Micron-scale ballistic thermal conduction and suppressed thermal conductivity in heterogeneously-interfaced nanowires
Tzu-Kan Hsiao1,2, Bor-Woei Huang1*, Hsu-Kai Chang3, Sz-Chian Liou1, Ming-Wen Chu1, Si-Chen Lee3, Chih-Wei Chang1
1Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
2Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
3Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, Taiwan
* presenting author:黃柏瑋, email:borwayhuang@yahoo.com.tw
We discover that micron-scale ballistic thermal conduction can be found in Si-Ge heterogeneously-interfaced nanowires exhibiting low thermal conductivities. The thermal conductivity of Si-Ge nanowires are accompanied with an elongation of phonon mean free paths over 5μm at room temperature, which is more than 25 times longer than that of Si or Ge. We estimate only 0.1% of the excited phonons carry out the heat transfer process and the low-frequency phonons in Si-Ge core-shell nanowires are found to be insensitive to twin-boundaries, defects, and local strain. The ballistic thermal conduction persisting over 5μm will enable wave-engineering of phonons at room temperature and inspire new improvements of thermoelectric devices.

Keywords: thermal conductivity, ballistic , phonon mean free path , thermal conductivity , heterogeneously-interfaced nanowires