Instruments
1）UHV-variable temperature electron transport measurement system
This is a laboratory-developed electron transport measurement system that can be operated under ultrahigh vacuum (UHV) environment (~1×10
mbar). Using this instrument, one can perform an all-in-situ experiment without breaking the UHV condition. The process includes preparation and characterization of a clean sample surface at the atomic level, fabrication of electrodes, and final electron transport measurement. This capability is crucial for measuring electron transport properties of atomically thin materials with a high reliability. Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) are used for sample characterization. The system is equipped with a variable-temperature-type cryostat cooled by liquid helium flow (Helitran, ARS, Inc.), which allows a transport measurement to be taken from room to very low temperatures (~1.8 K). Only several machines with such functions are available in the world. The STM is fully home-made.
2) UHV-VLT electron transport measurement system with a superconducting magnet
This is an electron transport measurement system under development, which can be operated at very low temperatures (VLT, ~0.4 K) and under high magnetic fields (5 T). A sample prepared in the above UHV-compatible electron transport measurement system can be loaded into a cryostat equipped with a superconducting magnet (Cryogentic Limited) via an exchange chamber. The sample is transferred between the two systems through a UHV Suitcase (Ferrovac GmbH). The whole process can be performed under the UHV condition to avoid deterioration of the sample. The sample orientation relative to the magnetic field can be precisely controlled using a nano-positioner stage (attocube systems AG). We are planning to achieve the highest magnetic field of ~10 K in the near future.
3) Cryogen-free superconducting magnet system
This is a cryogen-free cryostat equipped with a superconducting magnet for electrical transport measurements at low temperature and high magnetic fields. Two cryogen-free refrigerators cool the sample space and the superconducting magnet without the use of liquid helium. The lowest temperature is 1.4 K and the maximum magnetic field is 9 T. Custom-made probes can be inserted for dielectric measurements and measurements under microwave irradiation.
4) UHV-LT scanning tunneling microscope
This is a scanning tunneling microscope (STM) based on USM1200 (UNISOKU Co, Ltd) that can be operated under UHV (~1×10 mbar) and at low temperatures (4.6 K). It is equipped with two preparation chambers where various kinds of sample preparation and characterization with LEED are possible. The compact cryostat with a two-stage heat exchanger allows the operation of STM for a long time without storage of liquid nitrogen. The integrated Nanonis SPM controller (SPECS GmbH) enables user-friendly and powerful operations at the same time.
