Patent Application
20130203314
1. Technical Field
The present disclosure relates to an emitter and, in particularly, to an emitter employed with the carbon nanotubes and a method for manufacturing the same.
2. Description of the Related Art
Carbon nanotubes (CNTs) are widely used as field emitters for field emission displays (FEDs) and liquid crystal displays (LCDs). Such CNTs have good electron emission characteristics, and chemical and mechanical durability.
Conventional field emitters are typically micro tips made of a metal such as molybdenum (Mo). However, the life span of such a micro tip is shortened due to effects of atmospheric environment, such as non-uniform electric field, and the like. A somewhat viable alternative has been carbon nanotubes having a high aspect ratio, high durability, and high conductivity preferably adopted as field emitters.
In order to obtain a high current density from carbon nanotube emitters, carbon nanotubes must be uniformly distributed and arranged perpendicular to a substrate. The carbon nanotube emitters are generally grown from a substrate using a chemical vapor deposition (CVD). However, the carbon nanotubes formed by this process may be entangled with each other on the top thereof, which result in a poor morphology of CNTs and poor performance on emitting. Alternatively, the carbon nanotube emitters may also be manufactured by printing a paste obtained by combining carbon nanotubes with a resin to a substrate. This method is easier and less costly than CVD and thus preferred to CVD. However, the carbon nanotubes formed by this process are too dense to emit electrons effectively because of the strong screening effect generated between adjacent carbon nanotubes.
What is needed, therefore, is a carbon nanotube emitter and a method for manufacturing the same that can overcome the above-described shortcomings.
The present emitter and method for manufacturing the same are described in detail hereinafter, by way of example and description of an exemplary embodiment and with references to the accompanying drawings, in which:
A detailed explanation of an emitter and method for manufacturing the same according to an exemplary embodiment will now be made with references to the drawings attached hereto.
Referring to
The substrate 10 may be an electrode made of copper, tungsten, aurum, gold, molybdenum, platinum, ITO glass, and combinations thereof. Alternatively, the substrate 10 may be an insulating substrate, such as a silicon sheet, coated with a metal film with a predetermined thickness. The metal film maybe one of an aluminum (Al) film, silver (Ag) film or the like. In the present embodiment, the substrate 10 is a silicon sheet coated with an Al film and configured for supporting and electrically connecting to the carbon nanotubes 11 and may function as a cathode of a field emission display (FED) (not shown). If necessary, a gate insulating layer and a gate electrode may be optionally formed on the conductive substrate 10.
The carbon nanotubes 11 may be conductive single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), or multi-walled carbon nanotubes (MWCNT), or their mixture. The carbon nanotubes 11 are parallel to each other. Each of the carbon nanotubes 11 has the approximately same length and includes a first end 111 and a second end 112 opposite to the first end 111. The first end 111 is electrically connected to the conductive substrate 10 by Van der Waals Force. For enhancing a fastening force between the first end 111 and the conductive substrate 10, the first end 111 can be connected to the conductive substrate 10 via a conductive adhesive or by metal-bonding. The second end 112 extends away from the conductive substrate 10 and has a needle-shaped tip (not labeled). The needle-shaped tip is employed as an electron emitting source of the carbon nanotube emitter 100 for emitting electrons. The carbon nanotubes 11 each may have a diameter in a range from about 0.5 nm to about 50 nm and a length in a range about 100 μm to about 1 mm. The distance between the second ends 112 of the two adjacent carbon nanotubes 11 ranges from about 50 nm to about 500 nm. In the present embodiment, the carbon nanotubes 11 are SWCNTs having a diameter of about 1 nm and a length of about 150 mm. As shown in
Referring to
Referring to
In step S101, the carbon nanotube array may be acquired by the following method. The method may employ CVD, Arc-Evaporation Method, or Laser Ablation, but not limited to those methods. In the present embodiment, the method employs high temperature CVD. Referring also to
In step S201, the substrate maybe a silicon wafer or a silicon wafer coated with a silicon oxide film on the surface thereof. In one embodiment, the silicon wafer has flatness less than 1 μm, for providing flat for the formed carbon nanotube array.
In step S203, the catalyst film may have a thickness in a range from about 1 nm to about 900 nm and the catalyst material may be Fe, Co, Ni, or the like.
In step S203, the treatment is carried out at temperatures ranging form about 500° C. to about 700° C. for anywhere from about 5 hours to about 15 hours.
In step S204, the reaction chamber is heated up to about 500° C. to about 700° C. and filled with protective gas, such as inert gas or nitrogen for maintaining purity of the carbon nanotube array.
In step S205, the carbon source may be acetylene, ethylene or the like, and have a velocity of about 20 sccm (Standard Cubic Centimeter per Minute) to about 50 sccm. The carrier gas may be insert gas or nitrogen, and have a velocity of about 200 sccm to about 500 sccm.
In step S102, the two conductive substrates 20 are spaced apart from each other to apply tension to the carbon nanotubes 21 selected from the carbon nanotube array. The distance between the two conductive substrates 20 is limited by the length of the carbon nanotubes.
In step S103, the number of carbon nanotubes 21 are selected and drawn out from the carbon nanotube array provided in step S101 and opposite ends of the carbon nanotubes 21 are fixed onto the two conductive substrates 20, respectively. Referring to
In described method above, the metal may be copper, silver, and gold, or an alloy thereof. In the step S302, because of the strong molecular force between the carbon nanotube and the metal thread, some carbon nanotubes 21 can be adsorbed onto the metal thread. In step S303, a single segment of carbon nanotubes 21 is acquired. In the present embodiment, the acquired carbon nanotubes 21 have a length of about 2 μm to about 200 μm.
In step S104, the two conductive substrates 20 and the carbon nanotubes 21 are placed into a reaction chamber (not shown) for ensuring purity of the obtained carbon nanotubes 21 before supplying the voltage on the carbon nanotubes. The reaction chamber may be a vacuum chamber having pressure intensity less than 1×10-1 Pa or is filled with inert gas or nitrogen to prevent the carbon nanotubes 21 from oxidizing during breaking. In the present embodiment, the reaction chamber is a vacuum chamber having a pressure intensity of 2×10−5 Pa. As well known in the art, the voltage applied between the two conductive substrates 20 is determined according to the dimension of the carbon nanotubes 21. The supplied voltage may have a range from about 7V to about 10V. In the present embodiment, the applied voltage is 8.25V. When the current flows through the carbon nanotubes 21, heat, known as joule heat, can be generated. The joule heat can break the carbon nanotubes 21. After breaking, the current is turned off and the joule heat disappears quickly, thus annealing the formed carbon nanotubes 11. The anneal, which is advantageous for improving mechanical strength of the carbon nanotubes 11, can be carried out in a vacuum chamber for preventing the carbon nanotubes 11 from oxidizing. Thus, two emitters 100 are obtained. The obtained emitters 100 have an approximately as many second ends 112 each having a needle-shaped tip as there are carbon nanotubes.
The described method above for manufacturing the carbon nanotubes 11 of the emitter 100 can prevent pollutant from entering the carbon nanotubes 11 as the second ends 112 are closed and have a substantially uniform length, which can provide substantially uniform electron emitting characteristics. Moreover, the second ends 112 of the two adjacent carbon nanotubes 11 are spaced from each other by a distance greater than that of the first ends 111, thereby diminishing influence from the screening effect between adjacent carbon nanotubes.
It is to be understood that the above-described embodiments are intended to illustrates, rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.
It is to be understood that the above description and the claims drawn t a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200810067726.1 | Jun 2008 | CN | national |
This application is a continuation application of U.S. patent application Ser. No. 12/384243, filed on Apr. 2, 2009, and entitled, “EMITTER AND METHOD FOR MANUFACTURING SAME,” which claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 200810067726.1, filed on Jun. 13, 2008 in the China Intellectual Property Office, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12384243 | Apr 2009 | US |
| Child | 13792524 | US |
