Interactions of molecules and surface Au(111)

Author(s)

Filipe Camargo Dalmatti Alves Lima

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2015-05-15

Examining board members

Helena Maria Petrilli; Lucy Vitoria Credidio Assali; Armando Corbani Ferraz; Francisco Eduardo Gontijo Guimarães; Paulo Barbeitas Miranda

• Advisor: Helena Maria Petrilli

Abstract

The study of hybrid interfaces, e.g. organic/inorganic or solid/liquid, have been showing an increasing interest in electrochemistry and nanotechnology. Within this subject, there are basic and applied studies, such as electronic tongues, self-assembled monolayers (SAMs), photovoltaic devices, alternative batteries, drug carriers and others. In special, the preference for gold surface occurs due to its inert nature, allowing the exploration of a wide range of electrostatic potentials which induces electrolysis and chemical reactions in other surfaces. The Cyclic Voltammetry study in Peptide-SAMs modified by ferrocene has been investigated in the literature. In recent years, a controversy on the charge transfer mechanism in biological materials started: at one hand, there are arguments in favor of an electronic tunneling process from the oxidative center to the eletrode; on the other hand, some authors suggest electronic hopping from the amide groups of the peptides, generating an electron-hole pair that ``walks\'\' from the ferrocene to the eletrode. Furthermore, systems with primitive interfaces, such as water, are also subject of current research due to the complexity of the experimental results reported in the literature. Within this scenario, we selected two distinct problems using the surface Au(111): i) the study of charge transfer mechanism using a peptide modified by ferrocene; ii) the study of electronic and structural properties of water interacting with NaCl. In order to obtain the electronic properties, we employed the Density Functional Theory in the Kohn-Sham (KS) scheme. For the structural and dynamics properties, we also used classical molecular dynamics (MD). Based on different models for the ferrocene-peptide/Au(111) interface, we investigate the density of states, Löwdin charges and KS wavefunctions. We notice the presence of localized electronic states on the ferrocene and gold which are close to the Fermi energy in all studied cases. These results suggest an electronic tunneling from the ferrocene site to the surface Au(111) as the mechanism for the charge transfer. In the case of salt dissociated in water, we investigated the electronic properties in several different configurations. Furthermore, in a MD perspective, the orientation of the water molecules presented a high sensitivity for the Au(111) interface. These results represent a wide view of the electronic and dynamic behavior of systems using the surface Au(111) as a common subject. (AU)

• FAPESP's process: 12/02326-8 - Computational modeling of solid-molecule interaction in systems with nanotechnology interests
• Grantee: Filipe Camargo Dalmatti Alves Lima
• Support Opportunities: Scholarships in Brazil - Doctorate