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Book/Dissertation / PhD Thesis | FZJ-2017-04578 |
2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-245-0
Please use a persistent id in citations: http://hdl.handle.net/2128/15149 urn:nbn:de:0001-2017081712
Abstract: A systematic study of the growth of a heteromolecular adsorbate system in the submonolayer regime is presented in this work. The properties of such systems are determined by the interplay between molecule-substrate and molecule-molecule interactions, and hence a careful selection of molecule on the one hand, and substrates on the other hand is essential. The molecules PTCDA and CuPc were chosen as adsorbates since they represent a donor-acceptor model system for organic electronics. Their intermolecular interaction is very different in the homomolecular phases with an attraction between PTCDA molecules and a mostly repulsive interaction in the case of CuPc. Consequently, these molecules form compact islands (PTCDA) or a dilute disordered gas-like phase (CuPc) which enables fundamentally different ways of preparing the heteromolecular films. Two different substrates, which were employed to investigate the influence of the metal-molecule interaction on the growth, are Ag(111) and Cu(001). The phase diagram of the heteromolecular PTCDA-CuPc system on Ag(111) at 300K is the key finding in this work and is discussed in chapter 6.2.3.1. It contains eight different regions with one or two different crystalline phases which coexist with areas of a disordered phase of both molecules. Only the disordered phase is present on the surface in a ninth region. It is found that the local density of CuPc in the disordered phase is the decisive parameter for the occurrence of the different phases. Different phases exist when certain critical values of the CuPc density are exceeded. A number of other investigations have also been performed and most of their results are essential for the understanding of this phase diagram since its shape is determined by a complex interplay between different forces. $\textbf{Homomolecular systems}$ The growth of the homomolecular systems is studied in the first part of this work since it is impossible to understand the growth processes of heteromolecular systems without first understanding the growth of the respective homomolecular systems. Detailed analyses were performed to determined the interaction between the molecules and the molecules and the substrate. The attractive intermolecular interaction dominates the growth of PTCDA leading to the growth of crystalline islands already at very low coverages on both metal sub- strates. The island size distribution and the island density are used to quantitatively deter- mine the binding energy between the molecules on Cu(001) to be 1.6 eV which is the energy required to detach one molecules from a molecular cluster. This high binding[...]
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