Evaluation of sub-micrometer thick multilayered colloidal films by the method of resonant hypersound spectroscopy
Résumé
Resonant ultrasound spectroscopy, which consists in measuring the resonance frequencies of oscillations in ultrasonic frequency range, is a well-established technique for the evaluation of elastic properties of structures. The use of picosecond laser ultrasonics experimental technique for the generation and detection of acoustic vibrations, allows experimental evaluation of the resonance oscillations of sub-micrometer size structures, typically in the GHz, i.e. in hypersonic frequency domain. This communication exposes the results of an experimental evaluation of the elastic properties of sub-micrometer thick multilayered colloidal films. The individual layers of the films deposited on opaque substrate are disordered silica assemblies with well controlled nanoparticles surface chemistry. The nanoparticles diameter is 10nm. The colloidal films, composed of different number of layers, have all the same thickness of about H=400nm. Our experiments revealed the dependence of the resonance frequencies of the films on the number of identical individual layers composing the films. The experimental data are used to characterize the dependence of the elastic properties of the individual layers on their thickness and to estimate the quality of adhesion between the individual layers composing the films. These original results demonstrate the ability of picosecond acoustics methods to probe elasticity of soft colloidal films.
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