A versatile low-temperature scanning tunneling microscope

We present a new scanning tunneling microscope (STM) developed specifically for use at low temperatures within a standard helium cryostat. This compact STM (diameter 25 mm and length 61 mm) has been designed to be compatible with a superconducting magnet. It incorporates a novel approach system which operates in any orientation including the vertical one, without any mechanical connections to the STM. It is able to translate a sample by 30 A steps in any orientation. The coarse and the fine approach are driven by a single piezoelectric tube via inertial slip-stick motion of the sample holder. During the coarse approach, the translator can be moved over 15 mm at 0.25 mm/s against gravity. We have operated this STM down to 1.6 K and we have obtained images with atomic resolution on highly oriented pyrolitic graphite (HOPG) and NbSe₂ from 300 K down to 90 K. This partially thermal compensated instrument is able to monitor temperature dependent surface changes on atomic scale in real time.