The work of the « Equipe de Physique des Ondes, Nanostructures et Interfaces (ephoni) » is dealing with numerical and analytical modeling of wave propagation and elementary excitations in micro and nanostructured materials, especially phononic crystals as well as photonic and plasmonic nanostructures. The purpose is the discovery of new trends associated with the geometry of these heterogeneous materials. In particular, we are interested by the manipulation, guiding and selective transmission of waves at the scale of the wavelength.
Many works have been devoted to a comprehensive analysis of the band structure and defect modes (such as guide, cavity and coupled guide-cavity modes) in phononic crystals, especially in relation with guiding, filtering or multiplexing functionalities. Presently, we are interested by slabs of phononic crystals such as a membrane of silicon with a periodic array of holes or supporting a periodic array of dots. We have demonstrated that these thin films of phononic crystals can also display absolute band gaps and, therefore, the possibility of guiding and filtering functionalities. Two new directions in these materials are dealing respectively with the investigation of simultaneous confinement of phonons and photons with the purpose of enhancing their interaction ( FP7-ICT TAILPHOX project and ANR PHOXCRY), and the study of the thermal transport in relation with the effect of the geometry of the structure on the dispersion curves (FP7-ICT NANOPACK project). Another topic of interest is about metamaterials that display low frequency gaps associated to local resonances (figure 1) and therefore can be useful for sound isolation while the size of the sample remains below the wavelength. Besides the topics related to the existence of absolute band gaps, part of our work is dealing with refractive properties of phononic crystals, in particular controlling the propagation of sound with metamaterials. Finally, our calculations of the phononic band structures are also useful for exploring the properties of tunable phononic crystals, for instance in support of Brillouin light scattering experiments performed in hypersonic AAO crystals in which the band structure can be modified when filling the holes with different types of polymers that can also undergo liquid-solid phase transition, or in phononic crystals constituted by magnetostrictive materials in which the elastic properties can be drastically changed by the application of an external magnetic field.
Figure 1: First acoustic resonances in a metamaterial where the inclusions are constituted by a hard core covered with polymer and steel multilayers (Covered page, Physica Status Solidi C, Vol.6 , nÂ° 9 (2009) et Phy. Rev. B75, 066601(2007))
In the field of plasmonics, we investigate the guiding, filtering and multiplexing properties of sub-wavelength structures constituted by dielectric waveguides inserted in a metal and coupled to lateral or inside cavities or resonators (figure 2). Another topic concerns the evolution of the plasmon resonances of metallic nanostructures inserted in a dielectric as a function of the embedding media, especially as a support to the experimental investigations of bioplasmonic sensors in IRI.
Figure 2: Y shape plasmonic waveguides coupled with two resonators leading to the filtering of one waveleght in each branch (New Journal of Physics, 11, 103020 ( 2009))