| AVS 54th International Symposium | |
| Surface Science | Friday Sessions |
| Session SS2+EM+TF-FrM |
| Session: | Organic Films II: Semiconductors and C@sub 60@ |
| Presenter: | A. Andreev, Univ. of Leoben, Austria |
| Authors: | A. Andreev, Univ. of Leoben, Austria A. Montaigne, Univ. Linz, Austria T. Haber, Graz Univ. of Tech., Austria A. Kadashchuk, National Academy of Sci. of Ukraine G. Hlawacek, Univ. of Leoben, Austria D.-M. Smilgies, Cornell Univ. R. Resel, Graz Univ. of Tech., Austria A. Winkler, Graz Univ. of Tech., Austria H. Sitter, Univ. Linz, Austria N.S. Sariciftci, Univ. Linz, Austria C. Teichert, Univ. of Leoben, Austria |
| Correspondent: | Click to Email |
Para-sexiphenyl (6P) films grown on mica(001) and KCl(001) substrates show large morphological and optical anisotropy, which makes them attractive for nano-scale photonic devices. In this work we use Atomic Force Microscopy (AFM), electron microscopy, x-Ray diffraction (XRD), and photoluminescence (PL) in order to find the parameters controlling film morphology, structure, and quality. It is shown that the initial growth stage of 6P on KCl(001) is characterized by the formation of μm-long needles, generating a rectangular network in accordance with the substrate surface symmetry. With increasing coverage, terraced mounds composed of upright standing molecules developing between the needles are observed and subsequent growth is characterized by a coexistence of both features. It is demonstrated that both features grow directly on the substrate surface, i.e., there is no wetting layer during the deposition of 6P on KCl(001). It is also found that both needles and terraced mounds grown on KCl(001) are single crystalline, in contrast to mica(001), where different oriented 6P domains are formed inside of the chains. PL studies have shown that, as in 6P films on mica, the emission spectra contain two different components - a conventional structured spectrum due to intrinsic excitons and a broad red-shifted band ascribed to some kind of defects. The latter band most clearly can be distinguished in delayed fluorescence spectra of the studied films. It is remarkable, however, that the relative intensity of the defect band was much weaker in the films grown on KCl substrates comparing to that on mica, which corresponds well with results of morphological and structural investigations. This finding confirms the high quality of the films and implies that the defect band is rather sensitive to the structure and morphology of the films. We also discuss a correlation between growth condition of 6P and a relative intensity of the defect PL band.