Mechanical Damping of Longitudinal Acoustic Oscillations of Metal Nanoparticles in Solution

We present measurements and theoretical analysis of the damping of high-frequency acoustic vibrations of metal nanoparticles immersed in solution. Building on our previous work [Pelton, M.; Sader, J. E.; Burgin, J.; Liu, M.; Guyot-Sionnest, P.; Gosztola, D. Nat. Nanotechnol. 2009, 4, 492–495], we study several bipyramidal gold nanoparticle samples in a series of solvent environments in order to examine the origin of the measured damping. We use a fluid-structure interaction model to explain the damping due to the fluid surrounding the nanoparticles, extending the model to encompass the case of an arbitrary slender body. Good agreement with the theoretical model is found for a range of pure solvents and solvent mixtures, demonstrating that classical continuum theories for fluid mechanics are able to quantify high-frequency phenomena at the nanoscale. The remaining damping rate, which can be attributed to processes intrinsic to the nanoparticles, is consistent across all the measured samples. This demonstrates that the measured intrinsic damping is indeed a characteristic property of these bipyramidal metal nanoparticles, rather than being sample dependent.