Direct Observation of 2D Material Interfacial States within Devices Using STEM-EELS*

The 2D materials field continues to expand as novel layered materials are synthesized and embedded in various devices. However, the structure of the interface between an embedded 2D material and the rest of the device, which is critical to the device’s performance, remains poorly understood. Few experimental studies have focused on these interfaces likely because the device-embedded 2D material is difficult to access at the atomic scale. Here, we present an experimental study of the bonding interactions at the interface between MoS₂ and Ti contacts within a FET using STEM-EELS. Atomic-resolution STEM images of the Ti-MoS₂ interface show distinct differences in the crystal structure between interacting and non-interacting areas within the FET. Furthermore, EELS, measured layer-by-layer, shows systematic changes in the local density of electronic states at each layer of MoS₂ with distance away from the Ti contact. These results show how contacts affect the innate structure of 2D materials and how thick a 2D material must be to preserve its expected properties, both of which have significant implications for device performance.