Thesis presented July 16, 2015
Abstract:
Graphene, a monolayer of graphite, is composed of carbon atoms arranged in a honeycomb lattice. Its exceptional properties have attracted a worldwide interest, including the Novel Prize in Physics in 2010. Epitaxial graphene on a metal was rapidly identified as an efficient method for large-area production of high quality graphene, and also was the matter of intense activities exploiting surface science approaches to address the various properties of graphene and of advanced systems based on graphene, for instance ordered lattice of metal nanoparticles on graphene. This resulted in the study of growth, structure and defects of epitaxial graphene on a wide variety of substrates with various techniques such as scanning tunneling microscopy, angle-resolved photoemission spectroscopy or low-energy electron microscopy.
This work focuses on graphene grown on the (111) surface of iridium in ultra-high vacuum conditions and studied with several diffraction techniques (surface X-ray diffraction, grazing incidence X-ray diffraction, X-ray reflectivity, and reflection-high energy electron diffraction). These experiments were performed at the European Synchrotron Radiation Facility in Grenoble, France. The first step in our study was to determine the structure of graphene at the atomic scale. The system was found to have a tendency to commensurability, but that the precise structure depends on temperature and on preparation conditions. Moreover, with the combination of high resolution diffraction techniques, a precise characterization about the debated structure of graphene perpendicular to the surface was unveiled.
The system, exhibits a superstructure, typical of epitaxial graphene, called a moiré, as an equivalent of the moiré effect in optics. This is used as a template to grown nanoparticles on top of the system to achieve the self-organization of monodisperse nanoparticles. In this study, three type of nanoparticles were investigated, two different size of pure platinum ones and bimetallic ones, platinum and cobalt. These hybrid systems show very high degree of order, partly inherited by the superstructure lattice. The nanoparticles were found to strongly bond to their support, experience substantial surface strain related to their small size, and that bimetallic ones grown in a sequential manner retain a chemically layered structure.
Keywords: Graphene, Synchrotron, Growth, Structure, Self-Organization, Near field microscopy
On-line thesis.