JP2008044827A - Method for producing nanoparticle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method obtaing nanoparticles which have high crystallinity and are controlled in particle size highly precisely without separating by sizes. <P>SOLUTION: A nanoparticle raw material is charged into a reaction solvent, and is held at a presdetermined heating temperature for a predetermined time, so as to synthesize nanoparticles composed of the nanoparticle raw material (S1, S2). At this time, the particle sizes of the synthesized nanoparticles are controlled in accordance with the holding time at the prescribed temperature. Next, the synthesized nanoparticles are cleaned (S3 to S5). Thereafter, the nanoparticles are dispersed again into the reaction solvent, and holding is performed at a predetermined heating temperature for a predetermined time, so as to promote the crystallization of the nanoparticles (S6, S7). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing nanoparticles, and more particularly to a method for producing nanoparticles that are suitably used as a light emitter in an optical device.

  Nanoparticles are substances whose physicochemical properties vary greatly with particle size. In particular, it is known that semiconductor nanoparticles emit light with high efficiency depending on their crystallinity, and the wavelength thereof varies depending on the particle size.

  As a method for producing such semiconductor nanoparticles, a method utilizing colloid generation in an aqueous solution is common. In this method, in order to make the particle size uniform, [bis (2-ethylhexyl) sulfosuccinate sodium] (AOT) is used as a surfactant to form minute water droplets in an organic solvent. Nanoparticles are synthesized (see Non-Patent Document 1 below).

  In recent years, a production method using trioctylphosphine oxide (TOPO) as a reaction solvent has been proposed. In this method, since the solvent TOPO itself functions as a ligand surrounding the nanoparticles, despite the reaction at high temperature, it is possible to produce high-quality nanoparticles of the order of a single nanometer. .

  For example, for the production of nanoparticles composed of cadmium (Cd) -selenium (Se), TOPO and trioctylphosphine (TOP) are used as a reaction solvent, dimethylcadmium is used as a Cd raw material, selenium metal is used as a Se raw material, and 260 ° C. A method of synthesizing CdSe nanoparticles by heating at ˜300 ° C. for several tens of minutes has been disclosed (see Non-Patent Document 2 below).

  In addition, this manufacturing method is not limited to the synthesis | combination of II-VI group nanoparticles, such as CdSe, It is used as a general manufacturing method of the nanoparticle which consists of a metal and a compound semiconductor.

  Also, for example, for the production of nanoparticles composed of indium (In) -phosphorus (P), TOPO and TOP are used as reaction solvents, indium oxalate, indium fluoride, or indium chloride is used as the In raw material, and trimethylsilyl is used as the P raw material. Use phosphine. And the method of synthesize | combining InP nanoparticle by heating at 260 to 300 degreeC for 3 days in the state which mixed these is disclosed (refer the following patent document 3).

  In addition, for the production of InP nanoparticles, TOPO as a reaction solvent and Indium chloride are mixed and heated to 100 ° C., trimethylsilylphosphine is added thereto, heated to 265 ° C. and held for several days. Thus, a method of synthesizing InP nanoparticles has been disclosed (see Patent Document 4 below).

  As described above, besides the method using TOPO as a reaction solvent, a method using octadecene as a reaction solvent and myristic acid as a surface modifier is disclosed. For example, for the production of InP nanoparticles and InAs (arsenic) nanoparticles, indium acetate is used as the In raw material, trimethylsilylphosphine (or trimethylsilylarsenic as the As raw material) is used, and raw materials other than the P raw material (or As raw material) are used. Disclosed is a method of synthesizing InP nanoparticles and InAs (arsenic) nanoparticles by adding trimethylsilylphosphine by heating the dissolved solution to 300 ° C. and adding P raw material (or As raw material) dissolved in octadecene. (See Non-Patent Document 5 below).

J. Chem. Phys, 121, 10233, 2004, Heesun et al J. Am. Chem. Soc, 115, 8706, 1993, Murray et al "J. Phys. Chem. B" No.102, 1998, p.9791-9796 "J. Phys. Chem." No.100, 1996, p.7212-7219 “Nano Letters” vol.2, No.9, 2002, p.1027-1030

  However, the nanoparticle production method using the reaction solvent as described above can produce finer single-order nanoparticles, but has a large variation in particle size. For this reason, in order to obtain a desired physicochemical property, for example, an emission wavelength, it is common to perform a size separation process after the nanoparticles are synthesized.

  In the said nonpatent literature 5, it is supposed that the nanoparticle with a small dispersion | variation in particle size will be obtained. However, in this production method, since the dilution ratio of the particle raw material with respect to the reaction solvent is high, the synthesis yield of nanoparticles is low, and it is difficult to say that this is an industrially suitable production method.

  Therefore, an object of the present invention is to provide a production method capable of obtaining nanoparticles with high crystallinity whose particle size is controlled with high accuracy without size separation.

  The present invention for achieving such an object includes a step of synthesizing nanoparticles composed of the nanoparticle raw material by introducing the nanoparticle raw material into the reaction solvent and holding it at a predetermined heating temperature for a predetermined time; A step of promoting the crystallization of the nanoparticles by dispersing the nanoparticles in a reactive solvent and holding the nanoparticles at a predetermined heating temperature for a predetermined time.

  In such a manufacturing method, a step of promoting crystallization of the nanoparticles is provided as a step separate from the step of synthesizing the nanoparticles. As a result, in the process of synthesizing nanoparticles, the particle size is uniform with good controllability by setting the conditions focusing solely on particle size control without considering the crystallinity of the synthesized nanoparticles. Nanoparticles can be obtained. Here, from the experiments of the examples described below, in this synthesis, it is found that the particle size is made uniform by lowering the heating temperature, and the particle size grows by the holding time at the heating temperature. It was. For this reason, by performing synthesis for a predetermined holding time at a low heating temperature, it is possible to sufficiently promote crystallization of nanoparticles having a uniform particle size with good controllability in the subsequent crystallization promotion step. .

  As described above, according to the present invention, it is possible to obtain highly crystalline nanoparticles having a uniform particle size with high accuracy without size separation. Thereby, the manufacturing process of nanoparticles can be reduced, and a device using nanoparticles whose physicochemical properties are controlled with high accuracy can be produced.

  Hereinafter, an embodiment in which the present invention is applied to manufacture of nanoparticles made of a III-V compound semiconductor will be described based on the flowchart of FIG.

  First, in the next steps S1 and S2, nanoparticles are synthesized.

  In step S1, a reaction solvent having a boiling point higher than the synthesis process temperature is prepared, and a group III raw material serving as a group III element supply source is introduced and dissolved in the reaction solvent.

  As the reaction solvent, a coordinating organic solvent that coordinates to the surface of the synthesized nanoparticles is used singly or in combination. Examples of such a coordinating organic solvent include trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO).

  Moreover, you may use the reaction solvent combining the organic solvent which does not have coordination property, and a coordinating agent. Among these, examples of the organic solvent include hexadecylamine and octadecene. Examples of the coordinating agent include carboxylic acids such as myristic acid and oleic acid, thiols, and amines.

  Further, the reaction solvent may be used in combination with a coordinating organic solvent and an organic solvent having no coordinating property and a coordinating agent.

  As the group III material to be introduced into such a reactive solvent, an inorganic material, an organic material, or a group III element simple metal containing a group III element is used. Examples of inorganic materials include chlorides, hydroxides, oxalates, nitrates, sulfates, fluorides, bromides, iodides, and the like. On the other hand, examples of the organic material include carboxylate, metal alkoxide, and acetylacetonate salt. In addition, you may introduce | transduce such a III group raw material in a reaction solvent in combination of 1 type or multiple types.

  Next, in step S2, the reactive solvent in which the group III material is dissolved is heated to a predetermined heating temperature. The heating temperature here is higher than the temperature at which crystal nuclei are generated in the reaction solvent when the group V raw material described below is introduced. Also, as shown in the following examples, the higher the heating temperature here, the more likely the variation in the particle size of the synthesized nanoparticles will be, so in order to suppress the variation in the particle size, set the heating temperature as low as possible It is preferred that However, since the particle growth rate increases as the heating temperature increases, the heating temperature is set in consideration of the throughput of nanoparticle production. From the above, the heating temperature of the reaction solvent in which the group III raw material is dissolved is set to 100 ° C. or more and 250 ° C. or less.

  Then, a group V raw material serving as a supply source of the group V element is introduced into the reaction solvent heated to a predetermined heating temperature and held for a predetermined time. Thereby, nanoparticles having a predetermined particle size are synthesized.

  As the group V raw material, an inorganic material, an organic material containing a group V element, or a single group metal of a group V element is used. Examples of inorganic materials include chlorides, hydroxides, nitrates, sulfates, fluorides, bromides, iodides, and the like. On the other hand, examples of the organic material include carboxylate and metal alkoxide. In addition, you may introduce | transduce such a V group raw material in a reaction solvent in combination of 1 type or multiple types.

  The holding time is set in accordance with the particle size of the nanoparticles synthesized in consideration of the heating temperature. That is, as will be described in the following examples, the longer the retention time in step S2, the larger the particle size of the nanoparticles. Therefore, it is important to set the holding time according to the particle size to be obtained. However, since the growth rate varies depending on the heating temperature, the holding time is set in consideration of this heating temperature. As an example, this retention time is typically 30 minutes or less, preferably 20 minutes or less, and most preferably 10 minutes or less.

  After a predetermined holding time has elapsed, the reaction source is rapidly cooled by removing the heating source from the reaction vessel or adding a large amount of the reaction solvent to stop the synthesis of the nanoparticles.

  Next, in the following steps S3 to S5, the synthesized nanoparticles are washed.

  In step S3, impurities are removed by adding and aggregating the synthesized nanoparticles in a solvent having a low polarity such as methanol, and centrifuging and decanting.

  In step S4, the separated nanoparticles are introduced and dispersed in a solvent such as hexane.

  The above steps S3 and S4 are repeated a sufficient number of times until the impurities are sufficiently removed.

  Thereafter, in step S5, the solvent used in step 4 is removed and the cleaning is terminated.

  Next, in the following steps S6 and S7, crystallization of the washed nanoparticles is promoted.

  In step S6, the washed nanoparticles are dispersed in the reaction solvent. The reaction solvent is appropriately selected from the solvents exemplified in Step S1, and the same solvent as in Step S1 may be used.

  Next, in step S7, the reaction solvent in which the nanoparticles are dispersed is heated to a predetermined heating temperature and held for a predetermined time. This promotes crystallization of the synthesized nanoparticles.

  As the heating temperature and holding time at this time, a temperature at which particle growth of the synthesized nanoparticles does not occur is selected. In other words, even when there is no excess raw material in the reaction solvent, when this step is performed at a high temperature, the synthesized nanoparticles are dissolved and other particles are grown using this raw material. Because it is. Further, since the crystallization occurs at a lower temperature as the particle size is smaller, it is preferable to set a holding time that is long enough to allow crystallization to proceed sufficiently at a lower heating temperature. Therefore, here, the heating temperature is set in a range of 100 ° C. or higher and 250 ° C. or lower, and is held for a holding time (for example, 60 minutes to 330 minutes) corresponding to the degree of crystallization required for the nanoparticles. In the previous steps S3 to S5, the impurities in the synthesis solvent adhering to the nanoparticles are sufficiently removed, so that the particle growth of the nanoparticles in this step is prevented.

  After the above, the nanoparticle which promoted crystallization is taken out from the reaction solvent, and the nanoparticle production process is terminated.

  In the manufacturing method described above, steps S6 and S7 for promoting crystallization of the nanoparticles are provided separately from the step of synthesizing the nanoparticles in steps S1 and S2. Thereby, in the process (S1, S2) of synthesizing the nanoparticles, conditions such as the heating temperature and the holding time are mainly set only for controlling the particle size without considering the crystallinity of the synthesized nanoparticles. be able to. That is, according to the experiments of Examples and Comparative Examples described below, in this synthesis (S1, S2), the particle size is made uniform by lowering the heating temperature, and the particle size grows with the holding time. I understood. For this reason, it becomes possible to synthesize nanoparticles having a uniform particle size with good controllability.

  And in the process (S6, S7) which accelerates | stimulates crystallization after performing such a synthesis | combination, sufficient crystallization can be advanced with respect to the nanoparticle with uniform particle size.

  From the above, it is possible to obtain highly crystalline nanoparticles having a particle size controlled with high accuracy without performing size separation. As a result, it is possible to reduce the number of nano-particle manufacturing processes, and it is possible to manufacture a device using nanoparticles that can sufficiently control physicochemical properties and sufficiently exhibit high physical properties. . As a specific example, a display device having excellent color reproducibility can be realized by using nanoparticles that can emit light with high intensity in a narrow wavelength region. Further, in the synthesis of nanoparticles, it is not necessary to increase the dilution ratio of the raw material with respect to the reactive solvent to the dilution ratio described in Non-Patent Document 5. For this reason, the synthesis yield of the nanoparticles can be maintained high, and this is an industrially suitable production method.

  In the embodiment described above, the configuration in which the present invention is applied to the production of nanoparticles made of a III-V group compound semiconductor has been described. However, the present invention is not limited to application to such a method for producing nanoparticles, and the production of nanoparticles composed of other compound semiconductors, the production of nanoparticles composed of inorganic materials and conductive materials, The present invention is applicable to the production of nanoparticles using the above raw materials, and further to the production of nanoparticles composed of a single element, and the same effect can be obtained. That is, in the production of any nanoparticle, a procedure for separately promoting a crystallization of the nanoparticle is provided after the nanoparticle synthesis step. It should be noted that the nanoparticle synthesis step is a procedure suitable for the material constituting each nanoparticle. This makes it possible to obtain highly crystalline nanoparticles with particle size controlled with high accuracy.

<Examples 1-3>
InP nanoparticles were prepared as follows.

  First, TOPO and TOP, which are coordinating organic solvents, were mixed at a weight ratio of TOPO: TOP = 1: 9, and 10 ml was dispensed into a three-necked flask. To this, 0.6 g of indium chloride as an In raw material was introduced and stirred overnight at room temperature to obtain a transparent solution (step S1).

  This transparent solution was heated to 175 ° C., and 0.5 mg of trimethylsilylphosphine as a P raw material was added to the heated transparent solution using a syringe and held for 7 minutes. Thereby, InP nanoparticles were synthesized. After holding for 7 minutes, the heat source was removed from the three-necked flask (step S2).

  All the operations described above were performed in an atmosphere inactivated with argon.

  Next, the synthesized InP nanoparticles were aggregated with methanol, decanted after centrifugation (step S3), and dispersed in hexane to remove impurities contained in the solution (step S4). After repeating this process three times, hexane was removed from the InP nanoparticles using a rotary evaporator (step S5).

  The washed InP nanoparticles were dispersed in 10 ml of a reaction solvent in which TOPO and TOP were mixed at a weight ratio of TOPO: TOP = 1: 9 (step S6). The reaction solvent in which InP nanoparticles were dispersed was transferred to a three-necked flask and heated to 175 ° C. Then, after 60 minutes in Example 1, 150 minutes in Example 2, and 330 minutes in Example 3, the heating source was removed from the three-necked flask and the heating was terminated (Step S7).

Table 1 below shows the temperature history of each example.

<Comparative Example 1>
In the manufacturing method of the example, the InP nanoparticles synthesized in step S1 and step S2 were washed as in steps S3 to S5 and used as InP nanoparticles as they were without promoting crystallization.

<Comparative example 2>
In the production method of the example, the InP nanoparticles synthesized by changing the holding time in step S2 to 60 minutes are washed as in steps S3 to S5, and used as InP nanoparticles as they are without promoting crystallization. It was.

<Comparative Example 3>
In the manufacturing method of the example, the InP nanoparticles synthesized by changing the heating temperature in step S2 to 300 ° C. and the holding time to 5 hours are washed as in steps S3 to S5 without promoting crystallization. It was used as InP nanoparticles as it was.

  Table 1 also shows the temperature history of Comparative Examples 1 to 3.

<Evaluation results>
In FIG. 2, the result of having measured the X-ray-diffraction spectrum of the InP nanoparticle obtained by making it above is shown. In the figure, the X-ray diffraction spectrum of the InP nanoparticles obtained in Comparative Example 1 is representatively shown. From FIG. 2, it was confirmed that an InP crystal phase was generated in the InP nanoparticles.

  FIG. 3 shows the results of measuring the emission intensity with respect to the emission wavelength of the InP nanoparticles prepared in Example 3 and Comparative Example 1. As shown in this figure, the luminescence intensity of the InP nanoparticle of Example 3 that has undergone the crystallization promotion process after synthesis is higher than the luminescence intensity of the InP nanoparticle of Comparative Example 1 that does not perform the crystallization promotion process. ing. This confirmed the effect of promoting the crystallization of the synthesized InP nanoparticles by performing the crystallization promotion step after the synthesis.

  In FIG. 4, the result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticle produced in Examples 1-3 and the comparative example 1 is shown. As shown in this figure, the absorption spectra of the InP nanoparticles of Examples 1 to 3 that have undergone the crystallization promotion process after synthesis are almost the same as the absorption spectrum of the InP nanoparticles of Comparative Example 1 that does not perform the crystallization promotion process. The same. Accordingly, in combination with the result of FIG. 3 above, it was confirmed that in the crystallization promotion step after synthesis, the particle size of InP nanoparticles did not grow and only the crystallization promotion of InP nanoparticles was performed. Moreover, from this, it was confirmed that the particle size of InP nanoparticles was determined only by the synthesis step.

  In FIG. 5, the result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticle produced by the comparative examples 1 and 3 is shown. As shown in this figure, the InP nanoparticle of Comparative Example 3 having a heating temperature of 300 ° C. in the synthesis step is compared with the absorption spectrum of the InP nanoparticle of Comparative Example 1 having a heating temperature of 175 ° C. in the synthesis step. The absorption spectrum of the particles was gentle. The particle diameter estimated from this absorption spectrum is 3.3 nm to 3.7 nm in Comparative Example 1, while 2.3 nm to 5.7 nm in Comparative Example 3. Thereby, it was confirmed that variation in the particle size of InP nanoparticles can be reduced by lowering the heating temperature in the synthesis step.

  In FIG. 6, the result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticle produced by the comparative examples 1 and 2 is shown. As shown in this figure, the InP nanoparticle of Comparative Example 2 having a retention time of 60 minutes as compared with the absorption spectrum of InP nanoparticles of Comparative Example 1 having a retention time of 7 minutes at 175 ° C. also in the synthesis step. The absorption spectrum of the particles was shifted to the long wavelength side. Accordingly, if the heating temperature is constant in the synthesis process, the holding time is lengthened, the growth of InP nanoparticles is promoted, the particle size (particle diameter) is increased, and the particle size is controlled by the holding time. It was confirmed.

It is a flowchart which shows the manufacturing method of embodiment to which this invention is applied. 2 is an X-ray diffraction spectrum of InP nanoparticles prepared in Comparative Example 1. FIG. The result of having measured the light emission intensity with respect to light emission wavelength about the InP nanoparticle produced in Example 3 and Comparative Example 1 is shown. The result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticles produced in Examples 1 to 3 and Comparative Example 1 is shown. The result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticle produced by the comparative examples 1 and 3 is shown. The result of having measured the ultraviolet visible absorption spectrum about the InP nanoparticle produced by the comparative examples 1 and 2 is shown.

Claims (5)

Introducing a nanoparticle raw material into a reaction solvent, and synthesizing nanoparticles made of the nanoparticle raw material by holding at a predetermined heating temperature for a predetermined time; and
And a step of promoting the crystallization of the nanoparticles by dispersing the nanoparticles in a reactive solvent and holding the nanoparticles at a predetermined heating temperature for a predetermined time. The method for producing nanoparticles according to claim 1, wherein
A method for producing a nanoparticle, comprising controlling a particle size of the nanoparticle according to a holding time at the predetermined heating temperature in the step of synthesizing the nanoparticle. The method for producing nanoparticles according to claim 1, wherein
After the nanoparticle is synthesized, the nanoparticle is washed, and then a step of promoting crystallization of the nanoparticle is performed. The method for producing nanoparticles according to claim 1, wherein
A nanoparticle production method comprising synthesizing nanoparticles made of a compound semiconductor by using two or more kinds of raw materials containing different elements as the nanoparticle raw material. The method for producing nanoparticles according to claim 4, wherein
A nanoparticle production method comprising synthesizing a nanoparticle made of a III-V compound semiconductor as the nanoparticle.

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