Multiwalled carbon nanotube films as temperature nano-sensors

Most of the basic research on the electrical behavior of CNTs has been carried out on individual or bundle nanotubes. More recently random or oriented CNT networks (CNTN) are emerging as new material for electronic application. We present the fabrication of thick and dense CNTNs, in the form of freestanding films, and the study of their electric resistance as a function of the temperature, from -200 to +150 degrees C. A non-metallic behavior has been observed with a monotonic R(T). A good long-term stability and a behavioral accordance with the temperature measured Si or Pt thermistor are demonstrated. We underline that a transition from nonmetallic to metallic can take place at few degrees below 0 degrees C. A model involving regions of highly anisotropic metallic conduction separated by tunneling barrier regions can explain the non-metallic to metallic crossover, based on the competing mechanisms of the metallic resistance rise and the barrier resistance lowering.