Helicity Induced Thermal Conductivity Reduction in Superlattice Nanowires

V Varshney and AK Roy and J Lee and DS Dudis and BL Farmer, PHONONS 2012: XIV INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER, 1506, 28-34 (2012).

DOI: 10.1063/1.4772520

In this study, we have performed non-equilibrium molecular dynamics (NEMD) simulations to investigate thermal transport properties of 'model' bi-component helical nanowires. The results indicate that significant reduction in thermal conductivity, similar to that of flat superlattice nanostructures, can be achieved using a helical geometric configuration. The reduction is attributed to a plethora of transmissive and reflective phonon scattering events resulting from the steady alteration of phonon propagating direction that emerges from the continuous rotation of the helical interface. We also show that increasing the relative mass ratio of the two components lowers the phonon energy transmission at the interface (differences in vibrational frequency spectrum), thereby relatively 'easing' the phonon energy propagation along the helical pathway. While the proposed mechanisms result in a reduced lattice thermal conductivity, the continuous nature of the bi-component nanowire would not be expected to significantly reduce its electrical counterpart, as often occurs in superlattice/alloy nanostructures. Hence, we believe that the helical configuration of atomic arrangement should be a very attractive, general approach for improved thermoelectric material assemblies independent of the specific chemical composition.

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