Self-assembled monolayers of organic molecules on noble metals and two-dimensional materials

Abstract

This thesis reports a study of several two-dimensional supramolecular networks deposited on gold surface and two-dimensional materials. The work aims to evidence the formation of the molecular assemblies and their related interaction with the underling substrates. First, the metal-organic interface between Zn(II) tetraphenyl porphyrin (ZnTPP) and Au(111) is systematically characterized as a function of the molecular coverage. We found that the interaction between the gold surface and the molecular monolayer is considerable, unlike one might expect from this particular system. Moreover, the molecular diffusion process is also evidenced. Afterwards, the self-assembly of the Nile red molecules on Au(111) substrate, from sub- to mono- layer coverages, is reported for the first time. The dependence of molecular packing from the thermal treatments of the samples is evidenced, while further information are also gained on the intermolecular interaction and on molecular mobility. Later, supramolecular assembly of two carboxylic acids, i.e. benzene-1,4-dicarboxylic acid (terephthalic acid, TPA) and benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) deposited on graphene substrate were investigated. After determining the monolayer packing, the structural transition that occurs as molecular deposition proceeds over the monolayer coverage is determined. We evidence that, despite the chemical similarity between the two molecules, their monolayer-to-thin-film transitions are dramatically different. Finally, the effect of the deposition of the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on the surface of a prototypical topological insulator, i.e. bismuth selenide (Bi2Se3), is reported. The molecular assembly was determined, while a negligible charge transfer between the molecular layer and the substrate are also found. In addition to the main topic of the work, the thesis also reports other research activities connected to the two-dimensional systems. In particular, the growth and characterization of graphene films on copper foil, by means of Chemical Vapor Deposition (CVD) are performed. The different coupling of graphene layer on the Cu foil and the possibility to induce a variation of the graphene coupling with respect to the Cu substrate by visible-light irradiation above a proper power threshold are evidenced. Finally, the nucleation and growth of iron cluster on MgO/Ag(100) surface is considered. Relevant information are obtained on the cluster size dependence from deposition temperature of the substrate and from the nominal coverage.