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O: Fachverband Oberflächenphysik

O 43: Poster Session II - MA 141/144 (Surface Spectroscopy on Kondo Systems; Frontiers of Surface Sensitive Electron Microscopy; Methods: Scanning Probe Techniques+Electronic Structure Theory+Other; Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation; joined by SYNF posters)

O 43.29: Poster

Dienstag, 26. Februar 2008, 18:30–19:30, Poster F

Analyzing and determination of the different shear force interactions — •Kai Braun, Catrinel Stanciu, Dai Zhang, and Alfred J. Meixner — Institut für Physikalische und Theoretische Chemie, Auf der Morgenstelle, 72076 Tübingen

Shear-force feedback is among the most common used mechanisms for distance control in scanning near-field optical microscopes (SNOM). A reliable SNOM measurement requires extremely precise tuning of the distance between the tip and the sample. Although being widely used, the nature of the shear-force interaction is still not fully understood. The oscillating probe is usually modelled as a driven harmonic oscillator, influenced by different forces due to the interaction of the tip with the sample. We present here an extensive study of this interactions for different combinations of substrates (Au, Si, HOPG and glass) and tips (Au, W and glass). We measured the amplitude and phase of the tip oscillation as a function of the tip-sample distance in the non-contact range. The measurements allow us to distinguish the different forces between the tip and the substrate. The dominating nature of the interactions strongly depends on the material of both the tip and the substrate and also with the distance. In particular, gold tips on gold samples, of actual interest in tip-enhanced microscopy, undergo mainly elastic interaction for larger distances, with an attractive component evident for smaller distances. These results can help for a better understanding of optical near-field measurements, in particular for avoiding artefacts when measuring heterogeneous samples.