Ultra-low-Temperature High-Magnetic-Field Scanning Tunneling Microscope (LT HF STM)

We construct a 3He UHV STM system, which consists of a UHV preparation chamber and load-lock chamber. This enables us to transfer/prepare the tip and the sample between different UHV chambers. A double stage 4He-3He sorption cooler is used to cool down the STM head to T ~ 280 mK with the holding time ~ 24 hours by pumping the liquid helium reservoir and then the 4He pot. Such a fridge design is vibration-free because closed-cycled sorption pumping does not generate vibration. The electron temperature is determined to be ~400mK by fitting the measured superconducting gap (the bottom inset). Furthermore, we retrofit a novel double-deck sample stage on the STM head (the top inset), which gives us a simple way to clean the STM tip or to prepare a magnetic tip for spin polarized STM. Also, the original sample can be preserved in the STM head so the comparison can be made on the same field of view. Further information can be found in Ultramicroscopy 196, 180 (2019)

Components:

• Air Liquide 4He cryostat with the doubel-stage 4He-3He cooler and 4
• superconductor magnets (310 mK, 7 T)
• RHK SPM1000 controller
• Homemade STM scanner and coarse approach driven circuit
• Optical table with Newport vibration isolations

Fig. 1. The STM scanner		Fig. 2. The homemade stepper-driven circuit.

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