U.S. patent application number 11/380242 was filed with the patent office on 2007-02-15 for method for attaching rod-shaped nano structure to probe holder.
Invention is credited to Chang Soo Han, Eung Sug Lee, Hyung-Woo Lee.
Application Number | 20070033992 11/380242 |
Document ID | / |
Family ID | 33302334 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070033992 |
Kind Code |
A1 |
Han; Chang Soo ; et
al. |
February 15, 2007 |
METHOD FOR ATTACHING ROD-SHAPED NANO STRUCTURE TO PROBE HOLDER
Abstract
The present invention relates to a method for manufacturing a
probe for detecting surface signals or chemical signals through a
long and slender rod-shaped nano structure such as tungsten
nanowire, carbon nanotube, boron nanotube, etc., being attached to
a tip end portion thereof. According to the method, a holder,
acting as the probe, including a first electrode to which the
rod-shaped nano structure is attached, and a second electrode at a
predetermined distance from the first electrode are partially or
fully immersed in a solution containing the rod-shaped structure.
When a voltage is applied between two electrodes, an electrical
field is generated, and the rod-shaped nano structure is attached
to the holder, acting as the probe.
Inventors: |
Han; Chang Soo; (Daejeon,
KR) ; Lee; Eung Sug; (Daejeon, KR) ; Lee;
Hyung-Woo; (Haeundae-gu, KR) |
Correspondence
Address: |
SHERIDAN ROSS PC
1560 BROADWAY
SUITE 1200
DENVER
CO
80202
US
|
Family ID: |
33302334 |
Appl. No.: |
11/380242 |
Filed: |
April 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10651612 |
Aug 28, 2003 |
7082683 |
|
|
11380242 |
Apr 26, 2006 |
|
|
|
Current U.S.
Class: |
73/105 ;
73/866.5 |
Current CPC
Class: |
Y10T 29/49117 20150115;
G01Q 70/12 20130101; B82Y 35/00 20130101; Y10T 29/49204 20150115;
Y10T 29/49002 20150115; B82Y 30/00 20130101; B82Y 15/00
20130101 |
Class at
Publication: |
073/105 ;
073/866.5 |
International
Class: |
G01B 5/28 20060101
G01B005/28; G01D 21/00 20060101 G01D021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2003 |
KR |
10-2003-0025948 |
Jun 2, 2003 |
KR |
10-2003-0035429 |
Claims
1. A method for attaching a rod-shaped nano structure to a tip end
portion of SPM (Scanning Probe Microscope) probe, the method
comprising the steps of: disposing a first electrode having a
designated shape; manufacturing a conductive tip end portion of the
SPM probe for a voltage to be applied thereto, and disposing the
tip end portion at a predetermined distance from the first
electrode; supplying a solution in which the rod-shaped nano
structure is dispersed between the tip end portion of the SPM probe
and the first electrode such that at least part of the tip end
portion of the SPM probe and the electrode is immersed in the
solution; and attaching the nano structure being dispersed in the
solution to the tip end portion of the SPM probe by applying a
voltage to the electrodes.
2. The method according to claim 1, further comprising the step of:
after the attaching step, fastening the nano structure to the
holder more firmly by means of a fastening means like as coating
film or fusion-welding or deposition of inorganic material
islands.
3. A probe for detecting mechanical, electrical and chemical
signals, comprising: a holder; a rod-shaped nano structure, wherein
one end portion of the nano structure is connected to the holder to
be supported and the other end portion is relatively more protruded
than the holder for detecting signals; and an adhesion layer,
wherein is placed between the holder and nano structure, giving a
role of chemical bonding so as to attach the nano structure on the
holder.
4. A probe for detecting mechanical, electrical and chemical
signals, comprising: a holder; a rod-shaped nano structure, wherein
one end portion of the nano structure is connected to the holder to
be supported and the other end portion is relatively more protruded
than the holder for detecting signals; and inorganic material
islands for fastening the rod-shaped nano structure to the holder
more firmly, the inorganic material islands being formed on a
connection portion of the rod-shaped nano structure and the holder.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/651,612, filed Aug. 28, 2003, which claimed priority
under 35 U.S.C. 119(a) to Korean Patent Application Number
10-2003-0025948, filed on Apr. 24, 2003, and which also claimed
priority under 35 U.S.C. 119(a) to Korean Patent Application Number
10-2003-0035429, filed on Jun. 2, 2003. Each of the
above-identified patent applications is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a probe for signal
detection having a rod-shaped nano structure attached thereto and a
method for manufacturing the same, and more particularly, to a
probe for detection of a surface signal or a chemical signal having
a rod-shaped nano structure, such as tungsten nanowire, carbon
nanotube, boron nanotube, etc., which is attached to an tip portion
thereof and a method for manufacturing the same.
[0004] 2. Description of the Related Art
[0005] Until recently, the nano world of atom or molecular unit was
an unknown field as being too minute to be observed even by a
microscope of a high resolution. With introduction of an SPM
(scanning probe microscope) in 1980s, however, the nano world
finally has become structurally identified. The first kind of
atomic microscope such as the SPM was an STM (scanning tunneling
microscope) while the most commonly used one is an AFM (atomic
force microscope).
[0006] FIG. 1 shows a construction of the AFM in general. As shown
in FIG. 1, the AFM has a tapered tip 10 of a pyramid shape formed
at one end of a cantilever 12, a tiny rod (100 .mu.m.times.10
.mu.m.times.1 .mu.m), which is produced by micromachining. When the
tip 10 is approached to a surface of a sample 14, interactions
(repulsion or attraction) occur between the tip 10 and atoms on the
surface of the sample 14. The interactions comprise mainly Van Der
Waals force and are of about a nano Newton level or less (10.sup.-9
N). Because of such interactions, the cantilever 12 is bent or
shows a change in resonance frequency when it moves over the
surface of the sample 14. Thus, it is possible to determine a
geometrical morphology of the sample by measuring the bend and the
change in resonance frequency. Meanwhile, the bend and the change
in resonance frequency of the cantilever 12 can be measured by
using a laser 16 and a photodiode 18. At this stage, a feedback
control is used to continuously keep the measurement on the
surface, whereby a stage 20 having the cantilever 12 attached at
its end can continuously measure the bend of the cantilever 12
while maintaining a uniform distance between the tip and the
sample. Thus obtained results are analyzed to acquire surface
information on the sample.
[0007] The AFM is used as a fundamental research equipment to
measure or observe the nano level. The AFM is also used in various
fields as process equipments for production at the nano level. The
processing technologies using the AFM such as soft probe
lithography or scanning probe lithography (SPL) are under intensive
research and study recent days.
[0008] The most fundamental core technology of the AFM resides in
the probe tip. The image resolution and reproducibility of the AFM
are determined according to the shape and size of the probe
tip.
[0009] In general, tip of the cantilever of the AFM is formed to
have a pyramidically tapered shape. However, carbon nanotube (CNT)
is recently attracting public attention because of its abundant
advantageous characteristics. The CNT is attached to a tip of a
pyramid to be used as a probe.
[0010] The tip of the AFM is advantageously made of a material
atomically having a high aspect ratio and a high resilience. Seen
from this perspective, the CNT tips are known to have ideal
characteristics to improve performance of the AFM in terms of
measurement, operation and production, e.g., excellent sharpness, a
high aspect ratio, mechanical stiffness and resilience as well as
readiness in adjustment of chemical components. In addition, the
CNT tips have advantages in that they have a long life span and are
preferably used to measure a deep and narrow-width structure. The
CNT tips have a resolution as high as 1 nm or less.
[0011] However, it is very difficult to individually form a high
quality carbon nanotube in a desired shape at a desired position.
The conventional methods such as laser ablation or arc discharge
serve to form a nanotube like an entangled skein of thread. It is
very difficult to purify, separate and manipulate such an entangled
nanotube so as to be attached to a single device.
[0012] For instance, Oshima et. al. disclosed in U.S. Pat. No.
5,482,601 a method of vapor depositing carbon nanotube by means of
arc discharge, while Mandeville et al. disclosed in U.S. Pat. No.
5,500,200 a method of massively producing MWNT by using
catalyst.
[0013] Even though such methods are effective for developing a new
complex material by massively producing the carbon nanotube or
carbon fibril, it is almost impossible to separate individual
nanotube and precisely attach each one to a desired position, as
stated above. Thus, it is inappropriate to mount a nanotube tip on
the probe of the AFM as a commercial method.
[0014] Recently, Cheung et. al. developed a method of directly
growing MWNT or SWNT by coating catalyst on a microgroove, which
was manufactured on a silicon substrate by means of chemical vapor
deposition (CVD) (Carbon Nanotube Tips Direct Growth by Chemical
Vapor Deposition, PNAS, Chin Li Cheung et. al., Vol. 97, No. 8).
According to this method, catalyst particles are coated on a
silicon substrate so as to individually grow a probe tip of the
AFM. Thereafter, a carbon nanotube is grown by using carbonic oxide
gas of high temperature.
[0015] However, it is very difficult to attach catalyst particles
to the tip of the silicon pyramid. The SWNT grown at the tip of the
pyramid is sized 1 .mu.m-20 .mu.m. In fact, however, its size
should approximately be 30 nm-100 nm to be attached to the AFM.
Although discharging methods are used to reduce the size, they
rarely succeed in precisely adjusting the size.
[0016] In particular, Dai disclosed in U.S. Pat. 6,401,526 a more
effective method of manufacturing an AFM tip, to which a nanotube
has been attached. According to this method, a liquid phase
precursor is coated on the tip of the AFM, and the coated AFM is
grown by the CVD method. Discharging process is performed to adjust
size of the manufactured nanotube. Here, the liquid phase precursor
comprises salts including metals, a long-chain molecular compound,
and a solvent. Dai also suggested a method of simultaneously
coating the precursor on the tips of a plurality of pyramids by
means of micro contacting printing.
[0017] Another recently reported method is to coat the precursor on
a wafer, onto which a massive amount of silicon pyramid for AFM is
mounted, by means of spin coating. The precursor is removed from
the wafer except on the pyramid by means of etching. A carbon
nanotube is grown in the gas including carbon by means of the CVD
method. (Wafer Scale Production of Carbon Nanotube Scanning Probe
Tips for Atomic Force Microscopy, Applied Physics Letter, Vol. 80,
No. 12, Erhan Yenilmez etc., 2002, March, 00.2225-2227).
[0018] However, all of these methods pose a problem in that coating
the precursor exactly to a desired amount is very difficult
primarily because of mechanical and chemical properties of the
precursor.
[0019] Meanwhile, Nakayama et. al. disclosed in U.S. Pat. 6,528,785
a method for manufacturing an electrode (i.e. nanotube) on a holder
by fusion welding. According to this method, a carbon nanotube is
first positioned between two electrodes. Then approaching the
holder close to the carbon nanotube until they are attached to each
other, and by means of electron beam or coating film, the carbon
nanotube (CNT) is firmly fastened to the holder.
[0020] Although there have been introduced a variety of methods for
manufacturing coating films, basically all of the methods are
directed to one technique that material for use in coating is not
the one being coated. Rather, the coating film is formed by a
chemical reaction between a gas-exposed nanotube and a holder.
[0021] Unfortunately however, the above coating method driven by a
chemical reaction is unrealistic and thus, cannot be succeeded in
reality. This is because a microscopically protruded nanotube can
also be influenced of the chemical reaction, and the nanotube
itself can be damaged during a work process.
[0022] Besides the above, the method by Nakayama et. al. has a very
low yield, and thus, is not appropriate for mass production. First
of all, it is almost impossible to visually confirm whether the
carbon nanotube is firmly adhered to the holder. Also, because the
manufacturing process is usually conducted on SEM (Scanning probe
microscope), it takes a great deal of time. Even then, it only
raises concerns about the possibility of nanotube getting damages
during the process. Moreover, when a carbon nanotube, one of the
nano structures like SWNT (Single Wall NanoTube), gets too small,
it is difficult to confirm the carbon nanotube as a SEM, so the
process also becomes out of control, making the assembly thereof
virtually impossible.
SUMMARY OF THE INVENTION
[0023] It is, therefore, an object of the present invention to
solve the foregoing problems by providing a probe, which is capable
of detecting a surface signal or a chemical signal through a
rod-shaped nano structure such as tungsten nanowire, carbon
nanotube, boron nanotube and the like attached to a tip end portion
of the probe, and can be easily manufactured by mass-production
methods, and a method for attaching a rod-shaped nano structure to
a probe holder. Compared to the related art, the method of the
present invention has a very high success rate and a substantially
reduced assembling time by reducing and simplifying a step for
manufacturing a probe tip.
[0024] According to one aspect of the present invention, the method
for manufacturing a probe for detecting mechanical, electrical and
chemical signals having a rod-shaped nano structure attached
thereto includes the steps of:
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above objects, features and advantages of the present
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying
drawings, in which:
[0026] FIG. 1 is a schematic view illustrating a construction of a
general AFM;
[0027] FIG. 2 is a view for explaining the method for producing a
probe with a rod-shaped nano structure attached according to a
first embodiment of the present invention;
[0028] FIG. 3a is a view illustrating a SWNT (Single Wall Nano
Tube) which can be used in the present invention;
[0029] FIG. 3b is a view illustrating a MWNT (Multi Wall Nano Tube)
which can be used in the present invention;
[0030] FIG. 4 is a view illustrating a holder to which a rod-shaped
nano structure is attached by a fastening means;
[0031] FIGS. 5a to 5c are views for explaining the method for
producing a probe with a rod-shaped nano structure attached
according to a second embodiment of the present invention;
[0032] FIGS. 6a to 6d are views for explaining the method for
producing a probe with a rod-shaped nano structure attached
according to a third embodiment of the present invention;
[0033] FIGS. 7a to 7c are views for explaining the step to cut a
nano structure connected between two electrodes by lithography in
the method for producing a probe with a rod-shaped nano structure
attached according to the present invention; and
[0034] FIG. 8 shows a tip end of a probe to which a multi wall
carbon nanotube is attached according to an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] A preferred embodiment of the present invention will now be
described with reference to the accompanying drawings. In the
following description, same drawing reference numerals are used for
the same elements even in different drawings. The matters defined
in the description such as a detailed construction and elements of
a circuit are nothing but the ones provided to assist in a
comprehensive understanding of the invention. Thus, it is apparent
that the present invention can be carried out without those defined
matters. Also, well-known functions or constructions are not
described in detail since they would obscure the invention in
unnecessary detail.
[0036] FIG. 2 is a view for explaining the method for producing a
probe with a rod-shaped nano structure attached according to a
first embodiment of the present invention.
[0037] Referring to FIG. 2, well-conductive electrodes 100 are
disposed. Preferably, material with a high conductivity, e.g. Au,
Ag, Al, Cu, Ti, and the like, is utilized for the electrodes. On
the top portion of the electrodes is a supporter 300, which is also
conductive and made of a conductor or coated with a conductor,
maintaining a predetermined distance from the electrodes in a
horizontal direction. The supporter is usually made of silicon, and
to apply the electrodes to this silicon supporter, the supporter
can be coated with the metals mentioned above. A holder 400,
operating as an electrode, is disposed at a lower portion of the
supporter 300, again maintaining a predetermined distance from the
electrodes 100. The holder and the supporter can be combined to
each other. In such case, silicon is often used to form the shape,
and similar to the supporter, the combined body can be coated with
a highly conductive metal. A power supply 500 for supplying a
voltage to the electrodes 100 and the supporter 300 is connected to
one side of the electrode 100 and the supporter 300. A solution 200
in which a rod-shaped nano structure 200-1 is dispersed is dropped
in a space between the holder 400 and the electrode 100. At this
time, part of or the entire holder 400 should be immersed in the
solution. Typically, water, ethanol or isopropanol, cyclohexane
where nano structures are well dispersed is preferred as the
solution 200.
[0038] Based on the above construction, a method for manufacturing
a probe having a rod-shaped nano structure attached thereto is now
discussed below.
[0039] When a voltage is applied to the electrodes 100 and the
supporter 300 from the power supply 500, an electric field is
generated inside the solution 200, in which the holder 400 on the
top surface of the electrodes 100 is immersed. Meanwhile, the
rod-shaped nano structure being dispersed in the solution transfers
by like as an electrophoretic force and/or a dielectrophoretic
force, and is attached to the holder 400. After a predetermined
time, or when the solution 200 is evaporated after undergoing a
certain process, the rod-shaped nano structure 200-1 is left out,
being adhered to the holder 400.
[0040] Here, if the distance between the electrodes 100 and the
holder 400 is less than the size of the rod-shaped nano structure
200-1, the rod-shaped nano structure 200-1 is more likely to be
connected in-between the electrodes 100 and the holder 400. On the
other hand, if distance between the electrodes 100 and the holder
400 is relatively greater than the size of the rod-shaped nano
structure 200-1, the rod-shaped nano structure is attached only to
the electrode 100 or to the supporter 300.
[0041] Therefore, the electrodes 100, the holder 400, and the
supporter 300 are shifted from one position to another, to adjust
the space between the electrode 100 and the holder 400.
[0042] Thusly attached nano structure has a strong adhesive force
according to kind of material used in a metallic plate. In general,
although the nano structure being pulled out to both electrodes by
the applied voltage is supported by Van Der Waals force, it has a
relatively weak adhesive force. On the contrary, in case of the
electrodes like silver, copper or aluminum, n-alkanoic acid
[CH.sub.3(CH.sub.2).sub.mCOOH] forms a SAM (Self-Assembly
Monolayer) on the surfaces of those metals, and when the nano
structure is attached to the electrodes, generates not only Van Der
Waals force but also a strong chemical bonding ["Structural
Comparison of Self-Assembled Monolayers of n-Alkanoic Acids on the
Surfaces of Silver, Copper, and Aluminum", J. Am. Chem. Soc. 115,
4350-4358, Yu-Tai Tao, 1993]. As a result, no extra work for
attaching the nano structure to the electrode is required.
Moreover, at the absence of the adhesion through such chemical
bonding, other by-products (or impurities) of the electrical field
and nano structures are still bonded together, more strongly than
the Van Der Waals force in general. In short, the probe having the
nano structure attached thereto by one of the above methods is
adhered to the nano structure in a much more strength than the Van
Der Waals force that returns from one point of a sample in most
cases. Hence, the probe is highly advantageous as a signal
detection device.
[0043] One of the most persuasive explanations for the attachment
of the nano structure to the holder comes from electrophoresis
and/or dielectrophoresis. Objects with dipoles have an attraction
force by the electric field being generated, and they are attracted
to each other, and more particularly, they are attracted to a side
with a stronger electric field. According to well-known researches
about the electric field generated between an AFM tip and an
electrode, intensity of the electric field gets greater as the
distance between the AFM tip and the electrode is reduced. It is
also known that the sharper the tip is, the stronger the electric
field is. Although many believe an ideal tip has a zero radius on
its end portion, in reality it has a radius ranging from 10 to
100nm. Despite the above boundary condition on the tip of the AFM,
the electric field is usually strongest on the tip. This explains
why the nano structure in the solution is intensively attached to
the tip end portion where the electric field is stronger.
[0044] Therefore, electric field density is naturally highest at
the sharp tip end portion of the AFM. The reason for applying an AC
field can be found in the fact that long, slender rod-shaped carbon
nanotubes (CNT) are the ones being picked up first, compared to
other impurities, primarily because the carbon nanotubes have a
large dipole moment. Hence, manufacturing a sharp holder in a
protruding fashion, the electric field becomes strongest at the tip
end portion and more nano structures are gathered around the tip.
This method can be very advantageously used for attaching the
carbon nanotube to the sharp tip end like the AFM tip. Normally,
when a pure DC is applied, the nano structures as well as
impurities are drawn to electrodes, without much difference from
each other. This is because the charge being applied to the nano
structure has opposite poles, attracting to each other. A study
says that if a pure AC is applied, long, slender rod-shaped
nanotubes are more attracted to electrodes, compared to the DC
[Kunitoshi Yamamoto etc, Orientation and purification of carbon
nanotubes using ac electrophoresis, J. Phys. D: Appl. Phys. 31,
1998, L34-L36]. The same phenomenon occurs when a DC biased AC is
applied. However, this does not fully explain why the rod-shaped
nano structure like CNT approaches between two electrodes in the
solution or both sides, so its physical verification and the
associated phenomenon need to be researched continuously.
[0045] On a different subject, there are many kinds of rod-shaped
nano structures. Since the nano structure being discussed in the
present invention is not heavily dependent on its structural
physical properties but can be implemented easily. Thus nanotubes
(e.g. Carbon nanotube, Boron nanotube, BCN type nanotube and the
like) as well as nanowires or nano needles having different
configurations can also be used since they move in the solution
when a voltage is applied thereto [Peter A. Smith etc., electric
field assisted assembly and alignment of metallic nanowire, Applied
Physics letters, Vol.77, No.9, 2000]. This is actually a very
significant fact in that those nano structures being attached to
the tip of the probe (holder) can be used as sensors or measurement
devices.
[0046] FIG. 3 diagrammatically illustrates a carbon nanotube, the
typical example of rod-shaped nano structures. Carbon nanotubes
(CNT) is first discovered in a cathodic deposit generated by
Arc-discharge back in 1991. As the name implies, carbon atoms are
bonded together in a tube shape. FIG. 3a depicts a SWNT (Single
Wall Nano Tube), wherein carbon atoms are entangled with each other
in a single-sheet tube. FIG. 3b, on the other hand, depicts a MWNT
(Multi Wall Nano Tube) in a tubular structure with multi-layered
sheets. The MWNT has a radius that approximately ranges from
several nm to hundreds of nm. On the contrary, the SWNT can be as
small as possible such that its radius is less than 1 nm or
hundreds of um.
[0047] FIG. 4 shows that a fastening means can be sometimes used
for more firmly attaching the rod-shaped nano structure to the
holder. Mainly the fastening means is useful for reinforcing the
attachment of the nanotube to the holder by a chemical bonding or
for supporting the attachment of the nanotube to the holder by the
Van Der Waals force according to an assembly environment as
discussed before. For instance, the fastening means can be utilized
in case ware environment is easily exposed as in for nano
indentation or AFM Lithography. Now referring to FIG. 4, the
rod-shaped nano structure 200-1 is attached to the tip of the
holder 400, using a similar method with the one described in FIG.
2, and the fastening means causes the already-attached rod-shaped
nano structure 200-1 to be more firmly fastened to the holder 400.
The inventors prefer using inorganic islands 200-3 as the fastening
means, mainly because metals like chrome, aluminum or copper and
insulating materials like silicon dioxide are more easily deposited
on the holder and the connecting portion of the rod in form of
islands, simply with the help of a device like E-beam evaporator,
and no separate carbon gas is required in this case.
[0048] Meanwhile, in case of using the carbon nanotube as the
rod-shaped nano structure and using silicon for the holder and the
supporter, as in the present invention, metallic islands on which a
metal is deposited are attached to the silicon holder or supporter,
not to the carbon nanotube. Taking advantage of this property, it
is possible to attach the nanotube to the holder more strongly by
forming inorganic islands with a cluster form on the contact
portion of the silicon and the carbon nanotube, not on the
protruded carbon nanotube.
[0049] Besides the above method, general wafer processes, e.g.
fusion-welding using electron beams, a CVD (Chemical Vapor
Deposition) process or PVD (Physical Vapor Deposition) process,
wherein a coating film is attached to the connection portion of the
rod-shaped nano structure and the holder, can also be employed, to
fasten the rod-shaped nano structure to the holder more firmly.
[0050] FIGS. 5a to 5c are views for explaining the method for
producing a probe with the rod-shaped nano structure attached
according to a second embodiment of the present invention.
[0051] With reference to the drawings, a substrate 600 having a
groove 600-1 is disposed on a central part of a probe, and
electrodes 100 are placed on a top surface of the trench 600-1. The
electrodes 100 are formed by coating with layers according to a
deposition process, and the substrate 600 for forming the trench
600-1 is layered thereon. Here, the trench can be formed using a
general etching process. Since the electrodes and the substrate are
made of different materials, the electrodes are etched until they
are exposed. On the top portion of the electrodes 100 is a
supporter 300, which is conductive and made of conductive materials
or coated with a conductor, maintaining a predetermined distance
from the electrodes in a horizontal direction. A holder 400, acting
as an electrode, is disposed at the lower surface of the supporter
300, again maintaining a predetermined distance from the electrodes
100. A power supply 500 for supplying a voltage to the electrodes
100 and the supporter 300 is connected to one side of the electrode
100 and the supporter 300. A solution 200 in which a rod-shaped
nano structure 200-1 is dispersed is dropped into a space between
the holder 400 and the electrode 100. At this time, part of or the
entire holder 400 should be immersed in the solution (see FIG.
5b).
[0052] Based on the above construction, a method for manufacturing
a probe having a rod-shaped nano structure attached thereto is now
discussed below.
[0053] When a voltage is applied to the electrodes 100 and the
supporter 300 from the power supply 500, an electric field is
formed inside the solution 200, in which the holder 400 on the top
surface of the electrodes 100 is immersed. Meanwhile, the
rod-shaped nano structure being dispersed in the solution transfers
in an electrophoretic force or a dielectrophoretic force, and is
attached to the holder 400. After a predetermined time, or when the
solution 200 is evaporated after undergoing a certain process, the
rod-shaped nano structure 200-1 is left out, being adhered to the
holder 400.
[0054] During the process of FIG. 5b, if the distance between two
electrodes 100 is less than the size of the rod-shaped nano
structure 200-1, the rod-shaped nano structure 200-1 is more likely
to be connected in-between the two electrodes 100. Applying a
current and taking advantage of a discharge effect thereof, it is
possible to adjust the length of the nano structure being attached
to the holder.
[0055] As shown in FIG. 5c, in order to fasten the rod-shaped nano
structure 200-1 to the holder 400 more strongly, a coating process
that involves depositing inorganic material 700, the adhesive
medium, on the holder 400, can be additionally performed.
[0056] Particularly in the embodiments illustrated in FIGS. 2 and
5, the rod-shaped nano structure attached to the holder is in
proportion to the size of the nano structure being dispersed in the
solution. When the nano structure being dispersed in the solution
goes through a chemical process, the size of the nano structure
becomes uniform. Then, the nano structure gets attached to the
holder, substantially in a uniform size. Nevertheless, there can be
a portion that is more protruded than the tip end portion of the
holder, depending on fastening positions. If this happens, the
protruded portion of the nano structure can be properly adjusted
through a discharge process after all of the process is complete.
According to physical properties of nano structures, the amount of
voltage to be discharged and the intensity of current are properly
adjusted.
[0057] FIGS. 6a to 6d are views for explaining the method for
producing a probe with a rod-shaped nano structure attached
according to a third embodiment of the present invention.
[0058] As depicted in FIG. 6a, a substrate 600 is installed, and a
holder 800 composed of two metal electrodes coated with metals are
disposed on both sides of a top surface of the substrate, keeping a
predetermined distance from the center. As shown in FIG. 6d, a
lower end portion (or base end portion) of the holder 800 to be
etched is coated with a sacrificial layer in advance, to etch and
lift the holder 800 through a Lift-off process.
[0059] Now turning to FIG. 6b, the solution in which the rod-shaped
nano structure 200-1 is dispersed is dropped into between the two
electrodes on the substrate 600. At this time, the solution 200 is
dropped until adjacent end portions of those two electrodes are
immersed into the solution. Then applying a voltage to those two
metal electrodes, an electric field is generated between the two
electrodes in the solution 200.
[0060] When the solution 200 is evaporated after a certain amount
of time, the rod-shaped nano structure 200-1, influenced of a
charge effect, gets attached to the end portions of the two
electrodes, and the two metal electrodes being connected to each
other forms the holder 800. Here, if the nano structure is greater
than the distance between those two electrodes, those two metal
electrodes can be connected to each other. On the other hand, if
the nano structure is less than the distance between those two
electrodes, the nano structure is connected to only one side of
each of the electrodes As discussed before, however, the above
process is sufficient to yield an adhesive force that causes a
chemical bonding, and a fastening means 700 can be used for
obtaining an additional adhesive force, thereby fastening the
rod-shaped nano structure 200-1 to the holder 800 more
strongly.
[0061] On a different subject, to manufacture a probe having a
cantilever like SPM (Scanning Probe Microscope) and the holder in
addition to the above construction, as depicted in FIG. 6c, the
Lift-off process is applied to part of the two metal electrodes
having the rod-shaped nano structure attached thereto, and the
holder 800 is lifted off, until the holder has a "H" shape.
[0062] FIGS. 7a to 7c are views for explaining the step to cut a
rod-shaped nano structure connected between two metal electrodes
being connected to each other by the rod-shaped nano structure
obtained from the process shown in FIG. 6c.
[0063] The holder 800 in FIG. 7a, namely the two metal electrodes,
obtained from the process of FIG. 6c is connected by the rod-shaped
nano structure. To cut the rod-shaped nano structure attached to
those two metal electrodes, a gap 900 should be made first between
the two electrodes, using a lithography process as depicted in FIG.
7c. In this manner, it is possible to adjust a cutting site of the
rod-shaped nano structure 200-1, and cut the nano structure as much
as needed.
[0064] The gap is formed by coating the electrodes with a
photoresist, and then etching the photoresist as large as a
designated gap.
[0065] Afterwards, using the gap 900, the rod-shaped nano structure
200-1 is cut to constant length (see FIG. 7c).
[0066] FIG. 8, similar to the embodiment suggested in FIG. 3, one
electrode plate is placed at the base portion, and using an AFM tip
coated with metal to cause a current to be applied thereto, the two
electrodes are arranged in such a manner that the distance between
them is under 10 micrometers. After this, a solution containing
MultiWall Nanotube (40% purified sample produced by ILJINnanotech
Co.) is dropped into the gap, and a 7-volt, 5 MHz AC is applied
thereto. The pyramidically tapered protruded portion in the circle
is a Multi wal CNT. The CNT together with other impurities are
drawn to the AFM tip end portion, and eventually attached thereto.
At this time, a metal coating (film) can be attached to the AFM tip
end by applying one of AC, DC or biased AC.
[0067] As described in detail above, the present invention relates
to a method for attaching a rod-shaped nano structure to a
pyramidically tapered holder by applying an electric field, and
introduces a new structure of a probe for detecting electrical/
mechanical signals. According to the present invention, without
using a separate device, the rod-shaped nano structure can be
directly attached to an electrode with a high possibility. In
addition, the method of the present invention, compared to other
related art methods, is very simple and appropriate for mass
productions. Further, since the present invention can be
implemented using a wafer process, expense of manufacture of
sensors or detection devices to be manufactured by a batch process
can be substantially reduced.
[0068] In conclusion, the present invention is related to a method
for attaching a rod-shaped nano structure to a holder and a probe
using the same, to attach the nano structure to a protruded portion
of the holder in a protruding fashion. Attaching the nano structure
to a SPM probe holder in this manner, high-resolution images can be
obtained since the nano structure has a high aspect ratio and the
tip end has an extremely small radius. When this probe needle is
used for data storage, even more microscope signals can be
detected. Millepde of IBM, i.e. an AFM tip having carbon nanotube
attached thereto, for example, demonstrates relatively superior
read/write performances to those of general Si tips (Bernd Gotsmann
etc., "nano-indentation with heated tips: playing with temperature,
time, load, tip shape, and polymer material", Oxford 2003 SPM
conference). In case of applying a nano structure with an excellent
ware property, say, carbon nanotubes, to a lithography process
using SPM, failure rate is pretty low, meaning that manufacturing
work can be done for a long time without an interruption. Moreover,
a probe having this nano structure attached thereto is regarded as
an ideal device for detecting DNA or protein signals or an ideal
sensor for interacting with samples, specific DNAs or proteins,
taking advantage of specific physical properties of the nano
structure (e.g. carbon nanotubes). The probe can also be employed
as a sensor for measuring diverse chemical environments or chemical
element including air, vacuum, NH.sub.3 and the like. In recent
years, as many mass production methods of nanotubes, nano needles,
or nano wires at a low expense of manufacture appeared, it became
possible to purchase raw material as a low price. In other words,
applying the method of the present invention to the manufacture of
a probe tip, a probe being attached with a low-price nano structure
can be manufactured. Especially, the present invention can be
advantageously used for a probe tip in devices like STM, AFM, and
SNOM with a long lifespan and a high resolution.
[0069] While the invention has been shown and described with
reference to certain preferred embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
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