Low temperature Field Ion and Scanning Tunneling Microscope

Low temperature Field Ion and Scanning Tunneling Microscope (LT-FIM-STM)

Ben Wortmann and Rolf Möller

Building on the positive experiences with our homebuilt LT-STM and LT-AFM, the LT-FIM-STM is another project of our group. It is a compact, low temperature scanning tunnelling microscope (LT-STM) that allows in situ field ion microscopy (FIM) of a cooled tunnelling tip inside the STM. Therefore a characterization of the tip is possible without transfer to a different position in the UHV system so that the tip characterized by FIM is identical to the one used for the STM experiment. The geometry of the microscope resembles a cylinder with a height of only 13 cm and a diameter of 4 cm. Shutters at the bottom of the microscope can be opened to expose the tip to a channel plate or closed to assure even lower temperatures and minimal thermal drift while tunnelling. A combination of two piezo-electric accentuators is used to move a magnetically attached unit (*slider*) by a slip-stick motion. The tip is spot welded to the slider which can be easily exchanged in vacuum. The STM is screwed directly onto a commercially available continuous flow cryostat which allows cooling the tip and the sample to about 5-7 K. Insulation from vibration is provided by a combination of springs and eddy current damping. The very compact design minimises the helium consumption to about 1 liter/hour.