title: Engineering the hypersonic phononic band gap of hybrid Bragg stacks.
abstract: We report on the full control of phononic band diagrams for periodic stacks of alternating layers of poly(methyl methacrylate) and porous silica combining Brillouin light scattering spectroscopy and theoretical calculations. These structures exhibit large and robust on-axis band gaps determined by the longitudinal sound velocities, densities, and spacing ratio. A facile tuning of the gap width is realized at oblique incidence utilizing the vector nature of the elastic wave propagation. Off-axis propagation involves sagittal waves in the individual layers, allowing access to shear moduli at nanoscale. The full theoretical description discerns the most important features of the hypersonic one-dimensional crystals forward to a detailed understanding, a precondition to engineer dispersion relations in such structures.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schneider
authors.forename: Faroha
authors.initials: F
authors.lastname: Liaqat
authors.forename: El Houssaine
authors.initials: el H
authors.lastname: El Boudouti
authors.forename: Youssef
authors.initials: Y
authors.lastname: El Hassouani
authors.forename: Bahram
authors.initials: B
authors.lastname: Djafari-Rouhani
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Tremel
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Butt
authors.forename: George
authors.initials: G
authors.lastname: Fytas
mesh_terms: D003198:Computer Simulation; D008027:Light; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012031:Refractometry / Q000379:methods*; D012542:Scattering, Radiation