Characterization Of Thermophysical Properties Of Micro And Nano-Scale Materials And Thermal Transportation Mechanism Analysis

A harmonics detection system is developed to determine thermal conductivity and thermal diffusivity of nano-film on substrate, anisotropic laser crystal and multi-layer nano-film on Nd:YAG crystal, nanofluids, individual carbon fiber and individual single-walled carbon nanotubes on substrate.Analytical solution in term of series for temperature oscillation in the heater/thermometer film is derived for 3ωmeasurements. The complex temperature solution is divided in to the real and imaginary part, respectively. Analysis is performed to exhibit the effect of the combined parameter by ac frequency, heater width and sample thermal properties on the temperature oscillation. The mathematical model for the measurement is corrected based on the solution. Uncertainty analysis and comparison with the results from differential-3ωmethod and literature are made. The thermal conductivities of SiO₂ film and Si substrate are obtained simultaneously with the series solution and by extending to high frequency.The thermal conductivities of KTP crystal in the harmonic generation and radial direction are determined using the 3ωtechnique showing a strong anisotropy of thermal conduction in the KTP crystal. The sensitivities of parameters to fitted results were made. The thermal conductivities for Nd:YAG crystal and multi-layered antireflective films on its <111> surface were obtained with the combined measurements over low and high frequency range by 1ω, 2ωand 3ωtechniques.The principle in frequency domain for simultaneous determination of thermal conductivity and thermal diffusivity of nanofluids is established by using a Pt wire as the heater and sensor. The thermal conductivity and thermal diffusivity are obtained from the slope at low frequency and the intercept of the measured real part of temperature oscillation and those of calculated temperature rise at high frequency by including heat flux and the properties of the wire. The thermal conductivities of TiO₂/water and Al₂O₃/water at different temperatures are determined. The results show no anomalous enhancement of thermal conductivity with temperature. Brownian motion based micro-convective model does not give satisfactory prediction at high temperature and volume rate.We performed measurements on a Pt wire, and found that the measured thermal conductivity and thermal capacity agree well with literature values. The first successful measurements on an individual PAN-based carbon fiber were performed, which yielded the thermal conductivity and thermal difrusivity at room temperature. The relative uncertainty of the measurements was analyzed, and found to be approximately 6%. The thermal conductivity of single-wall carbon nanotubes is predicted to increase with length. Here we report the measurement of the length-dependent thermal conductivities of individual SWNTs on a Si substrate using a four-pad 3ωmethod. An increase in thermal conductivity with length was observed at room temperature, which agrees well with a theoretical prediction that considers higher order 3-phonon processes. When the length is longer than the phonon mean path, SWNTs showed dissipative thermal transport. The observed increase of thermal conductivity with length makes SWNTs ideal for thermal management.