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Quantitative characterization of thermal properties of nanorod (NR) arrays appears to be challenging due to the complex combination of high volume of air voids, anisotropy, and structural non-uniformity. This work investigates the structure-thermal property correlation of arrays consisting of either vertically aligned or slanted silicon dioxide (SiO2) NRs, fabricated by the dynamic shadowing growth technique. We apply the frequency-dependent time-domain thermoreflectance method to quantify the thermal properties of SiO2 NR arrays that may possess inhomogeneity along the depth direction. The effective thermal conductivities of four SiO2 NR array films and one reference capping layer for the SiO2 NR array are obtained. The impact of the structure on the effective thermal conductivities of the SiO2 NR array is discussed. The lowest effective thermal conductivity among all samples in this work is found to be 0.13 W m-1 K-1 for the slanted NR array. We attribute the reduction in the effective thermal conductivity of the NR array to the discontinuous nature of SiO2 NRs, which reduces the density of the thermal transport channels and thus prevents heat flux from propagating downwards along the through-plane direction. The results from this work facilitate the potential applications of NR-array-based thermal insulators for micro-thermal devices.
Bibliographical noteFunding Information:
This work was supported partially by the National Science Foundation (NSF) through the University of Minnesota MRSEC under Award No. DMR-1420013. J.Z. would like to thank the support from the National Natural Science Foundation of China (Grant Nos. 51336009 and 51206167). Y.Z. acknowledges the support from Suzhou International Sci. and Tech. Cooperation Program (SH201111); H.S. and Y.Z. were supported by the Strategic Leading Science and Technology Special of the Chinese Academy of Sciences (No. XDA06010705).
© 2016 Author(s).