Vibrational Energy Transport in Hybrid Ordered/Disordered Nanocomposites: Hybridization and Avoided Crossings of Localized and Delocalized Modes

• Published in: Advanced functional materials Vol. 28; no. 17
• Main Authors: Zhu, Taishan, Swaminathan‐Gopalan, Krishnan, Cruse, Kevin J., Stephani, Kelly, Ertekin, Elif
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 25.04.2018
• Subjects: Anharmonicity; avoided crossing; Crystal lattices; disorder; Energy management; Energy transfer; Hybrid systems; Hybridization; Lattice vibration; Materials science; Metamaterials; Nanocomposites; Reduction; Thermal conductivity; Thermal management; thermal property; Transport; vibrational energy transport
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201706268

Vibrational energy transport in disordered media is of fundamental importance to several fields spanning from sustainable energy to biomedicine to thermal management. This work investigates hybrid ordered/disordered nanocomposites that consist of crystalline membranes decorated by regularly patterned disordered regions formed by ion beam irradiation. The presence of the disordered regions results in reduced thermal conductivity, rendering these systems of interest for use as nanostructured thermoelectrics and thermal device components, yet their vibrational properties are not well understood. Here, the mechanism of vibrational transport and the reason underlying the observed reduction is established in detail. The hybrid systems are found to exhibit glass‐crystal duality in vibrational transport. Lattice dynamics reveals substantial hybridization between the localized and delocalized modes, which induces avoided crossings and harmonic broadening in the dispersion. Allen/Feldman theory shows that the hybridization and avoided crossings are the dominant drivers of the reduction. Anharmonic scattering is also enhanced in the patterned nanocomposites, further contributing to the reduction. The systems exhibit features reminiscent of both nanophononic materials and locally resonant nanophononic metamaterials, but operate in a manner distinct to both. These findings indicate that such “patterned disorder” can be a promising strategy to tailor vibrational transport through hybrid nanostructures. Vibrational energy transport in a hybrid ordered/disordered metamaterial, which is formed by ion beam irradiation, exhibits glass‐crystal duality and substantial hybridization between the localized and delocalized vibrational modes. Localization and anticrossing in dispersion curves are shown to be the dominant modifier of lattice conductivity. Anharmonic scattering is also enhanced in the patterned nanocomposites, further contributing to overall thermal resistance.