, and the like.

[0021]

EXAMPLES Specific examples of the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention.

Example 1 (Preparation of recording liquid) 11.1 mg of CdSe nanoparticles having an average particle diameter of 3.4 nm were dispersed in 0.5130 g of chloroform. To this solution, 1502.5 mg of sodium dodecyl sulfonate and 9530 mg of ion-exchanged water were added and shaken for about 5 minutes to prepare an emulsion containing nanoparticles.

[0023]

[Table 1] Composition of the nanoparticle-containing emulsion Used amount (parts by weight) CdSe nanoparticles having an average particle diameter of 34 ° 0.1 Sodium dodecylsulfonate 13.0 Chloroform 4.4 Deionized water 82.5 Total 100.0

(Preparation of Thin Film by Inkjet Method) Using an emulsion containing nanoparticles obtained by the method described in the above example, an inkjet printer (a product of Hewlett-Packard Company, trade name DeskWriter)
660C) OHP film for inkjet printer Model Number M manufactured by Mitsubishi Chemical Corporation
Inkjet coating was performed on C701 by solid printing of 12.6 cm × 6.1 cm.

(Measurement of Photoluminescence) The nanoparticle thin film on the OHP sheet prepared by the above method was placed at room temperature,
Stored in the dark for 24 hours and dried. To enhance light emission, four solid printed portions are cut into 3 cm x 3 cm sections, and superimposed photoluminescence (hereinafter referred to as PL)
Abbreviation). The superposition is performed to emphasize the PL peak. FIG. 1 shows the profile of this PL. Light emission by the CdSe ultrafine particles was confirmed at a wavelength around 555 nm, and it was found that good printing was performed. The peaks at the wavelengths of 535 nm and 600 nm are C
This is due to the molecular vibration of trioctylphosphine oxide, which is a capping agent used when synthesizing dSe by a colloid chemical technique.

(Confirmation of TDLM Phenomenon) After continuously irradiating the thin film containing CdSe nanoparticles with excitation light having a wavelength of 400 nm for one hour, the PL spectrum was measured again. As a result, the PL intensity was increased, and the TDLM phenomenon was confirmed. Was. This is shown in FIG.

[0027]

According to the method of the present invention, a nanoparticle thin film whose particle domain size and the like can be easily controlled can be produced without requiring a vacuum unlike the MBE method.

[Brief description of the drawings]

FIG. 1 is an emission spectrum of a semiconductor nanoparticle thin film formed on an OHP film by an inkjet method.

FIG. 2 is an emission spectrum of a semiconductor nanoparticle thin film formed on an OHP film by an inkjet method, which is further irradiated with excitation light having a wavelength of 400 nm for one hour.

Claims (15)

[Claims] 1. Ultrafine particles (hereinafter, referred to as "nanoparticles") having a function of increasing or increasing and memorizing photoluminescence intensity (hereinafter referred to as "emission intensity") as a function of irradiation time or irradiation amount of excitation light. Name)
In a method of forming a thin film composed of an aggregate of the above on a solid substrate, it is preferable to inkjet-coat a dispersion liquid in which nanoparticles are dispersed in an emulsion in which a continuous phase is an aqueous phase and a dispersed phase is an oil phase. Characteristic method of producing nanoparticle thin film. 2. The method according to claim 1, wherein the content of the nanoparticles in the emulsion is 0.01 to 10% by weight. 3. The method for producing a nanoparticle thin film according to claim 1, wherein the emulsion contains water, a surfactant, an organic compound, and a solvent for dispersing the nanoparticles. 4. The method for producing a nanoparticle thin film according to claim 3, wherein the amount of the organic compound in the emulsion is 1 / 10,000 or more based on the weight of the nanoparticles. 5. The organic compound as a solid at room temperature.
Or the method for producing a nanoparticle thin film according to 4. 6. The method for producing a nanoparticle thin film according to claim 1, wherein the ink-jet coating is followed by air drying at a temperature of −20 to 200 ° C. for 30 minutes or more at atmospheric pressure. 7. The time for increasing the emission intensity is 1 × 10
^The method for producing a nanoparticle thin film according to any one of claims 1 to 6, wherein the time is at least ^-12 seconds. 8. The method for producing a nanoparticle thin film according to claim 1, wherein the storage time of the emission intensity at a temperature of 77 K or more is 1 second or more. 9. The method for producing a nanoparticle thin film according to claim 1, wherein the rate of increase in luminescence intensity is 1.1 times or more the initial luminescence intensity. 10. The method for producing a nanoparticle thin film according to claim 1, wherein the nanoparticles have a particle size of 0.5 to 100 nm. 11. The method according to claim 1, wherein the nanoparticles are inorganic compounds.
11. The method for producing a nanoparticle thin film according to any one of items 10 to 10. 12. The method according to claim 1, wherein the nanoparticles are organic compounds.
11. The method for producing a nanoparticle thin film according to any one of items 10 to 10. 13. The method of claim 1, wherein the nanoparticles are metal oxides.
11. The method for producing a nanoparticle thin film according to any one of items 10 to 10. 14. The method according to claim 1, wherein the nanoparticles are semiconductors.
0. The method for producing a nanoparticle thin film according to any one of the above items. 15. The thickness of a thin film obtained by the production method according to claim 1 is a nanoparticle diameter of 1 to 1 m.
m is a nanoparticle thin film.