Dresden 2017 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 17: Scanning Probe Techniques: Method Development II

O 17.6: Vortrag

Montag, 20. März 2017, 17:00–17:15, TRE Phy

AFM investigation on CaF2(111) with atomically characterized tips — •Alexander Liebig, Angelo Peronio, Daniel Meuer, Alfred J. Weymouth, and Franz J. Giessibl — Universität Regensburg, Germany

In contrast to ionic crystals of the rock salt structure, the surface ions of CaF2(111) are all charged negatively, and AFM measurements on this surface had previously been used to identify positively- and negatively-terminated tips [1]. Similar to previous experiments on Cu2N [2], we imaged this surface with both metal- and CO-terminated tips that were characterized using the COFI method, where an adsorbed CO molecule is used to image the tip apex [3]. We simulated the AFM data with a simple electrostatic model, in which the surface atoms are represented as point charges and the tip as a dipole. For measurements acquired relatively far from the surface the electrostatic force is the dominant contribution to the AFM contrast and the model allows us to determine the sign of the net charge at the tip apex. However, this point-charge model fails to reproduce the data closer to the surface, where the bending of the CO molecule and Pauli repulsion become important [4,5]. These effects lead to a contrast inversion in the AFM images acquired with a CO-terminated tip at very close tip-sample distances.

[1] A.S. Foster et al., Phys. Rev. Lett. 86, 2373 (2001). [2] M. Schneiderbauer et al., Phys. Rev. Lett. 112, 166102 (2014). [3] J. Welker and F.J. Giessibl, Science 336, 6080 (2012). [4] L. Gross et al., Science 337, 6100 (2012). [5] M. Ellner et al., ACS Nano Letters 16, 3 (2016).