U.S. patent application number 10/214353 was filed with the patent office on 2003-03-13 for nanomaterials of composite metal oxides.
Invention is credited to He, Junhui, Ichinose, Izumi, Kunitake, Toyoki, Takaki, Rie.
Application Number | 20030047028 10/214353 |
Document ID | / |
Family ID | 27347298 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047028 |
Kind Code |
A1 |
Kunitake, Toyoki ; et
al. |
March 13, 2003 |
Nanomaterials of composite metal oxides
Abstract
Exchangeable metal ions are removed from an amorphous composite
metal oxide and different metal ions are introduced to manufacture
a nanomaterial of composite metal oxide. Based on this method, it
is possible to reliably form composite metal oxide nanomaterials
over a wide range of compositions.
Inventors: |
Kunitake, Toyoki;
(Kasuya-gun, JP) ; Ichinose, Izumi; (Tokyo,
JP) ; Takaki, Rie; (Asaka-shi, JP) ; He,
Junhui; (Wako-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
27347298 |
Appl. No.: |
10/214353 |
Filed: |
August 8, 2002 |
Current U.S.
Class: |
75/230 ; 148/403;
75/252 |
Current CPC
Class: |
C01G 23/053 20130101;
C01B 13/32 20130101; C01P 2002/02 20130101; C01P 2006/16 20130101;
C01P 2006/90 20130101 |
Class at
Publication: |
75/230 ; 148/403;
75/252 |
International
Class: |
C22C 029/00; C22C
001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2001 |
JP |
2001-240847 |
Dec 25, 2001 |
JP |
2001-392086 |
Jun 27, 2002 |
JP |
2002-188281 |
Claims
1. A nanomaterial satisfying at least one of the following
conditions (a), (b), (c) and (d): (a) A nanomaterial of composite
metal oxide which comprises an amorphous metal oxide with uniformly
dispersed nanopores containing exchangeable metal ions; (b) A
nanomaterial of composite metal oxide or amorphous metal oxide
wherein the composite metal oxide or the amorphous metal oxide has
uniformly dispersed nanopores capable of containing metal ions; (c)
A nanomaterial of composite metal oxide or amorphous metal oxide
wherein the composite metal oxide or the amorphous metal oxide has
uniformly dispersed nanopores capable of selectively containing
specific metal ions; and (d) A nanomaterial of composite metal
oxide or amorphous metal oxide which comprises a metal oxide
insoluble in acid aqueous solution with uniformly dispersed
nanopores containing metal ions soluble in acid aqueous
solutions.
2. The nanomaterial according to claim 1 which satisfies condition
(a).
3. The nanomaterial according to claim 1 which satisfies condition
(b).
4. The nanomaterial according to claim 1 which satisfies condition
(c).
5. The nanomaterial according to claim 1 which satisfies condition
(d).
6. The nanomaterial according to claim 1 which comprises no organic
ligand coordinated with the metal ion through a nitrogen atom, an
oxygen atom, a sulfur atom or a phosphorus atom.
7. The nanomaterial according to claim 1 in the form of a thin film
of from 0.5 to 100 nm in thickness.
8. A material consisting of a solid and a thin film of the
nanomaterial according to claim 1 formed on the solid.
9. The material according to claim 8 wherein the solid has a
surface having groups reactive with a metal alkoxide group and some
or all of the reactive groups are bonded to the thin film
nanomaterial.
10. The material according to claim 8 wherein the solid has
positive electrical charges and some or all of the positive
electrical charges are electrostatically bonded to the thin film
nanomaterial.
11. The material according to claim 8 wherein the solid has groups
reactive with a silicate oligomer and some or all of the reactive
groups are bonded to the thin film nanomaterial.
12. The material according to claim 8 manufactured by conducting
one or more times the steps of chemically adsorbing a metal
alkoxide compound on the surface of the solid having groups
reactive with metal alkoxide groups of the metal alkoxide compound,
and rinsing the surface.
13. The material according to claim 8 manufactured by conducting
one or more times the steps of: bringing a mixed solution of a
metal alkoxide compound capable of providing metal ions soluble in
an acidic aqueous solution following hydrolysis and a metal
alkoxide compound capable of providing metal oxide insoluble in
water following hydrolysis into contact with the surface of the
solid having groups reactive with metal alkoxide groups of the two
metal alkoxide compounds, thereby the two metal alkoxides are
adsorbed on the surface; rinsing away excess metal alkoxide
compounds; and hydrolyzing the metal alkoxide compounds present on
the solid surface to form a composite metal oxide thin film.
14. The material according to claim 8 manufactured by conducting at
least once the steps of steps (1) and (2) below in random order on
the surface of the solid having groups reactive with metal alkoxide
groups: step (1): bringing a solution of metal alkoxide compound
capable of providing metal ions soluble in acidic aqueous solution
following hydrolysis into contact with the surface of the solid,
rinsing away excess metal alkoxide compound, and then hydrolyzing
the metal alkoxide compound present on the solid surface to form a
metal oxide thin film; and step (2): bringing a solution of metal
alkoxide compound capable of providing metal oxide compound
insoluble in acidic aqueous solution following hydrolysis into
contact with the surface of the solid, rinsing away the excess
metal alkoxide compound, and hydrolyzing the metal alkoxide
compound present on the solid surface to form a metal oxide thin
film.
15. The material according to claim 8 manufactured by conducting
the steps of: forming an amorphous metal oxide thin film of
nano-thickness on the surface of the solid having groups reactive
with metal alkoxide groups, immersing the amorphous metal oxide
thin film in a solution comprising metal ions, and rinsing away
excess metal ions from the amorphous metal oxide thin film.
16. The material according to claim 8 manufactured by the steps of:
conducting one or more times the operations of bringing a metal
alkoxide compound capable of providing metal oxide insoluble in
water following hydrolysis into contact with the surface of a solid
comprising groups reactive with metal alkoxide groups of the metal
alkoxide compound whereby the metal alkoxide compound is adsorbed
on the surface, rinsing away excess metal alkoxide compound, and
hydrolyzing the metal alkoxide compound present on the solid
surface to form a metal oxide thin film; immersing the metal oxide
thin film in a solution comprising metal ions; and rinsing away
excess metal ions from the metal oxide thin film.
17. The material according to claim 8 manufactured by repeating the
steps of: conducting one or more times the operations of bringing a
metal alkoxide compound capable of providing metal oxide insoluble
in water following hydrolysis into contact with the surface of a
solid comprising groups reactive with metal alkoxide groups of the
metal alkoxide compound whereby the metal alkoxide compound is
adsorbed on the surface, rinsing away excess metal alkoxide
compound, and hydrolyzing the metal alkoxide compound present on
the solid surface to form a metal oxide thin film; immersing the
metal oxide thin film in a solution comprising metal ions; and
rinsing away excess metal ions from the metal oxide thin film.
18. The material according to claim 8 manufactured by the steps of:
bringing a silicate oligomer aqueous solution into contact with the
surface of a solid having groups reactive with the silicate
oligomer whereby the silicate oligomer is adsorbed on the surface;
and rinsing away the excess silicate oligomer from the surface.
19. The material according to claim 8 manufactured by the steps of:
bringing a silicate oligomer aqueous solution into contact with the
surface of a solid having groups reactive with the silicate
oligomer whereby the silicate oligomer is adsorbed on the surface;
rinsing away the excess silicate oligomer from the surface; and
immersing the resultant material in a solution of a metal ion
different from the metal ions contained in the material to
introduce the different metal ion.
20. The material according to claim 8 manufactured by repeating the
steps of: bringing a silicate oligomer aqueous solution into
contact with the surface of a solid comprising groups reactive with
the silicate oligomer whereby the silicate oligomer is adsorbed on
the surface; rinsing away the excess silicate oligomer from the
surface; and immersing the resultant material in a solution of
metal ions different from the metal ions contained in the material
to introduce these different metal ions.
21. The material according to claim 8 manufactured by any one of
the following procedures (a)-(h): (a) conducting one or more times
the steps of chemically adsorbing a metal alkoxide compound on the
surface of the solid having groups reactive with metal alkoxide
groups, and rinsing the surface; (b) conducting one or more times
the steps of: bringing a mixed solution of a metal alkoxide
compound capable of providing metal ions soluble in an acidic
aqueous solution following hydrolysis and a metal alkoxide compound
capable of providing metal oxide insoluble in water following
hydrolysis into contact with the surface of the solid having groups
reactive with metal alkoxide groups of the two metal alkoxides,
thereby the two metal alkoxides are adsorbed on the surface;
rinsing away excess metal alkoxide compounds; and hydrolyzing the
metal alkoxide compound present on the solid surface to form a
composite metal oxide thin film; (c) conducting at least once the
steps of steps (1) and (2) below in random order on the surface of
the solid having groups reactive with metal alkoxide groups: step
(1): bringing a solution of metal alkoxide compound capable of
providing metal ions soluble in acidic aqueous solution following
hydrolysis into contact with the surface of the solid, rinsing away
excess metal alkoxide compound, and then hydrolyzing the metal
alkoxide compound present on the solid surface to form a metal
oxide thin film; and step (2): bringing a solution of metal
alkoxide compound capable of providing metal oxide compound
insoluble in acidic aqueous solution following hydrolysis into
contact with the surface of the solid, rinsing away the excess
metal alkoxide compound, and hydrolyzing the metal alkoxide
compound present on the solid surface to form a metal oxide thin
film. (d) conducting the steps of: forming an amorphous metal oxide
thin film of nano-thickness on the surface of the solid having
groups reactive with metal alkoxide groups, immersing the amorphous
metal oxide thin film in a solution comprising metal ions, and
rinsing away excess metal ions from the amorphous metal oxide thin
film; (e) conducting the steps of: conducting one or more times the
operations of bringing a metal alkoxide compound capable of
providing metal oxide insoluble in water following hydrolysis into
contact with the surface of a solid comprising groups reactive with
metal alkoxide groups of the metal alkoxide compound whereby the
metal alkoxide compound is adsorbed on the surface, rinsing away
excess metal alkoxide compound, and hydrolyzing the metal alkoxide
compound present on the solid surface to form a metal oxide thin
film; immersing the metal oxide thin film in a solution comprising
metal ions; and rinsing away excess metal ions from the metal oxide
thin film (f) repeating the procedure (e); (g) repeating the steps
of: bringing a silicate oligomer aqueous solution into contact with
the surface of a solid having groups reactive with the silicate
oligomer whereby the silicate oligomer is adsorbed on the surface;
and rinsing away the excess silicate oligomer from the surface; (h)
conducting the steps of: bringing a silicate oligomer aqueous
solution into contact with the surface of a solid having groups
reactive with the silicate oligomer whereby the silicate oligomer
is adsorbed on the surface; rinsing away the excess silicate
oligomer from the surface; and immersing the resultant material in
a solution of a metal ion different from the metal ions contained
in the material to introduce the different metal ion.
22. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid, which is manufactured by the step
of immersing the material according to claim 21 in an acidic
aqueous solution to remove exchangeable metal ions.
23. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid, which is manufactured by the step
of immersing the material according to claim 22 in a solution of a
metal ion different from the metal ions contained in the material
to introduce the differing metal ion.
24. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid, which is manufactured by the step
of immersing the material according to claim 23 in a solution of
two or more metal ions different from the metal ions contained in
the material to introduce the two or more metal ions.
25. The nanomaterial according to claim 1 which is in the form of
particles from 1 to 500 nm in size.
26. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size wherein the material comprises a metal component
or a mixed valence metal oxide component obtained by reducing some
or all of the metal atoms in the material according to claim
21.
27. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size wherein the material comprises a metal component
or a mixed valence metal oxide component obtained by reducing some
or all of the metal atoms in the material according to claim
23.
28. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size wherein the material comprises a metal component
or a mixed valence metal oxide component obtained by reducing some
or all of the metal atoms in the material according to claim
24.
29. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size where in the material comprises a metal
chalcogenite component obtained by reacting some or all of the
metal atoms in the material according to claim 21 with a chalcogen
compound.
30. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size wherein the material comprises a metal
chalcogenite component obtained by reacting some or all of the
metal atoms in the material according to claim 23 with a chalcogen
compound.
31. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size wherein the material comprises a metal
chalcogenite component obtained by reacting some or all of the
metal atoms in the material according to claim 24 with a chalcogen
compound.
32. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid which is manufactured by
subjecting the material according to claim 21 to a heat treatment
or an oxygen plasma treatment to reduce the ion-exchange capability
of the exchangeable metal ions.
33. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid which is manufactured by
subjecting the material according to claim 23 to a heat treatment
or an oxygen plasma treatment to reduce the ion-exchange capability
of the exchangeable metal ions.
34. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid which is manufactured by
subjecting the material according to claim 24 to a heat treatment
or an oxygen plasma treatment to reduce the ion-exchange capability
of the exchangeable metal ions.
35. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by re-oxidizing at least a
portion of the metal component or mixed valence metal oxide
component that has been reduced by the step described in claim
26.
36. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by re-oxidizing at least a
portion of the metal component or mixed valence metal oxide
component that has been reduced by the step described in claim
27.
37. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by re-oxidizing at least a
portion of the metal component or mixed valence metal oxide
component that has been reduced by the step described in claim
28.
38. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by subjecting the metal
component or mixed valence metal oxide component that has been
re-oxidized by the step described in claim 35 to a reducing step or
an alternating sequence of a reducing step and an oxidizing step in
that order one or more times.
39. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by subjecting the metal
component or mixed valence metal oxide component that has been
re-oxidized by the step described in claim 36 to a reducing step or
an alternating sequence of a reducing step and an oxidizing step in
that order one or more times.
40. A material consisting of a solid and a thin film of the
nanomaterial formed on the solid or in the form of particles from 1
to 500 nm in size which is obtained by subjecting the metal
component or mixed valence metal oxide component that has been
re-oxidized by the step described in claim 37 to a reducing step or
an alternating sequence of a reducing step and an oxidizing step in
that order one or more times.
Description
TECHNICAL FIELD
[0001] The present invention relates to nanomaterials of amorphous
metal oxides. More particularly, the present invention relates to a
technique of manufacturing nanomaterials of composite metal oxides
by means of a novel technique of removing exchangeable metal ions
from nanopores of an amorphous metal oxide and introducing
different metal ions.
RELATED ART
[0002] In recent years, nanotechnology has drawn considerable
attention as an important scientific technology of the twenty-first
century. It is anticipated that the materials having a controlled
size, shape, composition, distribution, function, spatial
arrangement, and the like at the nanometer level will bring about
new electronic, physical, chemical, and biological functions.
Bottom-up compound synthesis processes that begin with atoms and
molecules are essential to manufacture such nanomaterials. Of
these, techniques of designing the composition and structure of
nanoparticles and ultra-thin films at the nanometer level have
become important basic techniques in a wide range of fields. A
general survey of prior art relating to nanomaterials of composite
metal oxides comprising two or more metal atoms is given below.
[0003] Thin-film materials of composite metal oxides, the thickness
of which is controlled at the nanometer level, are anticipated to
play important roles in such areas as improving the chemical,
mechanical, and optical characteristics of surfaces; catalysts; the
separation of materials such as gases; the manufacturing of fuel
cells, fluorescent materials, and magnetic materials; the
manufacturing of various sensors; and in high-density electronic
devices. The next generation of integrated circuit technology
requires the production of insulating thin films of extremely high
precision, with similar requirements existing for processes used to
manufacture high-precision memories and thin-film magnetic memory
heads.
[0004] Conventionally, composite metal oxide thin films have been
fabricated by spin-coating. As required, water and catalysts are
added to the mixed solutions of multiple metal alkoxide compounds.
By spin-coating these solutions onto substrate surfaces, it is
possible to readily manufacture thin films of about one micrometer.
It is possible to manufacture thin films of about 100 nm with this
method by controlling the concentration and viscosity of the
coating solution. However, in the spin-coating, the film thickness
is controlled by means of the viscosity of the coating solution and
the speed of rotation, making it difficult to obtain ultra-thin
films with uniform thicknesses of less than 100 nm. Particularly
when employing very large area substrates, the thickness of the
film obtained differs from center to edge.
[0005] When manufacturing composite metal oxide thin films by
spin-coating the mixed solutions of metal alkoxide compounds, a
micro phase separation structure is often produced. This becomes a
major problem in ultra-thin films of nanometer thickness. This
occurs because, due to differences in the hydrolysis rates of the
metal alkoxide compounds employed as starting materials, hydrolysis
and condensation of metal alkoxide compounds of high reactivity
takes place first, forming primary particles of metal oxides, with
metal alkoxides of low reactivity forming metal oxides by
hydrolysis and condensation around the primary particles. Double
alkoxides obtained by reacting in advance two metal alkoxides of
different reactivity are commercially available and can be employed
as the starting materials of composite metal oxides. However, it is
impossible to obtain composite metal oxides in which two components
have been uniformly dispersed at the molecular level over a broad
range of the compositions. When thin film materials of composite
metal oxides having micro phase separated structures are sintered,
crystalline composite metal oxide thin films are sometimes
obtained. However, the crystallization temperature of oxides is
generally high, and the use of sintering processes in applications
in which nanostructures play important roles is not easy.
[0006] When manufacturing composite metal oxide thin films as
structural elements of electronic devices and the like, MOCVD
employing multiple metal compounds as starting materials is often
employed. Laser abrasion, ion-beam sputtering, and the like are
employed in addition to the CVD method in the manufacturing of nano
films in which the film thickness and oxide composition are
controlled. Methods employing these vacuum techniques have become
important in the manufacturing of uniform thin films affording a
broad range of selection in pressure, substrate temperature,
target, and gas starting materials. However, except the epitaxially
grown of composite metal oxides, there are few composite metal
oxides wherein the composition and film thickness thereof can be
controlled at the nanometer level. This is because metal oxides are
not generally suited to CVD, tending to develop minute domains and
cracks. Further, even in the epitaxial growth of composite metal
oxides, the range of condition settings is narrow, precluding this
technique from becoming a practical thin-film manufacturing
technique.
[0007] Thin film materials of composite metal oxides such as barium
titanate can be obtained by electrochemically oxidizing titania
crystals in the presence of alkali salts. However, it is difficult
to uniformly manufacture ultra-thin films with thicknesses of 100
nm and below when employing such a soft solution process.
[0008] In any case, it is impossible over a broad range of
compositions to manufacture thin film materials of composite metal
oxides in which two components are uniformly distributed at the
molecular level by the above-described methods.
[0009] Ion implantation into oxide thin films by low-speed ion beam
is one method of manufacturing thin film materials of composite
metal oxides. However, the amount of metal ions that can be
introduced by ion beam is limited. Further, compositional
distribution is generated in develop perpendicular to the film
surface due to the concentrated introduction of metal ions at a
depth corresponding to the energy of the ion beam.
[0010] The fabrication of composite metal oxides by impregnation of
porous oxide thin films is a method similar to that of the present
invention. In prior art, catalysts have been manufactured by
methods of impregnation in which metal ions are supported in porous
metal oxides. However, in that case, counter anions end up being
incorporated in the step incorporating the metal ions. That is, in
the method of impregnation into porous metal oxides, minute metal
salts are simply incorporated into oxides.
[0011] Zeolite compounds and mesoporous materials typified by
MCM-41 have regular nanopores and internal exchangeable metal ions
such as sodium ions. Under suitable conditions, different metal
ions can be introduced into the nanopores of these materials. Thus,
zeolite compounds and mesoporous materials have characteristics
relating to the thin film materials of the composite metal oxides
obtained in the present invention, but they also have the following
differences. That is, zeolite compounds having regularly arranged
nanopores are crystalline materials, differing from amorphous metal
oxides having uniformly dispersed nanopores. Similarly, mesoporous
materials in which voids of certain size are regularly arranged are
micrometer-level crystalline materials. Due to the crystalline
properties of these materials, it is extremely difficult to
fabricate thin film materials with good thickness precision in the
nanometer range. Further, both zeolite compounds and mesoporous
materials are generally obtained by hydrothermal synthesis and
sintering, making it impossible to control the quantity of
exchangeable metal ions and rendering these compounds and materials
unsuitable as precursors for manufacturing composite metal oxides
over a wide range of compositions.
[0012] Problems to be solved in the manufacturing of thin film
materials of composite metal oxides in the nanometer region are the
improvement of uniformity in film thickness, the improvement of
thin film manufacturing processes at low temperatures, the
improvement of adhesion to the substrate, controlling physical
characteristics such as insulating properties, and the like. In
thin film manufacturing processes at low temperature, in
particular, it is possible to avoid heat-induced deterioration in
device characteristics such as insulation properties in ultrafine
processing techniques, making these processes indispensable in the
manufacturing of molecular devices employed in organic
materials.
[0013] The present inventors conducted extensive research into
ultra-thin films, resulting in the development of a novel nanometer
thin film manufacturing method named the surface sol-gel process.
In the surface sol-gel process, metal alkoxide compounds are
chemically adsorbed on a solid substrate having hydroxyl groups on
its surface, and then hydrolyzed to manufacture ultra-thin oxide
films of molecular thickness. The new hydroxyl groups produced by
hydrolysis of the alkoxide groups in the outermost layer can then
be used again in chemical adsorption of metal alkoxide compounds.
Thus, repeated adsorption and hydrolysis steps permit the
manufacturing of metal oxide multilayer films having a nanometer
thickness.
[0014] In this process, multiple metal alkoxide compounds are
employed for the stepwise adsorption, thereby permitting the
manufacture of composite metal oxide thin films controlled at the
nanometer level. The composition of such films can also be
controlled. Further, mixed solutions of metal alkoxide compounds
can be used to manufacture similar composite metal oxide thin
films.
[0015] With the surface sol-gel process, it is possible to
manufacture thin films of composite metal oxides on the surface of
a wide variety of materials, such as polymers, metals, and organic
and inorganic materials having functional groups such as hydroxyl
and carboxyl groups that are reactive with metal alkoxide groups.
Further, since this process is based on adsorption from solution,
it is possible to manufacture uniform composite metal oxide thin
films independent of the shape of the substrate.
[0016] However, the compounds that can be obtained by the surface
sol-gel process are limited to metal oxides capable of chemically
bonding to hydroxyl groups on the surface of solids such as metal
alkoxide compounds and capable of generating new hydroxyl groups
though hydrolysis. Further, chemical adsorption from organic
solutions is mainly employed to bring such metal compounds into
contact with solid surfaces, making this process unsuitable for
insoluble or nonvolatile metal oxides such as the lanthanide
series. Still further, since metal alkoxide compounds such as
alkali metals and alkaline earth metals cannot form their hydroxyl
groups on surfaces by hydrolysis, they are unsuited to application
to the surface sol-gel process. For these reasons the range of thin
film materials of composite metal oxides that can be manufactured
by the surface sol-gel process is limited.
[0017] Thus, no satisfactory method of manufacturing thin film
materials of composite metal oxides in the nanometer range
affording both good thickness precision over a broad range of
compositions and reliable formation has yet been developed.
Accordingly, the object of the present invention is to provide such
a nanomaterial.
SUMMARY OF THE INVENTION
[0018] The present inventors thought that if there were replaceable
metal ions in metal oxides, it would be possible to introduce
various metal ions in replacement of the replaceable metal ions by
ion exchange, yielding a broadly applicable method of manufacturing
nanomaterials of composite metal oxides.
[0019] When manufacturing nanomaterials of composite metal oxides
by such a method, it is necessary for replaceable metal ions to be
uniformly distributed in a metal oxide serving as matrix. Further,
at least a portion of the individual replaceable metal ions present
in the metal oxide must be in contact with the metal oxide serving
as matrix. That is, if exchangeable metal ions are present within
nanopores which are uniformly distributed in a metal oxide, a high
degree of dispersion of exchangeable metal ions can be achieved. In
that case, the size of the nanopores is desirably about the size of
molecules.
[0020] In obtaining thin film materials with good thickness
precision, it is desirable for the metal oxide serving as matrix to
be amorphous. Further, the amorphous metal oxide must be able to
retain its shape as a thin film during the elimination of the
exchangeable metal ions and the introduction of different metal
ions.
[0021] The present inventors conducted extensive research into the
manufacturing of thin film materials of composite metal oxides
based on chemical adsorption from solution and rinsing.
[0022] As a result, they discovered that it was possible to
manufacture thin film materials of composite metal oxides
containing exchangeable metal ions within nanopores uniformly
distributed in amorphous metal oxides by combining a metal alkoxide
compound providing metal ions soluble in an acidic aqueous solution
following hydrolysis and a metal alkoxide compound providing metal
oxide insoluble in water following hydrolysis in the process of
forming a thin film by the surface sol-gel process. They further
discovered that the amorphous metal oxide thin film materials of
nanometer thickness manufactured by the surface sol-gel process
rapidly adsorbs large quantities of metal ions. They also
discovered that when thin film formation by the surface sol-gel
process and metal ion adsorption were repeated, it was possible to
manufacture a thin film material of composite metal oxide
containing exchangeable metal ions in the nanopores uniformly
distributed in an amorphous metal oxide. A similar thin film
material was possible to be made by contacting an aqueous solution
of silicate oligomer with a solid surface. Further, the present
inventors discovered that it was possible to remove exchangeable
metal ions and introduce different metal ions in such thin film
materials.
[0023] Accordingly, the present invention provides a nanomaterial
of composite metal oxides containing exchangeable metal ions in
nanopores uniformly distributed in an amorphous metal oxide. Ametal
oxide or composite metal oxide nanomaterial manufactured by
removing exchangeable metal ions from such materials yields a
material in which nanopores that can accept metal ions are
uniformly dispersed, permitting the selective incorporation of
specific metal ions therein. The present invention further provides
a nanomaterial of composite metal oxides that is manufactured by
removing exchangeable metal ions and introducing different metal
ions. The present invention further provides a nanomaterial of
composite metal oxides or amorphous metal oxides in which nanopores
containing metal ions soluble in acidic aqueous solutions are
uniformly distributed in a metal oxide that is insoluble in acidic
aqueous solutions.
[0024] When configuring the nanomaterial of the present invention
as a thin film, it is desirably formed on a solid surface to a
thickness of from 0.5 to 100 nm. The use of a solid surface having
positive electric charges or a solid surface having groups reactive
with silicate oligomer or metal alkoxide groups is desirable.
Further, one embodiment of the nanomaterial of the present
invention does not comprise organic ligands coordinated with metal
ions through a nitrogen atom, an oxygen atom, a sulfur atom or a
phosphorus atom.
[0025] The repetition at least one time of the steps of chemically
adsorbing a metal alkoxide compound on a solid surface and rinsing
is desirable in the manufacturing of a thin film material, and the
method of bringing the solid surface into contact with a mixed
solution of a metal alkoxide compound providing metal ions soluble
in acidic aqueous solutions following hydrolysis and a metal
alkoxide compound providing a metal compound insoluble in water
following hydrolysis is particularly preferred. That is, when
manufacturing a thin film in the present invention, a metal
alkoxide compound is chemically adsorbed onto the solid surface,
the excess adsorbed metal alkoxide compound is removed by rinsing,
and the metal alkoxide compound present on the solid surface is
hydrolyzed to form a composite metal oxide thin film, with these
steps preferably being repeated one or more times. In the thin film
material of the present invention, in place of the mixed solution
of the above-described metal alkoxide compounds, a solution of a
metal alkoxide compound providing metal ions soluble in acidic
aqueous solutions following hydrolysis and a solution of a metal
alkoxide compound providing a metal oxide insoluble in water
following hydrolysis may be separately employed, and manufacturing
may be conducted by implementing one or more times the steps of
chemical adsorption of the respective metal alkoxide compounds,
rinsing, and hydrolysis.
[0026] The thin film material of the present invention may also be
manufactured by forming a thin film of amorphous metal oxide of
nanometer thickness on the above-described solid surface, immersing
this thin film in a solution containing metal ions, and rinsing
away the excess adsorbed metal ions. In that case, the surface
sol-gel process is the optimum means of manufacturing the thin film
of amorphous metal oxide compound of nanometer thickness. That is,
the thin film material of the present invention is desirably
manufactured by performing one or more times the steps of bringing
a metal alkoxide compound providing a metal oxide insoluble in
water following hydrolysis into contact with a solid surface having
groups reactive with metal alkoxide groups to chemically adsorb the
metal alkoxide compound, removing the excess metal alkoxide
compound by rinsing, and hydrolyzing the metal alkoxide compound
present on the solid surface to form a thin film of metal oxide
compound; then immersing the thin film in a solution comprising
metal ions and rinsing away the excess adsorbed metal ions. When
the steps of forming a thin film of amorphous metal oxide and
adsorbing metal ions are repeated, the thin film material of the
present invention is obtained with a film thickness restricted to
the nanometer level.
[0027] The thin film material of the present invention can be
manufactured by bringing an aqueous solution of silicate oligomer
into contact with a solid having a solid charge or having a surface
that is reactive with silicate oligomer to chemically adsorb the
oligomer, then rinsing away the excess adsorbed silicate oligomer.
Different metal ions can be introduced by ion exchange into the
thin film material of composite metal oxide thus obtained. Further,
repeating the steps of adsorbing silicate oligomer and introducing
metal ions by ion exchange can be repeated to obtain the thin film
material of the present invention with a film thickness restricted
to the nanometer level.
[0028] The thin film materials of the present invention includes
thin film materials of composite metal oxides comprising metal
components or mixed valence metal oxide components manufactured by
chemically reducing or reducing by a physical means such as
hydrogen plasma or light-irradiatation treatment of the thin film
material obtained by the above-described steps; thin film materials
of composite metal oxides comprising metal chalcogenite components
manufactured by reaction with a chalcogen compound; thin film
materials of composite metal oxides obtained by employing a heat
treatment or oxygen plasma treatment to reduce the ion exchange
capability of the exchangeable metal ions and thin film materials
obtained by repeat oxidation and reduction treatment such as
hydrogen plasma treatment and oxygen plasma treatment. Further, the
present invention mainly relates to solid surface thin film
materials, but nanomaterials of composite metal oxides containing
exchangeable metal ions are not necessarily limited to items with
thin shapes. For example, the nanomaterial of the present invention
can be manufactured as nanoparticles in a solution from which the
nanoparticles are then separated by centrifugal separation or the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a graph showing the change in frequency of a
quartz resonator based on stacking of the composite metal oxide
thin film of Embodiment 1, and the change in frequency of a quartz
resonator due to treatment by immersion in dilute hydrochloric acid
and by sodium hydroxide treatment.
[0030] FIG. 2 shows XPS spectra before and after the removal of
magnesium ions and following the introduction of gadolinium ions in
the composite metal oxide thin film of Embodiment 1.
[0031] FIG. 3 is a chart showing the introduction levels of various
metal ions into the composite metal oxide thin film of Embodiment
1.
[0032] FIG. 4 is a chart showing the levels of removal and
introduction with repeated introduction and removal of gadolinium
ions in the composite metal oxide thin film of Embodiment 1.
[0033] FIG. 5 is a scanning electron microscope photograph of the
surface of a thin film following the introduction of barium ions
into the composite metal oxide thin film of Embodiment 1.
[0034] FIG. 6 is a graph showing changes in ultraviolet and visible
absorption spectra based on stacking of the composite metal oxide
thin film of Embodiment 2.
[0035] FIG. 7 is a graph showing the change in frequency of a
quartz resonator based on stacking of the composite metal oxide
thin film of Embodiment 2, the removal of europium ions, and the
introduction of lanthanum ions.
[0036] FIG. 8 is a graph showing the change in frequency of a
quartz resonator based on stacking of thin films when a composite
metal oxide thin film of lanthanum and silicate oligomer was
fabricated on a thin film of titanium oxide in Embodiment 3.
[0037] FIG. 9 is a graph showing the change in frequency of a
quartz resonator based on the stacking of thin films when a
composite metal oxide thin film of lanthanum and silicate oligomer
was directly fabricated on the electrode surface of a quartz
resonator modified with mercaptoethanol in Embodiment 3.
[0038] FIG. 10 is a graph showing the change in frequency of a
quartz resonator based on the stacking of the composite metal oxide
thin film of Embodiment 3.
[0039] FIG. 11 is a transmission electron microscope photograph of
a composite metal oxide thin film containing nanoparticles of
silver in Embodiment 4.
[0040] FIG. 12 is a graph showing ultraviolet and visible
absorption spectra before and after the formation of nanoparticles
of CdS in Embodiment 5.
[0041] FIG. 13 is a transmission electron microscope photograph of
a composite metal oxide thin film containing nanoparticles of
palladium in Embodiment 7.
[0042] FIG. 14 is a graph showing an XPS spectrum of the thin film
material of Embodiment 8.
[0043] FIG. 15 is a transmission electron microscope photograph of
microparticles present in a suspension in Embodiment 9.
[0044] FIG. 16 shows ultraviolet and visible absorption spectra of
a composite metal oxide thin film. It shows the alternate formation
of composite metal oxide thin films containing nanoparticles of
silver and composite metal oxide thin layers containing
nanoparticles of silver oxide by alternately treating with hydrogen
plasma and oxygen plasma in Embodiment 10.
[0045] FIG. 17 shows a transmission electron microscope photograph
of a composite metal oxide thin film containing the silver
nanoparticles of Embodiment 10 (left) and a transmission electron
microscope photograph of a composite metal oxide thin film
containing silver oxide nanoparticles (right).
[0046] FIG. 18 shows charts of the particle size distribution of
silver nanoparticles (left) and silver oxide nanoparticles (right)
in the composite metal oxide thin film of Embodiment 10.
BEST MODES OF IMPLEMENTING THE INVENTION
[0047] The nanomaterial of the composite metal oxide of the present
invention is described below. In the present specification, the
symbol "-" is used to indicate that the numeric values before and
after it are included as minimum and maximum.
[0048] The nanomaterial of the composite metal oxide of the present
invention is characterized in that an amorphous metal oxide has
uniformly distributed nanopores which contain exchangeable metal
ions. Here, the term "uniformly distributed nanopores" is used to
mean that nanopores in the metal oxide serving as matrix are
uniformly distributed throughout the entire material. That is, the
nanopores referred to here are such that the material is of uniform
composition when evaluated on a scale larger than the size of the
nanopores. Further, the size of the nanopores is of about the same
size as the molecules in at least one dimension or the thickness
and they are not formed by removing some specific component from a
microscopic phase-separated structure. Here, the phrase "amorphous
metal oxides" is defined to mean that both the arrangement of the
atoms constituting the nanomaterial and the arrangement of the
nanopores in the nanomaterial are irregular. This states a
characteristic structural difference from zeolite compounds and
mesoporous materials having periodic holes. At least a portion of
the "exchangeable metal ion" referred to herein is in contact with
the metal oxide constituting the matrix. The exchangeable metal
ions in the amorphous metal oxide serving as matrix are present
within the internal space of the above-described nanopores. The
nanopores may have various shapes such as dot, line, net, and
planar shapes. However, as set forth above, the internal space must
be of about the same size as the molecule at least in width or in
thickness. Further, when removing one exchangeable metal ion and
replacing it with a different ion, the amorphous metal oxide
serving as matrix must be able to maintain its shape.
[0049] When obtaining a nanomaterial in the form of a thin film in
the present invention, the nanomaterial is desirably formed on a
solid surface. The type of solid surface is not specifically
limited provided that it permits the formation of a thin layer
thereon. Considering that many of the thin film materials of the
present invention are desirably manufactured with metal alkoxide
compounds, the use of a solid having groups reactive with metal
alkoxide groups is desirable. Hydroxyl groups and carboxyl groups
are preferred groups reactive with metal alkoxide groups. The
material making up the solid is not specifically limited and
examples of materials suitable for use include various materials
such as organic, inorganic, and metal materials. Specific examples
are glass, titanium oxide, silica gel, and other solids comprised
of inorganic materials; solids comprising organic compounds such as
polyacrylic resin, polyvinyl alcohol, cellulose, and phenol resins;
and metals with surfaces characterized by ready oxidation, such as
iron, aluminum, and silicon.
[0050] When forming the thin film material of the present invention
on a solid having no reactive groups (for example, cadmium sulfide,
polyaniline, or gold), it is recommended that hydroxyl groups or
carboxyl groups be incorporated into the solid surface in advance.
Hydroxyl groups can be incorporated by known methods without
restriction. For example, hydroxyl groups can be introduced to a
gold surface by adsorption of mercaptoethanol or the like. Further,
carboxyl groups can be introduced to substrate surfaces having
cationic charges by extremely thin adsorption of anionic polymer
electrolytes such as polyacrylic acid.
[0051] The quantity of hydroxyl groups or carboxylic groups present
on the solid surface affects the uniformity of the thin film
material of composite metal oxide that is to be formed. Thus, to
form a good thin film of composite metal oxide in the present
invention, the groups that are reactive with the solid surface
(particularly hydroxyl groups and carboxyl groups) are generally
present in a quantity of from 5.0.times.10.sup.13 to
5.0.times.10.sup.14 equivalent/cm.sup.2, preferably from
1.0.times.10.sup.14 to 2.0.times.10.sup.14 equivalent/cm.sup.2.
[0052] Further, considering that the thin film material of the
present invention can also be manufactured using an aqueous
solution of silicate oligomer, the use of a solid capable of
adsorbing the silicate oligomer employed is desirable. Solid
surfaces having cationic charges and the surfaces of metal oxides
on which hydroxyl groups are present may be suitably employed to
that end.
[0053] The shape and surface form of the solid are not specifically
limited. That is, so long as a thin film material of composite
metal oxide can be formed by chemical adsorption from a solution
and rinsing, there is not a requirement that the solid surface be
smooth. Thus, the thin film material of the present invention may
be formed on a variety of solid surfaces, such as the solid
surfaces of various items such as textiles, beads, powder, and thin
pieces, as well as on the inner walls of tubes and filters, on the
inner surfaces of porous materials, and items of even larger
surface area. Although not a specific limitation, it is possible to
form the thin film material of the present invention on metal oxide
thin films formed by methods such as the surface sol-gel
process.
[0054] The method of forming the composite metal oxide thin film of
the present invention on these solid surfaces is not specifically
limited. However, examples of preferred methods are a method
employing a combination of several metal alkexides (referred to as
"Method A" hereinafter), a method employing a combination of a
metal alkoxide compound and metal ions (referred to as "Method B"
hereinafter), and a method employing a water-soluble silicate
oligomer (referred to as "Method C" hereinafter).
[0055] [Method A]
[0056] In Method A, a metal alkoxide compound providing metal ions
soluble in acidic aqueous solutions following hydrolysis and a
metal alkoxide compound providing a metal oxide insoluble in water
following hydrolysis are desirably combined for use.
[0057] The "metal alkoxide compound providing metal ions soluble in
acidic aqueous solutions following hydrolysis" that is employed in
the present invention may be any known compound having such
characteristics. Examples of typical compounds include metal
alkoxide compounds comprising alkaline earth metals such as
magnesium ethoxide (Mg(OCH.sub.2CH.sub.3).sub.2), calcium
methoxyethoxide (Ca(OCH.sub.2CH.sub.2OCH.sub.3).sub.2), and barium
isopropoxide (Ba(O.sup.iPr).sub.2); metal alkoxide compounds
comprising alkali metals such as lithium ethoxide
(LiOCH.sub.2CH.sub.3); metal alkoxide compounds comprising alkali
metals such as potassium ethoxide (KOCH.sub.2CH.sub.3) and sodium
ethoxide (NaOCH.sub.2CH.sub.3); metal alkoxide compounds comprising
lanthanide series metals such as lanthanum methoxymethoxide
(La(OCH.sub.2CH.sub.2OCH.sub.3).sub.3); and metal alkoxide
compounds comprising transition metals, such as copper ethoxide
(Cu(OCH.sub.2CH.sub.3).sub.2).
[0058] The "metal alkoxide compound providing metal oxide insoluble
in water following hydrolysis" that is employed in the present
invention may be any known compound having such characteristics.
Examples of typical compounds include metal alkoxide compounds such
as titanium butoxide (Ti(O.sup.nBu).sub.4), zirconium propoxide
(Zr(O.sup.nPr).sub.4), aluminum butoxide (Al(O.sup.nBu).sub.3),
niobium butoxide (Nb(O.sup.nBu).sub.5), and tetramethoxysilane
(Si(OMe).sub.4); metal alkoxide compounds having two or more
alkoxide groups such as methyltrimethoxysilane (MeSi(OMe).sub.3);
and metal alkoxide compounds comprising two types of metal ions,
such as BaTi(OR).sub.x.
[0059] In Method A of the present invention, in addition to the
above-described metal alkoxide compound, an oligomer of metal
alkoxide compound obtained by partially hydrolyzing and condensing
the alkoxide by the addition of a small amount of water may be
employed. However, the combination of metal alkoxide compounds
sometimes results in the formation of fine particles exceeding the
nano size range due to the addition of an excess amount of water.
In such cases, they cannot be employed as the metal alkoxide
compound of the present invention. That is because the formation of
large fine particles results in a thin film material having a
phase-separated structure, precluding the uniform dispersion of
nanopores.
[0060] One preferred method employed as Method A is to chemically
adsorb a metal alkoxide compound by bringing a mixed solution of
the two above-described metal alkoxide compounds in contact with a
solid surface having groups reactive with metal alkoxide
groups.
[0061] Any method of saturation adsorption on the solid surface can
be employed without limitation in the contacting of the mixed
solution of metal alkoxide compounds. Generally, the solid is
either immersed in the mixed solution, or the solution is suitably
coated on the solid surface by a method such as spin-coating. The
solvent employed in this process is not specifically limited. For
example, methanol, ethanol, toluene, propanol, or benzene may be
employed singly or in combination.
[0062] The concentration of the "metal alkoxide compound providing
metal ions soluble in acidic aqueous solutions following
hydrolysis" is desirably from about 1 to 100 mM. Further, the
concentration of the "metal alkoxide compound providing metal oxide
insoluble in water following hydrolysis" is desirably from about 5
to 500 mM. The compositional ratio of the two cannot be specified
once for all conditions, but the "metal alkoxide compound providing
metal oxide insoluble in water following hydrolysis" is desirably
employed in an excess quantity of from about 5 to 20 times the
quantity of "metal alkoxide compound providing metal ions soluble
in acidic aqueous solutions following hydrolysis". The contact
period and temperature vary with the activity of the metal alkoxide
compound employed and cannot be specified once for all conditions,
but in general the selection of a contact period of from one minute
to several hours and the selection of a temperature of from 0 to
100.degree. C. are generally adequate.
[0063] Saturated adsorption of the "metal alkoxide compound
providing metal oxide insoluble in water following hydrolysis" and
the "metal alkoxide compound providing metal ions soluble in acidic
aqueous solutions following hydrolysis" against the hydroxyl or
carboxyl groups of a solid surface are achieved by the
above-described contact step. At the same time, metal alkoxide
compounds are present due to physical adsorption. Achieving a
uniform and homogeneous thin film may require removing the excess
adsorbed metal alkoxide compound.
[0064] The method of removing the excess metal alkoxide compound
may be any method of selectively removing the metal alkoxide
compound, without limitation. For example, rinsing with the
above-listed organic solvents is a suitable method. Rinsing may be
conducted by immersion rinsing in the organic solvent, spray
rinsing, vapor rinsing, or the like. The temperature employed in
the above-described contact step may be suitably employed for
rinsing.
[0065] Upon hydrolyzing, the "metal alkoxide compound providing
metal oxide insoluble in water following hydrolysis" and "metal
alkoxide compound providing metal ions soluble in acidic aqueous
solutions following hydrolysis" that have been chemically adsorbed
onto the solid surface condense to form a thin film material of
composite metal oxides.
[0066] This hydrolysis may be conducted by known methods without
specific limitation. For example, the most common operation is to
immerse in water the solid on which have been adsorbed the
above-described metal alkoxide compounds. The water employed is
desirably ion-exchange water to prevent the introduction of
impurities and the like and to produce high-purity metal oxides. It
is also possible to immerse the solid on which has been adsorbed
the metal alkoxide compound in an organic solvent containing a
small amount of water to conduct hydrolysis. Further, when
employing a combination of metal alkoxide compounds that are highly
reactive with water, hydrolysis can be conducted by reaction with
the water vapor in air.
[0067] As needed, following hydrolysis, the surface can be dried
with a drying gas such as nitrogen gas, yielding the thin film
material of composite metal oxides of the present invention.
[0068] In Method A, the thickness of the composite metal compound
can be adjusted at the nanometer level by repeating the above
series of steps one or more times. That is, hydrolysis generates on
the surface of the thin film new hydroxyl groups capable of
reacting with metal alkoxide compounds. By repeating chemical
adsorption through contact of the metal alkoxide compounds with the
surface hydroxyl groups, removal of excess adsorbed alkoxides, and
hydrolysis, it is possible to conduct nanometer level adjustment of
the film thickness of the thin film material of composite metal
oxides.
[0069] In Method A, the "metal alkoxide compound providing metal
oxide insoluble in water following hydrolysis" and "metal alkoxide
compound providing metal ions soluble in acidic aqueous solutions
following hydrolysis" may be prepared as separate solutions and the
above-described series of steps conducted with the respective metal
alkoxide compound solutions to produce the thin film material of
composite metal oxides. For example, after chemically adsorption
through contact of the "metal alkoxide compound providing metal
oxide insoluble in water following hydrolysis" with the solid,
removing the excess adsorption material, and conducting the
hydrolysis step, the solid surface is brought into contact with the
"metal alkoxide compound providing metal ions soluble in acidic
aqueous solutions following hydrolysis" to conduct chemical
adsorption, the excess adsorption material is removed, and
hydrolysis is conducted to obtain the thin film material of
composite metal oxides. Although there is no specific limitation to
the adsorption sequence, adsorption of the "metal alkoxide compound
providing metal ions soluble in acidic aqueous solutions following
hydrolysis" cannot be consecutively conducted three or more times.
This is because the consecutive adsorption of the "metal alkoxide
compound providing metal ions soluble in acidic aqueous solutions
following hydrolysis" produces a thin film material having a phase
separated structure, precluding uniform dispersion of
nanopores.
[0070] By means of the above-described steps, a thin film material
of composite metal oxides containing exchangeable metal ions in the
fine pores of an amorphous metal oxide having uniformly distributed
nanopores is formed on a solid surface. The thickness of the thin
film material varies with the type of metal alkoxide compounds
employed and the manufacturing conditions, but in general,
conducting one cycle of the series of steps of chemical adsorption,
rinsing, and hydrolysis yields a good thin film having a thickness
of from 0.5 to 5 nm, and often yields a thin film having a
thickness of from 0.5 to 2.0 nm.
[0071] Although not falling under any theory, the formation of
nanopores within the amorphous metal oxide by the step of Method A
is attributed to the following principles.
[0072] That is, in Method A of the present invention, the thin film
material of the composite metal oxide is formed by hydrolysis of
the adsorbed film of metal alkoxide compound of molecular
thickness. When a mixed solution of the "metal alkoxide compound
providing metal oxide insoluble in water following hydrolysis" and
"metal alkoxide compound providing metal ions soluble in acidic
aqueous solutions following hydrolysis" is employed as the solution
of metal alkoxide compounds, these metal alkoxide compounds are
uniformly adsorbed onto the solid surface. Even assuming that two
types of metal alkoxide compounds adsorbed nonuniformly onto the
solid surface and formed domains, the surface adsorbed metal
alkoxide compounds have a film thickness on the molecular level.
When the adsorption film of these metal alkoxide compounds is
hydrolyzed, a thin film of composite metal oxides is obtained. At
that time, the individual alkoxide compounds are chemically
adsorbed to the solid surface and cannot change position.
Accordingly, the domains of the metal oxides have a thickness of
molecular level. Accordingly, when the ratio of "metal alkoxide
compound providing metal oxide insoluble in water following
hydrolysis" against "metal alkoxide compound providing metal ions
soluble in acidic aqueous solutions following hydrolysis" is high,
the metal ions produced by the latter metal alkoxide compounds are
enclosed in a matrix of metal oxide compounds originating from the
"metal alkoxide compound providing metal oxide insoluble in water
following hydrolysis."
[0073] Similarly, in the case of thin film materials of composite
metal oxides manufactured by stacking metal oxide thin films of the
respective solutions of "a metal alkoxide compound providing metal
oxide insoluble in water following hydrolysis" and "a metal
alkoxide compound providing metal ions soluble in acidic aqueous
solutions following hydrolysis", the layer of "metal alkoxide
compound providing metal ions soluble in acidic aqueous solutions
following hydrolysis" is formed in two dimensions, preventing the
formation of micro phase-separated structures.
[0074] The composite metal oxide thin film formed by Method A in
the present invention has a structure in which nanosize regions of
the metal oxides containing the "metal alkoxide compound providing
metal ions soluble in acidic aqueous solutions following
hydrolysis" are formed in a matrix of "water-insoluble metal
oxides". When such a composite metal oxide thin film is immersed in
an acidic aqueous solution, the metal ions that are soluble in
acidic aqueous solutions are removed, protons compensating for the
lost cationic charges are incorporated, and a thin film material of
metal oxides is obtained. When it is desirable to remove the metal
ions under moderate conditions, it is possible to leave some level
of metal ions that are soluble in acidic aqueous solutions in the
metal oxide thin film.
[0075] The metal ions may be removed by immersion for several hours
in an aqueous solution of from pH 2 to 6, and in many cases,
immersion for several hours in an aqueous solution of from pH 3 to
4 affords adequate removal.
[0076] After removing the metal ions that are soluble in the acidic
aqueous solution, different metal ions can be introduced into the
composite metal oxide manufactured by Method A to produce a new
composite metal oxide. Although not a limitation, the method of
immersing a solid having composite metal oxides on its surface
manufactured by Method A in an aqueous solution of metal salts is
preferably employed.
[0077] The type of metal ion incorporated here is not specifically
limited provided that it be present in water as cation. Examples of
metal salt compounds with metal ions dissolving in water as cation
include chromium nitrate (Cr(NO.sub.3).sub.3), manganese nitrate
(Mn(NO.sub.3).sub.2), ferric nitrate (Fe(NO.sub.3).sub.3), cobalt
nitrate (Co(NO.sub.3).sub.2), and other salts of primary transition
metals; palladium nitrate (Pd(NO.sub.3).sub.2), silver nitrate
(AgNO.sub.3), cadmium nitrate (Cd(NO.sub.3).sub.2), and other salts
of secondary transition metals; lanthanum nitrate
(La(NO.sub.3).sub.3), gadolinium nitrate (Gd(NO.sub.3).sub.3), and
other salts of lanthanite metals, barium nitrate
(Ba(NO.sub.3).sub.2), calcium nitrate (Ca(NO.sub.3).sub.2) and
other salts of alkaline earth metals; and potassium nitrate
(KNO.sub.3), lithium nitrate (LiNO.sub.3), and other salts of
alkali metals. Counter anions of compounds providing metal cations
in water are not specifically limited. One example thereof is
sodium hydroxide (NaOH).
[0078] The duration of immersion of the solid having composite
metal oxides on its surface manufactured by Method A in the aqueous
solution of a metal salt is suitably determined within a range of
from one minute to 24 hours, and the immersion temperature is
desirably from 0 to 100.degree. C. The metal salt is desirably
employed in a concentration of from 1 to 100 mM, preferably a
concentration of about 10 mM.
[0079] The quantity of metal ions incorporated depends on the
quantity of "metal ion soluble in acidic aqueous solutions" in the
composite metal oxide manufactured by Method A, as well as on the
duration of the step of incorporating the metal ions and the
concentration of the metal salt. Following adequate immersion, the
quantity of metal ion incorporated becomes equivalent to the
quantity of "metal ions soluble in acidic aqueous solution"
initially present. However, in the case of metal ions readily
undergoing olation, such as iron ions, since the charge of the
metal ions diminishes per unit quantity due to olation, a quantity
of metal ions greater than the quantity of "metal ions soluble in
acidic aqueous solutions" present in the composite metal oxides
manufactured by Method A is incorporated.
[0080] The embodiments described further below can be consulted for
the details of methods of removing these "exchangeable metal ions"
and methods of incorporating other metal ions.
[0081] [Method B]
[0082] In Method B, a thin film material of composite metal oxides
is formed by forming an amorphous metal oxide thin film of
nanometer thickness on a solid surface, immersing the thin film in
a solution containing metal ions, and rinsing away excess adsorbed
metal ions. In this case, the surface sol-gel process is the
optimum means of forming the amorphous metal oxide thin film of
nanometer thickness. In Method B, when manufacturing an amorphous
metal oxide thin film of nanothickness by the surface sol-gel
process, it is desirable to employ a "metal alkoxide compound
providing metal oxide insoluble in water following hydrolysis" as
described in the implementation mode of Method A.
[0083] When employing the above-described metal alkoxide compound
as the means of manufacturing an amorphous metal oxide thin film of
nanometer thickness in Method B, the metal alkoxide compound is
chemically adsorbed by bringing a solution of the metal alkoxide
compound into contact with a solid surface which possesses groups
reactive with metal alkoxide groups. Here, the solvent used for the
metal alkoxide compound, contact duration, contact temperature, and
concentration of the metal alkoxide compound may be selected within
ranges such as those described for the implementation mode of
Method A. After conducting the contact step, a rinsing step and
hydrolysis step such as those conducted in the implementation mode
of Method A are performed. Following hydrolysis, as needed, the
surface is dried with a drying gas such as nitrogen gas. In Method
B, repeating the above-described series of steps permits
controlling the thickness of the amorphous metal oxide thin film at
the nanometer level. Further, when a "metal alkoxide compound
providing metal oxide insoluble in water following hydrolysis" is
combined for use, it is possible to stack two or more layers of
different amorphous metal oxides of nanothickness that are
insoluble in water.
[0084] Next, the solid having an amorphous metal oxide thin film of
nanometer thickness is immersed in a solution containing metal ions
and new metal ions are introduced to obtain a thin film material of
composite metal oxide in Method B of the present invention. The
type of metal ion introduced in Method B is desirably the type of
metal ion described in the implementation mode of Method A.
[0085] The duration of the period of immersion in solution
comprising metal ions of the solid having an amorphous metal oxide
thin film of nanometer thickness in Method B may be selected from
within a range of from one minute to 12 hours and immersion is
desirably conducted at a temperature of from 0 to 80.degree. C. The
metal ions are desirably employed at a concentration of from 1 to
100 mM, preferably at a concentration of about 10 mM.
[0086] In Method B, repeating the steps of forming the
above-described amorphous metal oxide thin film of nanometer
thickness and introducing metal ions makes it possible to control
the thickness of the composite metal oxide at the nanometer
level.
[0087] Although not falling under any theory, the incorporation of
metal ions within the amorphous metal oxide thin film of nanometer
thickness by the above-described steps is attributed to the
following principles.
[0088] In the surface sol-gel process, a thin film of molecular
thickness is formed by chemical adsorption of a metal alkoxide
compound and hydrolysis. An extremely flexible metal-oxygen bond
network is formed on the surface and in the immediate area of such
thin films, with numerous hydroxyl groups present. The protons of
these hydroxyl groups can be exchanged with metal ions.
Accordingly, in the case of an extremely thin nanofilm, the
amorphous metal oxide thin film becomes an ion-exchangeable thin
film. As is indicated in the embodiments, the steps of forming an
amorphous metal oxide thin film of nanothickness and of introducing
metal ions can be repeated to grow a thin film in which metal ions
are incorporated into an amorphous metal oxide thin film of nano
thickness, yielding an overall uniform composite metal oxide thin
film.
[0089] The metal ions introduced through ion exchange of the
protons of the hydroxyl groups in the amorphous metal oxide thin
film can be removed by immersion in an acidic aqueous solution.
When the thin film is immersed in a solution containing different
metal ions, the other metal ions can be introduced. The embodiments
described further below may be consulted for details regarding the
method of removing metal ions and the method of introducing
different metal ions.
[0090] [Method C]
[0091] In Method C, a solid surface having positive charges or
groups reactive with silicate oligomer is brought into contact with
an aqueous solution of silicate oligomer to chemically adsorb the
oligomer, after which the excess oligomer is removed by rinsing to
manufacture a thin film material of composite metal oxide. As set
forth above, the surface of a metal oxide having hydroxyl groups
manufactured by the surface sol-gel process is preferably employed
as the solid surface having groups reactive with the silicate
oligomer.
[0092] An aqueous solution of sodium silicate (Na.sub.2SiO.sub.3)
is preferably employed as the aqueous solution of silicate
oligomer. Sodium silicate has an anionic oligomer structure in
which orthosilicate is partially condensed, and has sodium ions as
counter ions. Further, in addition to sodium silicate, other metal
ions such as potassium silicate and lithium silicate can be
employed in the aqueous solution of silicate oligomer.
[0093] Further, in Method C of the present invention, in addition
to the above-described aqueous solution of silicate oligomer, small
quantities of acid may be added to the aqueous solution of silicate
oligomer, and a solution in which silicate oligomer condensed may
also be employed.
[0094] The method of saturation adsorption of silicate oligomer on
the solid surface by the contacting of the aqueous solution is not
specifically limited. The concentration of the silicate oligomer in
the above-described solution is desirably about from 1 to 100 mM
based on silicon. The contact period may generally be selected from
about one minute to one hour, and the contact temperature from 0 to
50.degree. C.
[0095] The above-described contact step causes a saturation
adsorption of silicate oligomer against the positive charges or
hydroxyl groups of the solid surface, with silicate oligomer being
simultaneously present through physical adsorption. Obtaining a
uniform and homogeneous thin film sometimes requires the removal of
the excess adsorbed silicate oligomer. The method of rinsing with
ion-exchange water is a preferred method of removing excess
silicate oligomer. Further, the temperature employed in the
above-described contact step is desirably employed as the rinsing
temperature. As required, following rinsing, the surface may be
dried with a drying gas such as nitrogen gas. Thus, a thin film
material of composite metal oxide can be obtained by Method C of
the present invention.
[0096] By the above-described steps, a thin film material of
composite metal oxides containing exchangeable metal ions in the
uniformly dispersed nanopores of amorphous silicate is formed on a
solid surface. The thickness of the thin film material varies with
the concentration of the silicate oligomer employed, and quantity
of acid added, but a good thin film with a film thickness of from
0.5 to 2 nm can generally be obtained.
[0097] Although not falling under any theory, the formation of
nanopores in the amorphous silicate by the steps of Method C is
attributed to the following principles.
[0098] The thin film material of composite metal oxides obtained by
Method C of the present invention is formed from an adsorled film
of silicate oligomer with molecular thickness. Originally, silicate
oligomer having anionic charges possesses metal ions (such as
sodium ions) as counter anions. Following the step of rinsing with
ion-exchange water, the silicate oligomer is partially protonated
and condensed, thereby forming a two-dimensional silicate network
structure on the solid surface with metal ions being uniformly
dispersed within the network. The reason the metal ions and
silicate do not form a microscopic phase separation structure is
that the state in which the metal ions are uniformly and
molecularly distributed is electrostatically stable. As is
indicated in the embodiments, a large quantity of exchangeable
metal ions is present in the thin film of silicate having a network
structure. These metal ions can be removed by immersion in an
acidic aqueous solution such as described above in the
implementation mode of Method A.
[0099] When a solid having on its surface a thin film of composite
metal oxide manufactured according to Method C is immersed in an
aqueous solution of different metal ions, it is possible to
incorporate the different metal ions into the thin film. The types
of metal ions that can be incorporated here are identical to those
in Method A. The immersion period here may be selected within a
range of from 1 to 10 minutes and the immersion temperature is
desirably from 0 to 50.degree. C. An aqueous solution with a
concentration of metal ions from 1 to 100 mM is desirably employed
to introduce the metal ions.
[0100] As indicated in the embodiments, when metal ions of bivalent
or large positive charge such as lanthanum ions (La.sup.3+) are
incorporated into the thin film material of composite metal oxide
manufactured by Method C, the charge in the surface layer of the
thin film reverses and the composite metal oxide obtained becomes
positively charged. The step of manufacturing a thin film material
of composite metal oxide by Method C on such a positively charged
surface can be repeatedly conducted. That is, positive charges are
generated on the surface of the thin film of composite metal oxides
due to adsoption of divalent or more positively charged metal ions
enough to adsorb silicate oligomers having anionic charges. By
repeating the step of manufacturing a thin film by Method C, it is
possible to adjust at the nanometer level the film thickness of the
thin film material of composite metal oxides.
[0101] The nanomaterial of the present invention can be
manufactured as a thin film on a solid substrate by Methods A
through C above. However, the nanomaterial of the present invention
does not necessarily assume the form of a thin film, and may assume
a variety of forms, such as granular, linear, and lattice-like
forms. For example, when the portion having groups reactive with
metal alkoxide compounds is present as a dot form in a limited
region of a solid surface, a dot-shaped nanomaterial can be
manufactured by the present invention. The surfaces of
nanoparticles can be employed to manufacture granular
nanomaterials. That is, in the present invention, the facts that
uniformly dispersed nanopores are present in amorphous metal
oxides, that it is possible to access metal ions in the pores, and
that the size of the material is within the nanometer range are
important; the shape thereof is not limited.
[0102] When at least some of the metal atoms of the nanomaterial
manufactured by Methods A through C are reduced, a nanomaterial of
composite metal oxides comprising a metal component or mixed
valance metal oxide component is obtained. Here, the reduction is
achieved by to known methods without limitation. For example, when
a nanomaterial containing exchangeable silver ions is mixed with
aqueous hydrazine, a nanomaterial containing silver nanoparticles
is obtainable. The surface of nanomaterials can be reduced by the
hydrogen plasma or light irradiation method.
[0103] [Method D]
[0104] In general, the nanomaterial of the present invention
permits the manufacturing of nanoparticles in solution. The method
of forming nanogranular composite metal oxides in the present
invention is not specifically limited. One example of a preferred
method is a method employing multiple metal alkoxide solutions
(referred to as "Method D" hereinafter).
[0105] In Method D, it is desirable to combine the metal alkoxide
compound providing metal ions soluble in acidic aqueous solutions
with the metal alkoxide compound providing metal oxide insoluble in
water following hydrolysis as described in Method A.
[0106] One preferred form of Method D is to dissolve the
above-described alkoxides in an organic solvent and add a small
quantity of water to conduct partial hydrolysis. The organic
solvent is not specifically limited; methanol, ethanol, propanol,
benzene and the like may be employed singly or in combination. The
concentration of the "metal alkoxide compound providing metal ions
soluble in acidic aqueous solutions following hydrolysis" in the
above-described solution is desirably about from 1 to 100 mM.
Further, the concentration of the "metal alkoxide compound
providing metal oxide insoluble in water following hydrolysis" is
desirably about from 5 to 500 mM. Although the compositional ratio
of the two is not comprehensively limited, the "metal alkoxide
compound providing metal oxide insoluble in water following
hydrolysis" is desirably employed in an excess quantity of from 5
to 20 times the quantity of "metal alkoxide compound providing
metal ions soluble in acidic aqueous solutions following
hydrolysis". Further, the quantity of water added to hydrolyze
these metal alkoxide compounds is desirably a quantity that
partially hydrolyzes the metal alkoxides.
[0107] The "partial hydrolysis" referred to here refers to the
conducting of hydrolysis with a quantity of water smaller than the
quantity that is stoichiometrically required to hydrolyze the metal
alkoxide compounds into metal oxides. For example, titanium
butoxide (Ti(O.sup.nBu).sub.4) is reacted with a double molar
quantity of water to produce titanium oxide and ethanol. When
titanium butoxide (Ti(O.sup.nBu).sub.4) is reacted with a quantity
of water less than a double molar quantity, the titanium butoxide
(Ti(O.sup.nBu).sub.4) does not completely hydrolyze, but only
partially hydrolyzes. Although an overall limitation cannot be
given, the quantity of water added in Method D is desirably
slightly in excess of the quantity required for stoichiometric
hydrolysis of the metal alkoxides.
[0108] The reaction temperature and duration of the above-described
solution varies with the activity of the metal alkoxide compounds
employed and cannot be limited comprehensively for all conditions.
However, the temperature can generally be determined within a range
of from one minute to several hours and the temperature within a
range of from 0 to 100.degree. C.
[0109] The "metal alkoxide compound providing metal oxide insoluble
in water following hydrolysis" and the "metal alkoxide compound
providing metal ions soluble in acidic aqueous solutions following
hydrolysis" are partially hydrolyzed in the organic solvent and
condensed based on the above-described step to form nanoparticles
of composite metal oxides. The size of these nanoparticles varies
with the reaction conditions and quantity of water added, but
nanoparticles from 1 to 500 nanometers can generally be
produced.
[0110] Although not falling under any theory, the formation of
nanopores within the amorphous metal oxide by the step of Method D
is attributed to the following principles.
[0111] In the nanomaterial of composite metal oxides obtained by
Method D of the present invention, the partial hydrolysis of the
"metal alkoxide compound providing metal oxide insoluble in water
following hydrolysis" and the "metal alkoxide compound providing
metal ions soluble in acidic aqueous solutions following
hydrolysis" yields nanoparticles containing the both comporents.
Here, when the "metal alkoxide compound providing metal oxide
insoluble in water following hydrolysis" is added in excess of the
"metal alkoxide compound providing metal ions soluble in acidic
aqueous solutions following hydrolysis", the metal ions produced
from the latter metal alkoxide compounds are enclosed in the matrix
of nanosized metal oxide originating from the former metal alkoxide
compounds.
[0112] In the nanoparticles of composite metal oxide formed by
Method D of the present invention, the nanosize region of metal
oxide containing the "metal ions soluble in acidic aqueous
solutions" are formed within the matrix of "metal oxide insoluble
in water". When an acidic aqueous solution is added to a solution
containing such nanoparticles, the metal ions soluble in acidic
aqueous solutions can be removed. Here, depending on the
conditions, the nanoparticles sometimes aggregate. It is clear
that, the nanoparticles formed by Method D have the exchangeable
metal ions that characterize the nanomaterial of the present
invention.
[0113] The metal ions are desirably removed by adding a 1 to 10
normal aqueous hydrochloric acid. The nanoparticles of metal oxide
obtained can be separated by a method such as centrifugal
separation.
[0114] After removing the metal ions by the addition or the acidic
solution, different metal ions can be introduced to the
nanoparticles of composite metal oxide manufactured by Method D to
produce new nanoparticles of composite metal oxide.
[0115] The metal oxide compounds employed in Method A are desirably
employed as the metal ions here.
[0116] Further, although the method of adding a metal salt is not
specifically limited, the addition of a saturated methanol solution
of metal salt is desirable. The nanoparticles of composite metal
oxide obtained can be separated by a method such as centrifugal
separation.
[0117] The nanomaterials manufactured by Methods A through D can be
reacted with chalcogen compounds to obtain nanomaterials of
composite metal oxide containing a metal chalcogenite component.
Any known reaction methods can be employed here without specific
limitation. For example, a nanomaterial containing exchangeable
cadmium ions can be mixed with an aqueous solution of sodium
sulfide to obtain a nanomaterial containing cadmium sulfide. In the
cares or nanomaterials on solid sarfaces a gaseous chalcogen
compound such as hydrogen sulfide gas can be exposed to react with
them.
[0118] Further, the nanomaterials manufactured by Methods A through
D can be heat treated or oxygen plasma treated to manufacture
nanomaterials of composite metal oxides in which the ion-exchange
capability of the exchangeable metal ions is diminished.
[0119] Some or all of the metal atoms constituting the
nanomaterials manufactured by Methods A through D can be reduced to
manufacture a material of a composite metal compound containing a
metal component or a mixed valence metal oxide component. Further,
conducting a subsequent oxidation treatment permits the
re-oxidation of at least a portion of the metal component or mixed
valence metal oxide component. Further, after conducting such a
reducing step and re-oxidation step, by alternating the reducing
step and the oxidation step in that order one or more times, the
size and standard deviation of the nanoparticles can be controlled.
Here, the phrase "alternating the reducing step and the oxidation
step in that order one or more times" includes the case where just
a reduction step is conducted; the case where an oxidation step is
conducted after a reduction step, the case where a reduction step,
an oxidation step, and a reduction step are conducted in that
order; and the case where four or more steps are alternately
performed in the order of reduction step followed by oxidation
step. Preferred examples of reduction steps and oxidation steps are
hydrogen plasma treatment and oxygen plasma treatment.
[0120] The embodiments described further below may be referred to
for methods of manufacturing novel nanomaterials by reducing,
reacting, heat treating, or plasma treating the nanomaterials
manufactured by Methods A-D. However, the scope of the present
invention is not limited to the methods of the embodiments
described further below.
[0121] The principal characteristics and industrial applications of
the nanomaterials of the present invention are as follows.
[0122] The present invention provides nanomaterials of composite
metal oxides with a wide range of different compositions and
structures. Further, it is possible to reliably manufacture
nanomaterials of composite metal oxides on surfaces of every
conceivable shape, patterned surfaces, and large surface area
substrates by means of simple steps under moderate conditions based
on adsorption from solution.
[0123] The nanomaterials of composite metal oxides can yield
materials with different physicochemical characteristics and
electronic characteristics from previous metal oxide materials.
Composite metal oxides exhibit a broad range of electrinic
properties, from insulators to conductors depending on the
combination of metal ions, permitting the manufacturing of
conductive materials, insulating materials, dielectrics, and the
like. Quantum effects are anticipated from semiconducting materials
in the nanometer range. In particular, these effects are
significant in dot-shaped or particulate nanomaterials. Further,
thin film materials containing large quantities of lanthanide
metals such as gadolinium are expected to become magnetic memory
materials in the next generation. Further, controlling the
refractive index of composite metal compounds is expected to yield
thin film materials having new optical characteristics. Further,
introducing metal ions having light-emitting characteristics such
as europium relates to the development of new light-emitting
materials, and the use of composite metal oxides containing
photosensitive ions such as silver ions a can be anticipated to be
photomemory materials. Further, the use of thin film materials of
composite metal oxides that absorb ultraviolet and visible light is
anticipated to capture light energy and as photoelectric
converters. Further, the introduction of metal ions having
catalytic activity such as transition metal ions permits the
development of highly efficient catalytic materials. Since the
composite metal oxide of the present invention contains an
exchangeable metal ion, applications as ion-exchange materials,
ion-extracting materials, and ion sensors can be anticipated, with
the possibility of development as a gas sensor. In particular, when
a thin film material of amorphous metal oxide containing nanopores
of the present invention is formed on the surface of a porous
substrate, the separation utilizing the ion-exchange
characteristics thereof becomes possible. Not only are applications
as an ion-exchange material possible, but applications as a means
of electrochemical synthesis or in fuel cells become possible. The
ion-exchange characteristics of the metal ions may also be employed
in methods of manufacturing batteries of nanothickness. Further,
the use of the metal ions dispersed in the nanopores of the metal
oxide matrix as precursors in material synthesis yields nanometer
level fine particles and permits the manufacturing of thin film
materials with highly dispersed magnetic particles and of thin film
materials having plasmon absorbing properties. Due to the good
mechanical characteristics, thermal stability, and chemical
stability of composite metal oxides, they also become useful as
coating reagent on the surfaces of materials. It also becomes
possible to control the molecular adsorption characteristics and
wetting properties of material surfaces by means of thin films of
composite metal oxides. That is, the use of thin films of composite
metal oxides is to be anticipated in the field of molecular
organization using small molecules, polymers, supermolecules,
biomolecules, inorganic microparticles, and organic
microparticles.
[0124] Embodiments
[0125] The characteristics of the present invention are described
more specifically below through embodiments. The materials, used
quantities, proportions, treatment contents, treatment procedures,
and the like indicated in the embodiments below may be suitably
modified without departing from the essence of the present
invention. Accordingly, the scope of the present invention is not
to be interpreted as being limited by the specific examples given
below.
[0126] In the embodiments below, in order to show the sequential,
constant-quantity stacking of thin film materials of composite
metal oxides, the thin film materials were formed on quartz
resonators and the increase in the weight of the thin film was
estimated from the change in frequency of the quartz resonator. The
quantity of exchangeable metal ions removed from the thin film
materials and the quantity of other metal ions introduced therein
were estimated from changes in the frequency of quartz resonators.
The quartz resonator is known as microbalance and is used as
devices capable of detecting the weight of thin films formed on the
electrode surfaces thereof to a precision of 10.sup.-9 g.
[0127] The quartz resonators with coated gold electrodes were
washed with a piranha solution (a 3:1 mixed solution of aqueous
solutions of 96 percent sulfuric acid and 30 percent hydrogen
peroxide), rinsed with pure water, and immersed for 12 h in 10 mM
mercaptoethanol solution to introduce hydroxyl groups onto the
surface, rinsed with ethanol, and blowed with nitrogen gas to
achieve thorough drying. The frequency of the quartz resonator at
that time was adopted as the reference value and the change in
weight of the thin film was estimated from the change in frequency
(-.DELTA.F) accompanying subsequent thin film formation.
[0128] The composition of the composite metal compound was
determined by X-ray photoelectron spectrometry (XPS). Further, the
shape of the thin film material obtained was evaluated by
observation by scanning electron microscopy (SEM) or transmission
electron microscopy (TEM).
[0129] (Embodiment 1)
[0130] Magnesium ethoxide and titanium butoxide were employed to
manufacture a composite metal oxide thin film by Method A as
Embodiment 1. In the present embodiment, nanopores were formed in a
matrix of porous titania. However, similar thin film materials have
been obtained employing other metal oxides such as zirconia. An
11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).sub.2) was dissolved in 10 mL of
2-ethoxyethanol, 0.353 mL of titanium butoxide
(Ti(O.sup.nBu).sub.4) was added, and the mixture was stirred. A
quartz resonator was immersed for 10 min in this solution at
25.degree. C., rinsed by immersion for 1 min in toluene at
25.degree. C., and blown dry with nitrogen gas. The quartz
resonator was then left standing in air for about 20 min until the
frequency of the quartz resonator stabilized to hydrolyze the metal
alkoxide compounds chemically adsorbed to the solid surface, and
the frequency of the quartz resonator was measured. This thin film
formation step was repeated to form a composite metal oxide thin
film. Next, the quartz resonator having the composite metal oxide
thin film on its surface was immersed for 10 min in a hydrochloric
acid aqueous solution of pH 4, immersion rinsed for 2 min in
ion-exchange water, and dried by blowing with nitrogen gas. The
frequency of the quartz resonator was then measured. The quartz
resonator was then immersed for 10 min in a sodium hydroxide
aqueous solution of pH 10 and dried by blowing with nitrogen gas.
The frequency of the quartz resonator was then measured. The quartz
resonator having on its surface the composite metal oxide thin film
manufactured in this manner was then immersed in an aqueous
solution containing various metal salts.
[0131] FIG. 1 shows the amount of reduction in the frequency of the
quartz resonator due to the stacking of the composite metal oxide
thin films of Embodiment 1. As indicated in the figure, the
frequency of the quartz resonator decreased in proportion to the
stacking of composite metal oxide thin films. This result indicates
that in the method of the present embodiment, a composite metal
oxide thin film of certain weight was successively formed on the
electrode surface of the quartz resonator.
[0132] The change in frequency (-.DELTA.F) after eight cycles was
1,217 Hz. Following immersion in a dilute hydrochloric acid aqueous
solution and sodium hydroxide treatment, the frequency increased by
141 Hz. This indicates the removal of the magnesium ions from the
composite metal oxide thin film of the present embodiment and the
introduction of sodium ions.
[0133] FIG. 2 shows the XPS spectra of a thin film material of
composite metal oxide containing magnesium ions manufactured by the
method of Embodiment 1 on a quartz substrate, the thin film
material following treatments with dilute hydrochloric acid aqueous
solution and sodium hydroxide aqueous solution, and the thin film
thus treated and subsequently immersed for 4 h in a 10 mM
gadolinium nitrate aqueous solution. These results indicate that
the method of the present embodiment reliably formed a titania
ultra thin film containing magnesium ions, and that the dilute
hydrochloric acid and sodium hydroxide treatments removed the
magnesium ions. They also show that the immersion in gadolinium
aqueous solution introduced gadolinium ions into the thin film.
There was no change in the peak intensities of the titania atoms
before and after these steps, indicating that the structure of the
amorphous titania thin film matrix was preserved. No nitrogen atoms
of nitric acid ions (NO.sub.3.sup.-) derived from gadolinium
nitrate were observed in the XPS spectra. Thus, it is clear that
the gadolinium ions were introduced by ion exchange in the present
embodiment.
[0134] FIG. 3 shows the quantities of metal ions introduced by
immersion in aqueous solutions of various metal ions when the
magnesium ions were removed by dilute hydrochloric acid and sodium
hydroxide treatments from thin film materials of composite metal
oxides containing magnesium ions manufactured by the method of
Embodiment 1 on quartz substrates. The metal salts employed were
LiNO.sub.3, KNO.sub.3, Mg(NO.sub.3).sub.2, Ca(NO.sub.3).sub.2,
Ba(NO.sub.3).sub.2, La(NO.sub.3).sub.3, and Gd(NO.sub.3).sub.2. The
concentration was 10 mM in all cases, and the immersion period was
20 min. In all of these tests, the quartz resonator of FIG. 1 was
employed. After the various metal ion incorporation tests, the
incorporated metal ions were removed by dilute hydrochloric acid
and sodium hydroxide treatments, and the samples were employed in
the subsequent metal ion incorporation tests. As will be apparent
in FIG. 3, the incorporation of metal ions was selective, with the
quantity incorporated increasing with the charge. These results
indicate that it was possible for the metal oxide thin films
manufactured by the steps of the present embodiment to selectively
remove specific metal ions from the aqueous solutions.
[0135] The metal ions introduced by the above-described steps can
be removed by treatments with dilute hydrochloric acid and sodium
hydroxide. Magnesium was removed by treatments with dilute
hydrochloric acid and sodium hydroxide from the thin film material
of composite metal oxides containing magnesium ions manufactured by
the method of Embodiment 1 on a quartz resonator. FIG. 4 shows the
quantity of gadolinium ions introduced when the resonator was
immersed for 20 min in a 10 mM aqueous solution of gadolinium
nitrate and rinsed by immersion for 2 min in ion-exchange water;
the quantity of gadolinium ions removed when the resonator was
immersed for 10 min in an aqueous solution of hydrochloric acid of
pH 4, rinsed by immersion for 2 min in ion-exchange water, immersed
for 10 min in a sodium hydroxide aqueous solution of pH 10, and
rinsed by immersion for 2 min in ion-exchange water; and the
quantity of gadolinium ions introduced and removed when the above
introduction and removal steps were repeated. As is apparent from
the figure, the gadolinium ions introduced into the thin film were
completely removed by the removal step. Further, when the
introduction and removal steps were repeated, a quantity of
gadolinium ions equal to the quantity introduced was removed. The
quantity of gadolinium ions introduced the third time around was 80
percent of the quantity removed the first time around, indicating
the structural stability of the amorphous metal oxide having
nanopores of the present embodiment.
[0136] FIG. 5 shows a photograph taken by scanning electron
microscopy of the surface of a thin film after magnesium ions had
been removed by treatments with dilute hydrochloric acid and sodium
hydroxide from a thin film material of composite metal oxide
comprising magnesium ions manufactured by the method of Embodiment
1 on a quartz substrate, the thin film had been immersed for 20 min
in 10 mM barium nitrate aqueous solution, and the film had been
rinsed by immersion in ion-exchange water and dried. The surface of
the thin film was smooth and no change in the surface due to doping
with barium ions was observed.
[0137] (Embodiment 2)
[0138] A compound metal oxide thin film was manufactured by Method
B as Embodiment 2.
[0139] Titanium butoxide (Ti(O.sup.nBu).sub.4) was dissolved to 100
mM in a 1:1 (vol/vol) mixed solution of toluene and ethanol. A
quartz resonator was immersed for 3 min at 25.degree. C. in this
solution, rinsed by immersion for 1 min in ethanol at 25.degree.
C., and then immersed for 1 min in ion-exchange water at 25.degree.
C. to form a metal oxide thin film. This film was then dried by
blowing with nitrogen gas. This step of forming a metal oxide thin
film was repeated 5 times. The frequency of the quartz resonator
was measured, The resonator was immersed for 1 min in an aqueous
solution (0.1 mM) of europium nitrate (III) hexahydrate
(Eu(NO.sub.3).sub.3(6H.sub.2O), rinsed by immersion in ion-exchange
water at 25.degree. C. for 1 min, and blown dry with nitrogen gas,
and then the frequency of the quartz resonator was measured. The
steps of forming the metal oxide thin film and adsorbing the
europium ions were then repeated to form a composite metal oxide
thin film.
[0140] Ultraviolet and visible absorption spectra were measured to
confirm the formation of the composite metal oxide thin film.
Samples were obtained by adsorbing ten cycles of titanium butoxide
and europium nitrate on a quartz substrate to form a composite
metal oxide thin film. As shown in FIG. 6, absorbance due to the
titania ultra-thin film was found near 230 nm, and the absorbance
increased with the adsorption cycle. These results indicate that a
composite metal oxide thin film on a solid surface was formed by
the method of the present embodiment.
[0141] The quartz resonator having the composite metal oxide thin
film on its surface was immersed for 10 min in aqueous hydrochloric
acid at pH 4, immersed for 1 min in ion-exchange water, and dried
by blowing with nitrogen gas. The frequency of the quartz resonator
was measured. The quartz resonator was immersed for 10 min in an
aqueous solution (0.1 mM) of lanthanum nitrate (III) hexahydrate
(La(NO.sub.3).sub.3.6H.sub.2O, the quartz resonator was rinsed by
immersion for 1 min in ion-exchange water, the resonator was blown
dry with nitrogen gas, and the frequency of the quartz resonator
was measured. The steps of adsorbing the lanthanum ions, rinsing
away the excess adsorbed ions, and drying were repeated seven
times.
[0142] FIG. 7 shows changes in the frequency of a quartz resonator
in the series of steps of Embodiment 2. As indicated in the figure,
the frequency of the quartz resonator decreased proportionately
with stacking of the composite metal oxide thin film. These results
indicate that the method of the present embodiment successively
formed a composite metal oxide thin film of a certain weight on the
electrode surface of the quartz resonator. The change in frequency
after 13 cycles (-.DELTA.F) was 2,053 Hz. Further, the total
reduction in value of the frequency due to adsorption of titanium
butoxide was 291 Hz. The total reduction in value of the frequency
due to adsorption of europium ions was 1,762. After immersion in a
dilute hydrochloric acid solution, the frequency of the quartz
resonator increased 1,765 Hz. These results indicate that magnitude
of the total decrease in frequency was about the same as that due
to adsorption of europium ions, indicating that the dilute
hydrochloric acid treatment of the present embodiment removed
europium ions. The total reduction in frequency due to adsorption
of lanthanum ions was 2,802 Hz, indicating that it was possible to
introduce other metal ions into the metal oxide thin film.
[0143] (Embodiment 3)
[0144] A composite metal oxide thin film was manufactured by Method
C as Embodiment 3.
[0145] Titanium butoxide (Ti(O.sup.nBu).sub.4) was dissolved to 100
mM in a 1:1 (vol/vol) mixed solution of toluene and ethanol, A
quartz resonator was immersed for 3 min at 25.degree. C. in this
solution, rinsed by immersion for 1 min in ethanol at 25.degree.
C., immersed for 1 min in ion-exchange water at 25.degree. C., and
dried by blowing with nitrogen gas. This step was repeated 3 times
to form a metal oxide thin film as a precursor film. The frequency
of the quartz resonator was measured. The quartz resonator was
immersed for 3 min in an aqueous solution (50 mM) of lanthanum
nitrate (III) hexahydrate (La(NO.sub.3).sub.3.6H.sub.2O, rinsed by
immersion in ion-exchange water at 25.degree. C. for 1 min, and
blown dry with nitrogen gas, and then the frequency of the quartz
resonator was measured. The quartz resonator was then immersed for
5 min in a 50 mM aqueous solution of sodium silicate
(Na.sub.2SiO.sub.3), rinsed by immersion for 1 min in ion-exchange
water, and dried with nitrogen gas. These steps were repeated to
manufacture a composite metal oxide thin film on the surface of the
precursor film.
[0146] As shown in FIG. 8, the frequency of the quartz resonator
decreased in proportion to the number of adsorption cycles of the
composite metal oxide thin film. These results indicate that the
method of the present embodiment successively formed a composite
metal oxide thin film of a certain weight on the electrode surface
of the quartz resonator. The change in frequency (-.DELTA.F) after
four cycles was 1,573 Hz. The total decrease in frequency due to
La(NO.sub.3).sub.3 adsorption was 1,393 Hz, and the total decrease
in frequency due to adsorption of sodium silicate was 137 Hz.
[0147] A composite metal oxide thin film was fabricated on a quartz
resonator not having a precursor film. The quartz resonator was
immersed for 1 min in an aqueous solution (50 mM) of lanthanum
nitrate (III) hexahydrate (La(NO.sub.3).sub.3.6H.sub.2O), rinsed by
immersion for 1 min in ion-exchange water at 25.degree. C., and
dried by blowing with nitrogen gas. The frequency of the quartz
resonator was measured. The quartz resonator was then again
immersed for 3 min in a 50 mM aqueous solution of sodium silicate
(Na.sub.2SiO.sub.3), rinsed by immersion for 1 min in ion-exchange
water, and dried by blowing with nitrogen gas. The above step was
repeated to manufacture a composite metal oxide thin film.
[0148] As shown in FIG. 9, the frequency of the quartz resonator
decreased in proportion to the number of cycles of adsorption of
composite metal oxide thin film. These results indicate that the
method of the present embodiment successively formed a composite
metal oxide thin film of certain weight on the electrode surface of
the quartz resonator. The change in frequency (-.DELTA.F) after
four cycles was 1,345 Hz. Further, the total decrease in frequency
due to La(NO.sub.3).sub.3 adsorption was 1,182 Hz and the total
decrease in frequency due to sodium silicate adsorption was 163
Hz.
[0149] The following test was conducted to show the feasibility of
manufacturing a composite metal oxide thin film by the
above-described step on a cationic surface.
[0150] Titanium butoxide (Ti(O.sup.nBu).sub.4) was dissolved to 100
mM in a 1:1 (vol/vol) mixed solution of toluene and ethanol, a A
quartz resonator was immersed for 3 min at 25.degree. C. in this
solution, and the quartz resonator was rinsed by immersion for 1
min in ethanol at 25.degree. C., immersed for 1 min in ion-exchange
water at 25.degree. C., and dried by blowing with nitrogen gas.
This step was repeated 5 times to form a metal oxide thin film as a
precursor film. The frequency of the quartz resonator was measured.
The quartz resonator was immersed for 3 min in an aqueous solution
(10 mg/mL) polydimethyl diallylammonium chloride (referred to
hereinafter as "PDDA"), rinsed by immersion for 1 min in
ion-exchange water at 25.degree. C., and blown dry with nitrogen
gas. The frequency of the quartz resonator was measured. The quartz
resonator was then again immersed for 3 min in a 50 mM aqueous
solution of sodium silicate (Na.sub.2SiO.sub.3), rinsed by
immersion for 1 min in ion-exchange water, and dried by blowing
with nitrogen gas. The above step was repeated to manufacture an
organic/inorganic metal oxide composite thin film. As shown in FIG.
10, the frequency of the quartz resonator decreased in proportion
to the number of cycles of adsorption of organic/metal oxide
nanocomposite thin film. The change in frequency (-.DELTA.F) after
five cycles was 235 Hz Farther, the total decrease in frequency due
to PDDA adsorption was 126 Hz and the total decrease in frequency
due to sodium silicate adsorption was 90 Hz. These results indicate
that the method of the present embodiment formed a composite metal
oxide thin film of certain weight on the cationic surface.
[0151] (Embodiment 4)
[0152] A thin film material of composite metal oxide obtained by
the method of the present invention was reduced to manufacture a
thin film material containing a metal component as Embodiment
4.
[0153] An 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).su- b.2) was dissolved in 10 mL of
2-ethoxyethanol, 0.353 mL of titanium butoxide
(Ti(O.sup.nBu).sub.4) was added and the mixture was stirred. A
quartz plate was immersed for 10 min at 25.degree. C. in this
solution, rinsed by immersion for 1 min in toluene at 25.degree.
C., dried by blowing with nitrogen gas, and then left standing in
air for about 20 min to hydrolyze the metal alkoxide compound that
had chemically adsorbed onto the solid surface. This thin film
forming step was repeated 8 times to form a composite metal oxide
thin film. Next, the quartz plate on the surface of which had been
formed the composite metal oxide thin film was immersed for 10 min
in pH 4 aqueous solution of hydrochloric acid, rinsed by immersion
for 2 min in ion-exchange water, and dried by blowing with
nitrogen. It was then immersed for 10 min in a pH 10 sodium
hydroxide aqueous solution and dried by blowing with nitrogen. The
quartz plate was immersed for 4 h in a 10 mM aqueous solution of
silver nitrate, rinsed by immersion for 1 min in ion-exchange
water, and dried by blowing with nitrogen. The quartz plate was
then immersed for 1 min in a 200 mM aqueous solution of sodium
borohydride (NaBH.sub.4) to reduce the silver ions in the thin film
and thus manufacture a thin film material containing a metal
component.
[0154] FIG. 11 shows a transmission electron microscope photograph
of the thin film material containing a metal component manufactured
in Embodiment 4. Silver nanoparticles of about 5 to 20 nm in
diameter were formed as confirmed by electron beam diffraction.
[0155] (Embodiment 5)
[0156] A thin film material of composite metal oxides obtained by
the method of the present invention was reacted to manufacture a
thin film material containing a metal chalcogenite component as
Embodiment 5.
[0157] An 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).su- b.2) was dissolved in 10 mL of
2-ethoxyethanol, 0.353 mL of titanium butoxide
(Ti(O.sup.nBu).sub.4) was added and the mixture was stirred. A
quartz plate was immersed for 10 min at 25.degree. C. in this
solution, rinsed by immersion for 1 min in toluene at 25.degree.
C., dried by blowing with nitrogen gas, and then left standing in
air for about 20 min to hydrolyze the metal alkoxide compound that
had chemically adsorbed onto the solid surface. This thin film
forming step was repeated 8 times to form a composite metal oxide
thin film. Next, the quartz plate on the surface of which had been
formed the composite metal oxide thin film was immersed for 10 min
in pH 4 aqueous solution of hydrochloric acid, rinsed by immersion
for 2 min in ion-exchange water, and dried by blowing with
nitrogen. It was then immersed for 10 min in a pH 10 sodium
hydroxide aqueous solution and dried by blowing with nitrogen. The
quartz plate was immersed for 4 h in a 10 mM aqueous solution of
cadmium nitrate, rinsed by immersion for 1 min in ion-exchange
water, and dried by blowing with nitrogen. The quartz plate was
then immersed for 20 min in a 1 weight percent aqueous solution of
sodium sulfide (Na.sub.2S) to react the cadmium ions in the thin
film with S-ions and thereby manufacture a thin film material
containing cadmium sulfide.
[0158] FIG. 12 shows ultraviolet and visible light absorption
spectra of the thin film incorporating cadmium ions and the thin
film containing cadmium sulfide of Embodiment 5. Prior to the
formation of cadmium sulfide, the thin film had an absorption peak
characteristic of titania gel near 280 nm. In the thin film in
which cadmium sulfide was formed, absorbance from 200 to 300 nm
increased and the absorption edge red-shifted by about 20 nm. The
absorption edge of cadmium sulfide is known to correspond to the
size of the nanoparticles. In Embodiment 5, the formation of CdS
nanoparticles about 10 to 20 nm in diameter was confirmed.
[0159] (Embodiment 6)
[0160] A thin film material of composite metal oxides obtained by
the method of the present invention was heat treated to manufacture
a thin film material in which the ion-exchange capability of the
exchangeable metal ions was reduced as Embodiment 6.
[0161] A 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).sub- .2) was dissolved in 10 mL of
2-ethoxyethanol, 0.353 mL of titanium butoxide
(Ti(O.sup.nBu).sub.4) was added and the mixture was stirred. A
quartz plate was immersed for 10 min at 25.degree. C. in this
solution, rinsed by immersion for 1 min in toluene at 25.degree.
C., dried by blowing with nitrogen gas, and then left standing in
air for about 20 min to hydrolyze the metal alkoxide compound that
had chemically adsorbed onto the solid surface. This thin film
forming step was repeated 8 times to form a composite metal oxide
thin film. Next, the quartz plate on the surface of which had been
formed the composite metal oxide thin film was immersed for 10 min
in pH 4 aqueous solution of hydrochloric acid, rinsed by immersion
for 2 min in ion-exchange water, and dried by blowing with
nitrogen. It was then immersed for 10 min in a pH 10 sodium
hydroxide aqueous solution and dried by blowing with nitrogen.
[0162] Composite metal oxide thin films were manufactured on two
quartz plates by the above-described step and one plate alone was
heat treated for 30 min at 450.degree. C. in air. Both plates were
immersed for 4 h in a 10 mM aqueous solution of barium nitrate and
the quantity of barium ions introduced was evaluated by XPS
measurement.
[0163] XPS measurement of the sample that had not been exposed to
the heat treatment revealed a composition ratio of barium to
titanium of Ba/Ti=1.4. XPS measurement of the sample that had been
heat treated revealed a composition ratio of barium to titanium of
Ba/Ti=0.14. These results show that the heat treatment reduced the
ion-exchange capability of exchangeable metal ions (sodium ions in
this example) in the composite metal oxides.
[0164] (Embodiment 7)
[0165] The thin film material of composite metal oxides obtained by
the method of the present invention was reduced to manufacture a
thin film material containing a metal component as Embodiment 7.
Embodiment 4 has already shown that a thin film material containing
silver nanoparticles can be obtained by reducing a thin film
material containing monovalent silver ions. Embodiment 7 gives an
example of the manufacturing of a thin film material containing a
metal component by reducing metal ions other than monovalent metal
ions.
[0166] A 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).sub- .2) was added to 10 mL of
2-ethoxyethanol and dissolved by stirring for 5 days. A 0.353 mL
quantity of titanium butoxide (Ti(O.sup.nBu).sub.4) was added and
the mixture was stirred for 1 h. A quartz plate was immersed for 10
min at 25.degree. C. in this solution, rinsed by immersion for 1
min in toluene at 25.degree. C., dried by blowing with nitrogen
gas, and then left standing in air for about 20 min to hydrolyze
the metal alkoxide compound that had chemically adsorbed onto the
solid surface. This thin film forming step was repeated 8 times to
form a composite metal oxide thin film. Next, the quartz plate on
the surface of which had been formed the composite metal oxide thin
film was immersed for 10 min in pH 4 aqueous solution of
hydrochloric acid, rinsed by immersion for 2 min in ion-exchange
water, and dried by blowing with nitrogen. It was then immersed for
10 min in a pH 10 sodium hydroxide aqueous solution and dried by
blowing with nitrogen. The quartz plate was immersed for 4 h in a
10 mM aqueous solution of palladium nitrate, rinsed by immersion
for 1 min in ion-exchange water, and dried by blowing with
nitrogen. The quartz plate was then exposured for 5 sec with a 10 W
hydrogen plasma (170 mTorr) to reduce the palladium ions present in
the thin film, thereby manufacturing a thin film material
containing a metal component.
[0167] FIG. 13 shows a transmission electron microscope photograph
of the thin film material containing a metal component of
Embodiment 7. Nanoparticles of from 3 to 7 nm in diameter were
formed in the thin film. The fact that palladium particles had been
formed in the thin film was confirmed by changes in absorbance in
the UV spectrum.
[0168] (Embodiment 8)
[0169] Multiple metal ions were introduced into the thin film
material of composite metal oxides obtained by the method of the
present invention to manufacture a thin film material incorporating
two or more metal ion components as Embodiment 8.
[0170] A 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).sub- .2) was added to 10 mL of
2-ethoxyethanol and dissolved by stirring for 5 days. A 0.353 mL
quantity of titanium butoxide (Ti(O.sup.nBu).sub.4) was added and
the mixture was stirred for 1 h. A quartz plate was immersed for 10
min at 25.degree. C. in this solution, rinsed by immersion for 1
min in toluene at 25.degree. C., dried by blowing with nitrogen
gas, and then left standing in air for about 20 min to hydrolyze
the metal alkoxide compound that had chemically adsorbed onto the
solid surface. This thin film forming step was repeated 8 times to
form a composite metal oxide thin film. Next, the quartz plate on
the surface of which had been formed the composite metal oxide thin
film was immersed for 10 min in pH 4 aqueous solution of
hydrochloric acid, rinsed by immersion for 2 min in ion-exchange
water, and dried by blowing with nitrogen. It was then immersed for
10 min in a pH 10 sodium hydroxide aqueous solution and dried by
blowing with nitrogen. The quartz plate was immersed for 4 h in an
aqueous solution comprising 10 mM each of cobalt nitrate and silver
nitrate, rinsed by immersion for 1 min in ion-exchange water, and
dried by blowing with nitrogen.
[0171] FIG. 14 shows an XPS spectrum of the thin film material
manufactured by the method of Embodiment 8. These results indicate
that a titania ultra-thin film containing cobalt ions and silver
ions was obtained by the method of the present embodiment. The
compositional ratio of metal ions as calculated from the peak
intensities in the XPS spectrum was
titanium:silver:cobalt=1:0.52:0.88.
[0172] (Embodiment 9)
[0173] A nanomaterial of composite metal oxides having a granular
shape was manufactured by the method of the present invention as
Embodiment 9.
[0174] A 0.068 quantity of magnesium ethoxide (Mg(O--Et).sub.2) was
dissolved in 60 mL of 2-propanol and stirred for 5 days. To this
were added 2.042 mL of titanium butoxide (Ti(O.sup.nBu).sub.4) and
the mixture was stirred for several hours. The composition of this
mixed solution comprised a 100 mM concentration of titanium
butoxide and a 10 mM concentration of magnesium ethoxide. A 0.054
mL quantity of ion-exchange water was added to 30 mL of this
solution and the mixture was stirred for several hours. A 0.2 mL
quantity of hydrochloric acid (2 N) aqueous solution was added to
20 mL of this solution to remove the magnesium ions. A solution of
0.032 g of sodium hydroxide in 0.8 mL of methanol was added. When
the sodium hydroxide was added, the solution become a milk-white
suspension.
[0175] FIG. 15 shows the results of observation by transmission
electron microscopy of the structure of fine particles present in
the suspension. Nanoparticles with diameters of from 100 to 200 nm
were formed in the solution.
[0176] The suspension was stirred overnight, 10 mL thereof was
divided out and separated in a centrifuge (10,000 rpm, 20 min), and
the solid was collected. The elemental composition of the powder
obtained was confirmed with an EDX spectrum. The results were:
carbon: 8.3 weight percent; oxygen: 42.3 weight percent; sodium:
7.8 weight percent; magnesium: 0.3 weight percent; and titanium:
41.3 weight percent. These results indicate that the nanoparticles
of the composite metal oxides can be reliably formed by the step of
the present embodiment.
[0177] A 0.2598 g quantity of a solution of lanthanum nitrate
(La(NO.sub.3).sub.3.(6H.sub.2O) in 1 mL of ethanol was added to the
remainder of the 10 mL after the above division. The mixture was
left standing overnight, the solution was centrifugally separated,
and the solid was collected. The elemental composition of the
powder obtained was confirmed with an EDX spectrum. The results
were: carbon: 6.2 weight percent; oxygen: 34.3 weight percent;
sodium: 1.2 weight percent; magnesium: 0.1 weight percent;
lanthanum: 25.3 weight percent; and titanium: 32.9 weight percent.
These results indicate that the sodium ions that were present in
the nanoparticles of composite metal oxides were replaced with
lanthanum ions and a nanomaterial of composite metal oxides of new
composition was formed.
[0178] (Embodiment 10)
[0179] The thin film material of composite metal oxides obtained by
the method of the present invention was reduced to manufacture a
thin film material containing metal nanoparticles, which was then
reoxidized to manufacture a thin film material containing metal
oxide nanoparticles as Embodiment 10. The reduction and oxidation
steps were then repeated to alternately manufacture metal
nanoparticles and metal oxide nanoparticles.
[0180] A 11.4 mg quantity of magnesium ethoxide
(Mg(OCH.sub.2CH.sub.3).sub- .2) was added to 10 mL of
2-ethoxyethanol and dissolved by stirring for 5 days. A 0.353 mL
quantity of titanium butoxide (Ti(O.sup.nBu).sub.4) was added and
the mixture was stirred for 1 h. A quartz plate was immersed for 10
min at 25.degree. C. in this solution, rinsed by immersion for 1
min in toluene at 25.degree. C., dried by blowing with nitrogen
gas, and then left standing in air for about 20 min to hydrolyze
the metal alkoxide compound that had chemically adsorbed onto the
solid surface. This thin film forming step was repeated 8 times to
form a composite metal oxide thin film. Next, the quartz plate on
the surface of which had been formed the composite metal oxide thin
film was immersed for 10 min in pH 4 aqueous solution of
hydrochloric acid, rinsed by immersion for 2 min in ion-exchange
water, and dried by blowing with nitrogen. It was then immersed for
10 min in a pH 10 sodium hydroxide aqueous solution and dried by
blowing with nitrogen. The quartz plate was immersed for 4 h in a
10 mM aqueous solution of silver nitrate, rinsed by immersion for 1
min in ion-exchange water, and dried by blowing with nitrogen. The
quartz plate was then irradiated exposured for 150 sec with a 10 W
hydrogen plasma (180 mTorr) to reduce the silver ions present in
the thin film, thereby manufacturing a thin film material
containing silver nanoparticles. The quartz plate was then further
irradiated with a 10 W oxygen plasma (180 mTorr) to oxidize the
silver nanoparticles in the thin film, thereby manufacturing a thin
film material containing silver oxide nanoparticles. Six cycles of
the hydrogen plasma treatment and oxygen plasma treatment were
conducted.
[0181] FIG. 16 shows ultraviolet and visible light absorption
spectra of the thin film material manufactured in Embodiment 10. In
the samples subjected to reduction treatment (spectrum 1), an
absorption peak derived from plasmon absorption of silver
nanoparticles appears near 460 nm. In the oxidation treated thin
film material (spectrum 1'), plasmon absorption completely
disappears. When the hydrogen plasma treatment and oxygen plasma
treatment were repeated, plasmon absorption appeared following
hydrogen plasma treatment (spectra 2, 3, 4, 5, 6), and plasmon
absorption completely disappeared following oxygen plasma treatment
(spectra 2', 3', 4', 5', 6'). These results show that repeated
reduction and oxidation alternately formed silver nanoparticles and
silver oxide nanoparticles in the thin film material.
[0182] FIG. 17 shows a transmission electron microscope photograph
of thin film material containing the silver nanoparticles (left)
manufactured in Embodiment 10 and the thin film material containing
silver oxide nanoparticles (right). A thin film material that had
been through one cycle of hydrogen plasma treatment (corresponding
to spectrum 1) and a thin film material that had been through six
repeat cycles of hydrogen plasma treatment and oxygen plasma
treatment were employed as samples. These results show that silver
nanoparticles and silver oxide nanoparticles were reliably formed
by the step of Embodiment 10.
[0183] FIG. 18 presents histograms of the diameters of the
nanoparticles observed in transmission electron microscope images
(FIG. 17). The silver nanoparticles formed after the initial
reducing step had an average particle size of 8.6 nm and a diameter
standard deviation of 3.0 nm (left in FIG. 18). The silver oxide
nanoparticles formed after six cycles of repeat reduction and
oxidation treatments had an average particle size of 3.9 nm and a
diameter standard deviation of 0.7 nm (right in FIG. 18). These
results indicate that repeat reduction and oxidation treatments
permit good control of the size and standard deviation of
nanoparticles in thin film materials. The reduction/oxidation
process in the thin film is an important method of controlling the
microcomposition of the nanomaterial of metal oxides.
[0184] The present invention as described above permits the
reliable formation with good thickness precision of thin film
materials of composite metal oxides in the nanometer region over a
broad range of compositions. Thus, the present invention can be
employed over a wide range of technical areas.
* * * * *