Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 23: Scanning probe methods II

O 23.4: Vortrag

Montag, 14. März 2011, 18:00–18:15, WIL C307

Amplitude dependence of long- versus short-range forces on Si(111)7x7 — •Joachim Welker, Thomas Hofmann, and Franz J. Giessibl — Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany

Atomic force microscopy (AFM) senses the forces that act between a tip and a sample. The forces are composed of long- and short range interactions. Sugimoto et al. [1] recently demonstrated chemical identification of atoms by AFM using the short range forces. However, chemical identification was only possible here, because the atoms under investigation all were lying in the top surface layer, such that the long-range van der Waals (vdW) force was the same for all atoms. At step edges, the vdW forces vary strongly and we also expect that corner holes and dimer rows on Si(111) 7x7 lead to a spatial alteration in the vdW forces.

In NC-AFM, the sensitivity to forces of a different decay length can be tuned by the oscillation amplitude of the cantilever. Small amplitudes lead to a lower contribution of van-der-Waals forces to the experimental observable (frequency shift) than larger amplitudes. We performed measurements on Silicon(111)7x7 in constant height mode with oscillation amplitudes from picometer to nanometer range, investigating the contribution of the in-plane local spatial variation, e.g., the corner holes, to the long range van-der-Waals force.

[1] Y. Sugimoto, P. Pou, M. Abe, P. Jelinek, R. Perez, S. Morita, and O. Custance, Chemical identification of individual surface atoms by atomic force microscopy Nature, 446, 64 (2007)