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O: Fachverband Oberflächenphysik

O 26: Oxides and insulators: Clean surfaces

O 26.1: Vortrag

Dienstag, 23. März 2010, 10:30–10:45, H40

Improved atomic scale contrast via bimodal dynamic force microscopy — Shigeki Kawai, Thilo Glatzel, •Sascha Koch, Bartosz Such, Alexis Baratoff, and Ernst Meyer — Department of Physics, University of Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland

We implemented a multi-frequency technique into atomically resolved frequency-modulation dynamic force microscopy for a further improvement of force sensitivity in ultra-high vacuum [1]. The first and second flexural resonance modes of a commercially available Si cantilever are simultaneously excited by controlled amplitudes, while the resonance frequency shifts (Δf_1st and Δf_2nd) are demodulated by two phase-locked loop circuits (Nanonis: Dual-OC4). The combination of sub-angstrom amplitude oscillation A_2nd at the second resonance with the commonly used large amplitude oscillation A_1st at the first resonance enables a high force sensitivity at Δf_2nd while avoiding atomic jump-to-contact instabilities caused by controlling the tip sample distance with Δf_1st [2-4].

Simultaneously in quasi-constant height mode recorded Δf_1st and Δf_2nd maps of KBr(001) show that the Δf_2nd signal has a higher tip-sample distance dependence. With A_1st=16 nm and A_2nd=50 pm at different tip-sample distances in the attractive region the signal-to-noise of Df2nd was higher than that of Δf_1st especially at close tip-sample distances. This high-sensitive detection of the short-range interaction clearly revealed tip/sample deformations.