Energy Dissipation for Nanometer Sized Acoustic Oscillators
Kuai Yu, Yiqi Jiang, C. M. Wright, Gregory V. Hartland
Abstract
Ultrafast laser excitation of nanostructures causes rapid heating that can excite vibrational modes that map onto the expansion coordinates. These modes lose energy by radiating sound waves into the environment. Recent experiments have focused on how liquid viscosity and associated viscoelasticity affect the energy dissipation process. In this Perspective we give an overview of the continuum mechanics theory used to describe the damping of the vibrational modes in solid and liquid environments and describe recent experimental measurements of damping. The theory focuses on the breathing modes of spheres, infinite cylinders, and infinite plates, as these are the most relevant to experiments and can be described analytically. We examine the differences between different shapes and how the relaxation times depends on the dimensions of the nanostructures. In particular, a complicated behavior occurs at sizes where the frequency of the vibrational modes becomes comparable to the relaxation time in the environment. In this regime the quality factors for the breathing modes can be used to estimate environmental relaxation times, providing unique information about the properties of materials at nanoscale dimensions.