Abstract

We have modified a dual-tip scanning tunneling microscope (STM) by electrically connecting the tips together with a short (3 mm) strip of flexible 25 μm thick Nb foil. For simultaneous topographic imaging with both tips, we moved each tip to within tunneling distance z of a surface and modulated one tip's z-piezo at 5 kHz and the other at 10 kHz. The resulting combined tunneling current has modulation at both frequencies which we detect using individual lock-in amplifiers. Each lock-in output is fed back to its corresponding tip's individual STM z-position controller to maintain a stable current in both junctions. During the tests at room temperature, simultaneous imaging was performed with both tips made of Pt-Ir on Au/mica and highly oriented pyrolytic graphite (HOPG) samples, where a small tip-to-tip mechanical coupling was observed. We describe the system's performance, show results from simultaneous imaging, and discuss the potential application of the system to imaging superconducting phase differences.

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