Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Temperature-dependent growth of C60 on CaF2(111)
Felix Loske, Philipp Maaß, Jens Schütte, and Angelika Kühnle
Department of Physics, Universität Osnarück, Barbarastraße 7, 49076 Osnabrück ,Germany
E-Mail: floske@uos.de
P.II-05
Non-contact atomic force microscopy was employed to study the system of C60
molecules on the CaF2(111) surface in-situ at various temperatures. The molecules were
observed to be very mobile on the surface at room temperature (RT), as they nucleate at
step edges and form large islands on the terraces. Both, regular triangular islands as well
as branched structures were observed to coexist (Fig. 1b and 1c). The branched structures
were seen to change shape during measuring. S. Burke et al. have previously reported
about such branched structures on alkali halides [1].
The compact islands of C60 on CaF2 are at least two layer high, and at higher coverages
C60 molecules grow in a dendritic manner onto the these compact C60 islands (Fig. 1d). In
contrast, at low temperatures (LT) hexagonal islands are predominant, which are initially
only one layer high. Here, already the second layer is growing in a dendritic manner (Fig.
1a).
These temperature-dependent measurements allow to gain insight into the molecular
dynamics of this system and to specify the diffusion barrier. Microscopic growth models
are shortly addressed to explain the measured island morphologies.
Figure 1: Topographic NC-AFM images. (a) C60 island with dendritic second layer at LT. (b)
and (c) represent the coexistence of compact triangular and branched islands at RT, with dendritic
growth starting at the second layer (d).
[1] S.A. Burke, J.M. Mativetsky, S. Fostner, P. Grütter, Phys. Rev. B 76, 035419 (2007)
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