An entirely enclosed scanning tunnelling microscope capable of being fully immersed in liquid helium.

Abstract

We present an ultrahigh-vacuum (UHV)-sealed high-stability scanning tunnelling microscope (STM) that can be entirely immersed in liquid helium and readily used in a commercial Dewar or superconducting magnet. The STM head features a horizontal microscanner that can become standalone and ultrastable when the coarse approach inertial motor retracts. Low voltage is enough to operate the STM even at low temperature owing to the powerful motor. It is housed in a tubular chamber of 49 mm outer diameter, which can be pumped via a detachable valve (DV), UHV-sealed and remain sealed after the DV is removed. The entire so-sealed chamber can then be inserted into liquid helium, where in situ sample cleavage is done via vacuum bellow. This allows sample cleavage and STM measurements to take place in better UHV with higher cooling power. Quality atomic resolution images of graphite and charge density wave on 1T-TiSe2 taken in ambient and 14 K conditions, respectively, are presented.