Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 151002

151002 - Semiconductive 1d Micro/nanscale Materials' Thermal Diffusivity Characterization 

One-dimensional (1D) micro/nanoscale materials play a crucial role in many sectors because of their distinctive characteristics. Thermal design, endurance, and stability of the systems depend critically on the thermophysical properties of 1D micro/nanostructures, particularly thermal conductivity (k) and thermal diffusivity (α). For this purpose, the transient electrothermal (TET) technique has been developed and is commonly used to measure the thermal diffusivity of fiber- and film-like materials. When a sample is heated with step current, its measured voltage-time (V-t) often exhibits a single trend of increasing or decreasing, based upon the temperature coefficient of its electrical resistivity (θ_T = dρ_e/dT, where ρ_e represents electrical resistivity and T denotes temperature). The past physical mode of the V-t profile is built on the generally accepted assumption that θ_T remains constant during TET measurement. However, for semiconductive materials, θ_T is temperature-dependent and depends on both the charge carrier density and the scattering time. As a result, θ_T exhibits a very significant nonlinear shift with temperature and occasionally changes sign during the TET measurements. This results in abnormal V-t profiles that have never been properly addressed; hence, traditional TET data processing is not practical in these kinds of situations. To take into account the strong nonlinear interaction between ρ_e and T to the third order, a novel physical model is established in this work. The validity of this novel idea is thoroughly verified by our numerical modeling. Additionally, the TET technique is used to evaluate graphene (GreF) and single-walled carbon nanotube (SWCNT) thin films over a broad temperature range. For the GreF, α varied from 1.57×10⁻³ m²s⁻¹ to 1.61×10⁻⁴ m²s⁻¹ over a temperature range of 84.5-690.9 K. For the SWCNT film, when T dropped from 290 to 12 K, α decreased from 1.81×10⁻⁵ to 4.0×10⁻⁶ m²s⁻¹. The primary reason for this is the degraded film structure brought on by the SWCNTs' thermal expansion and contraction. In fact, each sample experiences a semiconductive-to-metallic transition at a particular temperature, which is reflected in the resistance-temperature response and results in abnormal TET signals. Our nonlinear θ_T ~T model provides an excellent fit for these TET signals, allowing us to calculate α. Interestingly, the robustness of the model is confirmed by the determined α of the GreF for the transition phase, which follows the overall α~T trend. The thermal reffusivity theory and structure deterioration under temperature change are useful tools for interpreting the given α~T trend. With this work, TET's α measuring capabilities for semiconductors are greatly extended. Furthermore, the accuracy and control of measurements are significantly enhanced by the new methodology that was established for getting α at zero temperature rise. Finally, it helps determining α at a specified ambient temperature, especially when R is less sensitive to T change.

Presenting Author: Amin Karamati Iowa State University

Presenting Author Biography: Amin Karamati is pursuing his Ph.D. degree in Mechanical Engineering at Iowa State University since 2021. He received his M.S. and B.S. in Mechanical Engineering from K. N. Toosi University of Technology,
Iran, in 2016 and 2013, respectively. Thermal transport on 1D scale has been his research focus. Currently, he is conducting research on the thermal characterization of micro/nanowires using Raman Spectroscopy,
TET, and TPET techniques.

Authors:

Amin Karamati Iowa State University
Xinwei Wang Iowa State University