Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 89: Oxides and Insulator Surfaces II

O 89.2: Talk

Thursday, March 10, 2016, 15:15–15:30, H4

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

Contrast formation in atomic force microscopy (AFM) images of ionic systems is often dominated by the electrostatic interaction between the ions of the sample and the tip apex. Thus, the chemical identity of the latter determines the contrast pattern, as e.g. shown for NaCl bilayers on the Cu(111) surface by Gross et al. [1]. To optimize atomic contrast in AFM experiments, the tip is usually poked slightly into the surface, ending up with picking up a cluster of sample atoms by the tip. The tip termination is thus uncharacterized, hindering the discrimination of the different species of atoms in the AFM images. In this work, the CaF2(111) surface is studied by AFM measurements. In contrast to ionic crystals of the rock salt structure, the surface ions of CaF2(111) are all charged negatively [2] and the contrast of the image allows to determine the tip polarity [2,3]. Similar to previous experiments on Cu2N [4], we use tips that are characterized at the atomic level using COFI [5], where an adsorbed CO molecule is used to image the tip apex. Our goal is to characterize the imaging mechanisms and the electrostatics of our different tips on the CaF2(111) surface.

References: [1]: L. Gross et al., Phys. Rev. B 90, 155455 (2014). [2]: A. Foster et al., Phys. Rev. Lett. 86, 2373 (2001). [3]: F. J. Giessibl, M. Reichling, Nanotechnology 16, 118 (2005). [4]: M. Schneiderbauer et al., Phys. Rev. Lett. 112, 166102 (2014). [5]: J. Welker et al., ACS Nano 7, 7377 (2013).