4K-Scanning Tunneling Microscope
Figure: Schematic view of a Helium-4 bath cryostat STM setup. Details are described in O. Pietzsch et al., Rev. Sci. Instrum. 71, 424 (2000).
Direct access 4Helium bath cryostat setups are both reliable and versatile. They are ideal for spin-polarized STM studies of nanoscale structures at moderate magnetic fields. The inner 4He cooling system is surrounded by a second radiation shield, cooled by liquid nitrogen (T = 77 K). Cooling liquids have to be refilled every two days. Depending on the specific design of the radiation shields and the thermal conductances of materials and interfaces, sample temperatures close to T = 4.2 K, the temperature of liquid He, can be reached. Direct access allows controlled exchange of tips and samples, as well as evaporation of singles atoms onto the cold sample surface inside the STM.
The access openings restrict the position of the magnetic coils, which leads to comparatively large magnetic stray fields. In the specific setup shown here perpendicular fields of up to 2.5 Tesla at the sample position are reached with currents of 70 amps. Magnetic fields are essential for systematic SP-STM studies.