Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2003-03-18
2004-08-17
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06777637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nanotube product such as a nanotube probe needle for AFM, a light emissive and absorptive nanotube probe, a nanotube heat generation probe, etc., in which a nanotube is protruded from a holder thereof, and more particularly to a sharpening method of nanotubes in nanotube products that produces nanotubes having sharpened tip ends which are used for operating a sample surface, thus improving the operation precision of a nanotube.
2. Prior Art
Recently in order to observe the surface structure of a material, an atomic force microscope (abbreviated as AFM) has been used. AFM has a semiconductor cantilever which is constructed by forming a protruding portion at the cantilever portion, so that unevenness (projections and indentations) on the surface of the material can be imaged by means of scanning the surface of the material, using the tip end of the protruding portion as a probe needle.
In order to make the semiconductor cantilever higher efficient, the inventors of the present application have invented a nanotube cantilever wherein a nanotube such as a carbon nanotube, etc. is fastened at the protruding portion of the semiconductor cantilever with a coating film or by means of an electric current fusion welding. The high quality AFM which can image the surface of the material in the precision same as the section diameter of the nanotube is realized, owing to use the tip end of the nanotube protruded downward as a probe needle point. This has been published in Japanese Patent Application Laid-Open (Kokai) No. 2000-227435 and No. 2000-249712.
Moreover, the inventors accomplished a heat generation probe that records information by means of an on-off mode which is formed with fusion welded holes. In this heat generation probe, a nanotube is fastened at the protruding portion of a semiconductor cantilever with a coating film or by an electric current fusion welding, a heat generation material is held at the tip end portion of the nanotube, and the on-off mode is formed with the fusion welded holes by means of heating the surface of an organic material in a pin-point fashion. This has been published in Japanese Patent Application Laid-Open (Kokai) No. 2002-243880.
The inventors further invented a light receiving and emitting probe that irradiates light on a sample surface in a pin-point fashion and receives light emitted from a sample in a pin-point fashion. In this light receiving and emitting probe, a nanotube is fastened by a similar means as described above at a protruding portion of a semiconductor cantilever, and a light receiving and emitting material is held at the tip end portion of the nanotube. This has been proposed in Japanese Patent Application No. 2001-81672.
In this way, various nanotube products have been developed such as a nanotube cantilever, a nanotube heat generation probe, a light receiving and emitting nanotube probe, etc.; and it is expected that various nanotube products that use such nanotubes will increase from now on.
These nanotube products are to positively utilize the characteristics that the section diameter of the nanotube is extremely fine. The section diameter of the nanotube is distributed in from several nm to several tens nm, and the extreme fineness of the nanotube diameter can be understood from the fact that theoretical minimum diameter of the nanotube is inferred to be about 1 nm. It is understood that the tip end of the nanotube product is excellent in the degree of fineness (sharpness), by comparing with the protruding tip end portion of the usual semiconductor cantilever, of which diameter is from several 10 nm to about 100 nm.
However, an arc discharge method or a chemical vapor deposition method (CVD method) produces a large quantity of carbon fine powder, and the carbon fine powder contains a large quantity of carbon materials other than carbon nanotubes. Therefore, the operation to pick out selectively nanotubes from this carbon fine powder is necessary, when a nanotube product is manufactured. More specifically, the additional operation which picks out an extremely fine nanotube from the nanotubes is necessary, when an extremely fine nanotube is requested in order to improve the degree of sharpness of a tip end.
It is difficult to see an extremely fine nanotube by an electron microscope, and even if the nanotube can been seen, it is difficult to take out one nanotube from a lump of nanotubes, as many extremely fine nanotubes often form a bundle. Furthermore, in practice an extremely fine nanotube cannot be used as a nanotube probe in many cases, since an extremely fine nanotube is too highly flexible, so that the nanotube is like thread trash.
For such a reason, a nanotube product usually uses a comparatively thick nanotube, which has a section diameter of ten and several nm or more so that the nanotube has somewhat rigidity. However, when the nanotube of such a large diameter is used, there is a limit in precision of size in the operation of the nanotube product.
FIG. 8
is an AFM measurement diagram imaging the surface of a sample by the nanotube cantilever which uses a usual large diameter nanotube. A nanotube cantilever
6
comprises a protruding portion
10
which is formed at a cantilever
8
made of semiconductor and a nanotube
12
which is fastened with a coating film
14
at the protruding portion
10
.
The nanotube
12
is a large diameter nanotube that the section diameter is supposed to exceed 10 and several nm. In order to image the sample surface
22
of a sample
20
, the tip end portion
12
g
of the nanotube is caused to approach to or contact with the sample surface
22
so as to detect the force acting on the nanotube
12
from projections and indentations on the sample surface
22
by a laser beam so on, and the information is imaged in a display.
In the sample surface
22
, there exist many projections and indentations which contain widely from indentations with gentle inclination to indentations with steep inclination. On the other hand, the image of the indentation portion becomes unclear, when the diameter of the indentation portion is 10 and several nm or less, since the section diameter of the nanotube
12
exceeds 10 and several nm. In other words, when the section diameter of the nanotube
12
is large, as shown in the Figure, the tip end portion
12
g
cannot follow the inside of the indentation
22
a
, so that there exists a limit in the image precision of the sample surface. Namely, there exists the limit in precision as for the usual nanotube cantilever, according to a nanotube diameter. Such a fault exists in common in other nanotube products as well.
Next, the cause that the diameter of a nanotube becomes large is explained. There are a single layer nanotube (SWNT) and a multiple layer nanotube (MWNT). The single layer nanotube is such that a graphite layer surrounds a hollow portion in a cylinder shape and the multiple layer nanotube is such that multiple graphite layers surround a hollow portion in a concentric cylinder shape.
The above-described nanotube that theoretically minimum diameter is 1 nm is the single layer nanotube, and a graphite sheet (graphite net) is rolled strongly in a cylinder form with a minimum diameter. But, in practice, nanotubes manufactured by means of an arc discharge method or a chemical vapor deposition are almost multiple layer nanotubes, so that a procedure is necessary to find out extremely fine nanotubes from a large quantity of carbon fine powder. Besides, an extremely fine nanotube such as a single layer nanotube is like thread trash and is hardly useful.
As a result, a multiple layer nanotube with somewhat rigidity is used. Among the multiple layer nanotubes, if a tip end portion is closed in an acute angle fashion, the degree of sharpness of the tip end may be improved due to the acute angle shape of the tip end. However, the procedure to find out the nanotube which has the acute angle tip end is necessary, and even if obtaining acute angle nanotubes, the nanotube product of
Akita Seiji
Harada Akio
Nakayama Yoshikazu
Daiken Chemical Co., Ltd.
Evans Geoffrey S.
Koda & Androlia
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