Carrier transport and electron field-emission properties of a nonaligned carbon nanotube thick film mixed with conductive epoxy

Abstract

We have studied the conduction characteristics of multiwalled carbon nanotubes (MWNTs), which were screen printed in a thick film form for field-emission displays. Resistivity and magnetoresistance were measured as a function of temperature T in the range of 1.7–390 K and magnetic field, respectively. The resistivity of the MWNTs for temperatures of 10–390 K indicates that the system is intrinsically metallic and the resistivity–temperature characteristics are well described by the Mott’s T−1/4 law in temperatures above 10 K, suggesting that the density of states at the Fermi level is constant in the range of 10–100 K. We found that the main contribution to the conductivity comes from carriers that hop directly between localized states via variable-range hopping. The temperature dependence above 10 K is in good agreement with that of an individual multiwalled carbon nanotube. However, below 10 K the resistivity is well fit to Efros T−1/2 law, confirming the presence of a Coulomb gap for the system. With the decrease of temperature below 10 K the charge carriers in the system are localized by strong disorder, bringing a nearly insulating state. The thick-film form for large-area display resulted in a highly bright light as well as a very low turn-on field just like individual multiwalled nanotubes at room temperature. Also, the electron field-emission characteristics followed typical Fowler–Nordheim conduction under high electric field.