JP2003326637A - Manganic acid nano-sheet ultrathin film and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manganese oxide ultrathin film of which the ultrafine film thickness can be controlled in a sub-nanometer range by a method perfectly different from a conventional method, and a manufacturing method therefor. <P>SOLUTION: A colloid solution in which a manganic acid nano-sheet is suspended and a cationic polymer solution are prepared. A substrate is alternately immersed in these solutions and this immersion operation is repeated to respectively adsorb the nano-sheet and the polymer on the substrate. Both components are alternately and repeatedly laminated at an interval of from a sub-nm to nm level to form a film. Subsequently, the polymer is removed to obtain a manganic acid nano-sheet ultrathin film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrathin film in which manganate nanosheets and organic polymers are alternately accumulated, a manganate nanosheet ultrathin film obtained by removing the polymer, and a method for producing each of these ultrathin films. Is. In particular, it relates to a manganate nanosheet ultrathin film expected to be used as an electrode material and the like by utilizing the solid-state redox property, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, attention has been focused on transition metal oxides as part of the creation of new functions. In particular, active proposals and reports on the thin film technology have been sent to various academic societies and publications. The manganese oxide thin film is one of them and is no exception. As for the direction of the research, a wide range of reports have been made from extremely basic to proposals for specific utilization technologies. In addition, such research trends are reflected in the patent literature as well, and in various fields, inventions relating to a technique for forming a thin film of manganese oxide have been actively made. The film forming technique is manufactured by a sol-gel method, electrodeposition, a CVD method, or the like.

However, in the above-mentioned conventional method, it is difficult to control the film thickness in the nanometer range by the sol-gel method and the electrolytic oxidation method, and the CVD method requires an extremely expensive apparatus, and has advantages and disadvantages. . It is expected that extremely strict control of the film thickness will be required in the future as the advanced use of manganese oxide thin films progresses. In consideration of the above circumstances, the present invention intends to provide an ultrathin manganate nanosheet thin film capable of controlling the film thickness at an ultrafine film thickness level by a method completely different from the conventional method and a method for producing the same. Is.

[0004]

[Means for Solving the Problems] Therefore, as a result of diligent research, a manganate nanosheet was obtained by subjecting a layered manganese oxide to a specific chemical treatment as described later, and was prepared separately from the obtained manganate nanosheet. Organic polycations are self-assembled from the liquid phase to sub-nm ~
Films can be formed by alternately adsorbing to the substrate material with a thickness in the nm range and repeating this, and extremely fine control of the film thickness is possible by adjusting and selecting the number of adsorptions, and the film composition , It has been found that it is possible to provide an ultrathin film formed by layer-by-layer film formation while controlling the structure at the nano level, and a manufacturing method thereof. The present invention has been made based on this finding.

That is, the present invention intends to alternately adsorb manganate nanosheets and organic polycations onto a substrate, thereby providing an ultrathin film of manganate nanosheets and a method for producing the same, which has been difficult in the past. It is an object of the present invention to provide a new ultra-thin film capable of easily achieving extremely precise control of the thickness in sub-nm and a method for producing the same, and the configuration taken for that purpose is as follows (1) to (7) As described in.

(1) Manganese oxide nanosheets (two-dimensional crystallites) obtained by exfoliating layered manganese oxide microcrystals and polymers are alternately laminated, and are composed of manganate nanosheets and polymers. Ultra thin film. (2) The ultrathin film comprising a manganate nanosheet and a polymer as described in the above item (1), wherein the two-dimensional crystallite is a manganate nanosheet represented by MnO ₂ . (3) The nanosheet and the polymer are respectively adsorbed on the substrate by repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganate nanosheets are suspended and the cationic polymer solution, and the components are sub-nm to nm. A method for producing an ultra-thin film composed of a manganate nanosheet and a polymer, characterized by accumulating multilayer films which are alternately repeated at level intervals. (4) A two-dimensional crystallite (manganese acid nanosheet) obtained by exfoliating layered manganese oxide microcrystals and a polymer are alternately laminated, and then the polymer is removed to obtain an ultrathin manganate nanosheet film. Ultra thin film of manganate nanosheet. (5) The manganate nanosheet ultrathin film according to item (4), wherein the two-dimensional crystallite is a manganate nanosheet represented by MnO ₂ . (6) By repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganate nanosheets are suspended and the cationic polymer solution, the nanosheet and the polymer are adsorbed on the substrate, respectively, and both components are sub-nm to nm. A method for producing an ultra-thin manganate nanosheet thin film, which comprises stacking films that are alternately repeated at level intervals and then removing the polymer to obtain an ultra-thin manganate nanosheet thin film. (7) The method for producing an ultrathin manganese oxide film according to the item (6), wherein the means for removing the polymer is performed by heating and is removed by decomposition.

The manganate nanosheet, which is a direct raw material to be laminated on the substrate, is obtained by peeling up to one host layer by subjecting titanium oxide having a layered structure to a special chemical treatment. The manganese oxide-based nanomaterials have morphological and structural characteristics such as a molecular thickness of 1 nm or less and a high two-dimensional anisotropy that are not present in conventional manganese oxides. A separate patent application is pending on the same date).

The manganese oxide having a layered structure used as the starting material in the present invention is a composition formula A _x MnO ₂ (A is one or two selected from Li, Na, K, Rb, or Cs). Alkali metal above, x ≦
It is a group of compounds given in 1). The layered manganese oxide (K _0.45 MnO ₂ ) used in the present invention was synthesized by a unique method developed by the present inventors as described in Examples below and used. For the layered manganese oxide, see C.I. Delmas, C.I. Foua
by Ssier et al. “Les Phases K _X M
nO ₂ (x <1) ”under the title Z. anorg.
lg. Chem. vol. 420, p. 184-192
(1976).

As a result of earnest research, the present inventors have found that
Hydrogen form H _{X 'MnO} this layered manganese oxide by acid treatment
After being converted into ₂ · nH ₂ O (x ′ ≦ 1, 0 ≦ n ≦ 3), by shaking in an aqueous solution of an appropriate amine or the like, the layers constituting the mother crystal, that is, the nanosheets, are formed one by one in water. We succeeded in introducing a colloidal solution that was peeled off and dispersed into. It is the first time that the present inventors have isolated this nanosheet from the layered oxide and provided it independently, and its morphology, specificity of properties, and the like are the starting crystals as described later. It was revealed that they have completely different morphology, structure, and characteristics from both the mother crystal and the conventional fine powder of manganese oxide. The thickness of the nanosheet depends on the crystal structure of the starting mother crystal, but it is extremely thin at 1 nm or less. On the other hand, the lateral size is on the order of sub-μm to μm, and has a very high two-dimensional anisotropy.

Since this manganate nanosheet is a kind of polyanion having a negative charge, by combining it with a polymer having a positive charge, it is possible to adsorb the manganate nanosheets in a self-assembled manner alternately on the surface of a properly treated substrate. Become.
That is, it was revealed that when a substrate whose surface was positively charged was immersed in a colloidal solution in which manganate nanosheets were dispersed, the nanosheets had a unique property of being adsorbed on the substrate surface by electrostatic interaction.

When the surface is completely covered with the manganate nanosheets, the charge state on the substrate surface changes negatively, and the accumulation of further nanosheets does not proceed due to electrostatic repulsion, and the adsorption reaction self-stops. Then, the substrate is dipped in an organic polycation solution so that the surface is coated with the polycation in the future. By repeating this self-organizing adsorption reaction, manganate nanosheets and polymers are alternately accumulated in a layer-by-layer manner, and an ultrathin film can be synthesized.

As a result, the obtained thin film has a nanostructure in which manganate nanosheets and organic polymers are stacked in the nm range. The actual film-forming operation is the following procedure,
According to the point. First, a series of operations, in which the substrate is (1) immersed in a manganate nanosheet colloidal solution, (2) washed with pure water, (3) immersed in an organic polycation solution, and (4) washed with pure water, is defined as one cycle. Is repeated as many times as necessary.

As the organic polycation, poly (diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI), polyallylamine hydrochloride (PA)
H) and the like are suitable. Various materials such as a quartz glass plate, a Si wafer, a mica plate, a graphite plate, and an alumina plate can be used as the substrate, and the size is not limited in principle.

However, surface cleaning and pretreatment prior to the laminating operation is essential. The cleaning treatment is typically performed by washing with a neutral detergent, degreasing with an organic solvent, and washing with concentrated sulfuric acid. The pretreatment is an operation for stably starting the self-assembly reaction, and is immersed in an organic polycation solution such as PEI to adsorb the polycation and introduce a positive charge onto the substrate surface.

The growth of the multilayer ultrathin film can be monitored by measuring the UV-visible absorption spectrum for each cumulative operation. Fig. 1 shows a typical example of ultra-thin UV film obtained by combining manganate nanosheets and PDDA.
The data of visible absorption spectrum are shown. This data shows that the concentration of manganate nanosheet colloidal solution is 0.08g.
It is the observation data measured under dm ^-3 . PDDA has no significant absorption in this measurement wavelength region, and the observed absorption is derived from the manganate nanosheet. By increasing the absorbance almost in proportion to the number of times of accumulation (Fig. 2), it was found that a certain amount of manganate nanosheets were accumulated on the substrate for each accumulation operation, and regular thin film growth occurred. It is proved. FIG. 3 shows the change in color tone of the sample formed in this way, and it is confirmed that the dark brown characteristic of manganese oxide is gradually exhibited as the number of accumulation increases.

FIG. 4 shows X-ray diffraction data of a sample in the same film forming process. As the accumulation progresses, a broad diffraction peak appears near 2θ = 10 ° and its intensity gradually increases (FIG. 4). This peak can be considered to reflect the repetition period of the manganate nanosheet and PDDA, which also supports the regular growth of the multilayer ultrathin film. The fact that the plane spacing is around 0.80 nm confirms that it has a nanostructure in the sub-nm range.

The cumulative amount of manganate nanosheets in the multilayer ultrathin film can be controlled in a wide range by changing the concentration, pH, immersion time and the like of the nanosheet colloidal solution among the process parameters of the adsorption cycle. As an example, FIG. 5 shows the relationship between the cumulative number of times and the UV / visible absorption spectrum when a film was formed using a manganate nanosheet colloidal solution having a concentration of 0.01 g dm ^-3 . There is. It is possible to suppress the cumulative amount of manganate nanosheets by using a solution having an apparently low concentration. Even in such a case, regular growth of a layer-by-layer multilayer film is possible.

It is also possible to form an inorganic film by heating and removing the organic polymer from the organic / inorganic composite ultrathin film in which the manganate nanosheets and the polymer thus prepared are accumulated. Figure 6 shows manganate nanosheets / PDD
It is a figure clarified based on the X-ray diffraction pattern showing the relationship between the cumulative number of A ultrathin films and the heating process. In this figure, the arrow indicates the Bragg peak indicating the stacking period (0.8 nm) of the cumulative multilayer film, and the black circle indicates 222 reflection of Mn ₂ O ₃ . The halo in which 2θ is 15 to 30 ° is derived from the quartz glass substrate. As shown in FIG. 6, a diffraction peak reflecting the nanostructure of the manganate nanosheet / polymer is seen up to 100 ° C., but this heating line disappears by heating at 200 ° C. or higher. This is because the polymer was thermally decomposed and removed, and it can be seen that an inorganic film was obtained.
When heated further, Mn ₂ O ₃ crystallizes above 500 ° C,
A manganese oxide thin film is obtained.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, according to the present invention, a colloidal solution of manganese nanosheets obtained by subjecting a layered manganese oxide to a specific chemical treatment and a polymer solution are alternately immersed in a substrate. Then, the film thickness was controlled autonomously, and by controlling the number of times, etc., we succeeded in forming a manganese oxide film whose thickness can be easily controlled in the sub-nanometer range. Next, the present invention will be specifically described based on Examples. However, this example is merely for the purpose of explaining the aspects of the present invention based on specific examples and for helping the understanding of the present invention, and is not intended to limit the present invention.

[0020]

Example 1 0.4 g of layered manganic acid powder (H _0.13 MnO ₂ .0.7H ₂ O) obtained by acid-treating layered potassium manganate represented by the composition formula K _0.45 MnO ₂ was tetrabutylammonium hydroxide. The resultant solution was added to 100 cm ³ and shaken (150 rpm) at room temperature for about 1 week to obtain a colloidal solution in which manganate nanosheets were dispersed. This was diluted to a concentration of 0.08 g dm ^-3 and hydrochloric acid was added to adjust the pH to 9. On the other hand, a 2 wt% polydimethyldiallylammonium (PDDA) chloride aqueous solution was prepared and its pH was adjusted to 9. Next, a quartz glass plate (5c
m × 1 cm) was washed with a 2% solution of Extran MA02 manufactured by Merck, and then immersed in a 1: 1 solution of concentrated sulfuric acid and methanol for 30 minutes each. Remove from solution after 30 minutes
It was thoroughly washed with li-Q pure water.

Next, this substrate was immersed in a polyethyleneimine aqueous solution having a concentration of 0.25 wt% for 20 minutes to obtain Milli.
-Q It was thoroughly washed with pure water. The substrate thus washed and pretreated was immersed in (1) the manganate nanosheet colloidal solution. (2) After 20 minutes, Mill
It was thoroughly washed with i-Q pure water and dried by blowing an argon stream. (3) Next, this substrate was added to PDDA solution 20
It was soaked for a minute, and then (4) followed by thorough washing with Milli-Q pure water. By repeating the above operations (1) to (4), a manganate nanosheet ultrathin film was synthesized.

When the UV-visible absorption spectrum was measured every time the above film-forming cycle was repeated, a broad absorption due to the manganate nanosheet was observed (Fig. 1), and the absorbance was measured at each adsorption cycle. It was confirmed that it increased almost linearly (Fig. 2). As a result, it was found that almost equal amounts of nanosheets were adsorbed and accumulated on the substrate. From the X-ray diffraction data shown in FIG. 4, a black peak showing a periodic structure of about 0.8 nm appeared, and the intensity increased as the number of adsorptions increased. From the above data, it was confirmed that a multi-layer ultrathin film in which manganate nanosheets and PDDA were alternately repeated in the nanometer scale range could be constructed.

[0023]

Example 2 A quartz glass substrate which had been cleaned and pretreated in the same procedure as in Example 1 had a concentration of (1) 0.01 g.
dm ^-3 manganate nanosheet colloidal solution (pH =
9). (2) After 20 minutes, Milli-Q
It was thoroughly washed with pure water and dried by blowing an argon stream. (3) Next, this substrate was immersed in the PDDA solution of Example 1 for 20 minutes, and (4) subsequently, it was thoroughly washed with Milli-Q pure water. The above operations (1) to (4) are repeated,
As a result of investigating the film forming process in the same manner as in Example 1 (FIG. 5), the cumulative amount of manganate nanosheets was 1/100 of that in Example 1.
It was confirmed that a multilayer ultra-thin film having a thickness of 4 or less was produced.

[0024]

Example 3 The manganate nanosheet / PDDA multilayer ultrathin film synthesized in Example 1 was placed in a platinum crucible and heated in an electric furnace. The heating was performed by raising the temperature from room temperature at a rate of 5 ° C. min ⁻¹ , maintaining the target temperature for 1 hour, and then cooling the heater and allowing it to cool. After returning to room temperature, a sample was taken out and its X-ray diffraction pattern was measured (FIG. 6). As a result, it was revealed that the nanostructure of the multilayer film was destroyed at 200 ° C. It is considered that this is because PDDA was thermally decomposed, and formation of an inorganic film was confirmed. Mn ₂ O ₃ by heating above 500 ° C
It was also found to change to a thin film of.

[0025]

As disclosed above, the present invention has succeeded in providing a thin film of manganese oxide by a film forming method that has never existed before. The operation is to prepare two kinds of solutions, a colloidal solution of manganate nanosheets and an organic polymer solution, and immerse the material substrate, etc. to form a film in this solution alternately, and make the thickness self-sustaining in the sub-nanometer range. It is made possible by an extremely simple and reproducible unique method that can be controlled dynamically, and its significance is extremely large.

[Brief description of drawings]

FIG. 1 is an ultraviolet-visible absorption spectrum of a manganate nanosheet / PDDA multilayer ultrathin film during the accumulation process.

FIG. 2 is a diagram showing the relationship between the absorbance (340 nm) and the number of accumulations in the accumulation process of manganate nanosheets / PDDA ultrathin films.

FIG. 3 is a diagram observing the relationship between the cumulative number of manganate nanosheets / PDDA ultrathin films and the color tone.

FIG. 4 is an X-ray diffraction pattern of a cumulative process of manganate nanosheet / PDDA multilayer ultrathin film.

FIG. 5 is an ultraviolet / visible absorption spectrum of a manganate nanosheet / PDDA multilayer ultrathin film during the accumulation process.

FIG. 6 is an X-ray diffraction pattern of a heating process of a manganate nanosheet / PDDA multilayer ultrathin film (10 layers).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Watanabe             1-2-1, Sengen, Tsukuba-shi, Ibaraki Independent             National Institute for Materials Science F-term (reference) 4F100 AA02A AA02C AA17A AA17C                       AK01B AK31 BA03 BA04                       BA05 BA08 BA10A BA10B                       BA10C GB41 JA11A JA11C                       JL02 JM02A JM02C                 4G048 AA02 AB02 AC06 AD02 AD04                       AD06 AE05                 4G075 AA24 AA30 BA05 BB04 BB10                       CA02 CA51 EE12 FA12

Claims (7)

[Claims] 1. A manganese oxide nanosheet and a polymer, wherein a two-dimensional crystallite (hereinafter referred to as a manganate nanosheet) obtained by exfoliating layered manganese oxide microcrystals and a polymer are alternately laminated. An ultra thin film consisting of. 2. The manganic acid nanosheet represented by MnO ₂ is used as the two-dimensional crystallite.
An ultra-thin film comprising the manganate nanosheet according to 1. and a polymer. 3. The nanosheet and the polymer are respectively adsorbed on the substrate by repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganate nanosheets are suspended and the cationic polymer solution, and the both components are sub-nm. ~ Nm
A method for producing an ultra-thin film composed of a manganate nanosheet and a polymer, characterized by accumulating multilayer films which are alternately repeated at level intervals. 4. A two-dimensional crystallite (manganate nanosheet) obtained by exfoliating layered manganese oxide microcrystals and a polymer are alternately laminated, and then the polymer is removed to obtain an ultrathin manganate nanosheet film. Ultra-thin manganate nanosheet thin film. 5. The manganic acid nanosheet represented by MnO ₂ is used as the two-dimensional crystallite.
The ultrathin film of manganate nanosheet according to 1. 6. The nanosheet and the polymer are adsorbed on the substrate by repeating the operation of alternately immersing the substrate in the colloidal solution in which the manganate nanosheets are suspended and the cationic polymer solution, respectively, and the components are sub-nm. ~ Nm
A method for producing an ultra-thin manganate nanosheet thin film, which comprises stacking films that are alternately repeated at level intervals and then removing the polymer to obtain an ultra-thin manganate nanosheet thin film. 7. The method for producing an ultrathin manganese oxide film according to claim 6, wherein the means for removing the polymer is performed by heating and is removed by decomposition.