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Volumn 273, Issue 5274, 1996, Pages 483-487

Crystalline ropes of metallic carbon nanotubes

Author keywords

[No Author keywords available]

Indexed keywords

CARBON; COBALT; GRAPHITE; METAL; NICKEL;

EID: 6444244907     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5274.483     Document Type: Article
Times cited : (5421)

References (39)
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    • note
    • The diffractometer was a sealed Cu tube (wave-length λ = 1.54 Å) operating at 1 kW, with a flat graphite(002) monochromator, a fixed sample angle at grazing incidence, and a linear detector (radius 25 cm) that allowed parallel accumulation of 4096 channels covering 120° in 2θ. We assumed no preferred orientation of the rope crystallites, which was a concern because our flat-plate diffractometer had no provision for rotating the sample during data collection. Two observations convinced us that the rope axes were indeed randomly oriented within the mat: (i) We compared flat-plate profiles collected at several incident angles and found no difference in relative intensities, (ii) We measured a profile from a spinning capillary sample (Debye-Scherrer geometry) and again found relative intensities similar to those from the flat plate, albeit with a poorer signal/noise ratio because of the smaller scattering volume and the additional diffuse scattering from the capillary.
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    • -1 can also be indexed on the triangular lattice.
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    • 5v, symmetry].
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    • A single rope was attached to a sharpened Pt electrode and pulled out from a tangle of the raw SWNT mat material. Under an optical microscope (magnification x800), a current of 0.1 to 1 μA was run along the rope by connection of opposite poles of a stable dc current source to wires leading to the Pt electrode and the mat. The voltage drop along the SWNT rope was then measured between two arc-grown MWNTs mounted on carbon fibers [A. G. Rinzler et al., Science 269, 1550 (1995)] and positioned into contact on the side of the SWNT rope at a measured distance of 5 to 10 μm. The rope was then imaged directly by TEM to determine its diameter.
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    • ∥ reported above and provides further evidence that the ropes within the mat material are continuous for hundreds of micrometers. More-over, the mat measurement yielded a positive temperature derivative dp/dT near 300 K, a definitive sign of metallic behavior. In contrast, a recent measurement of an individual MWNT shows thermally activated conductance (negative dp/dT) [L. Langer et al., Phys. Rev. Lett. 76, 479 (1996)].
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    • ∥ reported above and provides further evidence that the ropes within the mat material are continuous for hundreds of micrometers. More-over, the mat measurement yielded a positive temperature derivative dp/dT near 300 K, a definitive sign of metallic behavior. In contrast, a recent measurement of an individual MWNT shows thermally activated conductance (negative dp/dT) [L. Langer et al., Phys. Rev. Lett. 76, 479 (1996)].
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    • We recently produced SWNTs 0.7 to 3 nm in diameter with preformed Ni-Co metal particles on a fumed alumina support from a CO reactant gas at 1 atm and 1100°C [H. Dai et al., in preparation]. Each of these SWNTs was found to have a metal particle at its tip, with a diameter appropriate to the tube it catalyzed.
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    • note
    • 4 atoms.
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    • note
    • tb = 2.0 eV from local density functional calculations (27). Zero-helicity armchair tubes are those with a = b.
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    • note
    • crit > 600 atoms.
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    • unpublished results
    • Electron diffraction with probe electron beams (diameter 1 to 2 nm) on individual ropes of this laser-oven SWNT material shows that the dominant tubes in these ropes are zero-helicity armchair tubes (J. Cowley, unpublished results).
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    • note
    • Supported by the Office of Naval Research (grant N0014-91-J1794 and order number N00014-95-F-0099), the Air Force Office of Scientific Research (grant F49620-95-0203), the Advanced Technology Program of the State of Texas (grant 003604-047), NSF (grants DMR-95-22251, CHE-93-21297, and PHY-92-24745), the Robert A. Welch Foundation (grant C-0689), the U.S. Department of Energy (grant DEFC02-86ER45254), and CNRS.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.