Probing buried interfaces in SiO_xN_y thin films via ultrafast acoustics: The role transducing layer thickness

Probing buried interfaces in thin films is a crucial task in many fields, including optical coating. Ultrafast acoustics provide a means to characterize the interfaces by using an acoustic wave localized on the nanometer scale. We provide a brief overview of our thorough study of the interface between SiO x N y thin films and Si substrate by using both single-color and broadband picosecond acoustics. The experiment allows us to track the effect of stoichiometry on the acoustics wave propagation and transition over the layer-substrate interface. To optimize the experiment, we also created simulations to study the effect of optoacoustic layer thickness. We show that the used Ti layer features an optimum thickness between 5-10 nm to reveal details of the interface properties.