Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
1999-11-09
2001-08-07
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S004000, C117S008000, C117S009000, C117S921000, C117S944000, C423S598000, C205S123000, C148S240000, C148S277000, C148S281000
Reexamination Certificate
active
06270571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing narrow wires comprising titanium oxide, and narrow wires and structures produced by the same method, in particular a method for producing titanium oxide whiskers. More particularly, the titanium oxide whisker is useful for a variety of areas as a functional material for electronic devices and microdevices, or as a structural material. More concretely, the whisker as a functional material is useful for, e.g., photoelectric transducers, photocatalytic devices and electron-emitting materials.
2. Related Background Art
Titanium oxide-based materials have been extensively studied to apply their photosemiconducting characteristics and photocatalytic functions to photovoltaic cells, decomposition of toxic materials and antimicrobial purposes.
For example, Japanese Patent Application Laid-Open No. 8-302498 discloses examples in which finely powdered titanium oxide is used as a construction material for its antimicrobial function.
M. Gratzel et al. made, on a trial basis, a wet type photovoltaic cell using microparticles of TiO
2
, several nm in size, prepared by spreading colloidal solution and heating (baking), which shows an energy conversion efficiency of 7.1 to 7.9% (B. O'Regan et al., “NATURE,” 353 (1991) 737). This relatively high conversion efficiency is realized by decreasing size of titanium oxide particles to the order of nanometer to increase their surface area.
More recently, it is reported that titanium oxide comes to show a unique surface characteristics of being macroscopically hydrophilic and oleophilic when irradiated with ultraviolet ray, because of formation of hydrophilic and oleophilic regions, 30 to 80 nm in size, on the surface (“NATURE,” 388 (1997) 431).
These phenomena suggest that titanium oxide potentially exhibits new functions, when its size is decreased to the order of nanometer. It is discussed that titanium oxide as an n-type semiconductor exhibits characteristic electrical, optical and chemical properties in containment of electrons and surface functions, when its size is decreased to a certain characteristic level. However, the mechanisms involved are largely left unknown.
Therefore, titanium oxide material is expected to have wide applications as a new functional material for, e.g., electronic devices and microdevices, and also as a structural material.
SUMMARY OF THE INVENTION
It is expected that titanium oxide material shows further improved electrical, optical and chemical properties, e.g., photoelectric conversion function, if it can be reduced in size to the order of nanometer and have high crystallinity. However, it was difficult to produce titanium oxide material having a nanometer-order size and high crystallinity by a simple procedure.
The methods to produce materials of the order of nanometer in size include photolithography, and other semiconductor processing techniques for fine pattern drawing, e.g., exposure to electron beams or X-ray. However, these methods involve disadvantages, such as insufficient product yield and high apparatus cost. Therefore, a method producing materials of desired properties at high repeatability by a simple procedure has been increasingly in demand.
The above-mentioned fine particle production method, proposed by above mentioned M. Gratzel et al., is a relatively simple one involving colloidal solution spreading and heating (baking). However, this method can stand further improvement in controllability and repeatability of crystallinity and fine particle shape of titanium oxide prepared.
One of the other methods proposed so far is the one by Masuda et al., in which a replica of alumina produced by anodic oxidation is made by titanium oxide, to form porous TiO
2
(“Jpn. J. Appl. Phys.,”, 31 (1992), L.1775 to L.1777, and “J. of Materials Sci. Lett.,” 15 (1996) 1228 to 1230). The disadvantages involved in this method are a number of time-consuming steps for production of the replica, and insufficient crystallinity of TiO
2
prepared by electrodeposition.
The whisker crystal is known as one of the materials of high crystallinity. It is produced by reduction or vapor-phase deposition of a halide as the starting material, and these methods are already applied to synthesis of titanium compounds, e.g., TiC and TiN.
One of the examples of the titanium oxide whisker is potassium titanate in size in submicron unit, which is being applied to fiber-reinforced plastics, metals and ceramics (“Magazine of Japan Metallurgical Society,” 58 (1994), 69 to 77). However, these are powdery, and have not been spread over a substrate. These whiskers have dimensions of 0.2 to 1.0 &mgr;m in diameter and 5 to 60 &mgr;m in length, and must be finer to bring about the effects which would be exhibited by those of the order of nanometer in size.
Another method is proposed by C. Coddet et al., heat treatment of a Ti plate in a H
2
O-containing atmosphere, to grow the titanium oxide whisker (“C. R. Acad. Sc. Paris,” t.281 (1975) 507 to 510). The whisker produced by this method, however, is relatively thick at around 10 &mgr;m in diameter.
The present invention provides titanium oxide materials of high crystallinity and free of the above problems, in particular narrow wires and whiskers of titanium oxide having a size of the order of nanometer, and a method for producing the same. The present invention also provides a nano-structure with the above narrow wires or whiskers of titanium oxide deposited on a base.
The present invention is developed to solve the above problems. A first preferred aspect of the present invention is a method for producing narrow wires comprising titanium oxide, wherein said method comprises:
(A) a first step of preparing a base having a titanium-comprising surface,
(B) a second step of discretely depositing a material other than titanium on the surface, and
(C) a third step of thermally treating the said titanium-comprising surface, obtained by the second step, in a titanium-oxidizing atmosphere.
A second preferred aspect of the present invention is a method for producing narrow wires comprising titanium oxide, wherein said method comprises:
(A) a first step of preparing a base having a titanium-comprising surface,
(B) a second step of depositing a material other than titanium on the surface in a island structure, and
(C) a third step of thermally treating said titanium-comprising surface, obtained by the second step, in a titanium-oxidizing atmosphere.
A third preferred aspect of the present invention is a method for producing narrow wires comprising titanium oxide, wherein said method comprises:
(A) a first step of preparing a base having a titanium-comprising surface,
(B) a second step of roughening the surface, and
(C) a third step of thermally treating the surface in a titanium-oxidizing atmosphere.
A fourth preferred aspect of the present invention is a method for producing narrow wires comprising titanium oxide, wherein said method comprises:
(A) a first step of preparing a base having a titanium-comprising surface,
(B) a second step of depositing a metallic element other than titanium over the surface, by bringing a liquid containing the metallic element in contact with the above surface, and
(C) a third step of thermally treating the surface in a titanium-oxidizing atmosphere.
A fifth preferred aspect of the present invention is a method for producing narrow wires comprising titanium oxide, wherein said method comprises:
(A) a first step of preparing a base having a titanium-comprising surface,
(B) a second step of irradiating the surface with ultraviolet ray, and
(C) a third step of thermally treating the above surface in a titanium-oxidizing atmosphere, to form narrow wires comprising titanium oxide on the surface.
The method of the present invention can produce, on a large scale, narrow wires comprising titanium oxide of high crystallinity and size of the order of nanometer, in particular titanium oxide whiskers, in a highly controllable manner.
REFERENCES:
patent: 8-302498 (1996-11-01), None
Den Tohru
Iwasaki Tatsuya
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kunemund Robert
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