Structural Phase Patterning of MoS₂

All modern electronics consist of three basic types of material: insulators, semiconductors, and metals. Finding new ways to condense the size of these materials is a persistent goal of the scientific community, with increasingly smaller electronics opening many new possibilities in device efficiency and capability. We aim to aid that endeavor by improving methods of selectively transforming regions of molybdenum di-sulfide (MoS₂) from its semiconductor phase into its metal phase. Using a 50 kV electron beam at 500 pA, we directly expose thin flakes of exfoliated MoS₂ on a SiO₂ substrate, to a variety of electron beam doses to create patterns of metallic regions. We use atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) to spatially map changes in topography and work function respectively. Our results show that all physical changes occur in the SiO₂ substrate while work function changes occur only in the MoS₂. Changes in the work function are consistent with our expectations for a structural phase transition in MoS₂ where the crystal lattice enters a higher energy configuration while energetic injected electrons can fall to lower energy states. The resulting metallic phase reduces its total energy and remains stable. This work paves the way to mono-material electronic devices, which will drastically both save space and material costs.