Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having growth from a solution comprising a solvent which is...
Reexamination Certificate
2002-04-09
2004-01-13
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having growth from a solution comprising a solvent which is...
Reexamination Certificate
active
06676749
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for preparing a layered perovskite compound thin film with organic ammonium layers and inorganic layers, and a layered perovskite compound thin film with organic ammonium layers and inorganic layers prepared thereby in which the organic ammonium molecule contains a functional chromophore.
BACKGROUND ART
It is known that a layered perovskite compound has a superlattice structure in which an organic layer and an inorganic layer are alternately stacked, and exhibits various interesting properties useful for low-dimensional semiconductors, magnetic bodies, luminous bodies or the like, depending on the type of inorganic halide layer. In addition, it is suggested that the layered perovskite compound has the potential of providing new functional materials capable of bringing out combined functionalities of organic layers and inorganic layers (M. Era, K. Maeda, and T. Tsutsui, Chemistry Letters, 1235-1236, 1997).
One of known layered perovskite compounds has a superlattice structure which is represented by the general formula A
2
MX
4
where A is an organic ammonium molecule, M is a group 4 element or transition metal and X is halogen (Cl, Br, I), and in which a layer of organic ammonium molecule “A” and a layer of inorganic halide “MX
4
” are alternately stacked (see
FIG. 10
showing a schematic diagram thereof). Further, another known layered perovskite compound has a superlattice structure which is represented by the general formula A
2
MX
4
, where A is organic ammonium ions, M is divalent rare earth metal cations and X is halogen (Cl, Br, I), and in which a layer of organic ammonium molecule “A” and a layer of inorganic halide “MX
4
” are alternately stacked (Japanese Patent Laid-Open Publication No. Hei 10-316685).
A conventional method for preparing a thin film from such layered perovskite compounds includes one method (a casting method or spin-coating method) in which a crystal of a layered perovskite compound or a mixture of an organic amine hydrohalic acid salt and an inorganic halide MX
2
is dissolved in an organic solvent and then a thin film is formed from the resulting solution, and another method (a two-source deposition method) in which an organic amine hydrohalic acid salt and an inorganic halide MX
2
are deposited simultaneously in vacuo.
Heretofore, as a method for depositing monomolecular films, there has been known the Langmuir-Blodgett method (LB method) used for manufacturing organic thin films. Japanese Patent Laid-Open Publication No. Hei 11-140656 disclosed a method for manufacturing an inorganic thin film in which monomolecular films are accumulated with controlling the composition and arrangement of metal elements by using the Langmuir-Blodgett method to form an organic thin film, and then the organic component of the organic thin film is decomposed and removed to form an inorganic thin film. However, such a method has not been successfully used for preparing layered perovskite compound thin films.
As shown in
FIG. 9
, the Langmuir-Blodgett method is a technique for preparing a thin film having a film thickness and structure controlled at the level of a monomolecular layer by forming a monomolecular film of amphipathic molecules on the water and transferring it onto a substrate (see “Physics and Chemistry Dictionary-5th Edition” published by Iwanami Shoten).
DISCLOSURE OF INVENTION
(Problem to be Solved by the Invention)
For using the above layered perovskite compound with organic ammonium layers and inorganic layers as device materials, it is a critical task to control a film thickness and structure stringently at the level of a monomolecular layer. Further, if such layered perovskite compounds can be combinedly formed at the level of a monomolecular layer, it would open the way to develop various materials having higher performance. However, the conventional techniques for preparing layered perovskite compounds have not been able to prepare such a thin film having a film thickness and structure controlled at the level of a monomolecular layer.
Therefore, it is an object of the present invention to provide a novel method for preparing a layered perovskite compound thin film with organic ammonium layers and inorganic layers which has a film thickness and structure controlled at the level of a monomolecular layer, and to provide a layered perovskite compound thin film with organic ammonium layers and inorganic layers which has a novel function useful for devices, through this method.
(Means for Solving the Problem)
The inventor has found a method for forming a monomolecular film of an organic-inorganic layered perovskite compound on the surface of a water solution. Based on this method and applying the Langmuir-Blodgett method, the inventor has made it possible to prepare a layered perovskite organic-inorganic superlattice material having a film thickness and structure controlled at the level of a monomolecular layer. Further, in combination with this method, the inventor has achieved to introduce a chromophore into the organic layers so as to allow the layered perovskite organic-inorganic superlattice material to be applied to electroluminescence (EL) devices.
More specifically, according to a first aspect of the present invention, there is provided a method for preparing a layered perovskite compound thin film with organic ammonium layers and inorganic layers which has a superlattice structure represented by the general formula A
2
MX
4
where “A” is an organic ammonium molecule, “M” is a group 4 element or transition metal and “X” is halogen (Cl, Br, I), and in which a layer of organic ammonium molecule “A” and a layer of inorganic halide “MX
4
” are alternately stacked, characterized in that an organic solvent solution having dissolved therein an organic ammonium molecule or a mixture of an organic ammonium molecule and an inorganic halide is dropped onto to the surface of a water solution having dissolved therein a water-soluble organic ammonium molecule and an inorganic halide to form a monomolecular film of an organic amine hydrohalic acid salt having a long-chain alkyl group and simultaneously to react the formed monomolecular film with the inorganic halide in the water solution so as to form a monomolecular film of a layered perovskite with organic ammonium layers and inorganic layers on the surface of the water solution, and then the formed monomolecular film is transferred onto a substrate by using the Langmuir-Blodgett method.
The group 4 element herein is Ge, Sn or Pb, and the transition metal is Cr, Mn, Fe, Co, Ni, Cu, Zn or Cd. The inorganic halide is a compound represented by the chemical formula MX
2
where M is a group 4 element or transition metal and X is halogen (Cl, Br, I). The substrate for the monomolecular film to be transferred thereon may be selected from the group consisting of a silicon substrate, a metal plate, a glass plate, a fused quartz substrate, and an inorganic compound single crystal substrate.
In the method according to the first aspect of the present invention, the organic ammonium molecule to be dissolved in the water solution may be a water-soluble alkylamine hydrohalic acid salt C
n
H
2n+1
NH
3
X, and the organic ammonium molecule to be dissolved in the organic solvent solution may contain a non-water-soluble alkylamine hydrohalic acid salt C
n
H
2n+1
NH
3
X. The water-soluble alkylamine hydrohalic acid salt C
n
H
2n+1
NH
3
X can facilitate the formation of the layered perovskite monomolecular film on the surface of the water solution.
Further, the non-water-soluble alkylamine hydrohalic acid salt C
n
H
2n+1
NH
3
X to be dissolved in the organic solvent solution may be a dococylamine hydrohalic acid salt C
22
H
45
NH
3
X. The dococylamine hydrohalic acid salt C
22
H
45
NH
3
X having a long-chain alkyl group allows a stable monomolecular film to be formed on the water solution.
In the method according to the first aspect of the present invention, the organic solvent may be chloroform or a mixture of chloroform and dimethylformamide. Th
Hiteshew Felisa
Japan Science and Technology Corporation
Westerman Hattori Daniels & Adrian LLP
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