Acoustic Vibrations of Au Nano-Bipyramids and their Modification under Ag Deposition: a Perspective for the Development of Nanobalances

Abstract

We investigated the acoustic vibrations of gold nanobipyramids and bimetallic goldÀsilver coreÀshell bipyramids, synthesized by wet chemistry techniques, using a high-sensitivity pumpÀprobe femtosecond setup. Three modes were observed and characterized in the gold core particles for lengths varying from 49 to 170 nm and diameters varying from 20 to 40 nm. The two strongest modes have been associated with the fundamental extensional and its first harmonic, and a weak mode has been associated with the fundamental radial mode, in very good agreement with numerical simulations. We then derived linear laws linking the periods to the dimensions both experimentally and numerically. To go further, we investigated the evolution of these modes under silver deposition on gold core bipyramids. We studied the evolution of the periods of the extensional modes, which were found to be in good qualitative agreement with numerical simulations. Moreover, we observed a strong enhancement of the radial mode amplitude when silver is deposited: we are typically sensitive to the deposition of 40 attograms of silver per gold core particle. This opens up possible applications in the field of mass sensing, where metallic nanobalances have an important role to play, taking advantage of their robustness and versatility.

Strong vibrational coupling in room temperature plasmonic resonators

“…In applications where nanoelectromechanical or nanooptomechanical systems are used for force and/or mass detection, the frequency noise in the measurement is given by 43 . The large quality factors and high SNR for the present materials mean that they are promising candidates for sensing applications 44,45 , exceeding the performance of traditional plasmonic nanoresonators by several orders of magnitude 46,47 .…”

Mechanisms of resonant low frequency Raman scattering from metallic nanoparticle Lamb modes

“…In the past decades, special attention was paid to localized acoustic modes, also called Lamb modes, because they can provide valuable information about the morphology, [1][2][3] the surface state, 4 and the crystallinity 5,6 of the probed nano-objects. Mostly metallic, 5,7-9 dielectric, 10,11 and semiconducting 12,13 spherical nanoparticles (NPs) have been studied but recent advances in chemistry-based synthesis have allowed us to consider other geometries of confinement such as nanoplates, 4,14,15 nanobipyramids, 16 or nanorods 17,18 with low size dispersion. Most useful information from Lamb modes is usually obtained by analysing the position and width of the LF Raman peaks 19,20 while less attention is paid to their intensities which are much harder to interpret due to intercompetition between several processes (multiple scattering, resonance conditions, re-absorption).…”

Nanoparticle–Fluid Interactions at Ultrahigh Acoustic Vibration Frequencies Studied by Femtosecond Time-Resolved Microscopy

“…Nanoparticle–fluid interactions represent an active area of research and have attracted broad attention especially for nanoparticle mechanical vibrations at ultrahigh frequencies (GHz to THz range), where the vibrational periods can be comparable to the liquid relaxation times. − Understanding how vibrational energy dissipation depends on the fluid properties is a prerequisite for designing high-quality-factor mechanical resonators that can operate in liquids. − Recently, simple liquids interacting with high-frequency resonators have shown the emergence of viscoelastic effects. − The strength of this effect depends on the form of the vibrational mode and the Deborah number for the liquid: De = ωλ, where ω is the frequency of the vibration and λ is the relaxation time of the liquid . Calculations and experimental results show that significant viscoelastic effects occur for vibrational modes that generate shear.…”