No.10 - June 2006
ANATOMY OF A PATENTING AREA: Deposition of carbon nanotubes
Based on the NanoSPRINT Encyclopedia of Carbon Nanotubes
This class of manipulation methods concerns the transfer of a solid coating of pure nanotubes on a pre-existing substrate. This class of manipulation techniques is required for applying thin-films of carbon nanotubes on substrates that cannot withstand high temperatures and do not allow direct grow methods. In addition, various devices can benefit from deposition techniques, without the need of dismantling them.
Thin films of pure carbon nanotubes have a broad range of applications. Nanotube coatings improve the heat transfer at interfaces between various substrates or might be employed in electromagnetic shielding applications. Several deposition methods allow the fabrication of transparent and yet conductive thin-films of nanotubes. Deposition is also required for obtaining field-emission coatings on cold cathodes or for large area patterns of nanotubes in nanoelectronic devices or sensors.
The early years (2000-2003)
In 2000, Liming Dai and Shaoming Huang patented "Multilayer carbon nanotube films" (CA2370022, applicant: Australian Commonwealth Scientific and Industrial Research Organization). Among other processes and methods, the invention addressed a process for the deposition of a substrate-free carbon nanotube film onto another nanotube film, or onto other materials, such as metals, semiconductors and polymers. Three years later, in 2003, both inventors protected a similar patent with an identical name (ZA200108303, applicant: Australian Commonwealth Scientific and Industrial Research Organization).
The list of patents regarding carbon nanotubes deposition continued with "Analysis of isolated and purified single walled carbon nanotube structures" (US2003012951). In their application form, Pavel Nikolaev, Mark Clarke and Sivaram Arepalli provided a method for depositing single-walled carbon nanotube structures dispersed in aqueous solutions on a suitable substrate and forming an array of isolated structures that were substantially free of contaminating material. Then Young Hee Lee, Jae Eun Yoo and Gye Hyeok Ahn were granted protection for a "Method for fabricating carbon nanotube thin film" (KR2003011398, applicant: Iljin Nanotech Inc.). In "Manufacturing method for an electron-emitting source of triode structure" (US2003049875), Chang Yu-Yang, Sheu Jyh-Rong, Lee Cheng-Chung, Cheng Hua-Chi and Ho Jia-Chong proposed a technique for depositing carbon nanotubes over a large area in the gate hole of the said triode structure.
Yahachi Saito and Takeshi Nishiyama patented a "Method for forming carbon nanotube film" (JP2003081618, applicant: Noritake Itron Corp) via ultrasonically dispersing a carbon nanotube into ethanol and spraying it on a substrate, which is subsequently heated in a vacuum. In "Optical element and method for manufacturing the same" (JP2003121892, applicant: National Institute of Advanced Industrial Science and Technology, Fuji Xerox Co Ltd), Kataura Hiromichi, Tokumoto Madoka, Sakakibara Yoichi, Tatsuura Satoshi and Achinami Hirotsugu also employed spray-coating of a nanotube dispersion.
In "Carbon Nanotube Coated Anode" (WO03043046, applicant: US Air Force), Donald Shiffler Jr. and Michael Haworth pyro-bonded the nanotube coating onto a carbonizable resin by heating the anode in several steps. Paul Glatkowski proposed other "Coatings comprising carbon nanotubes and methods for forming same" (US2003122111), for forming films with improved conductivity and transparency. In the same respect, Nakayama Yoshikazu, Shiozaki Hideki, Fujita Daisuke and Inazumi Chikashi patented an "Electrically Conductive Material Comprising Carbon Nanotubes And Process For Producing Same" (CA2477277, applicant: Hitachi Shipbuilding Eng Co). In this case deposition occurred by pressing carbon nanotubes against a heated conductive film.
The "Method of manufacturing carbon nanotube field emitter by electrophoretic deposition" (US6616497, applicant: Samsung Sdi Co Ltd) patented by Chung Deuk-Seok, Choi Won-Bong, Kim Hoon-Young and Kang Jung-Ho is rather self-explanatory, regarding its preferred approach. Toshiyuki Tsuboi also employed solution drying in his "Filming method of carbon nanotube and the field emission source using the film" (US6616495, Futaba Denshi Kogyo. Someya Masao and Fujii Takashi suggested depositing metal particles on the surface of an aligned carbon nanotube film grown on a substrate surface while fixing a low melting point metal film on a fixing substrate. Heating and bringing both films into contact allowed transferring the nanotube film to the fixing substrate. Another "Method For Transferring Aligned Carbon Nanotube Film" was patented in the same year by Mitsubishi Gas Chemical Co. (JP2003286017).
Then Yan Mei Wang and Alex Zettl came out with a completely new approach in "Controlled deposition of nanotubes" (US2003190278). They deposited single suspended carbon nanotubes at predetermined locations on a device pre-patterned with narrow trenches. Zhang Yafei, Guo Yinzhong and Xu Dong used a different kind of surface patterning, by transferring carbon nanotubes onto hydrophilic or hydrophobic substrates - "The control method of arranging carbon nanotubes selectively orientationally on the surface of a substrate" (WO03086968, applicant: Shang Hai Jiao Tong University - China).
2004 and after
Year 2004 started with an ingenious "Target vapor deposition method of nanotube, and electronic part" (JP2004042253, applicant: Infineon Technologies AG). Maik Liebau Duesberg and Eugen Unger employed a capillary of a range not more than a micrometer or a nanometer in order to diffuse a nanotube dispersing liquid over a certain surface. In "Enhanced field emission from carbon nanotubes mixed with particles" (WO2004034417, applicant: Nano Proprietary Inc.), Dongsheng Mao, Richard Fink and Zvi Yaniv presented their own method of depositing a layer of nanotubes and particles onto a substrate, while controlling the nanotubes density.
In a "Method for depositing and patterning carbon nanotubes using chemical self-assembly process" (EP1455007, applicant: Samsung Electronics Co Ltd), Park Jong Jin, Jung Myung Sup, Koo Bon Won, Jung Sung Ouk and Seo Seung Joo disclosed a method for forming a pattern of carbon nanotubes on a surface-treated substrate. The method used a photolithographic process, and carbon nanotubes were thereon laminated using a chemical self-assembly process.
Jeffrey Jordan, Joanne Ingram, Jan Smits, Russell Wincheski and Anthony Neal Watkins proposed later on a technique for "Controlled deposition and alignment of carbon nanotubes" (US2004228961, applicant: US Administration of the National Aeronautics). Herein, a carbon nanotube-attracting material was deposited in the gap region between two electrodes on a substrate. Nanotubes in a solution oriented themselves according to the electric potential applied to the electrodes, adhering to the nanotube-attracting material.
At the beginning of this year, Shimizu Masaaki, Yoshizawa Hisae and Horiuchi Kazunaga were granted a patent for "Carbon nanotube structures, carbon nanotube devices using the same and method for manufacturing carbon nanotube structures" (US2006062924, Fuji Xerox Co Ltd.), which employed a solution-processing technique of a high-viscosity solution of carbon nanotubes having electrical and/or magnetic connections. Recently, Pulickel Ajayan, Bingqing Wei , Alvaro Carrillo, Nirupama Chakrapani and Ravindra Kane presented a "Carbon nanotube foam and method of making and using thereof" (US2006073089, applicant: Rensselaer Polytechnic Institute). Their method consisted of wetting a nanotube array with a liquid, and evaporating the liquid to form specific patterns in the carbon nanotube array.
