Angle-Resolved Photoemission Spectroscopy on Two-Dimensional Heterostructures and Devices

The electronic structure of crystalline solids are the basis of all modern technology. As we seek smaller systems and novel quantum phenomena, two-dimensional materials have risen to be able to satisfy both conditions. They are relatively easy to create, control, and show an electric (and magnetic) tunability beyond most conventional crystalline growth techniques. Furthermore, device fabrication can be implemented to utilize these systems for energy harvesting, magnetic manipulation, birth superconductivity, and more. In this thesis, we seek to understand the tunability of these systems through the lens of their electronic structure by implementing micro- and nano-focused x-ray photoemission spectroscopy. By performing such an experiment on operating devices, we have a unique perspective of real-time tunable quantum states on operating devices, birthing the field of in − operando photoemission spectroscopy. Electron transport and angle-resolved photoemission spectroscopy are unified under a single experiment in order to extract, for the first time, the manybody effects that exist in the 2D crystal of interest. By doing this on mono and twisted bilayer graphene devices, we set the procedures and experimental pathway for extracting quasiparticle formation from more systems beyond graphene