Mode-Resolved Thermal Conductivity of Freestanding and Supported Bismuth Telluride Quintuple Layer

The successful exfoliation of atomically-thin bismuth telluride quintuple layer (QL) attracts tremendous interest in investigating the electron and phonon transport properties in this quasi-two-dimensional material. While experimental results show that thermal conductivity is significantly reduced in Bi₂Te₃ QL compared to the bulk phase, the underlying mechanisms for the reduction is still unclear. Also in some measurements, the Bi₂Te₃ QL is usually supported on the substrate and the effect of the substrate on heat transfer in Bi₂Te₃ QL is unknown. In this work, we have performed molecular dynamics simulations and normal mode analysis to study the mode-wise phonon properties in freestanding and supported Bi₂Te₃ QL. We found that the existing of substrate will decrease the phonon relaxation times in Bi₂Te₃ QL in the full frequency range. Thermal conductivity accumulation function for both freestanding and supported Bi₂Te₃ QL are constructed and compared. We found that half of heat transfer in freestanding Bi₂Te₃ QL contributed from phonons with mean free paths larger than 16.5 nm, while in supported Bi₂Te₃ QL this value is reduced to 11 nm. In both cases phonons with MFPs in the range of 10–30 nm are the dominate heat carriers, which contribute to 55% and 53% of thermal conductivity in freestanding and supported cases.