RESUMEN
The cooling dynamics of individual gold nanodisks synthesized using colloidal chemistry and deposited on solid substrates with different compositions and thicknesses were investigated using optical time-resolved spectroscopy and finite-element modeling. Experiments demonstrate a strong substrate-dependence of these cooling dynamics, which require the combination of heat transfer at the nanodisk/substrate interface and heat diffusion in the substrate. In the case of nanodisks deposited on a thick sapphire substrate, the dynamics are found to be mostly limited by the thermal resistance of the gold/sapphire interface, for which a value similar to that obtained in the context of previous experiments on sapphire-supported single gold nanodisks produced by electron beam lithography is deduced. In contrast, the cooling dynamics of nanodisks supported by nanometric silica and silicon nitride membranes are much slower and largely affected by heat diffusion in the membranes, whose efficiency is strongly reduced as compared to the thick sapphire case.
RESUMEN
The plasmonic and vibrational properties of single gold nanodisks patterned on a sapphire substrate are investigated via spatial modulation and pump-probe optical spectroscopies. The features of the measured extinction spectra and time-resolved signals are highly sensitive to minute deviations of the nanodisk morphology from a perfectly cylindrical one. An elliptical nanodisk section, as compared to a circular one, lifts the degeneracy of the two nanodisk in-plane dipolar surface plasmon resonances, which can be selectively excited by controlling the polarization of the incident light. This splitting effect, whose amplitude increases with nanodisk ellipticity, correlates with the detection of additional vibrational modes in the context of time-resolved spectroscopy. Analysis of the measurements is performed through the combination of optical and acoustic numerical models. This allows us first to estimate the dimensions of the investigated nanodisks from their plasmonic response and then to compare the measured and computed frequencies of their detectable vibrational modes, which are found to be in excellent agreement. This study demonstrates that single-particle optical spectroscopies are able to provide access to fine morphological characteristics, representing in this case a valuable alternative to traditional techniques aimed at postfabrication inspection of subwavelength nanodevice morphology.
RESUMEN
When reducing the size of a material from bulk down to nanoscale, the enhanced surface-to-volume ratio and the presence of interfaces make the properties of nano-objects very sensitive not only to confinement effects but also to their local environment. In the optical domain, the latter dependence can be exploited to tune the plasmonic response of metal nanoparticles by controlling their surroundings, notably applying high pressures. To date, only a few optical absorption experiments have demonstrated this feasibility, on ensembles of metal nanoparticles in a diamond anvil cell. Here, we report a nontrivial combination between a spatial modulation spectroscopy microscope and an ultraflat diamond anvil cell, allowing us to quantitatively investigate the high-pressure optical extinction spectrum of an individual nano-object. A large tuning of the surface plasmon resonance of a gold nanobipyramid is experimentally demonstrated up to 10 GPa, in quantitative agreement with finite-element simulations and an analytical model disentangling the impact of metal and local environment dielectric modifications. High-pressure optical characterizations of single nanoparticles allow for the accurate investigation and modeling of size, strain, and environment effects on physical properties of nano-objects and also enable fine-tuned applications in nanocomposites, nanoelectromechanical systems, or nanosensing devices.
