Extremely Low Thermal Conductivity of Polycrystalline Silicene
YF Gao and YG Zhou and XL Zhang and M Hu, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 9220-9228 (2018).
By performing Green-Kubo equilibrium molecular dynamics simulations, we study thermal transport in polycrystalline silicene with grain size up to an experimental scale of 50 nm and compare it with amorphous silicene. The thermal conductivity (TC) of polycrystalline silicene with small grain size is not only lower than that of one-dimensional (1D) polycrystalline silicon nanowires with the same grain size, but also lower than that of amorphous silicene. By introducing point defects, the TC of polycrystalline silicene with rather large grain size (30 nm) is comparable to polycrystalline silicon nanowires with extremely small grain size (2 nm). Through phonon spectral energy density analysis, we reveal that the ultralow TC of polycrystalline silicene originates from the violent phonon scattering exerted by the thin boundary of grains. For higher buckling distance, the phonon properties of amorphous silicene are prominently different from those of polycrystalline silicene and are closer to those of 3D bulk or 1D nanowire materials, and the scattering on the low-frequency phonons is weaker. In addition, the grain boundary mainly affects the long-wavelength phonons, while the point defects play dominant effect on high-frequency phonons. This study highlights the importance of 2D polycrystalline silicene for advanced thermoelectrics.
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