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arXiv · 1511.07398

Two-Dimensional Phononic Crystals: Disorder Matters

Markus R. Wagner·Bartlomiej Graczykowski·Juan Sebastian Reparaz·Alexandros El Sachat·Marianna Sledzinska·Francesc Alzina·Clivia M. Sotomayor Torres
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Abstract

The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.

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Markus R. Wagner, Bartlomiej Graczykowski, Juan Sebastian Reparaz, Alexandros El Sachat, Marianna Sledzinska, Francesc Alzina, Clivia M. Sotomayor Torres. 2016-09-03. Two-Dimensional Phononic Crystals: Disorder Matters. https://doi.org/10.1021/acs.nanolett.6b02305

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