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Published August 2015 | Supplemental Material
Journal Article Open

Spectral mapping of thermal conductivity through nanoscale ballistic transport

Abstract

Controlling thermal properties is central to many applications, such as thermoelectric energy conversion and the thermal management of integrated circuits. Progress has been made over the past decade by structuring materials at different length scales, but a clear relationship between structure size and thermal properties remains to be established. The main challenge comes from the unknown intrinsic spectral distribution of energy among heat carriers. Here, we experimentally measure this spectral distribution by probing quasi-ballistic transport near nanostructured heaters down to 30 nm using ultrafast optical spectroscopy. Our approach allows us to quantify up to 95% of the total spectral contribution to thermal conductivity from all phonon modes. The measurement agrees well with multiscale and first-principles-based simulations. We further demonstrate the direct construction of mean free path distributions. Our results provide a new fundamental understanding of thermal transport and will enable materials design in a rational way to achieve high performance.

Additional Information

© 2015 Macmillan Publishers Limited. Received 05 April 2014; Accepted 23 April 2015; Published online 01 June 2015. The authors thank J. Garg for providing DFT data on Si_(0.992)Ge_(0.008), and D. Broido, N.G. Hadjiconstantinou, A. Marconnet, J.K. Tong, J-P. Peraud, W. Dai, A. Maznev, K. Nelson, J. Cuffe, M. Luckyanova and K. Collins for discussions. This material is based on work supported as part of the 'Solid State Solar-Thermal Energy Conversion Center (S3TEC)', an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (grant no. DE-SC0001299/DE-FG02-09ER46577). Y.H. is partially supported by the Battelle/MIT Fellowship. Contributions: Y.H. and G.C. developed the concept. Y.H. prepared the samples and performed the experiments. L.Z. performed the Monte Carlo simulation. Y.H. performed the numerical calculations on convex optimizations. All authors discussed the results and commented on the manuscript. G.C. directed the research. Competing financial interests: The authors declare no competing financial interests.

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