Thermal Properties of Metal-Coated Vertically Aligned Single-Wall Nanotube Arrays

Owing to their high thermal conductivities, carbon nanotubes (CNTs) are promising for use in advanced thermal interface materials. While there has been much previous research on the properties of isolated CNTs, there are few thermal data for aligned films of single wall nanotubes. Furthermore, such data for nanotube films do not separate volume from interface thermal resistances. This paper uses a thermoreflectance technique to measure the volumetric heat capacity and thermal interface resistance and to place a lower bound on the internal volume resistance of a vertically aligned single wall CNT array capped with an aluminum film and palladium adhesion layer. The total thermal resistance of the structure, including volume and interface contributions, is $12m2KMW−1$⁠. The data show that the top and bottom interfaces of the CNT array strongly reduce its effective vertical thermal conductivity. A low measured value for the effective volumetric heat capacity of the CNT array shows that only a small volume fraction of the CNTs participate in thermal transport by bridging the two interfaces. A thermal model of transport in the array exploits the volumetric heat capacity to extract an individual CNT-metal contact resistance of $10m2K1GW−1$ (based on the annular area $Aa=πdb$⁠), which is equivalent to the volume resistance of $14nm$ of thermal $SiO2$⁠. This work strongly indicates that increasing the fraction of CNT-metal contacts can reduce the total thermal resistance below $1m2KMW−1$⁠.