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

Dependence of the atomic scale image of a Si adatom on the tip apex
termination: a DFT study
Anna Campbellova 1 , Pablo Pou 2 , Ruben Pérez 2 , Petr Klapetek 1 and Pavel Jelínek 3
1 Czech Metrology Institute, Brno, Czech Republic
2 Department of Physics, Yale University, New Haven, Spain.
3 Department of Thin Films, Institute of Physics of the ASCR, Prague, Czech Republic
Th-0900
High-resolution measurements of tip-sample forces became possible with dynamic force
spectroscopy (DFS) [1]. Furthermore this technique was adopted to measure threedimensional
force ?elds with atomic resolution [2,3]. In principle, these measurements
can provide, by separating the short-range contribution from the total tip-sample
interaction, detailed information about e.g. the surface energy landscape, adhesion forces
and inter-atomic forces. Sub-atomic resolution of Si adatoms on Si(111)-(7x7) has also
been reported and its interpretation is still source of debate.
Here we have performed DFT simulations of a 3D scan over a silicon cluster –that
reproduces the local coordination of a surface adatom--, using different Sibased tips [5].
Our aim is to reveal the effect of apex atomic termination on the resulting atomic scale
imaging of individual Si adatom. We have found a strong variation of the internal atomic
contrast with the symmetry and chemical composition of the tip apex. In particular, the
theoretical atomic image provided by a dimer-like Si tip with an oxygen atom positioned
on apex mimics very well the characteristic subatomic features observed experimentally
[4].
Figure 1: Theoretical DFT images of Si adatom provided by three different apex tip structures.
[1] M. A. Lantz et al, Science 291, 2580 (2001).
[2] H. Hölscher, S. M. Langkat, A. Schwarz, and R. Wiesendanger, Appl. Phys. Lett. 81, 4428 (2002).
[3] Y. Sugimoto, T. Namikawa, K. Miki, M. Abe, and S. Morita Phys. Rev. B 77, 195424 (2008).
[4] F. J. Giessibl, S. Hembacher, H. Bielefeldt, and J. Mannhart, Science 289, 422 (2000)
[5] P.Pou et al Nanotechnology accepted (2009)
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