Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 35: Poster Session II (Polymeric biomolecular films; Nanostructures; Electronic structure; Spin-orbit interaction; Phase transitions; Surface chemical reactions; Heterogeneous catalysis; Particles and clusters; Surface magnetism; Electron and spin dynamics; Surface dynamics; Methods; Electronic structure theory; Functional molecules)

O 35.118: Poster

Dienstag, 27. März 2012, 18:15–21:45, Poster B

Low noise, wide band current to voltage amplifier for low temperature scanning tunneling microscope operation — •Hanna Fedderwitz, David Hellmann, Ludwig Worbes, Konstantin Kloppstech, Nils Könne, and Achim Kittel — EHF, Fak.V Physik, Carl von Ossietzky Universität Oldenburg

We are interested in the heat transfer across a nanoscale vacuum gap between two surfaces mediated by evanescent electromagnetic fields [1]. The characteristic length scale depends on the temperature of the two opposing surfaces and increases drastically at low temperatures. To investigate this effect we are setting up a low temperature scanning tunneling microscope (LT-STM) which can be equipped with a coaxial thermocouple tip [2]. Therefore it is necessary to apply the tunnel voltage to the sample instead of the STM-tip as in most STM setups. We achieve this by choosing a two stage setup. The first stage features low-noise transimpedance amplification by using a commercial high performance FET operational amplifier together with a high-ohm feedback resistor. Giving access to the current which is drained into the tip at tunnel voltage level the amplifier has to be powered by a floating supply voltage. A second stage is employed to reference the output signal to ground needed by the feedback electronics. This stage makes use of a commercial instrumentation amplifier. The two-stage system shows a low inherent total current noise of 4pA and a stable frequency response up to 10kHz cutoff frequency. [1] Achim Kittel et al., Appl. Phys. Lett. 93, 193109 (2008). [2] Uli F. Wischnath et al., Rev. Sci. Instrum. 79, 073708 (2008).