Time-resolved study of two-dimensional phononic crystals based on self-assembled nanospheres

Phononic crystals, elastic analogues of photonic crystals, promise significant advances in controlling elastic energy propagation, crucial for tunable filters, heat management, and acousto-optical devices. By influencing phonon flow, they could control thermal conductivity. Colloidal self-assembly offers a cost-effective method to engineer phononic crystals with desired properties. This study investigates the hypersonic phononic properties of self-assembled two-dimensional colloidal crystals composed of polystyrene (PS) nanospheres on a silicon substrate. We demonstrate tunable hypersonic phononic bandgaps by varying interactions between neighboring PS nanospheres. Ultrafast pump-probe transient reflectivity techniques explore phononic modes across various frequency ranges. Phonon transport analysis via pump-probe methods confirms the phonon-insulating properties. Experimental observations are supported by a finite element method model. These findings underscore the potential of self-assembled colloidal crystals in creating tunable hypersonic phononic insulators, paving the way for advanced phononic applications.