High Frequency Acoustics in Colloid-Based Meso- and Nanostructures by Spontaneous Brillouin Light Scattering

Materials that can mold the ?ow of elastic waves of certain energy in certain directions are called phononic materials. The present thesis deals essentially with such phononic systems, which are structured in the mesoscale (\1 lm), and with their individual components. Such systems show interesting phononic properties in the hypersonic region, i.e., at frequencies in the GHz range. It is shown that colloidal systems are excellent model systems for the realization of such phononic materials. Therefore, different structures and particle architectures are investigated by Brillouin light scattering, the inelastic scattering of light by phonons. Both the mechanical properties of the individual colloidal particles, which manifest in their resonance vibrations (eigenmodes), as well as the acoustic propagation in colloidal structures have been investigated. The measurement of the eigenmodes allows for new insights into physical properties at the mesoscale, e.g., con?nement effects, copolymer behavior, or the non-destructive determination of nanomechanical properties of core-shell particles, supporting the working groups aim to achieve a deeper understanding of 'soft mechanics' at small length scales. Another novel contribution assigned to this thesis is the ?rst experimental rea- zation of a phononic band gap arising from the interaction of these particle - genmodes with the effective medium band (hybridization gap). This ?nding already gave new impulses to the whole ?eld of phononics.