Picosecond ultrasonics study of the vibrational modes of a nanostructure

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 nu(n) and damping rates Gamma(n) 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 nu(n) and Gamma(n) 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. (C) 2002 American Institute of Physics.