Probing the Roughness of Porphyrin Thin Films with X-ray Photoelectron Spectroscopy |
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Authors: | Dr. Elmar Kataev Daniel Wechsler Prof. Federico J. Williams Julia Köbl Dr. Natalia Tsud Dr. Stefano Franchi Prof. Hans-Peter Steinrück Dr. Ole Lytken |
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Affiliation: | 1. Department of Chemistry and Pharmacy, Friedrich-Alexander Universität Erlangen-Nürnberg, Egerlandstraße 3, Erlangen, 91058 Germany;2. Departamento de Química Inorgánica, Analítica y Química Física, Universidad de Buenos Aires, Pabellón 2, Buenos Aires, C1428EHA Argentina;3. Department of Surface and Plasma Science, Charles University, V Holešovičkách 2, Prague, 11636 Czech Republic;4. Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, via Fosso del Cavaliere, 100 Roma, Italy |
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Abstract: | Thin-film growth of molecular systems is of interest for many applications, such as for instance organic electronics. In this study, we demonstrate how X-ray photoelectron spectroscopy (XPS) can be used to study the growth behavior of such molecular systems. In XPS, coverages are often calculated assuming a uniform thickness across a surface. This results in an error for rough films, and the magnitude of this error depends on the kinetic energy of the photoelectrons analyzed. We have used this kinetic-energy dependency to estimate the roughnesses of thin porphyrin films grown on rutile TiO2(110). We used two different molecules: cobalt (II) monocarboxyphenyl-10,15,20-triphenylporphyrin (CoMCTPP), with carboxylic-acid anchor groups, and cobalt (II) tetraphenylporphyrin (CoTPP), without anchor groups. We find CoMCTPP to grow as rough films at room temperature across the studied coverage range, whereas for CoTPP the first two layers remain smooth and even; depositing additional CoTPP results in rough films. Although, XPS is not a common technique for measuring roughness, it is fast and provides information of both roughness and thickness in one measurement. |
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Keywords: | X-ray photoelectron spectroscopy Growth Porphyrin molecules Thin films |
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