SKM 2023 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 77: Scanning Probe Techniques: Method Development II
O 77.2: Vortrag
Donnerstag, 30. März 2023, 10:45–11:00, REC C 213
Ultrahigh Vacuum Scanning Tunneling Microscopy with z Resolution of 2 pm at 1.3 K using Combined Pulse Tube and Joule-Thomson Cooling — •Marcus Esser1, Marc Frömming1, Marco Pratzer1, Michael Krzyzowski2, and Markus Morgenstern1 — 12.Physikalische Institut B, RWTH Aachen University, Aachen, Germany — 2CryoVac GmbH & Co KG, Troisdorf, Germany
The cooling of scanning tunneling microscopes with liquid helium by bath or flux cryostats suffers from He losses that get increasingly expensive. However, alternative closed cycle systems based on pulse tube refrigerators can induce additional mechanical noise into the tunneling contact due to mechanical vibrations in the μm range and acoustic emissions. We will present an STM system that reaches temperatures of 1.3 K and a z resolution of 2 pm (feedback loop off) with the help of a pulse tube cooler and a Joule-Thomson stage. The challenge is to provide a good thermal coupling as well as an good vibration damping. For this purpose, a new concept with multiple decoupling stages including negative stiffness isolation, detached coaxially guided shields for the different temperature stages and an optimized conical microscope design made out of Shapal Hi M-soft has been realized. Numerical calculations of transfer functions are compared with measurements on test setups using accelerometers as well as the tunneling contact of the STM. Eventual measurements on Au(111) showed atomic resolution and mechanical vibrations below 2 pm. The ongoing work to optimize spectroscopic resolution will be reported.