Solving the Mystery of Bi Phase Formation at 2D Interfaces

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Nontechnical description: Bismuth is both an element and a material that has attracted tremendous interest from scientific researchers throughout history. For example, it was the first metal whose Fermi surface was experimentally identified and its study has led to the discovery of quantum (e.g. Shubnikov-de Haas) oscillations. It is also deemed a ‘magic element’ by chemists as it has rare chemical properties allowing it to form compounds with a diverse range of nuclei. A few years ago, the PI’s group made the discovery that ultralow contact resistance can be made to transition metal dichalcogenide (TMD, e.g. MoS2) devices when Bi is deposited on them. Initial structural analysis revealed that Bi formed epitaxial structures on TMD, which was understood as a particular semi-metallic phase of Bi at the time the work was published. Nevertheless, further recent studies indicated that previous understanding might be mistaken, which motivated this research to solve key mysteries and advance scientific knowledge. The findings will lead to discoveries of new 2D forms of materials and enable low power, high-performance devices for both conventional and quantum computing. The project will provide lab experience to undergraduate students and outreach to high school and other students. Technical description: This project will systematically investigate the phase and structures that Bi forms at the 2D material interface under various controlled conditions and will characterize the electrical and optical properties of the resulting structures. A layer-by-layer characterization will be carried out to examine the interfacial properties for one layer and multiple layers, to identify if any transitions occur as layer thickness increases. The unexpected and unexplored phenomena of Bi phase formation on a 2D substrate have revealed a knowledge gap in the 2D research field. Together with the particularly interesting outcomes – low contact resistance, much better thermal & chemical stability, and unusually high doping – these studies will not only provide a deeper understanding of the interfacial phenomena, but will also inspire other investigations of materials formation on 2D templates, and may have significant impact into technologically important areas such as electrical contact formation on 2D devices, high temperature quantum spin Hall materials, etc. The study of novel material phases and their formation will open new research directions, enabling new technologies for a wide range of applications, including energy, catalysis and biomedical. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.