2013-08-09 monograph Pentacen This thesis summarizes a number of studies regarding the preparation and spectroscopic characterizations of thin films of the organic semiconductor perfluoropentacene (PFP) and pentacene-tetrone (P-TET), as well as heterostructures of PFP and pentacene (PEN) and of PEN and Buckminster-Fullerene (C60). By combining various techniques, the morphology and structure of the thin films was analyzed and it was examined, how modifications of the preparation procedure such as the variation of the diffusion lengths of the molecules by tuning the substrate temperature influence the film formation. By specific choice of substrates with diverse geometrical and chemical properties, molecular films in different, highly ordered conformations have been prepared. This enabled detailed polarization-resolved spectroscopic characterizations, and thus allowed to determine the anisotropic electronic and vibrational characteristics of crystalline organic semiconductors. Furthermore, the influence of the nanoscopic quality of the substrate on the resulting thin films has been investigated for the combination of highly oriented pyrolitic graphite as substrate and PFP as well as P-TET as adsorbates. It was shown that the weak, but efficient interaction between substrate and adsorbate, results in planar adsorption conformation and large crystal sizes. This is especially interesting as it allows spectroscopic access to thin films with recumbent molecular orientation in the absence of chemical modification of the molecules by the substrate as often found in the case of metal substrates. Moreover, it was found that this template effect is suppressed even by microscopic substrate defects. In the case of deposition of PFP on HOPG a new crystalline structure (polymorph) has been identified and resolved, in which the PFP-molecules stack in parallel sequence relative to one another instead of adopting the common herringbone-motif. As this parallelism leads to effective overlap of the molecular $pi$-orbitals, it was found that the charge carrier mobility is enhanced by a factor greater than 10 compared to the bulk structure to a value which is even higher than the one found for pentacene. Furthermore, the PFP-metal-interfaces in case of the metals gold, silver and copper were studied. Because these interfaces are of great significance for the efficiency of actual devices, the comprehension and the stability of them is very important for the advancement of organic electronic devices. We found that the stability against catalytic processes, which had been ascribed to PFP, actually is not as high as projected. Instead, at reactive silver and copper surfaces, upon supply of thermal energy significant changes of the structural and electronic properties occur, which lead to complete dissociation of the molecule at high temperatures. Finally, studies have been conducted which are supposed to gain insights into structure formation and interaction of organic molecules with one another in so-called organic heterostructures. Organic heterostructures are of great importance, because a high number of prototypical electronic devices as organic solar cells and ambipolar organic field-effect transistors, are made of more than one compound. The efficiency of such devices in turn critically depends on the electronic interaction, the intermixture and the relative conformation. This leads to the necessity of conducting studies which investigate these correspondences with the aid of appropriate model systems. Such studies have been performed in this thesis, choosing heterostructures of PFP and PEN as well as PEN and C60 as model systems. Due to their high structural and electronic compatibility, crystalline molecular intermixture of PFP and PEN is found. It was furthermore shown that the proposed efficient quadrupolar of both compounds indeed results in electronic interaction and enhanced thermal stability of the heterostructure compared to the single compound. Moreover, different preparation methods of this heterostructure were compared and detailed insight was gained into the influence of the intermixture on the electronic properties. Although in turn heterostructures of PEN and C60 exhibit molecular separation, they nevertheless influence each other regarding their nanostructure. It was shown that by tuning the effective diffusion length of the fullerenes, C60 nanostructures of different dimensionality can be prepared, which furthermore renders possibilities to fabricate buried molecular nanostructures of low dimensionality. 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In: Applied Physics Letters 95 (2009), Nr. 21, 213302. http: //dx.doi.org/10.1063/1.3266857. – DOI 10.1063/1.3266857 Fachbereich Physik NEXAFS Rasterkraftmikroskopie Physik Perfluoropentacene Heterostruktur Buckminsterfulleren Organische Elektronik Diese Arbeit ist eine Zusammenfassung der Studien zur Präparation und spektroskopischen Charakterisierung von Dünnfilmen des organischen Halbleitermoleküls Perfluoropentacen (PFP) und Pentacenetetrone (P-TET), sowie von Heterostrukturen von PFP und Pentacen (PEN) und von PEN und Buckminster-Fulleren (C60). Durch die Kombination verschiedener Messtechniken wurden die Morphologie und Struktur der Dünnfilme analysiert und der Effekt von Veränderungen des Präparationsprozesses wie zum Beispiel der Variation der Diffusionslängen der Moleküle durch Einstellung der Substrattemperatur auf die Dünnfilme untersucht. Durch die gezielte Auswahl von Substraten verschiedener geometrischer und chemischer Eigenschaften wurden molekulare Dünnfilme in verschiedener, hochgeordneter Ausrichtung hergestellt. Dies ermöglichte die detaillierte polarisationsaufgelöste spektroskopische Vermessung dieser Dünnfilme, wodurch die anisotropen elektronischen, morphologischen und Vibrationseigenschaften der organischen Halbleitermoleküle in kristalliner Form bestimmt werden konnten. Weiterhin wurde der Einfluss der nanoskopischen Qualität des Trägersubstrates auf die resultierenden Dünnfilm-Eigenschaften für die Kombination von hochorientiertem pyrolitischen Graphit (HOPG) als Substrat und PFP und P-TET als Adsorbate untersucht. Hierbei zeigte sich, dass die schwache, aber effiziente Wechselwirkung zwischen dem Graphit-Substrat und dem Adsorbat in einer planaren Adsorptionsgeometrie und großer Kristallitgröße der Acene auf HOPG resultiert. Dies ist speziell interessant, da es spektroskopischen Zugang zu Dünnfilmen in liegender molekularer Orientierung ermöglicht, ohne dass die Moleküle durch starke Wechselwirkung mit dem Substrat chemisch verändert werden, wie es oft bei Kontakt mit Metalloberflächen der Fall ist. Durch Variation der Substratqualität wurde festgestellt, dass bereits mikroskopische Fehlstellen im Substrat diesen Effekt unterbinden, sodass die Substratqualität als kritischer Parameter für die Strukturbildung in molekularen Dünnfilmen identifiziert wurde. Im Falle der Deposition von PFP auf HOPG wurde eine neuartige Kristallphase (Polymorphismus) von PFP entdeckt, in der die PFP-Moleküle relativ zueinander parallel stapeln statt das typische Herringbone-Muster einzunehmen. Weiterhin wurden die PFP-Metall-Grenzflächen an den Metallen Gold, Silber und Kupfer studiert. Da diese Grenzflächen von entscheidender Bedeutung für die Effizienz realer Bauteile sind, ist ihr Verständnis und die Stabilität dieser Grenzfläche von großer Bedeutung für die Weiterentwicklung organischer elektronischer Bauteile. Es zeigte sich hierbei, dass die für PFP postulierte Stabilität gegenüber katalytischen Prozessen weitaus schwächer ist als vorhergesagt. Als Konsequenz treten an Grenzflächen mit reaktiven Silber- und Kupferoberflächen bei Zufuhr von thermischer Energie signifikante Veränderungen der strukturellen und elektronischen Eigenschaften auf, die bei hohen Temperaturen zu einer vollständigen Dissoziation des Moleküls führen. Zudem wurden Studien durchgeführt, die zu einem erweiterten Verständnis in der Strukturbildung und Wechselwirkung organischer Moleküle miteinander beitragen sollen. Solche organische Heterostrukturen sind von großer Bedeutung, da eine Vielzahl prototypialer elektronischer Bauelemente, wie beispielsweise organischer Solarzellen oder ambipolarer organischer Feldeffekttransistoren, auf Kombinationen mehrerer Komponenten zurückgreifen. Da die Effizienz dieser Bauteile wiederum kritisch von der elektronischen Wechselwirkung, der Durchmischung und relativen Anordnung der Komponenten zueinander bestimmt wird, sind die Ergebnisse dieser Arbeit, in der anhand geeigneter Modellsysteme eben solche Zusammenhänge untersucht wurden, von großer Bedeutung. Als Modellsysteme wurden Heterostrukturen von PFP und PEN sowie von PEN und C60 untersucht. Aufgrund der hohen strukturellen und elektronischen Kompatibilität tritt kristalline molekulare Durchmischung von PEN und PFP auf. Es wurde in dieser Arbeit nachgewiesen, dass die vorhergesagte effektive Quadruopol-Wechselwirkung beider Komponenten zu elektronischer Wechselwirkung und erhöhter thermischer Stabilität gegenüber den Einzelkomponenten führt. Darauf aufbauend wurden verschiedene Präparationsmethoden zu ihrer Herstellung verglichen. Zudem wurden detaillierte Erkenntnisse über die Auswirkungen der Durchmischung auf die elektronischen Eigenschaften gewonnen. Obwohl Heterostrukturen von PEN und C60 dagegen molekularer Entmischung unterliegen, beeinflussen sie sich dennoch in ihrer Nanostruktur. Es wurde gezeigt, dass durch Einstellung der Diffusionslängen der Fullerene C60-Nanostrukturen unterschiedlicher Dimensionalität mit gezielter Anlagerung an PEN-Molekularstufen hergestellt werden können. Dies bietet die Möglichkeit zur Fabrikation vergrabener molekularer Nanostrukturen, die spektroskopisch adressiert werden können. 2013 Physics Physik Preparation and Characterization of thin films of organic semiconductors and their heterostructures Dünne Schicht ths Prof. Dr. Witte Gregor Witte, Gregor (Prof. Dr.) https://doi.org/10.17192/z2013.0406 application/pdf Nanostruktur Herstellung und Charakterisierung von Dünnfilmen organischer Halbleiter und ihrer Heterostrukturen English Pentacene https://archiv.ub.uni-marburg.de/diss/z2013/0406/cover.png