Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Scanning Probe Techniques: Method Development II
O 17.8: Vortrag
Montag, 20. März 2017, 17:30–17:45, TRE Phy
Scanning tunneling microscopy and potentiometry using a cooled JFET electrometer — •Paul Graf, Meike Flebbe, Christian A. Bobisch, Hermann Nienhaus, and Rolf Möller — Faculty of Physics, Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, 47048 Duisburg, Germany
We show that a liquid nitrogen cooled junction field effect transistor can be used to measure either small electric charges or ultra low currents in the range of 10−18 A [1]. The leakage current between the gate electrode and the source-drain channel of the JFET drops to several 10−20 A at a temperature of 80 K, so that the gate can store charge for a time of several days. The gate voltage, hence the charge, can be easily measured by the source-drain current. Here, we combine this cooled JFET electrometer with a scanning tunneling microscope connecting the gate electrode of the JFET directly to the tunneling tip. Using an AC-bias voltage, STM imaging at low current becomes possible. Since the gate voltage automatically adjust to zero average current, the dc component directly yields the electrochemical potential. Laterally resolved images show topographic features such as atomic step edges and terraces but also lateral oscillations in the electrochemical potential, i.e. thermovoltage, which can be attributed to standing electron wave patterns, e.g., of the surface state of Cu(111).
[1] Rolf Möller and Hermann Nienhaus, patent pending, Open FET Sensor, Provendis Ref.-Nr. 4817