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O: Fachverband Oberflächenphysik

O 15: Scanning Probe Techniques: STM/AFM

O 15.2: Talk

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

Quantifying the virtual ground of a STM pre-amplifier — •Nirmalesh Kumar Sampath Kumar, Alferd J Weymouth, and Franz J Giessibl — Institute of Experimental and Applied Physics, University of Regensburg, Universitatstraße 31, 93053 Regensburg, Germany

In AFM, it is normal to apply a bias voltage between the tip and the sample, most often to compensate for the contact potential difference. In order to perform simultaneous STM, the tunneling current must be measured. This usually involves a preamplifier that holds its current input terminal at a virtual ground that is ideally equal to real ground. Limitations of amplifier bandwidth, gain and slew rate lead to time-dependent deviations of virtual ground from zero, causing a time-dependent variation of the electrostatic force between tip and sample. These time-dependent deviations can lead to artifacts in apparent dissipation and even to an apparent "self" excitation of the cantilever. Here, we monitor virtual ground and discuss the effect of virtual ground deviations to apparent dissipation.