Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Scanning Probe Techniques: STM/AFM

O 15.10: Talk

Monday, March 16, 2015, 17:15–17:30, MA 043

Response of a Kelvin probe force microscope to charge switching dynamics — •Martin Ondracek, Prokop Hapala, and Pavel Jelinek — Institute of Physics , Academy of Sciences of the Czech Republic, Prague, Czech Republic

Atomic or molecular structures which are capable of switching between two or more different charge states are of much interest as prospective building blocks for nanoelectronic devices. Kelvin probe force microscopy (KPFM), as a local and charge-sensitive probe, is a well-suited tool for studying such structures. Indeed, charge switching has been already observed for Au atoms on NaCl using an atomic force microscope [L. Gross et al., Science 324, 1428; J. Repp et al., Science 305, 493]. However, the time scale of charging and discharging can vary over several orders of magnitude, depending on the particular structure, tip distance, voltage bias, substrate conductivity etc. When the charge dynamics is too fast to be probed in real time, it can still manifest itself as a deviation of the measured curves from perfect Kelvin parabolas and as a contribution to the the dissipation signal. We have developed a simple numerical simulator that models the charge dynamics and interaction of KPFM with the chargeable structure. This enables us to predict the dependence of the characteristic features showing up in KPFM measurements on the time scales of charging and discharging as well as on the instrumental time scales of KPFM: the oscillation period of the cantilever, response time of the feedback loop, and the acquisition time of one data point in the KPFM measurement.