Visualizing Quantum States of Matter

Dilution Fridge Scanning Tunneling Microscope

DFSTM Schematic

We are in the process of commissioning a state-of-the-art STM that would be one of the few instruments capable of operating at dilution refrigerator temperatures (15 mK) and high magnetic fields (14 T) while maintaining a UHV environment. This system has the ability to prepare and exchange both samples and tips in a clean environment, while at the same time extending the parameter space, in temperature and magnetic field, of the phenomena to which PNML has access. This instrument consists of a specially designed UHV compatible cryostat that connects to UHV tip/sample preparation chambers at the bottom through a system of thermal shields and a gate valve (see illustration). The cryostat, which has been designed in collaboration with Oxford instruments, contains a 14 Tesla magnet within its He reservoir that will be used to align the orientation of the tip’s magnetic moment. The insert and the attached STM head can be lowered from the vector magnet’s center down through the shields at the bottom of the cryostat into the UHV chambers using a system of bellows and a vertical manipulator. This allows us to move the STM head between the measurement position at the center of the magnet and the sample/tip insertion location within the UHV chambers below the cryostat. The cryostat system is specially designed to be bakeable so as to achieve UHV conditions during its operation. It is also specially designed to have a very low boil off rate to conserve He and to reduce potential vibrations due to the boiling of liquid He. The UHV chambers contain all the components required for the preparation of samples and tips for various experiments. The chamber will include a home-built electron beam heater to heat samples and tips, commercial sputtering sources for cleaning substrates and tips, and evaporation sources for the controlled deposition of magnetic materials for test samples and tips. These chambers will have the required ion and turbo pumps to achieve UHV conditions and will have the appropriate manipulators to move the samples/tips inside and for their insertion to the STM head stage.