The field of organic-based opto-electronic devices such as organic light- emitting diodes (OLEDs) or field-effect transistors (OFETs) has grown in interest over the past two decades. Optimizing the performance of these applications requires a better understanding of the processes taking place inside the devices and especially at their interfaces. We focused in this Ph.D. work on the electronic structure of metal/organic interfaces where the charge injection mechanism occurs. The latter process can be modulated and fine tuned by the control of the work function of the metallic electrodes. Chemisorption of self-assembled monolayers (SAMs), i.e., a two-dimensional layer of polar molecules deposited onto metal surfaces proves to be an efficient way to tune the work function of electrodes in OLED and OFET devices. However, the role played by the dipole moment of the adsorbed molecules as well as the description of the electronic effects taking place at the metal/SAM interfaces are not yet well understood.
Our Ph.D. work aims at rationalizing at a theoretical level (via quantum- chemical calculations) the electronic processes occurring at metal/organic interfaces. For this goal, we focused our investigations on a well-characterized system : a methanethiolated SAM on gold-(111) surface. The adsorption energy and the influence of the anchoring site on the work function shift were evaluated beforehand in order to validate our methodology. The decomposition of the interfacial dipole moment into its interfacial and molecular components was assessed in a second stage for this system following two different procedures which differ by the treatment of the molecular backbone. The incorporation of a third component, generally not treated in an explicit way, was taken into consideration to unify the description of the interface dipole. The influence of the packing density was also described. In a next step, we have extended this study by changing the SAM chemical structure and by investigating the influence of a modification of the anchoring atom, a fluorination of the methyl group and a change in the nature of the metal surface (Ag, Cu, Pt). In order to probe the influence of intermolecular interactions, we have finally considered longer alkanethiol chains having various terminal chemical functions and analyzed the influence of the structural geometry on the change in the electrostatic potential.
| Identifer | oai:union.ndltd.org:BICfB/oai:umh.ac.be:ETDUMH:UMHetd-12202010-150355 |
| Date | 16 September 2010 |
| Creators | Cornil, David A. M. |
| Contributors | Crispin, Xavier, Vuillaume, Dominique, Robert, Toussaint, Brédas, Jean-Luc, Beljonne, David, Cornil, Jérôme, Villers, Didier |
| Publisher | Universite de Mons Hainaut |
| Source Sets | Bibliothèque interuniversitaire de la Communauté française de Belgique |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://theses.umh.ac.be/ETD-db/collection/available/UMHetd-12202010-150355/ |
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