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O: Fachverband Oberflächenphysik

O 64: Scanning Probe Techniques: Method development

O 64.4: Poster

Dienstag, 21. März 2017, 18:30–20:30, P2-OG3

Scanning Tunneling Microscopy with a JFET-sensor — •Stephanie Hoepken, Sebastian Bauer, Hermann Nienhaus, Christian A. Bobisch, and Rolf Möller — Faculty of Physics, Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 47057 Duisburg, Germany

We examined a new working mode for scanning tunneling microscopy (STM). It is an STM in which a junction-field-effect-transistor (JFET) serves as a sensor for the tunnelling current. The tunnelling tip is directly connected to the gate of the JFET, which is operated in an open-gate mode with no other electric connection to the gate. The drain current provides a corresponding signal at low impedance which is used for the electronic control of the tip sample distance. The technique allows us to work at very low currents in the range of about 100 to 200 fA. First of all the JFET was characterised to evaluate its operating point. At stable operation the tunnelling current is matched by the gate leakage current. By choosing the bias voltage applied to the sample, the tunnelling conductance can be set. In the recorded STM-pictures this voltage is about -1 to -2 V. Furthermore, an essential point in operating a JFET-STM is the control of the tip sample distance. The drain current's reaction to a changing tunnelling current is low pass filtered by the gate capacity, but it was found that a sufficient scanning speed can be accomplished by optimised control parameters mainly by using the proportional part of the feedback loop. With these parameters detailed pictures of an Au(111)-sample could be recorded.