WO2009152146A1

WO2009152146A1 - Improved cnt/topcoat processes for making a transplant conductor

Info

Publication number: WO2009152146A1
Application number: PCT/US2009/046738
Authority: WO
Inventors: Youngbae Park; Liangbing Hu; Corinne Ladous; Ting Huang; Glen Irvin; Paul Drzaic
Original assignee: Unidym, Inc.
Priority date: 2008-06-09
Filing date: 2009-06-09
Publication date: 2009-12-17
Also published as: KR20110036543A; JP5635981B2; CN102224596A; CN102224596B; KR101703845B1; JP2011527809A

Abstract

We disclose a method for making an optically transparent, electrically conductive nanostructure film, comprising coating a dispersion or a solution comprising a nanostructure selected from the group consisting of carbon nanotubes, fullerenes, graphene flakes/sheets, nanowires, and two or more thereof on a substrate. The film may also comprise a dopant in the dispersion or solution, as well as an encapsulant or topcoat.

Description

IMPROVED CNT/TOPCOAT PROCESSES FOR MAKING A TRANSPLANT CONDUCTOR

FIELD OF THE INVENTION

[0001] The present invention relates generally to nanostructure films, and more specifically to fabrication methods thereof.

BACKGROUND OF THE INVENTION

[0002] Many modern and/or emerging applications require at least one device electrode that has not only high electrical conductivity, but high optical transparency as well. Such applications include, but are not limited to, touch screens (e.g., analog, resistive, 4-wire resistive, 5-wire resistive, surface capacitive, projected capacitive, multi-touch, etc.), displays (e.g., flexible, rigid, electro-phoretic, electro-luminescent, electrochromatic, liquid crystal (LCD), plasma (PDP), organic light emitting diode (OLED), etc.), solar cells (e.g., silicon (amorphous, protocrystalline, nanocrystalline), cadmium telluride (CdTe), copper indium gallium selenide (CIGS), copper indium selenide (CIS), gallium arsenide (GaAs), light absorbing dyes, quantum dots, organic semiconductors (e.g., polymers, small-molecule compounds)), solid state lighting, fiber-optic communications (e.g., electro-optic and opto- electric modulators) and microfluidics (e.g., electrowetting on dielectric (EWOD)).

[0003] As used herein, a layer of material or a sequence of several layers of different materials is said to be "transparent" when the layer or layers permit at least 50% of the ambient electromagnetic radiation in relevant wavelengths to be transmitted through the layer or layers. Similarly, layers which permit some but less than 50% transmission of ambient electromagnetic radiation in relevant wavelengths are said to be "semi-transparent."

[0004] Currently, the most common transparent electrodes are transparent conducting oxides (TCOs), specifically indium-tin-oxide (ITO) on glass. However, ITO can be an inadequate solution for many of the above-mentioned applications (e.g., due to its relatively brittle nature, correspondingly inferior flexibility and abrasion resistance), and the indium component of ITO is rapidly becoming a scarce commodity. Additionally, ITO deposition usually requires expensive, high-temperature sputtering, which can be incompatible with many device process flows. Hence, more robust, abundant and easily-deposited transparent conductor materials are being explored.

SUMMARY OF THE INVENTION

[0005] The present invention describes nanostructure films. Nanostructures have attracted a great deal of recent attention due to their exceptional material properties. Nanostructures may include, but are not limited to, nanotubes (e.g., single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs), double-walled carbon nanotubes (DWNTs), few-walled carbon nanotubes (FWNTs)), other fullerenes (e.g., buckyballs), graphene flakes/sheets, and/or nanowires (e.g., metallic (e.g., Ag, Ni, Pt, Au), semiconducting (e.g., InP, Si, GaN), dielectric (e.g., SiO₂₅TiO₂), organic, inorganic). Nanostructure films may comprise at least one interconnected network of such nanostructures, and may similarly exhibit exceptional material properties. For example, nanostructure films comprising at least one interconnected network of substantially carbon nanotubes (CNTs) (e.g., wherein nanostructure density is above a percolation threshold) can exhibit extraordinary strength and electrical conductivity, as well as efficient heat conduction and substantial optical transparency. As used herein, "substantially" shall mean that at least 40% of components are of a given type.

[0006] In one embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a series of coating, drying, washing and baking stations. In one embodiment, a substrate may be passed through a cleaning/drying station, coated with a CNT dispersion, dried, washed, dried again, coated with an encapsulant/topcoat (e.g., slot die-coated cross-linked polymer) and then baked. In another embodiment, the wash and second drying steps may be removed to reduce TACT time and equipment costs (i.e., such that the dried CNT coating is coated with the encapsulant/topcoat without intermediate wash and drying steps). In another and/or further embodiment a dual-head slot die configuration (e.g., two-die in a single coater) may be employed to reduce TACT time and equipment costs (e.g., by allowing removal of the separate top-coat station).

[0007] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations. In another embodiment, a substrate may be passed through a cleaning/drying station, coated with mixture of a CNT dispersion and an encapsulant/topcoat (e.g., slot die- coated cross-linked polymer), baked, washed and then dried. In this embodiment a, single- slot die configuration may be employed to reduce TACT time and equipment costs (e.g., by allowing removal of the separate top-coat station and by employing a single-slot head die rather than a dual-head slot die configuration).

[0008] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations, and, in particular, a substrate may be passed through a cleaning/drying station, coated with a mixture of CNTs and a polymer mixed solution (e.g., slot die-coated cross-linked polymer), baked, washed and then dried. In another embodiment, a substrate may be passed through a cleaning/drying station, coated with a mixture of CNTs and a polymer mixed solution (e.g., slot die-coated cross-linked polymer), without one or more of the following steps of baking, washing and drying.

[0009] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations, and, in particular, a substrate may be passed through a cleaning/drying station, coated with a primer layer (e.g. by spray, slot, SAM-dip, etc. methods), coated with a CNT coating (e.g. with a slot die), coated with a top coat, baked, washed and dried. In another embodiment, a substrate may be passed through a cleaning/drying station, a substrate may be passed through a cleaning/drying station, coated with a primer layer (e.g. by spray, slot, SAM-dip, etc. methods), coated with a CNT coating (e.g. with a slot die), coated with a top coat, without one or more of the following steps of baking, washing and drying.

[0010] Other features and advantages of the invention will be apparent from the accompanying drawings and from the detailed description. One or more of the above- disclosed embodiments, in addition to certain alternatives, are provided in further detail below with reference to the attached figures. The invention is not limited to any particular embodiment disclosed; the present invention may be employed in not only transparent conductive film applications, but in other nanostructure applications as well (e.g., nontransparent electrodes, transistors, diodes, conductive composites, electrostatic shielding, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention is better understood from reading the following detailed description of the preferred embodiments, with reference to the accompanying figures in which:

[0012] FIG. IA is a scanning electron microscope (SEM) image of a nanostructure film according to one embodiment of the present invention;

[0013] FIG. IB shows the transmittance and relevant wavelengths of a number of nanostructure films according to one or more embodiments of the present invention; [0014] FIG. 2 is a schematic representation of a nanostructure film fabrication apparatus according to one embodiment of the present invention;

[0015] FIG. 3 is a schematic representation of a nanostructure film fabrication apparatus according to one embodiment of the present invention, wherein a dual head slot die is employed;

[0016] FIG. 4 A is a schematic representation of a nanostructure film coated over a primer/promotion layer, according to one embodiment of the present invention; and

[0017] FIGS. 4B and 5 are schematic representations of nanostructure-fϊlm patterning methods according to embodiments of the present invention.

[0018] Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments of the system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Referring to FIG. 1, a nanostructure film according to one embodiment of the present invention comprises at least one interconnected network of single-walled carbon nanotubes (SWNTs). Such film may additionally or alternatively comprise other nanotubes (e.g., MWNTs, DWNTs), other fullerenes (e.g., buckyballs), graphene flakes/sheets, and/or nanowires (e.g., metallic (e.g., Ag, Ni, Pt, Au), semiconducting (e.g., InP, Si, GaN), dielectric (e.g., SiO₂₅TiO₂), organic, inorganic).

[0020] Such nanostructure film may further comprise at least one functionalization material bonded to the nanostructure film. For example, a dopant bonded to the nanostructure film may increases the electrical conductivity of the film by increasing carrier concentration. Such dopant may comprise at least one of Iodine (I₂), Bromine (Br₂), polymer-supported Bromine (Br₂), Antimonypentafluride (SbF₅), Phosphoruspentachloride (PCl₅), Vanadiumoxytrifluride (VOF₃), Silver(II)Fluoride (AgF₂), 2,l,3-Benzoxadiazole-5- carboxylic acid, 2-(4-Biphenylyl)-5-phenyl-l,3,4-oxadiazole, 2,5-Bis-(4-aminophenyl)-l,3,4- oxadiazole, 2-(4-Bromophenyl)-5-phenyl- 1 ,3,4-oxadiazole, 4-Chloro-7-chlorosulfonyl-2, 1 ,3- benzoxadiazole, 2,5-Diphenyl-l,3,4-oxadiazole, 5-(4-Methoxyphenyl)-l,3,4-oxadiazole-2- thiol, 5-(4-Methylphenyl)-l,3,4-oxadiazole-2-thiol, 5-Phenyl-l,3,4-oxadiazole-2-thiol, 5-(4- Pyridyl)-l,3,4-oxadiazole-2-thiol, Methyl viologen dichloride hydrate, Fullerene-C60, N- Methylfulleropyrrolidine, N,N'-Bis(3 -methylphenyl)-N,N'-diphenylbenzidine, Triethylamine (TEA), Triethanolanime (TEA)-OH, Trioctylamine, Triphenylphosphine, Trioctylphosphine, Triethylphosphine, Trinapthylphosphine, Tetradimethylaminoethene,

Tris(diethylamino)phosphine, Pentacene, Tetracene, N,N'-Di-[(l-naphthyl)-N,N'-diphenyl]- l,r-biphenyl)-4,4'-diamine sublimed grade, 4-(Diphenylamino)benzaldehyde, Di-p- tolylamine, 3-Methyldiphenylamine, Triphenylamine, Tris[4-(diethylamino)phenyl] amine, Tri-p-tolylamine, Acradine Orange base, 3,8-Diamino-6-phenylphenanthridine, A- (Diphenylamino)benzaldehyde diphenylhydrazone, Poly(9-vinylcarbazole), PoIy(I- vinylnaphthalene), Poly(2-vinylpyridine)n-oxide, Triphenylphosphine, A-

Carboxybutyl)triphenylphosphonium bromide, Tetrabutylammonium benzoate, Tetrabutylammonium hydroxide 30-hydrate, Tetrabutylammonium triiodide, Tetrabutylammonium bis-trifluoromethanesulfonimidate, Tetraethylammonium trifluoromethanesulfonate, Oleum (H₂SO₄-SO₃), Triflic acid and/or Magic Acid.

[0021] Such dopant may be bonded covalently or noncovalently to the film. Moreover, the dopant may be bonded directly to the film or indirectly through and/or in conjunction with another molecule, such as a stabilizer that reduces desorption of dopant from the film. The stabilizer may be a relatively weak reducer (electron donor) or oxidizer (electron acceptor), where the dopant is a relatively strong reducer (electron donor) or oxidizer (electron acceptor) (i.e., the dopant has a greater doping potential than the stabilizer). Additionally or alternatively, the stabilizer and dopant may comprise a Lewis base and Lewis acid, respectively, or a Lewis acid and Lewis base, respectively. Exemplary stabilizers include, but are not limited to, aromatic amines, other aromatic compounds, other amines, imines, trizenes, boranes, other boron-containing compounds and polymers of the preceding compounds. Specifically, poly(4-vinylpyridine) and/or tri-phenyl amine have displayed substantial stabilizing behavior in accelerated atmospheric testing (e.g., 1000 hours at 65°C and 90% relative humidity).

[0022] Stabilization of a dopant bonded to a nanostructure film may also or alternatively be enhanced through use of an encapsulant. The stability of a non- functionalized or otherwise functionalized nanostructure film may also be enhanced through use of an encapsulant. Accordingly, yet another embodiment of the present invention comprises a nanostructure film coated with at least one encapsulation layer. This encapsulation layer preferably provides increased stability and environmental (e.g., heat, humidity and/or atmospheric gases) resistance. Multiple encapsulation layers (e.g., having different compositions) may be advantageous in tailoring encapsulant properties. Exemplary encapsulants comprise at least one of a fluoropolymer, acrylic, silane, polyimide and/or polyester encapsulant (e.g., PVDF (Hylar CN, Solvay), Teflon AF, Polyvinyl fluoride (PVF), Polychlorotrifluoroethylene (PCTFE), Polyvinylalkyl vinyl ether, Fluoropolymer dispersion from Dupont (TE 7224), Melamine/Acrylic blends, conformal acrylic coating dispersion, etc.). Encapsulants may additionally or alternatively comprise UV and/or heat cross-linkable polymers (e.g., Poly(4-vinyl-phenol)).

[0023] Electronic performance of a nanostructure film according to one embodiment may additionally or alternatively be enhanced by bonding metal (e.g., gold, silver) nanoparticles to nanotubes (e.g., using electro and/or electroless plating). Such bonding may be performed before, during and/or after the nanotubes have formed an interpenetrated network.

[0024] A nanostructure film according to one embodiment may additionally or alternatively comprise application-specific additives. For example, thin nanotube films can be inherently transparent to infrared radiation, thus it may be advantageous to add an infrared (IR) absorber thereto to change this material property (e.g., for window shielding applications). Exemplary IR absorbers include, but are not limited to, at least one of a cyanine, quinone, metal complex, and photochrome. Similarly, UV absorbers may be employed to limit the nanostructure film's level of direct UV exposure.

[0025] A nanostructure film according to one embodiment may be fabricated using solution-based processes. In such processes, nanostructures may be initially dispersed in a solution with a solvent and dispersion agent. Exemplary solvents include, but are not limited to, deionized (DI) water, alcohols and/or benzo-solvents (e.g., toluene, xylene). Exemplary dispersion agents include, but are not limited to, surfactants (e.g., sodium dodecyl sulfate (SDS), Triton X, behentrimonium chloride (BTAC), stearyl trimethyl ammonium chloride (STAC), distearyldimonium chloride (DSDC), NaDDBS) and biopolymers (e.g., carboxymethylcellulose (CMC)). Dispersion may be further aided by mechanical agitation, such as by cavitation (e.g., using probe and/or bath sonicators), shear (e.g., using a high-shear mixer and/or rotor-stator), impingement (e.g., rotor-stator) and/or homogenization (e.g., using a homogenizer). Coating aids may also be employed in the solution to attain desired coating parameters, e.g., wetting and adhesion to a given substrate; additionally or alternatively, coating aids may be applied to the substrate. Exemplary coating aids include, but are not limited to, aerosol OT, fluorinated surfactants (e.g., Zonyl FS300, FS500, FS62A), alcohols (e.g., hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, saponin, ethanol, propanol, butanol and/or pentanol), aliphatic amines (e.g., primary, secondary (e.g., dodecylamine), tertiary (e.g., triethanolamine), quartinary), TX-100, FT248, Tergitol TMN- 10, Olin 1OG and/or APG325.

[0026] The resulting dispersion may be coated onto a substrate using a variety of coating methods. Coating may entail a single or multiple passes, depending on the dispersion properties, substrate properties and/or desired nanostructure film properties. Exemplary coating methods include, but are not limited to, spray-coating, dip-coating, drop-coating and/or casting, roll-coating, transfer-stamping, slot-die coating, curtain coating, [micro] gravure printing, flexoprinting and/or inkjet printing. Exemplary substrates may be flexible or rigid, and include, but are not limited to, glass, elastomers (e.g., saturated rubbers, unsaturated rubbers, thermoplastic elastomers (TPE), thermoplastic vulcanizates (TPV), polyurethane rubber, polysulfϊde rubber, resilin and/or elastin) and/or plastics (e.g., polymethyl methacrylate (PMMA), polyolefm(s), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyethersulfone (PES) and/or Arton). Flexible substrates may be advantageous in having compatibility with roll-to-roll (a.k.a. reel- to-reel) processing, wherein one roll supports uncoated substrate while another roll supports coated substrate. As compared to a batch process, which handles only one component at a time, a roll-to-roll process represents a dramatic deviation from current manufacturing practices, and can reduce capital equipment and product costs, while significantly increasing throughput. Nanostructure films may be printed first on a flexible substrate, e.g., to take advantage of roll-to-roll capabilities, and subsequently transferred to a rigid substrate (e.g., where the flexible substrate comprises a release liner, laminate and/or other donor substrate or adhesion layer (e.g., A-187, AZ28, XAMA, PVP, CX-100, PU)). Substrate(s) may be pre- treated to improve adhesion of the nanotubes thereto (e.g., by first coating an adhesion layer/promoter onto the substrate). [0027] Once coated onto a substrate, the dispersion may be heated to remove solvent therefrom, such that a nanostructure film is formed on the substrate. Exemplary heating devices include a hot plate, heating rod, heating coil and/or oven. The resulting film may be washed (e.g., with water, ethanol and/or IPA) and/or oxidized (e.g., baked and/or rinsed with an oxidizer such as nitric acid, sulfuric acid and/or hydrochloric acid) to remove residual dispersion agent and/or coating aid therefrom.

[0028] Dopant, other additives and/or encapsulant may further be added to the film. Such materials may be applied to the nanostructures in the film before, during and/or after film formation, and may, depending on the specific material, be applied in gas, solid and/or liquid phase (e.g., gas phase NO₂ or liquid phase nitric acid (HNO3) dopants). Such materials may moreover be applied through controlled techniques, such as the coating techniques enumerated above in the case of liquid phase materials (e.g., slot-die coating a polymer encapsulant).

[0029] A nanostructure film according to one embodiment may be patterned before (e.g., using lift-off methods, pattern-pretreated substrate), during (e.g., patterned transfer printing, screen printing (e.g., using acid-paste as an etchant, with a subsequent water-wash), inkjet printing) and/or after (e.g., using laser ablation or masking/etching techniques) fabrication on a substrate.

[0030] In one exemplary embodiment, an optically transparent and electrically conductive nanostructure film comprising an interconnected network of SWNTs was fabricated on a transparent and flexible plastic substrate via a multi-step spray and wash process. A SWNT dispersion was initially formulated by dissolving commercially-available SWNT powder (e.g., P3 from Carbon Solutions) in DI water with 1% SDS, and probe sonicated for 30 minutes at 300W power. The resulting dispersion was then centrifuged at 10k rcf (relative centrifugal field) for 1 hour, to remove large agglomerations of SWNTs and impurities (e.g., amorphous carbon and/or residual catalyst particles). In parallel, a PC substrate was immersed in a silane solution (a coating aid comprising 1% weight of 3- aminopropyltriethoxysilane in DI water) for approximately five minutes, followed by rinsing with DI water and blow drying with nitrogen. The resulting pre-treated PC substrate (Tekra 0.03" thick with hard coating) was then spray-coated over a 100⁰C hot plate with the previously-prepared SWNT dispersion, immersed in DI water for 1 minute, then sprayed again, and immersed in DI water again. This process of spraying and immersing in water may be repeated multiple times until a desired sheet resistance (e.g., film thickness) is achieved.

[0031] In a related exemplary embodiment, a doped nanostructure film comprising an interconnected network of SWNTs was fabricated on a transparent and flexible substrate using the methods described in the previous example, but with a SWNT dispersion additionally containing a TCNQF₄ dopant. In another related embodiment, this doped nanostructure film was subsequently encapsulated by spin-coating a layer of parylene thereon and baking.

[0032] In another exemplary embodiment, a SWNT dispersion was first prepared by dissolving SWNT powder (e.g., P3 from Carbon Solutions) in DI water with 1% SDS and bath- sonicated for 16 hours at 100 W, then centrifuged at 15000 rcf for 30 minutes such that only the top 3/4 portion of the centrifuged dispersion is selected for further processing. The resulting dispersion was then vacuum filtered through an alumina filter with a pore size of 0.1-0.2 μm (Watman Inc.), such that an optically transparent and electrically conductive SWNT film is formed on the filter. DI water was subsequently vacuum filtered through the film for several minutes to remove SDS. The resulting film was then transferred to a PET substrate by a PDMS (poly-dimethylsiloxane) based transfer printing technique, wherein a patterned PDMS stamp is first placed in conformal contact with the film on the filter such that a patterned film is transferred from the filter to the stamp, and then placed in conformal contact with the PET substrate and heated to 80⁰C such that the patterned film is transferred to the PET. In a related exemplary embodiment, this patterned film may be subsequently doped via immersion in a gaseous NO₂ chamber. In another related exemplary embodiment, the film may be encapsulated by a layer of PMPV, which, in the case of a doped film, can reduce desorption of dopant from the film.

[0033] In yet another exemplary embodiment, an optically transparent, electrically conductive, doped and encapsulated nanostructure film comprising an interconnected network of FWNTs was fabricated on a transparent and flexible substrate. CVD-grown FWNTs (OE grade from Unidym, Inc.) were first dissolved in DI water with 0.5% Triton-X, and probe sonicated for one hour at 300W power. The resulting dispersion was then slot-die coated onto a PET substrate, and baked at about 100⁰C to evaporate the solvent. The Triton- X was subsequently removed from the resulting FWNT film by immersing the film for about 15-20 seconds in nitric acid (10 molar). Nitric acid may be effective as both an oxidizing agent for surfactant removal, and a doping agent as well, improving the sheet resistance of the film from 498 ohms/sq to about 131 ohms/sq at about 75% transparency, and 920 ohms/sq to about 230 ohms/sq at 80% transparency in exemplary films. In related exemplary embodiments, these films were subsequently coated with triphenylamine which stabilized the dopant (i.e., the film exhibited a less than 10% change in conductivity after 1000 hours under accelerated aging conditions (65⁰C)). In other related exemplary embodiments, the films were then encapsulated with Teflon AF.

[0034] In another exemplary embodiment, FWNT powder was initially dispersed in water with SDS (e.g., 1%) surfactant by sonication (e.g., bath sonication for 30 minutes, followed by probe sonication for 30 minutes); 1-dodecanol (e.g., 0.4%) was subsequently added to the dispersion by sonication (e.g., probe sonication for 5 minutes) as a coating aid, and the resulting dispersion was Meyer rod coated onto a PEN substrate. SDS was then removed by rinsing the film with DI water, and the 1-dodecanol was removed by rinsing with ethanol. This resulting optically transparent and electrically conductive film passed an industry-standard "tape test," (i.e., the FWNT film remained on the substrate when a piece of Scotch tape was pressed onto and then peeled off of the film); such adhesion between the FWNT film and PEN was not achieved with SDS dispersions absent use of a coating aid.

[0035] Referring to FIG. 2, an encapsulated nanostructure film according to the present invention may be fabricated using a series of coating, drying, washing and baking stations. In one embodiment, a substrate may be passed through a cleaning/drying station, coated with a CNT dispersion (e.g., as described above), dried, washed, dried again, coated with an encapsulant/topcoat (e.g., slot die-coated cross-linked polymer) and then baked.

[0036] In another embodiment, the wash and second drying steps may be removed to reduce TACT time and equipment costs (i.e., such that the dried CNT coating is coated with the encapsulant/topcoat without intermediate wash and drying steps). This process may be advantageous in coating substrates such as glass or color filter resin, as dried CNT coatings can delaminate from such substrate during wash procedures (e.g., a FWNT film formed by slot die coating and drying a BTAC-dispersed FWNT solution onto a glass substrate delaminated from the substrate when washed lightly with water). While it was previously thought that washing was essential to achieving good optoelectronic properties (i.e., by removing residual surfactant from the film), our experiments have surprisingly shown that omitting the washing step can yield comparable optoelectronic properties.

[0037] Referring to FIG. 3, in another and/or further embodiment a dual-head slot die configuration may be employed to reduce TACT time and equipment costs (e.g., by allowing removal of the separate top-coat station). In this embodiment, drying of the CNT dispersion to form a CNT film may take place during the brief gap between slot die heads. In another embodiment, a dual slot (e.g. two slot nip in a head) may be employed as an alternative to a dual-head slot die.

[0038] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations. In another embodiment, a substrate may be passed through a cleaning/drying station, coated with mixture of a CNT dispersion and an encapsulant/topcoat (e.g., slot die- coated cross-linked polymer), baked, washed and then dried. In this embodiment a, single- slot die configuration may be employed to reduce TACT time and equipment costs (e.g., by allowing removal of the separate top-coat station and by employing a single-slot head die rather than a dual-head slot die configuration). Because this embodiment can be done with one coating step, this embodiment facilitates coating in a cell (mother glass) and patterned coating. Furthermore, this embodiment provides for planarization of the top-coat layer which is photo-definable. In a further embodiment, a photoresist coating can be applied to the CNT coating after drying.

[0039] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations, and, in particular, a substrate may be passed through a cleaning/drying station, coated with a mixture of CNTs and a polymer mixed solution (e.g., slot die-coated cross-linked polymer), baked, washed and then dried. In a further embodiment, a photoresist coating can be applied to the CNT coating after drying. In another embodiment, a substrate may be passed through a cleaning/drying station, coated with a mixture of CNTs and a polymer mixed solution (e.g., slot die-coated cross-linked polymer), without one or more of the following steps of baking, washing and drying. Because these embodiments can be done with one coating step, these embodiments facilitate coating in a cell (mother glass) and patterned coating. [0040] In another embodiment, an encapsulated nanostructure film according to the present invention may be fabricated using a different series of coating, drying, washing and baking stations, and, in particular, a substrate may be passed through a cleaning/drying station, coated with a primer layer (e.g. by spray, slot, SAM-dip, etc. methods), coated with a CNT coating (e.g. with a slot die), coated with a top coat, baked, washed and dried. In a further embodiment, a photoresist coating can be applied to the CNT coating after drying. In another embodiment, a substrate may be passed through a cleaning/drying station, a substrate may be passed through a cleaning/drying station, coated with a primer layer (e.g. by spray, slot, SAM-dip, etc. methods), coated with a CNT coating (e.g. with a slot die), coated with a top coat, without one or more of the following steps of baking, washing and drying. Furthermore, these embodiments provide for planarization of the top-coat layer which is photo-definable.

[0041] In addition to the encapsulant/topcoat, use of surface treatment agents and/or surface activation may further aid CNT film adhesion to the underlying substrate (e.g., HMDS or silane or corona/plasma treatment). In the above embodiments, the encapsulant/topcoat may be a thermosetting polymer (e.g., such that the application of heat creates a cross-linked polymer network) and/or a UV-curable polymer (e.g., such that the application of UV radiation, visible radiation, electron beams and/or other radiation creates a cross-linked polymer network).

[0042] Referring to FIG. 4A, such encapsulant/topcoat materials may additionally or alternatively be deposited as a primer/promotion layer(s), e.g., to allow deposition of CNT films onto high surface energy substrates (e.g., Silicon nitride, glass, antiglare coatings, etc.) on which CNT films would not otherwise adhere well when deposited using certain solution- based deposition methods (including some of those described above). For example, a CNT film that did not otherwise adhere to a glass substrate was shown to pass an industry standard "tape test" when the glass substrate was first coated with a PVP (in Ethanol) primer/promotion layer via spin coating (3000 rpm for 30 seconds).

[0043] Referring to FIG. 4B, such encapsulant/topcoat may similarly be used to pattern nanostructure films. For example, adhesive layers comprising monomers, polymers and/or cross-linked polymers that strongly attract CNTs may be coated and patterned on a substrate, coated with a CNT film, and then washed and/or sonicated such that only portions of the CNT film that are coated over the adhesive layer remain. Exemplary polymer adhesive layers include poly(4-vinylphenol) (PVP), PVDF, poly(vinyl fomral), poly(melamine-co- formaldehyde) methylated, polyimide, COC, polyurethane latex (including sancure 898, 899, 825 and 835) and urethane/acrylic copolymers. Cross-linkers includes Silquest A- 187, CX- 100, MMF, Ethylene glycol diglycidyl ether, Propylene glycol diglycidyl ether, and many others. Monomers include acrylate monomers such as Methyl methacrylate, n-Butyl methacrylate, Hydroxy ethyl methacrylate, and many others. The adhesives can be UV- curable epoxies such as electro-lite 2728, 2900 and Loctite adhesives. The adhesive layer can be generated by, for example, screen printing through a mask, ink-jet printing, photolithography patterning (e.g., patterning photoresist (PR), coating adhesive over the substrates, then lifting off the PR), laser ablation, etc. The adhesive layer may be thin, e.g., in the range of 1-10 nm for adhesion primer/promotion purpose only. The substrates may be, for example, glass or ST 504 without primer coating.

[0044] Referring to FIG. 5, a CNT film may be selectively impregnated with an encapsulant/topcoat, such that unimpregnated portions of the film are removed by sonication, tape and/or mechanical abrasion to produce patterned, encapsulated CNT films.

[0045] It may be possible to remove the encapsulant/topcoat (e.g., organic solvents may be effective in removing non-cross-linked polymers). For example, 0.01-0.5% PVP in PGMEA was mixed with cross-linker Silquest A-187 (the weight of A- 187 is 1-20% of PVP), and 20 umL of the resulting mixture was drop coated onto select portions of an underlying CNT film; the polymer coated CNT film was then baked at 120 C for 10 minutes, and then washed to remove unencapsulated nanotubes.

[0046] The present invention has been described above with reference to preferred features and embodiments. Those skilled in the art will recognize, however, that changes and modifications may be made in these preferred embodiments without departing from the scope of the present invention.

Claims

Claims:

1. A method for making an optically transparent, electrically conductive nanostructure film, comprising: coating a dispersion or a solution comprising a nanostructure selected from the group consisting of carbon nanotubes, fullerenes, graphene flakes/sheets, nanowires, and two or more thereof on a substrate; baking the coating on the substrate; washing the coating on the substrate; and drying the coating on the substrate.

2. The method of claim 1 , wherein the nanostructure is selected from the group consisting of single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs), double-walled carbon nanotubes (DWNTs), few-walled carbon nanotubes (FWNTs), buckyballs, graphene flakes/sheets, metallic nanowires, semiconducting nanowires, dielectric nanowires, organic nanowires, inorganic nanowires, and two or more thereof.

3. The method of claim 1 , wherein the nanostructure film comprises a network of nanostructures.

4. The method of claim 1 , wherein the coating is done in a pattern.

5. The method of claim 4, wherein the coating is patterned before coating the nanostructure film on the substrate by a technique selected from the group consisting of liftoff methods and pattern-pretreated substrate; during coating the nanostructure film on the substrate by a technique selected from the group consisting of patterned transfer printing, screen printing, and inkjet printing; after coating the nanostructure film on the substrate by a technique selected from the group consisting of laser ablation or masking/etching techniques; or two or more of before, during, or after coating.

6. The method of claim 1, further comprising coating a dispersion or a solution comprising an encapsulant on the substrate.

7. The method of claim 6, wherein coating the dispersion or a solution comprising the encapsulant is performed after coating the dispersion or the solution comprising the nanostructure.

8. The method of claim 6, wherein coating the dispersion or a solution comprising the encapsulant is performed before coating the dispersion or the solution comprising the nanostructure.

9. The method of claim 6, wherein the encapsulant is selected from the group consisting of fluoropolymers, polyacrylates, polysilanes, polyimides, polyesters, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), polyvinylalkyl vinyl ether, melamine/acrylic blends, conformal acrylic coating dispersions, UV cross-linkable polymers, heat cross-linkable polymers, poly(4-vinyl-phenol), and mixtures thereof.

10. The method of claim 1, wherein the coating a dispersion or a solution comprising a nanostructure further comprises a dopant or the method further comprises coating a dispersion or a solution comprising the dopant on a substrate.

11. The method of claim 10, wherein the dopant is selected from the group consisting of Iodine (12), Bromine (Br2), polymer-supported Bromine (Br2), Antimonypentafluride (SbF5), Phosphoruspentachloride (PC15), Vanadiumoxytrifluride (VOF3), Silver(II)Fluoride (AgF2), 2,l,3-Benzoxadiazole-5-carboxylic acid, 2-(4- Biphenylyl)-5 -phenyl- 1, 3, 4-oxadiazole, 2,5-Bis-(4-aminophenyl)-l,3,4-oxadiazole, 2-(4- Bromophenyl)-5 -phenyl- 1, 3, 4-oxadiazole, 4-Chloro-7-chlorosulfonyl-2,l,3-benzoxadiazole, 2,5-Diphenyl-l,3,4-oxadiazole, 5-(4-Methoxyphenyl)-l,3,4-oxadiazole-2-thiol, 5-(4- Methylphenyl)-l,3,4-oxadiazole-2-thiol, 5-Phenyl-l,3,4-oxadiazole-2-thiol, 5-(4-Pyridyl)- l,3,4-oxadiazole-2-thiol, Methyl viologen dichloride hydrate, Fullerene-C60, N- Methylfulleropyrrolidine, N,N'-Bis(3 -methylphenyl)-N,N'-diphenylbenzidine, Triethylamine (TEA), Triethanolanime (TEA)-OH, Trioctylamine, Triphenylphosphine, Trioctylphosphine, Triethylphosphine, Trinapthylphosphine, Tetradimethylaminoethene,

Tris(diethylamino)phosphine, Pentacene, Tetracene, N,N'-Di-[(l-naphthyl)-N,N'-diphenyl]- l,r-biphenyl)-4,4'-diamine sublimed grade, 4-(Diphenylamino)benzaldehyde, Di-p- tolylamine, 3-Methyldiphenylamine, Triphenylamine, Tris[4-(diethylamino)phenyl] amine, Tri-p-tolylamine, Acradine Orange base, 3,8-Diamino-6-phenylphenanthridine, 4- (Diphenylamino)benzaldehyde diphenylhydrazone, Poly(9-vinylcarbazole), PoIy(I- vinylnaphthalene), Poly(2-vinylpyridine)n-oxide, Triphenylphosphine, 4-

Carboxybutyl)triphenylphosphonium bromide, Tetrabutylammonium benzoate, Tetrabutylammonium hydroxide 30-hydrate, Tetrabutylammonium triiodide, Tetrabutylammonium bis-trifluoromethanesulfonimidate, Tetraethylammonium trifluoromethanesulfonate, Oleum (H2SO4-SO3), Triflic acid, Magic Acid, and two or more thereof.

12. The method of claim 1, wherein the substrate is selected from the group consisting of glass, elastomers, saturated rubbers, unsaturated rubbers, thermoplastic elastomers (TPE), thermoplastic vulcanizates (TPV), polyurethane rubber, polysulfϊde rubber, resilin, elastin, plastics, polymethyl methacrylate (PMMA), polyolefm(s), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyethersulfone (PES), cyclic olefϊnic polymers, and two or more thereof.

13. The method of claim 1, wherein the substrate is flexible and the coating step is performed using roll-to-roll processing.

14. The method of claim 1 , wherein heating is performed using a hot plate, a heating rod, a heating coil, an oven, or two or more thereof.

15. The method of claim 1 , wherein washing is performed with water, ethanol, isopropyl alcohol, or two or more thereof.

16. The method of claim 1, further comprising rinsing the coated substrate with an oxidizer selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, and two or more thereof.