Thermal diffusivity characterization of semiconductive 1D micro/nanoscale structures.

• TET model for nonlinear ρ e ∼ T relation of semiconductive micro/nanoscale materials. • Robust thermal diffusivity (α) measurement by TET using the nonlinear ρ e ∼ T model. • First time thermal diffusivity determination at the zero temperature rise limit. • α ∼ T trend for graphene film is well interpreted by the thermal reffusivity theory. • α ∼ T trend for SWCNT mat reveals strong structure deterioration with T decreasing. The transient electrothermal (TET) technique was developed and has been widely used for measuring the thermal diffusivity of fiber- and film-like materials at the micro/nanoscale. Upon step-current heating, the measured voltage-time (V - t) of the sample usually follows a sole increasing or decreasing trend, depending on the temperature coefficient of its electrical resistivity (θ T = dρ e / dT, ρ e : electrical resistivity, T : temperature). Past physical mode for the V - t profile is based on an assumption that θ T is constant during TET measurement, which applies to a large variety of materials. However, for semiconductive materials, θ T depends on the charge carrier density and scattering time, and both vary with temperature. Therefore, θ T has very strong nonlinear change with temperature, sometimes changes sign during TET measurement. This leads to abnormal V - t profiles that have never been addressed well, thereby making TET measurement not applicable for such scenarios. In this work, a new physical model is developed to consider the strong nonlinear relation between ρ e and T to the third order. Our numerical modeling firmly proves the validity of this new model. Thin films of graphene (GreF) and single-walled carbon nanotube (SWCNTs) mat are measured using the TET technique over a wide temperature range: 84.5–690.9 K for the GreF, and 12–290 K for the SWCNT film. At a specific temperature for each sample, a semiconductive-to-metallic transition comes about and manifests in the resistance-temperature response, hence leading to abnormal TET signals. These TET signals are perfectly fitted using our nonlinear θ T ∼ T model to determine α. Intriguingly, the determined α of the GreF for the transition phase follows the overall α ∼ T trend, confirming the robustness of the model. The obtained α ∼ T trend is interpreted well using the thermal reffusivity theory and structure deterioration under temperature change. This work significantly extends the capability of TET to semiconductors for α measurement. Also, the new methodology developed for obtaining α at zero temperature rise significantly improves the measurement control and accuracy. [Display omitted] [ABSTRACT FROM AUTHOR]