Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 84: Scanning Probe Techniques: Method Developments

O 84.5: Talk

Thursday, March 10, 2016, 16:15–16:30, S054

The effect of non-ideal tunneling current amplifiers on force measurements — •Nirmalesh Kumar Sampath Kumar, A. J. Weymouth, V. Junk, F. Huber, and F. J. Giessibl — University of Regensburg, Regensburg, 93053, Germany

Measurements of the tunneling current are performed with a current-to-voltage converter typically implemented by returning the output of an operational amplifier with a resistor in the Mega- to Giga-Ohm range to the inverting input. With the sample is attached to inverting input, and the non inverting input at ground, an ideal operational amplifier would maintain the sample at ground. A real operational amplifier, however, has finite internal impedance and finite gain. This has been shown to affect STM measurements when the internal resistance of the operational amplifier starts to be on the same order of magnitude as the resistance of the tunneling junction. [1]

We have observed that the presence of the current-to-voltage converter can have a profound effect upon the excitation required to oscillate the cantilever. A phase shift between the non-ideal virtual ground and the cantilever oscillation can account for energy either being pumped into or drained from the cantilever as it oscillates. In this contribution, we discuss our observations and this effect in more detail.

References [1] L. Olesen et al. Phys. Rev. Lett. 76, 1485 (1996)