Joule-Thompson Scanning Tunnelling Microscope (JT-STM)
The JT-STM is a sophisticated tool dedicated to the study of the electronic and magnetic properties of functional magnetic nanostructures, e.g. magnetic molecules, under ultrahigh vacuum conditions (UHV) and at low temperatures, which are thought to serve as essential building blocks for spintronic devices.
The main instrumental features are the low operating temperature, the long holding times, and a magnetic field in the vertical direction. The instrument utilizes the Joule-Thompson effect of 4He and reaches a minimum temperature of about 1.1 K. Its low Helium consumption enables continuous measurements at low temperatures for more than four days.
A superconducting split coil magnet is mounted inside the UHV and generates magnetic fields of up to 3 T perpendicular to the sample surface. The extremely stable design leads to low drift rates (170 and 50 pm/h for the lateral and vertical direction, respectively). The z-noise of the STM tip is extremely low (1.4 and <1 pm rms in 0.4 – 40 Hz and 1 – 300 Hz range, respectively). Thus, the instrument allows extended time periods of measurements with the tip positioned on top of atomic-sized sample features.
The figure above shows the JT-STM head without cooling shields.
Figure: 3D model of the JT-STM
Figure: Experimental set-up of the Joule-Thompson STM system.
Figure: Atomically resolved Au(111) surface at 1.1K. Scanning parameter: Ugap = -0.45 V, IT = -1n A, W tip, image modified.
Figure: Herringbone reconstruction of the Au(111) surface at different magnetic fields. Scanning parameters: Ugap = 1.44 V, IT = 0.3791 nA, W tip, 16.4 nm x 16. 4nm, microscope temperature 1.16 K - 1.21 K.
Figure: Spectroscopic measurements of the superconducting gap of a Nb STM tip on Au(111) as function of the magnetic field.
Figure: Spectroscopic measurements of the superconducting gap of a Nb STM tip on Au(111) as function of the temperature.