An ultrahigh vacuum device for measuring the conductivity of surface structures by a four-probe method based on a closed-cycle refrigerator

An ultrahigh vacuum device for measuring the conductivity of surface structures based on a closed-cycle refrigerator is described. The device allows measurements of the conductivity of surface atomic structures as a function of the temperature (in the range 22-300 K) and electric field. The circuit for conductivity measurements allows operation with contact resistances of up to 10(10) Omega and currents as low as 10(-13)A. The operation of the device is demonstrated by an example of measuring the conductivity of a clean reconstructed Si(111)7 - 7 surface.