Conduction electron resonance and transport properties of a nonaligned carbon nanotube thick film for field emission display

We present electron spin resonance spectra and the electronic transport characteristics of multiwalled carbon nanotubes (CNTs) which were screen printed in a thick-film form for field emission displays. Electron spin resonance spectra showed a Dysonian line due to conduction electrons, and the reduced temperature dependence of the g-value indicates the metallic properties of CNTs. Zero-field resistivity and magnetoresistance were measured as a function of temperature T in the range 1.7-390 K and magnetic field, respectively. The resistivity of nanotubes for temperatures of 10-390 K indicates that the system is intrinsically metallic and the characteristics are well described by Mott's T^-1/4 law in temperatures above 10 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 CNT. 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 a decrease of the temperature below 10 K the charge carriers in the system are localized by strong disorder, bringing a nearly insulating state. Using a diode configuration, we measured the field electron emission characteristics and found that the CNT thick film appears to emit electrons with a density of 80 μA/cm², accompanying highly bright light emission. The emission current-voltage characteristics can be fitted to a straight line in agreement with the Fowler-Nordheim equation, which confirms that the emission current resulted from field emission of the CNT thick film.