# Patent

## Title
Method for manufacturing a one-dimensional nano-structure-based device

## Abstract

A method for manufacturing a one-dimensional nano-structure-based device comprises the steps of: preparing a solution (14) containing one-dimensional nano-structures (18); providing a pair of electrical conductors (10, 12) each having a tip (101, 121), the tips thereof being spaced apart from and opposite to each other; applying the solution to the tips of the electrical conductors thereby the tips being interconnected by the solution; applying a voltage (16) between the two conductors thereby at least one one-dimensional nano-structure being interconnected between the tips of the electrical conductors; and applying an external energy to at least one of the conductors and the one-dimensional nano-structure so as to disconnect the conductors from each other thereby obtaining at least one conductor having the tip with the one-dimensional nano-structure connected therewith.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to a copending U.S. patent application Ser. No. 11/371,991 filed on Mar. 8, 2006 entitled “Method For Manufacturing A One-dimensional Nano-Structure-based Device” with the same assignee, and a copending U.S. patent application Ser. No. 11/371,877 filed on Mar. 8, 2006 entitled “Method For Manufacturing A One-dimensional Nano-structure-based Device” with the same assignee. The disclosures of the above-identified applications are incorporated herein by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to nano-structure-based devices, and particularly to a method for manufacturing a one-dimensional nano-structure-based device.
2. Discussion of the Related Art
In nano technology field, a variety of nano-scale structures (hereinafter called nano-structures), such as carbon nanotubes, silicon nano-threads, and zinc oxide nano-threads, can be artificially synthesized. Nano-structures have been implemented into numerous fields, such as, field effect transistors, sensors, and atomic force microscopes (AFMs).
For example, as regards the AFM, the probe tip of the AFM generally comprises a nano-structure, such as a bundle of carbon nanotubes or a single carbon nanotube. The carbon nanotube/tubes are generally attached to the probe tip by the following methods: (1) drawing a bundle of carbon nanotubes or a single carbon nanotube out from bundles of carbon nanotubes using the probe tip under an optical microscope; (2) disposing the carbon nanotube/tubes onto the probe tip using another AFM; (3) forming the carbon nanotube/tubes as extensions of the probe tip.
However, the above-mentioned methods have common shortcomings, in that they are complicated processes, require a lot of time, and have low production efficiency.
What is needed, therefore is to provide a method for manufacturing a nano-structure-based device that is easy to control, and which is also less time consuming.
SUMMARY
A method for manufacturing an apparatus having one dimensional nano-material provided herein generally includes the steps of preparing a solution containing one-dimensional nano-structures; providing a pair of electrical conductors each having a tip, the tips thereof being spaced apart from and opposite to each other; applying the solution to the tips of the electrical conductors, the tips thereby being interconnected by the solution; applying a voltage between the two conductors, at least one one-dimensional nano-structure thereby being interconnected between the tips of the electrical conductors; and separating the tips of the electrical conductors to form at least one of tip having the one-dimensional nano-structure connecting therewith.
These and other features, aspects, and advantages of the present one-dimensional nano-structure-based device will become more apparent from the following detailed description and claims, and the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the present method for making the one-dimensional nano-structure-based device can be better understood with reference to the following drawings. The components in the drawings are not necessary to scale, the emphasis instead being placed upon clearly illustrating the principles of the present method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a schematic view showing a stage of a method for manufacturing a one-dimensional nano-structure-based device in accordance with one embodiment;
FIG. 2 is an image showing a carbon nanotube interconnected between tips of two electrical conductors, the image being taken using an optical microscopy; and
FIG. 3 is an image showing a single carbon nanotube connected with a tip of an electrical conductor, the image being taken using a scanning electron microscopy (SEM).



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a method for manufacturing a one-dimensional nano-structure-based device in accordance with an exemplary embodiment. It is to be noted that, the method may be employed to assemble almost all kinds of one-dimensional nano-structures such for example as, nanotubes, nano-rods, or nano-threads, to a semi-finished device. The one-dimensional nano-structures are advantageously electrical conductive material. In order to simplify the description of the present embodiment, the steps of the method will be described below in detail, using carbon nanotube as an example of the those kinds of the one-dimensional nano-structures. In the illustrated embodiment, the method comprises the steps of:
Step (1), preparing a solution 14 containing carbon nanotubes 18 and a liquid solvent;
Step (2), providing a pair of electrical conductors 10, 12, the electrical conductors 10, 12 having respective tips 101, 121; the tips 101, 121 being arranged to be spaced apart from and opposite to each other;
Step (3), applying at least a drop of the solution 14 to the tips 101, 121 of the electrical conductors 10, 12, the tips 101, 121 thereby being interconnected by the solution 14;
Step (4), applying a voltage 16 between the tips 101, 121, at least one carbon nanotube 18 thereby being connected with the tips 101, 121 of the electrical conductors 10, 12, and removing the liquid solvent of the solution 14; and
Step (5), applying an external energy to at least one of the conductors 10, 12 and the carbon nanotube 18 so as to disconnect the conductors 10, 12 from each other thereby obtaining at least one conductor 10, 12 having the tip with the carbon nanotube 18 connected therewith.
In the illustrated embodiment, the solution 14 contains isopropyl alcohol, and ethyl cellulose. The isopropyl alcohol is used as a main solvent. The ethyl cellulose is used as a stabilizer. The solution 14 is advantageously, but optionally, pretreated using an ultrasonic generator to distribute the carbon nanotubes evenly and uniformly therein before the solution 14 is applied to the tips 101, 121. However, it is to be understood that the solution 14 could be prepared by utilizing other similar suitable solvent and/or stabilizer. Furthermore, other treating steps such as filtrating could be used to obtain the stable uniform solution 14.
It is recognized that the higher the concentration of the carbon nanotubes in the solution 14, the greater the numbers of the carbon nanotubes that may be connected with the tips 101, 121. Thus, the numbers of the carbon nanotubes that is to be subsequently connected between the tips 101, 121 can be controlled by adjusting the concentration of the carbon nanotubes in the solution. If, for example, only one carbon nanotube is desired to connect with the tips 101, 121, the concentration of the carbon nanotubes in the solution should be as low as possible.
In step (2), the electrical conductors 10, 12 is made of a material comprised of tungsten or its alloy. Alternatively, other metals such as gold, molybdenum, platinum, or an alloy thereof could be also utilized instead. The electrical conductors 10, 12 are generally configured to be cylindrical or frustoconical in shape.
The tips 101, 121 are configured to be conical in shape. The tips 101, 121 preferably have a width/diameter in the range from about 10 microns to about 1000 microns. Alternatively, the micro tips 101, 121 could be configured to be frustoconical in shape. If the tips 101, 121 each have flat top surfaces, the micro tips 101, 121 should be arranged with parts of the top surfaces facing each other, for example, edges of the top surfaces facing each other. A distance between the micro tips 101, 121 is generally slightly less than the length of the carbon nanotube 18, the distance is generally below 100 microns. A preferable distance is below 10 microns.
In step (3), at least a drop of the solution 14 is applied between the tips 101, 121 by a syringe 17. The volume of the drop of the solution that is applied to the tips is in the range from about 0.01 to about 0.2 ml. Other suitable apparatus, such as a straw, or a pipet, can also be used instead. It should be noted that the volume of the solution 14 applied to the tips 101, 121 should be sufficient to interconnect the tips 101, 121. Alternatively, the tips 101, 121 could be directly dipped into a container (such as a beaker) having a tiny amount of the solution 14 therein.
In step (4), the voltage 16 is preferably an A.C. (alternating current) voltage 16. The A.C. voltage 16 has a peak value of about 10 volts or less, and has a frequency in the range from about 1000 Hz to about 10 M/z. Generally, the A.C. voltage 16 could be applied for a time period in the range from about several seconds to several tens of seconds, until at least one of the carbon nanotubes 18 is connected with at least one of the tips 101, 121. That is, the method takes relatively little time, and enables a high manufacturing efficiency to be attained.
The present method essentially operates based on the principle of double-directional electrophoresis. Once the A.C. voltage 16 is applied between the electrical conductors. An electrical field is correspondingly established between the tips of the electrical conductors 10, 12. The carbon nanotubes 18 in the solution 14 are then forced to move toward a direction in which electrical field intensity increases. Accordingly, the carbon nanotubes 18 are stretched and extend toward the tips 101, 121, at which the electrical field intensity is the highest. Eventually, at least one carbon nanotube may be connected with at least one of the tips 101, 121. By the present method, the carbon nanotube 18 can be firmly secured to the tips 101, 121 via Van der Waals attractions therebetween.
FIG. 2 is an image showing a carbon nanotube 18 interconnected between the tips 101, 121, the image being taken using optical microscopy. Furthermore, the carbon nanotube 18 is stretched to be substantially straight along a longitudinal direction thereof. This is because that the carbon nanotube 18 is polarized by the electrical field, thereby having electrical charges at two ends thereof. During the movement of the carbon nanotube 18 toward the tips 101, 102, the electrical field exerts a force to opposite ends of the carbon nanotube 18. The force stretches the carbon nanotube 18 to be substantially straight.
In step (4), when at least one of the carbon nanotube 18 is connected with the tips 101, 121, the A.C. voltage 16 is switched off, and the liquid solvent of the solution 14 is removed from the tips 101, 121.
In step (5), an exterior energy is applied to the tips 101, 121 of the electrical conductors connected by the carbon nanotube 18 in order to disconnect the electrical conductors from each other. Thereby, the tip of at least one of the electrical conductors with the carbon nanotube 18 connected thereto is obtained. The exterior energy may be a laser, an electric current, a force or other suitable energy. For instance, a probe having a high temperature could be utilized to burn out and then disconnect the carbon nanotube 18. The high temperature is generally higher than a fire point of the carbon nanotube 18. If the carbon nanotube 18 is cut out from its middle part, the tips 101, 121 may each have a part of the carbon nanotube 18 connected thereto. If the carbon nanotube 18 is cut out from its end near one of the tips 101, 121, only the other of the tips 101, 121 has the carbon nanotube 18 connected thereto. Otherwise, when a plurality of the carbon nanotubes 18 interconnect with the tips 101, 121, it is possible that each of the tips 101, 121 has a plurality of the carbon nanotubes 18 connected thereto.
FIG. 3 is an image showing a single carbon nanotube 18 connected with the tip 101 of the electrical conductor, the image being taken using scanning electron microscopy (SEM). Thereby, the apparatus having the one dimensional nano-material is obtained, and could be utilized in numerous electrical devices, for example, probes of atomic force microscopy (AFM).
Furthermore, if the one-dimensional nano-structure is to be interconnected between the tips of the electrical conductors, the method could further include a step of inspecting whether the one-dimensional nano-material is connected therebetween. For instance, in the illustrated embodiment, a resistor could be connected in series with the electrical conductors 10, 12. An oscillograph is connected in parallel with the resistor for showing an electrical current flowing through the resistor. If the carbon nanotube is interconnected between the tips of the electrical conductors, an electrical current will flow through the carbon nanotube. Therefore, the oscillograph will display a change in the electrical current. At this time, the alternating current voltage 16 is switched off. The liquid solvent of the solution 14 is then removed from the tips 101, 121. It should be understood that otherwise inspecting means could be utilized for the inspecting step, and it is not limited to the illustrated embodiment.
Therefore, the whole process of the method for manufacturing an apparatus having one-dimensional nano-structure could realize automatic operation and inspection. The producing efficiency associated therewith is manifestly improved. Furthermore, since the relative manufacturing machine is simple, the cost of the production is low. It is suitable for mass production of one-dimensional nano-structure-based device.
Finally, while the present invention has been described with reference to particular embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

## Claims

1. A method for manufacturing a one-dimensional nano-structure-based device, the method comprising the steps of:
preparing a solution containing one-dimensional nano-structures and a liquid solvent;
providing a pair of electrical conductors each having a tip, the tips thereof being spaced apart from each other;
placing the solution between the tips of the electrical conductors so that the tips are interconnected by the solution;
supplying a voltage between the pair of electrical conductors so that an electrical field is correspondingly established between the tips of the electrical conductors, and the one-dimensional nano-structures in the solution are stretched by the electrical field and extend toward the tips of the electrical conductors thereby at least one one-dimensional nano-structure is in contact with and located between the tips of the electrical conductors;
determining whether the one-dimensional nano-structure in the liquid solvent is interconnected between the tips of the electrical conductorsl, wherein the determining step comprises connecting a resistor in series with the electrical conductors, and connecting an oscillograph in parallel with the resistance for displaying an electric current flowing through the resistor so as to indicate whether the one-dimensional nano-structure is interconnected between the tips; and
applying an external energy to at least one of the electrical conductors and the at least one one-dimensional nano-structure so as to disconnect the electrical conductors from each other thereby obtaining at least one electrical conductor having the tip with one-dimensional nano-structure connected therewith, wherein the external energy is a laser, an electric current, or a high temperature.

2. The method according to claim 1, wherein the applying the external energy to at least one of the electrical conductors and the at least one one-dimensional nano-structure so as to disconnect the electrical conductors from each other comprises cutting the at least one one-dimensional nano-structure near the tip of one of the electrical conductors, so that only one tip of the electrical conductors has the at least one one-dimensional nano-structure connected thereto.

3. The method according to claim 1, wherein the applying the external energy to at least one of the electrical conductors and the at least one one-dimensional nano-structure so as to disconnect the electrical conductors from each other comprises cutting the at least one one-dimensional nano-structure such that each of the electrical conductors has a portion of the one-dimensional nano-structure connected to their tip.

4. The method according to claim 1, wherein the tips are spaced apart a distance which is slightly less than a length of the one-dimensional nano-structure.

5. The method according to claim 4, wherein a single one-dimensional nano-structure is interconnected between the tips of the electrical conductors.

6. The method according to claim 5, wherein the applying the external energy to at least one of the electrical conductors and the at least one one-dimensional nano-structure so as to disconnect the electrical conductors from each other comprises burning the single one-dimensional nano-structure by a probe having a high temperature.

7. The method according to claim 6, wherein the high temperature is higher than a melting point of the one-dimensional nano-structure.