Regulating phonon transport in silicon nanofilms by resonant nanopillars

Nanophononic materials have shown significant potential for advancing future thermoelectrics due to their ability to achieve low thermal conductivity. Recent studies have unveiled that thermal conductivity can be further diminished through the phenomenon of phonon resonance, which emerges from the incorporation of additional pillar structures. In this investigation, we delve into the realm of phonon resonance within silicon nanofilms (SiNFs) outfitted with resonant pillars, by employing classical molecular dynamics simulations. Our study reveals that SiNFs featuring resonant pillars exhibit a variable reduction in thermal conductivity contingent upon the thickness of the SiNFs. This reduction is notably influenced by the geometry of the pillars. Remarkably, thermal conductivity can be diminished by up to 20 % for SiNFs endowed with pillars on both sides, characterized by a pillar height of 0.8 nm and a duty cycle of 50 %. This reduction significantly surpasses the corresponding decrease observed in SiNFs equipped with unilateral pillars (13 %). Furthermore, the choice of an appropriate pillar height contributes to a more substantial drop in thermal conductivity. Specifically, a reduction of 14 % is observed for the model with a pillar height of 0.8 nm, while a height of 3.1 nm leads to a more pronounced reduction of 21 %. Intriguingly, we also identified that void defects present on the pillars have the potential to disrupt phonon resonance, thereby leading to an increase in thermal conductivity. The insights garnered from our findings offer valuable guidance for the strategic design of low-dimensional materials, capitalizing on the phenomenon of phonon resonance.