Surface and Constriction Engineering of Nanoparticle Based Structures Towards Ultra-Low Thermal Conductivity as Prospective Thermoelectric Materials

The superior thermal insulating properties of nanostructured semiconductor materials over their bulk counterparts, make them promising candidates for Thermo-Electric (TE) applications. In this study, the superior thermal insulating properties of a new class of one-dimensional nanostructures made by sintering linearly placed nanoparticles, called Nano Particle Chains (NPC) are analyzed for a variety of surface and constriction modifications. The NPC structure which has been shown to be capable of achieving a one-order reduction in thermal conductivity over comparably sized nanowires is revealed to house a new phonon suppression mechanism in addition to commonly discussed phonon boundary scattering and quantum confinement effects. In the current work, this quantum confinement based thermal conductivity reduction mechanism is revealed to be a variation in the phonon Density of States (DoS) along the longitudinal/transport direction of the structure due to the presence of the nanoscale constrictions. Subsequently, the phonons are forced to change the distribution of modes while traveling across the structure, thus resulting in lower thermal conductivity. Additionally, the effects of common phonon suppression techniques such as superlattice, shell alloy, and surface atom removal, used in semiconductor nanostructures are also evaluated on NPC configurations to fully determine the phonon transport characteristics within different classes of the material.