Combining an in situ device fabrication and six-probe electrical transport measurement system with low-energy electron microscopy.

Abstract

Two-dimensional (2D) quantum materials, including several analogs of graphene ("X-enes"), are of great current research interest. However, some of the potentially most exciting ones are reactive and sensitive to exposure to the atmosphere, which hampered the experimental study of their key physical properties. Here, we introduce an experimental setup that integrates sub-atomic-layer-resolved molecular beam epitaxy (MBE) synthesis, real-time low-energy electron microscopy (LEEM) and low-energy electron diffraction (LEED), and in situ six-probe electrical transport measurements. The six-probe apparatus is equipped with a dry cryocooler for reaching cryogenic temperatures, a piezoelectric XYZ nano-positioning stage for high-precision motion of the six probes, and an in situ device fabrication system for the deposition of custom-shaped gold electrodes. This design enables the six-probe system to perform both AC and DC resistance measurements on 2D quantum materials along multiple orientations within the temperature range of 5K < T < 400 K. The modules are interconnected under ultrahigh vacuum (UHV), and the samples can be synthesized by MBE, imaged by LEEM, and R(T) dependence measured without any surface contamination. We present the first experimental results that test and validate the performance of the six-probe system by transport measurements on several materials, including semiconductors and superconductors. This new instrument is proven to be a versatile platform for studying atmosphere-sensitive quantum materials.