Über den Einfluss von Phthalocyanin-Monolagen auf die Struktur organischer Dünnfilme auf Metalloberflächen

In der vorliegenden Dissertation wird der Einfluss von Monolagen der molekularen, organischen Halbleiter Kupferphthalocyanin (CuPc) und Titanyl- Phthalocyanin (TiOPc) auf das Wachstum und die Struktur von mehrschichtigen organischen Dünnfilmen auf Metallsubstraten untersucht. Im homomolekularen...

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Bibliographic Details
Main Author: Mänz, Alexander
Contributors: Witte, Gregor (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2017
Online Access:PDF Full Text
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In this work, the influence of monolayers of the molecular organic semiconductors Copper-Phthalocyanine (CuPc) and Titanyl-Phthalocyanine (TiOPc) on the growth and structure of organic thin films on metal substrates is investigated. TiOPc thin films are utilized as a model system for a homo-molecular multilayer structure, in which the metal-organic interface is formed by the organic thin film itself. Mono-, bi- and multilayer structures are investigated by scanning tunnelling microscopy (STM) with respect to coverage. In the submonolayer regime, 3 phases with different types of commensurism are found. The 2D unit cell size, as well as the molecular orientation relative to the substrate are analyzed and compared with results from low energy electron diffraction (LEED) and infrared adsorption spectroscopy (IRAS). Structures found for TiOPc (sub-)monolayers on Au(111) substrates show comparable phases with significantly higher inhomogeneity regarding the local coverage. A uniform vertical molecular orientation ist found for all monolayer phases and on all substrates, with the Oxygen pointing towards the vacuum. Consecutively deposited bilayer molecules adsorb in inverted geometry, establishing strong interactions with the underlying monolayer and the substrate and forming a stabilized double layer framework. Those frameworks are also the basis for multilayered systems, in which no wetting beyond the first bilayer framework is found. Instead, atomic force microscopy (AFM) reveals the occurrences of dewetted crystallites on Ag(111) and Au(111), as well as on KCl(001) and HOPG substrates. X-ray Diffraction (XRD) provides information on the adapted crystallographic polymorphs (phase I and beta-phase) dependent on the substrate. Adapted polymorphs are compared to the crystal structures found in raw TiOPc powder. Beside this assignment, no substrate-induced thin film phase is found. In the case of heteromolecular interfaces, CuPc monolayers are used as a contact layer between coinage metal substrates and thin films of the organic semiconductor pentacene (Pen). Firstly, a reliable and reproducible protocol for the preparation of CuPc monolayers is established. Its frontiers regarding the preparation parameters, structural stability and applicability to other systems are stated. We find a temperature range of 520K< T < 550K, in which CuPc multilayer desorption leads to long-range ordered monolayers on Ag(111) and Au(111) substrates. On Cu(001) surfaces, the strong adsorbate-substrate coupling denies a monolayer preparation at high molecular flux. Consecutive deposition of Pentacene leads to the growth of metastable structures at low coverages (~2nm) on Ag(111) and Au(111) substrates. The actual thickness of this metastable structure can be correlated to the interaction of different Van-der-Waals forces dependent on substrate characteristics. Upon further deposition, Pentacene arranges in pyramidal-shaped domains with upright molecular orientation and adopts the substrate-induced thin film phase, as revealed by AFM and XRD. The crystallinity of thin films with a thickness of 30nm strongly depends on the roughness of the underlying substrate. This is proven using distorted CuPc monolayers on Cu(001) as contact layer and poly-crystalline gold substrates. Regarding the multilayer structure only, the influence of a CuPc buffer layer between a metal substrate and a Pentacene multilayer film can be compared to the use of self-assembling monolayers (SAMs) as a contact layer.