Phonon properties in different types of single-walled carbon nanotube thin films probed by Raman spectroscopy

We report a temperature-dependent (70-450 K) Raman study of single-walled carbon nanotube (CNT) thin films as a function of their thickness and the conductivity type of the nanotubes used to fabricate these films. The CNT films Raman G mode positions and widths exhibit two apparent regimes, a nonlinear temperature dependence at low temperatures (<270 K), which is explained by the phenomenon of optical phonon decay, and a linear temperature dependence above 270 K. The first-order temperature coefficient, determined for the linear regime, depends on the film thickness and type of CNTs, changed up to 20%. In addition, we observed another factor causing phonon shifts that is not related to the temperature but strongly depend on the film thickness and conductivity type of the CNTs. Finally, we ascertained the local temperature changes of the film samples upon laser heating as a function of the global temperature, demonstrating significant differences in the heating process, suggesting that heat evacuation efficiency depends type of the film, its thickness and global temperature. These results contribute to the understanding of the thermal properties and heat dissipation in CNT films, which are crucial for use in a variety of future applications. (C) 2016 Elsevier Ltd. All rights reserved.