Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 73: Scanning Probe Methods II

O 73.2: Vortrag

Donnerstag, 3. April 2014, 10:45–11:00, WIL A317

Artifacts in combined STM/AFM due to non-ideal ground in an STM pre-amplifier — •Nirmalesh Kumar Sampath Kumar, Alfred John Weymouth, and Franz Josef Giessibl — Institute of Experimental and Applied Physics, University of Regensburg, 93040 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 pre-amplifier 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.