Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 81: Gerhard Ertl Young Investigator Award

O 81.5: Vortrag

Donnerstag, 19. März 2015, 12:30–13:00, MA 042

A phantom force and lateral force microscopy — •Alfred J. Weymouth and Franz J. Giessibl — University of Regensburg, 93040 Regensburg, Germany

Atomic force microscopy (AFM) allows us to investigate mechanical properties of surfaces and adsorbates at the atomic scale. With a conducting tip, scanning tunnelling microscopy (STM) can be simultaneously performed.

When we measured simultaneous STM and AFM on Si, the unsaturated Si atoms surprisingly appeared repulsive. Our theory is that this is due to a decrease of the electrostatic force [1]. The attractive chemical interaction is still present, but the electrostatic force can be detected at further tip-sample distances. We called this the phantom force, and explained it by an additional resistance within the sample [2]. This resistance can also affect STM measurements, and this effect has recently been observed on Cu surfaces with sub-monolayer oxide layers [3].

Although most AFM measurements are sensitive to vertical forces, we can rotate the AFM sensor and measure lateral forces, a technique we call Lateral Force Microscopy (LFM). We applied LFM to quantify the bending of a CO molecule at the apex of an AFM tip [4]. In this talk, I will compare these findings to new data with a bare metal tip.

[1] Weymouth et al, Phys. Rev. Lett. 106, 226801

[2] Weymouth and Giessibl, Appl. Phys. Lett. 101, 213105

[3] Matencio et al, submitted

[4] Weymouth, Hofmann and Giessibl, Science, 343, 1120