PhD Thesis Defense | Bruno Candelas Peñalba

Atomistic ab initio study of optical excitations in nanoplasmonic systems as probed by light and fast electrons

September 5, 11:00

CFM Auditorium

Candidate: Bruno Candelas Peñalba

Supervisors: Nerea Zabala and Javier Aizpurua

DOWNLOAD full thesis

SUMMARY

In this theoretical thesis, atomistic ab initio methods are used for studying the response of three canonical configurations in nanophotonics, with the aim of analyzing the influence of atomistic effects and other quantum effects on the response. We start with a short background on plasmonics and on the methodologies employed throughout the thesis. We then compute the optical response of organic molecules coupled to icosahedral silver clusters in different geometrical configurations, and we find that the dimer configuration has a significant effect on the coupling strength, as well as determining the emergence of other quantum phenomena such as charge transfer. Afterwards, we characterize the full plasmonic response of sodium nanoparticles as probed by penetrating electron beams with the help of two auxiliary models: a classical Hydrodynamic Model and a quantum Jellium model. This allows us to provide a thorough description of the complex excitation of Confined Bulk Plasmon modes and their behavior when varying the impact parameter. Additionally, we also show that penetrating electron beams also excite Bennett plasmons just below the plasma frequency. We finish the thesis with an analysis of the Raman response of fully periodic self-assembled monolayers. To do so, we first compute the optimal monolayer configurations with the help of a methodology based on Bayesian optimization. Then, we obtain the Raman spectra of the monolayers, and analyze how they are affected by several geometrical factors: the molecular orientation, the coverage density, and the reconstruction of the substrate. These results improve our understanding of the importance of atomistic and quantum effects on the response of small metallic nanoparticles and complex hybrid metal—organic systems.

Sketch of the configurations studied in the thesis. a) Optical absorption of coupled dimer–molecule systems. b) Electron energy-loss spectra of sodium clusters. c) Surface-enhanced Raman spectra of organic self-assembled monolayers.