A study of the vibrational modes of a nanostructure with picosecond ultrasonics

We describe experiments in which a sub-picosecond pump light pulse is used to excite vibrations in a nanostructure. The sample consists 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 data, it is possible to determine the frequencies ν n and damping rates Γ n of a number of the normal modes of the structure. These modes have frequencies lying in the range 1-30GHz. By comparison of the measured ν n and Γ n with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to identify the different normal modes and deduce their vibration patterns. © 2002 Published by Elsevier Science B.V.