Effect of intertube junctions on the thermoelectric power of monodispersed single walled carbon nanotube networks

The thermoelectric power (TEP) of single walled carbon nanotube (SWCNT) thin films in pure metallic SWCNT (m-SWCNT) and pure semiconducting SWCNT (s-SWCNT) networks as well as in m- and s-SWCNT mixtures is investigated. The TEP measured on the pure s-SWCNT film (≈88 μV/K) was found to be almost 7 times higher than that of the m-SWCNTs (≈13 μV/K). Moreover, a quasilinear increase of TEP of the mixed SWCNT networks was observed as the fraction of s-SWCNTs is increased. The experimentally determined relationship between TEP and the fraction of s-SWCNTs in the mixture allows fast and simple quantitative analysis of the s:m ratio in any as-prepared heterogeneous SWCNT network. Furthermore, a semiempirical model analyzing the effect of the intertube junctions is proposed and applied to describe the thermoelectric behavior of the prepared SWCNT networks. The results of calculations match well with the experimental data and clearly demonstrate that the measured TEP of thin SWCNT fi lms is principally controlled by the intertube junctions. The fundamental role of junctions in generating thermoelectric power is not limited to only SWCNT networks as discovered here, but also could be applied to systems where nanoparticles/nanotube form percolating paths in thin films and composite materials.