WO2005120205A2

WO2005120205A2 - Room temperature deposition of nanotube transistor networks

Info

Publication number: WO2005120205A2
Application number: PCT/US2005/003821
Authority: WO
Inventors: George Gruner; J. Fraser Stoddart; Kelly S. Chichak
Original assignee: The Regents Of The University Of California
Priority date: 2004-02-13
Filing date: 2005-02-07
Publication date: 2005-12-22
Also published as: WO2005120205A3

Abstract

A method for forming networks of nanotubes on a surface. A liquid is provided that includes nanotubes that have been treated with a solubilization agent. The liquid is deposited onto a surface to form a layer of the liquid. The solvent is removed to form a network layer of treated nanotubes. The solubilization agent is then removed to provide the final network of nanotubes. The nanotube networks may be formed as the conducting media (18) between the source electrode (10) and the drain electrode (12) of a bottom-gated transistor and other electronic devices.

Description

ROOM TEMPERATURE DEPOSITION OF NANOTUBE TRANSISTOR NETWORKS

[0001] This invention was made with government support under Grant No. N00014- 00-1-0216, awarded by the United States Office of Naval Research. The government has certain rights in this invention. .

BACKGROUND OF THE INVENTION

1. Field Of the Invention

[0002] The present invention relates generally to nanotube networks and the various methods that may be used to fabricate such networks. More particularly, the present invention is directed to nanotube networks that are suitable for use in electronic applications, such as transistors.

2. Description of Related Art

[0003] While transistors with individual nanotube or nanowire elements as conducting channels have been fabricated, (Bachtold, A.; Hadley, P.; Nakanishi, T.; Dekker, C. Science 2001, 294, 1317-1320, Martel, R.; Schmidt, T.; Shea, H. R; Hertel, T.; Avouris, P. Appl. Phys. Lett. 1998, 73; 24470) these do not have the fabrication consistency that allows large scale production, because of the variability of the nanotubes.

[0004] Mats of nanotubes (a dense set of nanotubes) have been fabricated before, such mats (often called bucky paper) have been used for exploration of the electrical characteristics of nanotubes or for sensors. Sensors with only a few (and ideally with a single) nanotube sensing elements have also been fabricated.

[0005] Current nanotube transistor network depositions are all based on Chemical Vapor Deposition (CVD) methods. See for example Snow, E. S., Novak, J. P., Campbell, P. M. & Park, D. Random networks of carbon nanotubes as an electronic material. Applied Physics Letters 82, 2145-2147 (2003), J-C Gabriel: Large Scale production of Carbon Nanotube Transistors. Mat. Res. Soc. Symp. Proc. Vol. 776, R.J. Chen et al: Noncovalent functionalization of caron nanotubes for highly specific biosensors PNAS 100, 49483 (2003)). Such CVD grown networks have also been transferred to a plastic substrate (K. Bradley, J.P. Gabriel and G. Gruner Flexible nanotube electronics Nano letters 2003.

[0006] The CVD method requires high temperatures (typically 900°C). The high temperatures lead to difficulties in contact deposition. Problems also arise when using CVD for deposition in flexible electronics, such as a platform that involves plastic substrates. In addition there is a substantial cost associated with CVD-type manufacturing processes. At the same time, such CVD-type fabrication methods can be applied to a limited surface area, and therefore cannot support large area device arrays. [0007] There is a need for a deposition method that can be compatible with patterning methods, such as dip pen lithography and other printing techniques.

SUMMARY OF THE INVENTION

[0008] The present invention fulfills the above need by providing simple and efficient methods that are based on the solubilization of nanotubes to form a solution that may be used in solution deposition methods to form a wide variety of nanotube arrays. [0009] The method of the present invention may be used to form networks of nanotubes on surfaces, such as those used in transistor devices. In accordance with the invention, a liquid is provided that includes nanotubes that have been treated with a solubilization agent. The liquid is deposited onto the surface to form a layer of the liquid. The solvent is removed to form a network layer of treated nanotubes. The solubilization agent is then removed to provide the final network of nanotubes. The nanotube networks may be used as the conducting channel between the source electrode and the drain electrode of bottom-gated transistors, liquid-gated transistors and other electronic devices. [00010] The above-described and many other features and attendant advantages of the present invention will become better understood with reference to the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[00011] FIG. 1 is a schematic representation of an exemplary bottom gated transistor wherein the nanotube network that connects the drain electrode and the source electrode is made in accordance with the present invention.

[00012] FIG. 2 is a schematic representation of an exemplary transistor wherein the nanotube network that connects the drain electrode and the source electrode is made in accordance with the present invention and the gate electrode is applied through the liquid.

DETAILED DESCRIPTION OF THE INVENTION

[00013] The geometry that can be fabricated by deposition methods in accordance with the present invention is fundamentally different, and allows device fabrication opportunities that mats do not possess. The devices contain a random array of nanotubes, covering a relatively large surface area, with a specified nanotube density at the surface to provide desired transistor operation. The geometry involves a large number of nanotubes, and therefore leads to statistical averaging. [00014] Several requirements have to be obeyed by such network density: 1. The network has to provide at least one conducting channel between the source and drain electrodes; and 2. A specified nanotube density, must be chosen for full substrate coverage to be achieved.

[00015] It is expected that arrays close to, and on the conducting side of the two- dimensional percolation limit will have appropriate transistor characteristics. Under such circumstances screening effects by the conducting nanotubes are expected to be small, but conduction is still provided by the nanotube network. Note that for even a poorly conducting substrate, a conducting channel can form where part of the current is supported not by the nanotube, but by the substrate.

[00016] The construction of networks using the solution method of the present invention has several advantages. The main advantage is that it is fault tolerant: the destruction of one channel leaves other channels still open. For a dense array, screening of the gate voltage by the conducting nanotubes is important, in a fashion similar to gate voltage screening due to a metal layer deposited on the device. For a rarified array, such screening is not important and the array can serve as the source-to-drain conducting channel. For an array involving both metallic and semiconducting nanotubes, the conductance of the off state (which can be reached by an application of a positive gate voltage) will be dominated by the conductance of the metallic tubes. Assuming the same conductance for metallic and negatively biased semiconducting nanotubes, the ratio of the metallic to semiconducting tubes of 1 to 3 would suggest a modulation (on-off conductance ratio) of three. This can be increased if imperfections lead to nonconducting (or poorly conducting) metallic nanotubes, or if metallic tubes are eliminated through ohmic annealing. Nanotube networks have also been fabricated, and their properties explored. ( Snow, E. S., Novak, J. P., Campbell, P. M. & Park, D. Random networks of carbon nanotubes as an electronic material. Applied Physics Letters 82, 2145-2147 (2003), J-C Gabriel: Large Scale production of Carbon Nanotube Transistors. Mat.Res. Soc. Symp. Proc. Vol. 776, R.J. Chen et a Noncovalent functionalization of caron nanotubes for highly specific biosensors PNAS 100, 49483 (2003)).

[00017] The present invention describes methods that can be used for low temperature (room temperature, but not above 100°C) deposition of nanotube (preferably carbon nanotube) networks with densities appropriate for a transistor operation both in air and in liquid environment. An exemplary transistor for operation in air is shown schematically in FIG. 1. The transistor is a conventional bottom-gated design that includes a source electrode 10, drain electrode 12, dielectric 14, gate 16 and a nanotube network 18 deposited using the method of the present invention. An exemplary measurement arrangement for a liquid-gated transistor is shown schematically in FIG. 2. The arrangement includes a non-conducting substrate 20, source electrode 22, drain electrode 24, a liquid 26 (such as a biological buffer), platinum electrode 28, reference electrode 30, a potentiostat 32 and a nanotube network 32 deposited using the method of the present invention.

[00018] The present invention provides for the deposition of treated nanotubes (nanotubes and solubilization agent) from solution onto pre-fabricated metal interconnects (electrodes) at room temperature (not above 100°C) followed by the removal of the solubilization agents at room temperature (not above 100°C). [00019] The method involves the following steps: 1. Solubilization of treated nanotubes in an appropriate solvent to form a liquid. The treated nanotubes are initially formed by adding an appropriate solubilization agent to the nanotubes; 2. Deposition of the liquid onto the desired surface; 3. Drying the solvent by any solvent removal method that leaves the nanotubes at the surface; and 4. Removing the solubilization agent.

[00020] The surface may be cleaned before and/or after deposition of the nanotube network in accordance with known cleaning techniques. Also, the device may be subjected to conditioning burn-in as is known.

[00021] The nanotubes that are treated with the solubilization agent can be pristine

(non-functionalized) or functionalized nanotubes. By "functionalized" it is meant that the nanotubes are modified by a chemical treatment, such as the attachment of a chemical

(functionalization agent) to the surface of the nanotube. The functionalization agent may be added to the nanotube before, after or at the same time that the solubilization agent is added.

[00022] Exemplary functionalization agents include chemicals that donate electrons or holes, such as those listed as follows: 1. Organic compounds, such as: Tetracyanoquinodimathane (TCNQ) Tetracyanoethylene (TCNE) 2. Polymers with electron acceptor groups, such as: Polyethylene imine 3. Inorganic species, such as: bromine chlorine iodine thionyl chloride sulphur trioxide nitrogen dioxide nitrododium tetrafluoroborate; and nitronium tetrafluoroborate . [00023] An example demonstrating the doping (functionalization) of carbon nanotubes with nitrogen dioxide is as follows:

[00024] To test the effects of chemical doping on the sheet resistance, and thus the transistor operation of the nanotube networks, several nanotube network samples were prepared by sonicating HipCO nanotubes (obtained from Carbon Nanotechnologies Inc.) in chloroform and depositing them on an alumina filter membrane. Two different samples, with the following characteristics were prepared: Sample 1 : 40 ml of 1 mg/L nanotubes in chloroform. Sample 2: 40 ml of 1 mg/L nanotubes in chloroform with 30 mg of NO₂BF₄ (NTFB) added in solution. The NO₂ groups donate holes (hole-dope) to the nanotubes.

[00025] Subsequently silver epoxy was painted on to form 2 straight contact leads and the result was measured as: Sample 1 : 225.7 Ohms with a 32 mm x 7 mm channel, thus the sheet resistance is 1031 Ohms/Sq. Sample 2: 123 Ohms with a 32mm x 7mm channel, 562 Ohms/Sq - sheet resistance. [00026] The only difference between the two samples was the addition of the NTFB functionalization agent before deposition, thus, upon treatment with NTFB, the sheet resistance decreases by about a factor of 2.

[00027] The nanotubes may also be functionalized with light absorbing functionalization agents, such as porphyrine. As an example of the method, carbon nanotubes were incubated in a solution that contains a light absorbing molecule porphyrine. After incubation the nanotube+porphyrine complex was deposited on a substrate and the response to light was measured. A weak response to light was observed for the pristine nanotubes. This effect has been observed before. Upon incubation with porphyrin, the response changes, which leads to a decrease of the resistance, which provides evidence for the effect of the porphyrin molecules leading to direct conversion of light into an electronic signal change. This observation demonstrates that: 1. the nanotube+porphyrine complex can be deposited jointly from the solution; and 2. the complex retained the functionality expected.

[00028] The formation of functionalized nanotubes in solution offers advantages including the full coating of the nanotubes with the functionalization agent and more effective interaction between the nanotubes and the functionalization molecules (agent). [00029] With or without the addition of a functionalization agent, there are two approaches available for solubilizing the nanotubes in accordance with the present invention. It should be noted that the invention is applicable to a wide variety of conducting and non-conducting nanotubes. However, the invention is especially well- suited for depositing single walled carbon nanotubes (SWNT's). The two solubilization routes are classed as either non-covalent or covalent methods. Non-covalent methods include side-wall and end-wall functionalizations with solvents, strong or weak acids, single molecules, surfactants and synthetic or biological polymers. Covalent methods typically involve side-wall and end-wall modifications for the solubilization of SWNTs. The covalent side- wall and end- wall modifications involve the addition of highly reactive organic, inorganic reagents, and synthetic or biological polymers to either defect sites or carboxylate functional groups present along or at the ends of SWNTs. [00030] One non-covalent method involves the attachment of biological polymers as the solubilzation agent. Biological polymers, such as DNA, peptides, and starch, have been shown to effectively wrap helically around SWNTs which solubilizes them in aqueous solutions. For example, such a process has been reduced to practice (United States Provisional application 60/487,071 filed on July 10, 2003, now United States Utility patent application 10/886,082). It is now easy to solubilize and purify carbon nanotubes cheaply, under ambient conditions using readily available starch complexes. See the following references for further details: (a) Nakashima, N.; Okuzono, S.; Murakami, H.; Nakai, T.; Yoshikawa, K. "DNA Dissolves Single- Walled Carbon Nanotubes in Water," Chem. Lett. 2003, 32, 456- 457; (b) Zheng, M.; Jagota, A.; Semke, E. D.; Diner, B. A.; Mclean, R. S.; Lustig, S. R.; Richardson, R. E.; Tassi, N. G. "DNA- Assisted Dispersion and Separation of Carbon Nanotubes," Nature Materials, 2003, 2, 338-342; (c) Wang, S.; Humphreys, E. S.; Chung, S.-Y.; Delduco, D. F.; Lustig, S. R.; Wang, H.; Parker, K. N.; Rizzo, N. W.; Subramoney, S.; Chiang, Y.-M.; Jagota, A. "Peptides with Selective Affinity for Carbon Nanotubes," Nature Materials, 2003, 2, 196-200; (d) Dieckmann, G. R.; Dalton, A. B.; Johnson, P. A.; Razal, J.; Chen, J.; Giordano, G. M.; Monoz, E.; Musselman, I. H.; Baughman, R. H.; Draper, R. K. "Controlled Assembly of Carbon Nanotubes by Designed Amphiphilic Peptide Helicies," J. Am. Chem. Soc. 2003, 125, 1770-1777; (e) Bandyopadhyaya, R.; Nativ-Roth, E.; Regev, O.; Yerushalmi-Rozen, R., "Stabilization of Individual Carbon Nanotubes in Aqueous Solutions," Nano Lett. 2002, 2, 25-28; (f) Kim, O.-H.; Je, J.; Baldwin, J. W.; Kooi, S.; Pehrsson, P. E.; Buckley, L. J. "Solubilization of Single- Walled Carbon Nanotubes by Supramolecular Encapsulation of Helical Amylose," J. Am. Chem. Soc. 2003, 125, 4426-4427; and (g) Star, A.; Steuerman, D. W.; Heath, J. R.; Stoddart, J. F. "Starched Carbon Nanotubes," Angew. Chem. Int. Ed., 2002, 41, 2508. [00031] Another non-covalent method involves the attachment of synthetic polymers as the solubilization agent. Exemplary synthetic polymer solubilization agents include: poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV), poly(para- phenylenevinylene) (PPV), polyphenylethylene (PPE), (polyphenylacetylene) PPA, NAFION, poly(N-vinylcarbazole) (PVK), Polyvinylpyrrolidone (PVP), poly(methylmethacrylate) (PMMA), poly(ethylmetacrylate) (PEMA), poly(vinylidene fluoride) (PVDF), poly(styrene-co-/>-(4-(4'-vinylphenyι)3-oxabutanoi) (PSV), poly(diallyldimethylammonium chloride) (PDMA), polyacrylonitrile (PAN) and derivatives of these polymers.

[00032] Single walled carbon nanotubes have been solubilized, in organic or aqueous solution by associating them robustly with linear and helical polymers. This association is characterized by tight, relatively uniform association of the polymers with the sides of the nanotubes. A general thermodynamic drive for this wrapping consists of disrupting the hydrophobic interface between nanotubes and the surrounding solvent molecules, and of the smooth interaction surface in the bulk solid. These nanotubes can be recovered from their polymeric wrapping by changing their solvent system or by chemical degrading the polymer coats. This solubilization process opens the door to solution chemistry on pristine nanotubes, as well as their introduction into biologically relevant systems. For additional details, see the following references: (a) Curran, S. A.; Ajayan, P. M.; Blau, W. J.; Carroll, D. L.; Coleman, J. N.; Dalton, A. B.; Davey, A. P. Drury, A.; McCarthy, B.; Maier, S.; Strevens, A. "A Composite from Poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) and Carbon Nanotube: A Novel Material for Molecular Optoelectronics," Adv. Mater. 1998, 10, 1091-1093; (b) Coleman, J. N.; Dalton, A. B.; Curran, S.; Rubio, A.; Davey, A. P.; Drury, A.; McCarthy, B.; Lahr, B.; Ajayan, P. M.; Roth, S.; Barklie, R. C; Blau, W. J. "Phase Separation of Carbon Nanotubes and Turbostratic Graphite Using a Functional Organic Polymer," Adv. Mater. 2000, 12, 213-216; (c) O'Connell, M. J.; Boul, P.; Ericson, L. M.; Huffman, C; Wang, Y.; Haroz, E.; Kuper, C; Tour, J.; Ausman, K. D.; Smalley, R. E. "Reversible Water-Solubilization of Single- Walled Carbon Nanotubes by Polymer Wrapping," Chem. Phys. Lett. 2001, 342, 265-271; (d) Wang, J.; Musameh, M.; Lin, Y. "Solubilization of Carbon Nanotubes by Nation toward the Preparation of Amperometric Biosensors," J. Am. Chem. Soc. 2003, 125, 2408-2409; (e) Li, D.; Wang, H.; Zhu, J.; Wang, X.; Lu, L.; Yang, X. "Dispersion of Carbon Nanotubes in Aqueous Solutions Containing Poly(diallyldimethylammonium chloride)," J. Mat. Science Lett. 2003, 22, 253-255; (f) Chen, J.; Lui. H; Weimer, W. A.; Halls, M. D.; Waldeck, D. H; Walker, G. C. "Noncovalent Engineering of Carbon Nanotube Surfaces by Rigid, Functional Conjugated Polymers," J. Am. Chem. Soc. 2003, 125, 9034-9035; (g) Star, A.; Liu, Y.; Grant, K.; Ridvan, L.; Stoddart, J. F.; Steuerman, D. W.; Diehl, M. R., Boukai; A.^"; Heath, J. R. "Noncovalent Side- Wall Functionalization of Single- Walled Carbon Nanotubes," Macromolecules 2003, 36, 553; (h) Star, A.; Stoddart, J.F.; Steuerman, D.W.; Diehl, M.; Boukai, A.; Wong, E.W.; Xang, X.; Chung, S.-W.; Choi, H; Heath, J.R., "Preparation and Properties of Polymer- Wrapped Single- Walled Carbon Nanotubes," Angew. Chem. Int. Ed. 2001, 40, 1721-1725; (i) Star, A.; Stoddart, J. F. "Dispersion and Solubilization of Single- Walled Carbon Nanotubes with a Hyperbranched Polymer," Macromolecules 2002, 35, 7516- 7520; (j) Steuerman, D.W.; Star, A.; Narizzano, R.; Choi, H; Ries, R.S.; Nicolini, C; Stoddart, J.F.; Heath, J.R., "Interactions between Conjugated Polymers and Single- Walled Carbon Nanotubes," J. Phys. Chem. B 2002, 106, 3124-3130; (k) Wu, W.; Li, J.; Liu, L.; Yanga, L.; Guo, Z.-X.; Dai, L.; Zhu, D. "The Photoconductivity of PVK-Carbon Nanotubes," Chem. Phys. Lett. 2002, 364, 196-199; (1) Tang, B. Z.; Xu, H. "Preparation, Alignment, and Optical Properties of Soluble Poly(phenylacetylene)-Wrapped Carbon Nanotube," Macromolecules 1999, 32, 2569-2576; (m) Jin, Z.; Pramoda, K. P.; Goh, S. H; Xu, G. "Poly(vinylidene fluoride)- Assisted Melt-Blending of Multi- Walled Carbon Nanotube/Poly(methyl methacrylate) Composites," Mat. Res. Bull. 2002, 37, 271-278; (n) Seoul, C; Kim, Y.-T.; Baek, C.-K. "Electrospinning of Poly(vinylidene fluoride)/Dimethylformaide Solutions with Carbon Nanotubes," J. Poly. Sci. B. 2003, 41, 1572-1577; (o) Pirlot, C; Willems, I.; Fonseca, A.; Nagy, J. B.; Delhalle, J. "Preparation and Characterization of Carbon Nanotube/Polyacrylonitrile Composites," Adv. Eng. Mater. 2002, 4, 109-114; and (p) Hill, D. E.; Lin, Y.; Rao, A. M.; Allard, L. F.; Sun, Y.-P. "Functionalization of Carbon Nanotubes with Polystyrene," Macromolecules 2002, 35, 9466-9471.

[00033] Another non-covalent solubilization method involves the use of dynamic organic and inorganic polymers as the solubilization agent(s). With respect to organic polymer solubilzation agents, the potential exists to solubilize SWNTs by employing dynamic covalent polymers that closely resemble their covalent PmPV counterparts. Using these protocols, small building blocks can be designed to form oligomers and polymers through the reversible formation of imine bonds that should interact with the curved surfaces of SWNTs. The polymeric product will interact with the SWNTs at different stages of its formation in such a way that these polymers can sense the polydispersity of lengths for the solubilized SWNTs. These polymer-coated SWNTs can be targeted for a range of organic and aqueous solutions by carefully tailoring the substituents on the periphery of each component. Again, the ability to render SWNTs soluble in almost any given solvent or water offers a larger range of deposition methods that can be used for device fabrication.

[00034] With respect to inorganic polymer solubilization agents, the potential exists to solubilize SWNTs by employing dynamic reaction procedures that involve the formation of polymeric, discrete macrocyclic, and closed-shelled complexes constructed from organic ligands (pyridyl, carboxyl and transition metal complexes with or without counterions). These complexes can be functionalized in a manner to provide SWNT solubility in a range of organic and aqueous solutions.

[00035] Another exemplary non-covalent solubilization method involves the attachment of surfactants, such as sodium dodecylsulfate (SDS), Triton-X and polyethylene glycol (PEG). Surfactant molecules or amphiphiles, such as SDS, Triton-X and PEGL have been shown to effectively solubilize SWNTs in aqueous solutions under mild temperatures by simple sonication. The surfactants form uniform tubular micelles around individual and bundled SWNTs that can then be deposited onto any substrate in accordance with the present invention. For additional details, see the following references: (a) O'Connell, M. J.; Bachilo, S. M.; Huffman, C. B.; Moore, V. C; Strano, M. S.; Haroz, E. H; Rialon, K. L.; Boul, P. J.; Noon, W. H; Kittrell, C; Ma, J.; Hauge, R. H; Weisman, R. B.; Smalley, R. E. "Band Gap Fluorescence from Individual Single- Walled Carbon Nanotubes," Science 2002, 297, 593-596; (b) Strano, M. S.; Huffman, C. B.; Moore, V. C; O'Connell, M. J.; Haroz, E. H; Hubbard, J.; Rialon, K.; Kittrell, C; Ramesh, S.; Hauge, R. H; Smalley, R. E. "Reversible, Band-Gap-Selective Protonation of Single- Walled Carbon Nanotubes in Solution," J. Phys. Chem. B 2003, 107, 6979-6985; (c) Bachilo, S. M.; Strano, M. S.; Kittrell, C; Hauge, R. H; Smalley, R. E.; Weisman, R. B. "Structure-Assigned Optical Spectra of Single- Walled Carbon Nanotubes," Science 2002, 298, 2361-2366; (d) Richard, C; Balavoine, F.; Schultz, P.; Ebbesen, T. W.; Mioskowski, C. "Supramolecular Self-Assembly of Lipid Derivatives on Carbon Nanotubes," Science 2003, 300, 775-778; (e) Islam, M. F.; Rojas, E.; Bergey, D. M.; Johnson, A. T.; Yodh, A. G. "High Weight Fraction Surfactant Solubilization of Single- Wall Carbon Nanotubes in Water," Nano Lett. 2003, 3, 269-273; (f) Duesberg, G. S.; Burghard, M.; Muster, J.; Philipp, G.; Roth, S. "Separation of Carbon Nanotubes by Size Exclusion Chromatography," Chem. Commun. 1998, 435-436; (g) Jiang, L.; Gao, L.; Sun, J. "Production of Aqueous Colloidal Dispersions of Carbon Nanotubes," J. Colloid Interface Sci. 2003, 260; (h) Nakashima, N.; Tomonari, Y.; Murakami, H. "Water-Soluble Single- Walled Carbon Nanotubes via Noncovalent Sidewall- Functionalization with a Pyrene- Carrying Ammonium Ion," Chem. Lett. 2002, 638-639; (i) Kang, Y.; Taton, T. A. "Micelle-Encapsulated Carbon Nanotubes: Route to Nanotube Composites," J. Am. Chem. Soc. 2003, 125, 5650-5651; (j) Zhao, W.; Song, C; Pehrsson, P. E. "Water-Soluble and Optically pH- Sensitive Single- Walled Carbon Nanotubes from Surface Modification," J. Am. Chem. Soc. 2002, 124, 12418-12419; and (k) Riggs, J. E.; Walker, D. B.; Carrol, D. L.; Sun, Y.-P. "Optical Limiting Properties of Suspended and Solubilized Carbon Nanotubes," J. Chem. Phys. B 2000, 104, 7071-7076.

[00036] Another non-covalent method for solubilizing nanotubers in accordance with the present invention involves using solvents. The use of a range of solvents and acids has been shown to effectively form stable suspensions of SWNTs under mild temperatures by simple sonication. The solvent molecules form uniform solvent shells around individual and bundled SWNTs, which can then be deposited onto any substrate. The solvent shells are very weakly bound and can be destroyed by changing pH, ionic strengths and temperatures, which can cause the precipitation of SWNTs from solutions. For further details on using solvents as the solubilzation agent, see the following references: (a) Zhang, M.; Yudasaka, M.; Koshio, A.; Iijima, S. "Thermogravimetric Analysis of Single- Walled Carbon Nanotubes Ultrasonicated in Monochlorobenzene," Chem. Phys. Lett. 2002, 364, 420-426; (b) Sun, Y.; Wilson, R.; Schuster, D. I. "High Dissolution and Strong Light Emission of Carbon Nanotubes in Aromatic Amine Solvents," J. Am. Chem. Soc. 2001, 123, 5348-5349; (c) Sreekumar, T. V.; Lui, T.; Kumar, S.; Ericson, L. M.; Hauge, R. H; Smalley, R. E. "Single- Wall Carbon Nanotube Films," Chem. Mater. 2003, 15, 175-178; (d) Bahr, J. L.; Mickelson, E. T.; Bronikowski, M. J.; Smalley, R. E.; Tour, J. M. "Dissolution of Small Diameter Single- Wall Carbon Nanotubes in Organic Solvents," Chem. Commun. 2001, 193-194; (e) Ausman, K. D.; Piner, R.; Lourie, O.; Ruoff, R. S.; Korobov, M. "Organic Solvent Dispersions of Single- Walled Carbon Nanotubes: Toward Solutions of Pristine Nanotubes," J. Phys. Chem. B 2000, 104, 8911-8915; (f) Kang, S.-Z.; Zeng, Q.; Wang, C; Xu, S.; Zhang, H.; Wang, Z.; Wan, L.; Bai, C. "Towards Total Dissolution of Full Length Unmodified Carbon Nanotubes (CNT) and Its Applications to Fabrication of Ultra-Thin CNT Films at the Water/Air Interface," J. Mater. Chem. 2003, 13, 1244-1247; (g) Lefrant, S.; Baltog, I.; Baibarac, M.; Mevellec, J. Y.; Chauvet, O. "SERS Studies on Single-walled Carbon Nanotubes Submitted to Chemical Transformation with Sulfuric Acid," Carbon 2002, 40, 2201-2211; and (h) Bower, C; Kleinhammes, A.; Wu, Y.; Zhou, O. "Intercalation and Partial Exfoliation of Single- Walled Carbon Nanotubes by Nitric Acid," Chem. Phys. Lett. 1998, 288, 481-486.

[00037] A covalent method for solubilizing nanotubes in accordance with the present invention involves the attachment of side-wall and end-wall functional groups. The attachment of different small organic molecules, such as alkyl and aryl amines, alcohols cyclic and acyclic, and carbohydrates to the carboxylic end groups to form esters and amides has led to derivatives that are soluble in some organic solvents. Also, transition metal complexes may be attached to the nanotubes as the solubilization agent. Reactive nitrenes, diazonium salts, azomethine ylides and carbenes have also been used for the direct side- wall modification of the SWNTs extended π framework which has led to their solubilization. Fewer examples exist on the modification of the SWNTs extended π framework using transition metal complexes, which have been shown to provide solubilities in organic solvents. For further details on the use of these side-wall and end- wall functional groups as solubilization agents, see the following references: (a) Chen, J.; Hamon, M. A.; Hu, H; Chen, Y.; Rao, A. M.; Eklund, P. C; Haddon, R. C. "Solution Properties of Single- Walled Carbon Nanotubes," Science 1998, 282, 95-98; (b) Hamon, M. A.; Hui, H; Itkis, H. M. E.; Haddon, R. C. "Ester- Functionalized Soluble Single- Walled Carbon Nanotubes," Appl. Phys. A 2002, 74, 333- 338; (c) Kahn, M. G. C; Banerjee, S.; Wong, S. S. "Solubilization of Oxidized Single- Walled Carbon Nanotubes in Organic and Aqueous Solvents through Organic Derivatization," Nano Lett. 2002, 2, 1215-1218; (d) Hazani, M.; Naaman, R.; Hennrich, F.; Kappes, M. M. "Confocal Fluorescence Imaging of DNA-Functionalized Carbon Nanotubes," Nano Lett. 2003, 3, 153-155; (e) Matsuura, K; Hayashi, K.; Kimizuka, N. "Lectin-mediated Supramolecular Junctions of Galactose-derivatized Single- Walled Carbon Nanotubes," Chem. Lett. 2003, 32, 212-213; (f) Huang, W.; Fernando, S.; Lin, Y.; Zhou, B.; Allard, L. F.; Sun, Y.-P. "Preferential Solubilzation of Smaller Single- Walled Carbon Nanotubes in Sequential Functionalization Reaction," Langmuir 2003, 19, 7084-7088; (g) Banerjee, S.; Wong, S. S. "Structural Characterization, Optical Properties, and Improved Solubility of Carbon Nanotubes Functionalized with Wilkinson's Catalyst," J. Am. Chem. Soc. 2002, 124, 8940-8948; (h) Banerjee, S.; Wong, S. S. "Rational Sidewall Functionalization and Purification of Single- Walled Carbon Nanotubes by Solution-Phase Ozonolysis," J. Phys. Chem. B 2002, 106, 12144-12151; (i) Holzinger, M.; Abraham, J.; Whelan, P.; Graupner, R.; Ley, L; Hennrich, F.; Kappes, M.; Hirsch, A. "Functionalization of Single- Walled Carbon Nanotubes with (R-)Oxycabonyl Nitrenes," J. Am. Chem. Soc. 2003, 125, 8566-8580; (j) Dyke, C. A.; Tour, J. M. "Solvent-Free Functionalization of Carbon Nanotubes," J. Am. Chem. Soc. 2003, 125, 1156-1157; (k) Huang, W.; Fernando, S.; Allard, L. F.; Sun, Y.-P. "Solubilzation of Single- Walled Carbon Nanotubes with Diamine-Terminated Oligomeric Poly(ethylene Glycol) in Different Functionalization Reactions," Nano Lett. 2003, 3, 565-568; (1) Riggs, J. E.; Walker, D. B.; Carrol, D. L.; Sun, Y.-P. "Optical Limiting Properties of Suspended and Solubilized Carbon Nanotubes," J. Chem. Phys. B 2000, 104, 7071-7076; and (m) J. Liu et al, Science 1998, 280, 1253. [00038] Another exemplary covalent method for solubilizing nanotubes in accordance with the present invention involves the use of side- wall / end- wall attached polymers. For example, the direct fluorination of the side-walls of SWNTs has been shown to effectively break apart bundles and ropes affording solubilities in a range of organic solvents. These fluorinated SWNTs have been shown to react with alkyl and aryl lithium reagents, Grignard reagents, alkoxides, hydrazine, diamines, peroxides, and halides providing an additional route towards side-wall functionalized SWNTs previously described in the literature that are soluble in a wider range of solutions. These fluorinated SWNTs can be cut into shorter lengths by high temperature pyrolysis. For further details regarding this solubilization method, see the following references: (a) Stevens, J. L.; Huang, A. Y.; Peng, H; Chiang, I. W.; Khabashesku, V. N.; Margrave, J. L. AgSidewall Amino-Functionalization of Single-Walled Carbon Nanotubes through Fluorination and Subsequent Reactions with Terminal Diamines," Nano Lett. 2003, 3, 331-336; (b) Khabashesku, V. N.; Billips, W. E.; Margrave, J. L. "Fluorination of Single- Wall Carbon Nanotubes and Subsequent Derivatization Reactions," Ace Chem. Res. 2002, 35, 1087-1095; (c) Gu, Z.; Peng, H; Hauge, R. H; Smalley, R. H; Margrave, J. L. "Cutting Single- Wall Carbon Nanotubes Through Fluorination," Nano Lett. 2002, 2, 1009-1013; and (d) Gu, Z.; Peng, H.; Cratty, J.; Hauge, R. H.; Smalley, R. H; Margrave, J. L. "Cutting, Solubilizing and Size-Sorting of Single- Wall Carbon Nanotubes," Nano Lett. 2002, 2, 139-142. Additional references where the method is described in a different context: L. Bahr et al J. Am. Chem. Soc 123,6536 (2002), M. Holzinger et al Angew. Chem. Int. Ed 40,4002 (2001), V. Geporgakilas et al., J. Am. Chem. Soc. 124,760 (2002). [00039] Once the nanotubes have been treated with a suitable solubilization agent (and optionally a functionalization agent), the treated nanotubes are mixed with a suitable solvent to form a liquid that is used for deposition of the nanotubes. Nanotube deposition from the liquid (solution) to the desired surface that has been conditioned and cleaned, can occur in various ways. Examples of suitable deposition methods are as follows: direct deposition from the solution; spin -casting the solution; dip-pen deposition; and printing of the solution to a surface. [00040] These methods are well known in the literature and can be reproduced by artisans familiar with the art. For example, direct deposition involves the application of the solvent with the required nanotube density to a surface and subsequent drying of the deposited material. In case of deposition of patterned material, additional steps may be necessary. Surface contours (troughs, ditches, wells) can be patterned on a surface using standard optical lithography. These contours can be decorated with molecules such that they are more hydrophilic or hydrophobic which will interact with the solubilizing agents so as to direct and control the deposition of SWNT solutions onto these surfaces. With regards to spin-casting, the method involves the use of a spin coater, a device well know in the literature. The rotating platform ensures the uniform distribution of the solution onto the surface. Drying and removal of the solubilization agent leads to the required nanotube network.

[00042] With regards to dip pen lithography for patterned deposition, solutions of SWNTs can be deposited between patterned electrodes on a range of substrates by employing dip-pen lithography. This approach has been shown to be effective at depositing solutes in patterns with precision on the nanometer scale. [00043] With regards to printing, direct printing of the network from a solution to a desired surface is also possible, by using well-established screen printing technologies. [00044] Lamination procedures may also be used where the nanotube network is deposited on the surface and then a second layer of parylene is deposited on top of the nanotube network. Portions of the second layer and the underlying nanotube network may then be removed by peeling off the second layer + nanotube network.

[00045] As a feature of the present invention, the solubilization agent is removed from the treated nanotubes once the liquid has been deposited, the network formed and the solvent removed. The particular procedure for removing the solubilization agent will depend on the particular agent that is used.

[00046] For example, biological polymer solubilization agents can be removed using purely biological methods where the polymer is degraded using enzymes which releases the SWNTs from their polymer coats in the device under biological conditions (standard pH, buffer, and temperatures). The removal of synthetic polymer solubilization agents requires a suitable method that must (i) selectively break the carbon-carbon bonds of the polymer in order to release them from surface of SWNTs networks and (ii) avoid breaking the double-bond networks of SWNTs. Methods may include the treatment with strong acids, strong bases, strong reducing agents, strong oxidizing agents, and ozonolysis.

[00047] For dynamic organic polymer solubilization agents, after solubilzation and deposition, the SWNTs' dynamic organic polymer coat can be removed by treating with mild acids which hydrolyze the imine bonds and cleaves the polymer back down into to its original starting components. Any of the components that remain on the substrate can be removed by washing with a suitable solvent.

[00048] With respect to surfactant solubilization agents, the surfactants form micelles reversibly and can be destroyed by changing pH and temperature which can cause the precipitation of SWNTs from solutions. These surfactant molecules can be removed after deposition by washing with any organic, inorganic, and/or aqueous solutions containing buffers, acids and bases.

[00049] With respect to solvent solubilization agents, the weakly bound solvent shells can be destroyed by changing pH, ionic strength, and temperatures which can cause the precipitation of SWNTs from solutions. These solvent molecules can be removed after deposition by washing with any organic, inorganic, and/or aqueous solutions containing buffers, acids and bases. Residual solvent molecules can be removed after deposition by placing the device in a low-pressure vacuum chamber under relatively mild temperatures. [00050] The removal of small molecule solubilzation agents that are covalently attached to the side-walls and end-walls of the nanotubes can be achieved by high- temperature heating. If the agents are attached as esters or amides these solubilizing agents can be removed using strong acids or bases and hydrogenation. If the solubilizing agents are biological molecules they can be removed by treatment with an appropriate enzyme.

[00051] The removal of polymer solubilization agents covalently attached to the side- walls and end-walls can be achieved by high-temperature heating. If the agents are attached as esters or amides these solubilizing agents can be removed using strong acids or bases and hydrogenation. If the solubilizing agents are biological polymers they can be removed by treatment with an appropriate enzyme.

[00052] An example of the deposition of a nanotube network in accordance with the present invention using the surfactant sodium doceylbenzenesulfonate (NaDDBS) as the solubilization agent is as follows:

[00053] 1.500 mg/L purified Hipco single walled carbon nanotubes in deionized water was obtained from Carbon Nanotechnologies Inc. The nanotubes were treated with sodium doceylbenzenesulfonate NaDDBS to form treated nanotubes that had a ratio of SWNT : NaDDBS by weight as given above. The deionized water solution of treated nanotubes was sonicated for 16 hours at the power of 100W. The upper three-quarters of the supernatant was then carefully removed and the remaining liquid containing the treated nanotubes was used for depositing the network.

[00054] The silicon (Si) substrates on which the liquid was to be deposited were treated with an H2O2:H2SO4 (1:4) solution at 100 °C for 20 minutes, so that the Si surface is hydrophilic.

[00055] The Si substrates were put into a vacuum container with a few drops of silanes inside for 2-10 hours. This silane treatment is preferred because it allows the tubes with surfactant to stick onto the substrates. [00056] The liquid containing the treated carbon nanotubes was then deposited onto the substrate. After 5 minute's incubation at room temperature °C, methanol was dropped onto the substrate to drive away the water and leave the carbon nanotube network on the substrates. The bundles of nanotubes that make up the network have less than about 10 nanotubes per bundle and in some cases have even less than 5 nanotubes per bundle. The deposited network of treated nanotubes was then rinsed with isopropyl alcohol (IP A) in order to remove the solubilization agent and then blown to dry with nitrogen or air.

[00057] Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations and modifications may be made within the scope of the present invention.

Claims

CLAIMSWhat is claimed is:

1. A method for forming a network of nanotubes on a surface, said method comprising the steps of: providing a liquid comprising treated nanotubes that comprise nanotubes and a solubilization agent, said liquid further comprising a sufficient amount of a solvent for said treated nanotubes to provide a suspension of said treated nanotubes in said solvent; providing a surface; depositing said liquid onto said surface to form a layer of liquid on said surface; removing said solvent from said layer of liquid to form a network layer consisting essentially of said treated nanotubes; and removing said solubilization agent from said treated nanotubes in said network layer to form said network of nanotubes on said surface.

2. A method for forming a network of nanotubes on a surface according to claim 1 wherein said nanotubes are single walled carbon nanotubes.

3. A method for forming a network of nanotubes on a surface according to claim 1 wherein said solubilization agent is added to said nanotubes to form said treated nanotubes using a non-covalent solubilization method.

4. A method for forming a network of nanotubes on a surface according to claim 1 wherein said solubilization agent is added to said nanotubes to form said treated nanotubes using a covalent solubilization method.

5. A method for forming a network of nanotubes on a surface according to claim 1 wherein said treated nanotube further comprises a functionalization agent.

6. A method for forming a network of nanotubes on a surface according to claim 2 wherein said treated nanotube further comprises a functionalization agent.

7. A method for forming a network of nanotubes on a surface according to claim 1 wherein said method includes the additional steps of providing a source electrode and a drain electrode on said surface wherein said liquid is deposited onto said surface so as to form said network of nanotubes which extends between said source electrode and said drain electrode.

8. A network of nanotubes located on a surface wherein said network of nanotubes is formed according to the method of claim 1.

9. An electronic device comprising a network of nanotubes according to claim 8, said electronic device further comprising a source electrode and a drain electrode wherein said source and drain electrodes are electrically connected together by said network of nanotubes.

10. A method for making a transistor device that comprises a source electrode and a drain electrode that are located on a surface at spaced locations and electrically connected together by a network of nanotubes, said method comprising the steps of: providing said source electrode and said drain electrode on said surface at said spaced locations; providing a liquid comprising treated nanotubes that comprise nanotubes and a solubilization agent, said liquid further comprising a sufficient amount of a solvent for said treated nanotubes to provide a suspension of said treated nanotubes in said solvent; depositing said liquid onto said surface to form a layer of liquid on said surface between said source electrode and said drain electrode; removing said solvent from said layer of liquid to form a network layer consisting essentially of said treated nanotubes; and removing said solubilization agent from said treated nanotubes in said network layer to form said network of nanotubes that electrically connects said source electrode to said drain electrode.

11. A method for making a transistor device according to claim 10 wherein said nanotubes are single walled carbon nanotubes.

12. A method for making a transistor device according to claim 10 wherein said solubilization agent is added to said nanotubes to form said treated nanotubes using a non-covalent solubilization method.

13. A method for making a transistor device according to claim 10 wherein said solubilization agent is added to said nanotubes to form said treated nanotubes using a covalent solubilization method.

14. A method for making a transistor device according to claim 10 wherein said treated nanotube further comprises a functionalization agent.

15. A method for making a transistor device according to claim 11 wherein said treated nanotube further comprises a functionalization agent.

16. A transistor device made according to the method of claim 10.

17. A transistor device according to claim 16 wherein said transistor device is a bottom-gated transistor.

18. A transistor device according to claim 16 wherein said transistor device is a liquid-gated transistor.

19. A transistor device according to claim 17 wherein said nanotubes consist essentially of single walled carbon nanotubes.

20. A transistor device according to claim 18 wherein said nanotubes consist essentially of single walled carbon nanotubes.