Determination of the anisotropic optical properties for perfluorinated vanadyl phthalocyanine thin films
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W. Michaelis Physical Chemistry 1, Institute of Pure and Applied Chemistry, Faculty of Science, University of Oldenburg, D-26111 Oldenburg, Germany
R. Kröger Institute of Solid State Physics, University of Bremen, D-28334 Bremen, Germany
T. Kampen Physics Institute, University of Technology Chemnitz, D-09107 Chemnitz, Germany
D. Schlettwein Physical Chemistry 1, Institute of Pure and Applied Chemistry, Faculty of Science, University of Oldenburg, D-26111 Oldenburg, Germany
D.R.T. Zahn Semiconductor Physics, University of Technology Chemnitz, D-09107 Chemnitz, Germany (Received 5 November 2003; accepted 22 January 2004)
Thin films of perfluorinated vanadyl phthalocyanine F16PcVO were prepared by physical vapor deposition in high vacuum on KBr and fused silica substrates. The absorption spectra in the visible region show that the films on different substrates have different structure. The optical constants for F16PcVO films were obtained in the spectral range of 0.7–4.5 eV from the simulation of ellipsometry spectra with an anisotropic uniaxial model. From the difference between the in-plane and out-of-plane components of the extinction coefficient the average tilt angle of the F16PcVO molecular planes with respect to the substrate plane was found to be 56° for fused silica substrates and between 0° and 3° for KBr substrates.
I. INTRODUCTION
The growing interest in obtaining new electronic devices implies the application of new materials. In the last decade, research has also focused on organic materials as potential candidates for active layers in devices. Amongst these materials which possess a high thermal and chemical stability, as well as high optical absorption in the visible range are, e.g., phthalocyanines (Pc’s).1–7 This class of organic materials has been extensively used in the past as dyes and more recently they have proven their applicability in devices such as organic photovoltaic cells,3,8 organic field effect transistors (OFETs),9 organic light emitting diode (OLEDs),10 and gas sensors.11 The phthalocyanine properties can be tuned by the choice of the central metal ion and by chemical substitutions at the ligand. This was demonstrated for unsubstituted phthalocyanines1,3,12 and in particular for perfluorinated phthalocynanies.13,14
II. EXPERIMENTAL
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0264 2008
http://journals.cambridge.org
For any optoelectronic device application, the knowledge of the optical constants is vitally important. Unlike most inorganic semiconductors organic semiconductors show a pronounced optical anisotropy as a result of their anisotropic molecular structure. Therefore the aim of this work is to determine the anisotropic optical properties using F16PcVO as a representative molecule of the Pc class of materials. Studies regarding the anisotropic optical properties of organic semiconductors employing spectroscopic ellipsometry are still rare. The implementation of new mathematical algorithms15 based on 4
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