Optical spectroscopy techniques represent a powerful tool to study the vibrational modes of nano-objects and address both their intrinsic properties (related to nanoparticle morphology, crystallinity, and local environment) and their interaction with light, which plays a key role for nanophotonics and optomechanics applications. In this paper, we report lowfrequency inelastic light scattering measurements on single gold nanocrystals, combined with detailed characterizations of their morphology and environment using transmission electron microscopy and tomography, and numerical simulations of their optical and vibrational responses. Our studies confirm the conclusions of previous ensemble measurements regarding the large impact of the nanoparticle crystallinity on inelastic scattering spectra. Moreover, their single-particle character allows us to address subtle shape and environment effects. We show that slight nanoparticle shape anisotropies induce further splitting of Raman-active modes. We also demonstrate that local environment anisotropies lead to richer inelastic light scattering spectra and allow the detection of vibrational modes predicted to be Ramaninactive by usual Raman selection rules, which are based on the (here invalid) assumption of a symmetric internal electric field.

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In situ electron irradiation effects on shape and size of plate-like Ag nanoparticles (NPs) embedded in silicon nitride self-standing % 70-nm-thick membranes are investigated as a function of the beam energy (120, 160 and 200 keV) and fluence using a conventional transmission electron microscope. The irradiations are performed at room temperature and cause a rapid spheroidization of the initially observed plate-like structures. Preferential sputtering of N and Si atoms exposes the resulting Ag NPs to the vacuum. At this point the sputtering of the Ag atoms causes a size decrease at distinct rates depending on the NP size and on the beam energy. This is modeled considering the influence of a size-dependent surface binding of the Ag atoms on the sputtering process. The results are compared with literature models for size-dependent cohesive energy. Our experiments discloses a new way to modify sizes and shapes and test for the size-dependent properties of thermally unstable nanoscopic objects.