Theoretical approach to atomic-scale nanoplasmonics as probed by light and swift electrons

Thesis by Mattin Urbieta Galarraga for the degree of Doctor of Philosophy in Physics.This thesis tackles the theoretical description of atomic-scale features in plasmonic nanostructures asprobed by light and swift electrons. Plasmonic nanostuctures are known to localize and enhanceelectromagnetic fields in their proximity, and thus serve as building blocks to perform improved andenhanced molecular spectroscopy on them. We focus on the analysis of the effect of atomic-scale featuresin the overall response of plasmonic nanoparticles and nanocavities. We apply ab initio atomisticquantum time-dependent density functional theory (TDDFT) to unveil the near-field distribution aroundmetallic antennas, and describe "classically" various atomic-scale features such as continuous protrusionson the surfaces of the metal using a Boundary Element Method (BEM), providing an extra localization ofthe field. Moreover, we propose an analytical model to address the signal increase observed in surfaceenhancedRaman scattering (SERS) spectra related to local variations of the electron density associated toatomic-scale defects. Last, we identify the excitation of confined bulk plasmons (CBP) within theTDDFT calculations for the electron energy loss (EEL) probability of atomistic clusters, and provide asemi-analytical expression within a Hydrodynamic Model (HDM) to address such excitations.This thesis was funded by the University of the Basque Country UPV/EHU Grant PIF15/237 with a PhD fellowship and project GIU18/202, Donostia International Physics Center (DIPC) (Reference 2015/11) and Materials Physics Center (MPC) for financial support at the initial steps of the PhD, the Basque Government for projects IT756-13 and IT1164-19, and and by Spanish Ministry of Economy and Competitiveness MINECO for projects FIS2013-41184-P, FIS2016-80174-P and PID2019-107432GB-I00. The author thanks DIPC for the computing facilities and CFM for its support.Peer reviewe