Temperature-dependent nonlinear phonon behavior in high-density carbon nanotube thin films

We report the temperature-dependent Raman spectra for high-density single-walled carbon nanotube thin films. We show that the position of the main Raman mode (G) softens as the temperature increases and is nonlinear in the range of 70-270 K. This effect is explained by optical phonon decay. In the linear regime, the first-order temperature coefficient (chi(T)) equals -0.02 cm(-1) /K, which is lower than for any other carbon nanotubes. Importantly, we found that local laser-induced temperature change shows a nonlinear trend as a function of global temperature with a minimum at 270K. Our results contribute to understand the thermal properties of carbon nanotube thin films that could be applied, for example, in photovoltaic or thermoelectric devices. (C) 2014 AIP Publishing LLC.