Exploring stress-grown carbon nanotubes in the optical regime
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Exploring stress-grown carbon nanotubes in the optical regime Michael S. Lowry1 1
Naval Surface Warfare Center – Dahlgren Division, Dahlgren, VA, 22448, U.S.A.
ABSTRACT Carbon nanotube arrays were grown in the presence of an applied mechanical stress (30 min, 60 mN/mm2 mechanical pressure) and dispersed in aqueous solution (0.08 - 2.3 mm2/mL). Optical (450-950 nm) transmission and right angle scattering measurements were performed on these dispersions and on an analogous set of conventional (non-stressed) carbon nanotubes. Results show similar transmission behavior and different right angle scattering dependence on concentration for stress-grown and conventional carbon nanotubes. This investigation provides the first evidence of differentiation between stress-grown and conventional carbon nanotubes in the optical regime, suggesting a point of departure for future applications. INTRODUCTION Stress-grown carbon nanotubes (SG-CNTs) are carbon-based nanomaterials that formed in the presence of an external stressor. The stressor creates a unique thermodynamic environment during molecular development and has been shown to manifest itself in the structure and symmetry of the resulting material.[1,2] Conventional (non-stressed) carbon nanotubes (CNTs) have been shown to have appealing optical, mechanical and chemical properties, and are being pursued as additives in composite materials to support a broad range of technologies including sensors and electronic systems.[3-6] SG-CNTs have not been previously explored as active components in optical mixtures or composite materials, but their similarities to (and differences from) conventional CNTs merit consideration in this area. The emphasis of the present work was on examining the interaction of SG-CNTs with electromagnetic radiation in the optical regime and comparing against conventional CNTs towards an understanding of future utility in optical mixtures, hybrid materials and related areas. EXPERIMENTAL DETAILS Vertically aligned carbon nanotube (CNT) arrays and stress-grown vertically aligned carbon nanotube (SG-CNT) arrays were grown via chemical vapor deposition following a standard procedure.[7] Active catalyst was exposed to a reactant gas mixture in a reducing environment at 750 oC for 30 min. The catalyst/growth substrate utilized in this experiment was iron (Fe, 1 nm) / aluminum oxide (Al2O3, 10 nm) / silicon dioxide (SiO2, 500 nm) on silicon (Si). The reactant gas was ethylene. In the case of SG-CNTs, mechanical stress was applied using a tungsten weight (60 mN/mm2).
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A series of dispersions was prepared via probe sonication of CNTs and SG-CNTs in 0.5% (w/w) aqueous sodium dodecylsulfate (SDS) solution. Initial dispersions were prepared by adding CNT and SG-CNT arrays to SDS to achieve an absorbance value of 2.0 at 609 nm
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