WO2005069337A1

WO2005069337A1 - Method for massive assembling of carbon nanotubes

Info

Publication number: WO2005069337A1
Application number: PCT/KR2004/000089
Authority: WO
Inventors: Kyu-Ho Hwang
Original assignee: M2N Inc.
Priority date: 2004-01-19
Filing date: 2004-01-19
Publication date: 2005-07-28

Abstract

In a method for depositing carbon nanotubes on metal electrodes of a substrate on a large scale, an upper substrate having a tip is coated with metal and a lower substrate having thereon corresponding connecting portion and an electrode are independently fabricated and lined up with respect to each other. Thereafter, a surface of the upper substrate is attached to the connecting portion of the lower substrate so that they are fixed while maintaining a predetermined gap between the tip and the electrode. Power is then applied to the tip and the electrode to thereby deposit carbon nanotubes on an end of the tip. Thereafter, each upper substrate is separated from the lower substrate. As a result, the carbon nanotubes can be deposited on a substrate on a large scale.

Description

METHOD FOR MASSIVE ASSEMBLING OF CARBON NANOTUBES

Technical Field The present invention relates to carbon nanotubes; more particularly, to a method of assembling carbon nanotubes on a tip provided on a substrate on a large scale.

Background Art

Carbon nanotubes have a strong" anisotropic property, have a diameter ranging from tens to hundreds of nanometers and a length of tens or hundreds of micrometers and has various structures, e.g., single walled, multi walled, roped and the like. Further, depending on their wound-up shape, carbon nanotubes may have the properties of a conductor or a semiconductor, and depending on their diameter, carbon nanotubes' energy gap is varied and they would have a semi one-dimensional structure so that a unique quantum effect would result. Additionally, carbon nanotubes have an appearance such that one layer of graphite is rolled up and have sp2 bonding same as graphite, thereby having a strong bond strength. Due to the aforementioned structure and physical properties of carbon nanotubes, there is a strong likelihood that they would be applied to a planar display component, a highly integrated memory component, a secondary battery and the like, all of which are essential to the information and communication industry while they are expected as the material with a great potential to overcome the limitations of conventional components. In order for carbon nanotubes to be applied to an electrical component, an input/output functionality should be implemented thereto. In most of the cases, for this kind of purpose, carbon nanotubes are made to have their size in micrometer unit and it is crucial to fuse carbon nanotubes precisely. In order to fuse carbon nanotubes with a fixed gap, there is proposed a method of growing carbon nanotubes from one end of the gap and a method of depositing carbon nanotubes in-between the gap. Specifically, by using a chemical gas phase deposition method, a single wall carbon nanotube (SWCNT) can be grown among the columns in the method of growing a tube. In this method, while growing a tube, an electrical field is applied thereto to align the carbon nanotubes in order to maintain their uniform direction. However, this method is limited such that a catalyst has to be used precisely, and a metal with a high melting point should be used as an electrode. Further, the method should be carried out in an extremely clean environment to prevent the formation of monolithic hydrocarbons . In addition, to selectively deposit carbon nanotubes, a method of chemical patterning has been used. In this method, carbon nanotubes are assembled or aligned due to interactive reactions of charges between patterned electric charge layers. However, since the interactive reactions of charges are very sensitive to a processing environment, a problem exists such that different results may be obtained depending on the kinds of carbon nanotubes or solvents used. As for the method of using an electric field, carbon nanotubes are deposited by means of applying DC or AC electric fields to the carbon nanotubes dispersed in a solvent. A dielectrophoretic force is used for filtering undesirable particles in this method. Each particle having a different size and component has its own unique characteristic frequency to an applied electric field. In a non-uniform electric field, since each particle has adifferent dielectrophoretic force which is induced based on the size and component of the particle, carbon nanotubes also have different dielectrophoretic force different from other particles. Therefore, in a case where an electric field having a characteristic frequency and magnitude is applied to in-between a gap, a repulsive force is acted upon other materials while an attractive force is acted only upon a specific carbon nanotube. Further, since carbon nanotubes are longer than a catalyst or monolithic carbon residue, they can be easily aligned in an electric field. With respect to this method, it is disclosed in "INTEGRATION OF SINGLE MULTI-WALLED CARBON NANOTUBE ON MICRO SYSTEMS", Proceedings of 2002 ASME International Mechanical Engineering Congress & Exposition, November 17-22, 2002 authored by Jaehyun Chung, Junghoon Lee, Rodney S. Ruoff and Wing Kam Liu. However, in the method of depositing carbon nanotubes by using the dielectrophoretic force, only one carbon nanotube can be deposited on one tip. Accordingly, the method for depositing carbon nanotubes on a large scale is required to achieve a high-speed operation and device integration along with a technological development. It is, therefore, an object of the present invention to provide a method for depositing carbon nanotubes on a large scale, which are formed with a predetermined size and shape at a predetermined location.

Disclosure of Invention It is, therefore, an object of the present invention to provide a method for depositing carbon nanotubes on a large scale on multiple tips provided on a substrate. In accordance with a preferred embodiment of the present invention, there is provided a method for depositing carbon nanotubes on the surface of a substrate, including the steps of: providing an upper substrate having a plurality of protruded tips and having a metal coated surface on which the plurality of protruded tips are formed, and a lower substrate having thereon a plurality of connecting portions and a plurality of electrodes; aligning the upper substrate and the lower substrate so that each of the tips of the upper substrate lines up with each of the corresponding electrodes of the lower substrate; fixing the upper substrate to the lower substrate so that a uniform gap is maintained between each of tips of the upper substrate and each of the corresponding electrodes of the lower substrate; providing a solvent, having carbon nanotubes dispersed therein, between the upper substrate and the lower substrate; depositing the carbon nanotubes on the plurality of tips by applying a voltage between the metal coating layer of the upper substrate and the plurality of electrodes of the lower substrate; separating the upper substrate from the lower substrate; and removing impurities remaining on the upper substrate. In accordance with another preferred embodiment of the present invention, there is provided a method for depositing carbon nanotubes on the surface of a substrate, including the steps of: providing an upper substrate having a plurality of probes, each of which having a downwardly protruded tip on one side thereof and having a metal coated surface on which the plurality of protruded probes are formed, and a lower substrate having thereon a plurality of connecting portions and a plurality of electrodes; aligning the upper substrate and the lower substrate so that each of the probes of the upper substrate lines up with each of the corresponding electrodes of the lower substrate; fixing the upper substrate to the lower substrate so that a uniform gap is maintained between each of tips of the upper substrate and each of the corresponding electrodes of the lower substrate; providing a solvent, having carbon nanotubes dispersed therein, between the upper substrate and the lower substrate; depositing the carbon nanotubes on the tips of the probes of the upper substrate by applying a voltage between the metal coating layer of the upper substrate and the plurality of electrodes of the lower substrate; separating the upper substrate from the lower substrate; and removing impurities remaining on the upper substrate.

Brief Description of Drawings

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments, given in conjunction with the accompanying drawings, in which: Fig. 1 shows schematic views of an upper substrate and a lower substrate manufactured in accordance with the present invention; Fig. 2 is a schematic view illustrating a state where an upper substrate and a lower substrate are attached to each other with adhesive in accordance with the present invention; and Fig. 3 shows a schematic view of an upper substrate to which carbon nanotubes are deposited in accordance with the present invention.

Best Mode for Carrying Out the Invention Hereinafter, the preferred embodiments of the present invention will now be described with reference to the drawings attached. As shown in Fig. 1, the upper substrate 1 and the lower substrate 2 are manufactured separately and lined up with respect to each other. The upper substrate where the carbon nanotubes are to be deposited is provided in the form of an array to be appropriate for arrangement processing. The upper substrate is attached to the table (not shown) and movable in all four directions, namely, up, down, left, and right. The upper substrate 1 has an elastic probe 3 protruded to the side, and a tip 10 where carbon nanotubes are to be deposited is provided on one end of the probe 3. One surface of the probe 3 where carbon nanotubes are deposited is coated with a metal layer 4. Through the metal layer 4, a voltage is applied to form an electric field required when depositing carbon nanotubes. As for the length of tip 10 protruded downward is preferably about 3 to 5 mm. As a metal used to coat one surface of the upper substrate, it is preferable to use gold or chrome. A semiconductor wafer or a glass substrate, and so forth are used as the upper substrate. The lower substrate 2 is formed as an array corresponding to the upper substrate 1 to be appropriate for arrangement processing. Further, the lower substrate 2 is provided with a connecting portion 6 fixed by having contact with the upper substrate 1 and also provided with an electrode 5 maintaining a uniform distance to the tip 10 of the probe 3. Between the electrode 5 and the lower substrate 2, an insulating body 6 is formed so that the electrode 5 is insulated from the lower substrate 2. The connecting portion 7 provided on the lower substrate 2 is a part that is fixed by having contact with the upper substrate 1 and the distance between the tip 10 of the probe 3 and the electrode 5 of the lower substrate 2 is controlled by adjusting the height of the connecting portion 7. An insulating layer 8 is provided on the upper surface of the connecting portion 7 such that a circuit is not become shorted when power is supplied during the deposition of carbon nanotubes. The available methods of fixing the upper substrate 1 and the lower substrate 2 are as follows: using an adhesive 9 between the upper substrate 1 and the connecting portion 7 of the lower substrate 2; applying heat between the upper substrate 1 and the lower substrate 2; using an anodic adhesion method, and so forth. In case the adhesive 9 is used as the method to fix the upper substrate 1 and the lower substrate 2, the adhesive 9 is sprayed on the insulating body 8 formed on the connecting portion 7. In this case, the thickness of the adhesive 9 can be used to adjust the distance between the tip 10 of the probe 3 and the electrode 5 of the lower substrate 2. As the adhesive 9, the following materials can be used: a wax, a dried thin film, a photoresist, a silicon oxide film and a silicon photoresist. However, the adhesive should allow a convenient separation of the upper substrate 1 and the lower substrate 2, and afterward, should not have an effect on the deposition of carbon nanotubes attached to the end of the tip 10 during the cleaning process wherein the residual impurities are removed from the upper substrate 1. Further, in case the attaching methods by heat application or by the anodic adhesion is used, the gap between the tip and the electrode can be adjusted by controlling the thickness of bonding area. Afterward, as shown in Fig. 2, the upper substrate 1 and the lower substrate 2 are fixed by gluing the upper substrate 1 and the connecting portion 7 of the lower substrate 2. Accordingly, once the gap between the tip 10 end of the probe 3 and the electrode 5 of the lower substrate 2 is adjusted to be constant, i.e., the gap of about 2 to 5 mm is preferably maintained, a solvent having carbon nanotubes dispersed therein, is supplied between the upper substrate 1 and the lower substrate 2. There is a higher possibility for the carbon nanotubes dispersed in the solvent to be deposited on the metal layer 4 covering the thin and sharp tip 10 end of the probe 3 than on the wide and flat electrode 5 of the lower substrate 2, because both ends of the carbon nanotubes are coated with metal . After supplying a solvent, a DC or AC voltage is applied to the electrode 5 of the lower substrate 2 and the metal 4, which is coated on one surface of the probe 3 of the upper substrate 1 from which the tip 10 is protruded. Due to the voltage applied, an electric field is formed between the tip 10 of the probe 3 and the electrode 5 of the lower substrate 2. By the formed electric field, an attractive force is acted upon between tip 10 and carbon nanotubes dispersed in the solvent so that the carbon nanotubes are mainly deposited on the end of the tip 10. More than one carbon nanotubes can be deposited on the end of the tip 10 and the deposited carbon nanotubes mainly have a shorter length than the gap between the tip 10 of the probe 3 and the electrode 5 of the lower substrate 2. Once one or more carbon nanotubes are attached on the end of the tip, the upper substrate 1 and the lower substrate 2 are separated and the cleaning process is performed to remove impurities such as residual adhesive remaining on the upper substrate 1. The cleaning process should not affect the carbon nanotubes deposited on the tip 10 of the probe 3. Fig. 3 shows the upper substrate 1 with carbon nanotubes deposited thereon, after the cleaning process is performed. The process described above in accordance with the present invention can be used to manufacture a parallel probe carbon nanotube tip and can be applied to semiconductors, and various types of sensors and motors. Fig. 4 shows the upper substrate and the lower substrate in accordance with another preferred embodiment of the present invention. In accordance with the present embodiment, rather than forming the tip at one end of the probe, there is provided a method for depositing carbon nanotubes at the ends of a plurality of tips protruding downward and disposed directly on the upper substrate. One surface of the upper substrate where the tip is provided is coated with metal. The upper substrate and the lower substrate are fixed to each other, while maintaining a constant gap between the tip and the electrode. Next, a solvent having carbon nanotubes dispersed therein is supplied between the upper substrate and the lower substrate and an electric field is formed between the metal and the electrode by applying electric power therebetween. Accordingly, the carbon nanotubes

Claims

dispersed in the solvent become attracted to the space between the tip and the electrode, and deposited mainly on the tip. After the carbon nanotubes are deposited, the upper substrate and the lower substrate are separated and the cleaning process is performed to remove impurities remaining on the upper substrate. Consequently, carbon nanotubes are deposited on a large scale on the tip of the upper substrate. Further, a desired amount of carbon nanotubes can be deposited on a desired location of the upper substrate. While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims . CLAIMS

1. A method of depositing carbon nanotubes on a substrate, comprising the steps of: providing an upper substrate having a plurality of protruded tips and having a metal coated surface on which the plurality of protruded tips are formed, and a lower substrate having thereon a plurality of connecting portions and a plurality of electrodes; aligning the upper substrate and the lower substrate so that each of the tips of the upper substrate lines up with each of the corresponding electrodes of the lower substrate; fixing the upper substrate to the lower substrate so that a uniform gap is maintained between each of tips of the upper substrate and each of the corresponding electrodes of the lower substrate; providing a solvent, having carbon nanotubes dispersed therein, between the upper substrate and the lower substrate; depositing the carbon nanotubes on the plurality of tips by applying a voltage between the metal coating layer of the upper substrate and the plurality of electrodes of the lower substrate; separating the upper substrate from the lower substrate; and removing impurities remaining on the upper substrate.

2. The method of claim 1, wherein the step of fixing the upper substrate to the lower substrate includes using an adhesive, a heat applying adhesion method or an anodic adhesion method to fix the upper substrate to the lower substrate .

3. The method of claim 2, wherein the adhesive is a wax, a dried thin film, a silicon oxide film or silicon.

4. The method of claim 1, wherein the gap between the tips of the upper substrate and the electrodes of the lower substrate is adjusted by the connecting portions' thickness.

5. A method for depositing carbon nanotubes on a substrate, comprising the steps of: providing an upper substrate having a plurality of probes, each of which having a downwardly protruded tip on one side thereof and having a metal coated surface on which the plurality of protruded probes are formed, and a lower substrate having thereon a plurality of connecting portions and a plurality of electrodes; aligning the upper substrate and the lower substrate so that each of the probes of the upper substrate lines up with each of the corresponding electrodes of the lower substrate; fixing the upper substrate to the lower substrate so that a uniform gap is maintained between each of tips of the upper substrate and each of the corresponding electrodes of the lower substrate; providing a solvent, having carbon nanotubes dispersed therein, between the upper substrate and the lower substrate; depositing the carbon nanotubes on the tips of the probes of the upper substrate by applying a voltage between the metal coating layer of the upper substrate and the plurality of electrodes of the lower substrate; separating the upper substrate from the lower substrate; and removing impurities remaining on the upper substrate.

6. The method of claim 5, wherein the step of fixing the upper substrate to the lower substrate includes using an adhesive, a heat applying adhesion method or an anodic adhesion method to fix the upper substrate to the lower substrate .

7. The method of claim 6, wherein the adhesive is a wax, a dried thin film, a silicon oxide film or silicon.

The method of claim 5, wherein the gap between the tips of the upper substrate and the electrodes of the lower substrate is adjusted by the connecting portions' thickness.