AVS 52nd International Symposium
    Electronic Materials and Processing Friday Sessions
       Session EM-FrM

Paper EM-FrM8
Growth and Chemical Structure of Crystalline Rubrene Films

Friday, November 4, 2005, 10:40 am, Room 309

Session: Organic Electronic Devices
Presenter: G. Witte, Ruhr-University Bochum, Germany
Authors: G. Witte, Ruhr-University Bochum, Germany
D. Kaefer, Ruhr-University Bochum, Germany
Ch. Woell, Ruhr-University Bochum, Germany
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Rubrene single crystals have recently been demonstrated to exhibit remarkably high charge carrier mobilities@footnote 1@ which favors the use of this organic semiconductor material for molecular electronics applications e.g. organic field effect transistors. In contrast to other oligomer semiconductors such as pentacene the growth of crystalline thin films, however, has not been achieved for rubrene. Using x-ray absorption spectroscopy (NEXAFS) we have analyzed the initial stage of film growth on various substrates and demonstrate the importance of molecular conformation which involves a loss of chirality in case of rubrene. Whereas organic molecular beam deposition at room temperature only leads to rather amorphous layers, dendritic films are obtained at high substrate temperatures but the size of the crystallites is mainly limited by competing dewetting and desorption. An improved crystallite growth is achieved by using a modified "hot wall"-type deposition cell which allows operation under UHV-conditions but at much higher vapor pressure. Moreover, by combining AFM and SEM with XPS and LDI-TOF mass spectroscopy the morphology of the films and the amount of rubrene-peroxide formed upon exposure to air was characterized. Large differences in the corresponding rubrene-peroxide concentrations and their depth profiles were found for the various films and crystals which is of great importance for applications in molecular electronics. @FootnoteText@@footnote 1@ V.C. Sundar et al. Science 303, 1644 (2004).