Shape- and Structure-Based Phonon Bandgap Tuning with Nanocrystal Superlattices

Abstract

In this paper we report, for the first time, the phononic band structure of nanocrystal superlattices with different shapes, sizes, compositions, and structures. For superlattices composed of a single type of nanocrystal core, we show that by merely changing the nanocrystal shape the bandgap width is affected significantly: nanocrystal shapes with higher surface to volume ratio result in larger phononic bandgaps. Furthermore, structural changes are shown to be important as face-centered cubic and body-centered cubic structures with the same nanocrystal core size present 28 and 76% smaller bandgaps compared to the simple cubic structure. For binary nanocrystal superlattices, we show that different structures can lead to a wide range of phononic bandgaps and that structures with larger combined nanoparticle core volume fractions introduce larger phononic bandgaps. Changing the composition of the binary systems while keeping the same structure is found to provide an effective means of tuning the phononic bandgaps. On the basis of their tunable bandgap widths and frequencies, nanocrystal superlattices provide promising materials for sound or heat manipulation purposes.