Growth and Structure of Pentacene Films on Graphite: Weak Adhesion as a key for Epitaxial Film Growth
- Autor: Götzen, J. / Käfer, D. /Witte, G. / Wöll, C. (2010)
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Quelle:
Phys. Rev. B. 81 (2010), 085440
- Datum: 2010
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Götzen, J. / Käfer, D. /Witte, G. / Wöll, C. (2010): „Growth and Structure of Pentacene Films on Graphite: Weak Adhesion as a key for Epitaxial Film Growth“. In: Phys. Rev. B. 81 (2010), 085440
Abstract
The microstructure of pentacene films grown on the basal plane of graphite has been investigated. By combining various complementary techniques including scanning tunneling microscopy, atomic force microscopy, x-ray diffraction, thermal desorption spectroscopy, and x-ray absorption spectroscopy the molecular orientation, crystalline structure, and morphology of the films as well as their thermal stability have been characterized in detail as a function of the film thickness.
Initial film growth leads to the formation of a commensurate monolayer consisting of flat-lying molecules while upon subsequent deposition epitaxially ordered (022)-oriented pentacene films are formed which adopt the Siegrist phase. The detailed analysis shows that this epitaxial growth of films with an essentially recumbent molecular orientation is brought about by a slight rotation of the molecules in the first layer around their long molecular axis upon deposition of overlying molecular layers.
Such a structural modification is unusual and becomes possible by the rather weak adsorption energy on graphite. In contrast, a very different film structure including an upright orientation of molecules even in the first layer is found on nonperfect but rough graphite surfaces leading to the formation of (001)-oriented films which initially reveal the thin-film phase and continue to grow in the Campbell phase of pentacene.
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Initial film growth leads to the formation of a commensurate monolayer consisting of flat-lying molecules while upon subsequent deposition epitaxially ordered (022)-oriented pentacene films are formed which adopt the Siegrist phase. The detailed analysis shows that this epitaxial growth of films with an essentially recumbent molecular orientation is brought about by a slight rotation of the molecules in the first layer around their long molecular axis upon deposition of overlying molecular layers.
Such a structural modification is unusual and becomes possible by the rather weak adsorption energy on graphite. In contrast, a very different film structure including an upright orientation of molecules even in the first layer is found on nonperfect but rough graphite surfaces leading to the formation of (001)-oriented films which initially reveal the thin-film phase and continue to grow in the Campbell phase of pentacene.
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