The understanding of the temperature dependence of the electric resistance of carbon nanotubes (CNTs) is a very important feature for the potential utilization as sensing element in temperature nano-sensors. The sensitivity and the time response to sudden temperature changes are crucial for a quality sensor and the CNTs are expected to have a very small time constant and provide an extremely rapid time response. Most of the basic research on the electrical behaviour of CNTs refers to individual or bundle nanotubes, but random or oriented CNT networks (CNTN) are emerging as new material for electronic application. We present the fabrication of thick and dense CNTN freestanding films and the study of their electric resistance as a function of the temperature, from -200 to 150 °C. We found both metallic and non-metallic behaviour, dependent of thickness and density of the film and likely of absorbed gases. In both cases a quite linear behaviour of R(T) has been found and a temperature coefficient of resistance from 0.003 to 0.0007 has been estimated. A good long-term stability and a faster time response (strongly reduced decay time) in comparison to commercial Si sensor has been evidenced. A phenomenological model involving regions of highly anisotropic metallic conduction separated by tunnelling barrier regions can explain the non-metallic to metallic crossover while the temperature is pushed up A further characterization of the local resistance and field emission properties of CNTN has been attempted with a STM/AFM probe.
Journal: TechConnect Briefs
Volume: 1, Nanotechnology 2008: Materials, Fabrication, Particles, and Characterization – Technical Proceedings of the 2008 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: June 1, 2008
Pages: 112 - 115
Industry sector: Advanced Materials & Manufacturing
Topics: Carbon Nano Structures & Devices