<br />The theoretical modeling of plasmonics is challenging due to the complex interplay between electromagnetic waves, the electronic properties of the material, and the geometrical arrangement of the substrate. In the last decades, the comprehension of plasmons related phenomena arising in noble metal nanostructures and in graphene has benefited from the development of several theoretical methods, which can be divided into two main categories: continuum and ab initio methods respectively. The first are based on classical electrodynamics principles and are limited to the study of systems with a simple shape only, because otherwise the resolution of Maxwell’s equation would be impossible.In addition, they may fail when quantum effects have a predominant role on the optical properties of the system, such as in the case of complex-shape structures and nanojunctions.On the contrary, ab initio methods are able to overcome such limitations and return a precise description of plasmonic substrates. However, due to their high computational cost, such methods are constrained to systems of a few thousand of atoms. In this context, classical, yet atomistic models can predict results close to ab initio methods, while being computationally efficient such as continuum models. In this thesis, the optical properties of plasmonic nanostructures are investigated by using a classic, atomistic model called ωFQ, which has been developed by the research group I joined during my Ph.D. internship. In ωFQ, the charge interaction between the atoms of the nanostructure is modeled in terms of electric conduction between nearest neighbors via a simple Drude mechanism, which is modulated by a Fermi-like step function that mimics quantum tunneling effects. In this way, ωFQ is able to take into account quantum effects and returns results in agreement with ab initio references. In particular, the Thesis discusses the developments performed during my Ph.D. research activity to the initial formulation of the ωFQ model. Attention is firstly paid to the extension of ωFQ to model the optical properties of noble metal NPs which are characterized by interband effects. Then, the coupling between a molecular system, treated at the quantum mechanical level, and a plasmonic substrate, described by means of the ωFQ model, is presented and analysed. In this way, the modeling of the enhanced Raman spectrum of target molecules adsorbed on a plasmonic substrate becomes possible.<br />
Modeling nanoplasmonics from an atomistic point of view: from theory to applications / Bonatti, Luca; relatore: CAPPELLI, Chiara; Scuola Normale Superiore, ciclo 35, 11-Jul-2023.
Modeling nanoplasmonics from an atomistic point of view: from theory to applications
BONATTI, Luca
2023
Abstract
The theoretical modeling of plasmonics is challenging due to the complex interplay between electromagnetic waves, the electronic properties of the material, and the geometrical arrangement of the substrate. In the last decades, the comprehension of plasmons related phenomena arising in noble metal nanostructures and in graphene has benefited from the development of several theoretical methods, which can be divided into two main categories: continuum and ab initio methods respectively. The first are based on classical electrodynamics principles and are limited to the study of systems with a simple shape only, because otherwise the resolution of Maxwell’s equation would be impossible.In addition, they may fail when quantum effects have a predominant role on the optical properties of the system, such as in the case of complex-shape structures and nanojunctions.On the contrary, ab initio methods are able to overcome such limitations and return a precise description of plasmonic substrates. However, due to their high computational cost, such methods are constrained to systems of a few thousand of atoms. In this context, classical, yet atomistic models can predict results close to ab initio methods, while being computationally efficient such as continuum models. In this thesis, the optical properties of plasmonic nanostructures are investigated by using a classic, atomistic model called ωFQ, which has been developed by the research group I joined during my Ph.D. internship. In ωFQ, the charge interaction between the atoms of the nanostructure is modeled in terms of electric conduction between nearest neighbors via a simple Drude mechanism, which is modulated by a Fermi-like step function that mimics quantum tunneling effects. In this way, ωFQ is able to take into account quantum effects and returns results in agreement with ab initio references. In particular, the Thesis discusses the developments performed during my Ph.D. research activity to the initial formulation of the ωFQ model. Attention is firstly paid to the extension of ωFQ to model the optical properties of noble metal NPs which are characterized by interband effects. Then, the coupling between a molecular system, treated at the quantum mechanical level, and a plasmonic substrate, described by means of the ωFQ model, is presented and analysed. In this way, the modeling of the enhanced Raman spectrum of target molecules adsorbed on a plasmonic substrate becomes possible.
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