Picosecond ultrasonics study of the vibrational modes of a nanostructure

Abstract

We report experiments in which a subpicosecond pump light pulse is used to excite vibrations in a nanostructure consisting of a periodic array of copper wires embedded in a glass matrix on a silicon substrate. The motion of the wires after excitation is detected using a time-delayed probe light pulse. From the measured data, it is possible to determine the frequencies νn and damping rates Γn of a number of the normal modes of the structure. These modes have frequencies lying in the range 1–30 GHz. By comparison of the measured νn and Γn with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to deduce the vibration patterns of six of the normal modes.

Thermomechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near-infrared pump-probe diffraction experiments

“…In particular, time-resolved reflectivity experiments, performed on gratings of metallic nanometric stripes (2-D confined) on transparent (SiO 2 ) or semitransparent (Si) substrates, evidenced oscillations in the GHz range [1,2,3,4], however their origin of these oscillations is still matter of debate [3,4]. The reason resides in the difficulty to model the strong mechanical coupling [5,6] between the nano-objects and the substrate and to calculate the mechanical eigenfrequencies of the coupled system.…”

Computations of geometrically linear and nonlinear Ginzburg-Landau mo dels for martensitic pattern formation

“…This framework allows comparison of geometrically nonlinear and linear models of martensitic phase transformations. Ultrasonic techniques can be used to measure the dispersion relation in a material from which it is possible to estimate elastic, dissipation and capillarity constants using the geometrically linear model [4,12,17] …”

High-Amplitude, Ultrashort Strain Solitons in Solids

“…Analysis of thin-film and nanostructured media: Currently this is the principle research area that is actively being studied. Next to the analysis of one-dimensional multilayer structures ('nano-seismology'), attempts have been made to characterize the acoustic behavior of composite and nanostructured media [25][26][27]. Additionally, the shape of the generated strain pulses is used to deduce the electron dynamics [22,23,28], and to study the wavelength-dependent elasto-optic coupling parameters [29] of the metal film.…”

“…As an extension of conventional ultrasonics into the nanometer size-regime, the method of picosecond ultrasonics has found wide application as an imaging tool in scientific and industrial environments [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. The small width of the strain pulses sets a limit to the spatial resolution that can otherwise only be achieved using x-ray radiation.…”