Thermal conductivity manipulation in Si/Ge core-shell nanowires by introducing nanopillars

Multi-structure integration synergistically hinders phonon transport, serving as an important strategy for reducing thermal conductivity (TC) applicable to thermoelectric materials, insulating materials, and thermal barrier coatings. Using non-equilibrium molecular dynamics (NEMD) simulations, we investigate the thermal transport behavior of nanopillar-modified Si/Ge core-shell nanowires. Results show that decorating core-shell nanowires with surface nanopillars leads to an additional reduction in TC of approximately 34% compared to the core-shell structure alone, achieving an ultralow TC. Phonon transport analysis reveals that, while the core-shell structure suppresses mid-to-low-frequency and high-frequency phonons, the nanopillars further weaken low-frequency propagating phonons. Moreover, Si nanopillars are more effective than Ge nanopillars in reducing TC. We also examine the effects of temperature, nanopillar length, and nanopillar width. These results demonstrate that combining a core-shell geometry with surface nanopillars provides a practical design strategy for achieving ultralow TC in nanowires.