JP2004275925A - Metal complex nano-crystal lb film and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable and two-dimensionally regular arrangement of nano-crystal. <P>SOLUTION: The production method of a metal complex nano-crystal LB (Langmuir-Blodgett) film is a method for producing a regular arrangement film of a nano-crystal containing mutually same or different two metal elements Ma and Mb and comprises (1) the first step of respectively preparing a first inverse micelle solution containing a metal complex anion having Ma as a center metal and a second inverse micelle solution containing Mb cation; (2) the second step of mixing the first inverse micelle solution and the second inverse micelle solution; and (3) the third step of isolating nano-crystal obtained by adding a long chain fatty acid to the mixed solution obtained in the second step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a metal complex nanocrystalline LB film and a method for producing the same. More specifically, metal ions prepared using the nano-bound space of the reverse micelles are atomized, and nanocrystals of a metal complex, which is precisely ordered at the molecular level, are optionally formed on various substrates as LB (Langmuir-Blodgett) films. And a method of regularly arraying them by thickness.
[0002]
[Prior art]
With the development of new electronic devices different from semiconductors being actively developed, strongly correlated electron systems, in which the degree of freedom of electron spin plays an important role, are attracting attention. Furthermore, the various properties (redox, magnetism, optical properties, and their composite properties (optical spin transfer, etc.)) generated by the electronic interaction between different transition metal ions can be found in nanometer-sized electronic devices (molecular devices). Is attracting attention as the basic operation principle of
[0003]
The three-dimensionally crosslinked complex has a possibility that the electron population itself undergoes a phase change due to an external field, and the physical properties thereof can be dramatically changed. That is, the three-dimensional cross-linked complex has an advantage that a sufficient output can be obtained even when the size is reduced to a nano-size because the electron group is involved in the phase change and a huge response can be obtained. Accordingly, nano-sizing can be an effective means for applying complex crystals to electronic devices. If the change in the electronic state of the metal ions present at the interface by the nano-size of the complex crystal is successfully controlled by an external field such as an electric field, a large stress will be applied to the electron group inside the crystal, It is possible to pioneer a new group of substances that can elicit high-speed huge responses (reversible physical property conversion).
[0004]
Therefore, in order to construct the target electronic element, it is necessary to establish (1) an advanced technology of crystal formation in which arbitrary different transition metal ions are precisely ordered at the atomic and molecular level, and (2) the crystal preparation. The method is simple, (3) the nano-size of the crystal and its particle size (crystal diameter) are uniform (monodispersity), and (4) the two-dimensional or three-dimensional regular arrangement of the obtained nano-crystal. Is an essential condition.
[0005]
On the other hand, the complex chemistry can freely handle various (organic and inorganic) ligands and the coordination structure of metal ions, and therefore the conditions of the above (1) and (2) are greatly different from other fields. Leading. For this reason, the properties exhibited by the complex bulk crystal have attracted great expectations as the operating principle of electronic devices.
[0006]
However, for practical use, the above-mentioned (3) and (4) remain problems. As a solution to the above-mentioned problem (3), S.S. Mann et al. (Non-Patent Document 1) have reported on nano-size control of heterometal complex crystals using a microemulsion. The present inventors have also prepared a heterometallic polynuclear complex by mixing different transition metal ions and a suitable bridging ligand by utilizing the nano-bound space of the reverse micelles, and thereby producing a heterometal polynuclear complex. Complex nanocrystals with extremely good properties) can be produced. For example, formation of a desired Fe—CN—Co complex nanocrystal and heterometal complex nanocrystal (Fe—CN—Fe, Fe—CN—La, Cr—CN—La, Cr—oxalato-La complex) The formation of is confirmed by various spectroscopic methods, and it has been confirmed that the reverse micelle solution containing nanocrystals is stable for a long time (one month or more).
[0007]
[Non-patent document 1]
NANO LETTERS Vol. 2, No. 3, 225-229, 2002
[Problems to be solved by the invention]
Accordingly, it is a primary object of the present invention to provide a stable ordered array of nanocrystals.
[0009]
[Means for Solving the Problems]
The present inventor has conducted intensive studies in view of the problems of the prior art, and as a result, has found that the above object can be achieved by adopting a manufacturing method having a specific process, and has completed the present invention.
[0010]
That is, the present invention relates to the following metal complex nanocrystal LB film and a method for producing the same.
[0011]
1. A method for producing a regular array film of nanocrystals containing two metal elements Ma and Mb which are the same or different from each other,
(1) a first step of preparing a first reverse micelle solution containing a metal complex anion having Ma as a central metal and a second reverse micelle solution containing a cation of Mb,
(2) a second step of mixing the first reverse micelle solution and the second reverse micelle solution, and (3) a long-chain fatty acid is added to the mixed solution obtained in the second step, and the obtained nanocrystals are converted into single crystals. Third step to release,
A method for producing a metal complex nanocrystal LB film, comprising:
[0012]
2. Item 2. The production method according to the above item 1, wherein the long-chain fatty acid is a fatty acid having 8 to 20 carbon atoms.
[0013]
3. 3. An LB film obtained by the production method according to item 1 or 2, wherein the LB film is composed of nanocrystals of a complex containing Ma and Mb, and a long-chain fatty acid is coordinated to Ma and Mb at a crystal interface. A metal complex nanocrystal LB film characterized by the above-mentioned.
[0014]
4. 2. The method according to the above item 1, wherein in preparing the first reverse micelle solution and the second reverse micelle solution, at least one of AOT (Di-2-ethylhexyl sulfosuccinate sodium salt) and DBS (Sodium dodecylbenzenesulfonate) is used as a reverse micelle agent. .
[0015]
5. Item 2. The production method according to Item 1, wherein the long-chain fatty acid is a monocarboxylic acid having 8 or more carbon atoms.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
1. The method for producing a metal complex nanocrystal LB film The production method of the present invention is a method for producing an ordered array of nanocrystals containing two same or different metal elements Ma and Mb,
(1) a first step of preparing a first reverse micelle solution containing a metal complex anion having Ma as a central metal and a second reverse micelle solution containing a metal complex cation having Mb as a central metal,
(2) a second step of mixing the first reverse micelle solution and the second reverse micelle solution, and (3) a long-chain fatty acid is added to the mixed solution obtained in the second step, and the obtained nanocrystals are converted into single crystals. Third step to release,
It is characterized by having.
[0017]
First step In the first step, a first reverse micelle solution containing a metal complex anion having Ma as a central metal and a second reverse micelle solution containing a cation of Mb are prepared.
[0018]
Ma and Mb are metal components constituting the ordered film, and can be appropriately selected according to the desired properties of the ordered film. For example, for Ma, Fe, Ru, Co, Cr, etc., and for Mb, Fe, Ru, Co, Cr, rare earth ions and the like can be mentioned. Ma and Mb may be the same or different from each other. The metal complex anion having Ma as the central metal can be appropriately selected according to the type of the central metal and the like. Therefore, there is no particular limitation on the type of ligand, the number of coordination, and the like. For example, cyano ion (CN ⁻ ), oxalato ion (C ₂ O ₄ ²⁻ ), oxo ion (O ^{2 −} ), sulfide ion (S ^{2 −} ), thiocyanato ion (SCN ⁻ ), chloro ion (Cl 2 ^- ) And the like can be mentioned as the ligand. Further, the type of Ma is not limited, but a divalent to tetravalent metal is preferable. Examples of the divalent cation include Mn ²⁺ , Fe ²⁺ , Cu ²⁺ , Co ²⁺ , and Ni ²⁺ . Examples of the trivalent cation include Fe ³⁺ , Co ³⁺ , La ³⁺ , and Cr ³⁺ . Examples of tetravalent cations include Ti ⁴⁺ and Zr ⁴⁺ . More specifically, for example, when the central metal is Ni, Ni (CN ₄ ) ^2- or the like can be used. If the center metal is Fe, Fe ^{_(CN) 6 3-} and the like can be used.
[0019]
On the other hand, the cation of Mb may be appropriately selected according to the type of metal or the like. Although the valence is not limited, it is particularly preferably divalent to tetravalent. Examples of the divalent cation include Mn ²⁺ , Fe ²⁺ , Cu ²⁺ , Co ²⁺ , and Ni ²⁺ . Examples of the trivalent cation include Fe ³⁺ , Co ³⁺ , La ³⁺ , and Cr ³⁺ . Examples of tetravalent cations include Ti ⁴⁺ and Zr ⁴⁺ . Further, Mb may be the same as Ma or may be different.
[0020]
The method for preparing the first reverse micelle solution and the second reverse micelle solution is not particularly limited. In the case of the first reverse micelle solution, a first solution containing a metal complex anion having Ma as a central metal is prepared in advance. The first solution is obtained by dissolving the above metal complex anion in water. The concentration of the first solution is desirably 0.1 to 1 mol / L. Next, the first reverse micelle solution is obtained by mixing the first solution with an organic solvent (hexane, toluene, etc.) in which the reverse micelle agent is dissolved. The type of the reverse micelle agent is not limited, but at least one of AOT (Di-2-ethylhexylsulfosuccinate salt) and DBS (Sodium dodecylbenzenesulfonate) is particularly desirable. The amount of the reverse micelle agent used may be a concentration at which the first solution is solubilized as reverse micelles. Generally, the molar ratio of water to the reverse micelle agent is W = [water] / [AOT]. Or DBS] may be adjusted to 5 to 50.
[0021]
Similarly, in the case of the second reverse micelle solution, a second solution containing a cation of Mb is prepared in the same manner, and this is mixed with an organic solvent in which a reverse micelle agent is dissolved, whereby the second reverse micelle solution is formed. can get. The second solution is an aqueous solution of a metal salt containing Mb (CoCl ₂ , Fe (NO ₃ ) ₃ , La (NO ₃ ) _3, etc.). The concentration of the second solution and the type and amount of the reverse micelle agent may be the same as in the case of the first reverse micelle solution. The volume of the organic solvent is not particularly limited, but is preferably about 10 to 100 ml.
[0022]
Second step In the second step, the first reverse micelle solution and the second reverse micelle solution are mixed. Basically, this mixture forms metal complex nanocrystals. The production rate of the nanocrystal can be adjusted by the concentration of the solution, the concentration of the reverse micelle agent, and the like.
[0023]
The mixing method is not particularly limited, and a known mixing device can be used. The mixing ratio of the two may be such that the molar ratio of metal complex anion: metal cation = 1: 0.7 to 1.3.
[0024]
Third step In the third step, first, a long-chain fatty acid is added to the mixture obtained in the second step. Preferably, the long-chain fatty acid is added immediately after mixing the first reverse micelle solution and the second reverse micelle solution.
[0025]
The long-chain fatty acid to be used can be appropriately selected according to the type of the metal component in the mixed solution, etc., and generally, a fatty acid having 8 or more carbon atoms, particularly a fatty acid having 8 to 20 carbon atoms is preferable. Further, the long-chain fatty acid may be either saturated or unsaturated. Further, the long chain fatty acids may be in the form of salts such as sodium salts, potassium salts and the like. In the present invention, as the long-chain fatty acid, a monocarboxylic acid such as nonanoic acid, decanoic acid, and stearic acid can be suitably used.
[0026]
After the addition of the long-chain fatty acids, the generated nanocrystals are isolated. Usually, the nanocrystal is a metal complex nanocrystal whose crystal interface is protected by the added long-chain fatty acid. The isolation method can be performed according to a known method. For example, a film may be formed by a known method using the obtained nanocrystal solution. More specifically, a solution in which the above nanocrystals are dissolved in a volatile solvent (such as chloroform) is spread on a water surface, and after the volatile solvent is evaporated, two-dimensionally using a known LB film forming apparatus or the like. An ordered film can be obtained. By placing this arrayed film on a substrate (such as an alumina substrate), a regular array film (two-dimensional regular array) of metal nanocrystals can be formed on the substrate. In addition, by repeating such an operation, the above-described ordered array film can be laminated to obtain a three-dimensional ordered array film.
[0027]
These two-dimensionally ordered films or three-dimensionally ordered films can be heat-treated as necessary. By performing the heat treatment, a composite oxide nanodot and a composite oxide nanothin film that maintain nanouniformity (the composition of the nanometer-sized composite oxide is uniform at the atomic level) can be obtained. The heat treatment temperature in this case differs depending on the type of the thin film and the like, and generally may be appropriately set from a range of about 400 to 600 ° C. (for example, about 500 ° C.).
2. Metal complex nanocrystal LB film The metal complex nanocrystal LB film of the present invention is an LB film obtained by the production method of the present invention, and is composed of nanocrystals of a complex containing Ma and Mb, and has a Ma at the crystal interface. And Mb are coordinated with long-chain fatty acids.
[0028]
As the coordinated long-chain fatty acid, the long-chain fatty acid used in the above-described production method is a component of the LB film of the present invention as it is. Therefore, the type of long-chain fatty acid differs depending on the long-chain fatty acid used in the production process. The content of the long-chain fatty acid also depends on the amount used in the production process, but strictly depends on the particle size of the nanocrystals, that is, the ratio of Ma and Mb present at the crystal interface with respect to all metal ions.
[0029]
The average particle size of the metal complex nanocrystals present in the LB film of the present invention can be controlled mainly by the value of W = [water] / [AOT or DBS]. Further, the thickness is generally about 5 to 20 nm, though it depends on the type of the metal element as a constituent element, its coordination structure, and the like. Further, the LB film of the present invention may be a single layer (two-dimensional regularly arranged film) or a laminated structure (three-dimensionally arranged film) in which two or more of the single layers are laminated.
[0030]
[Action]
The metal complex nanocrystals of the present invention, CN as a ligand for connecting the metal ion - (cyano ion), using C 2 O 4 2- (oxa Lato ions) or the like. For example, hexane of a reverse micelle containing an aqueous solution of a complex anion of the type Ma (CN) n− (n = 2, 3, or 4) and a cation of Mb n ′ + (n ′ = 2, 3, or 4), respectively. or toluene solutions were prepared, CN by mixing them - is (cyano ion) and C 2 O 4 2- (oxa Lato ions) crosslinked heterodimer metal complex nanocrystals obtained. FIG. 1 shows an image diagram of a process in which nanocrystals are generated by CN - crosslinking. AOT (Di-2-ethylhexyl sulfosuccinate sodium salt) or DBS (Sodium dodecylbenzenesulfonate) is used as a reverse micelle agent. AOT and DBS, which are sulfonic acid types, cannot stabilize nanocrystals because of weak coordination force to metals (Ma, Mb) existing at the interface of nanocrystals (bulk crystallization occurs due to bonding between nanocrystals). .
[0031]
For this reason, after preparing nanocrystals using reverse micelles of AOT or DBS, long-chain fatty acids are added and exchanged with AOT or DBS, and the long-chain fatty acids coordinate to metal ions at the crystal interface. A stabilized metal complex nanocrystal is obtained. Metal complex nanocrystals in which long-chain fatty acids are coordinated at the crystal interface and stabilized are isolated, this chloroform solution is spread on the water surface, and the two-dimensional regular array of nanocrystals is formed on the water surface using the LB film preparation technique. Make a membrane. At this time, the property of self-assembly of the nanocrystal is utilized by the interaction of the long-chain alkyl group present at the interface of the nanocrystal. FIG. 2 shows an image diagram when the nanocrystals are two-dimensionally fixed on a substrate. In addition, by laminating a two-dimensional ordered array film of nanocrystals with an arbitrary thickness on a substrate, three-dimensional ordered immobilization of nanocrystals can also be performed.
[0032]
Furthermore, a photoinduced phase change crystal in which photoexcitation directly contributes to a change in state phase is expected as an optical property conversion device or a high-density optical recording material. However, in the prior art, the slow optical response hinders its practical use, and at the present time, properties sufficient to surpass thermal phase change materials using laser light have not been realized. On the other hand, the nano sizing of the metal crystal as in the present invention enables a high-speed optical response. By arranging the individual nanocrystals exhibiting the high-speed optical phase transition characteristic on a substrate in a two-dimensional regular arrangement, it becomes possible to use the nanocrystals for a high-density optical recording material.
[0033]
Specifically, a nanocrystal of a cyano-bridged three-dimensional complex (Fe—CN—Co type complex) known as a photo-induced spin (phase) transition crystal is prepared by the method of the present invention, and AOT or DBS is converted to nonane. Exchange with acid to stabilize nanocrystals. Using an LB film forming apparatus, Fe-CN-Co complex nanocrystals are regularly arranged on a substrate. The spacing between nanocrystals can be fine-tuned by changing the carbon number of the long-chain alkyl group. FIG. 3 shows a reversible conversion of the stable potential of the internal structure due to oxidation-reduction of Co ions at the interface and a photo phase transition cycle by controlling the interfacial electric field. The Co ions present at the interface of the prepared nanocrystals are selectively redox-reduced (Co (II) / (III)), the size of the Co ions at the interface is expanded and contracted, and a huge surface pressure is exerted inside the nanocrystals. A large stress is applied to the internal electronic state, and electron transfer (Co (II) -Fe) between Fe and Co ions is performed by photostimulation in a form adapted to the ion size (valence) of Co (II / III) ions on the surface. (III) induces a phase transition with {Co (III) -Fe (II)). FIG. 3 shows a reversible conversion of the stable potential of the internal structure due to oxidation-reduction of Co ions at the interface and a photo phase transition cycle by controlling the interfacial electric field.
[0034]
In the method of the present invention, an arbitrary combination of metal ions is possible, and therefore, it is possible to apply metal complex nanocrystals having various optical properties, magnetic properties, and the like to regular arrangement on a substrate. In addition, if this is heat-treated at low temperature, any composite oxide nanodots that maintain nano-uniformity (when two-dimensionally fixed) can be produced, and similarly, any composite oxide nano thin film (three-dimensionally fixed) Can be produced.
[0035]
【The invention's effect】
According to the present invention, it is possible to provide a more stable two-dimensional ordered array of nanocrystals, and even a three-dimensional ordered array, by using a specific reverse micelle solution and using long-chain fatty acids. is there.
[0036]
Therefore, in the present invention, it is possible to pioneer a new group of substances that can elicit a high-speed huge response (reversible physical property conversion), and to fabricate next-generation nanometer-sized electronic devices (molecular devices) and maintain nano-uniformity. It can be expected to produce any composite oxide nanodots (when fixed in two dimensions) or any composite oxide nano thin film (when fixed in three dimensions), greatly contributing to the development of nanomaterials and their practical use it can.
[0037]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to these examples.
[0038]
Example 1
An aqueous solution (0.1 mol / L) containing Co 2+ and an aqueous solution (0.1 mol / L) containing Fe (CN) 6 3- were added to a hexane solution (0.2 mol / L) of AOT, and the reverse micelles were added. A solution was prepared. The two were mixed at a molar ratio of 1: 1 to form a reverse micelle solution containing nanocrystals of the Fe-CN-Co type complex, and immediately exchanged with AOT by adding nonanoic acid. Nanocrystals stabilized by coordination with metal ions at the crystal interface were fabricated. The produced nanocrystal was confirmed to be a monodisperse nanocrystal having a size of 10 to 20 nm by observation with a transmission electron microscope (TEM).
[0039]
After isolating the nanocrystals, dissolving them in chloroform, developing this solution on the water surface, evaporating the solvent, and using the self-assembly of alkyl chains using an LB film forming apparatus, The nanocrystals were two-dimensionally ordered. The regular sequence could be confirmed from the pie-A curve (surface pressure-area). This two-dimensionally ordered film is transferred to a substrate, and the fact that the nanocrystals are two-dimensionally regularly fixed on the substrate is determined by using an atomic force microscope (AFM), a scanning tunneling microscope (STM), and a TEM. Confirmed by
[0040]
Example 2
In the same manner as in Example 1, preparation of nanocrystals of Fe—CN—Fe type complex, Fe—CN—La type complex, Cr—CN—La type complex, and Cr—C 2 O 4 —La type complex and Two-dimensional regular arrangement on the substrate was performed. The formation of the ordered array film was confirmed by the AFM and STM techniques.
[0041]
Example 3
AOT reverse micelles containing Mn 2+ and MnO 4 − aqueous solution were mixed at an arbitrary molar ratio to prepare mixed-valent Mn oxide nanoparticles (nanocrystals) and stabilized with nonanoic acid. In the same manner as in Example 1, two-dimensional regular arrangement on the substrate was performed. The regular arrangement was confirmed by AFM, STM and TEM.
[0042]
Example 4
After the three-dimensional regular arrangement of nanocrystals of the Cr-CN-La type complex on the substrate, the thermal decomposition behavior was investigated by thermogravimetric (TG) measurement, the optimal firing temperature was studied, and the perovskite-type composite oxide was examined. A nano thin film was obtained. The composition was confirmed to be the target composition by electron beam probe microanalyzer (EPMA) analysis. The uniformity of the metal element distribution was confirmed by Auger spectroscopy. In addition, it was confirmed by the AFM and STM techniques that composite oxide nanodots can be formed after the heat treatment in the two-dimensionally ordered array on the substrate.
[0043]
Example 5
The same results as in Examples 1 to 4 were obtained by replacing AOT with DBS and replacing the solvent used for preparing the reverse micelles with toluene.
[Brief description of the drawings]
FIG. 1 is a diagram showing preparation of complex nanocrystals using reverse micelles.
FIG. 2 is a diagram showing a two-dimensional regular arrangement of nanocrystals on a substrate using an interaction between alkyl chains of a surfactant.
FIG. 3 is a diagram showing a reversible conversion of a stable potential of an internal structure due to oxidation-reduction of Co ions at an interface and a light phase transition cycle by controlling an interfacial electric field.

Claims (3)

A method for producing a regular array film of nanocrystals containing two metal elements Ma and Mb which are the same or different from each other,
(1) a first step of preparing a first reverse micelle solution containing a metal complex anion having Ma as a central metal and a second reverse micelle solution containing a cation of Mb,
(2) a second step of mixing the first reverse micelle solution and the second reverse micelle solution, and (3) a long-chain fatty acid is added to the mixed solution obtained in the second step, and the obtained nanocrystals are converted into single crystals. Third step to release,
A method for producing a metal complex nanocrystal LB film, comprising: The method according to claim 1, wherein the long-chain fatty acid is a fatty acid having 8 to 20 carbon atoms. An LB film obtained by the production method according to claim 1, wherein the LB film is composed of a nanocrystal of a complex containing Ma and Mb, and a long-chain fatty acid is coordinated to Ma and Mb at a crystal interface. A metal complex nanocrystal LB film characterized by the above-mentioned.

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