Off-axis Thermal Properties of Carbon Nanotube Films

Abstract

Theoretical calculations have predicted that individual Single-Walled Carbon Nanotubes (SWNT) have extremely high thermal conductivity (around 6.6 × 10⁴ W/m-K). The feasibility of constructing practical devices using the above mentioned properties, is critically dependent on the ability to synthesize high-thermal-conducting films. Highly conducting films would be of great use as heat sinks for the next generation of integrated chips. Excessive heating is currently a very serious problem in the endeavor for achieving faster and smaller chips. Since it is still not possible to perfectly align SWNT in the macroscopic scale, the thermal properties of the nano-films are therefore expected to have a statistical effect and thus lower than the intrinsic thermal conductivity of a single nanotube. Also the thermal conductivity perpendicular to the tube direction is more significant from a practical point of view. Multi-Walled Carbon Nanotubes (MWNT) were synthesized by Chemical Vapor Deposition (CVD) technique and subsequently characterized. The thin MWNT films were deposited by a solution casting technique over a metallic substrate. The off-axis thermal properties of these nano-films were studied by AC-calorimetry studies. In this method, the sample is heated by an AC source and the measurement of the relaxation rate is used to determine the thermal properties. This technique is well established for studying the thermal properties of complex fluids. Our results are contrasted with other thermal conductivity measurements intrinsic and bulk carbon nanotube samples. We have also measured off-axis thermal properties of nano-films synthesized from more crystalline SWNT samples and have compared this result with that of the MWNT-film. A model to explain the thermal conduction for our system is proposed.