Elastic inhomogeneity and anomalous thermal transport in ultrafine Si phononic crystals

Publication date: Available online 6 February 2020Source: Nano EnergyAuthor(s): Kouhei Takahashi, Masaki Fujikane, Yuxuan Liao, Makoto Kashiwagi, Takashi Kawasaki, Naoki Tambo, Shenghong Ju, Yasuyuki Naito, Junichiro ShiomiAbstractControlling nanoscale thermal transport via phonon engineering is a promising path for novel thermal management in electronic devices and high performance thermoelectrics. Here we report that ultrafine nanofabrication allows us to change the lattice vibrational properties such that reduces the material thermal conductivity in an unusual manner. This is demonstrated in ultrafine silicon (Si) phononic crystals with two-dimensional arrays of through-holes. We reveal that thermal conductivity of Si can be reduced far below the theoretical limit predicted from a phonon particle model when the through-holes are arranged at sub-100 nm periods. Significant elastic softening is identified in these fine phononic crystals, which indicates change in the lattice vibrational properties. Interestingly, we find that the change in elasticity occurs locally and non-uniformly, suggesting that additional phonon scattering mechanism or a change in sound velocity needs to be considered in phononic crystals. The present result provides new thinking for understanding thermal transport of solids and opens a new avenue to tailor phonon transport in thermal-energy-related materials and devices.Graphical abstract

Source: Nano Energy - February 10, 2020 Category: Nanotechnology Source Type: research