Periodic Reporting for period 3 - Smartphon (Small - and nano - scale soft phononics)
Reporting period: 2019-09-01 to 2021-02-28
The propagation of elastic waves (acoustic waves or phonons) in architected matter is a generic problem that impacts many areas of material science. Phonon propagation in structure composite structures depends on many interrelated parameters (four for each solid component). This number increases further when anisotropy is introduced in the design of the structures. Besides the structural and elastic parameters, phononic behavior is further influenced by additional factors such as complex structural relaxation, confinement and interfacial effects. There is therefore rich unexplored and hardly predictable fundamental science that needs a supporting foundation to be established. The key quantity is the dispersion relation ω(k), that relates the frequency ω and the wave vector k of the propagating wave, in the composite matter. Engineering of ω(k) to allow elastic wave propagation only on desired frequencies , polarizations and directions (metamaterials) requires control of both structure periodicity and component dimensions and elastic parameters. Extension to high frequency phononics, to enable simultaneous manipulation of hypersonic phonons and visible light, needs organization in the submicron and nanometer scale range via self-assembly and nanofabrication. This is a ubiquitous property of soft matter (polymers, colloids) that allows such fabrication of complex hierarchical structures with tailored and manifold functionalities. Control over the phonon dispersion and the anisotropic elasticity can impact the heat transport in dielectric hybrid materials. Many important questions in this young field of small-nano scale phononics are just being raised and require new conceptual and technical approaches to address them.
• Why is it important for society?
1) The advancement of a new field creates new knowledge in physics and engineering and challenges material nanofabrication. This know-how is being transferred to young scientists (PhD, Postdoc’s and visiting scholars) working in this program. 2) Mechanical properties and the stability of nanostructured materials are of paramount importance for a wide range of applications that comprise microelectronic, photonics, nano-electro-mechanical systems, nanofluidics, and biomedical technologies. Crowding, space-filling and confinement in soft condensed matter are conditions that can have severe effect on the material properties in particular at metastable states. 3) A detailed understanding of phonon propagation in soft nanostructured media is a precondition to access fundamental concepts such as heat management and phonon-photon interactions. Heat management is increasingly being recognized as a key technology to fuel the growth of our technology-driven society. Controlling the elusive flow of heat is a complex challenge across multiple materials, length scales, and ultimately devices. It suffices to mention the wastage through heat in ICT devices is enormous (several hundred TWh, only in Germany). Strong optoacoustic effect can find applications also in devices as nanoactuators. Other applications, e.g. in nondestructive metrology, can emerge from the still unprecedented phonon-matter interactions.
• What are the overall objectives?
The project addresses challenging objectives at the frontiers of the involved research: a) Develop new capabilities for phonon (elastic waves) management in mesoscopic soft matter with implementation on heat management. The integrated approach, utilization of the flexibility, versatility and multi-functionality of soft matter, will generate the missing information for phonon band structure engineering as is necessary to tailor the dispersion relations for a particular application. b) Extend concepts and techniques from polymer and colloid science into the new area of phononics. Structure and its component materials dictate the shape of the experimental phonon dispersion relations. Soft matter-based phononics utilize the main advantages of facile processing as well as architectural and topological changes of the constituent components. c) Determine currently unknown dimension-dependent thermo-mechanical properties. The ability to pattern substrates at the nanoscale has largely evolved as a result of advances in thin film technologies and electronics; the stability of nanostructured hybrid films is of paramount importance. d) Realize functional photonic devices based on soft matter systems. Since hypersonic phononic crystals have lattice constants in the range of visible/near IR light, phoxonic materials should enable localization of both sound and light in the same regions. The transfer of the hard-matter optomechanics to soft materials taking advantage of the rich structures accessible is of great interest but it constitutes a “formidable” challenge with high physical and engineering impact.