Controlled Deposition and Applied Field Alignment of Single Walled Carbon Nanotubes for CNT Device Fabrication.
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Controlled Deposition and Applied Field Alignment of Single Walled Carbon Nanotubes for CNT Device Fabrication. Jan Smits, Buzz Wincheski†, JoAnne Ingram††, Neal Watkins†, Jeff Jordan† Lockheed Martin Space Operations † NASA Langley Research Center †† Swales Aerospace Hampton VA, 23681
ABSTRACT Carbon nanotubes (CNTs) offer great potential for advanced sensing devices due to their unique electronic transport properties. However, a significant obstacle to the realization of practical CNT devices is the formation of controlled, reliable and reproducible CNT to metallic contacts. In this work, a procedure for the deposition and alignment of CNTs onto metallic electrodes using chemically functionalized lithographic patterns is reported. This method uses photo and electron beam lithography to pattern simple Cr/Au thin film circuits on oxidized Si substrates. The circuits are then re-patterned with a self-assembled monolayer (SAM) of 3aminopropyltriethoxysilane (APTES) to specify desired CNT locations between electrodes. The application of an electric field to the metallic contacts during the deposition of solution suspended single walled CNTs causes alignment of the CNTs in the field direction. This method consistently produces aligned CNTs in the defined locations.
INTRODUCTION Over the past several years, carbon nanotubes have been in the spotlight of materials research due to their remarkable strength and conductive properties [1]. The single walled carbon nanotube (SWNT) is the strongest known material with a Young’s modulus of approximately 1TPa making it an excellent candidate to be the mainstay of next generation structural materials. Also, the SWNT can be either a semiconductor or a metal based on the chirality of the tube while ballistically transporting electrons and maintaining their spin state down the length of the tube [1]. By exploiting these unique electronic transport properties, CNTs offer great potential for use in advanced sensing devices. However, a significant obstacle to the realization of practical CNT devices is reproducible, controlled formation of reliable CNT-to-metallic contacts. CNTs can be immobilized on a surface via electrostatic interactions between the nanotubes and surface-bound moieties. The strength of this interaction greatly depends on the nature of the terminal groups on the substrate. CNTs have previously been shown to adhere strongly to amino-terminated surfaces and weakly to methyl-terminated surfaces [2, 3, 4]. In this work, we report a procedure for the deposition and alignment of CNTs onto metallic electrodes using standard lithographic techniques and chemical surface functionalization as depicted in Figure 1. Photo and electron beam lithography first are used to pattern simple Cr/Au thin film circuits on oxidized Si substrates. The samples are then re-patterned with a selfassembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APTES) to delineate the desired
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CNT locations between electrodes. During the deposition of solution-suspended single walled
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