Increased Graphitization in Electrospun Single Suspended Carbon Nanowires Integrated with Carbon-MEMS and Carbon-NEMS Platforms Swati Sharma, † Ashutosh Sharma,* ,‡ Yoon-Kyoung Cho, † and Marc Madou* ,§ † School of Nano-Bioscience and Chemical Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea ‡ Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208016, U.P., India § Department of Mechanical & Aerospace Engineering, University of California, Irvine, California, United States 92697-3975 ABSTRACT: Single suspended carbon nanowires (CNWs) integrated on carbon-MEMS (CMEMS) structures are fabricated by electrospinning of SU-8 photoresist followed by pyrolysis. These monolithic CNW-CMEMS structures enable fabrication of very high aspect ratio CNWs of predefined length. The CNWs thus fabricated display core- shell structures having a graphitic shell with a glassy carbon core. The electrical conductivity of these CNWs is increased by about 100% compared to glassy carbon as a result of enhanced graphitization. We suggest some tunable fabrication and pyrolysis parameters that may improve graphitization in the resulting CNWs, making them a good replacement for several carbon nanostructure-based devices. KEYWORDS: carbon nanowire, carbon-MEMS, photolithography, electrospinning, graphitization I n the past two decades, carbon has received much attention as a material to possibly compete with silicon for the construction of miniaturized devices such as ICs and micro- and nano-electromechanical systems (MEMS and NEMS). 1-6 Carbon occupies a very special place both in nature and technology because of the widely different structures and properties of its various forms. 7-9 Glassy carbon electrodes offer a wide electrochemical stability window, low-background currents, and low cost. 1,10,11 Graphitic and hard carbons in battery applications are well suited because of their reversible Li intercalation/deintercalation capacity. 12 Further, carbon nano- tubes (CNTs), graphene and carbons with higher graphitic content are of tremendous current interest in both fundamental research and for nanoelectronics applications. 13-17 Here we introduce CMEMS and CNEMS platforms as a means of fabrication, positioning, and integration of single suspended carbon nanowires (CNWs) with good and reproducible ohmic contacts. The main challenges in the fabrication of single CNW or CNT based devices are their positioning and integration with the underlying platforms and in establishing a reliable ohmic contact. In most cases, the nanowires are first synthesized and isolated, and then carefully nanopositioned and integrated, e.g., by placing on a flat substrate followed by deposition of metal electrodes over their ends. 18-20 These are cumbersome and low-throughput techniques that are not suitable for manufactur- ing of solid-state devices. Also, the contact resistance varies from sample to sample and the contact with the substrate can interfere with the properties of the nanowires. Here we present a simple and scalable fabrication technique for positioning and integration of suspended CNWs with good ohmic contacts. This technique enables fabrication of single, well separated CNWs that are pulled in tension on the CMEMS, and isolation of a single CNW from bulk is not required. This is achieved by electrospining of polymer nanowires on an underlying polymeric MEMS platform fixed on a rotating drum, followed by pyrolysis of the suspended nanowires plus their platform to produce a carbon monolith. The current technique enables the fabrication of CNWs of predefined lengths at preselected locations of interest, which are difficult to achieve with other methods. Further, we show that this method produces CNWs of higher graphitic content and electrical conductivity than glassy carbon and the extent of graphitization can be tuned by controlling the fabrication parameters. It is known that in the pyrolysis process, polymer precursors retain their original morphology and chain configurations. 21 Therefore, it is extremely important to first obtain polymer nanofibers with maximized chain disentanglements in order to get more graphitic resulting CNWs. Tangled polymer chains yield glassy carbons that cannot be reverted back to graphite even at very high temperatures, 21-23 because it is not possible to unwind the polymer chains once converted to carbon. The parameters that may influence the extent of disen- tanglement of polymer chains, and in turn, the extent of Received: October 18, 2011 Accepted: January 3, 2012 Published: January 3, 2012 Letter www.acsami.org © 2012 American Chemical Society 34 dx.doi.org/10.1021/am2014376 | ACS Appl. Mater. Interfaces 2012, 4, 34-39