Ultrafast Laser Alignment and Processing of Carbon Nanotube Films
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Ultrafast Laser Alignment and Processing of Carbon Nanotube Films Ryan D. Murphy1, Michael J. Abere2, Huanan Zhang3, Haiping Sun2, Ben Torralva2, John F. Mansfield2, Nick Kotov3, and Steven M. Yalisove2 1 Applied Physics Program, University of Michigan, 2477 Randall Laboratory, Ann Arbor, MI 48109, U.S.A. 2 Department of Materials Science and Engineering, University of Michigan, 2300 Hayward St., Ann Arbor, MI 48109, U.S.A. 3 Department of Chemical Engineering, University of Michigan, 2300 Hayward St., Ann Arbor, MI 48109, U.S.A. ABSTRACT Organized nanostructures are formed after irradiation of layers of randomly aligned single-wall carbon nanotube (SWNT)-polymer composites by a Ti:Sapphire 775 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into long, parallel structures of SWNT’s. These structures have been created on both glass substrates and carbon grids. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) investigation of the structures reveal that they are composed of bundled nanotubes typically 400 nm – 1 micron long. Largearea laser patterning of the film allows for structuring of the film without detrimental decreases in conductivity. INTRODUCTION Layer-by-layer (LBL) assembly of nanotube-polymer composites allows for greater utilization of the unique mechanical properties of nanotubes on the macroscale while preserving the homogeneity and high degree of dispersion of SWNT’s [1,2]. By depositing alternating layers of a SWNT-polymer dispersion and a neutral polymer layer the resulting structure is a conductive network of mixed metallic and semiconducting SWNT’s lying in a 2-D plane. Groups using CNT films as conductors in organic photovoltaics (OPV) [3,4] suggest network optimization of CNT’s by controlling parameters such as contact resistance [5] can improve the performance of these devices. Currently directed alignment of nanotube-polymer composites using LBL is possible during growth [6], while laser processing has the potential to optimize these conductive networks after deposition. The intense electric fields of ultrafast lasers present a unique opportunity for further structuring and alignment of these materials while preserving their molecular structure and conductive properties by taking advantage of the short-lived pulses. Laser processing of CNT films opens the door for roll-to-roll processing of films after growth and deposition, obviating the need to alter current growth technologies to accommodate additional processing such as alignment. In this paper we present initial studies of the interaction of ultrafast pulses with CNT films and report on their resulting morphologies.
EXPERIMENT Purified HiPco SWNT’s, with lengths of ~1 μm and widths ~ 1nm, were purchased from Carbon Nanotechnologies Incorporated (CNI) and were dispersed in a 0.2 wt% poly(sodium 4styrene-sulfonate) (PSS) solution with 2 hours of sonication. Further details of the solution preparation ca
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