Ultra-low thermal conductivity of nanoparticle chains: A nanoparticle based structure for thermoelectric applications

P Henadeera and N Samaraweera and C Ranasinghe and A Wijewardane, JOURNAL OF APPLIED PHYSICS, 130, 064301 (2021).

DOI: 10.1063/5.0060487

Nanostructured semiconductors are promising candidates for thermoelectric materials owing to their superior thermal insulating properties over their bulk counterparts. In this study, a one- dimensional, crystalline nanostructure synthesized by sintering Si nanoparticles, called Nano Particle Chain (NPC) structures, is proposed. The structure is systematically analyzed for its thermal transport properties and compared with the nanowire counterparts. Both classical molecular dynamics and lattice dynamics tools were employed to evaluate lattice thermal conductivity (k) and to perform phonon mode level decomposition. A marked reduction in the phonon relaxation time of the NPC structure was observed indicating possible effects of phonon- boundary/constriction scatterings. This has resulted in a two-order reduction in k in NPC structures over bulk Si. Further, one order reduction of k of NPC structures was attained with respect to a nanowire of the same constriction size, indicating the effectiveness of the mismatch of particle and constriction diameters as an efficient thermal suppression mechanism. With the addition of a second material of different mass, the NPC structures can be further diversified to core/shell configurations. It was also identified that a non-monotonic variation of k exists, with a minimum in core/shell NPC structures. This effect is materialized by using a Ge-like fictitious material to coat the original Si nanoparticles, owing to competing effects of two phonon suppression mechanisms. Moreover, these core/shell NPC structures are compared with previously reported diameter modulated core/shell nanowire structures E. Blandre et al., Phys. Rev. B, 91, 115404 (2015) to highlight their capability to enhance the thermoelectric performance over conventional one-dimensional nanostructure configurations. Published under an exclusive license by AIP Publishing.

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