A promising way to locally probe the elasticity of micrometric to nanometric structures (e.g. solid state devices, biological media) is to exploit the high frequency acoustic field radiated by a single nanoparticle (NP). For instance, the femtosecond optical excitation of a 100 nm diameter gold nanoparticle generate in water an acoustic field with a 50 nm acoustic wavelength, i.e. far below the best optical resolution. The aim of this project is to design local GHz opto-acoustic transducers.

The optoacoustic response of a single submicron (430 nm) gold particle embedded in a silica thin film has been experimentally revealed by transient reflectivity measurements with a femtosecond pump-probe setup. The detection mechanism relies on an intrinsic common-path interferometer where the reference beam comes from a fixed interface of the sample. A semianalytical model is developed to calculate the transient reflectivity accounting for optical index changes in both media and for particle and film surface displacements. The displacement of the particle-film interface turns out to be the major contribution to the measured signal.

Related publications: 

• Y. Guillet et al. Appl. Phys. Lett. 95, 061909 (2009)
• Y. Guillet et al. J. Phys.: Conf. Ser. 214, 012046 (2010)
• F. Xu et al. Phys. Rev. B 97, 165412 (2018)

We investigate the GHz dynamics of the elastic contact between a single metallic nanoparticle and a substrate. We detect the known breathing mode of the nanoparticle but we also unravel the axial oscillation of the nanoparticle through an intrinsic common-path interferometer. We measured the eigenfrequency and the lifetime of this vertical motion, which are related to the contact stiffness and hysteresis, and to the acoustic leakage at the nanoparticle-substrate interface. Measurements have been performed for single particles with radii ranging from 60 to 700 nm.

Related publications:

• Y. Guillet et al.Phys. Rev. B. 86, 035456 (2012)