Unusual Twisting Phonons and Breathing Modes in Tube-Terminated Phosphorene Nanoribbons and Their Effects on Thermal Conductivity
XJ Liu and JF Gao and G Zhang and YW Zhang, ADVANCED FUNCTIONAL MATERIALS, 27, 1702776 (2017).
By studying tube-terminated phosphorene nanoribbons (PNRs), it is found that unusual phonon and thermal properties can emerge from topologically new edges. The lattice dynamics calculations show that in tube- terminated PNRs, the breaking of rotation symmetry suppresses the degeneracy of phonon modes, causing the emergence of twisting mode. An anomalous change of an out-of-plane acoustic mode to breathing modes with nonzero energy at the center of Brillouin zone occurs when the phosphorene sheet is converted into a tube-terminated PNR. These unusual twisting and breathing modes provide a larger phase space for scattering phonons, thus explaining the low thermal conductivity of tube-terminated PNRs revealed by molecular dynamics calculations. Due to the change in the stress field distribution caused by the tube edge, a nearly strain- independent thermal conductivity in tube-terminated PNRs is observed, which is in contrast to the apparent enhancement of thermal conductivity in pristine and dimer-terminated PNRs under tensile strain. The work reveals intriguing phononic and thermal behaviors of tube-terminated 2D materials.
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