Depth-profiling of chemical and electronic properties of large-area exfoliated two-dimensional materials

Two-dimensional materials such as transition metal dichalcogenides (TMDC) can be exfoliated to a desired thickness and then stacked into different van der Waals heterostructures, leading to emergent phenomena. Interlayer and material/substrate coupling significantly alters the electrical, optical, and vibrational properties of these materials. In this study we do a non-destructive depth-profiling of large area exfoliated TMDCs with few layer thicknesses using standing-wave x-ray photoemission spectroscopy (SW-XPS). This technique utilizes the standing-wave generated by the reflection of soft x-rays on the multilayer [Si/Mo] mirror substrate at the Bragg condition [1]. The core level and valence band data collected using SW-XPS provides answers about the evolution of the chemical bonding with depth and the impact of different experimental conditions to the TMDC materials, such as annealing or gaseous environment.

[1] Conti, G. et al. Characterization of free-standing InAs quantum membranes by standing wave hard x-ray photoemission spectroscopy. APL Materials 6, 058101 (2018).