Elasticity of ultrathin copper-phthalocyanine Langmuir–Blodgett films by picosecond ultrasonics

Abstract

The picosecond ultrasonic technique is used to investigate the elasticity of Langmuir–Blodgett submicronic films of copper (II) octabutoxyphthalocyanine. The amplitude of the acoustic echoes is measured against the number of monolayers (1–24, i.e., from a pure bidimensional behavior to a tridimensional one). The longitudinal sound velocity and the ultrasonic attenuation for frequencies up to about 40 GHz are deduced from this behavior. For the thinnest samples, the acoustic echoes are observed with a delay whose origin is analyzed. We show that the accuracy of the method is only limited by the precise knowledge of the density of the material.