Title : Plasmonic effects and localized melting in gold nanoparticles systems
Abstract:
Plasmonic materials are subjects of great interest due to their potential for a wide range of applications such as: catalysis, optoelectronics, drug delivery, etc. One particularly intriguing aspect is the ability of metal nanoparticles (NPs) to exhibit localized surface plasmon resonances (LSPR), which lead to the concentration of electromagnetic fields near the nanoparticle surface. The localized heating and melting in gold nanoparticles can be attributed to the interaction between the LSPR and the incident electromagnetic field but also to the excitation of interband transition. When the particle is excited with light of a suitable energy, generally resonant with the energy of the LSPR or interband transition, the absorption of the radiation by the nanoparticle leads to different phenomena. Indeed, the excitation at the LSPR wavelength leads to the formation of electromagnetic hot spots, whereas the excitation at the interband energy produces hot electrons, which are more homogeneously dispersed in the NP volume. Such differences can be exploited to obtain control over the melting of nanoparticles and optimize the features of the nanoparticle for the specific application [1,2]. Femtosecond transient absorption spectroscopy (FTAS) is a powerful tool for characterizing the features of plasmonic nanoparticles. FTAS allows us to obtain information into the fundamental physical processes related to the optical properties of these nanoparticles, which has important implications for using these materials in a wide range of applications. Indeed, FTAS is a time-resolved pump and probe technique that can probe the dynamics of plasmonic nanoparticles with high temporal resolution. We have applied this technique to separate the contributions of non-thermal and thermal electrons to the transient spectrum of arrays of gold nanoparticles in the first picoseconds after excitation to gain insight into the ultrafast dynamics of the photoexcited electrons [3]. The ability to induce localized heating and melting in gold nanoparticles is a route for using plasmonic nanoparticles in a variety of applications. For example, plasmonic nanoparticles have been proposed for cancer photothermal therapy, where localized heating can selectively kill cancer cells. Gold nanoparticles have also been proposed as a platform for drug delivery, where plasmonic heating can be exploited to release drugs previously bonded with the nanoparticle. Another promising application of plasmonic nanoparticles is in plasmon-enhanced photocatalysis. Indeed, plasmonic nanoparticles can be used to improve the efficiency of photocatalytic processes concentrating the light on the interface between the catalyst surface and gold nanoparticle and increasing the rate of electron transfer between the catalyst and the reactant. In conclusion, plasmonic effects and localized melting in gold nanoparticle systems represent a fascinating area of research in plasmonics with many potential applications. This research aims to understand the mechanisms of the melting of gold nanoparticles promoted by the excitation of the LSPR or interband transition and to develop new approaches for controlling the morphological properties of plasmonic nanostructures.
