A Compact and Versatile Scanning Tunnelling Microscope with High Energy Resolution for Use in a 3He Cryostat

We present a simple design for a very-low temperature STM for the investigationof mesoscopic superconductors. The nonmagnetic microscope operates in a conventional 3He cryostat at T =240mK and in magnetic fields up to B=1T. Efficient filtering of all electrical lines at base temperature results in a voltage resolution ≈20µV, which has been tested by measuring the differential conductance of superconducting aluminium. The successful operation in magnetic field is demonstrated by spectroscopy on superconducting aluminium as well as by demonstrating atomic resolution of HOPG