Thermal characterization of carbon nanotube fiber by time-domain differential Raman

Abstract

Most conventional Raman thermometry for thermal properties measurement is on steady-state basis, which utilizes either Joule heating effect or two lasers configurations coupled with increased complexity of system or measurement uncertainty. In this work, a new comprehensive approach including both transient and steady-state Raman method is proposed for thermal properties measurement of micro/nanowires. The transient method employs a modulated (pulsed) laser for transient heating and Raman excitation, and is termed time-domain differential Raman. The average elevated temperature during the transient heating period is probed simultaneously based on Raman thermometry. Thermal diffusivity can be readily determined by fitting normalized temperature rise against heating time with a transient heat conduction model. On the other hand, thermal conductivity can be obtained in the steady-state measurement by adjusting modulation settings. To verify this method, a carbon nanotube (CNT) fiber is measured with the thermal diffusivity of 1.74−0.20+0.20×10−5 m2/s and the thermal conductivity of 34.3−0.4+0.4 W/m K. The relatively low thermal transport values stem from numerous CNT-glue matrix and CNT–CNT thermal contact resistances. Compared with the conventional steady-state Raman method, the transient method requires no detailed laser absorption value and no temperature coefficient calibration. It can be easily applied to study transient thermal transport in materials.