A 300 mK ultra-high vacuum scanning tunneling microscope for spin-resolved spectroscopy at high energy resolution

We describe the design and development of a scanning tunneling micoscope (STM) working at very low temperatures in ultra-high vacuum (UHV) and at high magnetic fields. The STM is mounted to the He3 pot of an entirely UHV compatible He3 refrigerator inside a tube which can be baked out to achieve UHV conditions even at room temperature. A base temperature of 315 mK with a hold time of 30 h without any recondensing or refilling of cryogenics is achieved. The STM can be moved from the cryostat into a lower UHV-chamber system where STM-tips and -samples can be exchanged without breaking UHV. The chambers contain standard surface science tools for preparation and characterization of tips and samples in particular for spin-resolved scanning tunneling spectroscopy (STS). Test measurements using either superconducting tips or samples show that the system is adequate for performing STS with both high spatial and high energy resolution. The vertical stability of the tunnel junction is shown to be 5 pmpp and the energy resolution is about 100 μeV.