Characterization of Step-Edge Barriers in Organic Thin-Film Growth
Gregor Hlawacek,1
Peter Puschnig,2
Paul Frank,3
Adolf Winkler,3
Claudia Ambrosch-Draxl,2
Christian Teichert1*
Detailed understanding of growth mechanisms in organic thin-film
deposition is crucial for tailoring growth morphologies, which
in turn determine the physical properties of the resulting films.
For growth of the rodlike molecule
para-sexiphenyl, the evolution
of terraced mounds is observed by atomic force microscopy. Using
methods established in inorganic epitaxy, we demonstrate the
existence of an additional barrier (0.67 electron volt) for
step-edge crossing—the Ehrlich-Schwoebel barrier. This
result was confirmed by transition state theory, which revealed
a bending of the molecule at the step edge. A gradual reduction
of this barrier in the first layers led to an almost layer-by-layer
growth during early deposition stage. The reported phenomena
are a direct consequence of the complexity of the molecular
building blocks versus atomic systems.
2 Chair of Atomistic Modelling and Design of Materials, University of Leoben, 8700 Leoben, Austria.
3 Institute of Solid State Physics, Graz University of Technology, 8010 Graz, Austria.
* To whom correspondence should be addressed. E-mail: teichert{at}unileoben.ac.at
