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

We-1220
Theoretical study of the forces and atomic configurations of NC-AFM
P. Pou 1 , and R. Perez 1
experiments on low-dimension carbon materials.
1 Dpto. de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain
During the last years we have been witnessing the rise of low-dimension carbon-based
materials. Fullerenes, nanotubes and graphene are nowadays key materials nowadays key
materials for nanotechnology applications due to their promising electronic and
mechanical properties. The outstanding capabilities of NCAFM to image, manipulate and
determine the tip-surface forces at the atomic scale make it the technique of choice for
the study of the basic properties and for the development of these materials [1-5].
In this work we present a DFT study of the interaction of a large set of AFM tips
with different low-dimension carbon materials. We have considered several possible tip
terminations: reactive clean Si tip apexes, non-reactive apexes, oxygen contaminated Si
apexes and metallic tips. For each of these tips, we have characterized both the
conservative and non-conservative part of the tip-sample interaction, determining the
force versus distance curves during approach and retraction and calculating also the
dissipated energy. Our results provide insight into the origin of the atomic contrast
observed in recent experiments on both graphite and a SWNT [2-4]. Moreover, we have
studied the atomic origin of the particular 3D Force mapping obtained in the experiments
on peapods constituted by endo-fullerenes inserted in a SWNT [1] (see Fig. 1).
a) b)
Figure 1: (a) Ball-and-stick model of Si tip apex model over (Dy@C82)@SWNT. (b) Electronic
charge density calculated with DFT in a plane parallel to the peapod over the top atoms of the
SWNT. A slight modulation produced by the Dy@C82 is observed.
[1] M. Ashino et al. Nature Nanotech. 3, 337 (2008).
[2] B. J. Albers et al. Nature Nanotech. 4, 57 (2009).
[3] S. Hembacher et al. PNAS. 100, 12539-12542 (2003); S. Hembacher et al. PRL 94, 056101 (2005).
[4] M. Ashino et al. PRL 93, 136101 (2004); M. Ashino et al. Nanotechnology 16, S134-S137 (2005).
[5] H. Hölscher et al. Phys. Rev. B 62, 6967-6970 (2000).
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