METHODS FOR FORMING CARBON NANOTUBE/METAL COMPOSITE FILMS AND FIELD EMISSION CATHODES THEREFROM

Abstract

A method for fabricating an electron field emission cathode, the field emission cathode including a substrate having a field emission layer engaged therewith, where the field emission layer incorporates a carbon nanotube and metal composite film to improve adhesion between the material and the substrate and to improve field emission characteristics of the cathode and field emission cathode devices implementing such cathodes.

Claims

1. A method of forming a field emission cathode, comprising: forming a field emission material by dispersing at least one carbon nanotube, at least one matrix particle, at least one metal salt, and at least one charger in a liquid medium to form a suspension thereof; and depositing a layer of the field emission material on to at least a portion of a substrate via electrophoretic deposition to form the field emission cathode.

2. The method of claim 1, wherein forming the field emission material comprises forming the field emission material by dispersing the at least one matrix particle comprising a glass particle in the liquid medium.

3. The method of claim 1, wherein dispersing the at least one matrix particle comprises dispersing the at least one matrix particle having a diameter of about 100 nm to about 3 micrometers in the liquid medium.

4. The method of claim 1, wherein dispersing the at least one matrix particle comprises dispersing the at least one matrix particle in the liquid medium at up to 10 wt % of total liquid medium.

5. The method of claim 1, wherein forming the field emission material comprises forming the field emission material by dispersing the at least one metal salt selected from the group consisting of a silver salt, a copper salt, a platinum salt, a bismuth salt, a tungsten salt, a stibium salt, a gold salt, or combinations thereof in the liquid medium.

6. The method of claim 1, wherein dispersing the at least one metal salt comprises dispersing the at least one metal salt in the liquid medium at up to 10 wt % of total liquid medium.

7. The method of claim 1, wherein forming the field emission material comprises forming the field emission material by dispersing the at least one charger selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, a magnesium salt, an aluminum salt, a zinc salt, an iron salt, a cobalt salt, a nickel salt, an ammonium salt, or combinations thereof in the liquid medium.

8. The method of claim 1, wherein dispersing the at least one charger comprises dispersing the at least one charger in the liquid medium at up to 1 wt % of total liquid medium.

9. The method of claim 1, wherein forming the field emission material comprises forming the field emission material by dispersing the at least one carbon nanotube, the at least one matrix particle, the at least one metal salt, and the at least one charger in the liquid medium selected from the group consisting of water, methanol, ethanol, isopropanol, butanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or combinations thereof.

10. The method of claim 1, wherein depositing the layer of the field emission material comprises depositing the layer of the field emission material on to the at least a portion of the substrate comprising a metal, an alloy, a glass, or a ceramic.

11. The method of claim 1, wherein forming the field emission material comprises forming the field emission material by dispersing the at least one carbon nanotube, the at least one matrix particle, the at least one metal salt, and the at least one charger simultaneously in the liquid medium.

12. A method of forming a field emission composite, comprising: introducing at least one carbon nanotube into a liquid medium; introducing at least one matrix particle into the liquid medium; introducing at least one metal salt into the liquid medium; introducing at least one charger into the liquid medium; and dispersing the at least one carbon nanotube, the at least one matrix particle, the at least one metal salt, and the at least one charger simultaneously into the liquid medium to form a suspension thereof.

13. The method of claim 12, comprising depositing the suspension on to a substrate via electrophoretic deposition.

14. The method of claim 12, wherein introducing the at least one matrix particle comprises introducing the at least one matrix particle comprising a glass particle into the liquid medium.

15. The method of claim 12, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one matrix particle in the liquid medium at up to 10 wt % of total liquid medium.

16. The method of claim 12, wherein introducing the at least one metal salt comprises introducing the at least one metal salt selected from the group consisting of a silver salt, a copper salt, a platinum salt, a bismuth salt, a tungsten salt, a stibium salt, a gold salt, or combination thereof into the liquid medium.

17. The method of claim 12, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one metal salt in the liquid medium at up to 10 wt % of total liquid medium.

18. The method of claim 12, wherein introducing the at least one charger comprises introducing the at least one charger selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, a magnesium salt, an aluminum salt, a zinc salt, an of 8 iron salt, a cobalt salt, a nickel salt, an ammonium salt, or combinations thereof into the liquid medium.

19. The method of claim 12, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one charger in the liquid medium at up to 1 wt % of total liquid medium.

20. The method of claim 12, wherein introducing the at least one carbon nanotube comprises introducing the at least one carbon nanotube into the liquid medium selected from the group consisting of water, methanol, ethanol, isopropanol, butanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or combinations thereof.

21. A method of forming a field emission cathode, comprising: introducing at least one carbon nanotube into a liquid medium; introducing at least one matrix particle into the liquid medium; introducing at least one metal salt into the liquid medium; introducing at least one charger into the liquid medium; dispersing the at least one carbon nanotube, the at least one matrix particle, the at least one metal salt, and the at least one charger simultaneously into the liquid medium to form a suspension thereof, the suspension comprising a field emission composite; and depositing a layer of the field emission composite on to at least a portion of a substrate via electrophoretic deposition to form the field emission cathode.

22. The method of claim 21, wherein introducing the at least one matrix particle comprises introducing the at least one matrix particle comprising a glass particle into the liquid medium.

23. The method of claim 21, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one matrix particle in the liquid medium at up to 10 wt % of total liquid medium.

24. The method of claim 21, wherein introducing the at least one metal salt comprises introducing the at least one metal salt selected from the group consisting of a silver salt, a copper salt, a platinum salt, a bismuth salt, a tungsten salt, a stibium salt, a gold salt, or combination thereof into the liquid medium.

25. The method of claim 21, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one metal salt in the liquid medium at up to 10 wt % of total liquid medium.

26. The method of claim 21, wherein introducing the at least one charger comprises introducing the at least one charger selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, a magnesium salt, an aluminum salt, a zinc salt, an iron salt, a cobalt salt, a nickel salt, an ammonium salt, or combinations thereof into the liquid medium.

27. The method of claim 21, wherein dispersing the at least one carbon nanotube comprises dispersing the at least one charger in the liquid medium at up to 1 wt % of total liquid medium.

28. The method of claim 21, wherein introducing the at least one carbon nanotube comprises introducing the at least one carbon nanotube into the liquid medium selected from the group consisting of water, methanol, ethanol, isopropanol, butanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or combinations thereof.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0034] Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0035] FIG. 1 schematically illustrates an example of a field emission cathode and the nature of the field emission material deposition layer engaged with the cathode substrate, according to one or more aspects of the present disclosure;

[0036] FIG. 2 illustrates one example of a method of forming a field emission composite film, according to one or more aspects of the present disclosure; and

[0037] FIG. 3 illustrates one example of a method of forming a field emission cathode, according to one or more aspects of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0038] The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all aspects of the disclosure are shown. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the aspects set forth herein; rather, these aspects are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0039] FIG. 1 illustrates one example of a field emission cathode 100 that includes a substrate 102 and a layer of a field emission material 104 disposed on the substrate 102, and, if necessary, an additional layer of an adhesion material (not shown) disposed between the substrate 102 and the field emission material 104. The substrate 102 may be made of an electrically conductive material, such as a metallic material, such as a solid metal or alloy (e.g., stainless steel, doped silicon), conductive glass (e.g., Indium Tin Oxide (ITO) coated glass or other fused glass having a conductive coating on the surface); or a conductive ceramic (e.g., a metalized ceramic, such as aluminum oxide, beryllium oxide, and aluminum nitride). The field emission material 104 is a plurality of carbon nanotubes disposed within a matrix material. The layer of field emission material 104 is formed via deposition of the field emission material on to the substrate 102 by, for example electrophoretic deposition or a similar material processing technique using deposition of charged particles in a stable colloidal suspension on a conductive substrate, such as electro-coating, cathodic electro-deposition, anodic electro-deposition, and electrophoretic coating.

[0040] FIG. 2 illustrates a method 200 of forming a field emission composite precursor or composite film precursor. In one aspect of the method, a liquid medium is provided (step 210) into which several components are dispersed. The liquid medium may be selected from the group consisting of water, methanol, ethanol, isopropanol, butanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or combinations thereof. Steps 220, 230, 240, and 250 are directed to introducing the various components, such as at least one carbon nanotube, at least one matrix particle, at least one metal salt, at least one charger to the liquid medium, or combinations thereof. As shown at step 260, all of the preceding components are dispersed within the liquid medium simultaneously so as to form a suspension thereof. The components may be dispersed in the liquid medium in accordance with known methods, such as, for example, sonication or a magnetic stirrer.

[0041] The specific composition and quantities of the components may vary to suit a particular application. For example, the at least one matrix particle may be formed from commercially available glass particles that are processed via planetary ball milling to produce glass particles with a diameter of about 100 nm to about 3 micrometers, where the at least one matrix particle is dispersed in the liquid medium at up to 10 wt % of total liquid medium. Additionally, the at least one metal salt may be selected from the group consisting of a silver salt, a copper salt, a platinum salt, a bismuth salt, a tungsten salt, a stibium salt, a gold salt, or combinations thereof, where the at least one metal salt is dispersed in the liquid medium at up to 10 wt % of total liquid medium. The at least one charger may be selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, a magnesium salt, an aluminum salt, a zinc salt, an iron salt, a cobalt salt, a nickel salt, an ammonium salt, or combinations thereof, where the at least one charger is dispersed in the liquid medium at up to 1 wt % of total liquid medium.

[0042] Once the field emission composite precursor or composite film precursor has been created in the form of a liquid suspension, the precursor may be deposited on to a substrate via an electrophoretic deposition process (step 270) to provide the field emission composite as a solid form film on the substrate. The film may be subjected to one or more other processes after deposition on the substrate, such as drying, annealing and activating processes. The substrate may be made of a metal, an alloy, a conductive glass, or a metalized ceramic. The substrate may be provided to the appropriate equipment via, for example, a robotic material handling system or manually by a user. The substrate is configured to receive a layer of the field emission composite precursor or composite film precursor thereon.

[0043] FIG. 3 illustrates a method 300 of forming a field emission cathode using a carbon nanotube and metal composite or composite film. In one aspect of the method, a substrate, such as those described hereinabove, is provided to equipment configured for carrying out a deposition process (step 310). The method further includes forming a field emission material such as a field emission composite precursor or composite film precursor (step 320). In some cases, the field emission material is created prior to the substrate being provided. A layer of the field emission material is deposited on to at least a portion of the substrate via electrophoretic deposition process (step 330) to form a carbon nanotube/metal composite or composite film on the substrate. The film may be subjected to one or more other processes (such as drying annealing and activating) after deposition on the substrate, then the finished product is a field emission cathode. The substrate may be made of a metal, an alloy, a conductive glass, or a metalized ceramic. The substrate may be provided to the appropriate equipment via, for example, a robotic material handling system or manually by a user.

[0044] Step 340 illustrates one example of forming the field emission material by dispersing at least one carbon nanotube, at least one matrix particle, at least one metal salt, and at least one charger into a liquid medium to form a suspension thereof. The dispersion of the at least one carbon nanotube, the at least one matrix particle, the at least one metal salt, and the at least one charger into the liquid medium occurs simultaneously by, for example, sonication, a magnetic stirrer, or similar.

[0045] The specific composition and quantities of the components may vary to suit a particular application. For example, the at least one matrix particle may be formed from commercially available glass particles that are processed via planetary ball milling to produce glass particles with a diameter of about 100 nm to about 3 micrometers, where the at least one matrix particle is dispersed in the liquid medium at up to 10 wt % of total liquid medium. Additionally, the at least one metal salt may be selected from the group consisting of a silver salt, a copper salt, a platinum salt, a bismuth salt, a tungsten salt, a stibium salt, a gold salt, or combinations thereof, where the at least one metal salt is dispersed in the liquid medium at up to 10 wt % of total liquid medium. The at least one charger may be selected from the group consisting of a lithium salt, a sodium salt, a calcium salt, a magnesium salt, an aluminum salt, a zinc salt, an iron salt, a cobalt salt, a nickel salt, an ammonium salt, or combinations thereof, where the at least one charger is dispersed in the liquid medium at up to 1 wt % of total liquid medium. The carbon nanotubes may be manufactured by a chemical vapor deposition process, a laser ablation process, and/or an arc discharge method.

[0046] The foregoing methods provide for the homogeneous deposition of a composite film of carbon nanotubes and metals by co-depositing carbon nanotubes and metals onto a substrate by an electrophoretic deposition process. The methods improve not only the adhesion of the carbon nanotubes to the substrate, but also the conductivity of the carbon nanotube/metal composite films and the electron field emission cathodes made therewith. The methods also improve the work function of carbon nanotubes by the surface modification of carbon nanotubes in the fabricating process.

[0047] The carbon nanotube/metal composite films, electron field emission cathodes, and electron field emission cathode device, such as vacuum devices, fabricated by these processes demonstrate enhanced electron field emission characteristics, such as increased conductivity of layers of the field emission material and improved uniformity of the electric field at the cathode surface.

[0048] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these disclosed embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that embodiments of the invention are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the disclosure. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated within the scope of the disclosure. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0049] It should be understood that although the terms first, second, etc. may be used hereinto describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one operation or calculation from another. For example, a first calculation may be termed a second calculation, and, similarly, a second step may be termed a first step, without departing from the scope of this disclosure. As used herein, the term and/or and the I symbol includes any and all combinations of one or more of the associated listed items.

[0050] As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and/or including, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.