Raman spectroscopy and conductivity measurements on polymer-multiwalled carbon nanotubes composites
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Bernd Lahr and Werner Blau Department of Physics, Trinity College, Dublin 2, Ireland
Serge Lefranta) and Olivier Chauvet Laboratoire de Physique Cristalline, Institut des Mate´riaux Jean Rouxel, BP 32229, 44322 Nantes cedex 3, France (Received 5 February 2001; accepted 19 November 2001)
Thin films of poly(methyl methacrylate)–multiwalled nanotubes composites were produced by spin coating using different nanotube concentrations. The materials were characterized by scanning electron microscopy, energy-dispersive x-ray analysis, and Raman spectroscopy to obtain information on the possible interactions between the constituents and to control the homogeneity of the films. Electrical conductivity measurements of the composites, as a function of the nanotube concentration, show a percolation threshold at very low concentration. Also, the J–E characteristics exhibits a nonlinear behavior at low concentration, becoming linear far above the threshold.
I. INTRODUCTION
Carbon nanotubes belong to a new form of carbon with unique electrical properties. Depending on chirality and diameter, single-walled nanotubes (SWNTs) are expected to be metallic or semiconducting. Wildoer et al.1 and Odom et al.2 confirmed these predictions by measuring the conductivity of individual nanotubes by using a scanning tunneling microscope. Nanotubes are attractive materials for potential applications as field-emission electron sources,3–6 field effect transistors,7 etc. Composites based on polymers and nanotubes appear also promising in electronic devices as recently demonstrated with a poly(phenylene vinylene) conjugated polymer/ nanotubes system.8,9 The conductivity of these composites increases as a function of the nanotube concentration by many others of magnitude.9 More recently, singlewalled nanotubes were blended with poly(methyl methacrylate), a nonconjugated polymer,10 with the purpose of obtaining flexible and good conductive films which can be of interest as buffer layers in electronics, acting as impedance adaptors. In this work, we have extended our studies and investigated composites using multiwalled nanotubes (MWNTs) and poly(methyl methacrylate) as the nonconjugated polymer. First, we studied the homogeneity of
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J. Mater. Res., Vol. 17, No. 2, Feb 2002 Downloaded: 02 Mar 2015
the films by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). Second, Raman spectroscopy was used to characterize the composites and to examine the possible interactions between the two constituents. We studied also the electrical properties of the composite films by measurements of their conductivity as a function of the nanotube concentration, as well as the current–voltage characteristics in the whole range −100 to 100 V, limited to −5 to 5 V at high concentration.
II. EXPERIMENTAL DETAILS
MWNTs produced by the electric arc method9 and poly(methyl methacrylate) (PMMA) were mixed together in toluene with
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