Invited Paper
Linear and Ultrafast Plasmonics with Individual Metal and Hybrid Nanoparticles

Understanding and modeling the impact of size, shape and environment on the optical properties of nano-objects is an intense field of research with both fundamental and technological motivations. With the advance of single nanoparticle spectroscopy methods, the optical response of a single nano-object can now be addressed, and its morphology independently determined by electron microscopy, opening the way to precise comparison with theoretical models.

In this context we will describe investigation of individual nanoparticles deposited on a substrate, and analyze the influence of the latter on their optical absorption. Experiments are performed using the spatial modulation spectroscopy method, which yields access to the absorption cross-section spectra and amplitude of a single nano-object with size down to a few nanometers [1]. In the case of silica-coated nanorods, isolation from the substrate provided by the silica shell largely reduces interaction with the environment, also allowing investigation of quantum size effects [2-4]. This is no more the case for bare particles such as gold nanorods or bipyramids deposited on transparent or absorbing substrates, whose surface plasmon resonance (SPR) is strongly modified depending on particle-substrate distance and orientation, as determined by electron tomography.

While nano-objects formed by a single material have been extensively investigated, the optical properties of nano-hybrids formed by different materials are still little studied, though combination of the nanoscale responses of their components offer wide possibilities for developing novel plasmonic systems. In this talk, the linear and ultrafast optical response of Ag-Au hetero-dimers will be discussed [4]. Interaction of the silver SPR with the continuum of interband transitions in the gold component is predicted to lead to a Fano effect, which is however difficult to observe using linear spectroscopy. This has been singled-out using time-resolved pump-probe spectroscopy, that permits selective analysis of gold absorption in the individual dimer, yielding results in excellent agreement with theoretical predictions.

[1] O.Muskens et al. Phys. Rev. B 78, 205410 (2008)

[2] A.Lombardi et al. Langmuir 28, 9027 (2012)

[3] Y.Davletshin et al. ACS Nano 6, 8183 (2012)

[4] V.Juvé et al. Nano Letters 13, 2234 (2013)

[5] A.Lombardi et al. ACS Nano 7, 2522 (2013)

natalia.del-fatti@univ-lyon1.fr