Morphology and electronic properties of carbon nanotubes grown with Fe catalyst
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P. Byszewski Institute of Physics, PAS, al. Lotników 321/46, 02-668 Warsaw, Poland
P. Kowalczyk Department of Solid State Physics, University of Ło´dz´, ul. Pomorska 149/153, 90-236 Ło´dz´, Poland
K. Antonova Institute of Solid State Physics, BAS, blvd. Tzarigradsko chaussee 72, 1784 Sofia, Bulgaria
R. Diduszko Industrial Institute of Electronics, ul. Długa 44/50, 00-241 Warsaw, Poland
H. Lange Department of Chemistry, Warsaw University, ul. Pasteuro 1, 02-093 Warsaw, Poland
P. Dłuz˙ewski Institute of Physics, PAS, al. Lotników 32146, 02-668 Warsaw, Poland (Received 17 February 2003; accepted 16 July 2003)
We describe the synthesis and characterization of aligned carbon nanotubes deposited on quartz substrates by pyrolysis of a xylene–ferrocene mixture at 700 °C at atmospheric pressure. For microscopic characterization of the pyrolyzed products, scanning and transmission electron microscopies and scanning tunneling microcopy were used, and properties of bulk samples were characterized by Raman spectroscopy and x-ray powder diffraction methods. The nanotubes have topological defects and many contain metal particles. Scanning tunneling spectroscopy proved that the nanotubes had a metallic electrical conductivity with resonant states near the Fermi energy. The states are ascribed to the dangling bonds originating from the defects.
I. INTRODUCTION
Carbon nanotubes (CNTs) have been the subject of intense research since their discovery in 1991.1 There are two kinds of carbon nanotubes: multiwalled nanotubes (MWNTs) composed of from two to many graphene sheets with outer diameters from 10 to approximately 100 nm and single-walled nanotubes (SWNTs) with diameters in the range of 1 nm and made of a single graphene sheet. SWNTs exhibit unique physical properties; they are semiconducting or metallic depending on their geometric parameters and sizes.2,3 Individual SWNTs have been used as scanning probes in atomic force microscopes4 and as quantum wires.5 Ensembles of SWNTs or MWNTs have been used as chemical sensors of small concentrations of toxic gases,6 electron emitters,7 and templates for growth of inorganic oxide nanotubes,8 a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 10, Oct 2003
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and MWNTs have been used as nanotweezers9 for nanoscale manipulation and integration nanostructures. Other proposed applications of carbon nanotubes include storage of hydrogen.10 Practical applications of tubes in different fields require new methods of large-scale production and precise control of their diameters, helicity, and number of topological defects playing the crucial role in their electrical and mechanical properties. For these purposes, chemical vapor deposition (CVD) as a synthesis process seems to be useful.11–21 The size of active particles influences the diameter of growing nanotubes;12 therefore, well aligned matrices of carbon nanotubes can be prepared by the CVD method on various patterned substrates,
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