title: Ultrasensitive Characterization of Mechanical Oscillations and Plasmon Energy Shift in Gold Nanorods.
abstract: Mechanical vibrational resonances in metal nanoparticles are intensively studied because they provide insight into nanoscale elasticity and for their potential application to ultrasensitive mass detection. In this paper, we use broadband femtosecond pump-probe spectroscopy to study the longitudinal acoustic phonons of arrays of gold nanorods with different aspect ratios, fabricated by electron beam lithography with very high size uniformity. We follow in real time the impulsively excited extensional oscillations of the nanorods by measuring the transient shift of the localized surface plasmon band. Broadband and high-sensitivity detection of the time-dependent extinction spectra enables one to develop a model that quantitatively describes the periodic variation of the plasmon extinction coefficient starting from the steady-state spectrum with only one additional free parameter. This model allows us to retrieve the time-dependent elongation of the nanorods with an ultrahigh sensitivity and to measure oscillation amplitudes of just a few picometers and plasmon energy shifts on the order of 10(-2) meV.
authors.affiliation: Department of Physics, Politecnico di Milano , P.zza L. Da Vinci 32, 20133 Milano, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Soavi
authors.affiliation: Department of Physics, Politecnico di Milano , P.zza L. Da Vinci 32, 20133 Milano, Italy.
authors.forename: Iacopo
authors.initials: I
authors.lastname: Tempra
authors.affiliation: Laboratory of Bio-inspired & Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, Università di Trento , via Mesiano 77, 38123 Trento, Italy.
authors.forename: Maria F
authors.initials: MF
authors.lastname: Pantano
authors.affiliation: Laboratoire de Photonique et de Nanostructures, CNRS, Université Paris-Saclay , route de Nozay, F-91460 Marcoussis, France.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cattoni
authors.affiliation: Laboratoire de Photonique et de Nanostructures, CNRS, Université Paris-Saclay , route de Nozay, F-91460 Marcoussis, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Collin
authors.affiliation: Department of Physics, Politecnico di Milano , P.zza L. Da Vinci 32, 20133 Milano, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Biagioni
authors.affiliation: Laboratory of Bio-inspired & Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, Università di Trento , via Mesiano 77, 38123 Trento, Italy.|Center for Materials and Microsystems, Fondazione Bruno Kessler, Via Sommarive 18, 38123 Povo (TN), Italy.|School of Engineering and Materials Science, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom.
authors.forename: Nicola M
authors.initials: NM
authors.lastname: Pugno
authors.affiliation: Department of Physics, Politecnico di Milano , P.zza L. Da Vinci 32, 20133 Milano, Italy.|IFN-CNR, P.zza L. Da Vinci 32, 20133 Milano, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
keywords: coherent oscillations; metal nanoparticles; ultrafast spectroscopy