Note: a simple approach to fabricate a microscopic four-point probe for conductivity measurements in ultrahigh vacuum

We present a simple method to fabricate microscopic four-point probe (M4PP) with spacing of 70-100 μm for conductivity measurements in ultrahigh vacuum. The probe includes four gold wires with 30 μm diameter and a 0.5 mm thickness sapphire slice as cantilever. One of the dual scanning tunneling microscope (DSTM) is replaced by M4PP. As a result, in situ transport measurement could be performed by M4PP and investigation of surface morphology by STM. Finally, we measure conductivity of 14 monolayer Bi(111) epitaxial film on n type Si which is 1.6 × 10(-3) Ω(-1)∕[larger open square].