HK1140309A - Method for the electrochemical deposition of carbon nanotubes - Google Patents

Description

Electrochemical deposition method of carbon nano tube

This patent application claims priority to U.S. provisional application 60/903,260 filed 24/2/2007, which is incorporated by reference herein in its entirety for all purposes.

Technical Field

The present invention relates to electrochemical deposition of carbon nanotubes ("CNTs") on a substrate.

Background

Us patent 6,902,658 describes an electrophoretic deposition method in which a separate step of depositing a binder substance onto the substrate is performed prior to depositing the CNTs on the substrate. Accordingly, there is a need for a method that can simultaneously deposit CNTs and one or more additional materials on a substrate.

Summary of The Invention

In one embodiment, the present invention provides a method of depositing carbon nanotubes, the method comprising:

(a) providing an electrochemical cell comprising a cathode, an anode plate, a first conductive path connecting the cathode to a power source, and a second conductive path connecting the power source to the anode plate;

(b) providing a dispersion of a complex as an aqueous electrolyte, the aqueous electrolyte disposed between a cathode and an anode, the complex formed from carbon nanotubes and a first anionic polymer; and

(c) a voltage is applied to the electrochemical cell to deposit the complex on the anode.

In another embodiment, the present invention provides a film comprising a substrate, and disposed on the substrate (a) coagulant residue, and (b) a complex formed from carbon nanotubes and a first anionic polymer.

In another embodiment, the present invention provides a cathode assembly of a field emission device, the cathode assembly comprising a film as described above.

In another embodiment, the present invention provides a field emission device comprising a cathode assembly as described above.

Brief Description of Drawings

Figure 1 shows a schematic diagram of the deposition mechanism in one embodiment of the method of the present invention.

Fig. 2 shows the deposited material on the thin film prepared as in example 1.

Fig. 3 shows the configuration of an electrochemical cell as used in the various embodiments.

Fig. 4 shows the deposited material on the thin film prepared as in example 2.

Figure 5 shows a fluorescent material illumination image of the film as tested in example 3.

FIG. 6 shows a plot of the anodic current and anodic voltage logs from example 4.

Figure 7 shows a fluorescent material illumination image of the film tested in example 4.

Figure 8 shows a fluorescent material illumination image of the films tested in example 5.

Detailed Description

CNTs are well known to have unique and useful electrical properties and are commonly used in the manufacture of cathodes for field emission devices. However, the adoption of these materials is limited by their high cost. It is therefore an object of the present invention to provide a method for producing a uniform CNT thin film on a substrate, for example on a conductive substrate with good uniformity and low material consumption. Another object is to pattern CNT thin films to prepare them for electronic applications. The CNT thin film thus prepared can be used for a cathode assembly mounted in a field emission device.

CNT films are prepared using the methods of the present invention for depositing CNTs on a substrate using an electrochemical device, and to achieve this, the methods herein involve the use of an electrochemical cell. The battery includes a cathode, an anode plate, a first conductive path connecting the cathode to a power source, and a second conductive path connecting the power source to the anode plate. An aqueous electrolyte is provided for the cell and is disposed between the cathode and the anode. Contained in the electrolyte is a dispersion of a complex formed from CNTs and a first anionic polymer and optionally a coagulant.

As used herein, CNTs typically have a diameter of about 0.5-2nm, with a ratio of length and width dimensions, i.e., an aspect ratio, of at least 5. Generally, the aspect ratio is between 10 and 2000. CNTs are composed mainly of carbon atoms, however, other elements, such as metals, may be incorporated. The carbon nanotubes of the present invention may be either multiwall nanotubes (MWNTs) or Single Wall Nanotubes (SWNTs). E.g., MWNTs, which comprise several concentric nanotubes, each nanotube having a different diameter. Thus, the smallest diameter tube is encapsulated by a larger diameter tube, which in turn is encapsulated by another larger diameter nanotube. SWNTs, on the other hand, include only one nanotube.

CNTs can be prepared by a variety of methods, and are also commercially available. Methods for CNT synthesis include laser-evaporated graphite methods [ a. the et al, Science 273, 483(1996) ], arc discharge methods [ c. journet et al, Nature 388, 756(1997) ] and HiPCo (high pressure carbon monoxide) methods [ p. nikolaev et al, chem. phys. lett.313, 91-97(1999) ]. Chemical Vapor Deposition (CVD) methods may also be employed [ J.Kong et al, chem.Phys.Lett.292, 567-574 (1998); J.Kong et al, Nature 395, 878-879 (1998); cassell et al, J.Phys.chem.103, 6484-6492 (1999); dai et al, J.Phys.chem.103, 11246-11255(1999) ] to produce carbon nanotubes. CNTs can also be generated by catalytic methods in solution and on solid substrates [ Yan Li et al, chem.mater.; 2001; 13 (3); 1008-1014); franklin and h.dai, adv.mater.12, 890 (2000); cassell et al, J.Am.chem.Soc.121, 7975-7976(1999) ].

The main obstacle to the use of CNTs is the diversity of the following factors: tube diameter, chiral angle, and aggregation state of nanotube samples obtained by various preparation methods. Agglomeration is a particularly problematic issue because highly polarizable, smooth-sided fullerene tubes are susceptible to formation of parallel bundles or ropes of tubes via a large amount of van der waals binding energy. Such bundles disturb the electronic structure of the tubes, and almost all attempts to separate the tubes by size or type, or to use the tubes as individual macromolecular substances, are disturbed thereby.

The present invention provides a method for dispersing aggregated carbon nanotubes by contacting the aggregated nanotubes with an aqueous solution of an anionic polymer. Thereby forming a complex comprising the anionic polymer and the CNTs, but the association between the anionic polymer and the CNTs in the complex is a loose association, which is essentially formed by van der waals binding energy or some other non-covalent method, rather than by interaction of specific functional groups. The structural integrity of the CNTs is thus preserved, but the complex formed by the CNTs and the anionic polymer is suspended in the electrolyte in the form of a dispersion.

Since many anionic polymers favor the formation of polymer/CNT complexes, they can be used as dispersants for the purpose of dispersing CNTs in aqueous solutions, but the preferred polymer for this purpose is a stable solution of nucleic acids, especially nucleic acid molecules. Nucleic acids are extremely effective in dispersing CNTs because they can form nanotube-nucleic acid complexes based on non-covalent interactions between nanotubes and nucleic acid molecules. Thus, the methods of the present invention include methods of dispersing aggregated CNTs by contacting the nanotubes with a solution of an anionic polymer (e.g., a nucleic acid molecule).

The following discusses methods of forming complexes with CNTs using nucleic acid molecules and thereby dispersing CNTs, using the following terms and abbreviations:

"cDNA" refers to complementary DNA

"PNA" refers to peptide nucleic acids

"SEM" refers to scanning electron microscope

"ssDNA" refers to single-stranded DNA

"tRNA" refers to transfer RNA

"CNT" refers to carbon nanotube

"MWNT" refers to multiwalled nanotubes

"SWNT" refers to single-walled nanotubes

"TEM" refers to a transmission electron microscope

A "nucleic acid molecule" is defined as a polymer of RNA, DNA or Peptide Nucleic Acid (PNA) that is single-or double-stranded, optionally comprising synthetic, non-natural or altered nucleotide bases. Nucleic acid molecules in the form of DNA polymers may be composed of one or more segments of cDNA, genomic DNA, or synthetic DNA.

Where nucleic acids are involved, the letters "A", "G", "T" and "C" will denote the purine base adenine (C), respectively₅H₅N₅) Guanine (C)₅H₅N₅O), the pyrimidine base thymine (C)₅H₆N₂O₂) And cytosine (C)₄H₅N₃O)。

The term "peptide nucleic acid" refers to an extended material having nucleic acid polymers linked together by peptide linkers.

"Stable solution of nucleic acid molecules" refers to a solution of nucleic acid molecules that have been dissolved and are in a relaxed secondary conformational form.

By "nanotube-nucleic acid complex" is meant a composition comprising carbon nanotubes loosely associated with at least one nucleic acid molecule. Typically, the association between the nucleic acid and the nanotube is by van der waals bonding or some other non-covalent method.

The term "agitation means" refers to a device that facilitates dispersion of the nanotubes and nucleic acids. A typical agitation device is an ultrasonic degradation device.

The term "denaturant" refers to a substance that plays a role in the process of denaturing DNA and other nucleic acid molecules.

Standard DNA recombination and molecular biology techniques used herein are well known in the art and are described in the following references: molecular Cloning, by Sambrook, j., Fritsch, e.f., and manitis, t.: a Laboratory Manual, second edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY (1989) (hereinafter referred to as "Maniatis"); experiments with Gene Fusions, Cold Spring Harbor Laboratory Cold Press Spring Harbor, N.Y. (1984), by Silhavy, T.J., Bennan, M.L., and Enquist, L.W.; and Current protocols in Molecular Biology, Ausubel, F.M. et al, published by Greene Publishing Assoc. and Wiley-Interscience (1987).

The nucleic acid molecules used in the methods of the invention can be of any type and can be from any suitable source, including but not limited to DNA, RNA, and peptide nucleic acids. The nucleic acid molecules used herein may be produced synthetically or may be isolated from natural sources according to procedures well known in the art (Sambrook et al, supra). The nucleic acid molecule may be single-stranded or double-stranded, and may optionally be functionalized at any point by a variety of reactive groups, ligands, or reagents. However, functionalization of the nucleic acid is not necessary for association with the CNTs for dispersion purposes, and most nucleic acids used for dispersion herein lack functional groups and are therefore referred to herein as "unfunctionalized".

Peptide Nucleic Acids (PNAs) are particularly useful herein in terms of dispersion because they have the dual functionality of nucleic acids and peptides. Methods of synthesizing and using PNAs are well known in the art, see, e.g., ansypovitch, s.i., Peptide nucleic acids: structure, Russian chemical Reviews (2002), 71(1), 71-83.

The nucleic acid molecules used herein may have any combination of bases and may even consist of extensions of the same base (e.g., polyA or polyT) without impairing the ability of the nucleic acid molecule to disperse aggregated CNTs. The nucleic acid molecule preferably has less than about 2000 bases, more preferably has less than 1000 bases, and most preferably has from about 5 bases to about 1000 bases. Generally, the ability of nucleic acids to disperse CNTs appears to be independent of sequence or base composition, however some evidence suggests that the less interactions of G-C and T-a base pairs in the sequence, the higher the dispersion efficiency and that RNA and its variants are particularly effective in the dispersion process and are therefore preferred herein. Nucleic acid molecules suitable for use herein include, but are not limited to, nucleic acid molecules having the general formula:

an, wherein n is 1-2000;

tn, where n is 1-2000;

cn, wherein n is 1-2000;

gn, wherein n is 1-2000;

rn, wherein n ═ 1 to 2000, and wherein R can be a or G;

yn, wherein n ═ 1 to 2000, and wherein Y may be C or T;

mn, wherein n ═ 1 to 2000, and wherein M can be a or C;

kn, wherein n ═ 1 to 2000, and wherein K can be G or T;

sn, wherein n is 1-2000, and wherein S may be C or G;

wn, wherein n-1-2000, and wherein W may be a or T;

hn, wherein n-1-2000, and wherein H may be a or C or T;

bn, wherein n ═ 1-2000, and wherein B may be C or G or T;

vn, wherein n ═ 1 to 2000, and wherein V can be a or C or G;

dn, wherein n-1-2000, and wherein D may be a or G or T; and

nn, wherein N ═ 1 to 2000, and wherein N may be a or C or T or G.

In addition to the combinations listed above, any of these sequences may be replaced by one or more deoxyribonucleotides by ribonucleotides (i.e., RNA or RNA/DNA hybrids), or one or more phosphosaccharide linkages by peptide bonds (i.e., PNA or PNA/RNA/DNA hybrids).

As used herein, a nucleic acid molecule can be stabilized in a suitable solution. The nucleic acid molecules are preferably in a relaxed, secondary conformational form and only loosely associated with each other, thereby achieving maximum contact of each strand with the CNTs. Stable solutions of nucleic acids are common and well known in the art (see Sambrook et al, supra) and typically contain salts and buffers such as sodium and potassium salts, as well as TRIS (TRIS (2-aminoethyl) amine), HEPES (N- (2-hydroxyethyl) piperazine-N' - (2-ethanesulfonic acid), and MES (2- (N-morpholinyl) ethanesulfonic acid). preferred solvents to stabilize nucleic acid solutions are water-soluble solvents, where water is most preferred.

To prepare a dispersion according to the methods herein, one or more nucleic acid molecules can be contacted with a set of aggregated carbon nanotubes. Preferably (but not necessarily) the contacting is carried out using some type of stirring device. Typically, the agitation device employs an ultrasonic degradation device, but may also include a device that forms high shear mixing (i.e., homogenization) of the nucleic acid and CNTs, or any combination thereof. After stirring, the CNTs will disperse and form a nanotube-nucleic acid complex comprising at least one nucleic acid molecule loosely associated with the CNTs by hydrogen bonding or some other non-covalent means.

The temperature during the contacting of the CNTs with the nucleic acid may have an effect on the dispersion effect. If mixing at room temperature or higher, it is found that a longer dispersion time is required, whereas mixing at a temperature lower than room temperature (23 ℃), it appears that a shorter dispersion time is required, and a temperature of about 4 ℃ is preferred. The dispersion of CNTs by contact with nucleic acid molecules is also described in us patent 2004/0132072 and us patent 2004/0146904, both of which are incorporated by reference herein in their entirety for all purposes.

Use of one or more other anionic polymers, in addition to the above-mentioned nucleic acid molecules, for the preparation of an aqueous dispersion of CNTs. Other examples of anionic polymers that have been found to be useful in preparing CNT dispersions include, but are not limited to, ionized poly (acrylic acid) ("PAA") or ionized ethylene/(meth) acrylic acid copolymers ("EAA" or "EMAA"), any of which may be used with, for example, Na⁺、K⁺、NH₄ ⁺Or Cr⁺Such as neutralization of cations; styrene ionomers, such as styrene/sodium styrene sulfonate copolymer (PSS) or styrene/sodium styrene methacrylate copolymer; and ionised tetrafluoroethylene/sulfonic acid copolymers, e.g. Nafion^TMCopolymers (available from dupont) in which the sulfonic acid groups in the tetrafluoroethylene/perfluorovinyl ether copolymer are neutralized with sodium. As described above with respect to nucleic acid molecules, sonication or other mixing devices can be used to facilitate dispersion of CNTs in an aqueous solution of one or more anionic polymers discussed in this paragraph.

In one embodiment, when the complex formed by the CNTs and anionic polymer molecules is dispersed in an electrolyte solution contained within a battery, deposition of the complex on the anode plate of the battery may be facilitated by the addition of an optional coagulant therein. The coagulant will neutralize the negative charge on the anionic polymer in the complex. Since the anionic polymer/CNT complex group is maintained in a dispersed state mainly by repulsion of negatively charged complexes from each other (or by repulsion of two positively charged layers surrounding the complexes), neutralizing these negative charges with a coagulant (or compressing the two layers) will remove the force that keeps the complex group in a dispersed state in the electrolyte solution. Since the reaction of the coagulant to neutralize the complex occurs in close proximity to the anode plate, the complex (no longer dispersed) will change phase from solution to solid phase to a varying degree, gradually assuming an aggregated and agglomerated state (similar to the formation of floes and floes), and then aggregating and depositing on the surface of the anode plate. In addition to the CNT complex, the material deposited on the plate may also include coagulant residues.

If first and second anionic polymers are present in the electrolyte solution, such as a first polymer that forms a complex with the CNTs, and a second polymer that is more loosely associated or not associated with the CNTs than the first polymer, they may start to deposit simultaneously on the surface of the anode. The first polymer may, for example, be deposited in a matrix of the second polymer. If additional materials are required to enhance the effectiveness and performance of the anode plate in a field emission device, such as the presence of conductive or functionalized particles in the electrolyte solution, they can be deposited on the anode plate simultaneously with the anionic polymer/CNT complex. Figure 2 shows a typical example of the type of thin film formed by such deposition on the anode plate, the thin film having good uniformity due to the uniform deposition of the material and good adhesion over its entire surface.

Suitable coagulants for use herein in neutralizing the use of anionic polymer/CNT complexes include inorganic coagulants such as trivalent cations formed from metals including group VIII/VIIIA metals such as iron, cobalt, ruthenium or osmium. Since the effect of the trivalent cation neutralizing complex can be at most ten times that of the divalent cation, a convenient method of providing a coagulant is: providing divalent cations, e.g. ruthenium (II) terpyridyl chloride, 2 therein, to the electrolyte solution⁺The cations are oxidized to 3 by being abstracted by the anode plate⁺And (4) price. A representative schematic of this mechanism is shown in fig. 1.

In an alternative embodiment, however, no coagulant is used, wherein the anode plate is formed of a metal (e.g., silver or nickel). In this case, the metal on the plate dissolves in the electrolyte solution and the charge on the anionic polymer/CNT complex is neutralized by the cations formed by the metal atoms that go into solution from the solid metal forming the plate.

The methods herein are typically performed with the battery operating at a lower potential, such as less than about 5 volts, or from about 2 volts to about 3 volts. The thickness of the deposited film is directly related to the length of the deposition time to a large extent. Useful deposition times are in the range of about 1 to about 10 minutes, or in the range of about 1 to about 2 minutes. A positive potential is maintained at the anode plate relative to the cell cathode.

The methods herein can be used to generate thin films in which the deposition material is deposited in a predetermined pattern. This can be achieved by patterning the surface of the plate that acts as the anode using conventional photo-imaging techniques. Thus, the photoresist can be activated through a mask and then developed to provide a pattern, such as an array of circular holes, on the surface of the anode. Since the anionic polymer/CNT complexes are aggregated and precipitated out of solution, they are only deposited in the holes and the photoresist can be removed. The method provides a patterned CNT film in which an anode plate is used as a substrate for the film by mounting it for use in a field emission device.

After deposition of the CNT complex on the anode plate of the cell is complete, the plate can be removed from the cell, washed, dried and mounted under conditions to be used as part of the cathode assembly therein in a field emission device to provide electron emission. Alternatively, however, the plate may be baked and/or roasted to melt the deposited polymer before being mounted in the field emission device, and the polymer in this state is used as a binder to more firmly fix the CNTs on the surface of the plate, so that the CNT-containing film has excellent abrasion resistance.

In a field emission device that can be loaded with a plate coated with a deposition material as described above, an electron emitting material is deposited on a cathode, which material, when excited, bombards an anode with electrons. The electron emitting material may be an acicular substance such as carbon, a semiconductor, a metal, or a mixture thereof. As used herein, "acicular" refers to particles having an aspect ratio of 10 or greater. The electron emitting material is typically attached to a substrate in the cathode assembly using glass frit, metal powder or metal paint, or mixtures thereof.

Acicular carbon used as an electron emitting material may be of various types, but carbon nanotubes are the preferred acicular carbon, while single-walled CNTs are particularly preferred. Carbon fibers obtained by catalytic decomposition of carbon-containing gases on small metal particles may also be used as acicular carbon, other examples of which are polyacrylonitrile-based (PAN-based) carbon fibers and pitch-based carbon fibers.

Various methods can be used to attach the electron emissive material to the substrate. The joining method must be able to withstand the conditions of the manufacturing equipment in which the field emission cathode is placed and withstand the conditions of use and maintain its integrity, such as typical vacuum conditions and temperature conditions of up to about 450 ℃. The preferred method is: a paste consisting of an electron emitting material and a glass frit, metal powder or metal paint or a mixture thereof is screen printed onto a substrate in a desired pattern, and then the dried patterned paste is baked. For a wider variety of applications, such as those requiring finer resolution, the preferred method involves screen printing a paste further comprising a photoinitiator and a photocurable monomer, photopatterning the dried paste, and then baking the patterned paste.

The substrate may be any material as long as the paste composition can be adhered thereto. If the paste is non-conductive and a non-conductive substrate is used, a thin film of electrical conductor is required, which serves as a cathode electrode and provides a means of applying a voltage to the electron emitting material. Silicon, glass, metal, or refractory materials (e.g., alumina) may be used as the substrate. For display applications, the preferred substrate is glass, and soda lime glass is particularly preferred. To achieve the best conductivity on the glass, the silver paste can be pre-baked onto the glass in air or nitrogen, preferably in air, at 500-. The emitter paste can then be printed on the conductive layer so formed.

Pastes for screen printing typically comprise an electron emitting material, an organic medium, a solvent, a surfactant, and a low softening point frit, metal powder or metal paint or mixtures thereof. The function of the medium and solvent is to suspend and disperse the particulate components, i.e., solids. The solids in the paste have the appropriate rheology for typical patterning processes, such as screen printing. There are numerous organic media known for this purpose, including cellulosic resins, such as ethyl cellulose and alkyd resins of various molecular weights. Examples of useful solvents are butyl carbitol ester, butyl carbitol acetate, dibutyl carbitol, dibutyl phthalate and terpineol. These and other solvents are formulated to achieve the desired viscosity and volatility requirements.

A frit is also used that softens sufficiently at the firing temperature to adhere to the substrate and to the electron emissive material. Lead or bismuth frits may be used, as well as other glasses with low softening points, such as calcium and zinc borosilicates. The paste may also contain a metal, such as silver or gold, if a screen-printable composition with higher conductivity is desired. The paste typically comprises from about 40 wt% to about 80 wt% solids, based on the total weight of the paste. These solids include an electron emitting material and a glass frit and/or a metal component. Variations in the composition can be used to adjust the viscosity and the final thickness of the printed material.

Emitter pastes are typically prepared by three-roll milling a mixture of: electron emitting materials, organic media, surfactants, solvents, and low softening point frits, metal powders or metal coatings or mixtures thereof. The paste mixture may be screen printed using, for example, a 165-400 mesh stainless steel screen. The paste may be deposited in the form of a continuous film or desired pattern. If the substrate is glass, the paste is baked at a temperature of about 350 deg.C to about 550 deg.C, preferably about 450 deg.C to about 525 deg.C, under nitrogen for about 10 minutes. Higher baking temperatures that the substrate can withstand can be used, provided that the baking environment does not contain oxygen. However, the organic components in the paste are effectively volatilized at 350-450 ℃ leaving a composite layer of the electron-emitting material and the glass and/or metal conductor. During baking under nitrogen, the electron emitting material appeared to undergo no observable oxidation or other chemical or physical changes.

If the screen-printed paste is to be photopatterned, the paste may also contain a photoinitiator, a ductile binder, and a photocurable monomer containing, for example, at least one addition polymerizable ethylenically unsaturated compound having at least one polymerizable vinyl group. Typically, a paste prepared from electron emitting materials (e.g., carbon nanotubes, silver, and glass frit) will contain about 0.01 to 6.0 wt.% CNTs, about 40 to 75 wt.% silver (in the form of fine silver particles), and about 3 to 15 wt.% glass frit, based on the total weight of the paste.

The anode of the field emission device is an electrode coated with a conductive layer. When a field emission device is used in a display device, where the cathode has an array of pixels of thick film paste deposited as described above, the anode in the display device may comprise a fluorescent material that converts incident electrons to light. The substrate of the anode may also be selected to be a transparent substrate so that the resulting light can be transmitted. The cathode assembly and the anode constitute a sealed unit, wherein the cathode assembly and the anode are separated by a separator and an evacuated space is present between the anode and the cathode. The evacuated space needs to be partially evacuated so that electrons emitted from the cathode can be transported to the anode with only a small number of collisions with gas molecules. Typically, the evacuated space is pumped to less than 10^-5The pressure of the tray.

Such field emission devices are useful in a variety of electronic applications such as vacuum electronics, flat panel computer and television displays, backlights for liquid crystal displays, emission gate amplifiers, klystrons, and lighting devices. For example, flat panel displays have been proposed having a cathode employing a field emission electron source, i.e., a field emission material or field emitter, and a phosphor material capable of emitting light upon bombardment by electrons emitted by the field emitter. This type of display screen has both the visual display advantages of conventional cathode ray tubes and the depth, weight and power consumption advantages of other flat panel displays. The flat panel display may be planar or curved. U.S. Pat. Nos. 4,857,799 and 5,015,912 disclose matrix-addressed flat panel displays using microtip cathodes constructed of tungsten, molybdenum or silicon. WO 94-15352, WO 94-15350 and WO 94-28571 disclose flat panel displays in which the cathode has a relatively flat emission surface. These devices are also described in U.S. patent 2002/0074932, which is incorporated by reference herein in its entirety as part of the present disclosure for all purposes.

The Materials used in the methods herein can be made by methods known in the art or can be obtained commercially from suppliers such as Alfa Aesar (Ward Hill, Massachusetts), City Chemical (WestHaven, Connecticut), Fisher Scientific (Fairlawn, New Jersey), Sigma-Aldrich (st. louis, Missouri) or Stanford Materials (alioviejo, California).

Advantageous properties and effects of the present invention can be seen in a series of examples (examples 1 to 5) described below. The embodiments on which the examples are based are representative only, and the selection of those embodiments to illustrate the invention does not indicate that materials, conditions, specifications, components, reactants, techniques and protocols not described in the examples are not suitable for practicing the invention, nor does it indicate that subject matter not described in the examples is not included in the scope of the appended claims and their equivalents.

Examples

In 15mL of 1 XTBE [ tris boric acid (ethylenediaminetetraacetic acid) ]]In buffer (from SigmaAldrich), 150mg of laser ablated CNT (David)From CNI, Houston, Texas) was mixed with 30mg yeast RNA (from Sigma Aldrich). The mixture was sonicated using a probe sonicator at a power level of 20W for 30 minutes. The resulting dispersion was mixed with the other two components according to the following table (table 1) to make 100mL of the deposition solution. Ru used in deposition solution²⁺(bipyridine)₃Ruthenium (II) terpyridine chloride from Sigma Aldrich. EMMA is an ethylene/methacrylic acid ionomer sold under the trade name Surlyn^TMThe ionomer is obtained from dupont.

TABLE 1

Composition of deposition solution

Components	Concentration of stock solution	Adding amount of	Final concentration
				CNT dispersions	10mg/mL	4mL	0.04％
EMMA	10mg/mL	2mL	0.02％
				Ru2+(bipyridine)3	10mM	2mL	0.2mM
Water (W)		92mL

Example 1

A 2 'x 2' stainless steel plate (used as the cathode) and a 2 'x 2' indium tin oxide ("ITO") plate (used as the anode) were inserted in parallel into a rectangular electrochemical cell (configuration shown in fig. 3). 15mL of the deposition solution was charged into the cell as an electrolyte. A potential difference of 3.2V was applied between the two electrodes. After 1 minute, the deposition was stopped, and the ITO plate was removed from the cell, washed with deionized water and dried in air. A uniform deposition of material on the plate is obtained as shown in figure 2.

Example 2

An Indium Tin Oxide (ITO) substrate (2 '× 2') patterned with a Photoresist (PR) was used as an anode. The PR layer defines an array of circular holes of 20 μm diameter. These holes expose the surface of the ITO plate for CNT deposition. The PR-coated ITO plate was immersed in a 0.01% Triton X-100 solution before electrodeposition, and then taken out and dried by blowing nitrogen gas. This helps to coat the hydrophobic PR layer with a thin hydrophilic layer for better wetting. After this treatment, a 2 '× 2' stainless steel plate (used as cathode) and a PR-coated ITO plate (used as anode) were inserted in parallel into the same type of electrochemical cell as used in example 1. 15mL of the deposition solution was charged to the cell. An alternating potential (100 Hz square wave with 0 to 3.5V peak-to-peak voltage and 50% duty cycle) is applied between the two electrodes. After 1 minute, the deposition was stopped, and the ITO plate was removed from the cell, washed with deionized water and dried in air. The PR layer was removed by solvent treatment with acetone. Good uniformity of CNT material deposition in the exposed holes is obtained, as shown in fig. 4.

Example 3

The dried panels from example 1 and shown in fig. 2 were then baked at 420 ℃ for 10 minutes under nitrogen. A strip of adhesive tape was then laminated to the CNT film, which was subsequently removed. This process, commonly referred to as "activation," is known to break the film surface, thereby exposing and lifting the CNT filaments from the substrate surface to significantly enhance electron field emission. The diode field emission device was then assembled by using the CNT-coated ITO substrate as the cathode. An anode plate consisting of an ITO-coated glass substrate with a coating of fluorescent material is mounted opposite the "activated" cathode. An electrically insulating separator of 1mm thickness was used to maintain the distance between the cathode and anode substrates. Silver paint and copper tape were used to make electrical contact to the cathode and anode electrodes, completing the diode device. The device is mounted in a vacuum chamber which is pumped to a pressure below 1X 10^-5And (4) supporting. A pulsed square wave with a repetition rate of 60Hz and a pulse width of 60 mus was applied to the anode electrode. The cathode electrode is held at ground potential. An anodic current of 200. mu.A was obtained at an anodic voltage of 2 kV. Fig. 5 shows an illumination image of the fluorescent material obtained by the emission of electrons by the device.

Example 4

The dried panels from example 2 and shown in fig. 4 were then baked at 420 ℃ for 10 minutes in nitrogen as described in example 3. A strip of adhesive tape was used to activate the CNT dot surfaces as described in example 3. A diode field emission device was then assembled by using the CNT dot covered ITO substrate as the cathode and the ITO coated glass substrate with the phosphor coating as the anode. In this example, a 0.22mm thick glass spacer is usedThe distance between the cathode and anode substrates is maintained. The device is mounted in a vacuum chamber which is pumped to a pressure below 1X 10^-5And (4) supporting. A pulsed square wave with a repetition rate of 60Hz and a pulse width of 60 mus was applied to the anode electrode. The cathode electrode is held at ground potential. When the pulsed anode voltage reached 800V, an average anode current of 5 μ A was measured. The measured anode current increases with increasing pulsed anode voltage. At an anode voltage of 925V, an anode current of 40. mu.A was obtained. Fig. 6 shows a graph of the anode current and anode voltage recorded values obtained from the field emission device. Fig. 7 shows an illumination image of a fluorescent material obtained by emitting electrons by the device operating at an anode voltage of 975V and an anode current of 80 μ a. Each rectangular illuminated pixel on the anode is generated by a plurality of CNT dot arrays on the cathode.

Example 5

The process herein does not use the ITO coated flat glass substrate prepared in example 2 and used in example 4, but rather a top gate triode substrate is used to deposit the CNT dots. The top gate transistor substrate is typically comprised of two conductive layers with an insulating layer disposed between the two conductive layers. In this example, an ITO-coated glass substrate was used as the substrate of a top gate triode, and an ITO layer was used as the cathode. An insulating dielectric layer is deposited on top of the ITO layer. A metal gate electrode layer is deposited on the dielectric layer. In addition, an array of circular holes is etched through the metal and dielectric layers using a photoresist ("PR") and a mask, so that the surface of the ITO is exposed. As described in example 2, the array of circular holes defines a pattern on the PR layer covering the triode component. The opening diameter of the holes in the PR is smaller than the diameter of the holes extending through the metal and dielectric layers, but the circumference of the smaller holes is concentric with the larger holes. CNT dots were deposited on the ITO surface, baked and activated using a similar procedure as described in examples 2 and 4.

An anode plate is mounted opposite the activated triode cathode, and is comprised of an ITO coated glass substrate with a coating of fluorescent material. Make itThe distance between the cathode and anode substrates was maintained with a 3mm thick separator. Silver paint and copper tape were used to make electrical contact with the ITO cathode electrode, metal gate electrode, and ITO anode electrode to complete the top gate triode device. The device is mounted in a vacuum chamber which is pumped to a pressure below 1X 10^-5And (4) supporting. A dc voltage of 3kV was applied to the anode electrode. A pulsed square wave with a repetition rate of 120Hz and a pulse width of 30 mus was applied to the gate electrode. The cathode electrode is held at ground potential. When the pulse gate voltage reached 70V, the average anode current density was measured to be 5.0. mu.A/cm². Fig. 8 shows an illumination image of the phosphor material obtained by the emission of electrons by the triode device.

Features of certain devices of the invention are described herein in the context of one or more specific embodiments that combine various such features. The scope of the invention, however, is not limited to the description of only a few of the features in any particular embodiment, and the invention also includes (1) subcombinations of less than all of the features of any of the described embodiments, where such subcombinations are characterized by the absence of features omitted from forming such subcombinations; (2) each feature independently included in any combination of the embodiments; and (3) combinations of other features formed by merely categorizing selected features of two or more of the described embodiments, optionally together with other features disclosed elsewhere herein.

In this specification, unless explicitly stated otherwise or indicated to the contrary by the context of usage, where an embodiment of the subject matter hereof is stated or described as comprising, including, containing, having, being composed of or being constituted by or of certain features or elements, one or more features or elements in addition to those explicitly stated or described may also be present in the embodiment. However, an alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, wherein embodiment features or elements that would materially alter the principle of operation or the distinguishing characteristics of the embodiment are not present herein. Another alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, in which embodiment, or in insubstantial variations thereof, only the features or elements specifically discussed or described are present.

Claims (20)

1.A method of depositing carbon nanotubes, the method comprising:

(a) providing an electrochemical cell comprising a cathode, an anode plate, a first conductive path connecting the cathode to a power source, and a second conductive path connecting the power source to the anode plate;

(b) providing a dispersion of a complex as an aqueous electrolyte disposed between the cathode and the anode, the complex being formed from carbon nanotubes and a first anionic polymer; and

(c) applying a voltage to the electrochemical cell to deposit the complex on the anode.

2. The method of claim 1, wherein the aqueous electrolyte further comprises a coagulant.

3. The method according to claim 2, wherein coagulant residue is deposited on the anode together with the complex.

4. The method of claim 1, wherein the first polymer comprises a nucleic acid molecule.

5. The method according to claim 1, wherein the first polymer comprises RNA.

6. The method of claim 1, wherein the electrolyte further comprises a second anionic polymer.

7. The method according to claim 6, wherein the second ionic polymer comprises a styrene ionomer or an ionized ethylene/(meth) acrylic acid copolymer.

8. The method of claim 6, wherein the complex deposited on the anode is deposited in a matrix of the second anionic polymer.

9. The method of claim 7, wherein the first polymer comprises a nucleic acid molecule.

10. The method according to claim 7, wherein the first polymer comprises RNA.

11. The method of claim 1, further comprising the step of removing the anode plate from the cell and then installing it in a field emission device.

12. A film comprising a substrate, and disposed on the substrate (a) coagulant residue, and (b) a complex formed from carbon nanotubes and a first anionic polymer.

13. The method of claim 12, wherein the first polymer comprises a nucleic acid molecule.

14. The method according to claim 12, wherein the first polymer comprises RNA.

15. The film of claim 12, wherein a second anionic polymer is further disposed on the substrate.

16. The method according to claim 15, wherein the second ionic polymer comprises a styrene ionomer or an ionized ethylene/(meth) acrylic acid copolymer.

17. The method of claim 15, wherein the first polymer comprises a nucleic acid molecule.

18. The method according to claim 15, wherein the first polymer comprises RNA.

19. A cathode assembly for a field emission device, said cathode assembly comprising a film according to claim 1.

20. A field emission device comprising a cathode assembly according to claim 19.