Damping of the Acoustic Vibrations of Individual Gold Nanoparticles

Abstract

In this letter, the ultrafast vibrational dynamics of individual gold nanorings has been investigated by femtosecond transient absorption spectroscopy. Two acoustic vibration modes have been detected and identified. The influence of the mechanical coupling at the nanoparticle/substrate interface on the acoustic vibrations of the nano-objects is discussed. Moreover, by changing the environment of the nanoring, we provide a clear evidence of the impact of the surrounding medium on the damping of the acoustic vibrations. Such results are reported here for the first time on individual nanoparticles. This work points out a new sensing method based on the sensitivity of the acoustic vibration damping to the surrounding medium.

Acoustic vibrations of metal nano-objects: Time-domain investigations

“…Dashed green lines indicate the result of theoretical calculations for the breathing mode of spheres (a) and infinite cylinders (b)-(c) in homogeneous environment (water or silica). embedding a nano-object in higher viscosity medium, as observed for single lithographed gold nanorings in water and glycerol, in qualitative agreement with viscoelastic models (Section 2.2) [83]. Investigation of the environment behavior of two different modes of the same object is here particularly interesting as it can bring information on the involved coupling mechanisms.…”

“…This is no more the case when frequency-dependent µ and λ Lamé coefficients are used in order to include viscosity effects in liquids, deviations from a simple scaling law being obtained with increasing viscosity and mode frequency (i.e., decreasing the nano-object size) [67,[80][81][82]. However, in most conventional liquids these effects can be neglected, except for high viscosity solvents such as glycerol [59,[83][84][85], and will not be discussed in detail here.…”

“…Though results have been obtained in very high quality samples [45,59,84,98,151], limitation associated to particle morphology dispersion can be more generally circumvented by investigating single nano-objects. Such studies can be performed using femtosecond pump-probe far-field spectroscopy demonstrated for individual metal nanoparticles with size down to 20 nm [233], and applied to investigation of the acoustic vibrations of few tens to one hundred nanometer individual metal particles deposited or lithographed on a substrate, or optically trapped in a liquid [48,69,70,83,108,234].…”

“…Time-domain acoustic vibrations of individual nano-objects have been extensively studied for various different shapes: gold spheres [68], dumbbells [169], rods [70,234,249,250], prisms [108], rings [83] or wires [67], and silver cubes [69,248] or wires [55,69]. Different particle environments were explored using particles deposited (by spin-coating a colloidal solution) or fabricated on a substrate (by nanosphere or electron beam lithography), embedded in sub-micron thick polymer film, or optically trapped in a liquid, or suspended over a trench [55,[67][68][69][70]108,169,234,247,249,248].…”

“…Different investigations performed on substrate-supported (gold spheres, rods, prisms, rings or wires and silver cubes or wires), suspended (gold wire) or optically trapped particles (gold spheres in liquid) all show very large particle to particle variation of the measured damping rate, with weak correlation with the vibrational frequencies [48,55,67,69,70,83,108,234,248] (Figs. 20 and 21).…”